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1MB Gastroenterology > Biochemistry > Flashcards

Biochemistry Flashcards

1
Q

What is glycogenesis?

A

Synthesis of glycogen from glucose

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2
Q

What is glycogenolysis?

A

Breakdown of glycogen to form glucose

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3
Q

Glycogenolysis occurs by hydrolysis. True/False?

A

False

Occurs by phosphorolysis

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4
Q

Where is glycogen stored in the body?

A

Liver

Muscle cells

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5
Q

What is the role of muscle glycogen?

A

Not used to maintain blood glucose; provides energy via glycolysis and TCA cycle during physical activity

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6
Q

Which bonds link glucose molecules to form glycogen?

A

Alpha-1,4-glycosidic bonds

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7
Q

Which bonds create branches in the glycogen chain?

A

Alpha-1,6-glycosidic bonds

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8
Q

Glycogen formation can be started by two glucose monomers joining together. True/False?

A

False

Glucose residues can only be added to an existing glycogen chain

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9
Q

What is required to begin glycogen formation?

A

Glycogenin

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10
Q

What is Glycogenin?

A

A glycogen primer containing 4 glucose monomers

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11
Q

Which enzyme effectively adds glucose monomers to Glycogenin to produce glycogen?

A

Glycogen synthase

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12
Q

When enough glucose is present, glycogen synthesis begins: glucose-6-phosphate is converted to what?

A

Glucose-1-phosphate

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13
Q

What is formed from glucose-1-phosphate in glycogen synthesis?

A

UDP-glucose

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14
Q

What is UDP-glucose?

A

Essentially an active form of glucose

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15
Q

Glycogen synthase adds only one glucose at a time to UDP-glucose to ultimately form glycogen. True/False?

A

True

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16
Q

How often are branches introduced into the glycogen chain?

A

Every 10 glucose molecules

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17
Q

When does glycogenolysis occur?

A

Between meals to maintain blood glucose levels

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18
Q

Which enzyme catalyses glycogenolysis?

A

Glycogen phosphorylase

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19
Q

Glycogen phosphorylase cleaves off only one glucose at a time from glycogen. True/False?

A

True

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20
Q

What are the 2 regulatory actions of insulin upon glycogen synthesis?

A

Stimulates glycogen synthesis

Inhibits glycogen phosphorylase

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21
Q

What are the 2 regulatory actions of glucagon upon glycogenolysis?

A

Stimulates glycogen breakdown

Inhibits glycogen synthase

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22
Q

What is gluconeogenesis? When does it occur?

A

Synthesis of glucose from non-carbohydrate precursors

Occurs when glycogen stores are completely depleted

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23
Q

Where does gluconeogenesis mainly occur?

A

Liver

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24
Q

Name the 3 main precursors for gluconeogenesis

A

Lactate (lactic acid)
Amino acids
Glycerol

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25
Q

Which TCA cycle intermediate is needed for gluconeogenesis? Why is it needed?

A

Oxaloacetate (4C)

Accepts acetyl groups from fat breakdown

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26
Q

Describe the Cori Cycle

A

Blood transports lactate to liver
Liver converts lactate to glucose
Glucose is released into blood

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27
Q

Which type of amino acids can be used to synthesise new glucose?

A

Glucogenic amino acids

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28
Q

Which type of amino acids cannot be used to synthesise new glucose?

A

Ketogenic amino acids

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29
Q

What effect do insulin and glucagon have on gluconeogenesis?

A

Insulin inhibits gluconeogenesis

Glucagon stimulates gluconeogenesis

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30
Q

Does ATP stimulate gluconeogenesis?

A

Yes

31
Q

What happens when increased fat intake is not coupled with appropriate energy expenditure?

A

OBESITY

Increase in number and size of adipocytes

32
Q

Fat provides us with 2x more energy than carbohydrates. True/False?

A

True

33
Q

What are essential fatty acids?

A

Fatty acids required by, but cannot be synthesised by, the body

34
Q

Name some fat-soluble vitamins

A

Vitamin A, D, E, K

35
Q

What do triglycerides consist of?

A

Glycerol attached via ester bond to 3 fatty acids

36
Q

Double bonds in fatty acids are usually in the trans configuration. True/False?

A

False

Usually in cis configuration

37
Q

What effect do double bonds have on the melting point of fatty acids?

A

The greater the no. of double bonds, the lower the melting point

38
Q

What are the main products of lipid digestion?

A

Glycerol
Fatty acids
Monoglycerides

39
Q

What must happen to long-chain fatty acids to make them transportable?

A

Resynthesised to triglyceride and coated into a chylomicron, which enters the lymph

40
Q

What happens to chylomicrons at muscle and adipose tissue?

