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Flashcards in Clinical Genetics And Biochemistry Deck (239):
1

What is a transposon and how much of the human genome is made up of transposon repeats?

A mobile genetic element. 45% of human genome

2

Are transposons well or poorly conserved?

Poorly conserved

3

What are piRNAs?

Piwi protein interacting RNAs which control transposon activity. They are an example of non-coding RNA

4

What is heterochromatin and how much of the human genome is made up of it?

Tightly packed repetitive DNA with little or no active gene expression. Stains darkly with giemsa stain. Makes up 6.7% of the human genome.

5

What is euchromatin?

Loosely packed DNA with lots of active gene expression. Pale staining with giemsa.

6

What is chromatin?

DNA and histones

7

What makes up 3 - 4% of the human genome?

Non coding mRNA genes

8

Is heterochromatin well or poorly conserved?

Poorly conserved

9

What does non coding RNA do?

It regulates the expression of protein coding mRNA genes

10

Give examples of non-coding RNA

PiRNA and microRNA. PiRNA regulates transposon activity. MicroRNAs can silence protein coding mRNA or stop translation

11

What makes up 1.2% of the human genome?

Protein coding mRNA gene

12

Are RNA genes well or poorly conserved?

Well conserved

13

What are the three types of mutations?

Pathogenic
Non-pathogenic (polymorphism)
Conferring disease susceptibility (risk allele)

14

What is a polymorphism?

Non-pathogenic mutation

15

What are the 5 types of disease causing mutations in DNA and chromosomes?

SNPs (single nucleotide polymorphism aka point mutation)

Indels (small insertions or deletions)

CNV (copy number variants, large indels)

Microsatellites (dynamic) (expansion or contraction of tandemly repeated DNA)

Minisatellite (expansion or contraction of tandemly repeated DNA)

16

Which disease causing mutations are associated with repetitive DNA?

CNV
Microsatellites
Minisatellites

17

What is a SNP?

Single nucleotide polymorphism. It is pathogenic if it changes the open reading frame or is found in the promoter or regulatory region as this will change the amount of mRNA produced.

18

What is an indel?

Small insertions or deletions. SNP indel = 1 nucleotide inserted or deleted. Micro indel = more than 1 nucleotide inserted/deleted

19

What is a CNV?

Large indel, duplication or inversion

20

What are micro and mini satellites and which of them is dynamic?

Contractions or expansions of tandemly repeated DNA. Microsatellites are dynamic.

21

What is a Barr body?

Chromatin of an inactive X chromosome. It is seen as a blob of condensed chromatin at the edge of the nucleus of a cell in interphase.

22

What is a manifesting heterozygote?

A female carrier of an X linked recessive condition who shows some symptoms due to skewed X inactivation

23

What does hemizygous mean?

A boy with one affected X chromosome in an X linked recessive condition

24

What is a true homozygote?

Have inherited 2 copies of the same mutation (usually due to consanguineous mating)

25

What is a compound heterozygote?

Inherited 2 different mutations but has phenotype of homozygote (most homozygotes are actually compound heterozygotes, unless consanguineous mating is involved)

26

What is consanguineous mating?

1st cousin mating

27

What is a dynamic mutation?

The mutation increases in length between the parent and the child e.g. Microsatellites

28

What is genomic imprinting? Give an example

Where expression of an allele is dependent on its parental origin e.g. Paternal 15q12 deletion causes Prader-Willi syndrome in boys. Maternal 15q12 deletion causes angelman syndrome in girls.

29

7 Location of mutations in protein coding genes

Enhancer
Promoter
Start codon
Exon donor consensus
Exon acceptor consensus
Stop codon
Poly A tail

30

8 Location of mutations in protein coding genes

Enhancer
Promoter
Start codon
Intron donor consensus
Intron acceptor consensus
Within an exon
Stop codon
Poly A addition signal

31

What is the point of the untranslated region of a gene?

It is where microRNAs look for sequences to regulate gene expression

32

What happens if there is a mutation in the enhancer or promoter region of a gene?

There will be an increase or decrease in gene product

33

What happens if there is a mutation at the start codon?

No translation of abnormal translation

34

What happens if there is a mutation at the intron donor consensus (beginning of intron) or intron acceptor consensus (end of intron)?

Incorrect splicing

35

What is an intron?

Non coding section of a gene

36

What is an exon?

Coding section of a gene

37

What happens if there is a mutation in the stop codon?

