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Gastrointestinal Block > GI Biochemistry > Flashcards

GI Biochemistry Flashcards

1
Q

glycogen is a _____ consisting of ____ molecules

A

polymer

glucose

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2
Q

glycogen is the main storage form of glucose in which cells? (2)

A

liver

muscle

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3
Q

when is liver glycogen broken down?

A

between meals to release glucose into the blood

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4
Q

is liver or muscle glycogen responsible for maintaining homeostatic levels of blood glucose?

A

liver glycogen

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5
Q

when is muscle glycogen broken down?

A

to provide energy for muscles via glycolysis and the TCA cycle

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6
Q

what is glycogenesis?

A

the synthesis of glycogen from glucose

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7
Q

[GLYCOGENESIS] where does glycogenesis take place? (2)

A

liver

skeletal muscle

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8
Q

[GLYCOGENESIS] what is needed for glucose to be added to existing glycogen?

A

a primer which is covalently attached to glycogenin (a protein)

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9
Q

[GLYCOGENESIS] what catalyses the phosphorlyation of glucose to glucose-6-phosphate?

A

hexokinase

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10
Q

[GLYCOGENESIS] what converts glucose-6-phosphate into glucose-1-phosphate?

A

phosphoglucomutase

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11
Q

[GLYCOGENESIS] what converts glucose-1-phosphate to UDP-glucose?

A

UDP-glucose pyrophorylase

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12
Q

[GLYCOGENESIS] what adds UDP-glucose to glycogen?

A

glycogen synthase

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13
Q

[GLYCOGENESIS] glucose synthase:

adds ___ glucose molecule to glycogen at a time

A

one

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14
Q

[GLYCOGENESIS] can glucose synthase start new glucose molecules? (true/false)

A

false it can only extend existing glycogen molecules

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15
Q

[GLYCOGENESIS] glucose synthase cannot introduce branches into glycogen? (true/false)

A

true

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16
Q

[GLYCOGENESIS] glycogen synthase is the rate-limiting enzyme of glycogenesis? (true/false)

A

true

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17
Q

[GLYCOGENESIS] what enzyme introduces branches into glycogen?

A

transglycosylase

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18
Q

what is glycogenolysis?

A

breakdown of glycogen to form glucose

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19
Q

[GLYCOGENOLYSIS] generally, what happens in the process of glycogenolysis?

A

1 glucose molecule is cleaved off the ends of the glycogen at a time

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20
Q

[GLYCOGENOLYSIS] what is the rate limiting step of glycogenolysis?

A

glycogen + phosphate converting into glucose-1-phosphate+glycogen

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21
Q

[GLYCOGENOLYSIS] what converts glycogen + phosphate into glucose-1-phosphate+glycogen?

A

glycogen phosphorylase

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22
Q

[GLYCOGENOLYSIS] what converts glucose-1-phosphate into glucose-6-phosphate?

A

phosphoglucomutase

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23
Q

[GLYCOGENOLYSIS] what converts glucose-6-phosphate into glucose?

A

glucose-6-phosphatase

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24
Q

[GLYCOGENOLYSIS] in skeletal muscle why can’t glucose-6-phosphate be dephosphorylated into glucose?

A

glucose-6-phosphatase is a hepatic enzyme and is not present in skeletal muscle

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25
Q

[GLYCOGENOLYSIS] what is the fate of glucose-6-phosphate in skeletal muscle?

A

used in glycolysis and the TCA cycle to generate energy

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26
Q

what is gluconeogenesis?

A

the synthesis of glucose within the body from non-carbohydrate substrates

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27
Q

[GLUCONEOGENESIS] when is gluconeogenesis important?

A

during periods of fasting

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28
Q

[GLUCONEOGENESIS] why is gluconeogensis energetically expensive?

A

ATP is needed to drive unfavourable reactions

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29
Q

[GLUCONEOGENESIS] where does gluconeogensis take place? (2)

A

majority takes place in the liver

some takes place in the kidneys

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30
Q

[GLUCONEOGENESIS] how many irreversible reactions are present in glycolysis?

A

3

31
Q

[GLUCONEOGENESIS] why is gluconeogenesis not the reverse of glycolysis

A

because not all the reactions in glycolysis are reversible

32
Q

[GLUCONEOGENESIS] how are the 3 irreversible reactions of glycolysis reversed in gluconeogenesis?

A

by specific enzymes

33
Q

[GLUCONEOGENESIS] what is the enzyme pyruvate carboxylase responsible for?

A

converts pyruvate into oxaloacetate

34
Q

[GLUCONEOGENESIS] what is the enzyme PEP carboxykinase responsible for?

A

converts pyruvate into phosphoenol pyruvate (PEP)

35
Q

[GLUCONEOGENESIS] what is the enzyme fructose 1,6 -bisphosphatase responsible for?

A

converts fructose1,6-bisphosphate into fructose-6-phosphate

36
Q

[GLUCONEOGENESIS] what is the enzyme glucose-6-phosphatase responsible for?

