8.2 Cell respiration Understanding: Skills: Cell respiration involves the oxidation and reduction of compounds Phosphorylation of molecules makes them lesson stable In glycolysis, glucose is converted to pyruvate Glycolysis gives a small net gain of ATP with out the use of oxygen In aerobic cell respiration pyruvate is concerted into acetyl coenzyme A In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers Energy released by oxidation reactions is carried to the cristae of the mitochondria Transfer of electrons between carriers in the electron transport chain is couple to proton pumping In chemiosmosis protons diffuse through ATP synthase to generate ATP Oxygen is needed to bind with the free protons to form water to maintain the hydrogen gradient The structure of the mitochondria is adapted to the function it performs. Skills: Annotation of a diagram to indicate the adaptations of a mitochondrion to its function Applications: Electron tomography used to produce images of active mitochondria Nature of science: - Paradigm shifts: the chemiosmotic theory led to a paradigm shift in the field of bioenergetics

What is the role of each part? Draw a mitochondrion Inner membrane Outer membrane Cristae Matrix Inter membrane space What is the role of each part? Skills: Annotation of a diagram to indicate the adaptations of a mitochondrion to its function

Mitochondrion Drawing Skills: Annotation of a diagram to indicate the adaptations of a mitochondrion to its function

Mitochondrion Functions Inner membrane – Electron transport chain and ATP synthase Outer membrane – Creates a cellular compartment Cristae – projections of inner membrane which increase surface area for oxidative phosphorylation Matrix – Contains enzymes for Krebs cycle and link reaction Inter membrane space - Protons pumped into space by electron transport chain. Small space means concentration builds up quickly Don’t worry. Will will look at all these metabolic processes Understanding: The structure of the mitochondria is adapted to the function it performs.

Electron Tomography Allows a 3D image of mitochondria to be made Dr Carmen Mannella: Cristae are not just infoldings but are defining micro-compartments in the organelle Cristae are flexible and dynamic – change depending on the metabolism and other stimuli Specific proteins/lipids that actively regulate the inner membrane Applications: Electron tomography used to produce images of active mitochondria

Electron Tomography Changes in internal organization of mitochondria associated with cell death and disease: (A) Normal, isolated liver mitochondrion (B) Liver mitochondrion treated with a protein that induces programmed cell death (C) Mitochondrion from a patient with a mitochondrial myopathy (causes muscle weakness)

Oxidation and Reduction Always occur together Involve transferring electrons from one thing to another Oxidation = loss of electrons Reduction = gain of electrons For something to gain an electron, something has to lose one. OIL RIG Understanding: Cell respiration involves the oxidation and reduction of compounds

Oxidation and Reduction Understanding: Cell respiration involves the oxidation and reduction of compounds

e.g. Benedict's test Mix in some sugar Copper sulphate solution contains copper ions – Cu2+ This is a blue solution The sugar gives the Cu2+ electrons which converts them into Copper atoms–Cu. This forms a red precipitate What had been oxidised? What has been reduced?

Electron Carriers Electron carriers accept or give up electrons as required – linking oxidations and reductions in cells. The main electron carrier in respiration is NAD (nicotinamide adenine dinucleotide) Initially has a positive charge and exists normally as NAD+ What does it look like?

Reducing NAD Two hydrogen atoms removed from substance that is being oxidised?! during respiration (see later) The first hydrogen is split into a proton and an electron NAD+ accepts the electron, and the proton (H+) is released NAD accepts the proton and electron of the second hydrogen atom Reduction can therefore be the gaining of hydrogen atoms Oxidation can be losing hydrogen atoms NAD+ + 2H+ + 2e- NADH + H+ NAD+ + 2H NADH + H+ Oxidation can therefore be achieved by losing these Hydrogen atoms again Understanding: Cell respiration involves the oxidation and reduction of compounds

+ H+

Oxidation and reduction – describe what is happening below:

Phosphorylation Addition of a phosphate molecule to an organic molecule Make a molecule less stable – so more likely to react Reduces the activation energy required for reactions that follow – more likely to occur Understanding: Phosphorylation of molecules makes them less stable

