What is Substrate level phosphorylation
Direct transfer of a phosphate group from a donor molecule to ADP
Example anabolic reaction
- formation of ATP
Respiration
the enzymatic release of energy from organic compounds in living cells
Stages of aerobic respiration and their location
1) Glycosis - cytoplasm
2) link reaction - matrix
3) Krebs cycle - matrix
4) oxidative phosphorylation - inner mitochondrial membrane
Reactants required for glycosis
- one molecule of glucose
- two ATP molecules
Products of glycosis
- Four ATP molecules
- Two reduced NAD molecules
- Two pyruvate molecules
What is the net energy gain in Glycosis
- two ATP molecules
- two reduced NAD
per glucose molecule
Process of glycolysis
1) Phosphorylation - Two ATP molecules donate phosphate groups to glucose.
2) Lysis - The phosphorylated glucose molecule is split into two molecules of triose phosphate (TP).
3) Dehydrogenation - A hydrogen is removed from each TP molecule (they are oxidised) and used to form two molecules of reduced NAD.
4) Production of ATP - The TP molecules are converted into two pyruvate molecules, also producing four ATP molecules through substrate-linked phosphorylation.
Link reaction process
1) Active transport of pyruvate - Pyruvate from glycolysis is actively transported into the mitochondrial matrix by specific carrier proteins.
2) Decarboxylation - In the mitochondrial matrix, each pyruvate molecule is decarboxylated, losing one molecule of CO2.
3) Removal of CO2 - CO2 diffuses out of the mitochondria as a waste product
4) Oxidation of pyruvate - Two hydrogen atoms are removed from pyruvate to form a two-carbon molecule (acetate).
5) Reduction of NAD - The hydrogen atoms are used to reduce the coenzyme NAD, forming reduced NAD (an electron carrier).
6) Formation of acetyl CoA - Acetate binds to coenzyme A, forming acetyl coenzyme A (acetyl CoA).
Reactants of the link reaction
1) Pyruvate
2) NAD
3) Coenzyme A
Products of the link reaction
1) Acetyl coenzyme A
2) Reduced NAD
3) Carbon dioxide
What does the kreb cycle produces for each molecule of acetyl CoA
- Two molecules of carbon dioxide as a by-product.
- The electron carriers reduced NAD and reduced FAD, which are needed for oxidative phosphorylation.
- One molecule of ATP through substrate-level phosphorylation.
Krebs cycle process
1) The two-carbon (2C) acetyl CoA merges with a 4C molecule to create a 6C molecule.
2) The 6C molecule is also dehydrogenated (oxidised), releasing hydrogens that reduce NAD and FAD.
3) For each acetyl CoA that enters the cycle, one ATP (or GTP in some organisms) is synthesised directly via substrate-level phosphorylation
4) The 6C molecule is decarboxylated, releasing two molecules of carbon dioxide, so that 4C molecule is regenerated for the next turn of the cycle.
Example of coenzymes
- NAD
- FAD
- coenzyme A
How do NAD and FAD differ when they are reduced
- NAD acts as an oxidising agent, accepting an electron and a proton to form reduced NAD.
- FAD acts as an oxidising agent, accepting two protons and two electrons to form reduced FAD.
What is the importance of the Krebs cycle
- It oxidises and breaks down large nutrients into smaller ones, like carbon dioxide, which can be removed as a waste product.
- It generates reduced NAD and reduced FAD, which carry protons and electrons into oxidative phosphorylation.
- It continually regenerates the 4C molecule to combine with acetyl CoA molecules.
- It provides a variety of intermediate compounds required for the biosynthesis of essential cellular components such as fatty acids, amino acids, and chlorophyll
Structure of mitochondria
- outer membrane - This separates the contents of the mitochondrion from the rest of the cell.
- Intermembrane space - This is the space between the outer and inner membranes into which protons are pumped during oxidative phosphorylation.
- inner membrane - This contains the proteins involved in oxidative phosphorylation.
- Cristae - These are folds in the inner membrane of mitochondria.
- matrix - This is the space within the inner membrane that is the site of the link reaction and the Krebs cycle.
- Mitochondrial DNA - This codes for some of the proteins required for the mitochondrion to function.
- Mitochondrial ribosomes - These are used for protein synthesis within the mitochondria.
How does the structure of the mitochondria relate to function
- The matrix contains all the enzymes needed for the link reaction and the Krebs cycle.
- The mitochondrial DNA and ribosomes allow it to produce proteins like enzymes rapidly.
- The cristae significantly increase the inner membrane’s surface area, so it can contain more proteins like those in the electron transport chain and enzymes like ATP synthase.
- The intermembrane space is small, so the proton concentration gradient between the intermembrane space and the mitochondrial matrix builds up quickly.
Where does oxidative phosphorylation occur
Inner mitochondrial membrane of the membrane
Reactants of oxidative phosphorylation
Reduced NAD
Reduced FAD
Oxygen
ADP and inorganic phosphate
Products of oxidative phosphorylation
NAD
FAD
Water
ATP
Process of oxidative phosphorylation
1) Reduced NAD and reduced FAD release hydrogen, transferring protons (H+) and electrons (e-) into the mitochondrial matrix.
2) The electrons are passed along a series of electron carrier molecules in the electron transport chain embedded in the inner mitochondrial membrane, releasing energy as they are transferred.
3) The energy is used to pump protons across the inner mitochondrial membrane from the mitochondrial matrix into the intermembrane space.
4) The accumulation of protons in the intermembrane space sets up a steep electrochemical gradient of protons across the inner membrane
5) Protons diffuse back into the mitochondrial matrix down their electrochemical gradient through ATP synthase.
6) This releases energy and catalyses the synthesis of ATP from ADP and inorganic phosphate (Pi).
7) Oxygen is the final electron acceptor, and combines with electrons and protons to form water, helping to maintain the proton gradient.
What is chemiosis in aerobic respiration
the diffusion of protons across the partially permeable inner mitochondrial membrane, down their electrochemical gradient through ATP synthase channels.
How to calculate the net energy gain per glucose molecule
ATP synthesised - ATP used
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Exam Q7
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Keywords15
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Chapter 1 Carbs + Biological Molecules (1.1-1.6)90
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Chapter 1 Biological molecules - Enzymes (1.7-1.9)31
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Chapter 2 Nucleic Acids59
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Chapter 3 Microscope + Cells (3.1 - 3.6)46
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Chapter 3 Mitosis (3.7-3.8)34
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Chapter 4 Transport Across Cell Membrane39
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Chapter 5 - Immunity75
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Chapter 6 - Gas Exchange51
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Chapter 7 - Mass Transport61
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Chapter 8 - DNA genes and protein synhesis58
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Chapter 9 - Gene Diversity And Adaptation45
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Chapter 10 - Biodiversity69
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Chapter 11 - Photosynthesis22
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Chapter 12 - Respiration39
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Chapter 13 - Energy And Cycles52
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Chapter 14 - Responses To Stimuli52
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Chapter 15 - Nervous Coordination and Muscles42
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Chapter 16 - Homeostasis58
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Chapter 17 - Inherited Change22
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Chapter 18 - Populations And Evolution34
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Chapter 19 - Populations In Ecosystems50
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Chapter 20 - Control Of Gene Expression61
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Chapter 21 - Recombinant Genes45
