Respiration Things to cover: Structure and the mitochondria What happens in: Glycolysis (already done) Link reaction Krebs cycle Oxidative phosphorylation (next lesson)

Learning Objectives Success Criteria Produce accurate notes on the link reaction Summarise in a diagram the key events in the Krebs cycle Carry out an experiment and analyse the results to demonstrate the role of coenzymes in respiration Describe what the link reaction is Describe what happens during the Krebs cycle Explain the role of hydrogen carrier molecules in the Krebs cycle

Quick 5 (they start easy and get harder) Formula of Glucose Name of the first stage of aerobic respiration This can be divided into two phases; name them The energy released by respiration is used in which condensation reaction Name the Enzyme that catalyses this reaction

Review of last week’s learning Complete the Glycolysis gaps task. Easier – Ask me for a clue Harder –Turn it over and draw it out on the back Extension: More Pi is used to generate ATP in the energy pay off phase than is added onto the substrate by the hydrolysis of ATP – where does the extra Pi come from? The process of ATP formation in glycolysis is described as being by “substrate level phosphorylation” – suggest what this means

Glycolysis with gaps (level 2) Glucose (6 Carbon) __________ Fructose-6-phosphate Hexose___________ ( ___ carbon) 2 x Triose Phosphate (________) 2x intermediate compounds (3 carbon) 2x Pyruvate (3 carbon) 2 ADP +2 Pi 2ATP

Glycolysis steps Glucose (6 Carbon) Glucose-6-phosphate (6 carbon) Fructose-6-phosphate Hexose1,6-bisphospahe 2 x Triose Phosphate (3 carbon) 2x intermediate compounds (3 carbon) 2x Pyruvate (3 carbon) ATP ADP ATP ADP 2 x 2 x Oxidased NAD Reduced NAD 2 x 2 x ATP + Pi ATP 2 x 2 x ATP + Pi ATP

Glycolysis releases less than 25% of the chemical energy stored in Glucose. Where is the energy originally from? Where is the energy that is left

Tricarboxylic acid cycle

Respiration Part 2 The Link Reaction

Mitochondria

Glycolysis forms Pyruvate in the cytoplasm Glycolysis forms Pyruvate in the cytoplasm. Pyruvate is a polar molecule. The link reaction takes place in the mitochondrial matrix Which structures would you expect to find in the membranes of the mitochondrial envelope and why ?

Link Reaction Basics Connects Glycolysis to Krebs cycle (Respiration part 3) Takes place in the mitochondrial matrix Requires presence of oxygen (but does not use oxygen) Overview: Pyruvate is decarboxylated – a Carboxyl group is removed and forms CO2. 2Hydrogen are removed from Pyruvate and used to reduce NAD Produces Acetate (2 carbon molecule) that binds to Coenzyme A.

Link Reaction Start Pyruvate (3 carbon compound) Step1 Pyruvate decarboxylase removes a carboxyl group Formed =CO2 Step 2 Pyruvate dehydrogenase removes hydrogen atoms from the pyruvate Hydrogen atoms are accepted by NAD+ which is reduced to NADH Formed = NADH + Acetate (2 carbon compound)

Step 3 Coenzyme A (CoA) accepts the Acetate to form Acetyl Coenzyme A This carries acetate into the Krebs cycle 2 Pyruvate + 2NAD++ 2CoA  2CO2+2NADH+2acetyl CoA Why is there two of everything? What is being oxidised, what is being reduced?

Krebs cycle Takes place in the mitochondrial matrix Each step is enzyme controlled Does not require oxygen but can not take place if oxygen is not present therefore it is an aerobic process Respiratory substrates other than glucose can enter aerobic respiration at the beginning of the krebs cycle: Fatty acids – broken down to acetates enter via CoA Amino Acids – deaminated and changed to Acetate or pyruvate

Krebs cycle is: Oxidation of Acetate (from the link reaction) to Carbon dioixde Produces per acetate: 2 molecules of CO2 1 molecule of ATP (by substrate level phosphorylation) 3 NADH (Reduces 3 molecules of NAD+) 1 FADH (Reduces 1 molecule FAD+)

Step 1a: Coenzyme A releases the Acetate group Acetate (2 carbon compound) is joined to Oxaloacetate (4 carbon compound) Makes a 6 carbon compound called Citrate (6 carbon)

Step 1b: The citrate (6 carbon) is then shuffled using the enzyme aconitase to form Isocitrate (6 carbon) This means that oxidative decarboxylation (the next step) can take place

Step 2a: Decarboxylation of isocitrate Carboxyl group removed form isocitrate Produces: 1x CO2 1 x 5 carbon compound (α-Ketoglutarate)

