gluconeogenesis and glycogen

what are the sources of glucose during starvation

glycogen (polysaccharide of glucose) and gluconeogenesis (glucose synthesis)

what is glycogenolysis

glycogen degredation and mobilization of glucose during fasting

what occurs during glycogen degredation

• glycogen phosphorylase breaks alpha 1→4 bonds

• debranching enzyme breaks alpha 1→ 6 bonds

what occurs when glycogen phosphorylase breaks the alpha1→ 4 bond

releases glucose-1P, stops near branch point with alpha 1→ 6 bond

what occurs during debranching enzyme breaks alpha 1→ 6 bonds

transfer of extra glucose residues to another branch, breaking of alpha 1→ 6 bond, setting up glycogen phosphorylase to break remaining alpha 1→ 4 bonds

what is glycogenesis

glycogen synthesis, that replenishes stores of glycogen during well fed state

what occurs during glycogen synthesis

• glycogen synthase elongates alpha 1→ 4 chains,

• glycogen branching enzymes form alpha 1→6 bonds

• glycogenic starts glycogen synthesis

what occurs during glycogen synthase elongating alpha 1→ 4 chains

UDP used as cursor, input of 2 ATP equivalents

what occurs during glycogen branching enzyme forming alpha 1→ 6 bonds

makes more non-reducing ends (increase sites for synthesis and degradation), makes glycogen more water soluble

what happens when glycogenin starts glycogen synthesis

glycogen synthase cannot start a new chain of glycogen, so glycogenic stars the chain by adding the UDP glucose to itself then adding 7 glucose residues

• glycogenin remains part of glycogen granule

what are limits of glycogen

store are small/ quickly exhausted, must be replenished, not useful as long term source of glucose

how does gluconeogenesis differ from glycolysis

three different steps (where delta g was less than 0 and couldn’t be reverses) were replaced

what is unique step #1 of gluconeogenesis

phosphorylation of pyruvate to PEP, consumes 4 ATP equivalent

what is unique step #2 of gluconeogenesis

dephospho rylation of fructose 1,6 bisphosphate, phosphoryl group is hydrolyzed not transferred to ADP

what is unique step #3 of gluconeogenesis

dephosphorylation of glucose- 6p, phosphoryl group is hydrolyzed not transferred to ADP

what is the net reaction of gluconeogenesis

2 pyruvate + 4ATP + 2GTP+ 2 NADH+2 H+→ 1 glucose + 4 ADP+ 2GDP+ 6PI + 2NAD+

how is the TCA cycle related

intermediate scan feed into gluconeogenesis via oxaloacetate, any compound is glucogenic if it feeds into TCA cycle

what are some glycogenic compounds

lactate, glycerol (fats), 3-phosphoglycerate (photosynthesis)

what is propylene glycol

administered to cattle during ketosis ()ketone build up in blood), metabolized to lactate

why are fatty acids not glucogenic

fatty acids are catabolized to acetyl CoA, but acetyl CoA is completely oxidized to CO2 during the TCA cycle

what are sources of glucose during long term starvation n

AA, lactate, glycerol

what is the cori cycle

links glycogen and gluconeogenesis, replenished glycogen stores in muscle after hard exercise, lactate released during exercise goes to liver for gluconeogenesis