KREBS AND GLYCOLYSIS

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Krebs Cycle

Also known as the Citric Acid Cycle or TCA Cycle.

Krebs Cycle Function

A series of chemical reactions that break down the energy stored in glucose, fatty acids, and amino acids to produce energy.

Krebs Cycle Location

Occurs in the mitochondrial matrix of eukaryotic cells.

Krebs Cycle Stage

Second stage of aerobic cellular respiration.

Krebs Cycle Products

Main products are ATP, NADH, FADH2, and carbon dioxide (CO2).

Krebs Cycle Importance

Fundamental part of cellular respiration that provides energy carriers for the electron transport chain.

NAD+, NADH, and FADH2

Essential molecules in cellular metabolism and respiration.

Function of NAD+, NADH, and FADH2

They act as electron carriers that move high-energy electrons between reactions.

NAD+

Stands for Nicotinamide adenine dinucleotide.

NAD+ Form

Oxidized form of the molecule.

NAD+ Role

Acts like an empty shuttle bus ready to pick up electrons.

NAD+ Charge

Has a positive charge, shown by the "+" symbol.

NAD+ Function

A key coenzyme in glycolysis and the Krebs Cycle.

NAD+ Reaction

Accepts electrons and a proton to become NADH.

NADH

Reduced form of NAD+.

NADH Description

A full shuttle bus carrying high-energy electrons and hydrogen.

NADH Function

Carries electrons to the electron transport chain (ETC).

NADH ATP Yield

Each NADH produces about 1.5 to 2 ATP in the ETC.

NADH Role

Helps create large amounts of ATP, the cell’s main energy currency.

FAD

Flavin adenine dinucleotide.

FAD Form

Oxidized form of the molecule.

FAD Role

A coenzyme that acts as an electron carrier.

FAD Function

Accepts electrons and protons from succinate during the Krebs Cycle.

FADH2

Reduced form of FAD.

FADH2 Function

Carries two high-energy electrons and two protons.

FADH2 Production

Produced specifically during the Krebs Cycle.

FADH2 Role

Delivers electrons to the electron transport chain (ETC).

FADH2 ATP Yield

Produces about 2.5 to 3 ATP per molecule in the ETC.

FADH2 Entry Point

Enters the ETC at a different point than NADH, giving a slightly lower ATP yield.

Electron Carriers Summary

NAD+/NADH and FAD/FADH2 link glycolysis and Krebs Cycle to the electron transport chain.

Electron Carriers Purpose

They move energy in the form of electrons to produce ATP.

Citrate Formation

Step 1 of Krebs Cycle; Acetyl-CoA (2C) combines with oxaloacetate (4C) to form citrate (6C).

Isomerization of Citrate

Step 2; citrate rearranges to form isocitrate.

Oxidation and Decarboxylation

Step 3; isocitrate is oxidized and releases CO2, forming succinyl-CoA.

NADH Formation in Step 3

One NAD+ is reduced to NADH.

ATP or GTP Production

Step 4; succinyl-CoA is converted to succinate, producing 1 ATP or GTP.

Oxidation of Succinate

Step 5; succinate oxidized to fumarate, FAD reduced to FADH2.

Hydration of Fumarate

Step 6; water added to fumarate to form malate.

Final Oxidation

Step 7; malate oxidized back to oxaloacetate, reducing NAD+ to NADH.

Cycle Restart

Oxaloacetate is regenerated; the cycle repeats.

Krebs Cycle Summary Inputs

Acetyl-CoA, NAD+, FAD, ADP (or GDP).

Krebs Cycle Summary Outputs

CO2, NADH, FADH2, ATP (or GTP).

Krebs Cycle Net Gain

3 NADH, 1 FADH2, 1 ATP (per Acetyl-CoA).

Calvin Cycle

Metabolic pathway in plants that builds sugars using energy.

Calvin Cycle Type

Anabolic (constructive) process.

Calvin Cycle Function

Uses energy to synthesize sugar from carbon dioxide (CO2).

Calvin Cycle Occurs In

Stroma of chloroplasts.

Calvin Cycle Energy Source

Uses ATP and NADPH from light-dependent reactions.

Calvin Cycle Output

Produces glucose (sugar) for the plant.

Calvin Cycle Part Of

Photosynthesis; specifically the light-independent reactions.

Krebs Cycle Type

Catabolic (destructive) process.

Krebs Cycle Function

Breaks down food to release energy.

Krebs Cycle Part Of

Cellular respiration.

Krebs Cycle Location

Mitochondrial matrix of eukaryotic cells.

Krebs Cycle Inputs

Acetyl-CoA from carbohydrates, fats, and proteins.

Krebs Cycle Outputs

ATP, NADH, FADH2.

Krebs Cycle Next Stage

Energy carriers go to the electron transport chain.

Glycolysis

First stage of cellular respiration.

Glycolysis Location

Occurs in the cytoplasm of the cell.

Glycolysis Function

Breaks down glucose into two pyruvate molecules.

Glycolysis Enzymes

Consists of 10 enzyme-catalyzed reactions.

Glycolysis Phases

Has two phases: Energy-Requiring and Energy-Releasing.

Energy-Requiring Phase

First 5 steps where the cell uses ATP to modify glucose.

Energy-Releasing Phase

Last 5 steps where ATP and NADH are produced.

Glycolysis Step 1

Phosphorylation of glucose by hexokinase using 1 ATP.

Glycolysis Step 2

Isomerization of glucose-6-phosphate to fructose-6-phosphate.

Glycolysis Step 3

Second phosphorylation by phosphofructokinase using another ATP.

Glycolysis Step 4

Cleavage of fructose-1,6-bisphosphate into G3P and DHAP.

Glycolysis Step 5

Isomerization of DHAP into G3P by triose phosphate isomerase.

Glycolysis Step 6

Oxidation and phosphorylation of G3P to 1,3-bisphosphoglycerate; produces NADH.

Glycolysis Step 7

First ATP produced by substrate-level phosphorylation; forms 3-phosphoglycerate.

Glycolysis Step 8

Phosphate group moves to form 2-phosphoglycerate.

Glycolysis Step 9

Dehydration forms phosphoenolpyruvate (PEP).

Glycolysis Step 10

Second ATP produced; PEP converted to pyruvate by pyruvate kinase.

Glycolysis Input

1 glucose, 2 ATP, 2 NAD+, 4 ADP + 4 Pi.

Glycolysis Output

2 pyruvate, 4 ATP (gross), 2 NADH, 2 H+, 2 H2O.

Glycolysis Net Gain

2 ATP, 2 NADH, 2 pyruvate.

Glycolysis If Oxygen Present

Pyruvate enters the Krebs Cycle (aerobic respiration).

Glycolysis If No Oxygen

Pyruvate undergoes fermentation (anaerobic conditions).

Glycolysis Purpose

Provides quick energy and prepares pyruvate for further energy production.

Energy Carriers Role

NADH and FADH2 move electrons to the electron transport chain.

Electron Transport Chain Function

Uses electrons from NADH and FADH2 to produce large amounts of ATP.

ATP

Cell’s main energy currency used for movement, growth, and repair.

Calvin Cycle vs Krebs Cycle

Calvin builds food (anabolic); Krebs breaks down food (catabolic).

Calvin Cycle Location

Stroma of chloroplasts (plants).

Krebs Cycle Location

Mitochondrial matrix (animals and plants).

Calvin Cycle Input

CO2, ATP, NADPH.

Krebs Cycle Input

Acetyl-CoA, NAD+, FAD, ADP.

Calvin Cycle Output

Glucose.

Krebs Cycle Output

CO2, ATP, NADH, FADH2.