Respiration Learning Outcomes Discuss the role and production

Respiration

Learning Outcomes • Discuss the role and production of ATP with particular reference to the transfer of chemical energy, the role of ATP in cellular processes and the regeneration of ATP from ADP and inorganic phosphate (Pi).

Respiration • Respiration is the process by which chemical energy is released from food (by oxidation). • It occurs in every living cell and involves the regeneration of ATP by a series of chemical reactions.

Adenosine Triphosphate • Adenosine Triphosphate (ATP) is an important substance found in all living cells. It is created from the energy released during respiration and acts as an energy storage and transfer molecule. • A molecule of ATP is made up of Adenosine and 3 inorganic phosphate groups. Adenosine Pi Pi Pi

Adenosine Triphosphate • Energy stored in an ATP molecule is released when the bond attached to the terminal phosphate is broken down by enzyme action. When this bond is broken, energy is released Adenosine Pi Pi Pi • This results in the formation of Adenosine Diposphate and Pi.

Synthesis of ATP • The breakdown of ATP to ADP + Pi releases energy for the cell to use for a number of processes. • To build up ATP from ADP + Pi, this process uses energy. • The process of regenerating ATP from ADP + Pi is called phosphorylation. ATP (high energy state) Breakdown releasing energy Build up requiring energy ADP + Pi (Low energy state)

Formation of ATP • ATP is created by joining together an Adenosine Diphospate molecule to a free Inorganic Phosphate molecule (Pi). • In order to join these two molecules together, the energy released from the breakdown of glucose is used. None of the energy released from the breakdown of glucose is used for cell processes, it is all used to make ATP molecules.

Breakdown of ATP • ATP stores the energy released during respiration in the bond attaching its third Pi molecule. When energy is required for cellular processes, the bond can be broken - releasing the energy. Adenosine Pi Pi Pi Enzyme controlled reaction Adenosine Pi Pi + Pi. Pi

Role of ATP • Since ATP can easily revert to ADP + Pi, it is able to make energy available for energy requiring processes such as: – – Muscular contraction Synthesis of proteins and nucleic acids Active transport of molecules Transmission of nerve impulses

Learning Outcome • Describe Glycolysis in terms of the breakdown of glucose (6 C) to pyruvic acid (3 C) with a net production of ATP.

Oxidation and Reduction • Oxidation occurs when hydrogen is removed from a substrate and energy is added. • Oxidation occurs in a cell during respiration. • Reduction involves the addition of hydrogen to a substrate and the loss of energy. It happens during photosynthesis. Remember: OILRIG

Respiration • Respiration is a series of reactions in which 6 -carbon glucose is oxidised to form carbon dioxide. The energy released due to the oxidation of glucose is used to synthesize ATP from ADP + Pi. • Respiration is a series of reactions involving oxidation and reduction.

Respiration • There are 3 stages of respiration: – Stage 1 = Glycolysis – Stage 2 = the Krebs cycle – Stage 3 = the cytochrome system

Glycolysis • The first stage of respiration is called glycolysis and it happens in the cytoplasm. • In glycolysis, a molecule of 6 -carbon glucose is broken down to form 2 molecules of 3 -carbon pyruvic acid. • 2 ATP molecules are needed to start this process but 4 molecules are produced. So there is a net gain of 2 ATP during glycolysis.

Glycolysis • This first stage of respiration does not require oxygen, so it occurs during aerobic and anaerobic respiration.

Glycolysis • During glycolysis, the hydrogen that is oxidised from glucose becomes temporarily bound to a coenzyme molecule which acts as a hydrogen carrier. • The coenzyme involved is NAD, when it is reduced (gains hydrogen), it becomes NADH 2.

Learning Outcome • Describe how Co-enzyme A, in combining with (2 C) acetyl group to form acetyl Co. A, converts a (4 C) compound into (6 C) citric acid. • Give an account of the detailed structure and function of a mitochondrion with particular reference to the membrane, the matrix and the cristae.

Fate of Pyruvic acid • Each molecule of 3 carbon pyruvic acid that is made during glycolysis diffuses into the central matrix of a mitochondria. • Once there it is broken down to carbon dioxide and a 2 -Carbon fragment called an acetyl group.

Fate of pyruvic acid • Each 2 C acetyl group becomes attached to coenzyme A (Co. A) to form a molecule of acetyl Co. A. • This coenzyme ‘helps’ the 2 C acetyl group into the second stage of aerobic respiration: the krebs cycle.

Learning Objective • Describe the Krebs cycle in cells, identifying the main substrates and products involved.

The Krebs’ Cycle • The Krebs’ cycle is an aerobic stage of respiration that occurs in the matrix of the mitochondria. • The Krebs’ cycle starts with a 2 C acetyl Co. A molecule. • This reacts with a 4 -Carbon compound that is present in the matrix, to form 6 -Carbon citric acid.

Krebs’ Cycle • The 6 C citric acid is gradually converted back to the 4 -Carbon compound by a series of enzyme controlled reactions which release carbon dioxide and hydrogen (which combines with NAD).

Learning Outcome • Describe How the cytochrome system in a cell is used to generate most of the ATP used by the cell.

The cytochrome System • The third stage of aerobic respiration is the cytochrome system. • The hydrogen from previous stages is carried to the cytochrome system as NADH 2. • The NADH 2 transfers hydrogen to a chain of hydrogen carriers called the cytochrome system.

The cytochrome system • Each mitochodrion has many of these cytochrome systems attached to each of its cristae. • Oxygen is the final hydrogen acceptor. Hydrogen and oxygen combine to form water. • This stage is aerobic.

The cytochrome system • Oxygen is essential for hydrogen to pass along the cytochrome system. • In the absence of oxygen, the oxidation process can’t go beyond glycolysis. • This system of hydrogen carriers is the most important means of releasing energy during respiration.

The cytochrome system • Energy can be released from a few steps in the process of aerobic respiration, but most of the energy is made available by the cytochrome system. • A total of 38 ATP are produced during aerobic respiration- 2 during glycolysis and 36 during the aerobic stages. video

Alternative respiratory substrates • Glucose is the most common substrate used for respiration, however fats and proteins can also be used.