Translation will not be stopped and the protein will get bigger

38

What happens if there is a mutation in the poly A addition signal?

mRNA will not be polyadenylated resulting in less stable mRNA and hence less protein

39

What is the poly A tail added to?

It is added to mRNA to increase its stability

40

What effects can a mutation have on a protein?

Loss of function (little/no protein produced or faulty protein produced)

Gain of function (harmful product or enhanced function or new function)

Dominant negative (mutant protein interferes with function of wild type protein e.g. Mutation in one collage oligomer will disrupt the whole collagen structure)

41

What is snRNA?

Small nuclear RNA. It is involved in splicing.

42

What can mutations in miRNA cause?

Autosomal deafness
EDICT (eye disease)

43

What can mutations in snRNA cause?

MOPD type 1 which is a type of primordial dwarfism

44

What is long ncRNA?

Long non coding RNA (>200 bp)

45

What do mutations in long ncRNA cause?

Aplastic anaemia

46

What is a SNP RFLP?

Restriction fragment length polymorphism. Gain/loss of a restriction site.

47

What is a transition?

SNP which results in a purine to purine change (A to G) or a pyrimidine to pyrimidine change (T to C)

48

What is a purine

Adenine and guanine

49

What is a pyrimidine

Cytosine and thymine

50

Which bases bind together?

A binds T
G binds C

51

What is a transversion

Where a SNP results in a purine (A or G) being swapped for a pyrimidine (C or T) or vice versa

52

What is a synonymous SNP?

Silent mutation (amino acid remains the same)

53

What is a non-synonymous SNP?

Results in a different amino acid with very different properties from the original one

54

What is a Missense mutation?

Changes in the coding sequence result in one amino acid being swapped for another. Can be conservative or non-conservative.

55

What is a conservative Missense mutation?

Changes in the coding sequence result in an amino acid change. The new amino acid has similar properties to the old one.

56

What is a non-conservative Missense mutation?

Changes in the coding sequence result in a change in amino acid, the new amino acid does not have similar properties to the old one

57

What does a SNP indel cause?

A frameshift mutation, since it inserts/deletes 1 nucleotide (ie not a multiple of 3).

58

What causes a frameshift mutation?

Inserting/deleting a number of nucleotides which is not a multiple of 3

59

What is a nonsense mutation?

It causes insertion of a premature stop codon

60

What are the 3 methods of detecting SNPs?

Restriction digest followed by gel electrophoresis (SNP RFLP only)

ARMS (primers)

Microarray

61

Glycogenesis

Glycogen formation from glucose

62

Glycogenolysis

Glycogen breakdown to form glucose and glucose-6-phosphate

63

Gluconeogenesis

Production of glucose from other metabolic pathways (especially glucose from pyruvate)

64

What is glycolysis?

Anaerobic conversion of glucose to pyruvate

65

What are the products of glycolysis?

Net 2 ATP
2 pyruvate
2 NADH

66

What are the 3 stages of glycolysis?

Glucose to fructose-1-6-bisphosphate

DHAP to glutaraldehyde

Glutaraldehyde to pyruvate (occurs twice)

67

How many carbon atoms in pyruvate?

3

68

Where and how is glycolysis controlled?

At the formation of glucose-6-phosphate

At the formation of fructose-1,6-bisphosphate. Phosphofructokinase is regulated by fructose-2,6-bisphosphate. Lots of glucose = lots of fructose-2,6-bisphosphate which activates phosphofructokinase. Vice versa for low glucose.

69

What are the only tissues that have an absolute requirement for blood glucose for metabolism?

Rbc

Brain

70

What energy source can the brain use in starvation?

Ketones from fatty acid breakdown

71

When does most gluconeogenesis occur?

Sleep

72

Where is most glycogen stored?

Mainly in muscle but some in liver

73

Where is glycogen made?

Liver

74

Where is most glycogen stored?

Mainly in muscle but some in liver

75

When does most gluconeogenesis occur?

Sleep

76

What energy source can the brain use in starvation?

Ketones from fatty acid breakdown

77

What are the three steps of glycolysis which have a large negative delta G and are essentially irreversible?

Hexokinase
Phosphofructokinase
Pyruvate kinase

78

What is hexokinase inhibited by?

Glucose-6-phosphate

79

What is phosphofructokinase inhibited by?

Citrate and ATP

80

What is phosphofructokinase activated by?

Fructose-2,6-bisphosphate
And AMP

81

What is pyruvate kinase inhibited by?

Alanine and ATP

82

What is pyruvate kinase activated by?

Fructose-1,6-bisphosphate

83

What are all steroid hormones synthesised from?