A

Cleaved by lipoprotein lipase into free fatty acids

41
Q

What happens to free fatty acids at muscle and adipose tissue?

A

Resynthesised into triglyceride or oxidised to provide energy

42
Q

Where does further oxidation of fatty acid occur?

Why is this a problem for acyl-CoA?

A

Oxidation occurs in the mitochondrial matrix

acyl-CoA is formed in the cytoplasm!

43
Q

What transports acyl-CoA into the mitochondrial matrix?

A

Carnitine shuttle

44
Q

How is acyl-carnitine formed in the cytoplasm?

A

Fatty acids are transferred from acyl-CoA to carnitine to form acyl-carnitine

45
Q

How does acyl-carnitine get across the inner membrane into the matrix? What happens to the carnitine?

A

Via a transporter

Carnitine is cleaved off, leaving acyl group

46
Q

In the matrix, what happens to the free acyl- group?

A

Combines with CoA again to form acyl-CoA

Net effect: acyl-CoA ends up in the matrix!

47
Q

What happens to acyl-CoA in the matrix?

A

Shortened by 2C to form acetyl-CoA and a new acyl-CoA

48
Q

What are the products of one round of B-oxidation of fatty acid?

A

1 acetyl-CoA
1 acyl-CoA, shortened by 2C
1 FADH2
1 NADH + H

49
Q

How and where are ketone bodies formed?

A

Formed from acetyl-CoA during B-oxidation in liver mitochondria

50
Q

What is lipogenesis?

A

Synthesis of fatty acids

51
Q

Lipogenesis is a reductive process (electrons are required). True/False?

A

True

52
Q

What transports acetyl-CoA from mitochondrial matrix into cytoplasm?

A

Citrate

53
Q

What is the vital first step in lipogenesis from acetyl-CoA?

A

Activation of acetyl-CoA by acetyl-CoA carboxylase into malonyl-CoA

54
Q

Which enzyme catalyses synthesis of long chain fatty acid from malonyl-CoA, acetyl-CoA and NADH?

A

Fatty acid synthase

55
Q

Which component of fatty acid synthase carries the growing fatty acid chain during synthesis?

A

Acyl-carrier protein (ACP)

56
Q

When a fatty acid chain length of __C is reached, the fatty acid is released

A

16C

57
Q

Synthesis of fatty acids is maximal when carbohydrate is scarce. True/False?

A

False

Synthesis occurs when carbohydrate is in plentiful supply + fatty acids are scarce (otherwise lipolysis would occur)

58
Q

Amino acids which are not used for proteins are stored in the liver. True/False?

A

False

Amino acids cannot be stored and are degraded if not used as building blocks

59
Q

Where is the major site of amino acid degradation?

A

Liver

60
Q

What does amino acid degradation primarily produce?

A

Ammonia (NH3) and ammonium ions

61
Q

What are the 3 steps by which urea is formed?

A

Transaminiation
De-amination
Urea cycle

62
Q

Which organ is albumin secreted from?

A

Liver

63
Q

Name the main liver-derived plasma proteins (4), in order of increasing molecular weight

A

Albumin
alpha-globulins
beta-globulins
gamma-globulins

64
Q

What characteristic of plasma proteins enables them to maintain osmotic pressure which increases fluid movement out of the tissues into the blood?

A

They are insoluble - they do not diffuse into the interstitial fluid and only circulate in the blood

65
Q

List some hydrophobic substances that are carried in the blood by plasma proteins (4)

A

Steroid hormones
Free fatty acids
Bilirubin
Cholesterol

66
Q

Give 2 examples of alpha-globulin plasma proteins

A

Ceruloplasmin

Retinol-binding protein

67
Q

Give 2 examples of beta-globulin plasma proteins

A

Transferrin

Fibrinogen

68
Q

Transferrin transports Fe2+ (ferrous iron). True/False?

A

False

Transports Fe3+ (ferric iron)

69
Q

What is the most abundant plasma protein in the blood?

A

Albumin

70
Q

Insulin inhibits production of albumin. True/False?

A

False

Insulin stimulates production of albumin

71
Q

Are albumin levels low or high in liver disease?

A

Low

72
Q

Iron is transported in the ferrous/ferric state bound to ____, and is stored in the ferrous/ferric state bound to ____

A

Iron is transported in the ferric state bound to transferrin, and is stored in the ferrous state bound to ferritin

73
Q

Which plasma protein does copper bind to for transport?

A

Ceruloplasmin

74
Q

Which disease results due to accumulation of copper due to deficiency of ceruloplasmin?

A

Wilson’s disease

1MB Gastroenterology (23 decks)

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