Glycolysis and Gluconeogenesis Flashcards
Absorption of dietary sugars/carbohydrates from the lumen of the gutinto blood is only as a…
monosaccharide
Lactose is broken down to…
galactose and glucose
Starch is broken down to
glucose
Sucrose is broken down to
glucose and fructose
Galactose is converted to what in the liver?
glucose
Fructose can be converted to what in liver?
Glucose and F-6-P
Describe GLUT 1 & 3
low Km (hi affinity); unregulated activity - basal transport/uptake even when blood [glucose] low - “constant need” RBC, brain, kidney
Describe GLUT 4
low Km (hi affinity), regulated by insulin
mechanism: transporters moved to cell membrane
active only in fed state
muscle, adipose
muscle contraction (exercise) also activates GLUT 4
Describe GLUT 2
high Km (low affinity), unregulated
active mostly when blood [glucose] high (fed state)
found in cells that regulate blood [glucose] levels
pancreatic b-islet cells, liver
Recheck: What are insulin’s functions?
- master hormone that ”drives the recovery process”
- promotes uptake of glucose by muscle (& adipose)
- stimulates glycogenesis in muscle & liver
- stimulates protein synthesis in muscle
Note: Muscle is sensitized to insulin during exercise & for at least 2-4 hrs after exercise
Amino acids also stimulate insulin release by b-islet cells
– effect is synergistic with insulin
What are the enzymes required to prime glucose for metabolism?
Hexokinase/Glucokinase
What is the reaction for glucose once it gets into the cell?
ATP + glucose yields G-6-P + ADP (glucose was phosphorylated). This phosphorylation traps glucose inside the cells and enzymes pull it into the cell
What is the function of hexokinase?
It is found in most tissues
Low Km (~0.1 mM; hi affinity); end product inhibited by glucose-6-P
Glucose phosphorylated even when blood [glucose] low
Glucose uptake limited by glycolysis
Where is glucokinase found and what is its function?
Found in the liver and beta cells of pancreas
High Km (7.6 mM; low affinity); not inhibited by glucose-6-P
Glucose phosphorylated only when blood [glucose] high
High capacity - large quantities of glucose can be taken up
Glucose phosphorylation varies linearly with blood [glucose]
What is glycolysis and what are the steps?
Glycosis is partial oxidation of G-6-P to pyruvate in the cytosol
Glu comes into cell and hexokinase phosphorates it and activates it for metabolism. G-6-P is major metabolic intermediate. 6 C of G-6-P end up being 2 3-C pyruvate. In some cases we will park pyruavte as lactate.
What are the 4 steps to glycolysis?
Stage 1: E Investment: Glucokinase/Hexokinase rxn, 2 phosphate groups are put onto the end of the glucose molecule (2 ATP are converted to 2 ADP) The end product is Fruc-1,6-bp. (This is the activate sugar)
Stage 2: Sugar splitting. The Fruc 1,6 bp is cut into two activated sugars.
Stage 3: Oxidation-reduction. Get E out of the two molecules, a pair of energetic electrons and we put two more phosphate groups on each of the 3-C molecules.
Ste E present in the diphosphorylated sugards to make 4 atp. We end up with 2 3 C partially oxidized pyruvate molecules.
What is the input and final products of glycolysis?
6 C Glucose in 2 x 3 C Pyr out
2 NADH: out*
*We must regenerate NAD+ from NADH:
2 ATP in 4 made 2 ATP out
What is the major control point in glycolysis?
PFK. This tells us that we are going to go along with glycolysis and says yes we are going to make Fru 1,6, bp.
It is inhibited by: energy rich signals (ATP, NAHD:, citrate)
It is activated by Fructose-2,6 bp.
In aerobic (oxygen is present) environment what happens to pyruvate
It goes into the mitochondria to be a part of the Krebs cycle and ATP is made
In anaerobic environment what happens to pyruvate?
The 2 NADH: have electrons taken and they are put on the pyruvate to make lactate and NAD is regenerate. Gives us 2 ATP, 0 NADH, 2 lactate.
What is the synthesis of PFK controlled by?
Activated by fructose 2, 6, bis-P which amplifies glycolysis.
Hormone signals. In liver and adipose insulin causes an increase in PFK synthesis.
In muscle, epinephrine increases the synthesis of PFK.
What enzyme controls gluconeogenesis?
fructose-1,6-bis-phophatase. This decrease synthesis of PFK because this is trying to build up glucose stores not break them down.
What is pyruvate kinase?
The enzyme that makes ATP in glycolysis
When would you want to have a lot of glycolysis going on?
RBC need it all the time, O2 limiting activities, many tumor cells would want it.
