BMB 401 Exam 2

What is the rate-limiting enzyme of heme synthesis?

δ-Aminolevulinate synthase (ALAS)

What substrates are used by ALAS?

Glycine + Succinyl-CoA

What cofactor does ALAS require?

PLP (Vitamin B6)

What inhibits ALAS?

Heme (negative feedback)

What enzyme inserts Fe²⁺ into protoporphyrin IX?

Ferrochelatase

Which porphyria is caused by porphobilinogen deaminase deficiency?

Acute Intermittent Porphyria

Symptoms of Acute Intermittent Porphyria?

Abdominal pain and neurologic symptoms

What enzyme converts heme into biliverdin?

Heme oxygenase

What gas is produced during heme degradation?

Carbon monoxide (CO)

What causes jaundice?

Elevated bilirubin

What do enzymes lower?

Activation energy

Do enzymes change ΔG?

Hell Nah enzymes do not change ΔG

Do enzymes change equilibrium?

No they do not

What do enzymes stabilize?

Transition state

Difference between apoenzyme and holoenzyme?

Apoenzyme = protein only; Holoenzyme = protein + cofactor

What is an allosteric regulator?

Molecule that binds outside the active site and changes enzyme activity

ATP effect on ATCase?

Activator

CTP effect on ATCase?

Inhibitor

Protein kinase does what?

Adds phosphate

Protein phosphatase does what?

Removes phosphate

Define Vmax.

Maximum reaction velocity when enzyme is saturated

Define Km.

Substrate concentration at ½ Vmax

Low Km means what?

High substrate affinity

High Km means what?

Low substrate affinity

What is kcat?

Turnover number

What is catalytic efficiency?

kcat/Km

Metal ion in carbonic anhydrase?

Zn²⁺

Histidine's role in carbonic anhydrase?

Proton shuttle

Competitive inhibition effect on Km?

Increases Km

Competitive inhibition effect on Vmax?

No change (Competitive Inhibition)

Uncompetitive inhibition effect on Km?

Decreases Km

Uncompetitive inhibition effect on Vmax?

Decreases Vmax (Uncompetitive Inhibition)

Noncompetitive inhibition effect on Km?

Change = No

Noncompetitive inhibition effect on Vmax?

Decreases Vmax

Difference between catabolism and anabolism?

Catabolism breaks down; anabolism builds up

Why is ATP hydrolysis favorable?

Resonance stabilization, charge repulsion relief, entropy increase, hydration stabilization

ΔG < 0 means?

Spontaneous/exergonic

ΔG > 0 means?

Nonspontaneous/endergonic

Oxidized form of NAD?

NAD⁺

Reduced form of NAD?

NADH

Primary role of NADPH?

Biosynthesis

Primary role of CoA?

Acyl-group carrier

Central metabolic intermediate?

Acetyl-CoA

Storage polysaccharide in animals?

Glycogen

Storage polysaccharide in plants?

Starch

Structural polysaccharide in plants?

Cellulose

Why can't humans digest cellulose?

Lack cellulase

Viral protein that binds sialic acid?

Hemagglutinin

Viral protein that cleaves sialic acid?

Neuraminidase

How does Tamiflu work?

Neuraminidase inhibitor

N-linked glycosylation occurs on which amino acid?

Asparagine

O-linked glycosylation occurs on which amino acids?

Serine and threonine

Where does O-linked glycosylation occur?

Golgi

Function of dolichol phosphate?

Carries oligosaccharides during N-linked glycosylation

Three irreversible glycolysis enzymes?

Hexokinase, PFK-1, Pyruvate kinase

Committed step of glycolysis?

PFK-1

Most important regulatory enzyme of glycolysis?

PFK1 (regulatory enzyme of glycolysis)

Activators of PFK-1?

AMP and F2,6BP

Inhibitors of PFK-1?

ATP and citrate

What activates glycolysis: insulin or glucagon?

Insulin

What inhibits glycolysis: insulin or glucagon?

Glucagon

Net glycolysis products?

2 ATP, 2 NADH, 2 pyruvate

Purpose of gluconeogenesis?

Make glucose

Major organ of gluconeogenesis?

Liver

Why can't muscle release glucose?

Lacks glucose-6-phosphatase

Pyruvate → Oxaloacetate enzyme?

Pyruvate carboxylase

Cofactor for pyruvate carboxylase?

Biotin

Oxaloacetate → PEP enzyme?

PEPCK

Fructose-1,6-BP → Fructose-6-P enzyme?

Fructose-1,6-bisphosphatase

Glucose-6-P → Glucose enzyme?

Glucose-6-phosphatase

Major regulatory enzyme of gluconeogenesis?

Fructose-1,6-bisphosphatase

Effect of F2,6BP on glycolysis?

Activates glycolysis

Effect of F2,6BP on gluconeogenesis?

Inhibits gluconeogenesis

Insulin effect on F2,6BP?

Increases it

Glucagon effect on F2,6BP?

Decreases it

Purpose of PDC?

Convert pyruvate to acetyl-CoA

Where is PDC located?

Mitochondrial matrix

Is PDC reversible?

No, irreversible

E1 enzyme?

Pyruvate dehydrogenase

E2 enzyme?

Dihydrolipoyl transacetylase

E3 enzyme?

Dihydrolipoyl dehydrogenase

Five PDC cofactors?

TPP, Lipoamide, CoA, FAD, NAD⁺

Which cofactor comes from vitamin B1?

TPP

Rate-limiting step of PDC?

E1 decarboxylation of pyruvate

What does phosphorylation do to PDC?

Inactivates it

What does dephosphorylation do to PDC?

Activates it

High ATP turns PDC on or off?

Off

Disease caused by thiamine deficiency?

Beriberi

What toxin inhibits lipoamide?

Arsenic (also mercury)