Med Biochem L2 - Amino acids and Peptides

Question 1

Definition of protein:

Answer 1

derived from Greek protos (first, primary), meaning the most basic and important substance of animal and plant nutrition.

Question 2

Catalyst:

Answer 2

various enzymes, about 1/3 of human genes encode enzymes.

Question 3

Transporter:

Answer 3

Oxygen transport (hemoglobin),
Fatty acid transport (albumin),
Various nutrients,
Hormones,
Drugs,
Toxic substances, etc.

Question 4

Regulatory role:

Answer 4

Growth factors,
Transcription factors,
Various hormones such as insulin and
Glucagon, etc.

Question 5

Contraction:

Answer 5

Myosin and actin in muscle

Question 6

Immune system:

Answer 6

Immunoglobulins,
Complement proteins

Question 7

Blood clotting:

Answer 7

Fibrinogen and coagulation factors

Question 8

Strructural Functions:

Answer 8

Bones,
Ligaments,
Extracellular matrix proteins

Question 9

Cytoskeleton:

Answer 9

Keratin,
Microtubules,
Microfilaments, etc

Question 10

A variety of protein functions are possible by unique 3D structures that are …

Answer 10

dictated by unique amino acid sequences.

Question 11

Some amino acids have an amino group on another carbon, for example, …

Answer 11

on an epsilon carbon in Lys.

Question 12

Amino acids have 2 stereoisomers:

Answer 12

L and D isomer.
In nature, the L isomer is dominant

Question 13

L isomer is … configuration.

Answer 13

S

Question 14

Under acidic pH, amino acids are … charged.

Answer 14

positively

Question 15

Under basic pH, amino acids are … charged.

Answer 15

negatively

Question 16

Under neutral pH, amino acids have … form.

Answer 16

Zwitterionic

Question 17

The … form cannot exist under any pH.

Answer 17

nonionic

Question 18

(Hydropathy index)
Positive:

Answer 18

hydrophobic

Question 19

(Hydropathy index)
Negative:

Answer 19

hydrophilic

Question 20

… can form cystine

Answer 20

Cysteine

Question 21

… : nonpolar thioethergroup

Answer 21

Methionine

Question 22

Cystine is …

Answer 22

hydrophobic

Question 23

-SH - …

Answer 23

Sulfhydryl group

Question 24

-S-S- - …

Answer 24

Disulfide bond

Question 25

Absorbance maxima at … nm

Answer 25

280

Question 26

Lysine pKa of side chains …

Answer 26

10.5

Question 27

Arginine pKa of side chains …

Answer 27

12.5

Question 28

Histidine pKa of side chains …

Answer 28

6.0

The only AA that has a pKa near neutral pH

Question 29

Aspartate pKa of side chains …

Answer 29

3.65

Question 30

Glutamate pKa of side chains …

Answer 30

4.25

Question 31

Isoelectric Point (pI): the point where the net charge is …

Answer 31

0

pI = (pK1 + pK2) / 2 (average of two pKa values)

Question 32

At the neutral pH, Histidine side chain is …

Answer 32

not charged.

Question 33

The reverse reaction is favored. (K<1)

Answer 33

The amino group is a good nucleophile, but the hydroxyl group is a poor leaving group

Question 34

The pI of any polypeptide can be …

Answer 34

calculated.

Question 35

A polypeptide chain has …

Answer 35

only one alpha-amino group and one alpha-carboxyl group

Question 36

The pKa of the alpha-amino group in a polypeptide \
The pKa of the alpha-carboxyl group in a polypeptide - is …
The pKa of the side chains in a polypeptide /

Answer 36

slightly different from that in AA

Question 37

The peptide bond is not a single bond. This has some double bond characteristics. Double bonds are …

Answer 37

not rotatable.

So, the 6 atoms are stuck on a plane.

Question 38

Bond lengths

Answer 38

C-N 1.49 Angstrom
C=N 1.27 Angstrom
C-N in peptide 1.32 Angstrom