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biochemistry iii > LECTURE 5 (Lipid degradation) > Flashcards

LECTURE 5 (Lipid degradation) Flashcards

1
Q

What are the properties of Fatty acids in the body?

A
  • Stored in adipose tissue (as TAGs)
  • Serve as the body’s major fuel storage reserve
  • Yield from complete oxidation of Fatty acids to CO2 and H2O is 9 kcal/g (higher than in proteins + carbohydrates)
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2
Q

What is Hormone-sensitive lipase?

A

An enzyme that removes fatty acid from TAG in adipocytes

ACTIVATION: by glucagon and epinephrine

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3
Q

What happens when Fatty acids are released from TAG?

A

Free fatty acids move through the cell membrane of adipocyte -> Bind to plasma ALBUMIN -> Transported to tissues -> Oxidised for energy

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4
Q

What happens to Glycerol released during TAG degradation?

A

It cannot be metabolised by adipocytes because they lack GLYCEROL KINASE -> Glycerol is transported through the blood to the liver where it can be phosphorylated -> Glycerol phosphate can be used to form TAG in liver or converted to DHAP

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5
Q

Why is Glycerol easily transported to liver?

A

Glycerol is water-soluble

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6
Q

Which processes are Facilitated by Insulin?

A
  • Glucose entering White adipose tissue via GLUT 4
  • Lipogenesis (conversion into fatty acids)
  • Esterification of fatty acids into TAGs
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7
Q

Which process is inhibited by Insulin?

A

Breakdown of TAGs into Fatty acids

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8
Q

Describe Fatty acid breakdown

A
  • Fatty acids transported via Albumin
  • Taken up by tissues
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9
Q

What is Fatty acid breakdown not used by?

A
  • RBC: glycolysis only (no mitochondria)
  • BRAIN: glucose and ketones only
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10
Q

Why does brain metabolism not favour the burning of fatty acids to provide energy?

A
  • ATP generation linked to B-oxidation of fatty acids demands more O2 than glucose -> enhance risk for neurons to become HYPOXIC
  • B-oxidation of fatty acids generates SUPEROXIDE
    [poor anti-oxidative defense in neurons -> severe oxidative stress]
  • Rate of ATP generation from Fatty acids to too slow
    [cannot keep up with rapid, continuous neuronal firing]
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11
Q

What happens when Fatty acids reach tissues?

A

Fatty acids metabolised by BETA-OXIDATION mitochondrial pathway -> 2-carbon units are removed from FAs -> Produces acetyl-CoA, NADH and FADH2

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12
Q

What is the function of the Carnitine shuttle?

A

Transport long-chain fatty acyl CoA subunits across mitochondrial membranes from outside to inside

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13
Q

Describe the steps of Beta-oxidation of Fatty acids

A

1) Fatty acid conversion into FATTY ACYL-COA
2) Transport of fatty acyl-CoA from cytosol into inner mitochondria
3) Beta-oxidation

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14
Q

What is the Carnitine shuttle inhibited by?

A

MALONYL-COA

Explanation: When fatty acid synthesis occurs in cytosol -> newly make palmitate cannot be transferred into mitochondria and is degraded

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15
Q

What are the properties of Carnitine?

A
  • Obtained from meat
  • Synthesised from lysine and methionine
  • De novo synthesis only in liver & kidney
  • Skeletal muscle contains 97% of all carnitine in body
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16
Q

Describe Carnitine deficiencies

A

CAUSES:
- Malnutrition or strictly vegetarian diet
- Liver disease (decreased synthesis)
- Increased requirements (trauma, burns, pregnancy)
- Hemodialysis (decreased synthesis, loss through membranes)

MAJOR CONSEQUENCE:
Inability to transport long-chain fatty acids (LCFA) to mitochondria -> accumulation of LCFA in cells

SYMPTOMS:
- Muscle weakness
- Cardiomyopathy
- Hypoketotic hypoglycaemia
[ explanation: when fasting tissues overuse glucose & poor ketone synthesis without acid breakdown ]

17
Q

Describe Primary Systemic Carnitine deficiency

A

A rare metabolic disorder in which the body cannot properly process fats into energy. There is a mutation affecting carnitine uptake into cells which inhibits transport of LCFAs into mitochondria -> Toxic accumulation.

