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MCM - Rusheil > Fatty Acid Metabolism > Flashcards

Fatty Acid Metabolism Flashcards

1
Q

FA synthesis location

A

PRIMARILY liver.

Also, in adipose tissue, brain, kidneys, lactating mammary glands

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2
Q

How citrate gets from mitochondria to cytosol?

A

Citrate transporter

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3
Q

Citrate Lyase

A

Catalyzes conversion:
citrate —> Acetyl-CoA

  • Requires ATP
  • Forms oxaloacetate

Inhibited by: PUFA, leptin
Stimulated by: Glucose, Insulin

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4
Q

Acetyl-CoA Carboxylase (ACC)

A

Catalyzes conversion:
Acetyl-CoA —> Malonyl-CoA

  • Requires ATP, CO2 and Biotin as a CO-FACTOR
  • RATE-LIMITING ENZYME in FA synthesis

Allosterically regulated:
Stimulated by - Citrate (+)
Inhibited by - Long chain fatty acids I.e. palmitate (-)

ACC dimeric form = inactive, polymeric form = active

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5
Q

What does Malonyl-CoA inhibit?

A

Carnitine-Acyltransferase

  • Enzyme in FA degradation
  • Rate limiting step in the degradation

Prevents FA synthesis and degradation from occurring simultaneously

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6
Q

Malonyl-CoA

A

Substrate for Fatty Acid Synthase Complex (last phase of FA synthesis)

Requires 7 Malonyl-CoA molecules.

Malonyl-CoA is a 3C molecule, FA Synthase adds on 2 carbons from Malonyl-CoA to a growing fatty acid each time.

1 Acetyl-CoA (2C) + 7 Malonyl-CoA (2C each = 14C) —> 16C Palmitate

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7
Q

Fatty Acid Synthase

A

Multi-enzyme complex with 2 identical diners (260 kDa each)
- arranged in head to tail conformation

Each dimmer contains 7 enzyme activities plus an Acyl Carrier Protein (ACP)

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8
Q

Order of reactions catalyzed by Fatty Acid Synthase (FAS)

A
  1. Condensation
  2. Reduction
  3. Dehydration
  4. Reduction
    (Then repeat steps 2-4 x6)
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9
Q

What is the source of NADPH in FA synthesis?

A

Malic enzyme: 1

PPP: 2-12

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10
Q

Leptin

A

Hormone secreted by adipose tissue. “Fat-Brain axis”

Communicates with the brain (hypothalamus) to reduce food intake when the body is fed/full. Regulates body weight

Leptin K/O mice = obese
-If mice are given leptin —> weight reduced

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11
Q

Where is palmitate converted to longer-chain FA?

A

Smooth Endoplasmic Reticulum or Mitochondria
-Brain requires longer chain FA (C18-24)

SER uses Malonyl-CoA as carbon donor
Mitochondria uses Acetyl-CoA as carbon donor

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12
Q

Acyl CoA Desaturase

A

Introduces double bonds in FA’s.
-Occurs in the SER and uses NADPH

Cannot synthesize double-bond beyond C9-10 in humans (i.e. omega-3), must be obtained from diet.

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13
Q

Desaturase regulation

A

Insulin increases expression

PUFA suppress expression

Dietary cholesterol induces expression of delta9-Desaturase and suppresses all others

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14
Q

Fatty acid lengths regarding mitochondrial entry

A

Can diffuse into mitochondria:

  • Short chain FA (SCFA)
  • Medium chain FA (MCFA)

Need to be actively transported in:

- Long chain FA (LCFA)
- Very long chain FA (VLCFA) —>oxidized in peroxisomes to LCFA —> Carnitine shuttle
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15
Q

Fatty Acyl CoA Synthetase

A

In cytoplasm, adds a CoA to fatty acid —> Fatty Acyl CoA, so it can pass through the Outer Mitochondrial Membrane

  • Requires ATP
  • thioester bond formed between FA and Acyl CoA
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16
Q

Carnitine Palmitoyltransferase I (CPT-I)

A

Located in intermembrane space
-Catalyzes FA-CoA —> FA-Carnitine

RATE LIMITING ENZYME for FA degradation

Inhibited by Malonyl-CoA

17
Q

Carnitine-Acylcarnitine Translocase (CACT)

A

Transports FA-Carnitine into mitochondrial matrix.

