Oxidative Phosphorylation

April 1rst lecture

Purpose of Citric Acid cycle?

Oxidize Carbon

• Add a two carbon group and oxidizing two carbons if we do all the rxns

Hub of metabolism

• many different pathways

What are the two ways to make acetyl-coA?

Oxidizing pyruvate

• produces 2 acetyl-coA, 2 CO2, 2 NADH

Fatty acids

• made out of acetyl-coA, so if we break them down we make it

How many times do we do the krebs cycle?

We do the krebs cycle twice with the 2 oxaloacetate

• We don’t increase the number of oxaloacetate

What can we do with glycerol in triacylglycerol?

Glycerol is a small fraction of energy. However if we are starving then we could use it, which makes it very important

What is glycerol made of?

What can’t it be made from?

It is made from one of the 3 carbon intermediates

• glyceraldehyde-3-phosphate

Can only be made from triacylglycerol

• Can’t be made from the fatty acid part of the fat

How is glucose made when starving?

Glycerol from fat is one of the few things glucose can be made of

What are the two ways glucose can be made?

• Glycolysis: 2 pyruvate, net of 2 ATP

• Kreb’s: 1 ATP or GTP

  • This is done twice per glucose molecule so we get 2 ATP/GTP

What is gluconeogenic amino acids?

Turning amino acids into glucose

Done by converting them into the krebs cycle or into a pyruvate

What happens to our muscles when we are starving?

Our muscles are digested to oxidize carbon to obtain energy

How do you make half of an ATP?

You don’t.

• The reason they are not whole numbers is because we’re converting the energy in the electron pairs first into a proton (H+) gradient

• The energy used in the proton gradient is then used to make ATP

What is the electron transport chain?

• Take energy from the electron pairs and use the energy to move protons (H+) across the membrane

• Grabs protons (H+) and moves it into the little chamber

• Similar to charging a battery

  • Way of storing energy

• Think of a hydroelectric dam

How is the mitochondria like the Hoover Dam?

• The dam is the outer membrane of the mitochondria

• The water being filled in the dam are the protons (H+)

• The protons (H+) leave the chamber by going through the protein that is like a turbine

  • ATP synthase causes the protein to rotate

    • Creates mechanical energy that is used to make ATP

What is the chemiosmotic theory?

Use the energy from out electron pairs to fill a membranous chamber full of protons

• temporarily store the electrons as a proton gradient which is then used to make ATP through ATP synthase

This is done in all organisms

• Mammals: mitochondria

• Bacteria: bacteria

• Plants: mitochondria and something similar in the chloroplasts

What are the proteins in the ETC?

Complex 1, 3, 4

• Take electron from our electron carriers, add them to the proteins. Each time it goes through the protein, it changes the structure of the protein. This change in structure drains the energy from the electron

How could you compare the electron transport chain to a slinky going down stairs?

Each step, it loses energy

• the electron go through the proteins (complex) and lose their energy

The bottom step is where oxygen comes in because there’s no more energy

What is the importance of oxygen in the ETC?

It acts as the final electron acceptor

• Like a garbage can, we put electrons into it once we are done extracting energy out of them

• Take the O2, split it in half and take one of the oxygen atoms, add a pair of electrons to it and 2 protons (H+) and make water

• The waste product is just water.

Why does complex 2 differ from complex 1,3,4 in the ETC?

It is actually a kreb’s cycle enzyme that puts the electrons on FAD to become FADH2

Enzymes that came from FADH2, which are generated in the krebs cycle, don’t go through complex one

The energy from electrons on FADH2 are only extracted in complex 3,4

• fewer protons (H+) are moved across the membrane when using FADH2 compared to NADH. Hence why they make fewer ATP (1.5)

Explain the steps of the ETC?

1. NADH drops off electrons to complex 1, the protons (H+) is released there

   1. The electrons move through complex 1, each step in the protein causes a little bit of charge

   2. The electrons in complex 1 leave with less energy than when it entered

      1. Some of the energy was extracted and used to move the four protons across the membrane

2. Molecule Q shuttles the electrons from complex 1 to complex 3

   1. Q binds to complex 1 to pick up the pair of electrons that went through it and then delivers it to complex 3

   2. DOESN’T go through complex 2 because that is an enzyme from the Krebs cycle (one of the four oxidizing enzymes)

3. Complex 3 extracts more energy from the electron and uses that energy to move more protons (H+) across the membrane

   1. The electrons will leave with even less energy

4. Shuttle C takes the electrons from complex 3 and moves them to complex 4

5. Complex four then extracts more energy from from these electrons. The energy that is extracted from these electrons are used to move more protons across the membrane

6. After complex four, there is more more energy we can extract from the electrons, so we take O2, split it in half, put the pair of electrons on one oxygen with 2 protons (H+)

   1. The waste product is water

Does the ETC make ATP?

No. The purpose of it is to convert the energy in our electron pairs into high concentration of protons. These will then be used by another protein to make the ATP

What is ATP synthase?

• Once of the few ways protons are allowed to return to the matrix in the mitochondria

• Large proteins made out of lots of polypeptides that we divide into two halves

• Protons move across the membrane, “hitch” a ride on the wheel that is made of alpha helices, which causes the wheel to spin. The spinning wheel (specifically the axel) causes a part of the protein to change structure.

• We make 28 out of our 32 ATP here

How does ATP synthase work?

The proteins change into three structures: 1,2,3. Each time they go through those changes in structure, they make an ATP

• Structure one (OPEN): it doesn’t want to bind to anything

• Structure two (LOOSE): Loose configuration can bind ADP and bind a phosphate group, and then change its structure

• Structure three (TIGHT): the next change in shape bins the ADP and phosphate group and forms a covalent bond and is now holding onto ATP

What would happen if our ATP synthase stopped working?

We would die because we can’t make most of our ATP (28/32)

Temporarily survive by making ATP into glucose through fermentation