Cholesterol

84

What are 3 classes of steroid hormone?

Corticosteroids (glucocorticoids such as cortisol) (mineralocorticoids such as aldosterone)

Androgens

Estrogens

85

Where does steroid synthesis occur?

Adrenal cortex

Testes

Ovaries

86

Which enzymes are involved in steroid synthesis?

Members of the cytochrome P450 oxidase family

87

Which gene codes for enzymes involved in steroid synthesis?

CYP11

88

What are symptoms of diabetes?

Unexplained weight loss
Polyuria
Polydipsia
Blurred vision
Fatigue
Thrush
Slow healing of cuts
Ketone smell on breath due to ketoacidosis

89

What is the main difficulty in recognising diabetes symptoms?

Habituation

90

What is the main difference in symptoms between type 1 and type 2 diabetes?

Type 1 symptoms develop quickly

91

Compare insulin and glucagon levels in type 1 diabetes?

Insulin levels are low
Glucagon levels are high

92

What is the 1st step in diagnosing diabetes?

Glucose in urine test

93

What conditions are associated with type 2 diabetes?

Central obesity
High triglycerides
Low HDL cholesterol
High fasting glucose
High blood pressure

94

What is impaired glucose tolerance?

More insulin secreted as insulin receptors lose sensitivity

95

How do adipocytes contribute to insulin resistance?

They secrete adipokines which increase insulin resistance and they inhibit secretion of adiponectin which increases insulin sensitivity

96

What acute complications are associated with type 1 diabetes?

Hypoglycaemic coma (too much insulin or insufficient glucose from diet)

Ketoacidosis (coma)

97

What are chronic complications of diabetes?

Retinopathy and cataracts
Neuropathy and nephronopathy caused by diabetic microangiopathy. For type 2 diabetes major causes of death are stroke and peripheral vascular disease.

98

What are the 4 mechanisms of glucose mediated damage?

Production of ROS

Protein kinase C

Non-enzymatic glycation of proteins

Polyol pathway

99

How are blood glucose levels measured?

Using immobilised glucose oxidase which generates hydrogen peroxide which generates a colour change

100

What is HbA 1c?

Haemoglobin A which has been non-enzymatically modified by glycation

101

How does insulin resistance lead to type 2 diabetes?

Overproduction of insulin, high glucose levels and free fatty acid levels damage beta cells. (Beta cells die with age but obesity and insulin resistance increase rate of death)

102

What is meant by an unsaturated fat?

Double bonds in the fatty acids

103

What is a triacylglyceride made up of?

3 fatty acid chains bound to a glycerol by ester linkages

104

Compare fat and glycogen as energy stores?

7 x more energy in 1 gram of fat compared to 1 gram of glycogen because glycogen carries water for hydration. Also triacylglycerols are more reduced so release more energy when oxidised. The body can only store less than one day's worth of glycogen whereas fat stores can meet energy requirements for months

105

Where is fat found in the body?

Under the skin
In the abdominal cavity
Mammary glands

106

What is brown fat?

Fat found in newborns. Contains more mitochondria so appears brown

107

What are adipocytes?

Cells that store large amounts of triacylglycerols as fat droplets

108

What 4 functions does cholesterol have?

It maintains membrane fluidity
It is the precursor for steroid hormones
It is the precursor for bile acids
It is the precursor for vitamin D

109

Where does cholesterol come from

Half is synthesised de novo and half is from the diet

110

Where are the major synthesis sites for cholesterol?

Liver
Intestine
Skin (waterproofing)

111

What is the starting point for cholesterol synthesis?

Acetyl CoA

112

What is the main role of vitamin D?

Calcium homeostasis

113

What is the difference between cholesterol and cholesteryl esters?

Cholesteryl esters are more hydrophobic and cannot be incorporated into membranes

114

What is a PEST sequence?

An amino acid sequence on cell cycle proteins that targets them for rapid degradation

115

Names the types of mutations associated with repetitive dna in order of size

Microsatellites
Minisatellites
Copy number variants

116

What is anticipation?

When a disease gets more severe with each generation (associated with microsatellites which are dynamic)

117

How big are microsatellites?

Less than 100bp

118

Name a disease caused by microsatellites

Huntingtons

119

What techniques can be used to analyse microsatellites?

Southern blots
Triplet repeat primed pcr

120

How big are minisatellites?

1 - 400kb

121

Name a disease caused by minisatellites

Myoclonus epilepsy. There is a minisatellite repeat in the promoter region of the cystatin b gene

122

What do CNVs arise from?

