Lesson 3: Peptides & Classification of Proteins

Question 1

What are peptides ?

Answer 1

Short sequences of amino acids linked together by covalent bonding

Question 2

How are peptides formed ?

Answer 2

Carboxyl Group of an amino acid with an Amino Group of another amino acid

Question 3

How is an aa read ?

Answer 3

From N-terminus

Question 4

What is hydrolyctic cleavage ?

Answer 4

Cleaving peptide bonds to their constituant amino acids by the hydrolysis of peptide linkages

Question 5

What is the Acid-Base behavior of a peptide dependent on ?

Answer 5

N-terminus , C-terminus , Ionizable R-group

Question 6

What is labelling by FDNB ?

Answer 6

Amino terminal named as 1-fluro-2,4-dinitrobenzene

useful for the determination of primary structure of the peptide

Question 7

What is labelling by FDNB ?

Answer 7

Amino terminal named as 1-fluro-2,4-dinitrobenzene

useful for the determination of primary structure of the peptide

Question 8

How many aa residues does glutathione have ?

Answer 8

3

glutamate, cysteine and glycine

Question 9

What are the functions of Glutathione ?

Answer 9

1)co-enzyme
2)participates in the second phase of the xenobiotic metabolism
3) reduce hydrogen peroxide (free radicle damaging to tissues) to water (antioxidant action)

Question 10

How do trypsin and chymotrypsin bring about hydrolysis of peptide bonds ?

Answer 10

Through Proteolytic Cleavage

action is highly specific

Question 11

What is Thyrotropin-releasing hormone (TRH) ?

Answer 11

a tripeptide released from the hypothalamus

Question 12

How many aa residues does TRH have ?

Answer 12

3

Pyroglutamate-Histidine-Proline

Question 13

What are enkephalins also known as ?

Answer 13

endogenous opiates

bind to receptors same to which synthetic opiates ex:morphine bind to

Question 14

What does oxytocin do ? How many aa residues ?

Answer 14

Stimulates uterine contractions. 9

Question 15

What does Glucagon do ? How many aa residues ?

Answer 15

Pancreatic hormone –> glucose homeostasis. 29

Question 16

What is Partial Double Bond Character ?

Answer 16

• single bond (C–N) does not show rotational freedom
• the peptide bond is actually resonance hybrid of two electron isome

Question 17

aExplain φ and ψ Angles.

Answer 17

1. Rotation around the nitrogen-and- α carbon bond is measured as the f φ(phi) angle
2. Rotation around the peptide carbon and α -carbon bond as the c ψ(psi) angle

allow proteins to fold into secondary structures

Question 18

T/F: The peptide bond is positivaley charged.

Answer 18

False. Uncharged

Question 19

T/F: O and H are in CIS position

Answer 19

F. Trans

Question 20

What are the substituents of the peptide bond atoms ?

Answer 20

1) Alpha Carbon 1
2) Alpha Carbon 2
3) H atom
4) O atom

Question 21

What results in the H-Bond between the O and H in a peptide ?

Answer 21

The sharing of electrons between the C and the N.