Biochemistry Final: Exam #3 Review Flashcards Preview

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Flashcards in Biochemistry Final: Exam #3 Review Deck (157)
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1

What are the three sources of glutamate?

1) Diet (major)
2) Transamination of a-KG
3) Deamination of Glutamine

2

Transamination

Amino acid + a-KG--> Glutamate + a-ketoacid

- Amine group from amino acid is carried by B6(pyridoxal 5'-phosphate) to a-KG & swapped for carboxyl group
- Makes Glutamate & corresponding a-Ketoacid

3

Deamination of Glutamine

Glutamine--> Glutamate, via the enzyme "Glutaminase"

4

Why do we make glutamine?

Glutamine production in peripheral tissues in an important mechanism of ammonium ion removal

5

How do we make glutamine?

Glutamate--> Glutamine, via the enzyme "Glutamine Synthetase"

- Ammonium ion required (removes toxic substance too!)
- ATP hydrolyzed to ADP + Pi

6

Where does this glutamine go?

Enters the bloodstream and is absorbed by the:

- Kidneys
- Liver
- Gut

Here, the amide group is hydrolyzed by Glutaminase (Glutamine--> Glutamate), generating Glutamate & NH4+

7

What do the kidenys and liver do with ammonium ion (NH4) generated by the glutaminase reaction i.e. deamination of glutamate?

- Kidneys excrete NH4 directly
- Liver channels NH4 into the urea cycle
(Gut, NH4 serves as an important nutrient)

8

PLP

- Active form of pyridoxal phosphate
- Vitamin B6
- Cofactor that is required for aminotransferase reactions

9

ALT

Alanine + a-KG --> Pyruvate + Glutamate
Pyruvate + Glutamate--> a-KG + Alanine

- Alanine Aminotransferase (ALT)
- Requires Vitamin B6 (PLP)
- Connects muscle & liver metabolism
- Found primarily in the liver

10

Glucose-Alanine Cycle

- Muscle glycolysis produces pyruvate
- ALT converts pyruvate into alanine that is released into the blood
- Blood carries alanine to the liver
- In liver, ALT converts alanine back into pyruvate
- Pyruvate is used for gluconeogenesis

11

AST

1) Oxaloacetate + Glutamate --> a-KG + Aspartate
2) Aspartate + ATP + Glutamine--> Asparagine, via the enzyme "Asparagine Synthetase"

12

Clinical Significance of ALT vs. AST

Serum elevation of ALT is more specific for liver damage

13

Folate & THF

- Tetrahydrofolate (THF) Serves as an acceptor of 1-carbon groups (methylene)
- Derived from the vitamin, Folate

14

Most oxidized form of THF

N10-formyl THF

15

Most reduced from of THF

- N5-methyl THF
- Is NOT readily oxidized back to N10-formyl THF
- Thus, accumulates in the body

16

Which amino acid is the main donor of 1 carbon groups?

Serine

17

Serine Hydroxymethyl transferase

Serine + THF--> Glycine + N5, N10-methylene THF + H20

18

Phenylalanine Hydroxylase

Phenylalanine--> Tyrosine

- Requires oxygen, NADH, & the reduced cofactor tetrahydrobiopterin (THBtn) to oxidize the aromatic ring of phenylalanine

19

Dihydrobiopterin Reductase

Dihydrobiopterin (DHBtn, oxidized) -->Tetrahydrobiopterin (THBtn, reduced)

20

Phenylketonuira (PKU)

- Most common inborn error of metabolism
- Accumulation of phenylalanine that causes: severe intellectual disability, recurrent seizures, hypopigmentation, & eczematous skin rashes
- Caused by defect in phenylalanine hydroxylase OR DHBtn Reductase
- Must avoid nutrisweet/ aspartame

21

The overall rate of amino acid degradation is influenced by the activity of which enzyme? What inhibits this enzyme & what activates this enzyme?

Mitochondrial Glutamate Dehydrogenase

- Inhibited, high energy: GTP, ATP, NADH
- Activated, low energy: GDP, ADP, NAD+

22

Mitochondrial Glutamate Dehydrogenase

Glutamate + NAD+ + H20 --> a-KG + NADH + NH4+

23

Which amino acids can be converted into pyruvate? And what is pyruvate eventually used to make?

- Glycine
- Serine
- Cysteine
- Alanine

- OAA

24

Glycine, through several steps, can eventually be converted into pyruvate. How is glycine also related to the formation of kidney stones?

Glycine--> Serine --> Pyruvate = one possible path
Glycine--> Glyoxalate--> Oxalate= second possible path

- Oxalate is a metabolic end product that is excreted in the urine
- Oxalate also has a high affinity for Ca++, and can precipitate as kidney stones

25

Besides via pyruvate, two other amino acids can be shunted to make OAA. Which?

- Asparagine
- Aspartate

Asparagine--> Asparate, via enzyme "asparaginase"
Aspartate--> OAA, via AST

26

Which amino acid can be used to make a-KG?

Glutamine

Glutamine--> Glutamate, via enzyme "Glutaminase"
Glutamate--> a-KG, via Aminotransferases & Glutamate Dehydrogenase

Therefore, amino acids that can make glutamate, can also be used to make a-KG

27

Which amino acids can make glutamate?

- Proline
- Histidine
- Arginine

28

Glycine Encephalopathy

- Nonketotic hyperglycemia that presents soon after birth with symptoms of: lethargy, lack of muscle tone, & muscle twitching
- Caused by defects in glycine cleavage system

29

What amino acids can make propoionyl-CoA?

- Threonine
- Methionine
- Valine
- Isoleucine

30

What is propionyl-CoA eventually made into, and enzymes & cofactors are needed for that transformation?

Succinyl-CoA

1) Carboxylase= Propionyl-CoA--> D-methylmalonyl-CoA, requires Biotin
2) Racemase= D-methylmalonyl-CoA--> L-methylmalonyl-CoA
3) Mutase= L-methylmalonyl-CoA--> Succinyl-CoA, requires Vitamin B12