Glycolysis

where do metabolic pathways harvest energy from

they harvest energy from high energy molecules like glucose through the high energy stored in the C-H, C-C and some of the C-O bonds

what happens to some of the energy when glucose is oxidized to carbon dioxide

some of it is released as heat

how is glucose oxidized in cells

it is oxidized through a long series of carefully controlled redox reactions like glycolysis, CAC, ETC and oxidative phosphorylation the free energy is used to synthesize ATP and these reactions comprise cellular respiration

what happens during glycolysis

a six carbon glucose is broken down into two three carbon pyruvate through a sequence of enzyme-catalyzed reactions

what happens during pyruvate processing

each pyruvate is oxidized to form acetyl CoA

what happens during the CAC

each acetyl CoA is oxidized to CO2

what happens during ECT and oxidative phosphorylation

electrons move through a transport chain and their energy is used to set up a proton gradient, which is used to make ATP

what do amino acids, lipid, and other carbohydrates do in cellular respiration

they can be inserted into glycolysis or the CAC as one of the intermediated and they allow these cycles to proceed producing NADH and FADH2 even in the absence of glucose

what happens to pyruvate once its formed

it can be further aerobically oxidized or can be used as a precursor in biosynthesis of amino acids and lipids

what are the two stages of glycolysis

preparatory phase=energy investment phase and payoff phase=energy generation phase

what happens during the first step of glycolysis, the first priming phosphorylation of glucose

glucose gets trapped inside the cell and lowers intracellular glucose concentration to allow further uptake

one ATP is consumed per glucose molecule

nucleophilic oxygen at C6 of glucose attacks the last phosphate of ATP

highly thermodynamically favorable/irreversible and is regulated mainly by substrate inhibition and availability of glucose

catalyzed by hexokinases

what happens during the second step of glycolysis, phosphohexose isomerization

conversion of glucose 6-phosphate (an aldosterone) to fructose 6-phosphate (a ketose)

makes the next steps easier because C1 of fructose is easier to phosphorylate by PFK and it allows for symmetrical cleavage by aldolase

slightly theremodynamically unfavorable/reversible

what happens during the third step of glycolysis, second priming phosphorylation by phosphofructokinase-1

addition of extra phosphate group to fructose 6 phosphate which allows for further activation of glucose and for 1 phosphate/3-carbon sugar after step 4

first committed step of glycolysis since fructose 1, 6-bisphosphate is committed to become pyruvate and yield energy

used energy of ATP

highly thermodynamically favorable/irreversible

phosphofructokinase-1 is highly regulated by the availability of ATP, fructose-1,6 bisphosphate and other metabolites but it doesn’t convert glucose if there is plenty of ATP

what happens in step 4 of glycolysis, aldol cleavage of F-1,6=bP by aldolase

6 carbon sugar cleaved into two different three carbon sugars since three carbon sugars are high energy phosphate sugars

thermodynamically unfavorable/reversible since the product (GAP) concentration is kept low to pull the reaction forward

what happens in step 5 of glycolysis, triose phosphate interconversion by triose phosphate isomerase

DHAP must be converted to GAP to continue to the payoff phase which requires a shifting of a double bonded O and OH group

allows glycolysis to proceed to payoff phase by a single chemical pathway

only GAP is the substrate for the next enzyme

DHAP must be converted to GAP by triose phosphate isomerase

completes preparatory phase of glycolsis

thermodynamically unfavorable/reversible since GAP concentrations kept low to pull the reaction forward

what happens during the preparatory phase of glycolysis

one glucose molecule and 2 ATP are consumed

2 glyceraldehyde 3-phosphate are produced

both continue to the payoff phase

what is step 6 of glycolysis, oxidation of GAP by glyceraldehyde- 3 phosphate dehydrogenase

oxidation of GAP with NAD+ gives NADH

generation of a high energy phosphate compound

incorporated inorganic phosphate which allows for net production of ATP via glycolysis

first energy-yielding step in glycolysis

thermodynamically unfavorable/reversible and is coupled to the next reaction to pull it forward

what is step 7 of glycolysis, first production of ATP by phosphoglycerate kinase

production of the first ATP from ADP from the phosphate group on 1,3 bisphosphoglycerate and kinases

substrate-level phosphorylation to make ATP

highly thermodynamically favorable/reversible because of coupling to GAPDH reaction

what are kinases

they are a group of enzymes which specifically transfer phosphate groups between ATP and other molecules

what is 1,3-bisphosphoglycerate

it is a high energy compound that can donate the phosphate group to ADP to make ATP

what occurs during step 8 of glycolysis, migration of the phosphate by phosphoglycerate mutase

phosphoric group shifted between C2 and C3 of the glycerinate to be able to form high-energy phosphate compound

mutases catalyze the apparent migration of functional groups

thermodynamically unfavorable/reversible due to the reactant concentration kept high by PGK to push it forward

what occurs during step 9 of glycolysis, dehydration of 2-PG to PEP

water removed from phosphoglycerate which generates a high energy phosphate compound

2-phosphoglycerate is not a good enough phosphate donor to generate ATP, the 2 negative charges are close but the loss of phosphate from it would give a secondary alcohol with no further stabilization

slightly thermodynamically unfavorable/reversible since the product concentration is kept low to pull it forward

what occurs during step 10 of glycolysis, second production of ATP by pyruvate kinase

phosphate group from phosphoenolpyruvate used to generate ATP from ADP because substrate level phosphorylation makes ATP and there is a net production of 2 ATP/glucose

loss of phosphate from PEP yields an enos that tautomerizes into ketone

highly thermodynamically favorable/irreversible

what does tautomerization do

it effectively lowers the concentration of the reaction product and drives the reaction toward ATP formation

what happens during the payoff phase

four ATP are produced and two NADH which gives a net result of one glucose molecule that produces two ATP, two NADH and two pyruvate

what is glycolysis regulated by

it is regulated by feedback inhibition, high levels of ATP inhibit the third enzyme, phosphofructokinase

How many binding sites for ATP does phosphofructokinase have

it has 2 binding sites

What happens when ATP binds to the active site of phosphofuctokinase

it will cause the enzyme to catalyze the third step in glycolysis

when does ATP bind to the regulatory site of phosphofructokinase

when its levels are high it will bind and inhibit the enzyme

what is used up in glycolysis

1 glucose, 2 ATP, and 2 NAD+

What is made during glycolysis

2 pyruvate (with various different fates), 4 ATP (for energy requiring processes within the cell), 2 NADH (must be deoxidized to NAD+ in order for glycolysis to continue

why is glycolysis heavily regulated

it is heavily regulated to ensure proper use of nutrients and production of ATP only when needed

what enzymes catalyze an irreversible reaction in glycolysis

hexokinase, pyruvate kinase, and PFK-1

where does glycolysis take place

it takes place in the cytoplasm of the cells

what steps in glycolysis are not reversible

hexokinase, phosphofructokinase, pyruvate kinase

what product of the preparatory phase of glycolysis is required in the payoff phase, but at twice the concentration

ADP