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JL Gastrointestinal > Biochemistry > Flashcards

Flashcards in Biochemistry Deck (313):
1

What is glycogenolysis?

The breakdown of glycogen to form glucose. It is accomplished by phosphorylis.

2

What is the main storage form of glucose in the liver and muscle cells?

Glycogen

3

When is liver glycogen broken down?

In between meals

4

What is liver glycogen released to maintain?

Blood glucose levels for red blood cells and the brain

5

What type of glycogen can only be consumed within the muscle cells?

Muscle glycogen

6

Where can muscle cells not release glycogen into?

The blood stream

7

What provides energy via glycolysis and the TCA cycle during bursts of physical activity?

Muscle glycogen

8

What does glycogenolysis fluctuate depending upon?

Meal times

9

What is the name of the pathway which generates new glucose from non-carbohydrate precursors?

Gluconeogenesis

10

What is the primary source of glucose overnight when hepatic glycogen is depleted?

Gluconeogenesis

11

What is a polymer consisting of single glucose molecules linked together to form chains?

Glycogen

12

What are glycogen molecules joined by?

An alpha 1-4 glycosidic link.

13

What are the branches of glycogen introduced by?

Alpha 1-6- glycosidic link.

14

How are new molecules added, and old molecules cleaved off from glycogen?

Free glucose joins onot the ends and glucose molecules are cleaved off the ends

15

What can glucose residues only be added to?

An existing glycogen chain.

16

What protein is found in the centre of glycogen?

Glycogenin

17

What substance has a catalytic activity which adds small number of glucose molecules to itself?

Glycogenin

18

What is the enzyme which synthesises glycogen?

Glycogensythase

19

What is a glycogen primer containing at least 4 glucose residues covalantly attached to?

Glycogenin

20

What has to first happen to glucose before it can be used for any further metabolic pathways?

It has to be phosphorylated

21

What is glucose phosphorylated to?

Glucose-6-phosphate

22

What, in the initial pathway of glycogen synthesis, traps the glucose in the cell?

Phosphorylation of glucose to glucose-6-phosphate

23

Once glucose has been trapped in the cell, by phosphorylation of glucose to glucose-6-phosphate - what two choices does the cell have?

If cell needs energy it can breakdown glucose-6-phosphate in glycolysis, however if plenty of glucose is present then glucose-6-phosphate can be used for the synthesis of glycogen.

24

Once it has been decided that glucose-6-phosphate will synthesise glycogen, what is the initial step?

Glucose-6-phosphate has to be converted to glucose-1-phosphate

25

What catalyses glucose-6-phosphate to glucose-1-phosphate?

Phosphoglucomutase

26

In the synthesis of glycogen, once glucose-6-phosphate is converted to glucose-1-phosphate by phosphoglucomutase, what then happens to the glucose-1-phosphate?

It has to be activated to form UDP-glucose

27

What can be considered an actived form of glucose and acts as a substrate for glycogen synthase?

UDP-glucose

28

In the synthesis of glycogen, once UDP-glucose is activated, what does glycogen synthase do to it?

Takes the glucose part of UDP-glucose and covalently bonds it ontop hte ends of existing glycogen.

29

In glycogen synthesis, what happens to the UDP that is left over, once glycogen synthase has taken the glucose part away from it?

It is phosphorylated again to form UTP

30

How much ATP does the phosphorylation of UDP to UTP consume?

1 ATP

31

For each glucose that is added to glycogen, how much ATP is consumed?

1

32

In glycogen synthesis, what converts glucose-1-phosphate to UDP-glucose?

UDP-glucose pyrophosphorylase

33

What is a nucleotide like ADP and has a uricil base, ribose sugar and 2 phosphate groups?

UDP

34

What makes the glucose in UDP highly active?

Attached to the second phosphate group is glucose and the bond between them makes glucose highly active.

35

What is - simple precursors are first converted to activated intermediates - a common pathway of?

Biosynthetic pathways

36

What is an activated form of phosphate?

ADP

37

What is an activated form of acetate?

Acetyl-CoA

38

What does the phosphate ester linkage in a nucleotide sugar release on hydrolysis?

Free energy

39

What enzyme adds on one glucose molecule (from UDP-glucose) onto the end of glycogen at one time?

Glycogen synthase

40

What is the rate-limiting enzyme of glycogenesis?

Glycogen synthase

41

What branching enzyme, introduces alpha 1-6 glycosidic branches onto glycogen?

