Amino Acids (Lecture 27)

Question 1

which amino acids require 1 step degradation and what are their products?

Answer 1

glutamate ->alpha ketoglutarate (via GDH)

aspartate -> oxaloacetate (via aspartate transaminase)

Question 2

what are the 3 fates of amino acid catabolism?

Answer 2

gluconeogenic
ketogenic
gluconeo-ket-genic

Question 3

what does gluconeogenic mean?

Answer 3

amino acids (carbon skeleton) will branch back into the CAC to generate glucose

Question 4

what does ketogenic mean?

Answer 4

amino acids used to make ketone bodies

Question 5

which amino acids require a conversion reaction (2 steps)?

Answer 5

GLUTAMINE:
glutamine->glutamate ->alpha KG

ASPARAGINE:
asparagine->aspartate->oxaloacetate

this occurs via a deamination reaction (1st step)

Question 6

which amino acids are broken down in the urea cycle?

Answer 6

aspartate (combined with citruline) will be converted into arginosuccinate via ASS

arginosuccinate will then be broken down to fumarate and arginine via arginosuccinase

Question 7

what do gluconeogenic aa do?

Answer 7

replenish the substrates involved in the citric acid cycle via anapleurotic reactions

Question 8

what do ketogenic aa do?

Answer 8

aa will be broken down to acetyl coa and/or acetoacetate to then form beta-hydroxybutarate, to then serve as an energy source to the heart and brain (produce FADH2 and NADH)

Question 9

where are branched chain amino acids degraded?

Answer 9

muscle, adipose, kidney and brain tissue

Question 10

how are branched amino acids degraded?

Answer 10

the branched amino acids will undergo a transferase reaction via branched chain aminotransaminase to generate a keto-acid.

the alpha keto acid will then form acyl coa derivatives via branched chain alpha keto acid dehydrogenase complex (BCKD)

Question 11

deficiency in BCKD causes…

Answer 11

maple syrup urine disease

Question 12

how is BCKD regulated?

Answer 12

via phosphorylation by a kinase

the phosphorylation will inactivate the enzyme, and dephosphorylation activated the enzyme

the abundance of the branched chain (leucine) keto acids will inhibit BCKD

Question 13

what is alanine synthesized from?

Answer 13

pyruvate via aminotransferase

Question 14

what is aspartate synthesized from?

Answer 14

oxaloacetate via amino transferase

Question 15

what is asparagine synthesized from?

Answer 15

oxaloacetate via amino transferase AND aspartate (and glutamine + ATP) via asparagine synthase

Question 16

what is glutamate synthesized from?

Answer 16

alpha KG via aminotransferase

Question 17

what is glutamine synthesized from?

Answer 17

alpha KG via aminotransferase AND glutamate (and ATP + NH4) via glutamine synthase

Question 18

methionine metabolism

Answer 18

homocysteine needs a 1 carbon donor to produce methionine. This donor is 5-methyl-THF

this reaction occurs with the cofactor, vitamin B12

Question 19

how is homocysteine metabolized?

Answer 19

homocysteine is converted to propionyl-coa (odd chain FA beta oxidation) and then will be converted into succinylcholine coa molecule, which will feed into the CAC

Question 20

is methionine gluconeogenic, ketogenic or gluconeo-keto-genic AND why?

Answer 20

gluconeogenic because it replenishes succinylcholine coa for the CAC

Question 21

hyper-homocysteinemia

Answer 21

imbalance between the rate of production/breakdown of homocysteine

Question 22

what are causes of hyper-homocysteinemia

Answer 22

B12, folic acid deficiency

mutations in the enzyme converting homocysteine go cystathionine (cystathionine beta synthase) - causes accumulation of homocysteine

Question 23

hyper-homocysteinemia is associated to…

Answer 23

cardiovascular disease

cognitive impairment/dementia

developmental defects (neural tube defects and anencephaly)

Question 24

what is given to pregnant women to prevent developmental defects neural tube defects and anencephaly

Answer 24

folic acid to ensure that homocysteine is properly degraded

Question 25

how is cysteine synthesized?

Answer 25

via a transsulfuration reaction:

homocysteine is combined with serine and PLP as a cofactor
another round with PLP will remove NH3 to form alpha keto butyrate and cysteine