Proteins-1 Flashcards
What does an α-amino acid consist of?
A central carbon atom (α) linked to an amino group, carboxylic acid group, a hydrogen atom, and an R group.
What are some of the crucial functions in biological processes carried out by proteins?
Transport, cell-signalling, metabolic enzymes, structural support
As there are ____ different groups connected to the central carbon atom in an amino acid, it is _____.
As there are four different groups connected to the central carbon atom in an amino acid, it is chiral.
What isomer of amino acids are found in proteins?
L amino acids
Define zwitterion
An amino acid that has a net neutral charge
What type of bond links two amino acids together?
A peptide bond
What structure is formed when two amino acids join together?
A dipeptide
What is each amino acid unit called?
A residue
A sequence of amino acids is written starting at which terminal?
The amino-terminal (N-) residue
What causes restriction in residue rotation in a polypeptide chain?
Electrons in the C=O bond in the peptide linkage delocalise and are shared with the nitrogen atom. This causes restricted rotation.
What are the two configurations that a polypeptide can contain?
Cis and Trans
What spatial configuration is preferred in a polypeptide?
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.
What is the angle between the central carbon and the nitrogen atom in a residue?
Phi (φ)
What is the angle between the central carbon and the carboxylic acid carbon in a residue?
Psi (ψ)
What is a ramachandran plot?
A plot showing the likelihood of the combination of φ and ψ angles in proteins
Define protein
Proteins are linear polymers built of monomer units called amino acids, which are linked end to end.
What are some of the functional groups that a protein can contain?
- Alcohols
- Thiols
- Thioesters
- Carboxylic acids
- Carboxamindes
- Basic groups
What is the hydrophobic effect?
The tendency of hydrophobic groups to come together
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).
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).
What is the equivalent molecular weight of 1 dalton?
1 g mol-1
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 _______.
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.
The amino acid sequence of a protein is referred to as its _______ _________.
The amino acid sequence of a protein is referred to as its primary structure.
Why is it important to know the amino acid sequence of a protein?
- Essential for finding its mechanism of action
- To determine its 3D structure
- Medical reasons- relation to disease
- Reveals evolutionary history
Why is rotation restrained around the backbone of a peptide bond linking two amino acids?
The bond resonates between a single and a double bond
Define steric exclusion
The fact that two atoms cannot be in the same place at the same time
Describe the bonds that keep the structure of an α-helix
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.
