RespirationThings to cover:

• Structure and the mitochondria

• What happens in:–Glycolysis (already done)–Link reaction –Krebs cycle –Oxidative phosphorylation (next lesson)

Learning Objectives Success Criteria

Describe what the link reaction is

Describe what happens during the Krebs cycle

Explain the role of hydrogen carrier molecules in the Krebs cycle

• 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

Quick 5 (they start easy and get harder)

1. Formula of Glucose

2. Name of the first stage of aerobic respiration

3. This can be divided into two phases; name them

4. The energy released by respiration is used in which condensation reaction

5. 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)

__________(6 carbon)

Fructose-6-phosphate(6 carbon)

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(6 carbon)

Hexose1,6-bisphospahe(6 carbon)

2 x Triose Phosphate (3 carbon)

2x intermediate compounds (3 carbon)

2x Pyruvate (3 carbon)

ATP + Pi ATP2 x 2 x

Oxidased NAD

2 x Reduced NAD

ATP ADP

ATP ADP

2 x

ATP + Pi ATP2 x 2 x

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. 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.

Pyruvate (3 carbon compound)Start

Step1 Pyruvate decarboxylase removes a carboxyl groupFormed =CO2

Step 2

• Pyruvate dehydrogenase removes hydrogen atoms from the pyruvate

• Hydrogen atoms are accepted by NAD+ which is reduced to NADHFormed = NADH + Acetate (2 carbon compound)

Link Reaction

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

NAD

ReducedNAD

NAD

Reduced NAD

ADP + Pi

ATP

FAD

ReducedFAD

NADReduced

NAD

Coenzyme A

Acetyl Coenzyme A (2C)

2C

CO2

CO2

Citrate (6C)

(6C)

(5C)

(4C)

(4C)

(4C)

(4C)

Oxaloacetate (4C)

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

• 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

NAD

ReducedNAD

NAD

Reduced NAD

ADP + Pi

ATP

FAD

ReducedFAD

NADReduced

NAD

Coenzyme A

Acetyl Coenzyme A (2C)

2C

CO2

CO2

Citrate (6C)

(6C)

(5C)

(4C)

(4C)

(4C)

(4C)

DENA

DENAA

FA

NA Oxaloacetate (4C)

Krebs Cycle SummaryEach Acetyl CoA entering the cycle results in:

1. 2 CO2 molecules

2. 1 ATP molecules (S.L.P)

3. 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 dinucleotideFAD = Flavine adenine dinucleotide

Krebs Cycle SummaryEach Acetyl CoA entering the cycle results in:

1. 2 CO2 molecules

2. 1 ATP molecules (S.L.P)

3. 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 dinucleotideFAD = 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