SYMPTOMS:
- Weakness & Hypotonia
- Hypoketotic hypoglycaemia
- Hepatomegaly

Treatment:
- Avoid prolonged fats
- Adopt diet high in carbs and low in LCFA
- Supplemented with medium-chain fatty acids and carnitine

Infantile phenotype presents during the first two years of life

18
Q

Which Fatty acids can cross the inner mitochondrial membrane without the aid of carnitine?

A

Fatty acids shorter than 12 carbons

19
Q

What does Beta-oxidation generate?

A
  • NADH
  • FADH2
  • Acetyl-CoA
20
Q

Which enzyme adds a double bond between alpha and beta carbons?

A

Acyl-CoA dehydrogenase

[first step in Beta-oxidation]

21
Q

Acyl-CoA dehydrogenase is a family of which 4 enzymes?

A
  • Short (2-6)
  • Medium (6-12)
  • Long (13-21)
  • Very-long (>21)
    chain fatty acids
22
Q

Describe Medium-chain Acyl-CoA dehydrogenase (MCAD) deficiency

A

An autosomal recessive disorder that decreases the ability to break down 6-12 carbon fatty acids into acetyl-CoA causing an accumulation of FATTY ACYL CARNITINES IN BLOOD

SYMPTOMS:
- Hypoketotic hypoglycaemia
- Dicarboxylic acids in urine
- High acylcarnitine level

23
Q

Why is hypoglycaemia found in MCAD deficiency?

A

Gluconeogenesis is shutdown
[ explanation: pyruvate carboxylase activity depends on acetyl-coa and these levels are low in the absence of beta-oxidation ]

SYMPTOMS:
- Vomiting
- Lethargy
- Seizures
- Coma
- Can lead to sudden death in infants or children (SIDS)

Exacerbated in fasting/infection

TREATMENT:
- Avoid fasting

24
Q

Describe Odd-chain fatty acid metabolism

A
  • Beta-oxidation proceeds until 3 carbons remain
  • PROPRIONYL-COA -> SUCCINYL-COA -> TCA CYCLE
  • Odd-chain fatty acid -> can be used in gluconeogenesis -> to produce glucose
25
Q

Which acid is elevated in B12 deficiency?

A

Methylmalonic acid/MethylMalonyl-CoA

26
Q

What does Oxidation of molecule of Palmitoyl CoA to CO2 and H2O produce?

A
  • 8 acetyl-CoA
  • 7 NADH
  • 7 FADH2
  • 131 ATP
27
Q

What is the net yield of ATP from palmitate?

A

Activation of fatty acid required 2 ATP -> Net yield from palmitate is 129 ATP

28
Q

What is Peroxisome involved in?

A
  • Beta-oxidation of Very long-chain fatty acids (VLCFA)
  • Alpha-oxidation of branched-chain fatty acids
  • Catabolism of amino acids and ethanol
  • Synthesis of cholesterol, bile acids and plasmalogens
29
Q

What are the Peroxisome Clinical Correlations?

A
  • Zellweger syndrome
  • Refsum disease
  • Adrenoleukodystrophy
30
Q

Describe Zellweger syndrome

A

Autosomal recessive disorder of Peroxisome biogenesis due to mutated PEX genes

SYMPTOMS:
- Hypotonia
- Seizure
- Hepatomegaly
- Early death

31
Q

Describe Refsum disease

A

Autosomal recessive disorder of alpha-oxidation causing buildup of PHYTANIC ACID due to inability to degrade it

SYMPTOMS:
- Scaly skin
- Ataxia
- Cataracts/night blindness
- Shortening of 4th toe
- Epiphyseal dysplasia

32
Q

Describe Adrenoleukodystrophy

A

X-linked recessive disorder of beta-oxidation causing VLCFA buildup in adrenal glands, white (Leuko) matter of brain and in testes

33
Q
A

biochemistry iii (12 decks)

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