L5- Citric acid cycle and amino acid catabolism

What can pyruvate be broken down into

Pyruvate → Acetyl CoA

What can fatty acids be broken down into

• fatty acids → Acetyl CoA

What can amino acids be broken down into

• Can be broken down into pyruvate or Acetyl CoA

Whys is Acetyl CoA important

• important fuel

• combines with a 4 carbon compound to make a 6 carbon compound

• which then gradually broken down in citric acid cycle through series of redox reactions forming CO2, and many reduced Co enzymes to be used in OP

• also have a substrate level phosphorylation (can produce ATP or GTP depending on cell type)

What is the link reaction

• conversion of Pyruvate into Acetyl CoA (links glycolysis to aerobic metabilsm)

• Enzyme that does this si Pyruvate dehydrogenase

• Produces → Co2 and NADH

• the reaction is irreversible - Humans do not have the enzymes to do the backward reaction

What type of reaction is the link reaction

Oxidative decarboxylation reaction - very exothermic reaction

What happens in state of starvation to link reaction

• Pyruvate dehydrogenase is inhibited

• This is because low amount if glucose don’t want to be using ti on reactions we don’t need and reaction is irreversible so cannot get it back

In citric acid cycle where are most of the enzymes

• in Matrix

• EXCEPT FOR Succinate dehydrogenase which is in inner mitochondria membrane of ETC

• its a different way to enter the ETC

Citric acid cycle

What else is refered to as complex 2

• Succinate dehydrogenase but does not follow on form Complex 1

• So complex 1 and 2 produce something that can be used by complex 3

Does complex 2 generate energy to pump protons

NO does not pump our protons

When using succinate instead of NADH what do we end up with

• only 6 protons being pumped

• still get ½ O2 produced at end

• has a lower P:O ratio as less ATP’s overall being made

In combination with the electron transport chain (which requires O2), the oxidative catabolism of 1 mole of acetyl CoA produces…

more than 10 moles of ATP

what does citric acid cycle rely on

ETC as only way to getr NADH → NAD and reduced CoQ back to CoQ

Regulation of Citric acid cycle

• usually rate doese’t really change - not effected by fed or fasting state

• if cell is using more energy than citric acid cycle increases

this is done by:

• increasing activity of enxymes main ones ( Citrate synthase, isolactase dehydrigenase, alpha ketoglutamate dehydrigenase)

• Icrease supply of Acetly CoA

• Increase supply of intermediateds e.g. Oxolactetae or Alpha keto glutamate

Acetyl Co A sources in different states

What group is removed in amino acid catabolism

• amine group

• N is waste product urea which is excreted in urine

Amino acid catabolism in tissue

How many ways are there to break down amino acids

3

First way

Alanine → pyruvate

• transfers N to alpha - keto glutarate to make glutamate through enzyme amino transferase

2nd way

• Glutamate back to apha keto glutaminate through glutamate dehydrigenase

• N lost as ammonia

• Get glutamate converted into a citric acid cycle intermediate – lots of amino acids when broken down from various citric acid intermediates

Third way

• broken down to form Acetyl CoA

• These amino acids that can do this are called ketogenic

  • This is because they can be used to make ketones

what are amino acids that are broken down to form pyruvate or CAC intermediates called

-called glucogenic because can be used to make glucose

Does amino acid catabolism occur in the fed state:

-          Yes because in a meal tend to eat more amino acids than we require for protein synthesis

-          High levels of amino acids in blood can be harmful so want to remove them

Amino acid metabolism in stavation

-          In starvation increased metabolism of amino acids as want to avoid using up all the glucose that we have