Proteins 2

Question 1

Name 3 types of proteins which contain prosthetic groups?

Answer 1

Glycoproteins
Lipoproteins
Metalloproteins

Question 2

What is a glycoprotein?

Answer 2

Compound composed of protein and carbohydrate

Question 3

How are glycoproteins formed?

Answer 3

Post-translational modification (glycosylation) whereby a sugar molecule binds via an amino acid to the protein

Question 4

What are examples of glycoproteins?

Answer 4

Immunoglobulins

Blood group determinants

Question 5

Where does glycosylation occur?

Answer 5

ER and Golgi body

Question 6

What does glycosylation play a role in?

Answer 6

• Protein stabilisation
• Affects solubility
• Protein orientation
• Signalling
• Cell recognition

Question 7

How can glycoproteins be used in disease?

Answer 7

Provides a marker of long term diabetic control

Question 8

How are glycoproteins used in diabetes?

Answer 8

• Non-enzymatic reaction forms glycated haemoglobin
• Condensation reaction between N-terminal valine and glucose forms aldimine
• Aldimine undergoes amadori rearrangement to from stable ketoamine

Question 9

What are lipoproteins?

Answer 9

Proteins and lipids bonded together either covalently or non-covalently?

Question 10

What is the function of lipoproteins?

Answer 10

To transport water-insoluble fats and cholesterol in the blood e.g. HDL, LDL

Question 11

What are metalloproteins?

Answer 11

Protein molecules with a bound metal ion

Question 12

What are the functions of metalloproteins?

Answer 12

Enzymes
Transport
Storage
Signalling

Question 13

What functions can proteins have?

Answer 13

• Movement
• Enzymes
• Structural
• Protection
• Receptors
• Storage
• Hormones
• Transport
• Control of gene expression

Question 14

What functions do globular proteins have?

Answer 14

Varied functions:

• Enzymes
• Hormones
• Transporters
• Stock of amino acids
• Structural function (actin and tubulin)

Question 15

What functions do fibrous proteins have?

Answer 15

Structural function:

• Bone matrixes
• Muscle fibres
• Tendons
• Connective tissue

Question 16

What functions do membranous proteins have?

Answer 16

Associated with cell/organelle membrane:

• Relay signals
• Membrane transporters
• Membrane enzymes
• Cell adhesion molecule

Question 17

What is the binding ratio of haemoglobin to oxygen?

Answer 17

Haem group at the centre of each polypeptide chain binds one molecule of oxygen. One molecule of haemoglobin can bind four molecules of oxygen

Question 18

Co-operativity

Answer 18

The increase in affinity of polypeptide chains when a substance binds to a sister polypeptide chain

Question 19

What is the genetics behind sickle cell anaemia?

Answer 19

Single base change causes hydrophilic amino acid glutamic acid to be replace with hydrophobic valine

Question 20

What are the properties of Hb S?

Answer 20

• Insoluble

- At low O2 levels it forms crystals and polymerises to form long chains, causing the RBC to change shape

Question 21

What are the clinical features of Hb S?

Answer 21

• Sever haemolytic anaemia

- Hb S gives up oxygen in the tissues more easily than Hb A.

Question 22

What is collagen?

Answer 22

• Fibrous protein that makes up 25% of the total protein in humans
• High tensile strength

Question 23

What is collagen composed of?

Answer 23

Repeating unit Glycine-X-proline where X is alanine, hydroxyproline, lysine

Question 24

What is the structure of collagen like?

Answer 24

• Polypeptide chain coils to form a helix
• 3 polypeptides then coil around each other
• They are held together by hydrogen bonds which can interact to form fibrils increasing the strength

Question 25

What is vitamin C required for?

Answer 25

To convert proline to hydroxyproline and lysine to hydroxylysine.

Question 26

What happens when someone is deficient in vitamin C?

Answer 26

Scurvy: - Hydroxylysine and hydroxyproline are essential for stabilising the crosslinks between chains - Weaker collagen is produced

Question 27

Why does oesteogenesis imperfect occur?

Answer 27

- Glycine substituted for a larger amino acid - Protein unable to form tight coil - Reduced fibril interaction - Loss of secondary, tertiary structure - Weakened and brittle collagen produced

Question 28

What is an LDL receptor?

Answer 28

A glycoprotein present on the surface of all cells which binds to apoB and causes the internalisation of LDL.

Question 29

What are the classes of mutations relating to the LDL receptor?

Answer 29

- Class 1: no receptors produced - Class 2: Receptors never reach cell surface - Class 3: Receptors can't bind LDL - Class 4: Receptors don't internalise on binding LDL - Class 5: Receptors don't release LDL

Question 30

What is Familial Hypercholesterolemia?

Answer 30

An autosomal dominant disorder caused by mutations in LDL receptor

Question 31

What does FH cause?

Answer 31

Elevate LDL concentrations in the blood which leads to cholesterol deposits in the skin, tendons and arteries and as a result early CV disease