Lecture 3: Protein structure + composition

Question 1

What are the functions of enzymes

Answer 1

selective catalysts that can accelerate the rate of specific reactions

Question 2

How are proteins involved in defense

Answer 2

As antibodies, that bind to foreign invading bacteria or viruses allowing the immune system to recognise them

Question 3

How are proteins involved in storage

Answer 3

Proteins like ovalbumin help to provide all the amino acids required for a developing baby chicken

Question 4

How are proteins involved in transport

Answer 4

Haemoglobin- transporting o2, or transmembrane proteins

Question 5

How are proteins involved as hormones

Answer 5

Coordinate an organisms activity. Insulin stimulates uptake of glucose into tissues

Question 6

How are proteins involved as receptors

Answer 6

Embedded in the cell membrane, can detect the presence of signalling molecules outside the cell and communicate this to the inside of the cell. Eg, neurotransmitter

Question 7

How are proteins involved in movement

Answer 7

Contractile proteins- flagella pairs of microtubules, with the motor protein anchored to one pair of microtubules with the other side of the motor protein walk along another pair of microtubules, allowing bending and flexing.
Other is actin and myosin in muscle - contractile proteins.

Question 8

How are proteins involved in structure

Answer 8

Components of the cytoskeleton that maintain cell shape and size, anchoring organelles within the cell and by rearranging the actin filaments it can send out pseudopodia to help the cell move.
In ECM, proteins made by the cell - eg, collagen

Question 9

How are proteins involved in gene regulation

Answer 9

Can bind to specific regions of DNA controlling whether a gene is expressed as a functional protein. This allows cells to respond to changes in external environment and allows cells to differentiate into different functions

Question 10

The numerous unique 3D structures of proteins are linked to the numerous

Answer 10

functions of proteins

Question 11

What are the four main parts of the 20 amino acids

Answer 11

alpha carbon bonded to a carboxyl group and amino group, H and the side chain, whose properties determine the hydrophilic and hydrophobic nature

Question 12

Does cystine have a polar or non polar side chain

Answer 12

polar

Question 13

How are peptide bonds formed.

Answer 13

condensation of water the O from carboxyl and H from amino group. This reaction is done one by one. The nucleotide sequence in DNA determines the sequence.

Question 14

What determines the 2 and 3 level of folding of the protein, the final 3D shape and function of the protein

Answer 14

The sequence of amino acids with particular side chains being added together in the primary level of polypeptide

Question 15

What bonds stabilise secondary protein structures

Answer 15

H bonds between the C=O and the NH of the protein backbone. Individually H bonds are weak but numerous make it able to stabilise.

Question 16

The neighbouring side chains can stop hydrogen bonds from forming if there is

Answer 16

steric hindrance or charged groups

Question 17

Where do the bonds in an alpha helix form and what proteins are these.

Answer 17

H bonds are between every 4th amino acid. They are often found in the regions of transmembrane proteins that cross lipid bi layer

Question 18

Where do the bonds in an beta pleated sheets form and what proteins are these.

Answer 18

Bonds form between the O and H of up and down polypeptide strands. Very stable. They make up the core of many globular proteins.

Question 19

What are the interactions that can form between side chains in tertiary structures

Answer 19

Polar side chains can make H bonds. Non polar side chains can make hydrophobic interactions + van de waals interactions as they cluster in the centre of the protein. charged side chains can make ionic bonds - all of these are weak but strong in numbers.

The last is the disulfide covalent bond between (H-S) group in cysteine.

Question 20

what is quaternary structure

Answer 20

The final structure where proteins consist of two of more polypeptides, still held together by interactions between side chains. Several polypeptides come together

Question 21

What are the jobs chaperonins

Answer 21

That assist the folding of proteins by protecting the polypeptide while it folds from degradation and gives them the best environment to allow them to fold spontaneously. Some can help facilitate refolding or mark misfolded for destroying

Question 22

Whats the difference between where bonds that stabilise are formed for 2 vs 3

Answer 22

2 is with the backbone, 3 is with the side chain

Question 23

What are the two parts of the chaperonin

Answer 23

It has a cap that comes off and lets a protein come

Question 24

What does denaturing of protein mean

Answer 24

Destruction of 2,3,4 structure, left with only primary structure due to the destruction of H bonds, ionic bonds, hydrophobic interactions and S-S bonds

Question 25

What can denature proteins

Answer 25

Heat- breaks weak bonds, pH - change ionisation patterns of R groups

Question 26

What does hydrolysis mean

Answer 26

the breakdown of primary structure, adding water in

Question 27

If the denaturing agent is removed what can happen to denatured protein

Answer 27

it can renature