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SP MCAT Biochem > Lipid & Amino Acid Metabolism > Flashcards

Lipid & Amino Acid Metabolism Flashcards

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MCAT flashcards
1
Q

Where does mechanical digestion of lipids primarily occur?

A

mouth and stomach

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2
Q

What facilitates chemical digestion of lipids in the small intestine?

A
  • bile
  • pancreatic lipase
  • colipase
  • cholesterol esterase
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3
Q

How are short-chain fatty acids absorbed?

A

absorbed across the intestine into the blood via simple diffusion

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4
Q

How are long-chain fatty acids absorbed?

A

absorbed as micelles and assembled into chylomicrons for release into the lymphatic system

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5
Q

Micelles

A
  • collections of lipids with their hydrophobic ends oriented toward the center and their changed ends oriented toward the aqueous environment
  • collect lipids within their hydrophobic centers
  • water-soluble
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6
Q

Hormone-Sensitive Lipase

A
  • activated by a fall in insulin levels
  • hydrolyzes triacylglycerols, yielding fatty acids and glycerol
  • effective within adipose cells
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7
Q

Lipoprotein Lipase

A
  • necessary for metabolism of chylomicrons and very-low-density liporpoteins
  • enzyme that can release free fatty acids from triacylglycerols in lipoproteins
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8
Q

What is the ration of free fatty acids to glycerol?

A

3:1

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9
Q

What are free fatty acids associated with as they are transported through the blood?

A

albumin (carrier protein)

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10
Q

Lipoproteins

A
  • aggregates of apolipoproteins and lipids

- transport triacylglycerol and cholesterol in the blood

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11
Q

Chylomicrons

A
  • least dense
  • highest fat-to-protein ratio
  • transport dietary triacylglycerols, cholesterol, and cholesteryl esters from intestine to tissues
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12
Q

VLDL

A
  • produced and assembled in liver cells

- transports triacylglycerols and fatty acids from liver to tissues

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13
Q

IDL

A
  • intermediate density lipoprotein – VLDL remnants
  • picks up cholesteryl esters from HDL to become LDL
  • picked up by the liver
  • it is a transition state between VLDL and LDL, occurring as the primary lipid within the lipoprotein changes from triacylglycerol to cholesterol
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14
Q

LDL

A

delivers cholesterol into cells

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15
Q

HDL

A
  • picks up cholesterol accumulating in blood vessels and delivers it to liver and steroidogenic tissues
  • transfers apolipoproteins to other lipoproteins
  • synthesized in the liver and intestines
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16
Q

Cholesterol

A
  • ubiquitous component of all cells

- plays a major role in synthesis of cell membranes, steroid hormones, bile acids, and vitamin D

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17
Q

Lecithin-Cholesterol Acyltransferase (LCAT)

A
  • specialized enzyme involved in transport of cholesterol
  • enzyme found in the bloodstream that is activated by HDL apoproteins
  • adds a fatty acid to cholesterol which produces soluble cholesteryl esters
18
Q

Cholesteryl Ester Transfer Protein (CETP)

A

enzyme that promotes the transfer of cholesteryl esters from HDL to IDL, forming LDL

19
Q

Fatty Acid Synthesis

A
  • takes place when there is excess energy to store – excess acetyl-CoA
  • occurs in the cytosol of liver cells
  • starting materials: acetyl Co-A, malonyl-CoA
20
Q

Steps of Fatty Acid Synthesis (7):

A
  1. Acetyl-CoA Carboxylase adds CO2 to acetyl-CoA to form malonyl-CoA
  2. attachment of malonyl-CoA to Acyl Carrier Protein (subunit of Fatty Acid Synthase)
  3. BOND FORMATION between malonyl-ACP and growing fatty acid chain
  4. REDUCTION of carbonyl group in fatty acid chain to hydroxyl group, while oxidizing NADPH to NADP+
  5. DEHYDRATION of fatty acid chain
  6. REDUCTION of double bond in fatty acid chain while oxidizing NADPH to NADP+
  7. reactions above continue until the 16 carbon palmitate molecule is created
21
Q

Acetyl-CoA Carboxylase

A
  • rate-limiting enzyme of fatty acid synthesis
  • requires biotin and ATP to function
  • adds CO2 to acetyl-CoA to form malonyl-CoA
  • activated by insulin and citrate
22
Q

Fatty Acid Synthase

A
  • large multi-enzyme complex found in the cytosol
  • rapidly induced in the liver following a meal high in carbs due to increased insulin levels
  • contains an acyl carrier protein (ACP) that requires vitamin B5
  • requires NADPH
23
Q

What is the only fatty acid that can be synthesized by the human body?