Transglycosylase

42

Approximatly how many glucose residues apart is an alpha 1-6 glycosidic branched added?

10

43

If we need glucose, then how can muscle and liver cells remove glucose from its stored form?

By using glycogenolysis

44

What enzyme catalyses glycogenolysis?

Glycogen phosphorylase

45

What enzyme takes a glycogen molecule and cleaves one glucose off the end and adds a phosphate group to it?

Glycogen phosphorylase

46

What is the product of glycogen breakdown?

Glucose-phosphate

47

In glycogenolysis, what is glucose-1-phosphate converted to?

Glucose-6-phosphate

48

Where in the body, can glucose-6-phosphate be dephosphorylated and the resulting glucose released into the blood stream?

Liver

49

In skeletal muscle, glucose-6-phosphate cannot be dephosphorylated, so how can it provide energy?

Via glycolysis and the TCA cycle (debranching requires additional enzymes)

50

What transporter removes glucose from liver into blood?

GLUT2 transporter

51

What regulates glucogenesis and what regulates glycogenolysis

Glucogenesis - glycogen synthase
Gluconeolysis - Glycogen phosphorylase

52

What is the hormone of the fed state, and what does it signal the availability of?

Insulin - availability of carbohydrate in the blood stream

53

What does insulin stimulate the synthesis of?

Glycogen and glycogen synthase

54

What does insulin inhibit, at the same time as producing glycogen synthase?

Glycogen phosphorylase

55

What is the hormone of the starving state and what does it signal?

Glucagon - signals lack of glucose in the blood stream

56

What will glucagon stimulate and what will it inhibit?

Stimulate glycogenolysis and glycogen-phosphorylase

57

What does glucagon inhibit at the same time as stimulating glycogen-phosphorylase?

Glycogen synthase

58

What two other substances stimulate glycogen phosphorylase?

Adrenaline and cortisol

59

What diseases have increased glycogen deposits in the liver or muscle or both and each type is due to a defect in a different enzyme?

Glycogen storage diseases

60

What is glycogenesis?

Synthesis of glycogen from freely available glucose)

61

What are the three non-carbohydrate precursors for gluconeogenesis?

1. Lactate (lactic acid)
2. Amino acids
3. Glycerol

62

What is produced by skeletal muscles under anaerobic conditions?

Lactate

63

When skeletal muscle works hard and blood cannot supply sufficient oxygen for oxygen phosphorylation, what will muscle do?

Conduct glycolysis under anaerobic conditions

64

During glycolysis under anaerobic conditions in skeletal muscles, what does the muscle do to re-oxidise its NADH to NAD+?

It will convert pyruvate to lactic acid

65

How are amino acids derived from muscle protein?

By proteolysis

66

What is glycerol derived from?

Triglycerides (fat storage molecules)

67

What does lipolysis in adipose tissue produce?

Glycerol

68

Gluconeogenesis is very energy consuming - where does the energy come from?

Re-oxidation of stored molecules

69

Where does gluconeogenesis occur?

In the liver

70

What are the two main methods the liver used to keep the blood sugar levels constant?

1. Gluconeogenesis
2. Glycogen synthesis

71

Where are small amounts of glucose always synthesised?

In the kidneys

72

What does the energy from oxidation of fatty acids released from adipose tissue supply?

Gluconeogenesis

73

What three enzymes catalyse the three irreversible reactions in glycolysis?

1. Hexokinase
2. Phosphofructokinase
3. Pyruvate kinase

74

Gluconeogenesis requires 4 unique liver enzymes as well as proceeding via the synthesis of what?

Oxaloacetate in mitochondria

75

During stage 1 of glycolysis, what converts glucose to glucose-6-phosphate?

Hexokinase

76

In the first stage of glycolysis, what enzyme catalyses the reversible conversion of glucose-6-phosphate to fructose-6-phosphate?

Phosphoglucose isomerase

77

In stage 1 of glycolysis, what occurs after the conversion of glucose-6-phosphate to fructose-6-phosphate via phosphoglucose isomerase?

Fructose-6-phosphate converts to Fructose-1,6,-bisphosphate

78

What enzyme catalyses the irreversible reaction during stage 1 glycolysis, of fructose-6-phosphate to fructose-1,6-bisphosphate?

Phosphofructokinase

79

Gluconeogenesis is energetically expensive - how much ATP is required?

