Proteins IA %%+ (+ Flashcards
1
Q
Primary sequence
A
The unique sequence of amino acids that are linked by covalent peptide bonds to form a polypeptide chain
2
Q
Secondary sequence
A
- The repeated twisting or folding of neighboring amino acids in the polypeptide chain.
- Two common secondary structures are alpha helixes (clockwise spirals) and beta pleated sheets.
- The secondary structure of a protein is stabilized by hydrogen bonds, which form at regular intervals along the polypeptide backbone.
3
Q
Tertiary structure
A
- 3D shape of a polypeptide chain.
- Each protein has a unique tertiary structure that determines how it will function.
- The tertiary folding pattern may allow amino acids at opposite ends of the chain to be close neighbors
- Forces: van der Waals, Ionic interactions, Hydrogen bonds, Disulphide bridges, Hydrophobic interactions
4
Q
Quaternary structure
A
- In those proteins that contain more than one polypeptide chain (not all of them do), the arrangement of the individual polypeptide chains relative to one another is the quaternary structure
- The bonds that hold polypeptide chains together are similar to those that maintain the tertiary structur
5
Q
Alpha helix
A
The telephone cord shape of the α-helix is held in place by H-bonds between every N-H group and the oxygen of the C=O group in the next turn of the helix (4aa residues apart)
6
Q
Beta pleated sheet
A
The pleated sheet structure is held together by H-bonds between the amide groups of linear polypeptide chains.
7
Q
Ionic interaction
A
- These occur between 2 close, oppositely charged R groups.
- They are strong, but few in most proteins
8
Q
Van der Waals
A
- These are non-specific, weak attractions between atoms 0.3 – 0.4 nm apart
- They are individually weak but since many present, they stabilise the protein structure
9
Q
H-bond
A
- Occur when H is bonded to either O, N or F, and a lone pair of electrons are present
- Similar to van der Waals but are stronger and permanent
- 1/20 the strength of a covalent bond
10
Q
Hydrophobic interaction
A
- These are intra-polypeptide interactions which occur in an environment within proteins from which water is excluded
- So, in globular water-soluble proteins hydrophobic R groups tend to be on the inside of the protein
- hydrophilic R groups tend to be on the outside H-bonding to water, and making the protein water-soluble.
11
Q
Disulphide bridge
A
- These are strong covalent bonds between two cysteine residues
- They are common in extra-cellular proteins.
- They can occur between, as well as within a polypeptide
12
Q
Protein denaturation
A
- Involves the disruption and possible destruction of both the secondary and tertiary structures.
- Denaturation reactions are not strong enough to break the peptide bonds, so the primary structure remains the same after a denaturation process.
13
Q
Causes of denaturation
A
•Acids
•Heat
•Solvents e.g Ethanol, methanol
- Formaldehyde
- Chaotropic agents
- Urea
- Disulphide bond reducers
- 2 mercaptoethanol
14
Q
Effects of denaturation
A
- Decreased solubility (fucks hydrophobic bonds?)
- Altered water binding capacity (fucks hydrophobic bonds?)
- Loss of biological activity
- Improved digestibility
15
Q
Protein digestive enzymes
A
- PEPTIDASES-cleavage of peptide bonds
- EXOPEPTIDASES-cleavage of one amino acid at a time at end pieces of terminal amino acids
- CARBOXYPEPTIDASES -cleavage at –COOH
- AMINOPEPTIDASES -cleavage at –NH2
- ENDOPEPTIDASES-cleavage of internal, non-terminal bonds
18
Q
Lipoproteins
A
- Protein and lipids are either covalently or non-covalently bonded together
- Function - the transport of water-insoluble fats and cholesterol in the blood
- Eg HDL, LDL
19
Q
Metalloproteins
A
- Protein molecule with a bound metal ion
- ~ 1/3 of proteins require a metal ion to carry out their specific role
Functions:
- Enzymes
- Storage
- Signalling
- Transport
20
Q
Globular proteins
A
- Varied function
- E.g Enzymes, Messengers (hormones), Transporters, Stock of amino acids, Structural function e.g. actin and tubulin
21
Q
Fibrous protein
A
- Structural function
- E.g Bone matrices, Muscle fibre, Tendons, Connective tissue
23
Q
Haemoglobin
A
- Haem group at the centre of each polypeptide chain binds 1 molecule of oxygen.So one haemoglobin molecule can bind four molecules of oxygen
- The binding of O2 to one sub-unit alters its shape.
- This in turn causes a change in the shape of the other sub-units, so that they bind O2 more easily: ‘co-operative’ binding.
26
Q
Collagen 1
A
- Fibrous protein
- ~25% of the total protein in humans
- High tensile strength
- Composed of the repeat unit
- (glycine - X - proline)n where X = alanine, hydroxyproline, lysine
27
Q
Collagen 2
A
- Polypeptide coils to form a helix
- 3 polypeptides then coil around each other
- Held together by hydrogen bonds
- These can interact to form fibrils, Increasing the strength
