Proteins Flashcards
What is the main protein found in hair ?
Keratin
Which features found on some animals are made of keratin ?
Beaks and horns
Proteins provide mechanical support in which things ?
Bone, cartilage and teeth
What is one of the most important proteins found in teeth ?
Collagen
Which proteins are found in muscles ?
Actin and myosin
Which proteins are important in the storage and transport of oxygen ?
Myoglobin and haemoglobin
Summarise the structure of myoglobin
It has 1 polypeptide chain and so contains 1 haem group and can bind 1 oxygen molecule
What are the 2 groups into which proteins can be divided ?
Fibrous proteins - long, structural proteins
Globular proteins - functional roles
Which protein is involved in sight ?
Rhodopsin is present in the membrane of the retina and it changes shapes shape in response to the stimulus
What is a protein?
A linear sequence of amino acids folded to an elaborate functional structure
What are the monomers of proteins ?
Amino acids
What is the central carbon of an amino acid known as ?
Alpha carbon
What are the 2 groups of amino acids ?
L - amino acids (all amino acids in our DNA)
D - amino acids
What is the formula to calculate pH ?
pH = pKa + log[A-]/[HA]
[A-] = base
[HA] = acid
What is the isoelectic point ?
When the overall charge is 0
What are essential amino acids ?
Essential amino acids are required in the body but can’t be made
What are non - essential amino acids ?
They can be made in the body as as long as there is sufficient nitrogen available
Give a few examples of essential amino acids ?
Lysine, valine and methionine
How can we increase the amount of amino acids in our diet ?
Consuming high quality proteins which :
- contain all essential amino acids
- correct proportions required
- easily digestible
How do amino acids form amides ?
They react with ammonia or amines in a condensation reaction to form amides
How do amino acids form proteins ?
The amino group of one amino acid will react with the carboxylic acid group of another amino acid in a condensation reaction to form a peptide bond
What is an amino acid residue ?
A residue is each individual amino acid in the polypeptide chain
How is the primary structure of a protein determined ?
By the order of amino acids from the N terminus to the C terminus
Summarise the rotational property of the peptide bond
The lone pair of electrons on the nitrogen and the pi electrons of the C = O are delocalised across the peptide bond so it does not rotate
Is the nitrogen of the amino group a hydrogen bond donor or acceptor ?
Good hydrogen bond donor
Is the oxygen of the carboxylic acid group a hydrogen bond donor or acceptor ?
Good hydrogen bond acceptor
How is the tertiary structure of a protein determined ?
By the sequence of amino acids
How is protein structure organised ?
Protein structure has a hierarchical organisation :
- primary structure
- secondary structure
- tertiary structure
- quartenary structure
What are the properties of hydrogen bonds ?
- relatively weak bonds
- strongest when linear
- the length between N and O is 2.8 Å
What are some of the other bonds present in proteins ?
• Van der Waals or London forces - only significant when atoms are close
• ionic bonds (stronger than London forces)
Summarise the secondary structure of proteins
- alpha helix
- beta pleated sheet : parallel and anti parallel
How are the amino acids organised in an anti parallel beta pleated sheet ?
N terminus > C terminus
C terminus > N terminus
How are the amino acids organised in a parallel beta pleated sheet ?
N terminus > C terminus
N terminus > C terminus
Summarise the properties of an alpha helix
- hydrogen bonding
- right handed
- 3.6 residues per turn
How are disulphide bridges oxidised and reduced ?
They are oxidised with hydrogen peroxide allowing them to form
They are reduced with thioglycolate which causes them to break
Which amino acids are helix formers ?
- glutamate
- glutamine
- alanine
- histidine
Which amino acid is a helix destabiliser ?
Tyrosine
Which amino acid is a helix breaker ?
Proline
What is a structural motif ?
It is the arrangements of secondary structures
What is the secondary structure of immunoglobulin G ?
Anti parallel ß pleated sheet
What is a domain ?
A domain is a recognisable globular unit formed by folding of part of a polypeptide chain
What is the quarternary structure of a protein ?
Assembly of more than one polypeptide chain
What is a cofactor ?
It is a small molecule which is essential for function
They can be subdivided into cofactors and coenzymes
Cofactors - metals
Coenzymes - small organic molecules e.g. vitamins
