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USMLE Biochemistry > Fatty acids > Flashcards

Fatty acids Flashcards

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USMLE® Step 1 flashcards
1
Q

What 2 molecules make up a triglyceride?

A
  • 3 Fatty acids

- Glycerol

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2
Q

What are most lipids taken up as in the intestine?

A

Degraded to free fatty acids in intestine

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3
Q

What do enterocytes convert fatty acids to?

A

Triacylglycerol (triglycerides)

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4
Q

In what form are lipids carried through the plasma

A

As chylomicrons

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5
Q

What structure/fluid carried the chylomicrons away from the intestine?

A

The lymph in the lacteal

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6
Q

Once the triglycerides reach their target tissue what are the converted back into and by what enzyme?

A

Converted back to free fatty acids by lipoprotein lipase

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7
Q

Where can lipoprotein lipase be found?

A
  • Endothelial surface of capillaries

- Abundant in adipocytes and muscle tissue

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8
Q

What does saturated fat refer to?

A

Contains no double bonds

  • ‘Saturated’ w. hydrogen
  • Solid at room temo
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9
Q

What is an unsaturated fat?

A

Fat / fatty acid contains at least one double bound

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10
Q

What is a polyunsaturated and monounsturated fat?

A
  • Monounsaturated: One double bond

- Polyunsaturated: More than one double bond

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11
Q

What does trans and cis fats refer to?

What fats are good and bad?

A

The location of the double bond in an unsaturated fat

  • Trans fats have double bonds on both sides of the molecule -> making them straight
  • Cis fats have double bonds only on one side
  • Trans can increase LDL, lower HDL
  • Omega 3 (double bond, 3 carbons from omega end), can lower triglyceride levels
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12
Q

Through what process are trans fats created?

A

Partial hydrogenation (food processing method)

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13
Q

What are fatty acids synthesised from?

A
  • Liver
  • Mammary glands
  • Adipose tissue
  • Excess carbs and proteins -> fatty acids
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14
Q

Where are fatty acids stored and in what form?

A
  • Adipose tissue

- Stored as triglycerides

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15
Q

Through what process are fatty acids broken down into Acetyl CoA?

A

Beta-oxidation

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16
Q

What molecule are fatty acids broken down into to then yield ATP?

A

Acetyl CoA

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17
Q

How does a ‘fed’ individual get a high citrate level?

A

Lots of acetyl-CoA -> TCA cycle -> build up of ATP

  • ATP inhibits isocitrate dehydrogenase (rate limiting step of TCA cycle)
  • Citrate then builds up as TCA cycle has slowed down
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18
Q

What does a high citrate levels indicate?

A

Indicates high levels of excess energy in the cell

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19
Q

What enzyme combines acetyl-CoA and oxaloacetate to make citrate?

A

Citrate synthase

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20
Q

What molecule can cross the mitochondrial membrane acetyl coA or citrate?

A

Citrate - via the citrate shuttle

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21
Q

How does citrate block glycolysis?

A

Inhibits PFK1

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22
Q

Describe how citrate is converted to Acetyl-CoA

What are the other substrates?

What enzyme?

A

Citrate -> Acetyl CoA

CoA -> Oxaloacetate
ATP -> ADP

Enzyme: ATP-Citrate Lyase

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23
Q

What is the rate limiting step of fatty acid synthesis?

A

Acetyl coA -> Malonyl-CoA

CO2 -> (adds carbon)

Enzyme: Acetyl-CoA Carboxylase

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24
Q

What is the rate-limiting enzyme of fatty acid synthesis?

A

Acetyl-CoA carboxylase

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25
Q

What is the cofactor for acetyk-CoA Carboxylase?

A

Biotin

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26
Q

What substances increase the activity of Acetyl-CoA carboxylase?

A
  • Citrate

- Insulin

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27
Q

What substances decrease the activity of Acetyl-CoA carboxylase?

