18: Aerobic cellular respiration

Cellular respiration as an example of biochemical pathways I From Mr A's slideshows (remember more detail in edrolo vids and textbook notes)

What is cellular respiration?

The process of breaking down glucose in order to release energy in the form of ATP. Undergone in all living cells.

What is the energy released in cellular respiration used for?

To power all other reactions that take place in the cell

What is the chemical equation of cellular respiration?

What is the word equation for cellular respiration?

glucose + oxygen → carbon dioxide + water + 30-32 ATP

Cellular respiration is …lic and …ic

catabolic (larger molecules broken down into smaller molecules) and exergonic (energy is released)

Why is cellular respiration a biochemical pathway?

Each step begins with a substrate, which is then converted to a product, which then becomes the substrate for the next chemical reaction (each enzyme controlled)

Cellular respiration can be… (to do with oxygen)

Aerobic (oxygen requiring) or anaerobic (fermentation. Non-oxygen requiring).

What are the three stages of aerobic cellular respiration? (outline each)

1: Glycolysis - splits glucose (6 carbon molecules) into two pyruvate (3 carbon molecules)

2: Krebs Cycle (aka citric acid cycle) - makes a supply of energy-rich loaded coenzymes

3: Electron transport chain - transfers energy from electrons supplied by loaded coenzymes to make ATP

Where does glycolysis occur

in the cytosol of cells (where required enzymes are present)

does glycolysis require oxygen

No - involved in both aerobic and anaerobic pathways

Outline glycolysis

Glucose (C6H12O6) is broken down into two pyruvate (C3H4O3) molecules.

Net production of 2 ATP molecules (4 ATP produced, but 2 used up during this stage).

H+ and e- are released as glucose is split and collected by NAD+ to form NADH (2 NADH molecules produced)

Inputs and outputs of glycolysis

Inputs:

Glucose

ADP + Pi (x2)

NAD+ (x2)

Outputs:

Pyruvate (x2)

ATP (x2)

NADH (x2)

What does each mitochondria consist of and what is the purpose of each component?

A smooth outer membrane. Controls the passage of materials into and out of the mitochondrion.

A highly folded inner membrane. Folds are called cristae. Increases the surface area of the inner membrane. Embedded with enzymes

A fluid filled inner space called the matrix. Contains ribosomes, circular mitochondrial DNA and enzymes

Where does the Krebs Cycle occur?

In the matrix of the mitochondria

Outline the Krebs Cycle

If oxygen is present, the 2 pyruvate molecules produced during glycolysis diffuse across the mitochondrial membranes into the matrix.

Each pyruvate molecule first converted into acetyl coenzyme A, one molecule of CO2 and one molecule of NADH. Preparatory reaction, pyruvate oxidation.

Acetyl coenzyme A then enters the Krebs cycle. For each turn, one molecule of acetyl coenzyme A is converted into two molecules of CO2, three molecules of NADH, one molecule of FADH2 and one molecule of ATP.

Inputs and outputs of the Krebs Cycle (including preparatory pyruvate oxidation)

Inputs:

Pyruvate (x2)

ADP + Pi (x2)

NAD+ (x8)

FAD (x2)

Outputs:

CO2 (x6) - 2 during pyruvate oxidation and 4 during Krebs cycle component

ATP (x2)

NADH (x8) - 2 during pyruvate oxidation and 6 during Krebs cycle component

FADH2 (x2)

Where does the electron transport chain occur?

On the cristae of the mitochondria, where enzymes and cytochromes are embedded

Outline the electron transport chain

Energy from the NADH and FADH2 produced in glycolysis and Krebs cycle is used to produce ATP.

H+ combines with O2 to form H2O

A total of 26 or 28 ATP from each original glucose molecule is produced (28 in prokaryotes, 26 in eukaryotes, as 2 ATP used as NADH produced via glycolysis passes across mitochondrial membrane)

Little bit more detail about the electron transport chain (from edrolo - basically no details about this on slide past inputs and outputs so would be good to know just in case)

Hydrogens carried by NADH and FADH2 are removed, releasing high energy electrons and protons (H+). The electrons are passed to transmembrane carrier proteins in the cristae, and they lose energy as they are passed through. This energy is used to pump H+ ions across the inner membrane from the matrix to the intermembrane space, which then diffuse back to the matrix through ATP synthase which uses their energy to produce ATP.

At the end of the transport chain, oxygen accepts the H+ ions (protons) and electrons to form water (final electron acceptor).

Inputs and outputs (per initial glucose molecule) of the electron transport chain

Inputs:

O2 (6)

ADP + Pi (x26 or 28)

NADH (x10)

FADH2 (x2)

Outputs:

H2O (x6)

ATP (x26 or 28)

NAD+ (x10)

FAD (x2)