دمياط اليوم

Dr.Ehab Fathy Gabr Aboueladab (PhD in Biochemistry), Associate Prof.Dr. of Biochemistry, Damietta University, Faculty of Specific Education Damietta, New Damietta City, P.O.Box.34517, Egypt, Tel :002-057-2224444(HOME), 002-057-2403085(WORK), 002-0100-7834123(MOBIEL or HANDY), Email:ehab10f@gmail.com, ChatYahoo:ehababoueladab@yahoo.com, http://www.labhoo.com, http://www.citeulike.org,http://vadlo.com,www.thesciencejobs.com, http://medicalppt.blogspot.com,http://www.medbio.info,worldcat.org

Tuesday, November 13, 2012

hemoglobin

Q. What are the salient structural features of hemoglobin molecule?
A. Hb has four subunits, two alpha and two beta
units. It contains four iron atoms.

Q. How many molecules of oxygen can bind with hemoglobin?
A. Hb can bind four molecules of oxygen.

Q. 100 ml of blood can carry how much oxygen?
A. 20 ml.

Q. What is Bohr effect?
A. The influence of pH and pCO2 to facilitate oxygenation of Hb in the lungs and deoxygenation
at the tissues is known as the Bohr effect.

Q. What is chloride shift?
A. When CO2 is taken up, chloride ions from the plasma would enter. This is called chloride shift
or Hamburger effect.

Q. Hemoglobin carries how much CO2?
A. Seventy five percent as isohydric transport and 15% as carbamino hemoglobin.

Q. What are the forms in which carbon dioxide is transported?
A. Dissolved form, isohydric transport, and carbamino hemoglobin.

Q. What is isohydric transport of carbon dioxide?
A. There is minimum change in pH during the transport.

Q. How this is effected?
A. The H+ ions are buffered by the deoxy-Hb.

Q. Which will decrease the affinity of hemoglobin for oxygen?
A. 2,3-BPG level.

Q. What is the structural difference between HbA and HbF?
A. HbA has two alpha and two beta chains, but HbF has two alpha and two gamma chains.

Q. What are the laboratory tests to identify HbF?
A. HbF moves slower than HbA on electrophoresis, HbF is alkali resistant.

Q. What is the physiological significance of HbF?
A. Oxygen affinity is more for HbF than HbA. HbF is seen in foetal circulation.

Q. What is the clinical significance of HbF?
A. It is seen in adults in hemoglobinopathies and thalassemias.

Q. Why carbon monoxide becomes a poison?
A. Hb has more affinity to carbon monoxide than oxygen.

Q. What is the treatment for carbon monoxide poison?
A. Hyperbaric oxygen.

Q. Met-hemoglobin is found in which conditions?
A. Ingestion of nitrites, presence of HbM, GPD deficiency.

Q. What is met-hemoglobin?
A. Hemoglobin in which iron is in ferric state.

Q. What is the defect of met-hemoglobin?
A. It cannot release oxygen in tissues.

Q. What is the reagent used for colourimetric estimation of hemoglobin?
A. Drabkin’s reagent, to convert Hb to cyanmethemoglobin.

Q. What is hemoglobin S?
A. The glutamic acid in the 6th position of beta chain of HbA is changed to valine in HbS.

Q. What is the cause for sickle cell anemia?
A. Solubility of deoxy HbS is lower than deoxy HbA,so HbS is precipitated intracellularly, leading to
sickle shape of RBC.

Q. How HbS is identified?
A. HbS is slower moving on electrophoresis than HbA.

Q. What is sickle cell trait?
A. Heterozygous (AS) condition, one allele is normal, the other is abnormal, so half of Hb molecules are normal, and half abnormal.

Q. What is its clinical significance?
A. Sickle cell trait persons will not have any disease manifestations, usually. But, at higher altitudes,
hypoxia may cause manifestation of the disease.Chronic lung disorders may also produce
hypoxia-induced sickling in HbS trait.

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------

Water soluble vitamins

Q. What is the source of thiamine?
A. Aleurone layer of cereals (food grains) is a rich source of thiamine. Whole wheat flour and
unpolished rice and yeast are very good sources.

Q. Thiamine pyrophosphate is required for which reactions ?
A. Transketolase, pyruvate dehydrogenase, and alpha keto glutarate dehydrogenase.

Q. Which Vitamin is required for oxidative decarboxylation?
A. Thiamine pyrophosphate.

Q. In thiamine deficiency, what alterations are seen in blood ?
A. Increased pyruvic acid level and increased transketolase activity.

Q. What are the clinical manifestations of thiamine
deficiency?
A. Beriberi, Wernick’s syndrome, and polyneuritis.

Q. Beberi is due to the deficiency of which Vitamin?
A. Thiamine.

Q. What is the daily requirement of Vitamin B1 (thiamine) ?
A. 1 to 1.5 milligram.

Q. Chronic alcoholism may lead to the deficiency of which Vitamin?
A. Vitamin B1.

Q. Wernicke’s encephalopathy is due to the deficiency of which Vitamin?
A. Vitamin B1.

Q. What is the co-enzyme function of riboflavin ?
A. FMN and FAD dependent enzymes.

Q. What are the FAD dependent enzymes?
A. Succinate dehydrogenase, acyl CoA dehydrogenase,xanthine oxidase, glutathione reductase,
glycine cleavage system, pyruvate dehydrogenase,and alpha ketoglutarate dehydrogenase.

