Structure of Proteins 2

Question 1

What is tertiary structure?

Answer 1

The 3D folding of secondary structure

Question 2

In an aqueous environment, how is the tertiary structure organised?

Answer 2

Hydrophobic residues buried and hydrophilic residues are exposed outwards

Question 3

What is a protein domain?

Answer 3

Specific part of protein that gives a function

Question 4

What are the three possible tertiary structures?/

Answer 4

Alpha-helical

Beta sheets

A mixture of both

Question 5

What connects regions of alpha helix and beta sheets?

Answer 5

Loops and bends

Question 6

What bonds stabilize the tertiary structure?

Answer 6

Disulfide bonds

H-bonds

Ionic interactions

Van der Waals interactions

Hydrophobic interactions

Question 7

Where does a disulphide bridge occur?

Answer 7

Between cystine residues

Question 8

What is quaternary structure?

Answer 8

The association of more than one polypeptide

Question 9

What is a protein called that has more than one subunit?

Answer 9

Oligomeric

Question 10

What is the structure of mechanosensitive conductance channel?

Answer 10

7 identical subunits

Question 11

What is the structure of stored insulin?

Answer 11

6 identical subunits bound to zinc

Question 12

What is the structure of heterotrimeric G protein?

Answer 12

3 different subunits

Question 13

What is the structure of 70S ribosome?

Answer 13

30 different subunits

Question 14

What is the function of 70S ribosome?

Answer 14

Conversion of mRNA into proteins in bacteria

Question 15

What is the function of haemoglobin?

Answer 15

Carries oxygen in red blood cells

Question 16

What is the structure of haemoglobin?

Answer 16

2 alpha and 2 beta globin chains

Each chain contains a haem molecule

Question 17

What is haem?

Answer 17

Porphyrin ring with coordinated Fe atom

Question 18

What is haem held in place by?

Answer 18

Held in place by hydrogen bonds from histidine F8 and the bound oxygen molecule is stabilised by histidine E7

Question 19

What happens when oxygen binds to haem?

Answer 19

Changes the structure of haem

Provides an equalizing force on the bonds changing the ring from nonplanar to planar

Question 20

Describe cooperative oxygen binding

Answer 20

The affinity of the first oxygen molecule is low but binding of subsequent oxygen molecules is then increased

Question 21

What shape of a graph does cooperative oxygen binding create?

Answer 21

Sigmoidal

Question 22

Describe the effect of cooperative oxygen binding on the structure of haem?

Answer 22

The histidine that H-bonds to the haem molecule in helix F changes position

This conformation causes an increase in affinity of oxygen

Question 23

What is the biological significance of the cooperative oxygen binding?

Answer 23

This equated to tight oxygen binding in the lungs and subsequent release in tissues where oxygen concentration is lower

Question 24

What causes sickle cell anaemia?

Answer 24

Single amino acid change at position of 6 in the beta chain of haemoglobin

Hydrophilic glutamic acid to hydrophobic valine

Question 25

What effect does sickle cell anaemia have on erythrocytes?

Answer 25

Sickling of erythrocytes due to aggregation of mutated haemoglobin that forms stiff fibres

Question 26

What effect does pH have on oxygen binding?

Answer 26

Higher affinity caused by higher pH Lower affinity caused by lower pH

Question 27

Why is the build up of lactic acid in muscles good?

Answer 27

The acidic environment will decrease the affinity of oxygen so will have faster oxygen delivery

Question 28

What is the foetal structure of haemoglobin?

Answer 28

2 alpha and 2 gamma

Question 29

Why does foetal haemoglobin have a higher affinity for oxygen?

Answer 29

When maternal blood reaches the placenta it already has a low oxygen content so will require high affinity to bind as much as possible

Question 30

Where is collagen found?

Answer 30

Bone Tendons skin

Question 31

What is the building block of collagen?

Answer 31

Tropocollagen

Question 32

What does the triple left handed helix shape of tropocollagen form?

Answer 32

Microfibril

Question 33

What do many microfibril form?

Answer 33

Fibril

Question 34

What is the most common amino acid of tropocollagen?

Answer 34

Glycine

Question 35

How does glycine effect the tropocollagen?

Answer 35

Glycine occurs every 3 amino acid to allows tight turns as it is very small

Question 36

Why is proline vital for the structure of tropocollagen?

Answer 36

It imposes left hand twist in the helix that provides the main stabilising force

Question 37

What other form of proline can stabilise tropocollagen?

Answer 37

Proline is hydrolysed to hydroxyproline which can form strong hydrogen bonds

Question 38

Describe the formation of tropocollagen?

Answer 38

Individual strands come together called procollagen Procollagen peptidase cuts off ends leaving tropocollagen

Question 39

What is the quarter-stagger model in collagen?

Answer 39

Molecules are stitched together by covalent-crosslinks, each a quarter length further along than the one above

Question 40

What causes the crosslinks in collagen?

Answer 40

Lysine is deaminated to from allysine by lysyl oxidase These then from an aldol condensation product creating the crosslinks

Question 41

What is the mutation causing osteogenesis imperfecta?

Answer 41

Glycine being replaced by cysteine

Question 42

What is the consequence of the mutation causing osteogenesis imperfecta?

Answer 42

The tropocollagen subunits cannot pack together properly and there is a knock-on effect on collagen fibre formation

Question 43

What causes scurvy?

Answer 43

Lack of proline hydroxylation

Question 44

What causes Ehlers-Danloss syndrome?

Answer 44

Lack of procollagen peptidase or lysyl oxidase