Sunday, October 28, 2012

Chemistry Of Proteins-3

1. Why are amino acids called as Amino acids?
(Since they have an amino group and an acid group i.e. Carboxyl group which is ionized at the physiological p H and behaves as a proton donor and is thus an acid)
 2- What is meant by primary amino acids?
(Those amino acids which have a genetic information on the DNA for their synthesis are called as Primary or standard amino acids)
3- What is the linkage between the amino acids in a peptide?
(The amino acids are linked together by a peptide bond which is an anhydrous linkage between the amino acids)
4- Name the amino acids which are derived or modified after translation but are not incorporated in to the tissue proteins.
 (Homocysteine, GABA, Argino succinic acid, Ornithine, Citrulline, etc)
5- Define Denaturation
 ( It is the loss of secondary , tertiary or quaternary structure( if present ) of a protein on exposure to heat, UV light, acids, alkalies, heavy metal salts or even by vigorous shaking, the primary structure is left intact)
6-What is meant by a complete protein, give an example of a complete protein?
( A Complete protein contains all the essential amino acids in an appropriate amount  required for growth, repair and maintenance of body weight.  Example -Egg protein)
7- Give an example of a protein with axial ratios >10:1
(Fibrinogen, keratin, collagen )
8-How many amino acids can be accommodated in one turn of alpha helix?
(3.4 amino acids)
 9- What are chaperones?
 (These are the proteins which participate in the proper folding of the proteins)
10- What is the defect in “transmissible spongiform encephalopathies’?
(These are included under the category of Prion’s diseases and are fatal neurodegenerative diseases characterized by spongiform changes, astrocytic gliomas, and neuronal loss resulting from the deposition of insoluble protein aggregates in neural cells. The protein aggregates are formed of misfolded proteins.)
11-What is the difference between a homodimer and a heterodimer?
(Homodimer contains two copies of the same polypeptide chain, while in a heterodimer the polypeptides differ)
12-What are amphipathic helices?
(The alpha helices having predominantly hydrophobic R groups on one side of the axis of the helix and predominantly hydrophilic ones on the other side are called amphipathic helices)
13-All the amino acids except——- have a chiral centre.
14-What is meant by isoelectric  p H ?
 ( It is the p H at which amino acid carries no net electrical charge)
15-Proteins contain only D-amino acids, for which a left handed alpha helix is by far the more stable,  thus only left-handed helices are present in proteins. True or false?
 (False –Proteins contain only L-amino acids, for which a right-handed alpha helix is by far the most stable, and only right-handed alpha helices are present in proteins)
16-Give examples of metalloproteins-
( Alcohol dehydrogenase, glutamate dehydrogenase, Xanthine oxidase  etc. are the examples of metalloproteins
17-Give examples of non standard amino acids which are incorporated in to tissue proteins.
( Hydroxy proline, hydroxy lysine )
18– What is meant by zwitterion ?
( It is the form of amino acid present at its isoelectric p H,  both positive  and negative charges are there but the net charge is zero)
19-Name an indole ring containing amino acid-
20- Name the peptides which act as gastro intestinal hormones-
( Secretin, pancreozymin and cholecystokinin)
21- Name the amide group containing amino acids
(Asparagine, Glutamine)
22- What are derived proteins ?
(Proteoses, peptones and peptides etc, the product of digestion and denaturation are called as derived proteins )
23- Give two examples of antibiotic peptides
(Polymyxin, Penicillin, etc )
24-What is the difference between cysteine and cystine ?
( Two cystine residues are joined together by a disulfide bridge to from cystine )
25- What are histones? 
( Histones are simple proteins which can bind with DNA to form nucleoproteins, generally they are rich in basic amino acids like Arginine and lysine )
26- Which amino acid disrupts the alpha helical structure of the proteins ?
( Proline and hydroxy proline )
27- Name the components of Glutathione
(Glutamic acid, cysteine and glycine )
28- Name two proteins with a quaternary structure
( Immuno globulins, Hemoglobin, CPK , LDH etc )
29- What are brain peptides ?
( Met encephalin and Leuencephalin)
30- Name a Phospho protein
(Casein, Ovovitellin)
31-What is the product formed after decarboxylation of an amino acid ?
( Amines are formed after decarboxylation of amino acids- like Tryptamine, histamine Tyramine etc)
32-Name the sulphur-containing amino acids-
(Cysteine, cystine and Methionine)
33-Choose the aromatic amino acid out of the following-
Arginine, Histidine, lysine and Tyrosine —— (Tyrosine)
34-Choose an amino acid that does not participate in the alpha helical formation-
Methionine, tryptophan, serine, cysteine——
( Tryptophan )
 35- Millon’s reaction is specific for——- ?        
( Tyrosine )
36- Out of the followings which amino acid is not present in the proteins?
β- Alanine, Histidine, Glycine                    
(β- Alanine)
 37- Name a peptide which acts as a smooth muscle relaxant
( Bradykinin)
38-   What is the nature of prosthetic group in Ceruloplasmin ?
(Copper- It is metalloprotein)
 39- What is a nutritionally poor protein ?Give an example-
( A protein which lacks many essential amino acids is called a poor protein, E.g.- Gelatin
 40- Which protein is abundantly present in hair?     
(Keratin )
41-What is the significance of Biuret test?
 ( It is for the detection of proteins and peptides. Dipeptides and amino acids do not give this test positive, more than two peptide bonds are required for this test to be positive )
42- What is the nature of casein, the milk protein?
( It is a Phospho protein- A conjugated protein)
 43- What is the axial ratio in fibrous proteins?
 ( > 10:1)
 44- In proteins the alpha helical and beta pleated sheet structures are examples of-
Primary, secondary or tertiary structure ?            
( Secondary)
 45- Name an Imidazole ring containing amino acid 
46- Name a peptide  hormone which prevents diuresis –
( ADH)
47 What is the basis of using raw egg for heavy metal poisoning ?
( Egg protein binds with heavy metal to form metal proteinate complex, which is water-soluble and is excretable, else heavy protein binds with tissue proteins to cause damage)
48- The tertiary structure of a protein describes sequence of amino acids- true or false ?
( False- Tertiary structure describes the folding of the protein )
49- Give two examples of haemoproteins.
(Hemoglobin, Myoglobin, Cytochromes, Catalase, Peroxidase and Tryptophan Pyrrolase)
50-  In a protein the disulphide bridges can be broken by–
 ( Reduction )

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