Low copy repeats

123

Name 3 diseases associated with CNVs

Haemophilia A (x linked recessive)
Prader willi (imprinting deletion of 15q12)
Angelman (imprinting deletion of 15q12)

124

How are CNVs detected?

CGH microarrays
FISH
Karyotyping

125

Why is colchicine used in karyotyping?

It stops the cell cycle in metaphase

126

Which dye is used in karyotyping?

Giemsa

127

What causes down syndrome?

Trisomy 21

128

What does it mean to be homozygous for a minisatellite or microsatellite?

Same number of repeats

129

What does it mean to be heterozygous for microsatellites and minisatellites?

Different numbers of repeats

130

What is a haplotype?

Alleles which are inherited together

131

Which type of screening is used to test for cystic fibrosis and sickle cell disease?

ASO hybridisation

132

Which tests are used to screen for dystroglycanopathies

Multiplex pcr
MAPH

133

Where in a cell is glucose-6-phosphate converted to glucose?

ER

133

In which cells is it possible for glucose-6-phosphate to be converted to glucose?

Kidney cortex, beta cells, liver, muscle

133

Why are 5 proteins required to generate glucose from glucose-6-phosphate?

3 transport proteins, 1 glucose-6-phosphatase and 1 stabilising protein

134

In terms of glucose homeostasis what are the anabolic hormones?

Insulin

135

In terms of glucose homeostasis what are the catabolic hormones?

Glucagon, cortisol and catecholamines (adrenaline and noradrenaline)

136

Which cells secrete glucagon?

Alpha cells of the islets of langerhans in the pancreas

137

Which cells secrete insulin?

Beta cells of the islets of langerhans

138

What carries out the exocrine function of the pancreas?

Acini

139

What is the morphological difference between alpha and beta cells?

Alpha cells are larger and found at the periphery of the islets of langerhans

Beta cells are smaller and found at the centre of islets of langerhans

140

What do delta cells of the islets of langerhans secrete?

Somatostatin which inhibits growth hormone

141

What do pp cells of the islets of langerhans secrete?

Pancreatic polypeptide

142

Describe how insulin goes from preproinsulin to insulin?

It is secreted as preproinsulin in the ER where the signal peptide is cleaved to form proinsulin. Then the c peptide is cleaved in the secretory granule to form insulin (same process for glucagon, secreted from preproglucagon)

143

Describe the structure of insulin

Alpha and beta chain held together by 2 disulfide bonds

144

What are the 2 ways insulin can exist?

Monomer
Hexamer

145

What are triggers for insulin secretion?

Increased blood glucose levels
GI hormones
Glucagon
Parasympathetic stimulation (ACh)

146

Where is insulin stored?

Granules in beta cells in islets of langerhans in the pancreas

147

What happens to insulin when it reaches target cells?

It binds to insulin receptors, gets internalised, dimerises, aggregates, autophosphorylates and phosphorylates effector proteins

148

Which tissues does insulin target?

Liver
Adipose tissue
Muscle

149

What effects does insulin have on the liver?

Stimulates glycolysis, synthesis of glycogen, fatty acids, TAGs, VLDLs. Supresses gluconeogenesis

150

What effect does insulin have on adipose tissue?

Stimulates fatty acid synthesis
Upregulates glut4 for more glucose uptake

151

What effect does insulin have on muscle cells?

Increases glycogen synthesis
Increases amino acid uptake and protein synthesis
Upregulates GLUT4 for more glucose uptake

152

What is the cause of type 1 diabetes mellitus?

Autoimmune destruction of beta cells

153

What triggers glucagon secretion?

Low blood glucose conc
Some GI hormones

154

What decreases glucagon secretion?

High blood glucose
High FFA in blood
High insulin
Somatostatin

155

What is the half life of glucagon?

5 minutes

156

In which organs is glucagon degraded?

Liver and kidneys

157

Which tissues does glucagon affect?

Liver and adipose

158

How does glucagon affect the liver?

Stimulates gluconeogenesis
Stimulates breakdown of glycogen
Inhibits glycolysis (inhibiting PFK-1 with citrate and pyruvate kinase with alanine)
Inhibits production of glycogen
Inhibits lipogenesis (inhibition of acetyl coA carboxylase)

159

What effect does glucagon have on adipose tissue?

Stimulates lipolysis (cAMP activation of hormone lipase which converts TAGs to FFA and glycerol, FFA undergo beta oxidation to produce ATP. Glycerol is converted to glucose by gluconeogenesis).

