Enzymes

1. Group of organic catalysts, protein in nature, present inside the living cells

a- Enzymes

b- Catalysts

c- Hormones

d- None of the above

2. All of the following is true regarding enzymes except …..

a- Heat labile

b- Colloidal

c- Dialyzable

d- High molecular weight

3. Organic substance on which the enzyme acts …….

a- Substrate

b- Co-Enzyme

c- Product

d- None of the above

4. All of the following can be considered as a co Enzyme for transfer of H except

a- Biotin

b- ATP

c- FAD

d- Folic acid

5. One of the following can be considered as a co Enzyme for transfer of groups other than H except

a- Biotin

b- ATP

c- FAD

d- Folic acid

6. One of the following is considered a feature of Enzymes except ……

a- Globular Proteins

b- Undergo Denaturation

c- Simple Proteins

d- Non-Specific

7. Enzyme acts on a special type of bond at specific site and attached to specific groups ……

a- Group Specificity

b- Absolute Specificity

c- Relative Specificity

d- Optical Specificity

8. D-amino acid Oxidase represents ……

a- Group Specificity

b- Absolute Specificity

c- Relative Specificity

d- Optical Specificity

9. Pancreatic Lipase represents …….

a- Group Specificity

b- Absolute Specificity

c- Relative Specificity

d- Optical Specificity

10. Special sequence of amino acids in the protein molecule of the enzyme to which the substrate is attached…….

a- Catalytic Site

b- Active site

c- Allosteric Site

d- None of the above

11. All sequences of amino acids which affect the activity of the enzyme ……

a- Catalytic Site

b- Active site

c- Allosteric Site

d- All of the above

12. Substrate induces a conformational change in the catalytic site …….

a- Lock and key model

b- Flexible model of catalytic site

c- Rigid model of catalytic site

d- None of the above

13. Concentration of the product increases directly by time …….

a- Maximum Velocity

b- End velocity

c- Initial Velocity

d- None of the above

14. Increase in substrate concentration leads to ……..

a- Increase of velocity

b- Increase in enzyme activity

c- Increase of V max

d- All of the above

15. Substrate concentration which produces half maximal velocity (½Vmax.) ……….

a- Full Concentration

b- Null Concentration

c- Michael’s Concentration

d- All of the above

16. Increase in enzyme concentration ……. the rate of reaction

a- Increase

b- Decrease

c- No effect

d- Permissive effect

17. Complete irreversible loss of enzyme activity occurs at ……

a- 37 degree C

b- 45 degree C

c- 0 degree C

d- 60-65 degree C

18. Temperature at which the enzymatic reaction velocity is maximal ……

a- Optimum Temperature

b- 37 degree C

c- 65 degree C

d- A and b together

e- None of the above

19. Optimum PH for Trypsin is ……

a- 6.8

b- 8.4

c- 8

d- 2

20. Optimum PH for Alkaline Phosphatase

a- 6.8

b- 8.4

c- 8

d- 2

21. All of the following inhibits enzymatic activity except

a- Physical Agents

b- Heating

c- Shaking

d- Red and Blue lights

22. Pepsin is activated through ……..

a- Removal of inhibitory peptide

b- Reducing agent

c- Minerals

d- Allosteric activators

23. Glyceraldehyde 3-P dehydrogenase is activated through …..

a- Removal of inhibitory peptide

b- Reducing agent

c- Minerals

d- Allosteric activators

24. Metaloenzymes is activated through …..

a- Removal of inhibitory peptide

b- Reducing agent

c- Minerals

d- Allosteric activators

25. Tyrosinase requires ……

a- ZN ++

b- CU ++

c- CL –

d- MG ++

26. Phosphofructokinase enzyme is activated through …..

a- Removal of inhibitory peptide

b- Reducing agent

c- Minerals

d- Allosteric activators

27. Activation by Phosphorylation excludes one of the following …….

a- Hormone sensitive lipase

b- Glycogen Phosphyrlase

c- Glycogen Synthetase

d- None of the above

28. Competitive inhibition includes all of the following except

a- Chemical structure of the inhibitor closely resembles that of the substrate.

b- Combines Reversibly with the enzyme

c- When both the substrate and the inhibitor are present they compete for the same binding site.

d- V max is decreased

e- Is removed by increases the concentration of inhibitor

29. Reversible noncompetitive Inhibition includes all of the following except

a- I combine with the enzyme away from the catalytic site.

b- The I is not similar to the substrate in structure.

c- The I can combine with the free enzyme or with the enzyme substrate

d- increase the Km

30. Phosphoglyceraldehyde dehydrogenase Resembles …….

a- Reversible Non Competitive Inhibition

b- Irreversible noncompetitive Inhibition

c- Allosteric inhibition

d- Competitive inhibition

31. Increased product concentration …… the enzyme activity

a- Increases

b- Decreases

c- No effect

d- Permissive effect

32. Substances which stimulate gene expression into protein …….

a- Inducer

b- Suppressor

c- Repressors

d- Co-Enzymes

33. Concerning Isoenzymes …….

a- Have quaternary structure and the individual subunits in each isoenzyme are different from the others

b- They act on the different substrate and will give the same product

c- They have different affinity to the substrate.

d- They are present in different tissues.

