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Biochem Flashcards

1
Q

Pyruvate kinase deficiency?

A

GLYCOLYSIS
Benign
↓pyruvate -> ↓ATP in RBCs -> ↑ hemolysis -> ↓ O2 delivery

Compensation:
1) ↑ ATP synthesis in liver
2) ↑ 2,3-BPG -> ↓ O2-Hb binding
↑ O2

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2
Q

Aldolase B deficiency? (fructose intolerance)

A

GLYCOLYSIS
Accumulation of Fructose-1-P → TOXIC → poor feeding / failure to thrive in infants

  • Depletion of Pi req. for glycolysis
  • Fructosuria
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3
Q

Galactose-1-P uridyltransferase deficiency ? (Galactosemia)

A

GLYCOLYSIS
Accumulation of Galactose-1-P → TOXIC → brain/kidney damage + liver dysfunction - Jaundice

  • Galactosuria
  • Aldose reductase reduces accumulated galactose to galactitol → Osmotic damage to lens → CATARACTS
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4
Q

Pyruvate Dehydrogenase (PDH) deficiency? (rare)

A

TCA
Pyruvate accumulation
↑ Lactate -> Lactic acidosis
↓Acetyl-coA -> ↓ TCA cycle -> ↓ ATP -> neurodegeneration

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5
Q

Thiamine (Vit B1) deficiency [Beri-Beri] ?

A

TCA
- Thiamine req. to prod. TPP (essential cofactor for PDH and α-KG DH + Transketolase)

Chronic deficiency → ↓ATP
1) neurological: neuropathy, encephalopathy, cognitive impairment
2) cardiac : congestive cardiac failure

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6
Q

Arsenic/mercury poisoning?

A

TCA
- Arsenic / mercury inhibits lipoic acid (essential cofactor for PDH & α-KG DH)

Acute poisoning → ↓ATP → neurological dysfunction → organ failure → coma/death

Chronic poisoning → Skin (dew drops on a dusty road) + Nails (Mees lines)

Arsenic poisoning → recognizable by garlicky odor

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7
Q

MELAS

A

OXPHOS
- Myopathy, Encephalomyopathy, Lactic Acidosis & Stroke-like episodes

  • Mutation in mitochondrial tRNA → decreased ETC complexes (except II) → decreased ATP → neurological / muscle dysfunction
  • decreased ETC activity → decreased TCA cycle activity → Accumulation of pyruvate & lactate → Lactic acidosis
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8
Q

Characteristics of OXPHOS mitochondrial disease?

A
  • mitochondrial DNA is MATERNALLY inherited
  • only carrier females can pass it down
  • in every generation, affect both sexes
  • it encodes for all ETC complex subunits EXCEPT COMPLEX II & for ribosomes / tRNA for synthesis
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9
Q

Mitochondrial poisons?

A

OXPHOS

I : Rotenone (rat poison)
II : Malonate
III : Antimycin A (fish poison)
IV : Cyanide / CO
ATP synthase : Azide

Dinitrophenol (herbicide / illegal weight loss drug) : Increase proton leak across membrane -> Increase heat generation

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10
Q

G6PD deficiency?

A

HMP SHUNT
* X-linked recessive disease

Decreased production of NADPH in RBCs
[needed to maintain glutathione in reduced form] → less protection against oxidative stress in RBCs

1. Less severe form:
inadequate NADPH to protect against oxidative stress caused by drugs (anti- malarial, sulfur-based antibiotics), infections, mothballs → oxidation of proteins in RBCs (Heinz bodies) → decrease in membrane plasticity → increases hemolysis → Jaundice + Sclera icterus

2. Severe form:
infants with increased hemolysis → anemia + increase in bilirubin → cross BBB → neurological damage = Kernicterus **

  • BUT G6PD Deficiency may confer resistance to malaria by decreasing production of NADPH (utilised by the malaria parasite in RBCs)
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11
Q

Glucose-6-phosphatase deficiency?

