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Metabolism > Fats- Lipolysis and Beta Oxidation > Flashcards

Fats- Lipolysis and Beta Oxidation Flashcards

1
Q

What are fats composed of?

A

Carbon, hydrogen and oxygen

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2
Q

What is triacylglycerol?

A
  • Fats and oils
  • 1 glycerol and 3 fatty acid tails
  • Vary in length and location of double bonds in tails
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3
Q

Where do you find the omega carbon on a fatty acid?

A

At the methyl end

- Last carbon on the outside portion of the fatty acid

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4
Q

Where do you find the alpha carbon on a fatty acid chain?

A

At the carboxyl end of the chain

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5
Q

How are fatty acids named?

A
  • By the number of carbons in the chain and number and location of C=C double bonds
  • E.g. omega-3 fatty acids represent that the double bond is 3 carbons away from the omega carbon
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6
Q

What happens to fatty acids in the basal state?

A
  • A few hours after a meal

- During fasting, fatty acids released from adipose tissue after undergoing lipolysis

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7
Q

What is lipolysis?

A

Breakdown of triglycerides into fatty acids and glycerol

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8
Q

What happens to glycerol after lipolysis in the basal state?

A
  • Travels to liver and its carbons used for gluconeogenesis
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9
Q

What happens to fatty acids after lipolysis in the basal state?

A
  • Go to tissues requiring energy
  • Converted to acetyl coA
  • Muscle–> acetyl CoA enters TCA cycle
  • Liver–> Acetyl CoA converted to ketone bodies and delivered to the blood
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10
Q

What molecule do fatty acids form complexes with and what happens to them?

A
  • Albumin
  • Taken up by muscles, kidneys and other tissues
  • Complete oxidation to produce CO2, water and ATP (via beta-oxidation, TCA and electron transfer chain)
  • Partially oxidised in liver to form ketone bodies
  • Ketone bodies released in blood for uptake by other tissues to convert to acetyl CoA
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11
Q

What is the signal transduction pathway leads to lipolysis?

A
  • Glucagon/Adrenalin –> Adenylyl cyclase –> cAMP –> protein kinase A (PKA)
  • PKA activates hormone sensitive lipase (HSL)
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12
Q

What hormone deactivates HSL?

A

Insulin

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13
Q

What might be generated from beta oxidation?

A
  • Some ATP generated through reduction electron carriers

- Acetyl CoA (used to make ketone bodies)

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14
Q

Describe the metabolism of short chain fatty acids

A
  • 2-4 carbons
  • Site of catabolism- mitochondrion
  • Membrane transport- diffusion
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15
Q

Describe the metabolism of medium chain fatty acids

A
  • 4-12 carbons
  • Site of catabolism- mitochondrion
  • Membrane transport- diffusion
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16
Q

Describe the metabolism of long chain fatty acids

A
  • 12-20 carbons
  • Site of catabolism- mitochondrion
  • Membrane transport- carnitine cycle
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17
Q

Describe the metabolism of very-long chain fatty acids

A
  • Site of catabolism- peroxisome

- First shortened to long chains in the peroxisome

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18
Q

How are fatty acids activated?

A
  • Prior to oxidation, fatty acids are activated by a reaction that creates a thirster linkage to CoA
19
Q

What is the enzyme that catalyses the two-step process that forms fatty acyl CoA?

A

Fatty acid thiokinase

20
Q

What are the reactions that take place to form Acyl CoA from fatty acids?

A
  • Fatty acid + ATP –> Acyl adenylate + PPi
    (oxygen replaced with AMP)
  • Acyl adenylate + HS-CoA –> Acyl CoA + AMP
21
Q

Why is the carnitine shuttle required?

A
  • CoA is a large polar molecule derivative which cannot penetrate the inner mitochondrial membrane
22
Q

Describe the carnitine shuttle

A
  • CPT1 in the outer mitochondrial matrix swaps CoA bound to fatty acyl for carnitine
  • Enzyme transports fatty acyl carnitine into mitochondrial matrix
  • CPT-2 swaps carnitine back for CoA
  • Fatty acyl CoA is in matrix and free carnitine is pumped back into inter-membrane space
23
Q

What is CPT-1 and 2?

A

Carnitine palmitoyl transferase-1 and 2

24
Q

What enzyme transports fatty acyl carnitine into mitochondrial matrix?