6ATP

80

In gluconeogenesis what drives an unfavourable reaction?

ATP hydrolyses

81

How many pyruvates are needed to make glucose?

2

82

What are the two componenets of the 6ATP that are consumed to make one glucose in gluconeogenesis?

4ATP
2GTP

83

How much ATP is generated by glycolysis for each glucose that is oxidised?

2ATP

84

State the overall equation for gluconeogenesis?

2 pyruvate + 4ATP + 2GTP + 2NADH + (4H+) + 6H2O
=
glucose + 4ADP +2GDP + 6Pi + (2NAD+) + 2H+

85

Lactic acid is generated in muscle (by anaerobic exercise) - what does the muscle convert?

Pyruvate to generate ATP

86

To be able to continue glycolysis (in skeletal muscle anaerobic exercise), what happens to the pyruvate formed from glucose?

It is converted to lactic acid which regenerates ADP+

87

Why can lactic acid be so easily transported into the blood stream?

Because it is a polar molecule

88

Once the lactic acid is in the blood stream, after anaerobic exercise, where does it then go?

To the liver

89

What happens to lactic acid in the liver?

It is converted back to pyruvate and then back to glucose (costing 6ATP)

90

What is the Cori cycle?

1. Glycolysis in muscle breaking down glucose to lactate
2. Lactate moving to liver to be broken down to glucose (gluconeogenesis)
3. Glucose moved back to muscle for repeat of cycle

91

What are the two groups of amino acids?

1. Ketogenic
2. Glucogenic

92

What group of amino acids cannot be used for making glucose, and what group can be used as they serve as precursors for gluconeogenesis?

Ketogenic - cannot
Glucogenic - can

93

Where do all the glucogenic amino acids involved in gluconeogenesis enter, or become converted to?

The TCA cycle or converted to pyruvate

94

What does the first reaction in gluconeogenesis convert?

Pyruvate to oxaloacetate

95

What does gluconeogenesis proceed by?

Oxaloacetate

96

What can any molecule that enters the TCA cycle in one of the lower intermediates lead to the formation of?

Oxaloacetate which can then be used for glucose synthesis

97

What can any molecule that is converted to pyruvate also be directly converted to?

Oxaloacetate

98

What are ketogenic amino acids converted to?

Acetoacetyl CoA

99

What are the rules for ketogenic amino acids entering the TCA cycle?

1. Have to be converted to acetoacetyl CoA
2. Only enter if oxaloacetate is already present

100

What would happen if gluconeogenesis removed oxaloacetate?

Then TCA cycle cannot further accept acetyl groups

101

What does glucagon signal a need for glucose in? (Pathway is related to glycolysis)?

Gluconeogenesis

102

In gluconeogenesis, what does glucagon stimulate?

Fructose 1,6-bisphosphatase

103

As well as glucagon stimulating gluconeogenesis and fructose 1,6-bisphosphatase - what else does it inhibit?

Glycolysis

104

Because insulin signals the availability of glucose, what does it therefore inhibit and stimulate?

Inhibits Gluconeogenesis and stimulates glycolysis

105

What two levels are glycolysis and gluconeogenisis regulated at?

System level - done by hormones
Individual cellular - done by allosteric effectos

106

What two molecules signal the requirement for energy in individual cell level regulation?

AMP or ADP

107

In regulation of glycolysis and gluconeogenesis, what does the stimulation of AMP or ADP cause?

Breakdown of glucose which leasd to generation of energy

108

What do AMP or ADP inhibit, at cellular regulation of glycolysis and gluconeogenesis?

Gluconeogenesis - energy expensive process

109

What happens to glycolysis and gluconeogenesis in the company of ATP?

Switch off glycolysis and stimulate gluconeogenesis

110

What is an intermediate of glycolysis, and is in high concentrations in the fed state and low concentrations in the starved state?

Fructose-2,6-bisphosphate

111

What does fructose-2,6-bisphosphate stimulate and inhibit?

Stimulates - glycolysis at high concentrations
Inhibits - gluconeogenesis

112

What are citric acid, alanine and acetyl CoA all important for?

Precursor molecules for biosynthetic processes

113

What do high concentrations of citric acid, alanne and acetyl CoA stimulate and inhibit?

Stimulate gluconeogenesis and inhibit glycolysis

114

What does glycolysis start and end with?
What does gluconeogenesis start and end with?