A

GLUCONEOGENESIS
1. Can’t untrap glucose → Accumulation of G6P → Hypoglycemia

  1. Accumulated G6P
  • HMP shunt → increased nucleotide metabolism → Increased uric acid
  • Glycogen synthesis → Increased glycogen → Organomegaly
  1. Accumulation of pyruvate → Increased lactate
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12
Q

Pyruvate carboxylase deficiency?

A

GLUCONEOGENESIS
- Very rare, short life span of 6 months

  • Metabolic block in Pyruvate → OAA (1st step of 1st hurdle)
  1. Accumulation of Pyruvate → increased Lactate
  2. Depletion of OAA -> less TCA activity
    - decreased ATP production
    - decreased gluconeogenesis → hypoglycemia
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13
Q

Glycogen storage diseases?

A

Viagra Pills Cause A Major Hardon
I : Von Gierke -> G6Pase
II : Pompe -> 1,4-glucosidase
III : Cori -> Debrancher enzyme
IV : Andersen -> Branching enzyme
V : McArdel -> Muscle glycogen phosphorylase
VI : Her’s -> Liver glycogen phosphorylase

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14
Q

Which glycogen storage disease cause block in synthesis?

A

Type IV Andersen
- deficiency of branching enzyme
- accumulation of abnormal glycogen
- Hepatomegaly
- Early death

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15
Q

Symptoms of Von Gierke?

A

G6Pase deficiency
fasting hypoglycemia, organomegaly, lactic acidosis, increased uric acid (possibly gout)

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16
Q

Symptoms of Cori?

A

Type III
Debrancher enzyme deficiency [4:4 transferase + 1,6-glucosidase]

Fasting hypoglycemia

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17
Q

Symptoms of McArdle?

A

Type V
Deficiency in muscle glycogen phosphorylase

Exercise-induced muscle pain, cramps

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18
Q

How are carbohydrates absorbed?

A

Glucose & Galactose -> SGLT1 (secondary active transport) -> GLUT2 (facilitated transport)
-> SGLT1 is driven by Na-K-ATPase pump

Fructose -> GLUT5 -> GLUT2 [facilitated diffusion]

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19
Q

Importance of PFK1?

A

Catalyses the :
Irreversible step
Entry point to glycolysis
Major point of regulation

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20
Q

Importance of pyruvate kinase?

A

GLYCOLYSIS
Catalyses the :
Irreversible step
Substrate-level phosphorylation
Point of regulation

21
Q

How’s PFK-1 and pyruvate kinase regulated by energy state?

A

PFK1 : inhibited by ATP & citrate, activated by AMP

PK : inhibited by ATP

22
Q

Location of all carb metab pathways?

A

Glycolysis : cytoplasm

TCA : mitochondrial matrix (except SDH in inner membrane)

OXPHOS : mitochondria inner membrane

HMP shunt : cytosol

Gluconeogenesis : Cytosol

23
Q

How does fructose & galactose enter glycolysis?

A

Fructose ->(fructokinase) -> F1P -> (Aldolase B) -> DHAP <-> G3P

Galactose -> (Galactokinase) -> Galactose-1-P -> (Galactose-1-P uridyltransferase) -> G1P -> G6P

24
Q

How to regenerate NAD+ from NADH?

A
  1. Aerobic : OXPHOS shuttle
  2. Anaerobic : Cori cycle, when Pyruvate -> Lactate
25
Q

Rate-limiting step of TCA? & regulation?

A

Isocitrate -> aKG via isocitrate DH
activated by ADP, Ca2+
inhibited by NADH (pdt)

26
Q

How to replenish OAA? How is enzyme regulated?

A

Pyruvate -> OAA via PC
Biotin : co-factor

activated by acetyl-coA (substrate)
inhibited by ADP

27
Q

Which enzymes do Ca2+ activate in TCA?

A

Isocitrate DH
aKG DH

28
Q

Which enzymes do NADH inhibit in TCA?

A

Isocitrate DH
aKG DH
Malate DH

29
Q

Which enzyme does citrate inhibit in TCA?

