Lecture 31: Urea Cycle, Metabolic Priorities, and Diabetes Flashcards Preview

SMP - MNE Exam 2 > Lecture 31: Urea Cycle, Metabolic Priorities, and Diabetes > Flashcards

Flashcards in Lecture 31: Urea Cycle, Metabolic Priorities, and Diabetes Deck (81)
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1

What is the purpose of the urea cycle?

To dispose of excess Nitrogen in the form of urea?

2

What is urea?

H2N-C-NH2
||
O

3

What is the only organ that can perform the urea cycle?

Liver

4

What is ornithine?

A 5C nonstandard AA: not used in protein synthesis, intermediate or UC

5

Is ornithine expended in the UC?

No it's used and then regenerated

6

Urea Cycle Step 1: Enzyme?

CPS I: carbamoyl phosphate synthetase I

7

Urea Cycle Step 1: Location?

Mitosol

8

What is the first committed step of the urea cycle?

Step 1

9

What is the main regulatory step of the urea cycle?

Step 1

10

Ureal Cycle Step 1a: Reactants/Products?

HCO3- + ATP => Carbonic-phosphoric acid anhydride + ADP

11

Ureal Cycle Step 1b: Reactants/Products?

Carbonic-phosphoric acid anhydride + NH4+ => carbamate + Pi

12

Ureal Cycle Step 1c: Reactants/Products?

Carbamate + ATP => carbamoyl phosphate + ADP

13

What is the purpose of the 2 phosphorylations occurring in Step 1 of the UC?

They prepare the substrates for nucleophilic attacks

14

Where does the nitrogen used in step 1 of the UC come from?

Glutamate dehydrogenase: Glutamate + H2O + NADP/NAD+ => alpha-ketoglutarate + NADPH/NADH + NH4+

15

What is the center of nitrogen metabolism?

The mito

16

What regulates CPS I? How? Why?

N-acetylglutamate by allosteric regulation because high levels represent high levels of glutamate, which mean:
1. Low gluconeogenesis because glutamate is not being used (high levels of Nitrogen in the body)
2. High alpha-ketoglutarate levels = high rate of TCA cycle

=> LOW GLUCONEOGENESIS FROM AAs

17

How is N-acetylglutamate formed?

N-acetylglutamate synthase: acetyl-CoA + glutamate => N-acetylglutamate

18

Urea Cycle Step 2: Enzyme?

Ornithine transcarbamoylase

19

Urea Cycle Step 2: Location?

Mitosol

20

Ureal Cycle Step 2: Reactants/Products?

Carbamoyl phosphate + ornithine = citrulline + Pi

21

Net reaction of UC step 1?

HCO3- + 2 ATP + NH3 = carbamoyl phosphate + 2 ADP + Pi

22

How does the UC happen in both the mitosol and the cytosol?

Ornithine and citrulline can cross the mito membrane via transporters

23

Urea Cycle Step 3: Enzyme?

Argininosuccinate synthetase

24

Urea Cycle Step 3: Location?

Cytosol

25

Urea Cycle Step 3: Reactants/Products?

Citrulline + aspartate + ATP = arginino-succinate + AMP + PPi

26

Urea Cycle Step 4: Enzyme?

Argininosuccinase

27

Urea Cycle Step 4: Location?

Cytosol

28

Urea Cycle Step 4: Reactants/Products?

Arginino-succinate => fumarate + arginine

29

Urea Cycle Step 5: Enzyme?

Arginase

30

Urea Cycle Step 5: Location?

Cytosol