34. HMMM is present in ……..

a- Heart

b- Kidney

c- Liver

d- Muscles

35. HHMM is present in

a- Kidney

b- Muscles

c- Heart

d- None of the above

36. Non Functional plasma enzymes include all of the following except …..

a- Transaminases ( AST & ALT )

b- Alkaline Phosphatase

c- Lipoprotein lipase

d- None of the above

37. Increased in bone metastasis ………

a- Alkaline phosphatase

b- Creatine kinase

c- LDH

d- None of the above

38. Increased in Prostatic Carcinoma ………

a- Alkaline phosphatase

b- Creatine kinase

c- LDH

d- None of the above

39. Decreased in Galactosemia ………

a- Streptokinase

b- Digestive enzymes

c- Galactosyl transferase

d- α-chymotrypsin

40. Treatment of intraocular hemorrhage is done by

a- Streptokinase

b- Digestive enzymes

c- LDH

d- α-chymotrypsin

41. The oxidation process occurs by ………

a- Addition of oxygen.

b- Removal of hydrogen.

c- Loss of electron

d- All of the above

42. Redoxes that use oxygen as a hydrogen receptor are called ……..

a- Oxidases

b- Hyper peroxidases

c- Dehydrogenases

d- Oxygenases

43. Catalase is specifically abundant in all of the following except ……..

a- Liver

b- Kidney

c- Erythrocytes

d- Milk and leucocytes

44. Enzymes utilizing H2O2 as substrate ……….

a- Oxidases

b- Hyper peroxidases

c- Dehydrogenases

d- Oxygenases

45. LDH depends on ………. In dehydrogenation

a- Nicotinamide

b- FAD

c- C.AMP

d- None of the above

46. Enzymes which catalyze transfer of functional groups (G) other than hydrogen between a pair of substrates …….

a- Transferase

b- Oxygenases

c- Dehydrogenases

d- Hydrolases

47. All of the following are included in Transferase class of enzymes except …….

a- Transaminase

b- Hydrolase

c- Transglycosayl

d- None of the above

48. Split terminal peptide linkage splitting one amino acid at a time is ……..

a- Estrases

b- Endoeptidases

c- Exopeptidases

d- Glycosidases

49. Fumerase is an example of …….

a- Transferase

b- Hydrolase

c- Oxidase

d- Lyases

50. Lipase is an example of …….

a- Transferase

b- Estrases

c- Oxidases

d- Lyases

51. Enzymes link two molecules using energy from ATP ……

a- Lyases

b- Hydrolase

c- Ligase

d- Redox

52. Carboxylase is an example of …….

a- Transferase

b- Estrases

c- Oxidases

d- Ligases

Choose (A) for true and (B) For false of the following

53. Pepsin acts on peptide bonds between amino groups of aromatic amino acid and carboxylic group of another amino acid

54. Enzymes are usually specific in action

55. In Absolute specificity the enzyme acts at different rates on one type of bond in

Compounds chemically related

56. Enzymes may be considered to lower energy barriers for chemical reactions

57. Increase in the substrate concentration will lead to decrease in enzyme activity

58. Increase in enzyme concentration increase the rate of reaction

59. Some enzymes containing SH groups requires Minerals to be activated

60. In Competitive inhibition Vmax of the enzyme is not decreased

61. Inducers are substances which inhibit gene expression

62. Isoenzyme is oligomeric enzyme

Answers

1. A

2. C

3. A

4. C

5. C

6. D

7. A

8. D

9. C

10. A

11. B

12. B

13. C

14. A

15. C

16. A

17. D

18. D

19. C

20. B

21. D

22. A

23. B

24. C

25. B

26. D

27. C

28. D

29. D

30. A

31. B

32. A

33. B

34. D

35. A

36. A

37. A

38. B

39. C

40. D

41. D

42. A

43. D

44. B

45. A

46. A

47. B

48. C

49. D

50. B

51. C

52. D

53. A

54. A

55. B

56. A

57. B

58. A

59. B

60. A

61. B

62. A

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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.


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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


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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

 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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