Lec 30. Carbohydrate metabolism - gluconeogensis and glycogen

what are sources of glucose are used during starvation

* glycogen
* gluconeogenesis

T/F: gluconeogenesis and glycogen are no important sources of glucose

false; they are important to glucose, especially during starvation

T/F: the brain is an organ that uses nutrients and glucose to function

false; the brain ONLY uses glucose

T/F: glucose can come from the diet and used relatively slowly within hours of fasting

false; glucose can come from the diet but it is used within hours of fasting

T/F: the body uses three glucose sources to meet needs

false; there are two glucose services

what are the glucose sources that meet what the body needs

* glycogen (polysaccharide of glucose)
* gluconeogensis (glucose synthesis)

glucose synthesis

gluconeogenesis

glycogen

polysaccharide of glucose

T/F: glucose is mobolized to and from glycogen

that is true

glycogen granules can be found where in the body

in the liver

what happens in glycogen degradation

* mobilizes glucose during fasting
* also called glycogenolysis
* glycogen phosphorylase breaks (alpha 1→ 4) bonds
* debranching enzyme breaks (alpha 1 → 6) bonds

what happens in glycogen degradation: glycogen phosphorylase breaks (alpha 1 → 4) bonds:

* releases glucose- 1P
* conserves 1 ATP equivalent by releasing glucose- 1P, not glucose
* stops when near branch point with (alpha 1 → 6) bond

what happens in glycogen degradation: debranching enzyme breaks (alpha 1 →6) bonds

* also has a transferase activity shown in figure
* sets up glycogen phosphorylase to break remaining (alpha 1 → 4) bonds

glycogen synthesis is also called what

glycogenesis

summary of what happens glycogen synthesis

* replenishes stores of glycogen during well-fed state
* glycogen synthase elongates (alpha 1 → 4) chains
* glycogen-branching enzyme forms (alpha 1 → 6) bonds
* glycogenin starts glycogen synthesis

what happens in glycogen synthase elongates (alpha 1 → 4) chains

* uses UDP-glucose as precursor
* requires input of 2 ATP equivalents (for formation of UDP-glucose; not shown

what happens in glycogen-branching enzyme forms (alpha 1 → 6) bonds

* makes more non-reducing ends
* increase sites for synthesis and degradation
* makes glycogen more water-soluble

what happens in glycogenin starts glycogen synthesis

* glycogen synthase cannot start a new chain of glycogen
* glycogenin starts the chain by adding UDP-glucose to itself, then adding seven more glucose residues
* glycogenin (G) remains part of the glycogen granule
* glycogen is not all carbohydrate

what are the limits of glycogen

* stores are small
* liver stores exhausted within 12 to 24 h
* must be replenished during well-fed state
* not useful as long term source of glucose

what synthesizes glucose

gluconeogenesis

what does gluconeogensis synthesize

glucose

why does gluconeogensis need to synthesize glucose

* glucose provides longterm supply

what is the solution for gluconeogenesis synthesis since we cannot simply put glycolysis in reverse

circumvent those steps with unique ones

why can we not simply have gluconeogensis synthesize glucose by putting glycolysis in reverse?

three steps have change of Gr’ <

what are the three steps that prevent the putting glycolysis in reverse

* glucose + ATP → glucose 6-phosphate + ADP with change of G= -33.4 (kj/mol)
* fructose 6-phosphate + ATP → fructose 1,6-bisphosphate + ADP with change of G= -22.2 (kj/mol)
* phosphoenolpyruvate + ADP → pyruvate + ATP with change of G= -16.7 (kj/mol)

T/F: gluconeogenesis differs from glycolysis at 2 different steps

false; 3 steps differ

how does gluconeogenesis differ from glycolysis with unique step #1

* phosphorylation of pyruvate to PEP
* actually two different steps, with oxaloacetate as the intermediate
* consumes 2 ATP equivalents
* drives reaction forward

how does gluconeogenesis differ from glycolysis with unique step #2

* dephosphorylation of fructose 1,6- bisphosphate
* phosphoryl group is hydrolyzed, not transferred to ADP
* drives reaction forward

how does gluconeogenesis differ from glycolysis with unique step #3

* dephosphorylation of glucose-6P
* phosphoryl group is hydrolyzed

what is net reaction of gluconeogensis

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

* expensive, but worth it

TCA cycle *__* and other compounds are __

* intermediate
* glucogenic

how does TCA cycle intermediates feed into gluconeogenesis

it can feed via oxaloacetate

T/F: any compound is glucogenic if it feeds into TCA cycle

true

what is an example of a compund that glucogenic if it feeds into TCA cycle

some amino acids

what are other glucogenic compounds

* lactate
* glycerol (from fats)
* phosphoglycerate (from photosynthesis)

what is propylene glycol

* administered to cattle during ketosis
* metabolized to lactate

what is ketosis

dangerous buildup of ketones in blood (occurs in 1/5 of early lactation cows)

T/F: fatty acid are glucogenic

false; fatty acids are NOT glucogenic

T/F: acetyl-CoA is glucogenic

false; it is NOT glucogenic

what are fatty acids catabolized to

acetyl- CoA

what is acetyl-CoA completely oxidized to what and when

what: CO2

when: during TCA cycle

T/F: Acetyl-CoA is completely oxidized to CO2 during TCA cycle

true

T/F: there is a net of synthesis of oxaloacetate when acetyl-CoA is completely oxidized to CO2 during the TCA cycle

false; there is NOT a net of synthesis of oxaloacetate

what are the sources of glucose during long-term starvation

* amino acids
* lactate
* glycerol

what are not the sources of glucose during long-term starvation

* fatty acids

t/f: fatty acids are a source of glucose during long-term starvation

falso; fatty acids are not a source of glucose

T/F; cori cycle links glycogen and glucogeneogenesis

true

what happens in cori cycle

* replenishes glycogen stores in muscle after vigorous exercise
* lactate released during exercise used for gluconeogenesis in liver

__ and __ supply glucose furing times of fasting

glycogen and gluconeogenesis

what are the three precursors for gluconeogenesis

amino acids, lactate, and glycerol

t/f: glycogen can provide glucose but stores are exhausted in less than 24 hours

true

t/f: gluconeogensis requires a large amount of ATP synthesize glucose, but it is worth it

truuuuee