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BM 210: Introduction to Biochemistry > Block D Part 2: Post-Absorptive State > Flashcards

Block D Part 2: Post-Absorptive State Flashcards

1
Q

What are the only 2 fats that are essential to our diet?

A

Linoleic acid [C18:2] and linolenic acid [C18:3]
(Lecture 2, Slide 4)

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2
Q

What 4 lipid-soluble vitamins are only present in dietary fat and require fat for absroption?

A

Vitamins A,D,E and K
(Lecture 2, Slide 4)

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3
Q

What does fat do to food in the mouth?

A

It lubricates it and contains most of the favour
(Lecture 2, Slide 4)

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4
Q

What are the 3 types of fat in our diet and body?

A

Triacylglycerols
Phospholipids
Cholesterol
(Lecture 2, Slide 5)

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5
Q

What are phospholipids made of?

A

2 fatty acids and a head group attached to glycerol
(Lecture 2, Slide 5)

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6
Q

What are 4 common head groups of phospholipids?

A

Phosphocholine
Phosphoethanolamine
Phosphoserine
Phosphoinositol
(Lecture 2, Slide 8)

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7
Q

What carries out digestion of fat?

A

Lipases
(Lecture 2, Slide 9)

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8
Q

What are 4 types of lipase?

A

Lingual lipase
Gastric lipase
Pancreatic lipase
Phospholipase
(Lecture 2, Slide 9)

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9
Q

Are lipids hydrophilic or hydrophobic?

A

Hydrophobic
(Lecture 2, Slide 10)

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10
Q

Are lipids insoluble or soluble in aqueous environments?

A

Insoluble
(Lecture 2, Slide 10)

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11
Q

What are needed to transport lipids around the body?

A

Lipoproteins
(Lecture 2, Slide 10)

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12
Q

What is the process of fatty acid oxidation called?

A

ß-oxidation
(Lecture 2, Slide 11)

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13
Q

What are the 5 major steps in the oxidation of fatty acids in the mitochondria?

A

Activation
Oxidation
Hydration
Oxidation
Thiolysis
(Lecture 2, Slide 11)

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14
Q

What occurs in the activation stage of oxidation of fatty acids?

A

The fatty acid forms a thioester bond with CoA and then gets transported into the mitochondria
(Lecture 2, Slide 11)

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15
Q

What occurs in the first oxidation stage of oxidation of fatty acids?

A

2H removed forming an additional C=C double bond
(Lecture 2, Slide 11)

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16
Q

What occurs in the hydration stage of oxidation of fatty acids?

A

H2O is added across the double bond
(Lecture 2, Slide 11)

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17
Q

What occurs in the 2nd oxidation stage of oxidation of fatty acids?

A

C-OH bond is converted into C=O
(Lecture 2, Slide 11)

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18
Q

What occurs in the thiolysis stage of oxidation of fatty acids?

A

Acetyl-CoA cleaved from activated end
(Lecture 2, Slide 11)

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19
Q

What carrier does the transport of fatty acids into the mitochondria use?

A

Carnitine
(Lecture 2, Slide 13)

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20
Q

What is carnitine?

A

An acyl-carrier that transports fatty acid chains
(Lecture 2, Slide 13)

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21
Q

How are fatty acyls (fatty acids) converted to acetyl-CoAs?

A

Steps 2-5 of the oxidation process is repeated until the entire chain is converted into acetyl-CoAs
(Lecture 2, Slide 15)

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22
Q

How much ATP does each ß-oxidation cycle produce?

A

14
(Lecture 2, Slide 15)

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23
Q

How does each ß-oxidation cycle produce 14 ATP?

A

NADH - 2.5ATP
FADH2 - 1.5ATP
Acetyl CoA - 10ATP (via TCA cycle generating NADH, FADH2, GTP)
(Lecture 2, Slide 15)

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24
Q

How many cycles of oxidation does palmitate (C16:0) need to undergo to be completely converted to Acetyl CoA?

A

7
(Lecture 2, Slide 15)

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25
Q

What is the total yield of ATP from palmitate (C16:0)?

A

106
(Lecture 2, Slide 15)

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26
Q

How is 106 ATP produced from palmitate (C16:0)?

A

14 ATP from each ß-oxidation cycle x 7 cycles needed to fully convert palmitate to acetyl CoAs = 108 ATP - 2 ATPs needed to activate the fatty acid = 106 ATP
(Lecture 2, Slide 15)

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27
Q

What 2 additional enzymes are required in the degradation of unsaturated fatty acids?

