GI Biochem

Question 1

Glycogenesis

Answer 1

Synthesis of glycogen from glucose

Main storage form

Question 2

Liver glycogen

Muscle glycogen

Answer 2

Liver glycogen /

• Broken down between meals and released to maintain blood glucose levels for RBCs and brain

Muscle Glycogen /

• Not available for maintenance of blood glucose levels
• Provides energy via glycolysis and the TCA during exercise

Question 3

The liver keeps blood/sugar levels…

Answer 3

Constant between meal times

Question 4

What process happens at night when liver glycogen stores have been depleted?

Answer 4

Gluconeogenesis

Question 5

What is at the centre of glycogen? (protein)

Answer 5

Glycogenin

Catalytic activity

Can add up to 4 glucose molecules to itself

Question 6

Glucose can only be added to…

Answer 6

an existing glycogen chain

Question 7

What is needed for glucose to attach?

Answer 7

A glycogen “primer”

This primer is covalently attached to glycogenin

Question 8

Glucose –> G-6-P catalysed by?

Answer 8

Hexokinase

and ATP

Question 9

G-6-P –> G-1-P

Answer 9

By phosphoglucomutase

Question 10

G-1-P –> UDP glucose

Answer 10

UDP glucose is the activated form of glucose

by pyrophosphorylase

Question 11

UDP glucose acts as a substrate for

Answer 11

Glycogen synthase

to gie GLYCOGEN + UDP

Question 12

How many ATP are used to attach one glucose to glycogen?

Answer 12

1 ATP molecule

Question 13

Glycogen synthase is the ____ limiting enzyme of glycogenesis

Answer 13

Rate limiting

Question 14

Branching enzyme (introduces an alpha 1,6 glycosidic branch into glycogen. Which enzyme

Answer 14

Transglycosylase

Question 15

Glycogenolysis

Answer 15

Breakdown of glycogen

Catalysed by glycogen phosphorylase

One glucose molecule is cleaved off the ends at a time

G-1-P –> G-6-P by phosphglucomutase

Question 16

Fates of glycogenolysis?

Answer 16

G-6-P —– g-6-p-atase —> Glucose —> Blood (via GLUT2)

Glycolysis to muscles

Question 17

INSULIN

Answer 17

Stimulates synthesis of glycogen
Stimulates synthase (storage)
Inhibits phosphorylase

inhibits gluconeogenesis

stimulates glycolysis

Question 18

GLUCAGON

Answer 18

Signals lack of glucose in blood stream
Stimulates glycogen phosphorylase (breakdown)
Inhibits glycogen synthase

stimulates gluconeogenesis

Question 19

Adrenaline & cortisol

Answer 19

Both stimulate glycogen phosphorylase (breakdown)

Question 20

Gluconeogenesis

what is it?
when does it happen?

Answer 20

Synthesis of glucose within the body from NON-CARBOHYDRATE precursors

Prolonged starvation (when glycogen stores are depleted)

Question 21

Gluconeogenesis - precursor molecules

Answer 21

Lactate - anaerobi cconditions

Amino acids - derived from muscle protein by proteolysis

Glycerol - derived from triglycerides by lipolysis in adipose tissue

Question 22

Is gluconeogenesis energy consuming?

Answer 22

Very much

6 ATP

Question 23

Is gluconeogenesis the reverse of glycolysis?

Answer 23

NOOOOOOOOOOOOO

Question 24

How many enzymes does gluconeogenesis require?

Answer 24

4

Proceeds via synthesis of OXALOACETATE in mitochondria

Question 25

Lactic acid (cori) cycle - lactate (precursor)

Answer 25

Precursor for gluconeogenesis (anaerobic) Blood transports lactate to liver Liver converts lactate to glucose

Question 26

Amino acids (precursor molecule)

Answer 26

2 classes/ * Ketogenic - can't be used for making glucose * Glucogenic - CAN be used for making new glucose

Question 27

Lipid catabolism

Answer 27

Increased fat intake ↑ No of adipocytes more fat in adipocytes --> Disease

Question 28

Lipids Simple Compound Steroid

Answer 28

> Simple lipids (fatty acids, triglycerides, waxes > Compound lipids (phosphor, glycol, lipo-protein) > Steroids (cholesterol, steroid hormones)

Question 29

Triglycerides

Answer 29

Main energy storage form Hydrophobic Glycerol + 3 fatty acids

Question 30

Fatty acids can be...