Q. What are the manifestations of riboflavin deficiency?
A. Glossitis, cheilosis, angular stomatits, andcircumcorneal vascularisation.

Q. What is the dietary sources of riboflavin?
A. Rich sources are liver, dried yeast, egg, and milk.

Q. What is the daily requirement of riboflavin?
A. 1.5 mg per day.

Q. Which Vitamin is synthesised in the body?
A. Niacin.

Q. What is the co-enzyme function of niacin?
A. NAD and NADP.

Q. Name some important NAD dependent enzymes.
A. Lactate dehydrogenase, glyceraldehyde-3-phosphate dehydrogenase, pyruvate dehydrogenase,
beta hydroxy acyl CoA dehydrogenase,and mitochondrial isocitrate dehydrogenase.

Q. Name the NADPH generating reactions.
A. Glucose-6-phosphate dehydrogenase, 6-phosphogluconate dehydrogenase, malic enzyme, and
cytoplasmic isocitrate dehydrogenase.

Q. What are the important NADPH utilising reactions?
A. Beta keto acyl ACP dehydrogenase, alpha, betaunsaturated ACP dehydrogenase, HMGCoA
reductase, met-hemoglobin reductase, dihydrofolatere ductase, and phenylalanine hydroxylase.

Q. Pellagra is seen in the deficiency of which Vitamin?
A. Niacin.

Q. What are the features of pellagra ?
A. Dermatitis, diarrhea, and dementia.

Q. What is the precursor of niacin?
A. Tryptophan.

Q. Tryptophan will give rise to how much niacin?
A. About 60 mg of tryptophan will yield 1 mg of niacin.

Q. Tryptophan is deficient in which food stuff?
A. Maize and corn.

Q. Which conditions will lead to symptoms of pellagra?
A. Isoniazid therapy, low tryptophan content in diet,niacin deficiency, hartnup disease, and carcinoid
syndrome.

Q. What is the dietary sources of niacin?
A. Natural sources of niacin are dried yeast, rice polishing,liver, peanut, whole cereals, legumes, meat and fish. About half of the requirement is met by the conversion of tryptophan to niacin. About 60 mg of tryptophan will yield 1 mg of niacin.

Q. What is the daily requirement of niacin?
A. The R.D.A is 20 mg/day.

Q. Transamination reaction requires which Vitamin?
A. Pyridoxal phosphate.

Q. Pyridoxal phosphate is required for what reactions?
A. Transamination reactions, decarboxylation of amino acids, ALA synthase, glycogen phosphorylase.

Q. Give an example of transamination reaction.
A. Alanine transaminase (ALT) will catalyse the reaction, alanine to pyruvate.

Q. What is its clinical significance?
A. Blood level of ALT is increased in liver diseases,AST is increased in myocardial infarction.

Q. Give some examples of decarboxylation reactions.
A. Glutamate to GABA (gamma aminobutyric acid),histidine to histamine, 5-hydroxy tryptophan to
serotonin, cysteine to taurine, and serine to ethanol amine.

Q. Xanthurenic acid in urine is seen in the deficiency of which Vitamin?
A. Pyridoxal deficiency.

Q. What are the manifestations of pyridoxal deficiency?
A. Infantile convulsions, peripheral neuritis,pellagra, and anemia.

Q. What is the reason for infantile convulsions in pyridoxal deficiency?
A. Pyridoxal phosphate is required for the formation of GABA, and it is an inhibitory neurotransmitter,
absence of which leads to hyper-excitation
and convulsions.

Q. What is the reason for peripheral neuritis in pyridoxal deficiency?
A. PLP is involved in the synthesis of sphingolipids,so B6 deficiency leads to demyelination of nerves
and consequent peripheral neuritis.

Q. What is the reason for pellagra-like disease in pyridoxal deficiency?
A. Since niacin is produced from tryptophan, one of the enzymes of this pathway is PLP dependent.
So B6 deficiency in turn leads to niacin deficiency which is manifested as pellagra.

Q. Can you give an exmple of one Vitamin deficiency leading to another Vitamin deficiency?
A. PLP deficiency in turn leads to niacin deficiency which is manifested as pellagra.

Q. What is the reason for anemia in pyridoxal deficiency?
A. PLP is required for ALA synthase. In adults hypochromic microcytic anemia may occur due
to the inhibition of heme biosynthesis.

Q. What are the drugs which cause pyridoxal deficiency?
A. Isonicotinic acid hydrazide (INH) (isoniazid),cycloserine, penicillamine and oral contraceptives
act as B6 antagonists. Ethanol in the body is converted to acetaldehyde, which inactivates PLP.

Q. What are the dietary sources of pyridoxal?
A. Rich sources are yeast, rice polishing, wheat germs, cereals, legumes (pulses), egg, milk, meat,
fish and green leafy vegetables.

