Respiration- Energy Transfers In and Out of Organisms

Where does aerobic respiration take place?

Mitochondria

What is the difference between aerobic and anaerobic respiration?

Aerobic requires oxygen, anaerobic doesn’t

What is glycolysis?

An anaerobic process, involving the splitting of a 6-carbon glucose into two 2-carbon pyruvate molcules

It is the first step in both anaerobic and aerobic respiration

Where does glycolysis take place in the cell?

Cytoplasm

What are the steps of glycolysis?

• Phosphorylation of glucose: 2 ATP molecules add 2 phosphate groups to the 6-carbon glucose molecule

• This molecule is then broken down into two 3-carbon molecules called triose phosphate

• Each triose phosphate is oxidised, where hydrogen and ions and electrons are removed and transferred to the coenzyme NAD, so it becomes reduced NAD

• The TP then becomes pyruvate

  • The conversion of TP to pyruvate releases enough energy to convert 4 ADP+Pi molecules into 4 ATP molecules (2 for each TP)

What is the energy yield for glycolysis?

2:

4 ATP produced- 2 used for the phosphorylation

What is the link reaction?

The 3-carbon pyruvate molecules enter into a series of reactions which lead to the formation of acetyl coenzyme A (a 2-carbon molecule)

What are the steps of the link reactions?

• The pyruvate molecules in the cytoplasm produced in glycolysis are actively transported into the matrix of mitochondria

• The pyruvate is oxidised to Wacetate. The 3-carbon pyruvate loses a CO2 molecule and two hydrogens

• The hydrogens are accepted by NAD to form reduced NAD

• The 2-carbon acetate combines with coenzyme A to produce a compound called acetylcoenzyme A

What is the overall equation of the series of reactions in the Link Reaction?

pyruvate + NAD + CoA → acetylcoenzyme A + reduced NAD + CO2

What occurs in Krebs Cycle?

Introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large quantity of reduced NAD and FAD

What are the steps involved in Krebs Cycle?

• The 2-carbon acetylcoenzyme A combines with a 4-carbon molecule to produce a 6-carbon molecule

• Due to substrate-level phosphorylation, the 6-carbon molecule loses carbon dioxide and hydrogen to give a 4-carbon molecule and a single molecule of ATP

• This 4-carbon molecule can now combine with a new molecule of acetylcoenzyme A to begin the cycle again

What are the products of the link reaction and Krebs cycle?

• reduced coenzymes (NAD and FAD) used to provide energy to produce ATP by oxidative phosphorylation

• one molecule of ATP

• three molecules of carbon dioxide

What is oxidative phosphorylation?

The use of electrons, associated with reduced NAD and FAD released from Krebs cycle, to synthesise ATP with water produced as a by-product

Where does oxidative phosphorylation occur?

Inner membrane of mitochondria

What is the electron transfer chain?

• The hydrogen atoms produced during glycolysis and Krebs cycle combine with the coenzymes NAD and FAD

• The reduced NAD and FAD donate the electrons of the hydrogen atoms they are carrying to the first molecule in the electron transfer chain

• The electrons pass along a chain of electron transfer carrier molecules in a series of oxidation-reduction reactions

• As the electrons flow along the chain, they release energy which is used in the active transport of protons across the inner mitochondrial membrane and into inter-membranal space

• The protons accumulate in the inter-membranal space before they diffuse back into the mitochondrial matrix through ATP synthase channels embedded in the inner mitochondrial membrane

• At the end of the chain, the electrons combine with these protons and oxygen to form water

• Oxygen is therefore the final proton acceptor of electrons in the ETC

What are alternative respiratory substances?

Other respiratory substrates include the breakdown products of lipids and amino acids, which enter the Krebs cycle.

Which processes can’t occur in anaerobic respiration?

Krebs cycle and electron transfer chain, as all the FAD and NAD will be reduced

How is the reduced NAD regenerated to NAD?

Pyruvate molecule from glycolysis accepts the hydrogen from the reduced NAD. The oxidised NAD produced can then be used in further glycolysis

What does the pyruvate convert to in plants and animals in anaerobic respiration?

Plants- ethanol and carbon dioxide

Animals- lactate