B9 summary pt II

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You asked part 1

Since Charlotte asked about the proton pumps, I thought I’d go into a bit more detail.

The pumps are referred to as complexes, given Roman numerals I, II, III and IV. Complex I is really an enzyme, called NADH dehydrogenase (why is it called a complex? There are 45 separate polypetide chains). 2 electrons are passed onto a substance called ubiquinone (or just Q), which is reduced to ubiquinol (QH2). This is lipid soluble, and moves easily through the membrane. 4 protons are pumped through the membrane.

Complex II (aka succinate dehydrogenase)  gives additional electrons to Q, which is then passed to Complex III (aka cytochrome bc complex). Here the electrons are passed on to another molecule, cytochrome C. 6 protons in total are translocated (moved across the membrane) at this point. Finally cytochrome C (whgich is a water soluble, integral protein membrane) electrons on to Complex IV, where the electrons are removed and used in reducing oxygen to water. Cytochrome C is inhibited by cyanide – a poison which will stop aerobic respiration.

Here’s a nice summary from wikipedia:

In eukaryotes, NADH is the most important electron donor. The associated electron transport chain is

NADHComplex IQComplex IIIcytochrome cComplex IVO2 where Complexes I, III and IV are proton pumps, while Q and cytochrome c are mobile electron carriers. The electron acceptor is molecular oxygen.

Remember, you will be tested on what is in the specification, but reading further in your subject will always help.

Keep it simple people…

Despite what you may think, the stuff we’ve covered so far in respiration is actually pretty straightforward. Just as we found out that our original formula for respiration (glucose + oxygen…) is hiding a wealth of sub-reactions that aren’t shown, the simple pathways of glycolysis and Krebs cycle have many steps that don’t need to concern us. If you want to look at them in more depth then fire away. Anyone considering following a biochemical course may wish to poke around further.

It is one of the areas of A2 that can be remembered by rote, however we have spent time trying to get an overview that will make understanding it a lot easier. Even so, you will forget most of this over the summer break, so anything you are not sure on now is the time to find out.

A few links that may be of help.

Cellular respiration flash

Glycolysis animation

The Student Room questions on glycolysis

Animation Krebs cycle

Another Krebs cycle

Youtube is also pretty good for videos, have a look if you can spare the time between looking at clips of dogs falling over and things that are ‘the funniest thing EVER’, which of course, they never are.