Q. What is the daily requirement of pyridoxal phosphate?
A. 1 to 2 mg/day.

Q. What is the co-enzyme form of pantothenic acid?
A. Co-enzyme A.

Q. What is the function of CoA?
A. Oxidation of pyruvic acid and activation of acylgroups.

Q. Deficiency of pantothenic acid leads to what?
A. Burning foot syndrome.

Q. What are the donors for acetyl CoA pool?
A. Pyruvate, fatty acid, and amino acids.

Q. Acetyl CoA is used for what purposes?
A. Oxidation in TCA cycle, fatty acid synthesis,cholesterol synthesis, steroid synthesis, and
ketone body formation.

Q. Succinyl CoA is used for what purposes?
A. Oxidation in TCA cycle, heme synthesis, and activation of acetoacetate.

Q. What is the function of biotin?
A. Carboxylation reactions.

Q. Name some reactions dependent on biotin.
A. Acetyl CoA carboxylase, propionyl CoA carboxylase, and pyruvate carboxylase.

Q. What is the antagonist for biotin?
A. Avidin.

Q. What is its use in laboratory?
A. Biotin-avidin reaction is used in immunosorbent assays.

Q. What is the chemical nature of folic acid?
A. Pteroyl glutamic acid (pteridine + PABA + glutamic acid).

Q. What is PABA?
A. Para amino benzoic acid.

Q. What is the co-enzyme form of folic acid?
A. Tetrahydro folic acid.

Q. What is the main function of folic acid?
A. Tetrahydro folic acid is the carrier of one carbon units.

Q. What are the causes of folate deficiency?
A. Pregnancy, defective absorption (sprue, celiac disease), anticonvulsant drugs (hydantoin,
dilantin, phenytoin, phenobarbitone), hemolytic anemias, and dietary deficiency.

Q. What is the major manifestation of folic acid deficiency?
A. Macrocytic anemia.

Q. Folic acid deficiency in pregnancy is associated with what?
A. Folic acid deficiency during pregnancy may lead to neural tube defects in the fetus. Folic acid
prevents birth defects (fetal malformations such as spina bifida).

Q. What are the other minor effects of folic acid?
A. Folic acid is also useful to reduce the level of homo-cysteine in blood, and therefore helps in
preventing heart diseases. Folic acid is beneficial in prevention of cancer.

Q. What are the laboratory findings in folic acid deficiency?
A. (1) Normal folic acid level in serum is decreased.(2) FIGLU is excretion is more, especially after
histidine load. (3) AICAR excretion in urine. (4) Peripheral blood picture shows macrocytic anemia. (5)
Homocysteine level in blood is increased

Q. What are the sources of folic acid?
A. Yeast, liver, egg, green leafy vegetables, cereals,and pulses.

Q. What is the daily requirement of folic acid?
A. The RDA of free folate is 200 mg/day. In pregnancy the requirement is increased to 400 mg/day.

Q. What is the mechanism of action of sulphonamides?
A. They are anti-bacterial agents. They have structural similarity with PABA. Therefore they competitively
inhibit the enzyme responsible for the incorporation of PABA into folic acid.

Q. What is the mechanism of action of trimethoprim?
A. It inhibits the folate reductase and so formation of THFA is reduced. It is bactericidal agent.

Q. What is mechanism of action of methotrexate?
A. It inhibits folate reductase, and is a powerful anticancer drug.

Q. What are inhibitors of folic acid?
A. Methotrexate, trimethoprim, pyrimethamine and sulphonamide.

Q. Name a water soluble Vitamin, which is stored in the body.
A. Vitamin B12.

Q. What is the metal present in Vitamin B12?
A. Cobalt.

Q. What is the ring system present in Vitamin B 12?
A. Corrin ring.

Q. Vitamin B12 is absorbed from where?
A. Ileum.

Q. What is the transport form of Vitamin B12?
A. Methyl B 12.

Q. What is the carrier of Vitamin B12 in blood?
A. Transcobalamin-II, a glycoprotein, is the specific carrier.

Q. What is the storage form of Vitamin B12?
A. It is stored in the liver cells, as ado-B12 form, in combination with transcobalamin-I or transcorrin.

Q. What is the co-enzyme function of Vitamin B 12?
A. Methyl malonyl CoA isomerase, and homocysteine methyl transferase.

Q. What abnormalities are seen in Vitamin B 12 deficiency?
A. Methyl malonic aciduria, accumulation of methylmalonic acid, breakdown of myelin sheaths and
interruption in nerve transmission. Homocysteinuria is also seen.

Q. What abnormal compound is excreted in Vitamin B12 deficiency?
A. Methyl malonic acid in urine.

Q. What is folate trap?
A. The production of methyl THFA is an irreversible step. Therefore, the only way for generation of free
THFA is methyl THFA to THFA, by a Vitamin B12 dependent step. When B12 is deficient, this
reaction cannot take place. This is called the methyl folate trap.

Q. What is the clinical importance of folate trap?
A. This leads to the associated folic acid scarcity in B12 deficiency.

Q. What is the explanation of demyelination in Vitamin B12 deficiency?
A. In Vitamin B12 deficiency, there is non-availability of active methionine. Therefore, methylation
of phosphatidyl ethanolamine to phosphatidylcholine is not adequate. This leads to
deficient formation of myelin sheaths of nerves.

Q. What are the causes of B12 deficiency?
A. Nutritional B12 deficiency, decrease in absorption,addisonian pernicious anemia, atrophy of
gastric epithelium, and pregnancy.

