Protein Structure and Function - Done

Question 1

What is the function of myoglobin?

Answer 1

Oxygen and iron binding protein found in muscles

Question 2

What is the function of calmodulin?

Answer 2

Calcium modulating protein - binds to other proteins to help them function

Question 3

Where is porin found?

Answer 3

In the membrane of a cell - transmembrane protein

Question 4

What is the importance of cytochrome C?

Answer 4

Important in the electron transport chain - oxidation and reduction reactions.

Inner membrane of mitochondria

Question 5

What do lysozymes do?

Answer 5

Break down bacterial cell walls - glycoside hydrolase

Question 6

What’s the function of alcohol dehydrogenase?

Answer 6

To remove hydrogen from alcohol, oxidising to aldehydes/ketones

(NAD+ goes to NADH)

Question 7

What’s the function of collagen?

Answer 7

Main component of connective tissue - contains 2 uncommon amino acid derivatives which are at specific locations relative to glycine - modified post-translationally by different enzymes

Both enzymes require vitamin C as cofactor

Question 8

In what form are amino acids?

Answer 8

L form

N —> C

Question 9

Why is a trans arrangement of secondary amides favoured?

Answer 9

Trans form is more stable than Cis form.

Question 10

Where does H-bonding occur in alpha helices?

Answer 10

At every Fourth amino acid - NH of one peptide bond is H-bonded to the C=O of another in the same chain

Question 11

How many amino acids per helical turn in alpha helixes?

Answer 11

3.6 amino acids per turn

Question 12

What do transmembrane proteins often contain?

Answer 12

An alpha helix - hydrophobic side chains interact w hydrophobic tails of phospholipids

Hydrophilic parts of backbone from internal H-bonds - allow polar molecule to pass through the membrane

Question 13

What form of Beta sheet is stronger parallel or anti-parallel?

Answer 13

Antiparallel as amino acids residues are at right angles to each other - more stable bond formed

Parallel Beta sheets form weaker, longer H-bonds

Question 14

What is a ‘domain’ in a protein?

Answer 14

A sub section of a tertiary structure that might have a distinct role of function - usually 100-250 amino acids long

Question 15

What is the most stable conformation of any protein? How does this relate to ∆G?

Answer 15

With polar amino acids on the outer surface - so can interact with water - caused by repulsion of water against hydrophobic groups.

Protein is folded in such a way the free energy of the folded form is minimised (so ∆G is maximised)

Question 16

What are incorrectly folded proteins called?

Answer 16

Aggregates - can cause serious damage as neurodegenerative diseases like Alzheimer’s

Question 17

What are chaperone proteins?

Answer 17

Proteins that assist with the folding of other proteins along the most energetically favourable pathway.

Question 18

What are prions and what’s the danger they pose?

Answer 18

Prions are proteins that have misfolded, considered infectious as prion protein can cause normal protein to misfold - can spread from cell to cell.

Question 19

What subunits make up haemoglobin?

Answer 19

2 alpha-globin

2 beta-globin

All held together by non-covalent interactions

Question 20

What is the significance of the ‘coiled-coil’?

Answer 20

2/3 Alpha helices wrap around each other - occurs when hydrophobic side chains are on one side, reducing H-bonding disruption in cytosol

Structural purpose - skin & muscle contraction

Question 21

What’s the significance of collagen’s structure?

Answer 21

Triple helix containing glycine residues at every third amino acid, forcing glycine into the centre to give long overlapping arrays of strong fibrils.

Question 22

How doe elastin differ from collagen?

Answer 22

Elastin is loose with unstructured polypeptides which are cross linked - allowing the protein to stretch and relax

Question 23

What is retinal’s function and where does it bind?

Answer 23

Binds to Rhodopsin, a purple, light sensitive pigment made by rod cells. It binds to the protein via a covalent bond to a lysine side chain

Helps detect light as retinal changes shape by absorbing a photon.

Question 24

What is the heme group in haemoglobin?

Answer 24

A cofactor - Fe binds to oxygen reversibly

Question 25

What are antibodies classed as?

Answer 25

Immunoglobulin proteins

Question 26

Where does antibody specificity lie in antibodies?

Answer 26

Specificity lies in the antigen binding site

Question 27

How are antibodies held together?

Answer 27

With numerous disulphide bridges

Question 28

What are antibodies made up of?

Answer 28

Antiparallel Beta - pleated sheets, aside from the hyper variable loops that bind to the antigen

Question 29

What do lysozymes do and why does it occur?

Answer 29

They are natural antibiotics that sever polysaccharide chains in bacterial cell walls - burst. Can hold 6 linked sugars at a time.

It occurs because the free energy of the severed chain is lower than the intact chain - energetically favourable.

Question 30

Where dose trypsin cleave?

Answer 30

At carboxyl terminal of lysine or arginine

Question 31

Where does elastase cleave?

Answer 31

At carboxyl terminal of alanine, valine, serine, glycine, leucine & isoleucine.

Question 32

Where does chymotrypsin cleave?

Answer 32

At carboxyl terminal of phenylalanine, tryptophan & tyrosine

Question 33

Define feedback inhibition and state why it occurs

Answer 33

An enzyme acting early in a reaction pathway is inhibited by a late product of that pathway -

Occur when large quantities of final product accumulate, slowing catalytic action of the enzyme

Question 34

What does aspartate transcarbamoylase catalyse?

Answer 34

Catalyses important reaction that starts synthesis of pyrimidine rings

Question 35

How does cytosine triphosphate cause feedback inhibition?

Answer 35

When plentiful it binds to aspartate transcarbamoylase, turning it off