MCAT - Krebs Cycle

Products of the Citric Acid Cycle

- 1 GTP - 3 NADH - 1 FADH₂ - 2 CO₂ - Regenerated oxaloacetate

Step two of the Citric Acid Cycle

- Energy is released when the 6-carbon arrangement is oxidized. One carbon removed. - The removed carbon molecule combines with oxygen, making CO₂. - Some electrons are captured in formation of high-energy compound, NADH. - The high energy electrons that are handed to NAD⁺ for reduction come from the oxidation from the carbon molecule here.

Step four of the Citric Acid Cycle

- Rearrangement occurs, allowing the 4-carbon molecule to find a more comfortable configuration. - During this rearrangement, non-carbon groups are added to and removed from the molecule. - GTP and FADH₂ are made in these steps.

Step three of the Citric Acid Cycle

- Same type of reaction in step one happens again. - Another carbon is cleaved off the 5-carbon molecule resulting in a 4-carbon molecule and CO₂ - Some electrons released from cleaving is used to reduce NAD⁺ to NADH.

Step five of the Citric Acid Cycle

- The 4-carbon molecule rearranges its carbons one last time, producing oxaloacetate. - Oxaloacetate will be used again in the next cycle. - Some electrons released is transferred to reduce NAD⁺ to NADH.

citric acid cycle overview

- called a cycle because the starting molecule, oxaloacetate (which has 4 carbons), is regenerated at the end of the cycle. - oxaloacetate is transformed into several different molecules (as carbon atoms are added to and removed from it) - at the end of the cycle it always turns back into oxaloacetate. - energy captured because several of the steps are energetically favourable. - released energy is captured as the electron shuttles (NAD⁺ and FAD) are reduced to NADH and FADH₂

Where does the citric acid cycle fit into cellular respiration

1. Glycolysis 2. Pyruvate --> Acetyl CoA 3. Citric Acid cycle 4. Oxydative Phosporylation

Transformation of pyruvate to Acetyl CoA

The 3-carbon pyruvate molecule made in glycolysis loses a carbon to produce a new, 2-carbon molecule called acetyl CoA. The carbon that is removed takes two oxygens from pyruvate with it, and exits the body as carbon dioxide (CO₂). CO₂ is the waste product that you release when you exhale.

What does it mean to be energetically favorable (thus capturing energy in the krebs cycle)?

When a step is favoured, it means that the products of the reaction have lower energy than the reactants. The difference in energy between the products and the reactants is the energy that is released when the reaction takes place.

What happens in oxidative phosphorylation

it is converted to a usable form of cellular energy, ATP (adenosine triphosphate). We can then use that energy to move, breathe, make our hearts beat, and think (among other things)!

high energy molecules

ATP and GTP

NADH

An energy shuttle which delivers high energy electrons to the electron transport chain where they will eventually power the production of 2 to 3 ATP molecules. When this electron shuttle is not carrying high energy electrons, meaning it has been oxidized (lost its electrons), it is left with a positive charge and is called NAD⁺

Step one of the Citric Acid Cycle

An enzyme rearranges the atoms in the citric acid molecule (6 carbons) into a new 6-caron arrangement.

energy shuttles

NADH and FADH₂

Oxidative Phosphorilation

NADH and FADH₂ are transported to the electron transport chain, where electrons will ultimately drive synthesis of ATP.

GTP

Similar to ATP, GTP can be easily converted to ATP in the cell.

Glycolysis

Step One of Cellular Respiration: A 6-carbon glucose molecule is split into two 3-carbon molecules called pyruvates. Pyruvate is needed in order to create acetyl CoA.

ATP

The basic energy currency of the cell. It's a form of energy that cells can use right away.

What does the citric acid cycle do?

The citric acid cycle captures the energy stored in the chemical bonds of acetyl CoA (processed glucose) in a step-by-step process, trapping it in the form of high-energy intermediate molecules.

How does the citric acid cycle start?

an enzyme fuses Acetyl CoA with oxaloacetate to make citric acid, a six carbon molecule

What can we break down in the Krebs cycle?

complex carbs, fats and proteins

What are fats broken down into?

either glucose or basic parts to form Acetyl CoA

FADH₂

energy shuttle that carries high energy electrons to the electron transport chain, where they will ultimately drive production of 1 to 2 ATP molecules. The oxidized form of FADH₂ is FAD and happens just like in NADH.

What are the key players in the citric acid cycle?

energy shuttles and high energy molecules

What are carbs broken down into?

glucose

What are proteins broken down into?

their basic parts that form Acetyl CoA