Q. What is the cause for pernicious anemia?
A. It is an autoimmune disease with a strong familial background. Antibodies are generated against
intrinsic factor. So IF is deficient, leading to defective absorption of B12.

Q. What are the manifestations of Vitamin B12 deficiency?
A. Megaloblastic anemia and subacute combined egeneration.

Q. What is the difference in folate deficiency and B12 deficiency?
A. In folate deficiency, there is macrocytic anemia,and in B12 deficiency, there is additional
neurological symptoms also.

Q. What is the daily requirement of Vitamin B12?
A. One to two microgram/per day.

Q. A patient who has undergone gastrectomy is likely to develop deficiency of which Vitamin?
A. Vitamin B12.

Q. In Vitamin B12 deficiency, what are the abnormalities seen in urine?
A. Urine may contain methyl malonic acid, homocystine,cystathione, and formimino glutamic acid.

Q. Which is the Vitamin totally absent in plant sources?
A. Vitamin B12.

Q. What are the sources of Vitamin B12?
A. Liver, meat, fish, and curd.

Q. What is the chemical structure of Vitamin C?
A. L-ascorbic acid.

Q. How it is synthesised?
A. Man and primates cannot synthesise ascorbic acids. Lower animals could synthesise it from
glucose through glucuronic acid pathway.

Q. What are the major functions of ascorbic acid?
A. Ascorbic acid promotes collagen formation through its action on post-translational
hydroxylation of proline and lysine residues.

Q. What are the other functions of ascorbic acid?
A. Parahydroxy phenyl pyruvate oxidation to homogentisic acid, iron absorption from the intestine,
reconversion of methemoglobin to hemoglobin,and adrenal steroidogenesis.

Q. Which Vitamin is required for post-translational modifications?
A. Ascorbic acid.

Q. What is the daily requirement of ascorbic acid?
A. 75 mg per day.

Q. Scurvy is due to the deficiency of which Vitamin?
A. Ascorbic acid.

Q. What are the important features of scurvy?
A. Hemorrhagic tendency, microcytic anemia, bone pain, bleeding gums

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------

Vitamin

Q. What is the pro-Vitamin for Vitamin A?

A. Beta carotene present in plants.

Q. What is the major function of Vitamin A?

A. In vision, as the Wald's visual cycle.

Q. What causes the nerve impulse in retina?

A. Photo-isomerisation of 11-cis retinal to all trans- retinal.

Q. How is all trans-retinal regenerated?

A. Trans-retinal is taken to liver, where it is made to trans-retinol, then isomerised to cis-retinol and then to cis retinal.

Q. What are the enzymes required for this regeneration?

A. Alcohol dehydrogenase and retinol isomerase.

Q. What are other minor biological roles of Vitamin A?

A. Normal maintenance of epithelium and skin, glycoprotein synthesis, reproduction, cell differentiation, and anti-oxidant role.

Q. What are the sources of Vitamin A?

A. Carrot, mangoes, papaya, green leafy vegetables, and fish liver oil.

Q. What are the deficiency manifestations of Vitamin A?

A. Night blindness, xerophthalmia, keratomalacia, and keratinisation of epithelium.

Q. Nyctalopia is due to the deficiency of which Vitamin?

A. Vitamin A.

Q. What is the daily requirement of Vitamin A?

A. 750 to 1000 microgram.

Q. How cholecalciferol is synthesised?

A. From 7-dehydro cholesterol in the malpighian layer of epidermis, by the action of ultra violet rays.

Q. How Vitamin D is activated?

A. Cholecalciferol from skin reaches liver. There it is hydroxylated to form 25-hydroxy cholecalciferol (25-HCC). It then reaches kidney, where further hydroxylation takes place to form 1,25-dihydroxy cholecalciferol (DHCC).

Q. What is calcitriol?

A. 1,25-dihydroxy cholecalciferol, or active Vitamin D, contains three hydroxyl groups at 1, 3 and 25 positions. So it is called calcitriol.

Q. Which Vitamin acts as a pro-hormone?

A. Vitamin D.

Q. What is the function of Vitamin D?

A. It increases absorption of calcium from intestine, and it also increases mineralisation of bone.

Q. How Vitamin D increases absorption of calcium?

A. Calcitriol binds to a cytoplasmic receptor. The hormone-receptor complex interacts with DNA and causes transcription of specific genes that code for calbindin. Due to the increased availability of calcium binding protein, the absorption of calcium is increased.

Q. How is Vitamin D deficiency manifested?

A. Rickets in children and osteomalacia in adults.

Q. In renal disease, oral doses of Vitamin D may not be effective, why?

A. Hydroxylation and activation of Vitamin is taking place in kidney.

Q. What are the causes of rickets?

A. Chronic renal failure, liver diseases, and under- exposure to sunlight.

Q. What is the daily requirement of Vitamin D?

A. 5-10 microgram.

Q. What is the chemical nature of Vitamin E?

A. Alpha tocopherol.

Q. What is the function of Vitamin E ?

A. Anti-oxidant.

Q. What is the relationship of selenium with Vita- min E?

A. They act synergistically as anti-oxidants.

Q. What is the source of Vitamin E?

A. Vegetable oils are rich sources of Vitamin E, e.g. wheat germ oil, sunflower oil, safflower oil, cotton seed oil, and palm oil.

