Carbohydrate Metabolism

Question 1

Where is glycogen found?

Answer 1

Found in liver + muscle

Question 2

What is role of liver?

Answer 2

Supplier and store of glycogen

Question 3

Muscle is source…..

Answer 3

Source of energy and net user

Question 4

What are symptoms of hypoglycaemia?

Answer 4

Muscle weakness, loss of coordination, muscle confusion, sweating, hypoglycaemic coma + death

Question 5

What are symptoms of hyperglycaemia?

Answer 5

Non enzymatic modification of proteins: cataracts, lipoproteins important in atherosclerosis:hyperosmolar coma

Question 6

What processes are involved with excess blood glucose?

Answer 6

Glycogen synthesis
Pentode phosphate pathway
Fatty acid synthesis

Question 7

What processes involved with lack of blood glucose ?

Answer 7

Glycogen breakdown

Gluconeogensis

Question 8

Describe the structure of glycogen?

Answer 8

Large branched molecule
Branches are essentially glucose residues which are linked together by a1-4 + a1-6 links
Alpha 1-6 links=> branched part of molecule
Alpha 1-4 links=> linear part of molecule
Consists of molecule called glycogenin
Glycogenin is essential component of glycogen as without it glycogen cannot be formed

Question 9

What is name of enzyme that makes a1-6 links?

Answer 9

Branching enzyme

Question 10

Glucose 6 phosphate to glucose 1 phosphate

Is catalysed by….

Answer 10

Phosphoglucomutase

Question 11

What enzyme catalyses the reaction glucose 6 phosphate to UDP glucose?

Answer 11

UDP glucose pyrophosphorylase

Question 12

What does glycogen synthase do?

Answer 12

It adds glucose residues + will attach them in a1-4 configuration => there is continuation of this addition until it gets 11 length of residues

Question 13

Why use glycogen instead of glucose?

Answer 13

Cannot store glucose as it’s osmotically active
Glycogen is heavily branched so can be broken down => many residues can be released
Glucose can be metabolised in absence of oxygen

Question 14

What are 2 activities Debranching enzyme is associated with it?

Answer 14

It takes all but last residue + transfer it to end of neighbouring a1-4 chain
It remove branch group + breaks a1-6 links + glucose is generated

Question 15

What are enzymes involved in glycogen breakdown?

Answer 15

Debranching enzyme 
Transferase/translocase 
Phosphorylase 
Phosphoglucomutase 
Glucose 6 phosphatase

Question 16

Describe the structure of glycogen phosphorylase and what it is involved in?

Answer 16

Key enzyme for glycogenolysis + its activity forms glucose 1 phosphate
Large multi subunit enzyme
Is an example of allosteric enzyme one that sites away from active site that control its activity by inducing shape changes in protein

Question 17

Phosphorylase b is converted by active form called phosphorylase a by enzyme called

Answer 17

Phosphorylase b kinase
It transfers phosphate from ATP to one serine residue on each phosphorylase subunit
It also adds phosphates to phosphorylase b to form phosphorylase a

Question 18

Hormone regulation of glycogenolysis

Answer 18

Adrenaline stimulates cAMP
cAMP activates protein kinase A
Protein kinase A phosphorylate phosphorylase kinase
Phosphorylase kinase phosphorylates phosphorylase kinase b
Phosphorylase kinase a generates glucose 1 phosphate
Protein kinase A phosphorylates glycogen synthase a to give glycogen synthase b => phosphorylationun glycogen synthase activates it

Question 19

Describe the control of glycogen phosphorylase

Answer 19

In muscle, glycogen phosphorylase b can be activated by 5’ AMP which binds to another allosteric site without being phosphorylated
ATP binds to same site +blocks activation
Glucose 6 phosphate blocks 5’AMP activation
In liver, activated phosphorylase a is inhibited by glucose

Question 20

Activation of phosphorylase b kinase by Ca2+

Answer 20

Ca2+ ions activate phosphorylase b kinase=> in muscle, mediating glycogenolysis during muscle contraction
Only get max activity with Ca2+ and phosphorylation=> in liver, a-adrenergic activation stimulates Ca2+ release

Question 21

Glycogen synthesis and degradation is ….

.. regulated

Answer 21

Reciprocal regulation

Question 22

Glycogen synthase is activated by…

Answer 22

Activated in times of plenty of glucose
Activated by ATP +GTP
Activated by dephosphorylation by protein phosphatase 1)

Question 23

Glycogen synthase is inactivated ……

Answer 23

Phosphorylation by protein kinase A

Question 24

Glycogen phosphorylase is activated by….

Answer 24

Activated when glucose is in short supply

Activated by phosphorylation by phosphorylase b kinase

Question 25

Glycogen phosphorylase is inactivated by…

Answer 25

Dephosphorylation by protein phosphatase 1

Question 26

Pentose phosphate pathway is activated when…

Answer 26

Activated when there is a lot of glucose 6 phosphate

Question 27

What is product of pentose phosphate pathway?

Answer 27

Ribose 5 phosphate (pentose phosphate) which is precursor for nucleotides, coenzymes, DNA + RNA
NADH is also produced

Question 28

What is NADPH important for ?

Answer 28

In synthesis of molecules which protect cell from oxidative stress
NADPH is required for fatty acid synthesis

Question 29

What is gluconeogensis?

Answer 29

Formation of glucose from non-carbohydrates sources