A

cis-D 3-Enoyl CoA isomerase and 2,4-Dienoyl CoA reductase
(Lecture 2, Slide 16)

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28
Q

Why are cis-D 3-Enoyl isomerase and 2,4-Dienyol CoA reductase needed to degrade unsaturated amino acids?

A

cis-D 3-Enoyl CoA isomerase is needed for one C=C double bond and both cis-D 3-Enoyl CoA and 2,4-Dienoyl CoA reductase are needed for 2 C=C double bonds
(Lecture 2, Slide 16)

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29
Q

What is an odd chain fatty acid?

A

A fatty acid containing an odd number of carbons in its hydrocarbon chain
(Lecture 2, Slide 17)

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30
Q

What do odd chain fatty acids yield at the end of degradation?

A

Propionyl-CoA (3C)
(Lecture 2, Slide 17)

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31
Q

How is propionyl-CoA generated at the end of odd chain fatty acid degradation converted to succinyl CoA?

A

By the addition of bicarbonate
(Lecture 2, Slide 17)

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32
Q

What happens to succinyl-CoA after it has been converted from propionyl-CoA?

A

It enters the TCA cycle
(Lecture 2, Slide 17)

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33
Q

What is gluconeogenesis?

A

The conversion of pyruvate into glucose
(Lecture 2, Slide 20)

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34
Q

Where does pyruvate mainly occur?

A

In the liver
(Lecture 2, Slide 20)

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35
Q

What precursors can enter the gluconeogenesis pathway at later intermediates?

A

Non-carbohydrate precursors
(Lecture 2, Slide 20)

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36
Q

What are 4 major non-carbohydrate precursors?

A

Lactate
Propionate
Amino acids
Glycerol
(Lecture 2, Slide 20)

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37
Q

How are propionate and glycerol generated?

A

From hydrolysis of triacylglycerols
(Lecture 2, Slide 20)

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38
Q

What are the 3 irreversible steps (control sites) in the gluconeogenic pathway?

A

Glucose 6-phosphatase
Fructose 1,6-bisphosphatase
Pyruvate carboxylase + Phosphoenolpyruvate carboxylkinase
(Lecture 2, Slide 21)

39
Q

What 2 cells is glucose 6-phosphatase located in?

A

Liver cells (hepatocytes) and kidney cells
(Lecture 2, Slide 23)

40
Q

Where in the cell is glucose 6-phosphatase located?

A

In the membrane of the endoplasmic reticulum (ER)
(Lecture 2, Slide 23)

41
Q

How many proteins are needed to transform glucose 6-phosphate into glucose?

A

5
(Lecture 2, Slide 24)

42
Q

Which 5 proteins are required to convert glucose 6-phosphate into glucose and why?

A

Glucose 6-phosphatase to catalyse the hydrolysis of glucose 6-phosphate
SP - Ca2+ binding stabilising protein (binds to glucose 6-phosphatase)
T1 to transport glucose 6-phosphate into the endoplasmic reticulum (ER)
T2 to transport phosphate out the ER
T3 to transport glucose out the ER
(Lecture 2, Slide 24)

43
Q

How is glucose 6-phosphate converted into glucose?

A

It is transported into the endoplasmic reticulum and hydrolysed to give phosphate and glucose
(Lecture 2, Slide 24)

44
Q

What happens to phosphate and glucose after they are formed from glucose 6-phosphate during gluconeogenesis?

A

They are transported into the cytosol
(Lecture 2, Slide 24)

45
Q

What is the function of glucose 6-phosphatase?

A

It’s an enzyme which catalyses the hydrolysis of glucose 6-phosphate

Do not confuse glucose 6-phosphate with glucose 6-phosphatase, glucose 6-phosphate is the substrate and glucose 6-phosphatase is the enzyme
(Lecture 2, Slide 24)

46
Q

What is fructose 1,6-bisphosphatase?

A

A biologically active tetrameric enzyme which catalyses the hydrolysis of fructose 1,6-bisphosphate

Do not confuse fructose 1,6-bisphosphate with fructose 1,6-bisphosphatase, fructose 1,6-bisphosphate is the substrate and fructose 1,6-bisphosphatase is the enzyme
(Lecture 2, Slide 26)

47
Q

What is synergetic inhibition?

A

When the combined effects of 2 or more inhibitors on enzyme activity is greater than the sum of their individual effects
(Lecture 2, Slide 26)

48
Q

What 2 things synergistically inhibit fructose 1,6-bisphosphatase?

A

AMP and fructose 2,6-bisphosphate
(Lecture 2, Slide 26)

49
Q

How does AMP inhibit fructose 1,6-bisphosphatase?

