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BB 491 > Nitrogen & Nucleotide Metabolism > Flashcards

Nitrogen & Nucleotide Metabolism Flashcards

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1
Q

What are the “goals” of the oxidative phase of the PPP?

A

Produce NADPH and 5 C sugars (ribulose-5-phosphate)

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2
Q

What is the “goal” of the nonoxidative phase of the PPP?

A

Convert pentose phosphates to glycolytic intermediates

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3
Q

What is the molecule that is partitioned between glucose and the PPP?

A

Glucose-6-Phosphate (goes into PPP if NADPH is needed, into glycolysis if ATP is needed)

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4
Q

What happens to NADPH made in the oxidative phase of the PPP?

A

It is used to support reductive biosynthesis (e.g. used for NAD+, FAD synthesis)

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5
Q

What are examples of tissues that might need NADPH?

A

Those synthesizing fatty acids, cholesterol, steroid hormones

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6
Q

What can be made from R-5-P?

A

Nucleotides, NAD+, FAD, CoA

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7
Q

Which molecule in the PPP is used for amino acid synthesis?

A

E4P; bacteria use to make aromatic AAs

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8
Q

Which nucleotide form is attached to ribose throughout its synthesis?

A

Purines

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9
Q

A Nucleoside

A

Adenosine

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10
Q

G Nucleoside

A

Guanosine

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11
Q

T Nucleoside

A

Thymidine

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12
Q

U Nucleoside

A

Uridine

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13
Q

C Nucleoside

A

Cytidine

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14
Q

What are the metabolic precursors for de novo synthesis of purines?

A

AAs, R5P, CO2, NH3

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15
Q

What is the committed step of purine synthesis?

A

Conversion of Glu to Gln

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16
Q

How does allopurinol work?

A

Prevents conversion of xanthine to uric acid (competes with hypoxanthine for access to xanthine oxidase)

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17
Q

Hydroxyurea molecular mechanism

A

Disrupts tyrosyl radical on RNR

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18
Q

How does muscle get the molecules that it needs?

A
  • Own stored fuels
  • Other organs
  • Creatine Kinase Reaction
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19
Q

What is the fate of dietary glucose?

A

1/3 to liver glycogen, 1/2 of remainder to muscle glycogen, other 1/2 of remainder oxidized for immediate needs

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20
Q

What does glucokinase do?

A

Converts glucose to G6P, lower affinity for glucose than other hexokinases (high BG needed for binding)

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21
Q

Pathways for G6P in liver

A
  • Back to glucose (blood glucose)
  • Glycolysis
  • ATP
  • Acetyl CoA (FA synth)
  • PPP
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22
Q

Pathways for lipids in liver

A
  • TAG, PLs
  • B Ox to Acetyl CoA (ATP, KBs, sterol synthesis)
  • Heart & muscle for energy
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23
Q

Pathways for AAs in liver

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A
  • Proteins, other organs
  • Precursors for proteins, nucleotides, hormones, etc.
  • Pyruvate & ammonia:
  • Ammonia –> Urea
  • Pyruvate –> GNG
  • Acetyl CoA
  • CAC/OxPhos
    *Lipid Storage
    *GNG
24
Q

Phosphocreatine Cycle

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A

Phosphocreatine + ADP –> Creatine + ATP

25
How does the heart obtain its ATP?
Mostly from FA oxidation, glucose and KBs are other source
26
Cori Cycle
Glucose --> Pyruvate --> Lactate (Reversed in liver) --> Glucose back to muscle
27
What are the three reasons that proteins would need to be degraded?
- Damaged - Unnecessary - Misfolded (DUM)
28
What molecule is used to test protein half-lives? How does it work?
Cyclohexylamine (CHX), inhibits translation)
29
Destabilizing N Terminal Residues
Leu, Lys, Asp, Arg, Phe (LLAAPS)
30
Stabilizing N Terminal Residues
Val, Met, Thr, Ala, Gly (VM TAGS)
31
PEST Proteins
Pro (P), Glu (E), Ser (S), Thr (T), quickly degraded
32
What are the two major degradation pathways?
- Endosome-Lysosomal Path (extracellular, endocytosis) - Autophagy (intracellular)
33
Cathepsins
Proteases in the lysosome that act at low pH
34
Where does the pool of available amino acids come from?
Diet, digestion, De novo synthesis (DDD)
35
What are the three ways the amino acid pool is used?
- Ketogenesis - Gluconeogenesis - Synthesis of N-containing nonproteins
36
What amino acids are glucogenic?
Those that can be transformed and incorporated into the OAA (CAC, pyruvate)
37
What amino acids are ketogenic?
Those that can be transformed into acetyl CoA
38
What organisms fix nitrogen?
Cyanobacteria, rhizobia
39
Why is hyperammonemia damaging to the CNS?
Glutamine synthetase combines ammonium and glutamate to form glutamine, which changes the osmotic gradient in the brain.
40
Transaminases are a form of ________ reaction.
Double displacement reaction
41
Glucose-Alanine Cycle
Muscles: Glucose --> Pyruvate --> Ala (ALT) Luver: Ala --> Pyruvate --> Glucose
42
What ratio is used to determine progression of liver disease?
AST/ALT
43
What do aquatic animals excrete?
Ammonia
44
What do amphibians excrete?
Urea
45
What do reptiles and insects excrete?
Uric Acid
46
Where does the urea cycle take place?
Mitochondria and cytosol of liver
47
Which inborn disorder of metabolism is associated with Marfanoid symptoms?
Homocystinuria
48
Where do the carbon skeletons used in AA synthesis come from?
- CAC (OAA) - Glycolysis (pyruvate) - PPP (R5P)
49
Where does the nitrogen used in AA synthesis come from?
Glu or Gln
50
Patchwork Assembly Model
Ancestral enzymes could bind a number of substrates to carry out the same reaction. Duplication, then divergence has led to the affinity and specificity we see today.
51
What does CBS do?
Catalyzes the formation of cystathionine
52
What does CGS do?
- Removes ammonia - Cleaves cystathionine to yield Cys
53
What are tannins, alkaloids, natural flavorings, and salicylate derived from?
Phe & Tyr
54
Concerted Inhibition
Additive effect associated with 2+ inhibitors acting on an enzyme (usually the enzyme's products)
55
What are key characteristics of the regulation of AA biosynthesis at the cellular level?
- Several isozymes regulate the same reaction - Overlapping feedback inhibition (e.g. Leu and Ile) - Negative feedback

BB 491 (7 decks)

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