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Flashcards in Alex's Metabolism Notes Qs Deck (113)
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1
Q

What is glycogenesis?

A

Creation of glycogen from glucose

2
Q

Which 3 enzymes are used in glycogenesis?

A

Hexokinase/glucokinase
Phosphoglucomutase
Branching enzyme

3
Q

Describe the process of glycogenesis

A
Glucose
Glucose-6-phosphate
Glucose-1-phosphate
UDP-glucose
Added to current glycogen stores
4
Q

Describe the process of glycogenolysis

A

Glycogen store
Glucose-6-phosphate using phosphoglucomutase
Enters glycolysis and broken down by glucose-6-phosphatase

5
Q

What is Von Gierke’s disease?

A

Glycogen storage disease. Absence of glucose-6-phosphatase

6
Q

What is lipogenesis?

A

Process of creating long chain fatty acids using ATP and acetyl CoA

7
Q

Which enzyme is used in lipogenesis?

A

Acetyl carboxylase

8
Q

Which 2 compounds allosterically regulate lipogenesis?

A

Citrate –> increases

AMP –> decreases

9
Q

What are the two main free oxide radicals?

A

Nitric oxide

Hydroxyl groups

10
Q

Which two enzymes are responsible for removing/converting free oxide radicals?

A
Superoxide dismutase  (SOD)
Catalase
11
Q

Which two forms of glutathione can be found in a cell?

A

GSH

GSSG

12
Q

How does the free form of glutathione GSH become GSSH?

A

GSH donates a hydrogen ion and conjugates with another GSH molecule to form GSSG

13
Q

Which molecule is responsible for converting GSSH back into GSH?

A

NADPH provides a hydrogen ion

14
Q

Why may nitric oxide be produced naturally by the body?

A

It has potent vasodilator effects

15
Q

Which molecule is nitric oxide formed from?

A

Arginine

16
Q

Describe the process of insulin release from beta cells in the pancreas

A

Increased glucose uptake via GLUT2 channels causes an increase in ATP
ATP sensitive potassium channel closes
Increased K+ in the cell
Depolarises membrane so more Ca2+ enters cell
Insulin vesicles fuse with the cell membrane and insulin in released

17
Q

Name the 3 layers of the cortex of the adrenals

A

Zona glomerulosa
Zona fasciculata
Zona reticularis

18
Q

What is secreted from the zona glomerulosa?

A

Mineralocorticoids- eg. aldosterone

19
Q

What is secreted from the zona fasciculata?

A

Glucocorticoids- eg. cortisol

20
Q

What is secreted from the zona reticularis?

A

Androgens- eg. testosterone

21
Q

Which layer lies superficially to the adrenal cortex?

A

Capsule

22
Q

Which layer lies inferiorly to the adrenal cortex?

A

Medulla

23
Q

What is secreted from the medulla?

A

Catecholamines- adrenaline and noradrenaline

24
Q

Which cells secrete catecholamines in the medulla of the adrenal glands?

A

Chromaffin cells (by sympathetic stimulation)

25
Q

What is the action of aldosterone?

A

Acts in the DVT to upregulate Na/K ATPase and increase expression of ENaC

26
Q

What are the main actions of cortisol?

A

Stimulate gluconeogenesis
Breakdown proteins
Redistribute fat to become more centralised

27
Q

Describe the HPA axis system involved in the release of cortisol from the adrenal glands

A

CRH released from the hypothalamus
ACTH released from the anterior pituitary
Cortisol secreted and feeds back negatively to the hypothalamus and pituitary

28
Q

Give some examples of cushingoid signs

A
Dorso-cervical fat pad
Muscle atrophy 
Hypertension 
Striae
Weight gain 
Hyperpigmentation
29
Q

Why does excess cortisol cause hyperpigmentation?

A

When POMC is broken down to produce ACTH, it also produces alpha-MSH which stimulates melanocytes

30
Q

When are cortisol levels in the body highest?

A

In the morning

31
Q

Where is the thyroid gland located?

A

Anterior trachea, inferior to cricoid cartilage

32
Q

What structure separates the two lobes of the thyroid?

A

Isthmus

33
Q

Which cells produce thyroid hormone?

A

Thyrocytes

34
Q

What substance is found in high concentrations in the colloid?

A

Thyroglobulin

35
Q

Which hormone is primarily secreted by the thyroid?

A

T4

36
Q

Which hormone released from the thyroid is the most potent?

A

T3

37
Q

Which thyroid hormone is most commonly found in the circulating system?

A

T3

38
Q

Which 2 plasma proteins are mainly bound to thyroid hormones?

A

Albumin

Thyrotropin releasing hormone (TRH)

39
Q

What hormone is released from the anterior pituitary to stimulate release from the thyroid hormone?

A

Thyroid stimulating hormone (TSH)

40
Q

What ion is used in the production of thyroxine?

A

Iodine

41
Q

How does iodine enter the thyrocytes?

A

Na/K-ATPase extrudes Na from the cell into the blood so iodine can use the Na gradient to move into the cell via the sodium-iodine symporter (NIS).

