Step 1 - Biochem - Actions Of Enzymes

Front 1

What does pyruvate dehydrogenase do?

Back 1

Converts pyruvate to acetyl CoA

Front 2

What five cofactors does pyruvate DH require?

Back 2

Pyrophosphate (thiamine, TPP), FAD (riboflavin), NAD (niacin), CoA (pantothenate), lipoic acid. It needs vitamins B1,B2,B3,B5. Synthesis of B3 requires B6.

Front 3

What does the malate-aspartate shuttle do?

Back 3

Involved in aerobic metabolism in the heart and liver, producing 32 ATP per glucose

Front 4

What does the glycerol-3-phosphate shuttle do?

Back 4

Involved in aerobic metabolism in muscle, producing 30 ATP per glucose

Front 5

Does alanine inhibit or induce pyruvate kinase?

Back 5

Inhibit

Front 6

What is the most potent activator of PFK-1?

Back 6

F2,6BP. It overrides inhibition by ATP and citrate. It is formed by PFK-2 (fed state) and converted back to F-6-P by fructose bisphosphatase (fasting state)

Front 7

These anatomic sites rely on glycolysis for their energy needs

Back 7

Leukocytes and erythrocytes; kidney medulla, lens, testes, cornea (hypoxic environments)

Front 8

What does pyruvate carboxylase do?

Back 8

Converts pyruvate to oxaloacetate

Front 9

What does citrate synthase do?

Back 9

Irreversibly converts oxaloacetate to citrate (with the addition of acetyl CoA)

Front 10

What does isocitrate dehydrogenase do?

Back 10

Irreversibly converts isocitrate to alpha-ketoglutarate

Front 11

What does alpha-ketoglutarate dehydrogenase do?

Back 11

Irreversibly converts alpha-ketoglutarate to succinyl-CoA. It exists as a complex (similar to pyruvate DH, and requiring the same cofactors)

Front 12

How many acetyl CoA are made from one glucose?

Back 12

Two

Front 13

How many ATP are generated from one acetyl CoA?

Back 13

12 ATP

Front 14

What is the role of NADH in glycolysis and the TCA cycle?

Back 14

It is an inhibitor of both. It is an energy carrier (it has a proton to donate to oxphos), so high levels correspond to high energy states.

Front 15

What is the role of alanine in glycolysis?

Back 15

It is an inhibitor of pyruvate kinase, which converts PEP to pyruvate

Front 16

What does pyruvate kinase do?

Back 16

It converts phosphoenolpyruvate (PEP) to pyruvate.

IT IS NAMED FOR ITS REVERSE REACTION, I.E., THE CONVERSION OF PYRUVATE TO PEP

Front 17

What inhibits isocitrate DH?

Back 17

ATP, NADH

Front 18

What stimulates isocitrate DH?

Back 18

ADP

Front 19

What are the products of the TCA cycle per molecule of acetyl CoA? Per molecule of glucose?

Back 19

3 NADH, 1 FADH2, 2 CO2, 1 GTP, 12 ATP per acetyl CoA.

6 NADH, 2 FADH2, 4 CO2, 2GTP, 24 ATP per glucose.

Front 20

What "cycles" in the TCA cycle?

Back 20

Citrate is regenerated from oxaloacetate with an input of acetyl CoA.

Front 21

What does homogentistic acid oxidase do?

Back 21

Degradative enzyme of tyrosine

Front 22

What does tyrosinase do?

Back 22

Converts tyrosine to melanin

Front 23

What are the three possible causes of homocystinuria?

Back 23

(All autosomal recessive.) Cystathionine synthase deficiency, decreased affinity of cystathionine synthase for pyroxidol phosphate; and homocysteine methyltransferase deficiency

Front 24

What does homocysteine methyltransferase do?

Back 24

Interconverts methionine and homocysteine (needs SAM and THF)

Front 25

What does cystathionine synthase do?

Back 25

Converts homocysteine to cystathionine (which is then converted to cysteine)

Front 26

What does tetrahydrofolate do?

Back 26

Carries 1-carbon unit. Needed to make methionine from homocysteine. Also used in purine synthesis (nucleic acids).
(SAM is used for the reverse reaction; think of SAM as taking off the "meth" from methionine to make homocysteine)

Front 27

What does SAM do?

Back 27

Carries CH3 unit. Needed to make homocysteine from methionine.

Front 28

What does cobalamin do?

Back 28

Helps carry the 1-carbon unit of CH3THF in methionine synthesis from homocysteine (catalyzed by homocysteine methyltransferase)

Front 29

What pathways require thiamine (TPP, aldehyde carrier)?

Back 29

HMP shunt (transketolase)
Pyruvate dehydrogenase (bridging glycolysis and Kreb's)
TCA cycle (alpha-ketoglutarate DH)

Front 30

What pathways require biotin (CO2 carrier)?