Glycolysis starts with glucose and ends with pyruvate
Gluconeogenesis starts with pyruvate and ends with glucose

115

In gluconeogenesis, what is the first product of the first reaction starting with pyruvate?

Oxaloacetate

116

What is an intermediate in the TCA cycle and is the 1-4 carbon molecule that accepts the acetyl groups in the very first step of TCA cycle?

Oxaloacetate

117

What are the 4 specific enzymes which are required to bypass the irreversible reactions in glycolysis?

1. Pyruvate carboxylase
2. PEP carboxykinase
3. Fructose-1,6-bisphosphatase
4. Glucose-6-phosphatase

118

Where does lactate enter the gluconeogenesis pathway?

Pyruvate

119

Where do amino acids enter the gluconeogenesis pathway?

Pyruvate and oxaloacetate (mitochondrial matrix)

120

Where does glycerol enter the gluconeogenesis pathway?

Dihydroxyacetone-P (before converting to fructose-1,6-bisP)

121

What does glucose-6-phosphatase convert?

Glucose-6-phosphate to glucose

122

What does fructose-1,6-bisphosphatase convert?

Fructose-1,6-bisphosphate to fructose-6-phosphate

123

What does pyruvate carboxylase convert in gluconeogenesis?

Pyruvate to oxaloacetate

124

What does PEP carboxykinase convert in gluconeogenesis?

Oxaloacetate to PEP

125

What is associated with disease but is also important because it is an energy source?

Fat metabolism

126

What are essential fatty acids?

Fatty acids that cannot be sythesised un our body

127

Give an example of essential fatty acids?

Polyunsaturated fatty esential fatty acids

128

What 4 vitamins are associated with fat?

A, D, K, E

129

What are the three classes of lipids?

1. Simple
2. Compound
3. Steroids

130

Give two examples of simple lipids?

Fatty acids and triglycerides

131

Give 5 examples of compound lipids?

1. Phosphate groups
2. Phospholipids
3. Carbohydrates
4. Glycolipids
5. Lipoproteins

132

Give two examples of steroid lipids?

1. Steroid hormones
2. Cholesterol

133

What are predominantly hydrocarbons?

Lipids

134

Are lipids insolbule or soluble?

Insoluble

135

What are the main energy forms in adipose tissue?

Triglycerides

136

Why can fat be stored without lots of water arround?

Its hydrophobic nature

137

What are the 3 hydroxyl groups of glycerol esterified with to produce triglyceride?

Fatty acid

138

What are straight chains and aliphatic (no rings)?

Fatty acids

139

Do fatty acids usually contain an even number of carbon atoms or an odd number?

Even number (2-20)

140

What are the three types of fatty acids?

1. Saturated
2. Unsaturated
3. Polyunsaturated

141

What is a fatty acid with no double bonds?

Saturated

142

What is a fatty acid with a single double bond?

Unsaturated

143

What formation are fatty acid double bonds in?

Cis

144

What are the three main fatty acids?

1. Palmitic acid (16:0)
2. Stearic acid (18:0)
3. Oleic acid (18:1)

145

(16:0) - what is the first number and what is the second number?

First number is number of carbons
Second number is number of double bonds

146

What can our body not make double bonds further away than?

9 carbons from the carboxyl group of the fatty acid

147

What are polyunsaturated fatty acids with double bonds further away than 9 carbons from carboxyl end called?

Essential fatty acids

148

How many carbons does Linoleic acid have and how many double bonds?

18:2

149

In greek nomenclature for fatty acids, what is the carbon adjacent to the carboxyl molecule called and what is the furtheset away called?

The alpha carbon
The omega carbon

150

What are fatty acids with up to 8 carbons like at room temperature?

Liquids

151

What is an alcohol that is readily absorbed into the epithelial cells of the intestine?

Glycerol

152

Fatty acids which are short can directly enter the portal blood, what happens to longer chain and monoglycerides?

Manipulated first

153

What do epithelial cells re-synthesise the fatty acids and monoglycerides back into?

Triglycerides

154

In fat absoprtion, once epithelial cells have re-synthesised the fatty acids and monoglycerides back into triglycerides, what are the triglycerides then coated with that makes them transportable in the blood stream?

Proteins, phospholipids and cholesterol

155

In fat absorption, what are teh complexes consiting of absorbed triglyceride and protein phjospholipid cholesterol termed?

Chylomicrons

156

What are chylomicrons a type of?

Lipoprotein

157

What are the three main products of fat digestion?