A

Palmitic Acid (16:0)

24
Q

How many Acetyl-CoA groups are required to produce palmitic acid?

A

8

25
Q

Beta-Oxidation

A
  • fatty acid catabolism – reverse process of fatty acid synthesis by oxidizing and releasing (rather than reducing and linking)
  • occurs in the mitochondria of the liver
  • inhibited by insulin
  • activated by glucagon
  • pathway is a repetition of 4 steps
  • each 4 step cycle releases 1 acetyl-CoA and reduces NAD+ to FAD (producing NADH and FADH2)
26
Q

Steps of Beta-Oxidation:

A
  1. OXIDATION of fatty acid to form a double bond, while reducing FAD to FADH2
  2. HYDRATION of double bond in fatty acid to from a hydroxyl group
  3. OXIDATION of hydroxyl group to form a carbonyl (beta-ketoacid) while reducing NAD+ to NADH
  4. SPLITTING of the beta-ketoacid into a shorter acyl-CoA and acetyl-CoA
  5. process continues until chain has been shortened to two carbons, creating a final acetyl-CoA
27
Q

What does beta-oxidation of an even-numbered fatty acid yield?

A

2 acetyl-CoA molecules

28
Q

What does beta-oxidation of an odd-numbered fatty acid yield?

A

1 acetyl-CoA and 1 propionyl-CoA (which is eventually converted into succinyl-CoA)

29
Q

___-___ fatty acids represent an exception to the rule that fatty acids cannot be converted to glucose in humans

A

odd-carbon

30
Q

How does beta-oxidation of unsaturated fatty acids differ from that of saturated fatty acids?

A

there is an additional isomerase (Enoyl-CoA Isomerase) and an additional reductase (2,4-Dienoyl-CoA Reductase) for the beta-oxidation of unsaturated fatty acids, which provide the stereochemistry necessary for further oxidation

31
Q

Ketone Bodies

A
  • essentially transportable forms of acetyl-CoA
  • produced by the liver when it converts excess acetyl-CoA from beta-oxidation of fatty acids into these
  • used by other tissues during prolonged starvation
32
Q

Ketogenesis

A
  • occurs in mitochondria of liver cells when excess acetyl-CoA accumulates in the fasting state
  • acetyl-CoA is broken down by HMG-CoA Synthase into HMG-COA which is then broken down by HMG-CoA Lyase into Acetoacetate
  • minor side product of this is acetone which can be found in the blood
33
Q

Ketolysis

A
  • regenerates acetyl-CoA for use as an energy source in peripheral tissues
  • acetoacetate picked up from blood is activated in the mitochondria by Succinyl-CoA Acetoacetyl-CoA Transferase to form acetoacetyl-CoA which then turns into 2 acetyl-CoA that can be used in CAC
34
Q

Can the liver catabolize the ketone bodies that it produces?

A

No, because it lacks the enzyme Succinyl-CoA Acetoacetyl-CoA Transferase

35
Q

Proteolysis

A
  • breakdown of proteins

- primarily occurs in the small intestine

36
Q

Protein Catabolism

A
  • only occurs under conditions of starvation

- results in 3 products: carbon skeleton, amino group, sde chains

37
Q

What is the fate of the carbon skeleton after protein catabolism?

A

transport to the liver for processing into glucose or ketone bodies

38
Q

What is the fate of the amino group after protein catabolism?

A

feed into the urea cycle for excretion

39
Q

What is the fate of the side chains after protein catabolism?

A
  • processed depending on their composition
  • basic side chains will be processed like amino groups while other functional groups will be treated lie the carbon skeleton
  • glucogenic amino acids can be converted into glucose through gluconeogenesis
  • ketogenic amino acids can be converted into acetyl-CoA and ketone bodies
40
Q

What amino acids are ketogenic?

A
  • lysine

- leucine

41
Q

What amino acids are both ketogenic and glucogenic?

A
  • Tabbys Take Pictures In Turrets*
  • Tyrosine
  • Tryptophan
  • Phenylalanine
  • Isoleucine
  • Threonine

SP MCAT Biochem (16 decks)

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