Step 2b: Oxidation of isocitrate Dehydrogenation of isocitrate molecule Hydrogen atoms removed by dehydrogenase enzymes Hydrogen accepted by NAD+ which is reduced Produces 1 x NADH

Step 3a: α-Ketoglutarate (5 carbon) is oxidised to Succinyl (4 carbon) Decarboxylation of α-Ketoglutarate (5 carbon) Produces: 1x CO2 1 x 4 carbon compound (Succinyl)

Step 3b: α-Ketoglutarate (5 carbon) is oxidised to Succinyl (4 carbon) Dehydrogenation of Ketogluterate Hydrogen atoms removed by dehydrogenase enzymes Hydrogen accepted by NAD+ which is reduced Produces 1 x NADH

Step 4: Succinyl converted to Succinate (4 carbon compound). Succinyl (4 carbon compound) is converted to Succinate (4 carbon compound). The energy released by this step is directly used in a condensation reaction to form ATP from ADP This is substrate level phosphorylation Produces 1x ATP

Step 5: Succinate (4 carbon compound) oxidised to Fumerate (4 carbon compound). Dehydrogenation of Succinate Hydrogen atoms removed by dehydrogenase enzymes Hydrogen accepted by FAD+ which is reduced Produces 1 x FADH

Step 5b: The secret step Fumerate (4 carbon compound) converted to Malate (4 carbon compound)

Step 6: Malate (4 carbon compound) oxidised to Oxaloacetate (4 carbon compound). Dehydrogenation of Malate (4 carbon compound) Hydrogen atoms removed by dehydrogenase enzymes Hydrogen accepted by NAD+ which is reduced Produces 1 x NADH (Oxaloacetate used in step 1 is regenerated – ready to accept another acetate)

The Products of the Link Reaction go to the Krebs Cycle and the ETC So for each glucose molecule: 2 acetyl coenzyme A (go into the Krebs cycle) 2 Carbon dioxide (released as a waste products) 2 Reduced NAD (go to the electron transport chain)

Krebs Cycle II http://highered.mheducation.com/sites/0072507470/student_view0/chapter25/animation__how_the_krebs_cycle_works__quiz_1_.html Use the animation to further annotate your H/W from last lesson

Tricarboxylic acid cycle

The Krebs Cycle Acetyl Coenzyme A (2C) NAD Coenzyme A 2C Reduced NAD Oxaloacetate (4C) Citrate (6C) (6C) (4C) NAD (4C) CO2 FAD Reduced NAD Reduced FAD CO2 (5C) (4C) NAD ADP + Pi ATP (4C) Reduced NAD

DeNa DeNa A Fa... Na This little tune will help you to remember the Krebs Cycle. Remember, respiration is all about releasing energy from your food. Oxidation releases energy. When a carbon compound is oxidised, coenzymes are reduced. The coenzymes involved are: NAD and FAD. Decarboxylation is the removal of CO2. Remember this: 665 and five 4’s.

DENA DENA A FA... NA DENA: Decarboxylation and production of reduced NAD A: Production of ATP FA... : Production of reduced FAD (The ‘...’ means a gap) NA: Production of reduced NAD

The Krebs Cycle: DENA DENA A FA... NA Acetyl Coenzyme A (2C) NAD Coenzyme A 2C NA Reduced NAD Oxaloacetate (4C) Citrate (6C) (6C) (4C) NAD (4C) DENA CO2 FAD Reduced NAD FA Reduced FAD CO2 (5C) (4C) DENA NAD ADP + Pi ATP A (4C) Reduced NAD

Krebs Cycle Summary 2 CO2 molecules 1 ATP molecules (S.L.P) Each Acetyl CoA entering the cycle results in: 2 CO2 molecules 1 ATP molecules (S.L.P) 4 pairs of H atoms (Later used in the E.T.C to produce ATP) Used to reduce NAD and FAD. Three reduced NAD are produced and 1 reduced FAD per cycle. NAD = Nicotinamide adenine dinucleotide FAD = Flavine adenine dinucleotide

Krebs Cycle Summary 2 CO2 molecules 1 ATP molecules (S.L.P) Each Acetyl CoA entering the cycle results in: 2 CO2 molecules 1 ATP molecules (S.L.P) 4 pairs of H atoms (Later used in the E.T.C to produce ATP) Used to reduce NAD and FAD. Three reduced NAD are produced and 1 reduced FAD per cycle. NAD = Nicotinamide adenine dinucleotide FAD = Flavine adenine dinucleotide

How many times does the Krebs cycle “turn” for each molecule of glucose that enters respiration? Give a reason for your answer. What are the products of the Link reaction and Krebs cycle for one molecule of glucose Suggest which genes may be found on a mitochondria contain a DNA plasmid.

Tasks P55 text book read the text and answer the questions Exam Questions

Glycolysis

Krebs Cycle