For Professor Jay?

Question

I know you're a very busy Professor, but I would greatly appreciate the professional help for my midterm ( university of course) I totally understand if you don't have the time. Thanks

And for others that can explain this to me.. Very welcome.. Thank you to all.

Why does the cell have checkpoints in the cell cycle? Name one. ( this one is quite important.. i dont really understand how the cell cycle does.. like why is it soo important...)

Why do many molecules not break down rapidly into smaller molecules, even when it is energetically favorable?

Where do competitive inhibitors of enzymes bind?

Why would a cell prefer respiration over fermentation?

What is alternative splicing?

Thanks guys :)

Answer 1

The cell cycle has checkpoints at every stage. The checkpoints just make sure that everything is progressing normally. Here are a couple of examples of checkpoints.
1. DNA damage checkpoint - makes sure that the DNA is intact and undamaged.
2. The G1 checkpoint, or restriction checkpoint - at the end of the G1 stage of interphase - determines if the cell will stay in that stage or continue on in the cell cycle. If a cell is going to continue through cell division, it has to overcome this checkpoint.

Do you mean that you don't understand what the cell cycle does or do you mean you don't understand what the checkpoints do? The cell cycle is just the life cycle of cells that divide. It has three main parts: interphase, mitosis, and cytokinesis. It's so important because organisms need cell division for growth, development, repair, replacement of worn out cells, and so on.

Why do many molecules not break down rapidly into smaller molecules, even when it is energetically favorable? Breaking down rapidly would release too much energy at once in an uncontrolled fashion. This would damage the cell instead of helping it. Just think of the way your car burns gasoline - a little puff of gasoline at a time is burned. You could get a lot more energy out of the gasoline quickly by throwing a match into the gas tank, but that isn't a good idea. Same thing for controlled, regulated energy release within cells.

Competitve inhibitors bind to the enzyme in the same place that the substrate would normally bind. The inhibitors "compete" for the binding site with the substrate.

Cellular respiration is far more efficient than fermentation. Respiration yields 38-40 ATP per molecule of glucose. Fermentation yields only the 2 ATP that were gained during glycolysis.

That's all I've got!!!

Answer 2

1. As you know in the cell cycle (including mitosis, growth, meiosis) various processes must occur IN sequence. Think about what would happen if a cell began dividing before DNA was replicated! Thus, checkpoints help coordinate the mechanisms in a cell to perform correctly.

2. There are various molecules that stabilize macromolecules. Molecular chaperones such as heat shock proteins (hsps) are a good example.

3. At the active site (the same site as the substrate does). In contrast, noncompetitive inhibitors bind at an allosteric site, or another site away from the active site; the idea is they don't "compete" for the active site.

4. Respiration produces much more ATP, but requires an electron acceptor (almost exclusively oxygen).

5. A given gene may actually be translated into several different types of proteins based on their splicing pattern. During mRNA processing, splicing occurs where introns are removed; if you can imagine one splicing pattern removing introns 1, 2, 5, and another splicing pattern removing introns 1, 2, 3, 4, 5, you should see that different proteins would ultimately be produced.