Proteins and Enzyme Kinetics Flashcards
How many amino acids are there which form the building blocks of proteins?
20
Define the term peptide….
A molecule consisting of amino acids (generally 30 or fewer) linked by peptide bonds.
Define the term protein…..
A functional molecule made up of one or more polypeptide chains.
How can the size of a polypeptide/protein be defined?
A. Number of amino acids.
B. By quoting the molecular mass in Daltons (Da or kilodaltons (kDa), where a Dalton is approx. equal to the mass of a hydrogen atom.
Explain the structure of an amino acid…..
A central C atom, amino, and carboxyl groups, and a H atom are all common to an amino acid molecule. There is a side chain (R) which is variable. It carries a positive and negative charge with the amino group accepting and ion and the carboxyl group losing one.
How is a peptide bond formed?
A condensation reaction occurring between the free amino group (-NH3+) of one amino acid and the free carboxyl group (-COO-) of another, with the removal of H2O.
Why is the term ‘residues’ used to describe chains of amino acids?
Once amino acids have been linked together the term residues is often used to describe them (e.g. a 20 residue peptide) as it reflects the loss of some atoms of each amino acid when the peptide bond is formed. What is left of each amino acid in the peptide is termed a residue.
Why is it important to have some knowledge of the properties of the amino acids that make up proteins?
An amino acids properties affect the interactions occurring between them and their environment and the way in which it folds, which is crucial to its function.
Why if there are over 500 amino acids do we focus only focus on 20?
There are 20 amino acids used in all organisms for protein synthesis by translation. It is important to explore their role in supporting life by exploring their structures and functions.
What are the two types of abbreviation routinely used to identify amino acids?
Three-letter and single-letter codes.
How do we classify amino acids?
According to the structures and properties of their side chains.
Why is it useful to classify amino acids as charged or not?
Whether or not a side chain is basic (proton acceptors (+)) or acidic (proton donors (-)) will affect how the amino acid interacts with other chemical groups, i.e. is it hydrophilic or hydrophobic. This strongly influences how the polypeptide chain will fold into 3 dimensions. Hydrophilic chains will be found on the outside of the structure while, hydrophobic ones will be ‘hidden’ on the inside.
Are non-polar and polar side chains hydrophilic or hydrophobic?
Non-polar»_space;> Hydrophobic
Polar»_space;> Hydrophilic
Which 3 amino acids cannot be easily defined as having hydrophobic or hydrophilic side chains?
Tyrosine, cysteine, and glycine.
Why can tyrosine not be classified as hydrophilic or hydrophobic?
It has a polar hydrophilic hydroxyl group, as well as a large non-polar, hydrophobic benzene ring. Its position in a folded protein depends on factors such as the amino acid residues in the protein that interact with it.