Q. What is the normal daily requirement of Vitamin E?

A. 15 mg or 33 international units.

Q. What is the chemical nature of Vitamin K?

A. Naphthoquinone derivative.

Q. What is menadione?

A. It is synthetic water soluble Vitamin K, widely used in clinical practice.

Q. What is the function of Vitamin K?

A. Gamma carboxylation of clotting factors such as prothrombin.

Q. Deficiency of Vitamin K can occur in which conditions?

A. Obstructive jaundice, antibiotic therapy, and administration of dicoumarol.

Q. What is the mechanism of action of dicoumarol?

A. It competitively inhibits Vitamin K epoxide reductase.

Q. So, dicoumarol is used for what purpose?

A. To prevent intravascular thrombosis.

Q. Excess dicoumarol will produce what?

A. Bleeding tendency.

Q. Which substance will inhibit Vitamin K?

A. Dicoumarol.

Q. Excess dose of Vitamin K in neonates may lead to which condition?

A. Hemolysis and jaundice.

Q. Bleeding tendency is common in the deficiency of which?

A. Vitamin K, Vitamin C, and platelets.

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------

Difference between Primary Cell Wall and Secondary Cell Wall

Primary and Secondary Cell wall

Cell wall was first discovered by Robert Hooke in 1665. In cells of bacteria, cyanobacteria, protists, fungi and plants, a thick, rigid, protective cell wall is present outside the plasma membrane. One of the most important differences between plant and animal cells is the presence of cell wall in plant cells.

Composition of cell wall: The composition of cell wall varies in different groups.

Bacteria: Peptidoglycan cell wall: Cell wall is composed of protein-lipid-polysaccharides having two important chemical components: N -acetyl glucosamine (NAG) and N-acetyl muramic acid (NAM).

Bacterial Cell wall & Gram Staining

Bacteria can be divided into two large groups on the basis of differential staining technique called Gram Stain developed by Christian Gram.

Gram Staining

Procedure

How Gram Stain Works? Gram Staining Principle: Step by step procedure with explanation

Gram Positive Bacteria

Split into a low and high GC group which reflects the GC content of their DNA.
ex: Staphylococcus, Actinobacteria, Streptococcus, Lactobacillus, Cornyebacterium, Listeria ,Bacillus, Nocardia, Clostridium

Gram negative bacteria

Proteobacteria is the largest and diverse group of bacteria including many of the more commonly known gram-negative bacteria
Ex: Escherichia coli (E.coli),Helicobcater, Salmonella,Cyanobacteria, Klebsiella,Hemophilus, Neisseria, Pseudomona

A comparison of cell walls of gram positive and gram negative bacteria

Algae: Cell wall contains cellulose and a variety of glycoproteins.

Cell wall

In plant cells, apart from the plasma membrane, there is a hard protective covering which is called the cell wall.

Plant cell wall

Why do plants have cell wall? What would happen if we possess cell wall?

The advantage of having a cell wall is, it is primarily made up of cellulose, a tough substance that provides great protection from external injuries. Like two sides of a coin, this protection is delivered at the expense of free movement. We can move in search of food as we don’t have cell wall. Plants cannot move and have to find their food from the rooted site itself. Definitely, their capability of photosynthesis clearly overcomes this disadvantage.

In plant cells, cell wall is made up of cellulose, hemicelluloses, pectin and proteins.

Remember fungal cell wall is made up of chitin (polymer of N-acetyl glucosamine) and bacterium has a peptidoglyacan cell wall.

Cell wall is a stiff protective layer outside plasma membrane and provides mechanical support and also determines the shape of the cell.

Plant cell wall, what is it made up of?

Cell wall is composed of variety of polysaccharides. Cellulose microfibril is the basic building unit of primary wall surrounded by a matrix of hemicelluloses and pectins. Secondary wall consists of cellulose microfibrils surrounded by lignin. The orientation of microfibrils is governed by cytoskeleton.

Cellulose is a linear, unbranched polymer, consisting of straight polysaccharide chains made of glucose units linked by 1-4 β glycosidic bond.

Structure of cell wall

What are microfibrils?

Each microfibril is a ribbon like flat fibre of 25-30 nm in diameter. Each microfibril cosists of three elementary fibrils (micelles). Each elementary fibril is made up of 100 cellulose units. Each cellulose molecule consists of 40-70 glucan chains.

Thus 1 microfibril=3x100x70=~21000 glucan chains. Microfibrils have great tensile strength similar to that of rubber.

In short

Primary wall=cellulose microfibrils+ hemicelluloses+pectin

Middle lamella=pectin

Secondary wall=cellulose microfibrils+ lignin

What are Hemicelluloses?

Are short branched heteropolymers made up of various kinds of monosaccharides like xylose, mannose, glucose etc.

Eg: glucomannans, xyloglucans, xylans.

What are Pectins?

A water soluble branched polysaccharide made up of negatively charged D-galacturonic acid and D-glucoronic acid residues.

Other depositions include cutin (made of fatty acids), Suberin (water resistant coat comprising of fatty acids found in many plant cell walls and cork. Mineral deposits are present in the cell wall of families Cruciferae and Cucurbitaceae (Calcium deposits), whereas silicate deposits are common in the cell wall of Graminae, grass family.

