73166
Description
Flashcards by sophiakostich, updated more than 1 year ago
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Created by sophiakostich
almost 11 years ago
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| Question | Answer |
| What enzyme is used to make mevalonate from acetoacetyl CoA and acetyl CoA? | 3-hydroxy-3-methygluamyl CoA reductase (called HMG CoA reductase for short) |
| What is the committed, rate determining step in cholesterol synthesis? | The first step with HMG CoA reductase |
| What electron carrier molecule is required in the first step of cholesterol synthesis? | NADPH |
| What are the four ways in which the first step of cholesterol synthesis can be regulated? | 1. Transcription 2. Translation 3. enzyme breakdown 4. covalent modification/dephosphorylation |
| What is the transcription factor that binds to HMG CoA Reductase if cholesterol levels are low? | SREB |
| If there is low cholesterol does mRNA translation increase or decrease? | It increases. |
| True or false: if there is lots of cholesterol in the body then there is less proteolysis of HMG CoA Reductase (breakdown)? | FALSE. If cholesterol levels are high then synthesis of cholesterol is not required so there is more proteolysis (breakdown of the enzyme). |
| What causes the enzyme HMG CoA Reductase to become inactivated? | Low AMP levels which results in an increase in kinase and an increase in phosphorylation of the enzyme. |
| Why is it that high AMP levels cause less phosphorylation of the enzyme HMG CoA reductase? | High AMP levels indicate that there are low ATP levels therefore the enzyme needs to be working to produce cholesterol and not in the phosphorylated form. |
| What kind of reaction is the first step in cholesterol synthesis? What indicates this? | A redox reaction. The presence of NADPH which then becomes oxidised whilst substrate is reduced. |
| What kind of reaction is the second reaction in cholesterol synthesis? How many ATP are used and how many times does it occur? | It is a condensation reaction that occurs 6 times using a total of 18 ATP. |
| What is the final step in cholesterol synthesis (that we need to know)? What is the product? | Cyclisation which has 19 steps. It results in 27C cholesterol. |
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