Proteins-1

Question 0

What does an α-amino acid consist of?

Answer 0

A central carbon atom (α) linked to an amino group, carboxylic acid group, a hydrogen atom, and an R group.

Question 1

What are some of the crucial functions in biological processes carried out by proteins?

Answer 1

Transport, cell-signalling, metabolic enzymes, structural support

Question 2

As there are ____ different groups connected to the central carbon atom in an amino acid, it is _____.

Answer 2

As there are four different groups connected to the central carbon atom in an amino acid, it is chiral.

Question 3

What isomer of amino acids are found in proteins?

Answer 3

L amino acids

Question 4

Define zwitterion

Answer 4

An amino acid that has a net neutral charge

Question 5

What type of bond links two amino acids together?

Answer 5

A peptide bond

Question 6

What structure is formed when two amino acids join together?

Answer 6

A dipeptide

Question 7

What is each amino acid unit called?

Answer 7

A residue

Question 8

A sequence of amino acids is written starting at which terminal?

Answer 8

The amino-terminal (N-) residue

Question 9

What causes restriction in residue rotation in a polypeptide chain?

Answer 9

Electrons in the C=O bond in the peptide linkage delocalise and are shared with the nitrogen atom. This causes restricted rotation.

Question 10

What are the two configurations that a polypeptide can contain?

Answer 10

Cis and Trans

Question 11

What spatial configuration is preferred in a polypeptide?

Answer 11

Trans. This is due to there being steric clashes in the cis formation. The exception is when there is a proline residue, then it prefers the cis configuration.

Question 12

What is the angle between the central carbon and the nitrogen atom in a residue?

Answer 12

Phi (φ)

Question 13

What is the angle between the central carbon and the carboxylic acid carbon in a residue?

Answer 13

Psi (ψ)

Question 14

What is a ramachandran plot?

Answer 14

A plot showing the likelihood of the combination of φ and ψ angles in proteins

Question 15

Define protein

Answer 15

Proteins are linear polymers built of monomer units called amino acids, which are linked end to end.

Question 16

What are some of the functional groups that a protein can contain?

Answer 16

• Alcohols
• Thiols
• Thioesters
• Carboxylic acids
• Carboxamindes
• Basic groups

Question 17

What is the hydrophobic effect?

Answer 17

The tendency of hydrophobic groups to come together

Question 18

The polypeptide backbone is rich in hydrogen-bonding potential. Each reisue contains a ________ group (C=O), which is a good hydrogen-bond _________, and an __ group which is a good hydrogen-bond _____ (except proline).

Answer 18

The polypeptide backbone is rich in hydrogen-bonding potential. Each reisue contains a carbonyl group (C=O), which is a good hydrogen-bond acceptor, and an NH group which is a good hydrogen-bond donor ​(except proline).

Question 19

What is the equivalent molecular weight of 1 dalton?

Answer 19

1 g mol^-1

Question 20

In some proteins, the linear polypeptide chain is cross-linked. The most common cross-links are ___________ _____, formed by the oxidation of a pair of ________ residues. The resulting unit of two linked _________ is called _______.

Answer 20

In some proteins, the linear polypeptide chain is cross-linked. The most common cross-links are disulphide bonds, formed by the oxidation of a pair of cysteine residues. The resulting unit of two linked cysteines is called cystine​.

Question 21

The amino acid sequence of a protein is referred to as its _______ _________.

Answer 21

The amino acid sequence of a protein is referred to as its primary structure​.

Question 22

Why is it important to know the amino acid sequence of a protein?

Answer 22

1. Essential for finding its mechanism of action
2. To determine its 3D structure
3. Medical reasons- relation to disease
4. Reveals evolutionary history

Question 23

Why is rotation restrained around the backbone of a peptide bond linking two amino acids?

Answer 23

The bond resonates between a single and a double bond

Question 24

Define steric exclusion

Answer 24

The fact that two atoms cannot be in the same place at the same time

Question 25

Describe the bonds that keep the structure of an α-helix

Answer 25

Hydrogen bonds form between the CO and NH groups in the backbone of the polypeptide that are four residues apart. These bonds run parallel to the length of the helix.