Cell wall synthesis?

Primary cell wall is the first formed boundary of the cell that is formed when cell is increasing in size. It is thin and permeable but cutin deposition makes it impermeable at some sites. Cellulose is synthesised from uridine diphosphoglucose (UDP-glucose) by an enzyme complex, cellulose synthase. Matrix materials, hemicelluloses and pectin are synthesised in the golgi apparatus and transported to the plasma membranes as vesicles where it is discharged and deposited.

Why wood is so hard?

Secondary wall is thick and permeable and consists of cellulose microfibrils and lignin. Even the master digesters, fungus cannot degrade lignin that offers mechanical protection from fungal pathogens. Lignin deposition is very common in wood.

The formation of the secondary wall is not uniform in all the cells. The differentiation of various types off cells like parenchyma, collenchyma, sclerenchyma, fibres and tracheids are due to the secondary wall formation

Tertiary wall: In some tissues a tertiary cell wall is formed on the inner surface of the seconary cell wall. This layer is very thin and is found in the xylem tracheids of gymnosperms. It is composed of mainly of xylan, instead of cellulose.

Structure of lignocellulose:The main component of lignocellulose is cellulose, a beta(1–4)-linked chain of glucose molecules. Hydrogen bonds between different layers of the polysaccharides contribute to the resistance of crystalline cellulose to degradation. Hemicellulose, is composed of various 5- and 6-carbon sugars such as arabinose, galactose, glucose, mannose and xylose. Lignin is composed of three major phenolic components, namely p-coumaryl alcohol (H), coniferyl alcohol (G) and sinapyl alcohol (S). Lignin is synthesized by polymerization of these components and their ratio within the polymer varies between different plants, wood tissues and cell wall layers. Cellulose, hemicellulose and lignin form structures called microfibrils, which are organized into macrofibrils that mediate structural stability in the plant cell wall.

How adjacent cells are joined?

Middle lamella: It is thin amorphous layer of cemeting material present between the adjacent cells. It is chiefly made up of calcium pectate. It is formed at the time of cytokinesis by the joint activity of the cells between it lies.

How plant cells communicate with each other?

Plasmodesmata

Plamodesmata and desmotubule

The cell wall is perforated by narrow pores or pits at many places.Through these narrow pores, fine strands of cytoplasm are extending. These strands are called plasmodesma connections or plasmodesmata. These connect the cytoplasm of adjacent cells and facilitate the movement of substance between cells.

Plasmodesmata are narrow channels through the wall bound by plasmalemmma containing cytoplasm and often a desmotubule. The desmotubule is the cental core and is composed of protein subunits consists of modified membraneous structure continuous with the endoplasmic reticulam of the adjoining cells.These membraneous structures probably originate from the ER. Desmotubule acts as valve to control the direction of flow of materials.The functions of plasmodesmata may vary. It is concerned with the transport of materials from one cell to another and also conduction of stimuli. In the case of certain parasites like Viscum, Loranthus, Cuscuta etc plasmodesmata connections exist between the haustoria and the cells of their host. Through these channels food and virus are transported.

Functions of the cell wall

Cell walls primary function is mechanical support. It acts like a skeletal framework of the plants.
Cell wall is tough and has high tensile strength. Still plant cell is fully permeable to water and solutes. Plant cell wall has minute water filled channels through which water,hormones and gases passes to and fro.
Cell wall shows plasticity and elasticity during cell growth.
It helps to maintain the balance of intracellular osmotic pressure with that of its surrondings
Lignification of secondary walls greatly enhances compressive strength permitting woody structures to reach the sky. Cell wall upon lignification becomes dead as it becomes impermeable and thus protoplasm has no access to take up solutes that is why lignified tissue is always dead.
Lignin provided extra mechanical strength and also provides a water resistant channel for transport of solutes.

Additional Points

Algal cell wall:

Algae typically possess walls constructed of glycoproteins and polysaccharides, however certain algal species may have a cell wall composed of silicic acid. Alginic acid is common polysaccharide in the cell walls of brown algae. Manosyl form microfibrils in the cell walls of a number of marine green algae, such as Acetabularia as well as as in the walls of the some red algae, like Bangia and Porphyra.Sulphonated polysaccharides occur in the cell walls of most algae, those common in red algae include agarose, carrageenan, porphyran, furcelleran and funoran.The group of algae known as the diatoms synthesise their cell walls from silicic acid ( specially orthosilicic acid, H₂SiO₄).

Fungi: Cell wall is made up of chitin (Polymer of N-acetyl glucosamine)

Plants: Cell wall is made up of cellulose (β-D-glucose units), hemicellulose (Arabinose, mannose, xylose, galactose, etc.) and pectin (Galactose, galacturonic acid and arabinose).

A typical cell is made up of four layers: middle lamella, primary, secondary and tertiary wall. Middle lamella is the cementing layer between the cells. It is made up of Ca and Mg pectates.

