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
