Glycogenesis and Glycogenolysis

Question 1

what is the structure of glycogen

Answer 1

Polysaccharide of glucose – polymers of glucose
The many non-reducing end-branches of glycogen facilitate its rapid synthesis and catabolism.
Branching improves solubility inside the cytoplasm
The highly branched structure has many non-reducing ends.

Question 2

Why is glycogen branched rather than a linear molecule?

Answer 2

Lots more active reducing ends

More soluble within the cytoplasm

Able to interact with several enzymes at once

Question 3

what happens with Short sustained bursts of energy

Answer 3

primary glucose dependent pathways utilized

Question 4

what happens with Long, sustained energy requirements

Answer 4

glucose + fat utilized

Question 5

what does SODAS stand for

Answer 5

storage
osmolality
digestion
atp yield
solubility

Question 6

what are the SODAS for carbohydrates (glycogen)

Answer 6

short term energy storage
more effect on osmotic pressure
more readily digested
stores half as much atp per gram
water soluble as monomers- easier to transport

Question 7

what are the SODAS for lipids

Answer 7

long term energy storage
less effect on osmotic pressure
less easily digested
stores twice as much ATP per gram
not water soluble - more difficult to transport

Question 8

what are the SODAS for lipids

Answer 8

long term energy storage
less effect on osmotic pressure
less easily digested
stores twice as much ATP per gram
not water soluble - more difficult to transport

Question 9

what are the main events in glycogenesis

Answer 9

Formation of ADP-Glucose/UDP-Glucose, active forms of glucose, starts process
ADP-Glucose/UDP-Glucose is added to the nonreducing end of glycogen molecules by glycogen synthase
UDP/ADP is then liberated after inclusion
(amylo-(1,4-1,6) transglycosylase) forms branches via formation of 1-6 bonds at non-terminal glucose residues

Question 10

what is glycogen degradation

Answer 10

Glycogenolysis - degradation of glycogen
Glycogen breakdown yields G1P which can be converted to G6P for metabolism via glycolysis and the citric acid cycle
Most G6P in the liver is converted to glucose and delivered to other cells such as brain. Primary goal is to maintain plasma glucose levels and brain function

Question 11

What is the Structure of Glycogen Phosphorylase

Answer 11

1. Catalytic sites are in clefts between the two domains of each subunit
2. Binding sites for glycogen and allosteric effectors (and a phosphorylation site)
3. Phosphorylase a (phosphorylated) active form
4. Phosphorylase b (dephosphorylated) less active

Question 12

what is the product of glycogenolysis

Answer 12

Glucose 1-phosphate- it is converted to G6P by phosphoglucomutase

Question 13

Glucose 6-phosphate is an intermediate in several cellular pathways of what kind

Answer 13

glycolysis, glycogen synthesis and pentose phosphate pathway

Question 14

what are the main events in Glycogenolysis

Answer 14

GP can only cleave alpha 1-4 bonds and stops at the 4th closest branch residue (limit dextrin)

Glycogen is then remodeled with 3 of the residues transferred to the terminal end leaving only 1 alpha 1-6 bond remaining

G1P can be used in glycolysis/CAC (muscle) or converted to glucose in the liver

Question 15

what is Muscle glycogen a fuel for

Answer 15

muscle contraction

Question 16

why is Liver glycogen mostly converted to glucose for

Answer 16

bloodstream transport to other tissues

Question 17

what are the mobilisation and synthesis of glycogen regulated by

Answer 17

hormones

Question 18

how big is insulin

Answer 18

51 amino acid polypeptide

Question 19

what is insulin

Answer 19

produced by b-cells of the pancreas (secreted when the concentration of glucose in the blood increases (> 5 mmol/L) – elevated insulin associated with the fed state)

Question 20

what is the function of insulin

Answer 20

increases the rate of glucose transport into muscle and adipose tissue via the GLUT4 glucose transporter
Stimulates glycogen synthesis in the liver

Question 21

how big is glucagon

Answer 21

29 amino acid polypeptide

Question 22

whites glucagon

Answer 22

Secreted by the a cells of the pancreas in response to low blood glucose (elevated glucagon is associated with the fasted state)

Question 23

what is the function of glucagon

Answer 23

Stimulates glycogen degradation to restore blood glucose to steady-state levels

Question 24

what are the islets of langerhans

Answer 24

Endocrine units of the pancreas

Clusters of hormone secreting cells

Question 25

what is adrenaline

Answer 25

Released from the adrenal glands in response to sudden energy requirement (“fight or flight”)
Stimulates the breakdown of glycogen to G1P (which is converted to G6P)

Question 26

what happens when blood glucose is low

Answer 26

adrenaline and glucagon activate intracellular signaling pathways

Glycogenolysis is increased (increases circulating glucose concentration)

Glycogen synthesis (Glycogenesis) is decreased

Question 27

what is Glycogen metabolism regulated by

Answer 27

hormones

Question 28

what is the order of ATP being produced

Answer 28

ATP produced via Glycolysis > Krebs cycle > ETC

Question 29

what does gluconeogenesis require

Answer 29

Gluconeogenesis requires NADH and ATP

Question 30

why do Insulin and glucagon maintain a balancing

Answer 30

to influence blood glucose levels and glycogen storage, relating back to the balance of glycolysis/gluconeogenesis

Question 31

what is Glycogen utilised to store

Answer 31

surplus glucose and is metabolised to release glucose in fasting states