A

Carnitine acyl carnitine translocase

25
Q

What is the first oxidation step of beta oxidation?

A
  • Activated fatty acid
  • Enzyme Acyl CoA dehydrogenase
  • FAD –> FADH2
  • Forms Acyl- CoA
26
Q

Describe the hydration step of beta oxidation

A
  • Addition of water

- Hydratase enzyme

27
Q

Describe the 2nd oxidation step of beta oxidation

A
  • Hydroxy acyl CoA dehydrogenase enzyme
  • NAD+ –> NADH H+
  • Beta carbon is oxidised to a ketone and electrons are transferred to NAD+
28
Q

Describe cleavage step of beta oxidation

A
  • Thiolase enzyme
  • Addition of CoA
  • Cleavage of last 2 carbons with CoA attached. (2 carbon = acetyl CoA)
    Produces Acetyl CoA that can enter TCA cycle
  • Remaining chain undergoes beta oxidation again until all used up
29
Q

How is beta oxidation different in unsaturated fatty acids?

A
  • Already partially oxidised and so produces less FADH2 , so less ATP, requires additional enzymes both to manipulate double bonds
30
Q

How is beta oxidation different in odd chain fatty acids?

A
  • Oxidation proceeds in the same way until final round of degradation
  • 3-carbon propionyl CoA is formed by last thiolase cleavage reaction
  • Propionyl converted to succinyl-CoA by a separate pathway and the enters TCA cycle
31
Q

How do branched chain fatty acids undergo beta oxidation?

A
  • An enzyme (acyl CoA Alpha-hydroxylase) will cleave a carbon dioxide and the chain left undergoes beta-oxidation.
32
Q

What is Adult Refsum Disease?

A
  • Type of leukodystrophies, which damage white matter if brain and affect motor movements
  • Autosomal recessive deficiency of PHYH needed for phytanic acid metabolism
  • Toxic levels of phytanic acid build up in brain, blood and other tissues
33
Q

What are the consequences of high levels of phytanic acid in ARD?

A
  • Late childhood onset with nigh blindness due to retinitis pigments and anosmia
  • deafness, ataxia, peripheral neuropathy, ichthyosis and cardiac arrythmias
  • Shortened bones in fingers and toes
34
Q

What is the treatment for ARD?

A

Avoid foods that contain phytanic acid- plasma exchange

35
Q

What are Peroxisome Biogenesis Disorders?

A
  • 3 autosomal recessive inherited disorders
  • Mutations in any of 13 PEX genes that encode peroxins- proteins necessary to make peroxisomes
  • Very long chain fatty acids are shortened to long chains in peroxisome
36
Q

How does peroxisome biogenesis disorder affect plasma concentration of VLCFA?

A
  • Elevated concentration of very long chain fatty acid

- Indicates defects in peroxisomal fatty acid metabolism

37
Q

What are the three peroxisome biogenesis disorders?

A
  • Zellweger syndrome
  • Neonatal adrenoleukodystrophy
  • infantile refuse disease
38
Q

What can brain disorders result in?

A
  • Skeletal and craniofacial dysmorphism
  • Liver dysfunction
  • Progressive sensorineural hearing loss
  • Retinopathy
39
Q

Which peroxisome biogenesis disorder is the most severe?

A

Zellweger syndrome

  • Most infants do not survive past 1st 6 months
  • Death from respiratory distress, GI bleeding or liver failure
40
Q

What is Medium-Chain Acyl CoA Dehydrogenase deficiency (MCAD)?

A
  • Recessive deficiency of medium chain acyl-CoA dehydrogenase, most common genetic disease relating to fatty acid metabolism
  • Linked to sudden infant death
41
Q

What is MCAD characterised by?

A
  • Hyoketotic hypoglycaemia
  • In response to fasting or metabolic stress (e.g. illness)
  • Body unable to metabolise fat (so no ketones produced)
  • Continues to metabolise glucose producing hypoglycaemia
42
Q

How does MCAD present?

A
  • Infants older than three months when overnight feeding reduced
  • Gap between feeds long enough for acute hypoglycaemia to occur
  • Produces symptoms of preprandial irritability, drowsiness, jitteriness, sweating, coma and seizures
43
Q

What is the treatment for MCAD?

A

Avioid fasting

Metabolism (9 decks)

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