Proteins

Question 1

What is released when a peptide bond is formed?

Answer 1

Water

Question 2

What is the primary structure of a protein

Answer 2

The sequence of amino acids

Question 3

What is the secondary structure of a protein?

Answer 3

The spatial arrangement of amino acid residues that are near each other in the linear sequence

Question 4

What are the two structural forms of the secondary structure?

Answer 4

Alpha helix, beta sheets

Question 5

What stabilises the alpha helix structure?

Answer 5

H bonds between the NH groups and the CO groups in the next turn of the helix

Question 6

What stabilises the beta sheets?

Answer 6

H bonds between the amide groups of the linear polypeptide chains

Question 7

What is the tertiary structure?

Answer 7

The spatial arrangements of amino acids residues that are far apart in the linear sequence

Question 8

What is the tertiary structure held together by?

Answer 8

Van der waals forces
Ionic interactions
Hydrogen bonds
Disulphide bridges
Hydrophobic interactions

Question 9

Where do ionic interactions take place?

Answer 9

Between two oppositely charged R groups

Question 10

What environment is needed for intra polypeptide hydrophobic interactions to occur?

Answer 10

An environment within proteins from which water is excluded

Question 11

Where do disulphide bridges occur?

Answer 11

They are strong covalent bonds that occur between two cysteine residues
They are common in extra-cellular proteins
They can occur between as well as within a polypeptide

Question 12

What is the quaternary structure?

Answer 12

The spatial arrangement of individual polypeptide chains in a multi-subunit protein

Question 13

What structure remains in tact after denaturation?

Answer 13

The primary structure

Question 14

What are common causes of denaturation?

Answer 14

Acids
Heat
Solvents (ethanol)
Cross linking reagents (formaldehyde)
Chaotropic agents (urea)
Disulphide bond reducers (2 mercaptoehanol)

Question 15

What is the effect of denaturation?

Answer 15

Decrease in solubility
Altered water binding capacity
Loss of biological activity
Improved digestibility

Question 16

What is glycosylation?

Answer 16

Post translational modification whereby a sugar molecule binds via an amino acid to the protein

Question 17

Give an example of a glycoprotein

Answer 17

Immunoglobulins

Question 18

Where does glycosylation occur?

Answer 18

In the ER and the golgi apparatus

Question 19

What is the roles of glycosylation?

Answer 19

Protein stabilisation
Affects solubility
Protein orientation
Signalling
Cell recognition

Question 20

What is the function of lipoproteins?

Answer 20

Transport of water, insoluble fats and cholesterol in the blood

Question 21

What are metalloproteins?

Answer 21

Protein molecule with a bound metal ion

Question 22

What are the functions of metalloproteins?

Answer 22

Enzymes
Storage
Signalling
Transport

Question 23

Why does haemoglobin have four subunits?

Answer 23

The binding of O2 to one sub unit alters its shape
This in turn causes a change in shape of the other sub-units so that they bind O2 more easily

Co-operative binding

Question 24

How does sickle cell anaemia arise?

Answer 24

Substitution of one amino acid, hydrophilic Glutamic acid is replaced with hydrophobic amino acid Valine

Question 25

What are the clinical features of sickle cell anaemia?

Answer 25

Severe haemolytic anaemia

Oxygen is given up more easily in the tissues

Question 26

What is the structure of collagen?

Answer 26

Polypeptides coil to form a helix

Held together by hydrogen bonds
Interactions form fibrils which increases strength

Question 27

What is the effect of scurvy?

Answer 27

Vitamin C deficiency, there is less hydroxyproline and hydroxylysine which are essential in stabilising cross links between chains of collagen, so collagen produced is weaker

Question 28

What is the effect of osteogenesis imperfecta?

Answer 28

Protein cannot form into a tight coil due to amino acid substitution

There is less interaction between fibrils

Loss of secondary and tertiary structure

Weakened and brittle collagen is produced

Question 29

What are the possible mutations of the LDL receptor?

Answer 29

No receptors produced
Receptors never reach cell surface
Receptors can't bind LDL
Receptors don't internalise on binding LDL
Receptors don't release LDL

Question 30

What disease can result as an effect of LDL mutation?

Answer 30

Familial hypercholesterolemia, resulting in early cardiovascular disease