42
Q

Where do iodine ions bind to thyroglobulin in the colloid?

A

Tyrosine residues

43
Q

Which enzyme allows iodine to bind to thyroglobulin?

A

Thyroid peroxidase

44
Q

What are the 4 functions of thyrocytes?

A

Uptake of iodine ions from the blood
Secretion of thyroglobulin into the colloid
Addition of iodine to the free tyrosine residues
Secretion of T4 and T3 into the blood

45
Q

What is Grave’s disease?

A

Hyperthyroidism caused by a circulating antibody which stimulates excess thyroid hormone production

46
Q

What is a goitre?

A

Enlarged neck due to thyroid disease

47
Q

Give 3 symptoms of hyperthyroidism

A
Thinning hair
Heat intolerance
Irritability 
Nervousness
Weight loss
Palpitations
48
Q

What is Hashimoto’s disease?

A

Hypothyroidism caused by autoimmune destruction of the thyroid gland

49
Q

What can untreated hypothyroidism at birth cause?

A

Stunted growth
Delayed sexual development
Protruding tongue
Significant mental retardation

50
Q

Which bone is the pituitary found in?

A

Sphenoid

51
Q

What embryological derivative is the anterior pituitary derived from?

A

Infundibulum

52
Q

What embryological derivative is the posterior pituitary derived from?

A

Rathke’s pouch

53
Q

Which two hormones does the posterior pituitary release?

A

ADH

Oxytocin

54
Q

Which hormones are secreted by the anterior pituitary?

A
LH
FSH
GH 
TSH
ACTH
Prolactin
55
Q

What is Cushing’s disease?

A

Pituitary adenoma secreting excessive ACTH

56
Q

What is Cushing’s syndrome?

A

Overactive adrenal glands secreting too much cortisol

57
Q

From which structure can ectopic secretions of ACTH most commonly be secreted from?

A

(Paraneoplastic syndrome) Small cell lung carcinoma

58
Q

Explain how a dexamethasone suppression test can identify the cause of hypercortisolism

A

Dexamethasone suppresses the pituitary gland’s ability to produce ACTH.
In Cushing’s disease ACTH levels will fall and therefore cortisol levels should also fall
In Cushing’s syndrome and ectopic ACTH secretion the levels of cortisol will remain high

59
Q

What is pharmacokinetics?

A

What the body does to a drug

60
Q

What is pharmacodynamics?

A

What the drug does to the body

61
Q

What is phase I metabolism of a drug?

A

Oxidation, reduction or hydrolysis of the drug to convert it to the active form

62
Q

What is phase II metabolism of a drug?

A

Conjugation of the drug so it becomes soluble and can be excreted

63
Q

Give 3 ways a drug can be conjugated in phase II metabolism

A

Glucuronidation
Sulphate conjugation
Glutathione conjugation

64
Q

Explain the metabolism of paracetamol at high concentrations

A

The normal metabolic pathways of paracetamol become saturated so it goes through a phase I pathway to become NAPQI. NAPQI builds up in the cells as the phase II metabolism (glutathione conjugation) is saturated. The NAPQI build-up causes toxic effects to the hepatocytes

65
Q

What can be given to reverse the effects of paracetamol overdose?

A

N-acetyl cysteine

66
Q

Explain the Phase I and Phase II metabolism of alcohol

A

Alcohol
Acetaldehyde via alcohol dehydrogenase
Acetic acid via aldehyde dehydrogenase

67
Q

Which drug can be given to alcoholics to inhibit aldehyde dehydrogenase to give extreme hangovers?

A

Disulfiram

68
Q

Give 3 important enzymes involved in glycolysis and the steps they are involved with

A

Hexokinase (step 1)
Phosphofructokinase (step 3)
Pyruvate kinase (step 10)

69
Q

What is the action of hexokinase in glycolysis?

A

Breaks down glucose to glucose-6-phosphate

70
Q

What does pyruvate kinase form in the final step of glycolysis?

A

Pyruvate and ATP

71
Q

In the absence of oxygen what happens to pyruvate produced in glycolysis?

A

Converted to lactate by lactate dehydrogenase

72
Q

What is the function of the pentose phosphate pathway?

A

Produce 5 carbon sugars used in DNA + RNA synthesis

Produce NAPDH

73
Q

Explain the metabolism of the pentose phosphate pathway

A

Glucose-6-phosphate

Becomes pentose sugar using glucose-6-phosphate dehydrogenase (G6PD)

74
Q

What is the effect of a deficiency in G6PD?

A

NADPH stores in the blood not regenerated resulting in disulphide bond formation in RBCs
GSH remains in its GSSG form and produces Heinz bodies
This results in haemolytic anaemia

75
Q

What enzyme is responsible for the breakdown of pyruvate in the Kreb’s cycle?
What does it form?

A

Pyruvate dehydrogenase

Forms acetyl Co-A

76
Q

How does the acetyl Co-A enter the mitochondria?

A

Carnitine shuttle

77
Q

What is gained from 1 rotation of the Kreb’s cycle?