Glycerol (readily absorbed in intestinal epithelial cells)
Fatty acids
Monoglycerides

158

What is a way of transporting dietary fat through the human body?

Chylomicrons

159

What happens to chhylomicrons when they reach any tissue wich requires fats?

They are attacked by lipoprotein lipases and these lipoprotein lipases cleave the triglycerides within the chylomicrons.

160

At target tissues, what happens to the fatty acids?

They are either again re-synthesised into triglycerides for example for storage in fat cells, or can be oxidised in muscle cells

161

What do hormone sensitive lipases catalyse?

LIPOLYSIS

162

What does the initial cleavage of fat?

Hormone sensitive lipases (adrenaline-sensitive)

163

Before fatty acids can be oxidised, they have to be activated, how does this occur?

By linking the fatty acid to co-enzyme A

164

Where does the process of linking the fatty acid to co-enzyme A to activate it occur?

In the cytoplasm of cells

165

How much ATP is needed to link fatty acids to CoA?

2ATP

166

What two things is acel coA formed from?

Fatty acid linked to CoA

167

Where does further oxidation of fatty acids occur?

In the mitochondrial matrix

168

What specific carrier, transports acyl CoA from the cytoplasm to the mitochondrial matrix for further oxidation?

Carnitine shuttle

169

Explain the carnitine shuttle

1. In cytoplasm the fatty acid of the acyl CoA is transferred onto a carrier protein called carnitine, forming acyl carnitine
2. Acyl carnitine now can be transported by a specific transporter molecule across the inner mitochondrial membrane into the matrix.
3. On the matrix side of the mitochondrial, the acyl group is cleaved off the acyl carnitine and again transferred onto a CoA coenzyme.
4. The resulting carnitine is moved out again and the cycle can continue.

170

In the carnitine shuttle, what molecules are never transported across the membrane?

CoA molecules - the pools in the cytoplasm and matrix remain seperate

171

Where does beta-oxidation occur?

In the mitochondrial matrix

172

The type of process is beta-oxidation?

An oxidative

173

What does the cycle of reactions that is beta-oxidation, take as its substrate?

Acyl CoA

174

In beta-oxidation, once the acyl CoA has been transported into the mitochondrial matrix by carnitine, what happens to the aceyl CoA?

It is shortened by two carbons in a serioes of four reactions.

175

In beta-oxidation, as a result of the four reactions which shorted acyl CoA by two carbons, what is produced?

One acetyl CoA and a second product is a new acyl CoA which is shortened by two carbons

176

Within the 4 steps in beta-oxidation, how many reactions are oxidation reactions?

2

177

In beta-oxidation, electrons are removed from the substrate and tehse electrons are transferred onto electron carriers, and in this case what 2 substances are required?

1 FAD and 1 NAD

178

What 4 substances are generated in one round of beta-oxidation?

1. FADH
2. NADH
3. 1 Acetyl CoA
4. Shortened acyl CoA

179

The circle of reactions in beta-oxidation takes as long as it needs to to convert what?

Acyl CoA into acetyl CoA parts

180

After the last cycle of the beta-oxidation pathway, what is formed?

2 Acetyl CoAs

181

Give the four products of each cycle in beta-oxidation?

1. 1 acetyl-CoA
2. 1 FADH2
3. 1 NADH + H+
4. 1 fatty acyl-CoA, shortened by 2 carbon atoms

182

To cut an 18 fatty acid into 9, 2 carbon chunks, how many cutting actions are needed and so how many cycles in beta-oxidation occur?

8 cutting actions and so repeated 8 times

183

In beta-oxidation, what do the products of one cycle FAD2 and NADH generate?

ATP

184

When 8 cycles of the beta-oxidation pathway occur, how many FADH, NADH and acetyl CoA molecules are produced?

FADH - 8
NADH - 8
Acetyl CoA molecules - 9

185

Once beta-oxidation has produced acetyl CoA molecules, what happens to them?

Completely oxidised in the TCA cycle

186

What are acetyl-CoA molecules oxidised to in the TCA cycle?

CO2

187

What does 1 round of the citric acid cycle produce?

1 FADH2
3 NADH + H
1 GTP

188

What is used to calculate how many ATP in total can be obtained from the oxidation of an acid?

Use the p/o ratio (amount of ATP we can obtain for the reduction of a single oxygen atom to water)

189

What is the p/o ratio for FAD?