A
  • Glucagon

- Epinephrine

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28
Q

What does Malonyl-coA inhibit?

A

B-oxidation

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29
Q

What does biotin act as a cofactor for?

A

Caboxylation enzymes

  • Adds 1-carbon groups via CO2
  • Pyruvate carboxylase (gluconeogenesis)
  • Acetyl-CoA carboxylase (fatty acid synthesis)
  • Propionyl-CoA carboxylase
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30
Q

What is Palmitate a result of combining?

A
  • Acetyl CoA

- Malonyl CoA

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31
Q

How many carbons are in palmitate?

A

16

32
Q

What enzyme converts Acetyl CoA and Malonyl CoA into Palmitate?

A

Fatty acid synthase (final step of fatty acid synthesis)

33
Q

What does Fatty acid synthase require to convert Acetyl CoA and Malonyl CoA into Palmitate?

A

NADPH (from HMP shunt)

34
Q

What are fatty acids stored as?`

A

Triacylglycerols in adipose tissue

35
Q

What is the key enzyme in fatty acid breakdown?

A

Hormone sensitive lipase

36
Q

What is hormone sensitive lipase activated by?

A
  • Glucagon

- Epinephrine

37
Q

What does Hormone sensitive lipase do?

A

Removes fatty acids from TAG in adipocytes

38
Q

What intermediate of glycolysis/gluconeogenesis can Glycerol be converted into in the liver?

A

Dihydroxyacetone Phosphate

39
Q

What is Glycerol first converted into before Dihydroxyacetone Phosphate?

A

Glycerol-3-Phosphate (via Glycerol Kinase)

40
Q

What enzyme converts Glycerol into Glycerol-3-Phosphate?

A

Glycerol Kinase

41
Q

What enzyme converts Glycerol-3-Phosphate into Dihydroxyacetone phosphate?

A

Glycerol-3-Phosphate Dehydrogenase

42
Q

What are fatty acids transported via?

A

Albumin

- Glycerol is soluble so can freely transport

43
Q

What tissues do not use fatty acids as energy?

A
  • RBCs (glycolysis only, no mitochondria)

- Brain (glucose and ketones only)

44
Q

What does B-oxidation produce from fatty acids?

A
  • Acetyl CoA
  • NADH
  • FADH2
45
Q

What does the first step of Beta-oxidation involve?

A

Fatty acid being converted to fatty acyl CoA by:

  • Long chain fatty acyl CoA synthetase
  • CoA added
  • ATP -> ADP
46
Q

What does the second step od B-oxidation involve?

A

Transport of fatty acyl coA to the inner mitochondria

47
Q

How is fatty acyl coA transported to the inner mitochondria?

A

Carnitine shuttle

48
Q

How can you get carnitine?

A

Diet

From lysine and methionine

  • Liver and kidney denovo
  • Muscle and heart depened on diet or other tissues
49
Q

How is fatty acyl CoA transported to the mitochondrial matrix?

A

Can pass into inner membrane space

  • Converted here to Acyl Carnitine by Carnitine Palmitoyl Transferase-1 (requires carnitine)
  • Acyl Carnitine can travel through inner membrane
  • CPT-2 enzyme with CoA can convert Acyl Carnitine into Fatty acyl CoA
50
Q

What does Carnitine Palmitoyl Transferase-1 do?

A

Replaces the CoA on Fatty Acyl CoA with Carnitine to make Acyl Carnitine

51
Q

Where is Carnitine Palmitoyl Transferase-1 found?

A

On the outer membrane of the mitochondria

- Molecules in cytosol can effect it

52
Q

What inhibits Carnitine Palmitoyl Transferase-1?

A

Malonyl-CoA

53
Q

What enzyme converts Acyl Carnitine in the mitochondrial matrix into Fatty Acyl CoA?

A

CPT-2 (with CoA)

54
Q

What can cause carntine deficiency?