-Antiporter: FA-Carnitine (in) Carnitine (out)

18
Q

CPT-II

A

Located on inner mitochondrial membrane
-Catalyzes FA-Carnitine —> (back to) FA-CoA

FA-CoA now in the matrix —> Ready of beta-oxidation

19
Q

Order of steps of B-oxidation

A
  1. Oxidation
  2. Hydration
  3. Oxidation
  4. Thiolysis

(Opposite of

20
Q

Acyl CoA dehydrogenase (ACAD)

A

First enzyme in FA degradation
-Oxidizes FA via FAD+ —>FADH2 (to CoQ in ETC = 1.5 ATP)

Four types of ACADs:
Short Chain Acyl CoA Dehydrogenase (SCAD)
Medium chain ————————-—- (MCAD) 
Long Chain ——— ————————(LCAD)
Very Long Chain —————————(VLCAD)
21
Q

Enol CoA Hydratase

A

Step 2 in FA degradation: Hydration - adds water to the alkene forming beta-hydroxy Acyl CoA

22
Q

Beta-hydroxyl Acyl CoA dehydrogenase

A

Step 3 of FA degradation - oxidizes the beta carbon to form double bond.

-NADH produced (2.5 ATP in ETC)

23
Q

Acyl CoA acyltransferase (beta ketothiolase)

A

Last enzyme in FA degradation

Attaches sulfur of a new CoA to ketone formed after cleavage of Acetyl-CoA from Fatty Acyl chain —-shortened by 2 carbons

Acetyl-CoA = 12 ATP

24
Q

ATP generated from beta-oxidation of palmitic acid

A

129 ATP

25
Q

Propionyl CoA Carboxylase

A

First enzyme in degradation of Odd #C FA chain once FA is degraded down until Propionyl-CoA remains.

Carboxylates Propionyl-CoA —> Methylmalonyl-CoA
-Requires ATP

26
Q

Methylmalonyl CoA Mutase

A

2nd enzyme used in odd #C FA degradation.

Catalyzes Methylmalonyl CoA —> Succinyl-CoA

Succinyl-CoA enters TCA cycle

27
Q

Reductase and Isomerase

A

Enzymes used in degradation of UNsaturated FA.

Reductase: reduces double bond

Isomerase: moves disruptive bond

28
Q

Peroxisomes

A

Degrade VLCFAs greater than 20C.

Beta-oxidizes but FADH produced but electron energy transferred to O2 to make H2O2 instead of TCA.

First step catalyzed by Acyl-CoA oxidase

When FA < 20 —> Sent to mitochondria for further beta-oxidation

29
Q

MCAD Deficiency

A

Disorder of FA beta-oxidation that impairs breakdown of MCFAs.

  • Autosomal recessive
  • Leads to secondary Carnitine deficiency = excessive excretion of MCA carnitines in urine
  • C8 FA accumulate in liver - poisonous and interferes with urea cycle - elevated ammonia
  • Patient requires glucose as energy source
  • Hypoglycemia/sudden death without timely intervention
30
Q

Three ketone bodies

A
  1. Acetoacetate - 23 ATP
  2. Beta-hydroxybutyrate - 26 ATP
  3. Acetone
31
Q

Ketone body properties and purpose

A

Water-soluble, acidic compounds

Provide energy for peripheral tissues during fasting/starvation

32
Q

Where are ketone bodies produced?

A

Liver only - Mitochondrial matrix of hepatocytes

33
Q

Where/when ketone bodies are used?

A

Brain: Starvation when glucose is completely depleted

Muscle: During fasting

Kidneys: During fasting

34
Q

Pathological ketoacidosis

A

Occurs when glucagon/insulin ratio is high - Favoring FA breakdown

Increased Acetyl-CoA and hepatic mitochondria —> increased ketone bodies

Acetoacetate and b-hydroxybutyrate are strong acids —> lower blood pH causing acidosis. Increased concentration found in urine

35
Q

Diabetic Ketoacidosis

A

Diabetics cannot take up glucose from the blood.

Adipose tissue releases FA to be beta-oxidized in the liver for energy

Ketone bodies form —> blood pH drops —> coma/death

MCM - Rusheil (6 decks)

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