1.5

190

What is the p/o ratio for NADH?

2.5

191

What two substances from beta-oxidation are used for ATP generation in oxidative phosphorylation?

FADH and NADH + H

192

If beta oxidation produces 8 FADH2, 8 NADH + 8H+ and 9 acetyl-CoA, what is the total ATP yield? (hint* remember acetyl-CoA is oxidised in TCA cycle)

:9 acetyl-CoA makes 9 FADH2, 27 NADH + 27H+, 9 GTP

FADH2 NADH GTP (2 from activation step)
[17 x 1.5] + [35 x 2.5] + [9 - 2] = 120 ATP

193

Unsaturated fatty acids are already partially oxidised, so what do they yield less of?

FADH2

194

What do odd chain fatty acids yield in last step, and what is it converted to, then where does it enter?

Yield propionyl-CoA (3 carbons), converted to succinyl-CoA, enters TCA cycle directly

195

In branched chain fatty acids, what is C-1 oxidised to, and what can be said about the amount of acetyl- and propionyl CoA released?

Oxidised to CO2
Released in equal numbers

196

What can glycerol be phosphorylated to?

Glycerol-3-phosphate

197

What does glycerol kinase do to glycerol?

Activates it into glycerol-3-phosphate

198

Where is glycerol-3-phosphate present in?

Liver and kidney

199

In the breakdown of glycerol, what happens to the activated glycerol-3-phospate?

Dehydrogenated to dihydroxyacetone phosphate

200

What catalyses glycerol-3-phosphate to dihydroxyacetone phosphate?

Glycerol phosphate dehydrogenase

201

What are associated with the breakdown of fats by beta-oxidation?

Ketone bodies

202

What are ketone bodies derived from?

Acetyl CoA

203

Name 3 ketone groups?

1. Acetoacetate
2. Acetone
3. Hydroxybutyrate

204

Where is the production of ketone bodies normally occur?

In liver mitochondria

205

Why can ketone bodies easily diffuse into the blood stream?

Because they are hydrophilic molecules (polar)

206

What happens when peripheral tissues pick up ketone bodies?

Convert them back into acetyl CoA and make them enter the TCA cycle where they are oxidised

207

In what two states can ketone bodies produce problems?

In starvation and uncontrolled diabetes

208

What two muscles in particular are ketone bodies an important source of energy for?

Heart
Renal cortex

209

What step of which pathway does this occur in: A C4 compound called oxaloacetate is linked to the acetyl group from acetyl CoA, forming citric acid?

First step of TCA

210

In starvation and uncontrolled diabetes, what happens to oxaloacetate?

It is consumed for gluconeogenesis

211

During starvation and uncontrolled diabetes, what does the liver produce which leads to the removal of oxaloacetate from the cell?

Glucose

212

In ketosis in starvation and diabetes: Synthesis of glucose costs energy, so where is this provided from?

Beta-oxidation of fatty acids

213

In ketosis in starvation and diabetes: what happens to the excess acetyl Co-A from increased beta-oxidation of fatty acids?

Converted to ketone bodies

214

What does the accumulation of ketone bodies in the blood lead to?

Acidosis

215

In diabetic ketoacidosis, what can be smelt on the breath?

Acetone

216

What is the main organ for the conversion of dietary carbohydrate into fatty acids?

The liver

217

Does lipogenesis act during food shortage times?

No

218

What are free fatty acids transported bound to?

Albumin

219

How are triglycerides formed in the liver transported in the blood?

In the form of a lipoprotein called VLDL

220

What is the opposite of beta-oxidation?

The genesis of new fatty acids - a reductive process

221

What is required for the synthesis of fatty acids?

Electrons

222

Why is lipogenesis a reductive process?

Because electrons are required

223

During the process of how dietary starch is converted into stored triglyceride: what is dietary starch first converted to?

Acetyl-CoA

224

What is the precursor molecules for the conversion of dietary carbohydrate into fatty acids?

Acetyl-CoA

225

Once fatty acid synthesis has started with acetyl-CoA and formed fattya cids, what are these fatty acids esterified with?

Glycerol to form triglycerides

226

Where does the synthesis of fatty acids from acetyl-CoA occur in?

The cytoplasm of liver cells

227

Where and from what is acetyl-coA generated?

In the mitochondrial matrix by dehydrogenase complex

228

What is the inner mitochondrail membrane impermeable to?