A

By binding 28 Å away from the active site - allosteric inhibition
(Lecture 2, Slide 26)

50
Q

How does fructose 2,6-bisphosphate inhibit fructose 1,6-bisphoshatase?

A

By competing with fructose 1,6-bisphosphate in the active site
(Lecture 2, Slide 26)

51
Q

How much does fructose 2,6-bisphosphate enhance AMP inhibition of fructose 1,6-bisphosphatase?

A

3 - 10x
(Lecture 2, Slide 26)

52
Q

What activates fructose 1,6-bisphosphatase?

A

Citrate
(Lecture 2, Slide 26)

53
Q

Why can pyruvate not be converted to phosphoenolpyruvate (PEP) by pyruvate kinase?

A

As the reaction is irreversible under intracellular conditions
(Lecture 2, Slide 28)

54
Q

How is the reaction of phosphoenolpyruvate (PEP) to pyruvate by pyruvate kinase reversed?

A

By the coupling of 2 reactions requiring ATP and GTP
(Lecture 2, Slide 28)

55
Q

What is the first coupled reaction required in order to convert pyruvate into phosphoenolpyruvate and what enzyme does this require?

A

The conversion of pyruvate to oxaloacetate requiring the enzyme pyruvate carboxylase
(Lecture 2, Slide 29)

56
Q

Where in the cell is pyruvate carboxylase located?

A

In the mitochondria
(Lecture 2, Slide 29)

57
Q

What prosthetic group does pyruvate carboxylase carry?

A

Biotin
(Lecture 2, Slide 29)

58
Q

What does biotin function as?

A

A carrier for activated CO2
(Lecture 2, Slide 29)

59
Q

What complex does activated CO2 form with the biotin carried by the pyruvate carboxylase enzyme?

A

A carboxybiotin-enzyme complex
(Lecture 2, Slide 29)

60
Q

How is oxaloacetate formed from pyruvate?

A

The activated carboxyl group is transferred from the carboxybiotin-enzyme complex to pyruvate, forming oxaloacetate (carboxylation reaction)
(Lecture 2, Slide 29)

61
Q

Where does the oxaloacetate produced by pyruvate carboxylase need to be transported to in order for gluconeogenesis to proceed?

A

From the mitochondria to the cytosol
(Lecture 2, Slide 30)

62
Q

Oxaloacetate cannot leave the mitochondria to move into the cytosol, what are 3 ways it can become cytosolic?

A

Reduction to malate
Transamination to aspartate
Conversion to phosphoenolpyruvate (PEP)
(Lecture 2, Slide 30)

63
Q

What reduces oxaloacetate to malate?

A

Malate dehydrogenase linked to NADH
(Lecture 2, Slide 31)

64
Q

What happens to malate formed by reducing oxaloacetate, after it has been transported across the mitochondrial membrane?

A

It is oxidised back to oxaloacetate by cytosolic NAD+-linked malate dehydrogenase
(Lecture 2, Slide 31)

65
Q

When is oxaloacetate converted to aspartate?

A

When there is a lot of NADH in the cytoplasm
(Lecture 2, Slide 32)

66
Q

What reaction does oxaloacetate to be converted to aspartate?

A

Transamination
(Lecture 2, Slide 32)

67
Q

What is transamination?

A

The transfer of the amino group of an amino acid to an α-ketoacid
(Lecture 2, Slide 32)

68
Q

What 2 products are produced from a transamination reaction?

A

An amino acid equivalent of the original α-ketoacid and the α-ketoacid equivalent of the original amino acid
(Lecture 2, Slide 32)

69
Q

What does oxaloacetate react with to become aspartate and what are the 2 products formed?

A

Oxaloacetate reacts with glutamate to form aspartate and α-ketoglutarate
(Lecture 2, Slide 32)

70
Q

Why is oxaloacetate either converted into malate or aspartate before being converted back into oxaloacetate?

A

As oxaloacetate cannot cross the mitochondrial membrane to reach the cytosol, but malate and aspartate can. They are then converted back into oxaloacetate in order for it to then be converted into phosphoenolpyruvate
(Lecture 2, Slides 30,31 & 32)

71
Q

Why is a carboxylation and a decarboxylation required to form phosphoenolpyruvate from pyruvate?

A

As the addition of a phosphoryl group to pyruvate is an energetically unfavourable reaction (ΔG= +31kJ mol-1)
Carboxylation decarboxylation leads to ΔG = +0.8 kJ mol -1
(Lecture 2, Slide 33)

72
Q

What is used to power the carboxylation of pyruvate?

