Amino Acids and Peptide Bonds in Biochemistry

Questions and Answers

What is the main function of the peptide bond between amino acids?

To catalyze enzymatic reactions

To provide structural importance to the protein

To form hydrogen bonds with other peptide units (correct)

To facilitate the transportation of ions and molecules

Which type of glycosylation involves the -NH2 group of asparagine?

O-linked glycosylation

Hydroxylation

N-linked glycosylation (correct)

Phosphorylation

Which of the following is NOT a type of non-covalent interaction that maintains the tertiary structure of proteins?

Phosphodiester bonds (correct)

van der Waals interactions

Ionic interactions

Hydrogen bonds

What is the name of the secondary structure formed by hydrogen bonds between peptide chains?

β-pleated sheet Signup and view all the answers

What determines the unique conformation of a protein?

The primary sequence of amino acids Signup and view all the answers

What is the characteristic of the side chains in a β-pleated sheet?

They alternate above and below the plane of the sheet Signup and view all the answers

Which of the following proteins is an example of a receptor protein?

Acetylcholine receptor Signup and view all the answers

What is the term for the process by which a protein assumes its unique 3D structure?

Protein folding Signup and view all the answers

Which protein has a quaternary structure consisting of two α-subunits and two β-subunits?

Haemoglobin Signup and view all the answers

Which of the following is a consequence of defects in amino acid metabolism and mis-folding?

Disease Signup and view all the answers

What is the function of hydrogen bonds in protein structure?

To stabilize the tertiary structure of proteins Signup and view all the answers

Which of the following is NOT a type of non-covalent force that stabilizes protein structure?

Ionic bonds Signup and view all the answers

What is the term for the covalent bond that forms between two cysteine residues?

Disulphide bridge Signup and view all the answers

What is the name of the helical structure formed by three polypeptide chains?

Collagen triple helix Signup and view all the answers

Which of the following proteins is an example of a structural protein?

Collagen Signup and view all the answers

Which type of protein has a high percentage of β-sheet structure?

Fibrillar protein Signup and view all the answers

Which of the following atoms is NOT a hydrogen bond acceptor?

Carbon Signup and view all the answers

What is the approximate distance of a hydrogen bond?

2.8 Å Signup and view all the answers

At physiological pH, which of the following groups is NOT ionised?

His imidazole groups Signup and view all the answers

What is the main reason for the existence of Van der Waals forces?

Unequal distribution of electrons in a covalent bond Signup and view all the answers

What is the primary reason why hydrophobic regions are unable to form hydrogen bonds?

As a result of their non-polar nature Signup and view all the answers

Which of the following is a characteristic of Van der Waals forces?

They are dependent on the distance between atoms Signup and view all the answers

What is the main driving force for hydrophobic regions of a protein to fold in a specific way?

Minimise the contact with aqueous environment Signup and view all the answers

What determines the final structure and folding pathway of a protein?

The amino acid sequence only Signup and view all the answers

Why are proteins sensitive to denaturation by pH, temperature, and ionic strength?

Since the stabilization energy in a protein is very low Signup and view all the answers

What type of bond has a typical energy of 12 kJ mol-1?

Hydrogen bond Signup and view all the answers

What is the significance of the alpha helix and beta-pleated sheet structures?

They are essential for protein function Signup and view all the answers

Which of the following side chains is NOT involved in hydrogen bonding?

Lys Signup and view all the answers

Why is protein misfolding a concern in human disease?

Since it results in the loss of protein function Signup and view all the answers

What is the relationship between the number of possible protein structures and their functionality?

There are thousands of possible structures, only one of which is functional Signup and view all the answers

Study Notes

Protein Structure and Function

Proteins perform various biological functions, including:
- Structural roles (e.g., collagen, keratin)
- Movement (e.g., actin, myosin)
- Enzymatic functions (e.g., trypsin, DNA polymerase)
- Transport (e.g., hemoglobin, transferrin)
- Hormone regulation (e.g., insulin)
- Receptor functions (e.g., acetylcholine receptor)
- Defense mechanisms (e.g., antibodies, clotting factors)
- Gene regulation (e.g., histones)
- Chromosome separation (e.g., tubulin)

Primary Structure

A polypeptide chain consists of 20 common amino acids
The first amino acid has an NH3+ group (N-terminal end)
The last amino acid has a COO- group (C-terminal end)

Secondary Structure

α-helix:
- Formed by hydrogen bonds between peptide bonds in the same polypeptide chain
- Regular right-handed helix with 3.6 residues per turn
- R groups are on the outside of the helix
- Stabilized by hydrogen bonds
β-pleated sheet:
- Formed by hydrogen bonds between peptide chains
- Linear peptide chains with side chains alternately above and below the plane of the sheet

Tertiary Structure

The 3D shape of a polypeptide chain
Consists of a number of different supersecondary structures (domains)

Quaternary Structure

The 3D shape of a functional protein formed by multiple subunits
Examples: hemoglobin (α2β2)

Forces that Stabilize Protein Structure

Covalent:
- Disulfide bridges (not present in all proteins)
Non-covalent:
- Hydrogen bonds
- Electrostatic interactions
- Van der Waals forces
- Hydrophobic effect

Hydrogen Bonds

Formed between two electronegative atoms competing for the same H atom
H-Bond donors (D): O-H, N-H
H-Bond acceptors (A): C=O, =N-

Electrostatic Interactions

Between charged side chains
At physiological pH, Asp and Glu are ionized, while Lys and Arg are also ionized

Van der Waals Forces

The sum of attractive or repulsive forces between molecules
Excludes covalent bonds, hydrogen bonds, and electrostatic interactions
Dependent on the dipole effect caused by the unequal distribution of electrons

Hydrophobic Effects

Hydrophobic regions of a protein fold to minimize contact with the aqueous environment
Hydrophobic regions are unable to form hydrogen bonds

Protein Folding and Stability

The amount of stabilization energy in a protein is quite small
Proteins are sensitive to denaturation by pH, temperature, and ionic strength
Amino acid sequence encodes the final structure and the pathway that leads to that structure
Misfolding can cause disease

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Description

This quiz covers the structures and functions of amino acids, including their side chains and peptide bonds, as well as the importance of hydrogen bonds in biochemistry.