Respiration

Link Reaction and Krebs Cycle

Glycolysis recap

• Where does it happen?• Why is it required?• What does it produce?

• Anaerobic versus Aerobic

Link Reaction

• Pyruvate needs to be OXIDISED before it enters the Krebs Cycle

• What is a good oxidising agent?

Link Reaction

• Pyruvate needs to be OXIDISED before it enters the Krebs Cycle

• What is a good oxidising agent?– Nicotinamide adenine dinucleotide

Link Reaction

Link Reaction

Investigation Bio 6T/Q11• access to a yeast culture in a large flask and to a yeast

culture in a small flask● 250 cm3 sterile beaker● sterile measuring cylinder● sterile water● sterile glass rods● sterile graduated pipettes or syringes● spreader in sterilising solution● 2 sterile agar plates● marker pen● acetate grid● sticky tape and scissors

• Aim:• Variables:• Null Hypothesis:• Which test will you choose?• How many samples will you choose

and how will you choose them?

Investigation Bio 6T/Q11

Session 1

1. Shake the sample of yeast culture from the small conical flask.2. Take 1 cm3 of the yeast culture and add it to a 250 cm3 beaker.3. Add 200 cm3 of sterile water to the beaker.4. Stir the mixture and immediately remove 0.1 cm3 of the diluted yeast culture from the beaker using a 1 cm3 graduated pipette or syringe.5. Lift the lid of an agar plate carefully so you can just put the tip of the graduated pipette or syringe through the small gap.6. Put the 0.1 cm3 of the diluted yeast culture onto the agar keeping the lid as near the plate aspossible.7. Shake the spreader to remove excess sterilising solution if necessary. Use the sterile end of the spreader to spread the yeast culture evenly over the agar.8. Close the lid. Label the plate clearly at the edge to show the size of the conical flask from which the yeast culture was taken.9. Repeat steps 1 to 8 with the large flask.10. Put small pieces of sticky tape on the edges of the plates to hold the lids on.11. Incubate the plates for 24 hours.

12. Turn one agar plate upside down so that its base faces upwards.13. Place the acetate grid on the base of the agar plate.14. Select 15 separate 10 mm squares at random. Count the number of yeast colonies in each of the 15 squares.15. Repeat steps 12 to 14 with the second agar plate.

ResultsSample Small Conical

FlaskLarge Conical Flask

1 1 2

2 0 1

3 0 1

4 2 3

5 1 2

6 1 3

7 3 0

8 2 3

9 1 2

10 1 1

11 0 3

12 0 3

13 2 3

14 0 2

15 1 1

• Statistical test

• Graph

• Test Statistic

Link Reaction and Krebs Cycle

KREBS CYCLE

The pyruvic acid (pyruvate) molecules formed during glycolysis diffuseinto the fluid matrix of the mitochondrion

Each three carbon pyruvic acid molecule is converted into a two carboncompound called Acetyl CoA

Pyruvic acid is oxidised toAcetyl CoA through theremoval of a pair ofhydrogen atoms

The hydrogen atoms areaccepted by the hydrogencarrier NAD

The two carbon acetylgroup is needed to driveKrebs Cycle

The Coenzyme A group is recycled

The Link Reaction yields:A 2-carbon acetyl group

needed to drive Krebs Cycle;The reduced hydrogen carrier

NADH2; a molecule of CO2

2H NADH2

carbon dioxideCoenzyme A

recycled

CO2 is removed from pyruvic acid to reduce the number of carbon atoms to two – this process is called decarboxylation

2H NADH2

The 2C acetyl group of AcetylCoA combines with the 4C acid,Oxaloacetic Acid, to form the 6CAcid, Citric Acid

Coenzyme A is recycled

The 6C Citric Acid is oxidised tothe 5C Keto AcidOxidation involves the removalof a pair of hydrogen atoms thatare accepted by the hydrogen carrier NAD to form NADH2

This step also generates sufficientenergy to form amolecule of ATP

The 4C succinic acid isoxidised to the 4C malicacid

In this case the hydrogen carrier is FAD

The 4C malic acid isfinally oxidised backto the 4C oxaloaceticacid enabling the cycleto operate again

NAD accepts the pairof hydrogen atoms fromthis oxidation

5C KetoGlutaric acid

The number of carbon atomsis reduced by the removal ofcarbon dioxide - decarboxylation

4C Oxaloaceticacid

6C CitricAcid

The 5C acid is oxidisedto the 4C succinic acidgenerating another NADH2 and CO2 molecule

CO2

CO2

4C MalicAcid

2HFADH2

2H

NADH2

4CSuccinic

Acid

2H NADH2

RESPIRATION