A

1 GTP
(Lecture 2, Slide 33)

73
Q

What do the Cori and Glucose-Alanine cycles provide and what do they both require as their primary energy source?

A

They provide a mechanism for continuous energy supply for tissues and both require glucose as their primary energy source
(Lecture 2, Slide 36)

74
Q

What 2 things must peripheral tissues do to participate in the Cori or Glucose-Alanine cycles?

A

Either lactate (as the end produce of glucose metabolism) or alanine, and not oxidise glucose completely to CO2 and H2O
(Lecture 2, Slide 36)

75
Q

How does the Cori cycle cost the body 4 ATP?

A

As gluconeogenesis from lactate requires 6 ATP but only 2 ATP is gained from anaerobic glycolysis
(Lecture 2, Slide 37)

76
Q

How is pyruvate converted to alanine?

A

By transamination
(Lecture 2, Slide 39)

77
Q

What enzyme catalyses the transamination of pyruvate to alanine?

A

Alanine transaminase (remember ALT)
(Lecture 2, Slide 39)

78
Q

What happens to alanine generated by pyruvate via transamination?

A

It is returned to the liver for gluconeogenesis
(Lecture 2, Slide 39)

79
Q

Can carbons of fatty acids be used for net synthesis of glucose?

A

No
(Lecture 2, Slide 40)

80
Q

What is glycerol phosphorylated to and what enzyme facilitates this?

A

It’s phosphorylated to glycerol-3-phosphate by glycerol kinase
(Lecture 2, Slide 40)

81
Q

What is glycerol-3-phosphate dehydrogenated to and what is the enzyme that facilitates this?

A

It’s dehydrogenated to dihydroxyacetone phosphate by glyceraldehyde-3- phosphate dehydrogenase
(Lecture 2, Slide 40)

82
Q

What facilitates glycogen’s rapid synthesis and catabolism (breakdown)?

A

Its many non-reducing ends
(Lecture 2, Slide 41)

83
Q

What is glycogen breakdown called?

A

Glycogenolysis
(Lecture 2, Slide 42)

84
Q

Why are 4 enzymes required to breakdown glycogen?

A

1 to degrade glycogen
2 to remodel glycogen so that it remains a substrate for degradation
1 to convert the product into a metabolizable form
(Lecture 2, Slide 42)

85
Q

What are the 4 enzymes needed to break down glycogen?

A

Glycogen phosphorylase
Transferase
α-1,6-glucosidase
Phosphoglucomutase
(Lecture 2, Slide 42)

86
Q

In eukaryotes’, what 2 enzymes required to breakdown glycogen are on the same polypeptide?

A

Transferase and α-1,6-glucosidiase (“debranching enzyme”)
(Lecture 2, Slide 42)

87
Q

What is phosphorolysis?

A

Addition of orthophosphate to yield glucose 1-phosphate
(Lecture 2, Slide 43)

88
Q

What enzyme catalyses the phosphorolysis of glycogen?

A

Glycogen phosphorylase
(Lecture 2, Slide 43)

89
Q

What are 2 reasons why glycogen undergoes phosphorolysis and not hydrolysis?

A

Hydrolysis would result in glucose, which can exit the cell

Glucose would have to be phosphorylated at the expense of ATP to enter glycolytic pathway whereas phosphorolysis yields and already phosphorylated glucose
(Lecture 2, Slide 44)

90
Q

What is the problem with glycogen phosphorylase when it is degrading glycogen by phosphorolysis?

A

It cannot cleave the α-1,6-glycosidic bonds at the branch points, and even stops 4 residues away from the branch points
(Lecture 2, Slide 45)

91
Q

How does the transferase part of the debranching enzyme help fix the problem that glycogen phosphorylase stops 4 residues away from branch points during glycogen breakdown?

A

It transfers a block of 3 glucose units from one branch to another, leaving a single glucose unit making it easier to process
(Lecture 2, Slide 46)

92
Q

How does the α-1,6-glucosidase part of the debranching enzyme do to the lone glucose left by the transferase part of the debranching enzyme?

A

It hydrolyses it, resulting in the release of a free glucose unit
(Lecture 2, Slide 46)

93
Q

What happens to the glucose 1-phosphates generated by glycogen breakdown?

A

They undergo a reversible reaction catalysed by phosphoglucomutase to become glucose 6-phosphates
(Lecture 2, Slide 47)

94
Q

Why are the glucose 1-phosphates generated by the breakdown of glycogen converted to glucose 6-phosphates?

A

To be converted to pyruvate in glycolysis
(Lecture 2, Slide 47)

BM 210: Introduction to Biochemistry (12 decks)

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