Key area = production of ATP Phosphorylation Key area = production of ATP (ADP ATP) Understanding: Phosphorylation of molecules makes them less stable

Oxidation/Reduction Phosphorylation

Respiration Glycolysis Link Reaction Krebs cycle Oxidative Phosphorylation Electron transport chain Chemiosmosis

Glycolysis Glucose (6C) converted into pyruvate (two) (3C) In the cytoplasm of the cell (outside of mitochondrion) Not a single step process – metabolic pathway 1 glucose 2 pyruvate Reduced NAD (NADH) made (has gained electrons) Phosphorylation of ADP – overall 2 ATP produced Understanding: In glycolysis, glucose is converted to pyruvate Glycolysis gives a small net gain of ATP with out the use of oxygen In aerobic cell respiration pyruvate is concerted into acetyl coenzyme A

“Names of intermediate compounds in glycolysis are not required” A good example of a metabolic pathway

Glycolysis 2 ATP used to phosphorylate one molecule of glucose Metabolic pathways lead to two molecules of triose phosphate Each is then oxidised Hydrogen is accepted by NAD+ to make NADH + H+ Phosphate group transferred to ADP to produce 2 ATP molecules and (two) pyruvate molecule Understanding: In glycolysis, glucose is converted to pyruvate Glycolysis gives a small net gain of ATP with out the use of oxygen

Outline the process of Glycolysis (5 marks) Occurs in the cytoplasm Glucose is phosphorylated using ATP Split (lysis) into two triose phosphates Oxidation of triose phosphates (two) NAD reduced to NADH (+ H+) Net gain of two ATP molecules/two ATP use and four ATP produced (two) Pyruvate at the end of glycolysis

The Link Reaction In the mitochondrial matrix Two molecules of pyruvate produced in glycolysis per molecule of glucose. If oxygen is present (AEROBIC) – pyruvate absorbed into mitochondria where it is oxidised (lose hydrogen atoms). NAD is reduced forming NADH Pyruvate is decarboxylated (Decarboxylated = take away carboxyl group and forms CO2) CO2 removed to form an acetyl group (acetate). Acetyl group then joined to coenzyme A to make acetyl coenzyme A (CoA) How many times does this happen per glucose molecule?? Understanding: In aerobic cell respiration pyruvate is concerted into acetyl coenzyme A

Link reaction - links glycolysis with the Krebs cycle The Link Reaction Link reaction - links glycolysis with the Krebs cycle Krebs Cycle Happens twice per glucose molecule

The Krebs Cycle The CoA goes back to be reused in the link reaction Acetyl CoA (2C) from link reaction combines with a 4 carbon compound, making a 6 carbon compound. This is oxidized and decarboxylated to form a 5 carbon compound. Carbon is released and combines with oxygen to form carbon dioxide. NAD+ is reduced to NADH 1. 2. Understanding: In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers Energy released by oxidation reactions is carried to the cristae of the mitochondria

The Krebs Cycle 3. The 5 carbon compound is oxidized and decarboxylated to form a 4 carbon compound. This forms carbon dioxide and another NADH 4. The 4 carbon compound undergoes various changes resulting in more products: FAD to FADH2 NAD to NADH ADP to ATP 4. 3. What is happening in these situations? Understanding: In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers Energy released by oxidation reactions is carried to the cristae of the mitochondria

The Krebs Cycle Must spin twice for each glucose molecule as two pyruvates are formed in glycolysis. Every 1 glucose molecule (2 spins) produces: 6 NADH (oxidation and reduction) of? 4 CO2 (decarboxylation) 2 FADH2 (oxidation and reduction) of? 2 ATP (phosphorylation) Substrate* phosphorylation – ATP produced Energy stored in NADH and FADH passed on to the final part of respiration: oxidative phosphorylation (electron transport chain) Half of these per spin Understanding: In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers Energy released by oxidation reactions is carried to the cristae of the mitochondria

