Glycolysis and Cellular Respiration

Goal

Turn glucose (sugar from food) into ATP (the energy currency your cells use to run)

Glycolysis Phase 1: Energy investment (steps 1-5)

your cell has to spend 2 ATP to get the process started

you have to spend money to make money

Glycolysis Phase 2: Energy yield (steps 6-10)

the modified sugar is broken down, releasing energy

It produces 4 ATP and 2 NADH

Net gain: Since you spent 2 ATP and made 4 ATP, your net profit is 2 ATP and 2 NADH per glucose molecule

The enzyme in charge of Glycolysis

Phosphofructokinase (PFK)

Catalyzes the first “committed” step of glycolysis; once this step happens, the molecule is locked into the pathway

How Glycolysis is controlled/regulated

Feedback inhibition

High amounts of ATP act as a stop sign. If the cell already has plenty of energy, ATP binds to PFK and slows it down so the cell doesn’t waste glucose

High amounts of AMP or ADP (low energy signals) tell PFK to speed up

What happens after glycolysis makes pyruvate?

the cell checks for oxygen

If oxygen is present: Pyruvate enters the mitochondria for the Citric Acid Cycle and Oxidative Phosphorylation (yielding lots of ATP)

If oxygen is not present: the cell undergoes Fermentation (producing lactic acid or alcohol) to keep glycolysis running, though it yields far less energy

Which site on PFK has a higher affinity for ATP- the active site or the regulatory/allosteric site?

The active site has a higher affinity. When ATP levels are low, ATP binds only to the active site so glycolysis runs. When ATP levels are high, excess ATP binds to the lower-affinity regulatory site, shutting the enzyme off

Explain the relationship between PFK activity and ATP when plenty of fructose-6-phosphate are available

At very low ATP, PFK rises quickly because ATP acts as a necessary substrate. Once ATP gets too high, PFK activity drops sharply because ATP begins binding to the inhibitory regulatory site

Further Explanation:

PFK needs an ATP molecule to take a phosphate group off of it and stick it onto fructose-6-phosphate

Even when energy levels are low, ATP must bind to PFK’s active site so glycolysis can run and make more energy. The active site has a HIGH AFFINITY for ATP

What other compounds might inhibit PFK via feedback inhibition?

downstream products like citrate (from the citric acid cycle) or excess NADH