A

3 NADH
1 FADH2
2 CO2

78
Q

Describe the process of the electron transport chain

A

NADH and FADH2 release electrons into the ECT and become oxidised.
The electrons move down the chain and pump H+ ions into the intermembrane space
The electrons bind to hydrogen and oxygen to form water at the end of the chain
The high H+ concentration in the intermembrane space flows back into the matrix via ATPsynthase which produces ATP.

79
Q

What substance is produced from brown adipose tissue and what action does it have on the ECT?

A

Thermogenin

Uncouples the ECT from ATPsynthase to release heat instead of ATP

80
Q

Give the 4 types of lipoprotein

A

Chylomicrons
VLDLs
LDLs
HDLs

81
Q

Where/ and in what cell are chylomicrons produced?

A

Intestine- enterocytes

82
Q

How do chylomicrons reach the systemic circulation?

A

Transfer through lacteal (intestinal) lymphatic system and enter into the left subclavian vein

83
Q

Where are LDLs formed?

A

Liver

84
Q

Which apoprotein is expressed on the surface of LDLs?

A

B100

85
Q

Where are HDLs produced?

A

Tissues

86
Q

How are levels of cholesterol assessed in the blood?

A

HDL/LDL ratio

87
Q

How do fats normally circulate in the blood?

A

TAGs (triacylglycerols)

88
Q

What is a TAG made up of?

A

Glycerol backbone

3 fatty acid chains

89
Q

What is lipolysis?

A

Breakdown of TAGs

90
Q

How can fatty acids enter the mitochondria?

A

Activated by acetyl Co-A and moved through the carnitine shuttle

91
Q

Describe the process of beta oxidation of fatty acids

A

Series of oxidation reactions by FAD and NAD occur in the mitochondrial matrix.
Each oxidation reaction produces a molecule of acetyl Co-A and a fatty acid chain 2 carbons shorter than previously

92
Q

Describe the metabolsim of an acetyl Co-A molecule to form a ketone body

A

Acetyl Co-A
HMG
(using HMG CoA reductase)
Ketone bodies

93
Q

What is the body’s main source of nitrogen?

A

Amino acids from dietary protein

94
Q

How is the toxic nitrogen (in the amine group of an amino acid) neutralised in the body?

A

Transamination- adding amine group to another molecule

Deamination- removal of amine group to form ammonia

95
Q

Which enzymes are used in transamination?

A

ALT- alanine aminotransferase

AST- aspartate aminotransferase

96
Q

How is urea produced in the body?

A

Ammonia or glutamate enter the urea cycle
Converted to arginine
Arginine broken down into urea and ornithine

97
Q

What happens to the urea and ornithine produced in the urea cycle?

A

Urea excreted in the urine

Ornithine recycled

98
Q

What is refeeding syndrome?

A

Chronic lack of food causes depression of the urea cycle as nitrogen levels are low
Sudden excess protein causes build up of nitrogen as urea cycle cannot cope with the sudden influx.
Ammonia accumulates in the blood and causes toxicity

99
Q

What structure regulates appetite?

A

Arcuate nucleus in the hypothalamus

100
Q

Explain the process of stimulating appetite

A

Primary fibres secrete neuropeptide Y

Secondary fibres cause hypothalamus to secrete Ghrelin

101
Q

Explain the process of inhibiting appetite

A

Primary fibres secrete POMC

Secondary fibres cause hypothalamus to secrete PYY

102
Q

Where is leptin secreted from?

A

Adipocytes

103
Q

What is the action of leptin?

A

Works on arcuate nucleus to secrete inhibitory hormones to suppress appetite

104
Q

What is galactosaemia?

A

Galactose cannot be metabolised

105
Q

Explain the normal metabolism of galactose

A

Galactose
Galactose-1-phosphate (via galactokinase)
UDP-galactose (via galactose-1-phosphate uridyl transferase)

106
Q

Which enzyme is more commonly affected in galactosaemia?

A

G1P uridyl transferase

107
Q

In galactosaemia, how is galactose metabolised?

A

Galactose becomes galactitol via aldose reductase- uses NADPH

108
Q

Why do patients with galactosaemia present with cataracts?

A

NADPH stores diminished
Disulfide bonds form and patient at higher risk of ROS attack
Proteins aggregate in the eye causing cataracts

109
Q

What is phenylketonuria?

A

Deficiency in phenylalanine hydroxylase enzyme

Usually converts phenylalanine to tyrosine

110
Q

What abnormal metabolism occurs in phenylketonuria?

A

Phenylalanine is converted to phenylpyruate which is excreted in the urine

111
Q

Why do patients with phenylketonuria suffer from mental retardation?

A

Excessive phenylalanine blocks non-specific amino acid tranporters at the BBB so essential amino acids cannot work to provide normal CNS development

112
Q

What is homocystinuria?

A

Deficiency in cystathione beta synthase (CBS) enxyme.

It is normally used to breakdown homocysteine to cystathionine which is then converted to cysteine

113
Q

In homocystinuria, what happens to the excess homocysteine?

A

Some converted to methionine

Excreted in urine