A

Citrate synthase

30
Q

Which enzyme does ADP activate in TCA?

A

Isocitrate DH

31
Q

How is PDH regulated? (entry of pyruvate into TCA)

A

Activated by : NAD+, CoASH, ADP, pyruvate, Ca2+

Inhibited by : NADH, Acetyl-coA

32
Q

Difference between 2 shuttles in OXPHOS?

A

Glycerol-3-P shuttle
- muscle
- faster but lower ATP yield
- transf e- to complex II
- NADH -> FADH2

Malate-aspartate shuttle
- liver & heart
- slower but higher ATP yield
- transf e- to complex I
- NADH -> NADH

33
Q

Side products from OXPHOS?

A
  1. ROS
    - superoxide, peroxide, hydroxyl radical
  2. Heat
    - short circuiting of proton-gradient
    - protons go thru UCP w/o generation of ATP
    - dissipation of H+ gradient -> heat
    - UCP in brown fat
34
Q

Rate-limiting step of HMP shunt? & regulation?

A

G6PD
- activated by low NADPH/NADP+ ratio
- inhibited by high NADPH/NADP+ ratio

35
Q

When is TPP needed as a co-factor?

A
  1. aKG DH / PDH in TCA
  2. rearrangement of R5P in HMP shunt
    - assay for thiamine
36
Q

What are the uses of NADPH?

A
  1. cholesterol synthesis
  2. detox
  3. glutathione reduction
  4. generation of ROS
  5. synthesis of NO
37
Q

How is F-1,6-Bisphosphatase regulated?

A

activated by ATP, citrate, glucagon
inhibited by AMP, F-2,6-P2, insulin

38
Q

Substrates for gluconeogenesis?

A
  1. Lactate -> cori cycle -> pyruvate
  2. Alanine -> glucose-alanine cycle -> pyruvate
  3. Glutamine -> OAA
  4. Lipids -> Lipolysis -> glycerol -> Glycerol 3P -> DHAP
39
Q

Rate-limiting step of lipogenesis? & regulation?

A

ACC
activated by citrate, insulin
inhibited by pdt, glucagon, epinephrine

40
Q

Location of lipids metab?

A

Lipogenesis : cytosol
Lipolysis : cytosol then shuttle into mitochondria
KB synthesis : mitochondria
Cholesterol synthesis : cytosol

41
Q

Rate-limiting step of lipolysis? & regulation?

A

CPT-I
inhibited by Malonyl CoA

42
Q

HMG-coA synthase in cytosol & mitochondria?

A

C for cholesterol synthesis !
Mito : Kb synthesis

43
Q

Rate-limiting step of cholesterol synthesis?

A

Hmg-CoA reductase
- committed step too

44
Q

What is req. in cholesterol synthesis?

A

all carbons come from acetyl-coa
req. NADPH, ATP, O2

45
Q

Direct reverse cholesterol transport by HDL?

A
  1. HDL take up cholesterol from extrahepatic tissues
  2. Convert cholesterol to cholesterol esters
  3. HDL2 (lipid-rich) bind to SR-B1 -> release C & CE + TG hydrolysed by HTGL
  4. HDL3 (lipid-poor) released & can pick up more C & CE
46
Q

Indirect reverse cholesterol transport by HDL?

A
  1. HDL exchange CE for TG with VLDL via CETP
  2. VLDL lose tg -> IDL
  3. IDL either taken up by ApoE receptors or
  4. IDL lose tg -> LDL
  5. LDL taken up by LDL receptor
47
Q

How is bile acid/salt synthesised?

A

cholesterol -> 7a-hydroxycholesterol [via 7a-hydroxylase]->->-> primary bile acids -> (conjugation) -> primary bile salts

then pri bile salts secreted into intestinal lumen as bile -> (deconjugation by intestinal bacteria) -> secondary bile acids

48
Q

How is vitamin D synthesised?

A

UV light -> Skin -> 7-dehydrocholesterol ->-> Vitamin D3 ->-> -> Calcitrol (Active vit D3)

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