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biotechnology

1. Highest capacity vector is

a) Cosmid

b) YAC

c) Yeast integrative vector

d) Bacteriophage vector

Ans: b

Cosmid: A plasmid with a cos site of lambda phage.Insert size: 30-45 kb
YAC: yeast artificial chromosome. Insert size: 1 Mb
Bacteriophage vectors: refers to lambda and M13 phage vectors
Lambda phage vectors: Insert size: 8-23 kb
M13 vectors used for obtaining single stranded copies of cloned DNA that are suited for DNA sequencing
BAC: Bacterial Artificial Chromosome. Insert size: 300 kb

2. The C value denotes the total number of DNA in a

a) Diploid

b) Haploid

c) Aneuploid

d) Polyploid

Ans:b

C value: Haploid DNA content of an organism or the amount of DNA in haploid nuclei like a gamete.
C value paradox: refers to the phenomenon that huge genomic content has nothing to do with the complexity of an organism.For eg: Protists has genome size much larger than humans.

3. Cdc mutants are useful for the study of

a) Chromosome breakpoint

b) Apoptopsis

c) Various stages of Cell cycle

d) Homeodomain

Ans: c cdc refers to cell division cycle

4. RNA is very much susceptible to hydrolysis in alkali because

a) It contains Uracil residues in its structure

b) Its 2’ OH groove participate in intramolecular cleavage of phosphodiester backbone

c) Cleavage occurs in the glycosilic bonds of purine bases

d)Cleavage occurs in the glycosilic bonds of pyrimidine bases

Ans:b

Because of the presence of 2’ OH group in the ribose sugar
DNA is more stable than RNA because of the presence of H at 2’ position in DNA rather than OH in RNA.

5. Which one of the following is not a requirement of a PCR reaction?

a) DNA template

b) NTPs

c) MgCl2

d) Taq polymerase

Ans:d

Here the best option is MgCl2 even though it is required for DNA polymerase activity. (It can be avoided)

6. The heterozygosity of any locus can be ascertained by

a) SNPs

b) RFLPs

c) FISH analysis

d) Either RFLP analysis or SNP

Ans: d

SNP: single nucleotide polymorphism refers to the variation in the lengths of some DNA btw individuals due to single base changes

Application: used in DNA finger printing

RFLP: restriction fragment length polymorphism: refers to the variation in the restriction fragment length between individuals of a species.
FISH: florescence insitu hybridization: hybridizing fluorescently labelled DNA probes on to human chromosome preparations allows genes to be mapped directly to their chromosomal locations.

7. Hormone pairs requires for a callus to differentiate are

a) Auxin and Cytokinin

b) Auxin and Gibberellin

c) Cytokinin and Gibberellin

d) Ethylene and Gibberllin

Ans: a

Auxin induces rooting whereas cytokinins promote shooting if supplied in optimum ratio.

8. Embryo rescue is a useful technique to

a) Grow /generate hybrids between different plant species

b) Complete the growth of embryos susceptible to defects in seed development

c) Break the dormancy of seeds

d) All of the above

Ans:d

9. Antibody diversity is generated by

a) protein splicing

b) somatic mutations

c) allelic exclusion

d) interchromosomal recombination

Ans: b

Somatic mutation: a mechanism by which point mutations are introduced into rearranged immunoglobulin variable region genes during activation and proliferation of B cells. It contributes significantly to antibody diversity.
Allelic exclusion: a process that permits the expression of only one of the allelic forms of a gene. It contributes to specificity of IgGs

10. The precursor for penicillin-G biosynthesis during fermentation process is

a)Phenylacetic acid

b)Acetic acid

c)Phenoxy acetic acid

d)None of the above

Ans:c

11.Plastome is

a)Plasmalemma protein

b)A type of plasmid

c)An organellar genome

d)None of the above

Ans: plastome: Genetic material of plastid like Chloroplast

12. Which of the following process require energy

a) ligation

b) restriction digestion

c) hybridization

d) transformation

Ans:a

Ligation: sealing of single stranded nicks or breaks by ligase enzyme. The process requires ATP and NADP⁺.

13) Enhanced axillary branching for multiple shoot production is promoted by

a)2,4-D

b)Abscisic acid

c)BA (Benzyl adenine)

d)Gibberellic acid

Ans:a

2,4-D is an auxin and auxin is responsible for sustaining apical dominance there by promoting axillary branching

14. Viral replication within cells is inhibited by

a)IL-4

b)IL-1

c)IFN alpha

d)TNF alpha

Ans:c

Interferons: are antiviral agents (proteins) secreted by virus infected cells and induces a virus resistant state to the surrounding cells by inhibiting its replication.

15. In the course of cell cycle, the level of the protein cyclin abruptly falls during

a) G1phase

b) G2 phase

c) S phase

d) M phase

Ans:d

16. Protein binding regions of DNA are identified by one of the following techniques

a) Finger printing

b) Foot printing

c) Southern blotting

d) Western blotting

Ans: (b) Foot Printing

Foot Printing: The identification of a protein-binding site on a DNA molecule by determining which phosphodiester bonds are protected from cleavage by DNase I.
Southern Blotting: The technique used for identifying specific DNA fragment using labelled probe.