A

converts glucose-6-phosphate into glucose

37
Q

[GLUCONEOGENESIS] name the 4 gluconeogenic enzymes

A

Pyruvate carboxylase
PEP carboxylase
Fructose -1,6 -bisphosphatase
Glucose-6-phosphatase

38
Q

[GLUCONEOGENESIS] name some of the precursors used in gluconeogenesis (4)

A

pyruvate
lactate (from skeletal muscle)
amino acids (from protein)
glycerol (from adipose tissue)

39
Q

[GLUCONEOGENESIS] how is lactate converted into glucose? (3 steps)

A
  • blood transports lactate to the liver
  • liver converts lactate into pyruvate in the cori cycle
  • pyruvate is then used to generate glucose
40
Q

[GLUCONEOGENESIS] how are amino acids converted into glucose? (4 steps)

A
  • amino acids are degraded into TCA cycle intermediates
  • converted into oxacloacetate
  • converted into pyruvate
  • pyruvate is used to generate glucose
41
Q

in glycolysis what effects do glucagon and insulin have on phosphofructokinase?

A

glucagon inhibits

insulin stimulates

42
Q

in gluconeogenesis what effects do glucagon and insulin have on fructose-1,6-bisphosphatase?

A

insulin inhibits

glucagon stimulates

43
Q

in glycogenesis what effects do glucagon and insulin have on glycogen synthase?

A

glucagon inhibits

insulin stimulates

44
Q

in glycogenolysis what enzymes stimulate glycogen phosphorylase and what enzyme inhibits?

A

insulin inhibits

glucagon, adrenaline and cortisol stimulate

45
Q

High AMP and ADP stimulate ____ and inhibit ____

A

glycolysis

gluconeogenesis

46
Q

high ATP inhibits ____

A

glycolysis

47
Q

fructose 2,6-bisphosphate is __ in fed state and __ in starved state

A

high (stimulates glycolysis and inhibits gluconeogenesis)

low (stimulates gluconeogenesis and inhibits glycolysis)

48
Q

where is fat stored?

A

adipose tissue

49
Q

fats are a subgroup of ____ called _____

A

lipid

triglyceridesd

50
Q

what are the uses of fat? (3)

A

energy store
gain essential fatty acids
metabolism of fat-soluble vitamins

51
Q

what makes up triglycerides?

A

glycerol

3 fatty acids

52
Q

what variation between fatty acids can effect their function within the body?

A

melting point

53
Q

what are the products of fat (triglyceride) digestion that need to be absorbed? (3)

A

glycerol
fatty acids
monoglycerides

54
Q

which product of fat digestion is readily absorbed in intestinal epithelial cells?

A

glycerol

55
Q

what kind of fatty acids enter portal blood and go to the liver?

A

short and medium length fatty acids

56
Q

what is re-synthesised into triglycerides?

A

monoglycerides

fatty acids

57
Q

in the enterocytes what are the triglycerides packaged into?

A

chlyomicrons

58
Q

where does the chylomicron take the triglycerides?

A

lymph then blood stream then muscle and adipose tissue

59
Q

how are the fatty acids released from the triglycerides in the muscle and adipose tissue?

A

lipoprotein lipase

60
Q

how do fatty acids generate energy?

A

they are oxidised

61
Q

what does the fatty acid have to be converted to in order to be activated?

A

acyl-CoA

62
Q

__ ATP are used to convert fatty acids into acyl-CoA

A

2

63
Q

how is acyl-CoA transported into the mitochondria for further oxidation?

A

carnitine shuttle

64
Q

what compounds are involved in the carnitine shuttle?

A

acyl carnitine

carnitine

65
Q

where does beta oxidation of fatty acids take place?

A

mitochondrial matrix

66
Q

what is produced in beta oxidation and how are they used?

A

1 acetyl-CoA (used in the TCA cycle)
1 FADH2 (used in oxidative phosphorlyation)
1 NADH + H+ (used in oxidative phosphorlyation)
1 fatty acyl-CoA shortened by 2 carbons

67
Q

why is acyl-CoA shortened by 2 carbons in beta oxidation?

A

acetyl-CoA (which has 2 carbons) has been removed from it

68
Q

glycerol is broken down into glycerol-3-phosphate by _______ _______

A

glycerol kinase (which is found in the liver and kidneys)

69
Q

glycerol-3-phosphate is further broken down into _________ ________

A

dihydroxyacetone phosphate (which is a normal intermediate for carbohydrate metabolism

70
Q

ketone bodies are formed in the ______ mitochondria from _____ produced from beta oxidation

A

liver

acetyl-CoA

71
Q

ketone bodies are important for energy production in the ____ _____ and the ____ ____ where they are converted back into acetyl-CoA

A

heart muscle

renal cortex

72
Q

what is ketosis?

A

raised levels of ketone bodies in the blood

73
Q

in what conditions are ketone bodies produced by the liver? (3)

A

starvation
alcoholism
diabetes

Gastrointestinal Block (8 decks)

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