Metabolism > Fats- Lipolysis and Beta Oxidation > Flashcards

Fats- Lipolysis and Beta Oxidation Flashcards

(43 cards)

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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?

Study These Flashcards
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?

Study These Flashcards
A

Fatty acid thiokinase

20
Q

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

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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?

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

Describe the carnitine shuttle

Study These Flashcards
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?

Study These Flashcards
A

Carnitine palmitoyl transferase-1 and 2

24
Q

What enzyme transports fatty acyl carnitine into mitochondrial matrix?

Study These Flashcards
A

Carnitine acyl carnitine translocase

25
What is the first oxidation step of beta oxidation?
- Activated fatty acid - Enzyme Acyl CoA dehydrogenase - FAD --> FADH2 - Forms Acyl- CoA
26
Describe the hydration step of beta oxidation
- Addition of water | - Hydratase enzyme
27
Describe the 2nd oxidation step of beta oxidation
- Hydroxy acyl CoA dehydrogenase enzyme - NAD+ --> NADH H+ - Beta carbon is oxidised to a ketone and electrons are transferred to NAD+
28
Describe cleavage step of beta oxidation
- 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
How is beta oxidation different in unsaturated fatty acids?
- Already partially oxidised and so produces less FADH2 , so less ATP, requires additional enzymes both to manipulate double bonds
30
How is beta oxidation different in odd chain fatty acids?
- 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
How do branched chain fatty acids undergo beta oxidation?
- An enzyme (acyl CoA Alpha-hydroxylase) will cleave a carbon dioxide and the chain left undergoes beta-oxidation.
32
What is Adult Refsum Disease?
- 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
What are the consequences of high levels of phytanic acid in ARD?
- 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
What is the treatment for ARD?
Avoid foods that contain phytanic acid- plasma exchange
35
What are Peroxisome Biogenesis Disorders?
- 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
How does peroxisome biogenesis disorder affect plasma concentration of VLCFA?
- Elevated concentration of very long chain fatty acid | - Indicates defects in peroxisomal fatty acid metabolism
37
What are the three peroxisome biogenesis disorders?
- Zellweger syndrome - Neonatal adrenoleukodystrophy - infantile refuse disease
38
What can brain disorders result in?
- Skeletal and craniofacial dysmorphism - Liver dysfunction - Progressive sensorineural hearing loss - Retinopathy
39
Which peroxisome biogenesis disorder is the most severe?
Zellweger syndrome - Most infants do not survive past 1st 6 months - Death from respiratory distress, GI bleeding or liver failure
40
What is Medium-Chain Acyl CoA Dehydrogenase deficiency (MCAD)?
- Recessive deficiency of medium chain acyl-CoA dehydrogenase, most common genetic disease relating to fatty acid metabolism - Linked to sudden infant death
41
What is MCAD characterised by?
- 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
How does MCAD present?
- 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
What is the treatment for MCAD?
Avioid fasting

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