Answer 30

Saturated Unsaturated Polyunsaturated (Several double bonds) Usually in cis config. (hydrogen on same side)

Question 31

Unsaturated fats are essential/non-essential

Answer 31

ESSENTIAL

Question 32

What is the main product of fat digestion?

Answer 32

Glycerol absorbed into mucosal cells of intestine

Question 33

What happens to short and medium length fatty acids?

Answer 33

They enter portal blood Longer chains and monoglycerides are resynthesised --> triglycerides

Question 34

What happens to triglycerides?

Answer 34

Coateed with protein, phospholipid and cholesterol --> CHYLOMICRONS enter lymph then blood stream at muscle and adipose tissue chylomicrons are cleared by lipoprotein lipases

Question 35

Fatty acid oxidation

Answer 35

Occurs in cytoplasm Requires 2 ATP Fatty acid + CoA ---> Acyl -CoA (not acetyl CoA) Further oxidation in mitochondra

Question 36

What shuttle moves fatty acids from acyl-CoA to the mitochondria

Answer 36

Carnitine shuttle acyl carnitine into mitochondrion Acyl breaks off and carnitine is carried out of cell. Acyl binds with CoA in mitochondrion to from acyl CoA again.

Question 37

Beta-oxidation

Answer 37

Acyl CoA is substrate Massive energy gain

Question 38

Ketone bodies

Answer 38

Formed in liver mitochondria Diffuse into bloodstream and peripheral tissues Molecules of energy metabolism for heart muscle and renal cortex

Question 39

Ketosis

Answer 39

Starvation or diabetes acetyl CoA converted to ketone bodies because oxaloacetate has been used in gluconeogenesis Leads to acidosis Impairs CNS --> coma Smell of acetone on breath DEATH

Question 40

Lipogenesis

Answer 40

Liver Excess energy intake reductive process

Question 41

How are free fatty acids transported in the blood?

Answer 41

Albumin

Question 42

What enzyme catalyses synthesis of long chain fatty acids?

Answer 42

Fatty acid synthase From malonyl CoA, acetyl CoA and NADPH (electron donor)

Question 43

Palmitic acid is the

Answer 43

longest faty acid produced by FAS

Question 44

What happens to amino acids that are not used as building blocks?

Answer 44

Degraded (not stored) in LIVER

Question 45

What are the toxic bi products of amino acid breakdown?

Answer 45

NH3 and NH4+ Excreted in urea

Question 46

Urea synthesis 3 steps

Answer 46

1. Transamination/ - amino group of an amino acid is transferred onto a keto acid - forms a keto acid and a new amino acid 2. De-amination/ - removal of amino group from glutamic acid in liver - resulting in formation of alpha-keto gluterate 3. Urea cycle - free ammonium ion is converted to urea - second nitrogen is derived from aspartic acid (Urea N2H4CO)

Question 47

What are the major carriers of nitrogen in the blood?

Answer 47

Alanine and glutamine

Question 48

Carbon skeletons

Answer 48

Removal of amino group leaves a carbon skeleton. Converted into major metabolic intermediates Can be used for gluconeogenesis or oxidised in TCA cycle

Question 49

Alcaptonuria

Answer 49

Degradation of phenylalanine and tyrosine is blocked

Question 50

Maple syrup wine disease

Answer 50

Degradation of valine, isoleucine and leucine is BLOCKED urine smells like maple syrup mental and physical retardation appropriate diet

Question 51

Phenylketonuria

Answer 51

Phenylalanine accumulates in all body fluids mental retardation therapy - low phenylalanine diet