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