The Krebs Cycle By the end of the Krebs cycle, only 4 ATPs have been gained. 4 from glycolysis (but 2 used up in the process) 2 from Krebs cycle All by substrate level phosphorylation* During respiration a total of 36 ATPs gained overall from 1 glucose molecule. (32 produced in the Electron transport chain and chemiosmosis) Understanding: In the Krebs cycle, the oxidation of acetyl groups is coupled to the reduction of hydrogen carriers Energy released by oxidation reactions is carried to the cristae of the mitochondria

Phosphorylation What we have seen so far Substrate level: ATP produced via transport of phosphate group directly to ADP Oxidative: Oxidative phosphorylation is the metabolic pathway in which cells use enzymes to oxidise compounds (reduced NAD and reduced FAD), thereby taking energy to the electon transport chain which is used to form ATP. Understanding: Phosphorylation of molecules makes them less stable

Oxidative Phosphorylation - Electron Transport Chain and Chemiosmosis Across the inner membrane Series of small steps, carried out by a chain of electron carriers. Generates ATP with the energy from previous oxidation reactions* * FADH2 also Understanding: Transfer of electrons between carriers in the electron transport chain is couple to proton pumping In chemiosmosis protons diffuse through ATP synthase to generate ATP Oxygen is needed to bind with the free protons to form water to maintain the hydrogen gradient

Oxidative Phosphorylation - Electron Transport Chain and Chemiosmosis Across the inner membrane NADH is oxidised and releases 2 hydrogen artoms. NAD returns to matrix. Both H atoms split into H+ and e-. The electrons move down the electron transport chain via electron carriers (membrane proteins), losing energy at each one. This provides the carriers with energy to pump protons (H+) into the intermembrane space. A concentration gradient of proteins builds up. 4. 2. 1. FADH2 also 3.

Oxidative Phosphorylation - Electron Transport Chain and Chemiosmosis Across the inner membrane 5. In order for electrons to carry on flowing they must be transferred to a terminal electron acceptor – oxygen which becomes O2- (gets reduced), but then combines with two H+ (from the matrix) to form water. By using up H+ the proton gradient across the inner membrane is maintained 6. Protons pass from the intermembrane space, through ATP synthase, into the matrix. As they move down their concentration gradient, energy is released and used by ATP synthase to phosphorylate ADP to ATP. 6. 5. _ FADH2 also

How many ATP molecules are made from one glucose molecule?

How many ATP molecules are made from one glucose molecule?

Respiration Step 1: Mitochondria Step 2: Steps in respiration 1. 2. 3. 4. 5. Step 3: Step 4 & 5:

Create a respiration diagram Use a piece of A3/A4 paper Create a respiration diagram – go step by step from the start. Include: Glycolysis Link reaction Krebs cycle Oxidative phosphorylation Electron transport chain Chemiosmosis Where do they happen Is reduced NAD/FAD produced Is ATP produced What is made from that process What happens here Is it substrate level phosphorylation or oxidative phosphorylation

8 marks Explain the process of aerobic respiration including oxidative phosphorylation.

glucose converted to pyruvate (two molecules); by glycolysis; pyruvate enters the mitochondria; pyruvate converted to acetyl CoA; by oxidation and decarboxylation / NADH and CO2 formed; acetyl CoA enter the Krebs cycle (by link reaction); FAD / NAD+ reduced to NADH / FADH2; FADH2 / NADH donates electrons to electron transport chain (reject donates H+); electrons release energy as they pass along the chain; oxygen final electron acceptor; production of water; builds up proton gradient/protons pumped across inner membrane; protons flow into matrix of mitochondria through ATPase / ATP synthase; ATP produced; produces 36 / 38 ATP (per glucose); 8 max Accept any appropriate terminology for NAD and FAD. (Plus up to [2] for quality)

Respirometers

Anaerobic Respiration Does not use oxygen Only gets as far as glycolysis Produces lactate (lactic acid) +2 ATP The production of lactate regenerates NAD. This means glycolysis can continue 2 ATP produced per glucose

Breakdown of lactic acid in animals Cells convert the lactic acid back into pyruvate (which re-enters aerobic respiration when oxygen is present) Liver cells can convert the lactic acid back into glucose (which can be respired or stored)