Biochemistry glycolysis steps and enzymes

What is glycolysis?

Glycolysis is a metabolic pathway that converts glucose into pyruvate, yielding energy.

Where does glycolysis occur?

Glycolysis occurs in the cytoplasm of the cell.

True or False: Glycolysis requires oxygen.

False. Glycolysis is an anaerobic process and does not require oxygen.

List the main products of glycolysis.

- 2 Pyruvate - 2 ATP - 2 NADH

What is the significance of glycolysis?

Glycolysis is critical for energy production and provides intermediates for other metabolic pathways.

Fill in the blank: Glycolysis starts with _______.

Glucose.

Comparison: Glycolysis vs. Gluconeogenesis.

Glycolysis breaks down glucose; gluconeogenesis synthesizes glucose from non-carbohydrates.

What is the net gain of ATP in glycolysis?

The net gain is 2 ATP per glucose molecule.

Name an important coenzyme in glycolysis.

NAD+ is essential for accepting electrons.

What happens to pyruvate after glycolysis?

Pyruvate can be converted to acetyl-CoA or lactate, depending on oxygen availability.

Cause → Effect: High ATP levels affect glycolysis how?

High ATP levels inhibit glycolysis, reducing glucose breakdown.

What two phases comprise glycolysis?

The energy investment phase and the energy payoff phase.

True or False: Glycolysis produces more ATP than the citric acid cycle.

False. Glycolysis produces less ATP compared to the citric acid cycle.

What is the role of hexokinase in glycolysis?

Hexokinase phosphorylates glucose to form glucose-6-phosphate, trapping it in the cell.

Fill in the blank: The end product of glycolysis is _______.

Pyruvate.

How many enzymatic steps are in glycolysis?

There are ten enzymatic steps in glycolysis.

What is the first step in glycolysis?

Glucose is phosphorylated to glucose-6-phosphate by hexokinase, using one ATP.

Hexokinase role in glycolysis?

Hexokinase catalyzes the conversion of glucose to glucose-6-phosphate, trapping glucose in the cell.

What happens in step 2?

Glucose-6-phosphate is isomerized to fructose-6-phosphate by phosphoglucose isomerase.

Fructose-6-phosphate to fructose-1,6-bisphosphate?

Phosphofructokinase-1 (PFK-1) catalyzes this step, consuming another ATP.

True or False: PFK-1 is a key regulatory enzyme.

True. PFK-1 is the main control step of glycolysis, responding to energy levels.

Step 4: Split fructose-1,6-bisphosphate?

Aldolase cleaves it into dihydroxyacetone phosphate (DHAP) and glyceraldehyde-3-phosphate (G3P).

What is produced from DHAP?

DHAP can be converted to G3P by triose phosphate isomerase, leading to two G3P molecules.

Step 6 involves which enzyme?

Glyceraldehyde-3-phosphate dehydrogenase (GAPDH) converts G3P into 1,3-bisphosphoglycerate (1,3-BPG) while reducing NAD+ to NADH.

What happens in step 7?

Phosphoglycerate kinase converts 1,3-BPG to 3-phosphoglycerate (3-PG), generating ATP via substrate-level phosphorylation.

Difference between substrate-level phosphorylation and oxidative phosphorylation?

Substrate-level phosphorylation occurs in glycolysis directly producing ATP; oxidative phosphorylation occurs in mitochondria using electron transport chain.

What occurs in step 8?

Phosphoglycerate mutase shifts the phosphate group in 3-PG to form 2-phosphoglycerate (2-PG).

Step 9: 2-PG to phosphoenolpyruvate?

Enolase removes water from 2-PG to generate phosphoenolpyruvate (PEP), which is a high-energy compound.

Final step of glycolysis?

Pyruvate kinase catalyzes the conversion of PEP to pyruvate, producing another ATP.

How many ATPs are produced in glycolysis?

Net gain of 2 ATPs. 4 ATPs produced minus 2 ATPs used.

Step 1: enzyme and product?

Hexokinase converts glucose to glucose-6-phosphate.

What is the fate of pyruvate?

Pyruvate can enter aerobic respiration or anaerobic fermentation, depending on oxygen availability.

Glycolysis occurs in which cellular location?

Glycolysis takes place in the cytoplasm of the cell.

What is the overall equation for glycolysis?

Glucose + 2 NAD+ + 2 ADP + 2 P$\displaystyle _i$ → 2 Pyruvate + 2 NADH + 2 ATP + 2 H$\displaystyle _2$O.

What are the main products of glycolysis?

2 Pyruvate, 2 NADH, and a net gain of 2 ATP.

What is glycolysis?

Glycolysis is the metabolic pathway that converts glucose into pyruvate, producing energy.

Hexokinase function

Catalyzes the phosphorylation of glucose to glucose-6-phosphate. This is the first step in glycolysis. It traps glucose in the cell.

Phosphofructokinase-1 role

Key regulatory enzyme in glycolysis. Converts fructose-6-phosphate to fructose-1,6-bisphosphate. Highly regulated by ATP and AMP levels.

True or False: Isomerase enzymes are used in glycolysis.

True. Isomerases convert glucose-6-phosphate to fructose-6-phosphate.

Enolase function

Catalyzes the conversion of 2-phosphoglycerate to phosphoenolpyruvate. This reaction generates water and is crucial for the next step.

Pyruvate kinase action

Catalyzes the final step of glycolysis, converting phosphoenolpyruvate to pyruvate, producing ATP. This step is irreversible and regulated.

Fill in the blank: __________ catalyzes the conversion of glucose to glucose-6-phosphate.

Hexokinase.