17.Si RNA (s) interfere at

a) Transcriptional level

b) Post -transcriptional level

c) DNA replication level

d)Translational level

Ans: (b) Post -transcriptional level

18. Plant secondary metabolites

a) Help to increase the growth rate of plant

b) Help in plant reproduction processes

c) Provide defence mechanisms against microbial attack

d) Make the plant susceptible to unfavourable conditions

Ans: (c) Provide defence mechanisms against microbial attack

19. Mobile genetic elements present in human genome are

P) LINES

Q) SINES

R) P elements

S) IS elements

(a) Q, R (b) P, Q (c) P, R (d) Q, S

Ans: (b) P, Q

20. Meristems escape virus invasion because

a)Vascular system is absent in the meristem

b) of low metabolic activity in the meristem

c) of low endogenous auxin level

d) the virus inactivating system has low activity in the meristem

Ans: b) of low metabolic activity in the meristem

21. The enzyme that can be used in 5’end labeling of DNA are

P) Alkaline phosphatase

Q) DNA ligase

R) Terminal transferase

S) Polynucleotide kinase

(a) P, S (b) R, Q (c) P, R (d) R, S

Ans: (a) P, S

22. Identify the natural plant growth regulators from the following list

P) Zeatin

Q) Benzylamino purine (BAP)

R) Indole Acetic Acid (IAA)

S) 2,4-Dichlorophenoxyacetic acid (2,4-D)

(a)P, Q (b) Q, S (c) P, R(d) R,S

Ans: c) P, R

23. Cells of meristemoid are best described as

a) differentiated and non dividing

b) Dedifferentiated and dividing

c) differentiated and dividing

d) dedifferentiated and non dividing

Ans: c) differentiated and dividing

24. Ultra filtration process cannot be used for

a)Fractionation of Proteins

b)Desalting

c) Harvesting of cells

d)Selective removal of solvents

Ans: c) Harvesting of cells

25. The number of replicons in a typical mammalian cell is

a) 40-200

b) 400

c) 1000-2000

d) 50000-100000

Ans: a) 40-200

26. What product will result from complete hydrolysis of soluble dextran

a) Sucrose only

b) Fructose only

c) Glucose &Fructose only

d) Glucose only

Ans: d) Glucose only

27. The mobility of DNA in agarose gel electrophoresis is solely based on its

a) Charge

b) Conformation

c) Size

d) None of these

Ans: c) Size

28. Which of the following fluorescent probes is used to monitor the progress of amplification of Real Time PCR?

a) SYBR Green

b) FITC

c) Cyan Blue

d) Rhodamine

Ans: b) FITC

29. Expression of which of the following reporter genes does not require addition of specific substrate for detection

a) Luciferase

b) β- Glucuronidase

c) β-Glucosidase

d) Green Fluorescent Protein (GFP)

Ans: a) Luciferase

30. Zinc fingers are characteristic of

(a) Blood clotting Proteins

(b) RNA Chaperones

(d) Lysosomal hydrolyses

Ans: DNA binding proteins

Chaperons: proteins that assist in proper folding of proteins.

31. Multiplication of genetically identical copies of a cultivar by asexual reproduction is known as

(a) aclonal propagation

(b) clonal propagaation

(d) vegetative propagation

Ans: clonal propagaation

32. Parthenogenetic embryos in plant are those are formed by

(a) unfertilized eggs

(b) fertilized eggs

(d) sporophytic cells

Ans: unfertilized eggs

Parthenogenesis: The development of an individual from an egg without fertilization.

33. Which one of the following is the growth factor used for growth of tissues and organs in plant tissue culture?

(a) Cytokinin

(b) Cysteine

(d) Cyclic AMP

Ans: Cytokinin

Cysteine :Sulphur containing amino acid
Cytidylate: an enzyme with kinase activity
Cyclic AMP: second messenger in intracellular signal transduction

34. Which of the following techniques is best suited for immobilizing an affinity ligand?

(a) Physical adsorption

(b) Gel entrapment

(d) Covalent linkage to a spacer arm

Ans: Covalent linkage to a spacer arm

35. To be a cloning vector, a plasmid does NOT require

a) an origin of replication

b) a restriction site

c) an antibiotic resistance marker

d) to have a high copy number

Ans: d) to have a high copy number

Properties of a Cloning Vector

Should be able to replicate autonomously
Easy to transform
Should have suitable marker
Unique restriction sites
For expression vector, control elements like promoter, operator etc should be there.

36. Enzyme papain is used with success to

a) increase in meat production

b) leaven bread

c) ripen papaya fruit

d) tenderize meat

Ans: d) tenderize meat

Source: papaya fruit

37. For protoplast fusion to be successful in plant cells

a) fusion agents other than polyethylene glycol should be used

b) cellwall of the two strains of cells should be compatible

c) DNA between the two cells should be compatible

d) osmolarity of the medium is not important

Ans: DNA between the two cells should be compatible

38. In animal cell culture, the addition of serum to media is essential for providing

a) amino acids for protein synthesis

b) nucleotides for DNA synthesis

c) growth factors

d) All of the above

Ans: All of the above

39. Which one of the following reactions is used for the purpose of recycling enzymes in bioprocesses?

a) isomerisation

b) immobilisation

c) phosphorylation

d) polymerisation

Ans: Immobilisation

Technique used for the fixation of enzymes or cells on to solid supports
Advantage: reuse of enzyme for many reactions
Methods of enzyme immobilization:-adsorption, covalent bonding, entrapment, membrane confinement

------------------------------------------ Best Wishes: Dr.Ehab Aboueladab, Tel:01007834123 Email:ehab10f@gmail.com,ehababoueladab@yahoo.com ------------------------------------------