A
  • Malnutrition
  • Liver disease
  • Increased requirements (trauma, burns, pregnancy)
  • Hemodialysis (decreased synthesis; loss through membranes)
55
Q

What does carnitine deficiency result in?

A
  • Inability to transport LCFA to mitochondria
  • Accumulation of LCFA in cells
  • Low serum carnitine and acylcarnitine levels
56
Q

What are the symtpoms/signs of carnitine deficiency?

A
  • Muscle weakness, esp during exercise
  • Cardiomyopathy
  • Hypoketotic hypoglycemia when fasting, tissues overuse glucose, poor ketone synthesis w/o fatty acid breakdown
57
Q

What is primary systemic carnitine deficiency a mutation in?

A
  • Mutation affecting carnitine uptake into cells
58
Q

What are the signs symptoms of primary systemic carnitine deficiency?

A

Infantile phenotype presents in first two years of life

  • Encephalopathy
  • Hepatomegaly
  • Hyperammonia (liver dysfunction)
  • Hypoketoic hypoglycemia
  • Low serum carnitine, kidneys cannot resorb it
  • Reduced carnitine levels in muscle, liver, heart (biopsies)

All due to build-up of fatty acids which cannot be metabolised

59
Q

What does Beta oxidation involve?

What does it generate?

A

Removal of 2 carbons in each beta oxidation cycle

  • Shortens chain
  • Generates NADH, FADH2, Acetyl CoA
60
Q

What is the enzyme in the first step of B-oxidation?

A

Acyl-CoA dehydrogenase

  • Adds double bond between alpha and B carbon
  • B carbon is oxidised
  • alpha carbon and acetyl coA broken off
  • Genrates an FADH2
61
Q

What are the 4 acyl-CoA Dehydrogenases?

A
  • Short
  • Medium
  • Long
  • Very long
62
Q

What acyl-CoA Dehydrogenase is most commonly deficient?

A

Medium chain Aceyl-CoA dehydrogenase (MCAD)

63
Q

What are the specific signs of MCAD deficiency? why do you get these signs?

A
  • Poor oxidation of 6-10 carbon fatty acids
  • Dicarboxylic acids 6-10 carbons in urine
  • High acylcarnitine levels (as build up)
  • Severe hypoglycemia w/o ketones
  • Gluconeogenesis shut-down as pyruvate carboxylase requires acetyl oA which is low in absnce of B-oxidation
64
Q

How is MCAD deficiency inherited?

A

Aut Recessive

65
Q

How is MCAD deficiency exacerbated?

A

Fasting/infection

- Treatment is to avoid fasting

66
Q

What are odd chain fatty acids broken down into by B-oxidation (acyl-CoA Dehydrogenase)?

A

Propionyl-CoA (cannot be broken down further)

67
Q

What is propionyl coA then converted into if it cannot be fully broken down by B-oxidation (acyl-CoA Dehydrogenase)?

A

Converted to Succinyl-CoA

68
Q

What enzyme breaks down propionyl-CoA into Succinyl-CoA?

A

Propionyl-CoA Carboxylase (biotin cofactor)

69
Q

Can odd or even FA be converted to glucose?

A

Only odd chain

70
Q

What is proprionyl coA first converted into before Succinyl-CoA?

A

MethylMalonyl-CoA (biotin required)

71
Q

What reaction requires B12?

A

MethylMalonyl-CoA to Succinyl-CoA

72
Q

What can be converted to Proprionyl coA?

A

Amino acids
Cholesterol
Odd chain fatty acids

73
Q

What is methylmalonic acidemia due to a deficiency in?

A

Deficiency in Methylmalonyl-CoA mutase
Converts:
- MMCoA -> Succinyl CoA

74
Q

What are the signs/symptoms of Methylmalonic acidemia?

A
  • Anion gap acidosis
  • CNS dysfunction
  • Often fatal in early life
75
Q

How are Methylmalonyl-CoA and Succinyl-CoA similar?

A

Isomers of each other

USMLE Biochemistry (44 decks)

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