Comparison: Hexokinase vs. Glucokinase

Hexokinase: low km, works in all tissues; Glucokinase: high km, specific to liver and pancreas.

Aldolase function

Catalyzes the cleavage of fructose-1,6-bisphosphate into glyceraldehyde-3-phosphate and dihydroxyacetone phosphate. Important for splitting the sugar.

Glyceraldehyde-3-phosphate dehydrogenase role

Converts glyceraldehyde-3-phosphate to 1,3-bisphosphoglycerate while reducing NAD+ to NADH. This step is coupled to ATP generation.

True or False: All enzymes in glycolysis are irreversible.

False. Most enzymes are reversible, but key steps like those catalyzed by hexokinase and pyruvate kinase are irreversible.

Phosphoglycerate mutase function

Catalyzes the conversion of 3-phosphoglycerate to 2-phosphoglycerate. This is necessary for the subsequent enolase step.

Question: What does phosphofructokinase-1 regulate?

It regulates the pathway in response to cellular energy levels. ATP inhibits; AMP activates.

True or False: Aldolase is a key regulatory enzyme.

False. Aldolase is important but not the main regulatory point in glycolysis.

Creatine kinase vs. Pyruvate kinase

Creatine kinase: involved in ATP regeneration; Pyruvate kinase: final step in glycolysis, produces ATP.

Enzymes that produce ATP

- Phosphoglycerate kinase - Pyruvate kinase Both are substrate-level phosphorylation steps.

True or False: NAD+ is not involved in glycolysis.

False. NAD+ is crucial for the oxidation of glyceraldehyde-3-phosphate.

Triose phosphate isomerase function

Interconverts dihydroxyacetone phosphate and glyceraldehyde-3-phosphate. Ensures efficient utilization of triose phosphates.

Question: What does enolase produce?

It produces phosphoenolpyruvate and water from 2-phosphoglycerate.

Fill in the blank: Pyruvate kinase produces _____ during glycolysis.

ATP and pyruvate.

Lactate dehydrogenase's connection

Converts pyruvate to lactate under anaerobic conditions, regenerating NAD+ for continued glycolysis.

Role of phosphoglycerate kinase

Catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, generating ATP. This is a substrate-level phosphorylation reaction.

What is the role of phosphoglycerate kinase?

Phosphoglycerate kinase catalyzes the conversion of 1,3-bisphosphoglycerate to 3-phosphoglycerate, producing ATP. - Substrate-level phosphorylation - Key in energy production - Involved in glycolytic pathway

What is the primary regulatory enzyme of glycolysis?

Phosphofructokinase-1 (PFK-1) is the main regulatory enzyme, controlling the conversion of fructose-6-phosphate to fructose-1,6-bisphosphate.

Role of ATP in glycolysis regulation?

ATP acts as an allosteric inhibitor of PFK-1, signaling high energy status and slowing glycolysis.

What effect does AMP have on glycolysis?

AMP acts as an allosteric activator of PFK-1, indicating low energy status and promoting glycolysis.

True or False: Citrate inhibits glycolysis.

True. Citrate, a product of the citric acid cycle, signals sufficient energy and inhibits PFK-1.

What is the role of fructose-2,6-bisphosphate?

Fructose-2,6-bisphosphate enhances PFK-1 activity, promoting glycolysis when glucose is abundant.

Fill in the blank: Insulin _____ glycolysis.

Insulin stimulates glycolysis, promoting glucose uptake and increasing levels of fructose-2,6-bisphosphate.

How does glucagon affect glycolysis?

Glucagon decreases glycolysis by lowering fructose-2,6-bisphosphate levels, thus reducing PFK-1 activity.

Comparison: PFK-1 vs. Pyruvate kinase.

Both are key regulatory enzymes; PFK-1 controls an early step, while pyruvate kinase regulates the final step in glycolysis.

What happens when glucose is scarce?

When glucose is scarce, glycolysis is downregulated through increased glucagon and decreased insulin signaling.

How does pH affect glycolysis?

Low pH (acidic conditions) inhibits PFK-1, slowing glycolysis during anaerobic conditions.

What is the impact of high citrate levels?

High citrate levels indicate sufficient energy and inhibit PFK-1, slowing glycolysis.

What is the physiological effect of high fructose-2,6-bisphosphate?

High levels promote glycolysis, enhancing glucose breakdown and energy production.

True or False: Glycolysis is accelerated during intense exercise.

True. Increased AMP and decreased ATP levels during exercise enhance PFK-1 activity, accelerating glycolysis.

What role do hormones play in glycolysis regulation?

Hormones like insulin and glucagon regulate glycolysis by altering enzyme activity through signaling pathways.

Cause → Effect: High energy charge →

Inhibition of glycolysis due to high levels of ATP and citrate signaling abundant energy.

What is the connection between glycolysis and gluconeogenesis?

They are oppositional pathways; glycolysis breaks down glucose, while gluconeogenesis synthesizes glucose from non-carbohydrate sources.

What is the role of NAD+ in glycolysis?

NAD+ is essential for glycolysis; it acts as an electron acceptor, allowing for continued ATP production.

How does fructose metabolism differ from glucose in glycolysis?

Fructose bypasses key regulatory steps, entering glycolysis at the triose phosphate stage and affecting overall regulation.

Fill in the blank: High ADP levels _____ glycolysis.

High ADP levels activate PFK-1, stimulating glycolysis and energy production.

How do hormones influence glycolysis regulation?

- Insulin promotes glycolysis. - Glucagon inhibits glycolysis. - Epinephrine stimulates glycolysis during stress. - Hormonal responses adjust metabolic needs based on energy status.