Carbohydrates 3 Flashcards
What is glycolysis?
Biochemical reaction, not involving oxygen, that splits carbohydrates into pyruvic or lactic acid whilst producing ATP
What kind of phosphorylation does glyclysis produce ATP through?
Substrate level phosphorylation
What is the only way that energy can be made when O2 is not present?
Substrate level phosphorylation
Why is glycolysis often the process used to generate energy initially during exercise?
O2 cannot get to the cells quick enough
What are the 2 phases of glycolysis?
Preparation phase
Payoff phase
What happens during the preparative phase of glycolysis?
Two molecules of glucose-3-phosphate are produced per molecule of glucose
What happens during the payoff phase of glycolysis?
ATP is produced
What is the net gain of ATP in glycolysis and how is this distributed between the preparative and payoff phases?
2 ATP is used during the preparative phase and 4 ATP is gained during the payoff phase
Net gain of 2 ATP per molecule of glucose
How many steps are there in glycolysis?
10
How many of the 10 glycolysis steps are irreversible?
3
Why are the irreversible steps of glycolysis irreversible?
Delta G during those reactions is to highly negative, too much energy put be required to reverse the reaction
What are the 10 steps of glycolysis?
- Phosphorylation of glucose (glucose → glucose-6-phosphate)
- Conversion of G-6-P to F-6-P
- Phosphorylation of F-6-P to F-1,6-bisP
- Cleavege to F-1,6-bisP
- Interconversion of triose sugars
- Oxidation of glyceraldehyde-3-phosphate (G-3-P) to 1,3-bisphosphoglycerate (1,3-bisPG)
- P transfer from 1,3-bisPG to ADP
- Conversion of 3-PG to 2-PG
- Dehydrogenase of 2-PG to phosphoenolpyruvate (PEP)
- Transfer of P from PEP to ADP, producing pyruvate
What is fructose-1,6-bisP broken down to into step 4 of glycolysis?
Glyceraldehyde-3-P or dihydroxyacetone-P
What are the 3 irreversible steps of glycolysis?
Step 1 - Phosphorylation of glucose (glucose → glucose-6-phosphate)
Step 3 - Phosphorylation of F-6-P to F-1,6-bisP
Step 10 - Transfer of P from PEP to ADP, producing pyruvate
Why is glucose converted to fructose in step 3?
This lowers the activation energy to proceed due to the negative charges of fructose repelling each other
What is the first commited step of glycolysis?
Phosphorylation of F-6-P to F-1,6-bisP because previous intermediates can be used for other pathways but F-1,6bisP is destined for glycolysis
What is a difference in the requirments of substrate level phosphorylation compared to oxidative phosphorylation, in terms of enzymes?
Substrate level phosphorylation requires soluble enzymes and chemical intermediates, whereas oxidative phosphorylation involves membrane bound enzymes and gradients of protons
What does a diagram of glycolysis look like?
Why does NAD+ need to be regenerated?
It is limited in the cell
Where does NAD+ come from?
Niacin which is an essential vitamin
What do all fates of pyruvate do?
Regenerate NAD+ to replinish what was used during glycolysis
What is redox balance?
The replinishment of NAD+ after glycolysis
What are the 3 pathways that pyruvate can take?
Fermentation in yeast to ethanol
Aerobic respiration to CO2
Fermentation in vigorously contracting muscle cells to lactate
What does the reaction of yeast producing ethanol look like?
How much pyruvate is produced per molecule of glucose?
2
How much lactate can be produced per molecule of pyruvate?
1
How much acetyl coenzyme A can be produced per molecule of pyruvate?
1
What does pyruvate becoming in the absence of oxygen?
Lactate
What does the reaction of pyruvate to lactate look like?
What is the Cori cycle?
Metabolic pathway where lactate is produced by anaerobic glycolysis
What happens if we exercise vigorously?
Muscles don’t recieve O2 fast enough to make ATP by oxidative phosphorylation, instead using substrate level phosphorylation producing lactate
What is the fate of lactate that is produced from pyruvate?
Transfered to the liver and converted to glucose through gluconeogenisis
Where does glycolysis happen?
In a cells cytoplasm
What happens to pyruvate when cells have access to O2?
Oxidised to form acetyl coenzyme A
Where does the reaction of pyruvate to acetyl coenzyme A take place?
In the mitochondria of cells
Why can red blood cells only do glycolysis (substrate level phosphorylation)?
They do not have any mitochondria to do oxidative level phosphorylation
What is also formed when pyruvate is converted into acetyl coenzyme A?
NADH which later gives up its hydride ion (H-) in the electron transport chain
What does the reaction of pyruvate to acetyl conenzyme A look like?