Back 30

Fatty acid synthesis (conversion of acetyl CoA to malonyl CoA by ACC)
Fatty acid oxidation (conversion of propionyl CoA to methylmalonyl CoA by propionyl CoA carboxylase)
Conversion of pyruvate to oxaloacetate by pyruvate carboxylase (eg, gluconeogenesis)

Needed for carboxylase activity

Front 31

What metabolic fuels are provided from amino acids via the urea cycle?

Back 31

Pyruvate, acetyl CoA, fumarate

Front 32

What does argininosuccinase do?

Back 32

Converts argininosuccinate to arginine, producing fumarate which can enter TCA cycle

Front 33

What does argininosuccinate synthetase do?

Back 33

Converts citrulline and aspartate to argininosuccinate

Front 34

What does ornithine transcarbamoylase do?

Back 34

Converts ornithine and carbamoyl phosphate to citrulline

Front 35

What does carbamoyl phosphate synthetase I do?

Back 35

Creates carbamoyl phosphate from CO2 and NH4 (ammonium) in the mitochondrion, kicking off the urea cycle which then continues in the cytoplasm

Front 36

What is urea constructed from in the urea cycle?

Back 36

NH4, CO2 and asparate

Front 37

What is the purpose of the urea cycle?

Back 37

Catabolism of amino acids, and handling of nitrogenous waste

Front 38

What does alanine transaminase do?
(Aka, alanine aminotransferase, serum glutamic pyruvic transaminase.)

Back 38

Transfers amino group from alanine to a-ketoglutarate, forming pyruvate and glutamate. Reversible.

Front 39

What do aminotransferases in general do?

Back 39

Transfer an amino (nitrogen, NH3) group to alpha-keto acids

Front 40

How is ammonia stored and transported?

Back 40

Glutamine (glutamate + ammonia)

Front 41

What does glutamine synthetase do?

Back 41

Forms glutamine from glutamate and ammonia

Front 42

Where is glutaminase found?

Back 42

Kidney; it removes the ammonia from glutamine to produce glutamate, which is recycled, and ammonia, which is excreted

Front 43

How is ammonia excreted from the body?

Back 43

In the urine, but also in the feces due to urease activity of some bacteria

Front 44

What is the purpose of alanine and aspartate in nitrogen metabolism?

Back 44

They transfer amino groups to glutamate, forming glutamine, which is the primary storage and transport form of ammonia.

Front 45

What does hyperammonemia cause?

Back 45

Inhibition of TCA cycle, due to depletion of alpha-ketoglutarates which are used to form glutamates/gluatamine, the storage and transport form of ammonia

Front 46

What does phenylalanine hydroxylase do?

Back 46

Converts phenylalanine to tyrosine, requiring input of tetrahydrobiopterin (remember THF is used for homocysteine pathway, THB for phenylalanine pathway).

Front 47

What does tetrahydrobiopterin do?

Back 47

Cofactor for conversion of phenylalanine to tyrosine

Front 48

What does dihydropterin reductase do?

Back 48

Regenerates tetrahydrobiopterine, using NADPH

Front 49

What are the possible causes of phenylketonuria?

Back 49

Decreased phenylalanine hydroxylase; decreased tetrahydrobiopterin (cofactor). THB can be depleted due to dihydropterin reductase deficiency.

Phe builds up, Tyr becomes essential

Front 50

What causes alkaptonuria?

Back 50

Congenital deficiency of homogentisic acid oxidase
(from degradative pathway of tyrosine)

Front 51

This disease is characterized by mental and growth retardation, seizures, fair skin.

Back 51

Phenylketonuria

Fair skin is due to inability to synthesize tyrosine, which is a precursor of melanin. Some tyrosine is still acquired in the diet.

Front 52

This disease is characterized by dark connective tissue, pigmented sclera, urine turning black on standing

Back 52

Alkaptonuria (benign)

Front 53

This disease can be charactierized by debilitating athralgia

Back 53

Alkaptonuria

Front 54

What causes albinism?

Back 54

Three possible causes: tyrosinase deficiency, tyrosine transporter deficiency; or lack of migration of neural crest cells

Front 55

This disease is characterized by osteoporosis, tall stature, kyphosis, lens subluxation and atherosclerosis

Back 55

Homocystinuria

Front 56

This disease is characterized by increased risk of stroke and MI

Back 56

Homocystinuria

Front 57

This disease is characterized by increased risk of kidney stones

Back 57

Cystinuria

Front 58

What causes maple syrup urine disease?

Back 58

Defective alpha-ketoacid dehydrogenase; branched amino acids cannot be degraded

Front 59

What does alpha-ketoacid dehydrogenase do?

Back 59

Degradative enzyme of branched amino acids (Ile, Leu, Val)

Think of alpha-1,6 branching

Front 60

This disease is characterized by increased alpha-ketoacids in the blood

Back 60

Maple syrup urine disease

(recall that alpha-ketoacid implies branched amino acid)

Front 61

This disease is characterized by severe CNS defects, mental retardation and death

Back 61

Maple syrup urine disease