160

Which tissues are affected by adrenaline?

Liver and muscle

161

What affects on glucose homeostasis does adrenaline have?

Similar effects to glucagon. Stimulates gluconeogenesis and inhibits glycogen and fat synthesis

162

Which receptors does adrenaline bind to in the liver?

Alpha receptors

163

Which receptors does adrenaline bind to in muscle?

Beta receptors

164

Where is adrenaline and noradrenaline stored?

Granules in adrenal chromaffin cells

165

What is non-enzymatic glycation of proteins?

Where glucose binds to valine and lysine side chains forming advanced glycation end products. Receptor for advanced glycation end products causes inflammation

166

What is the polyol pathway?

Where glucose is converted to sorbitol by aldose reductase. Sorbitol accumulates in cells that do not possess sorbitol dehydrogenase. Sorbitol accumulation causes cataracts and neuropathy by reducing myo-inositol uptake

167

What are the treatments for type 2 diabetes mellitus?

Acarbose
Metformin
Sulphonylureas

168

What does acarbose do?

Slows breakdown of carbohydrates in the gut by inhibiting alpha glucosidase

169

How does metformin work?

Affects insulin signalling and sensitivity

170

How do sulfonylureas work?

Increase sensitivity of beta cells to glucose to increase insulin synthesis

171

What are the steps in cortisol production?

Cholesterol to pregnenolone to cortisol

172

Which enzyme converts cholesterol to pregnenolone?

Desmolase

173

Which enzyme converts pregnenolone to cortisol?

A cytochrome p450 oxidase

174

Where is cortisol produced?

The zona fasciculata of the adrenal cortex

175

What is cortisol bound to in the blood?

Corticosteroid binding globulin or albumin

176

How does cortisol affect the immune system?

Decreases circulating leukocytes and impairs b cell and t cell response

177

What 6 things does cortisol affect?

Metabolism
Central nervous system
Immune system
Cardiovascular system
Connective tissue
Bone and calcium metabolism

178

What is cortisol's affect on the central nervous system?

Increased appetite
Decreased libido
Insomnia

179

What effect does cortisol have on connective tissue?

Inhibits fibroblasts leading to loss of collagen, thinning of skin and easy bruising

180

How does cortisol affect the cardiovascular system?

Increases cardiac output

181

How does cortisol affect bone and calcium metabolism?

Inhibits bone formation
Decreases calcium uptake from the gut
Increases parathyroid release

182

What is also secreted with ACTH?

MSH

183

How do pyrimidine and purine de novo synthesis differ?

Pyrimidine the ring is built and added onto activated ribose. Purine the ring is built onto activated ribose

184

What is the starting point for pyrimidine synthesis?

Carbomoyl phosphate

185

How is de novo pyrimidine synthesis regulated?

ATCase is allosterically inhibited by CTP

186

How is oritidylate converted into UMP?

Decarboxylation

187

How is UTP converted to CTP?

Amidation

188

How is dUMP converted to dTMP?

Methylation - this step is blocked by anticancer drugs

189

What is needed for the salvage pathway for purines?

APRT
HPRT

190

What is lesch-nyhan syndrome?

Loss of HPRT activity so loss of salvage pathway for purines. Mental deficiencies and self destructive behaviour

191

What is the defect in severe combined immunodeficiency?

ADA deficiency.

192

What are the treatments for SCID?

Bone marrow transplant
PEGylated ADA injection
Gene therapy

193

How does allopurinol treat gout?

It inhibits xanthine oxidase which is an enzyme in uric acid production from purines

194

How is glycerol converted to glucose in gluconeogenesis?

Glycerol kinase converts it to glycerol 3 phosphate. Which is then converted to DHAP which is then converted to glucose

195

Why is glutamine required for nucleotide synthesis?

Provides NH4 for amidation of UTP to CTP in pyrimidine synthesis.

Provides NH4 for amidation of activated ribose in the first step of purine synthesis to form 5-phosphoribosyl-1-amine

196

How are ribonucleotides converted to deoxyribonucleotides?

Reduction using NADPH and catalysed by ribonucleotide reductase

197

Which enzyme is used in the salvage pathway for pyrimidines?

Phosphoribosyl transferase

198

What happens to triacylglycerols in the lumen of the intestine?

They are hydrolysed by lipases to fatty acids and monoacylglycerols which diffuse into mucosal cells

199

In terms of dietary fat digestion what happens in mucosal cells?

