Protein And Amino Acid Metabolism

Question 1

What is a positive nitrogen balance?

Answer 1

Intake greater than loss

Occurs in pregnancy and growth as it is required for growth

Question 2

What is a negative nitrogen balance?

Answer 2

Intake less than loss

Occurs with trauma, malnutrition and infection

Never physiological

Question 3

What does the Michaelis - Mentes model describe?

Answer 3

Describes that a specific complex between enzyme and the substrate is an essential intermediate step in the overall equatiom

Question 4

What are isoenzymes?

Answer 4

Different forms of the same enzyme which are generated from the same gene but spliced differently

They have different kinetic properties such they can increase or decrease affinity

Question 5

What is product inhibition?

Answer 5

As the concentration of the product increases accumulation can prevent the forward reaction from occurring.

Question 6

What happens when a allosteric inhibitor binds?

Answer 6

All the active sites preset change
Enzyme can’t work
Enzyme in T state
Lower affinity

Question 7

What happens when a allosteric activator binds

Answer 7

All active sites increase in function
Enzyme in R state
Higher affinity

Question 8

What is cooperativity?

Answer 8

When a substrate binds to the active site it can act as an allosteric activator by increasing the activity of the other active sites

Question 9

What are activators of phosphofructokinase?

Answer 9

AMP
Fructose-2,6-bisphosphate

These increase the breakdown of glucose

Question 10

Inhibitors of phosphofructokinase

Answer 10

Citrate
H+
ATP

Question 11

What is covalent modification?

Answer 11

Enzymes modified by another molecule being attached by covalent bonds

This affects the activity of the enzyme

Often reversible

Question 12

Examples of covalent modification.

Answer 12

Phosphorylation

Acetylation

Question 13

What do protein kinases do?

Answer 13

Transfer the terminal phosphate from ATP to the -OH group of Serine, Threonine and tyrosine- residues

Question 14

What do protein phosphatases do?

Answer 14

Reverse the effects of kinase by catalysing the hydrolysis removal of phosphoryl groups from proteins

Question 15

Why is protein phosphorylation so effective?

Answer 15

Free energy of phosphorylation is large

Adds 2 negative charges- can allow activity to be altered as new interactions can be made

A phosphoryl group can make H bonds

Rate of phosphorylation/ dephosphorylation can be adjusted

Links energy status of the cell to metabolism through ATP

Allow for amplification effects

Question 16

What are inactive precursor molecules called

Answer 16

Proenzymes and zymogens

Question 17

Where is the protease function kept?

Answer 17

C terminal domain

Question 18

What keeps prothrombin in the inactive form?

Answer 18

Two Kringle domains

Question 19

What targets prothrombin to its appropriate site for activation?

Answer 19

Gla domains

Question 20

What are fibrinopeptides?

Answer 20

They prevent fibrinogen molecules coming together

Question 21

Structure of fibrinogen

Answer 21

Precursor molecule

Composed of 3 polypeptide chains

2 globular heads separated by rod like triple helical alpha helixes

Question 22

What converts fibrinogen into fibrin? How?

Answer 22

Thrombin- cuts of fibrnopeptides to produce fibrin

Fibrin monomers assemble to form non-covalent interactions- soft clot

Cross linking of soft clot by covalent bonds between lysine and glutamine - catalysed by transglutaminase

Question 23

How are Gla residues formed? -

Answer 23

During post translational modification of prothrombin, carboxylic groups are added to glutamate residues found on proteins to form carboxyglutamate groups

Dependent on vitamin K

Gla domains allow interaction with sites of damage ad brings together clotting factors as they are so negative

Question 24

How do you stop clotting?

Answer 24

Localisation of prothrombin- dilute blood flow and remove in the liver

Digestion by protease

Question 25

How do you break the clot?

Answer 25

Plasminogen is converted into plasmin in by streptokinase and t-PA (tissue plasminogen activator)

Plasmin breaks down the fibrin clot

Question 26

Important control points in blood clotting

Answer 26

Inactive zymogens kept at low concentrations

Activation of proteolytic mechanisms

Activation of feedback system by thrombin to ensure continuation of the clotting process

Multiple mechanisms cause the termination of clotting

Activation of a proteolytic process to lead to clot breakdown

Amplification of the initial signal by cascade mechanism