Monoacylglycerols and fatty acids are converted to TAGs again and are packages into chylomicrons with cholesterol and apolipoprotein c-11. Chylomicrons then move into the lymph and blood

200

What happens to chylomicrons in capillaries?

Apo c-11 activates lipoprotein lipases which hydrolyse TAGs to fatty acids and glycerol. Glycerol goes to the liver for glycolysis or gluconeogenesis. Fatty acids either go to the muscle for beta oxidation or adipose tissue for storage

201

How are fatty acids transported in the blood?

Bound to albumin

202

Where does beta oxidation take place?

Mitochondria or peroxisomes

203

How are substances activated for fatty acid degradation/synthesis?

Attached to carrier protein

204

What is the carrier protein for fatty acid degradation?

Coenzyme A

205

What is the carrier protein for fatty acid synthesis?

ACP

206

What is the product of fatty acid activation?

Acyl coA

207

Which enzyme carries out fatty acid activation?

Acyl coA synthetase

208

Where does fatty acid oxidation occur?

Mitochondrial membrane

209

What is used to transport acyl coA into mitochondria?

Carnitine

210

What does carnitine acyltransferase I do?

Attaches acyl coA to carnitine

211

What does carnitine acyltransferase II do?

Recycles carntine out of the mitochondrial matrix

212

What is the end product of beta oxidation?

An acyl coA which is 2 carbons shorter and acetyl coA

213

How many steps in beta oxidation?

4

214

What occurs in step 1 of mitochondrial beta oxidation?

Oxidation catalysed by acyl coA dehydrogenase. FADH2 is formed

215

What are the 4 steps of mitochondrial beta oxidation?

Oxidation
Hydration
Oxidation
Cleavage

216

What happens to acetyl CoA formed in beta oxidation?

It enters the citric acid cycle where is it converted to water and carbon dioxide. The electrons formed are used in oxidative phosphorylation to form ATP

217

What is MCAD deficiency

Medium chain acyl dehydrogenase deficiency. Cannot breakdown acyl coA chains of lengths C6 - C12

218

What are the symptoms of MCAD deficiency?

Fat accumulation in the liver
Low blood glucose levels
High blood octanic acid levels
High concs of C6 - C12 carboxylic acids in urine

219

When is beta oxidation in peroxisomes used?

For very long chain fatty acids

220

What is the inheritance of MCAD?

Autosomal recessive

221

How is beta oxidation in peroxisomes different to beta oxidation in mitochondria?

In peroxisomes hydrogen peroxide is made in the first step rather than FADH2. Hydrogen peroxide is immediately broken down by catalase. No ATP is produced, only heat.

222

What is x linked adrenoleukodystrophy?

Lack of transporters for v long chain fatty acids = accumulation of v long chain fatty acids in blood and death

223

What is zellweger syndrome?

Lack of peroxisomes = v long chain fatty acids in blood = death

224

What are the fates of acetyl coA?

Citric acid cycle

Forms ketone bodies in the liver when oxaloacetate is consumed in Gluconeogenesis

Used for fatty acid and cholesterol synthesis

225

Where are ketone bodies formed?

Liver

226

Name some ketone bodies?

Acetone
Acetoacetate
D-3-hydroxybutyrate

227

What is the affect of ketone body formation?

Ketoacidoisis and coma due to decrease in blood pH
Ketone smell on breath

228

Where does fatty acid synthesis take place?

Cytoplasm of liver cells and adipocytes

229

How is acetyl coA transported from the mitochondrial matrix to the cytoplasm for fatty acid synthesis?

Via citrate

230

What is the first committed step (irreversible) in fatty acid synthesis?

Acetyl coA is converted to malonyl coA. Catalysed by acetyl coA carboxylase and requires ATP

231

Which enzyme produces acetyl-CoA and malonyl coA?

Transacyclase

232

What is the role of desatuare?

Adds double bonds to fatty acids

233

Which enzymes are used in cholesteryl ester synthesis?

Acyl coA cholesterol acyl transferase

234

What is used to treat high cholesterol?

Resins and statins

235

How do statins work?

They are competitive inhibitors of HMG-coA reductase, they increase the number of LDL receptors, they stabilise atherosclerotic plaques, they are anti-inflammatory, they improve endothelium

236

What is the enterohepatic cycle?

Bile salts are reabsorbed in the small intestine and returned to the liver by the hepatic portal vein where they returned to circulation

237

What do resins do?

Prevent reabsorption of bile salts in the intestine and hence inhibit the enterohepatic cycle. Also increase LDL receptors