Acetyl-CoA, so acetyl-CoA cannot easily escape from the mitochondrial matrix to the cytoplasm.

229

When present at high concentrations, where is citrate transported to?

The cytoplasm

230

If acetyl-CoA is present in high concentrations in the mitochondrial matrix then what will this lead to?

An increase in the citric acid concentration in the mitochondria.

231

What is the vital first step, before fatty acids can be synthesised from acetyl-CoA?

Activation of acetly-CoA to malonyl CoA by acetyl-CoA carboxylase

232

Where is acetly-CoA carboxylase mainly expressed?

In the liver and adipose tissue and is an essential regulatory enzyme.

233

What does acetyl-CoA carboxylase decide?

How much fatty acid is synthesised at any time

234

What does malonyl-CoA donate?

Carbon atoms to new lipids

235

What enzyme takes away an acetyl-CoA and adds on an additional third carbon molecule to the acetly group?

Acetyl-CoA carboxylase

236

What enzyme makes a three carbon malonyl group out of a two carbon acetyl group and some bicarbonate, and how much energy is required?

Acetyl-CoA carboxylase
1 ATP consumed for each acetyl-CoA that is converted to malonyl-CoA

237

The carbon that ends up in the fatty acid is derived from what - malonyl-CoA or Acetyl-CoA?

Malonyl CoA

238

What is fatty acid synthesis catalysed by?

Fatty acid synthase

239

What does fatty acid synthase do to acetyl-CoA and malonyl-CoA?

Converts carbon on these molecules to long chain fatty acids. It makes only saturated straight chain fatty acids.

240

What molecule provides the source of electrons (reduction process) for fatty acid synthesis?

NADPH

241

What is a dimer and consists of two identical subunits of the same polypeptide?

Fatty acid synthase

242

How many different reactions can fatty acid synthase catalyse?

7

243

What does fatty acid synthase contain within its peptides?

Acyl carrier protein (ACP)

244

What part of fatty acid synthase carriers the growing fatty acid chain during synthesis?

Acyl Carrier Protein

245

In the first step of fatty acid synthesis, what is one acyl carrier protein load with and what does it form?
What does the second acyl carrier protein get loaded with?

An acetly group forming acetyl-CoA
Malonyl group from malonyl-CoA

246

In the first cycle of reactions in fatty acid synthesis, what are two carbon atoms from the malonyl-CoA transferred onto?

The acetyl group and that then turns it into a four carbon fatty acyl chain.

247

What occurs in each cycle of initial reactions in fatty acid synthesis?

Adds two carbons to the growing fatty acid chain and these two carbon atoms are always derived from a malonyl-CoA.

248

What is the growing fatty acid always attached to?

The acyl carrier protein until it is completely finished

249

In intial cycle of reactions in fatty acid synthesis, how long to the cycles repeat for?

Until the growing acyl chain has reached 16 carbons

250

Once the fatty acid has reached 16 carbons, what happens to it?

It is released from the acyl carrier protein

251

What are the two precursors in fatty acid synthesis?

Acetyl-CoA and malonyl-CoA

252

What is the longest fatty acid made by fatty acid synthase?

Palmitic (16C)

253

What enzyme does the control of fatty acid synthesis occur in and what does it catalyse?

Acetyl-CoA carboxylase
Catalyses the fromation of malonyl-CoA from acetyl-CoA

254

When is sythesis of fatty acids maximal?

When carbohydrate and energy are plentiful, and when fatty acids are scarce

255

How many hormones regulate acetyl-CoA carboxylase?

3

256

What does the secretion of insulin stimulated?

Acetly-CoA carboxylase

257

What does glucagon stimulate in relation to fatty acids?

Switches off fatty acid synthesis

258

Name a hormone other than glucagon which signals the requirement of energy?

Epinephrine/adrenaline

259

What does epinephrine inhibit?

acetyl-CoA carboxylase

260

If there is a lot of acetyl-CoA present, what happens to the concentration of citric acid

Increases

261

What do high concentrations of citric acid stimulate?

Acetyl-CoA carboxylase

262

When is palmitoyl-CoA present?

In high concentration when fatty acids are in excess

263

What does the synthesis of triglycerides require?

Glycerol-3-phosphate

264

What does the liver produce Glycwerol-3-phosphate from?

Glycerol

265

What does adipose tissue produce G-3-P from?

Glucose

266

What stimulates adipose tissue uptake of glucose

Insulin

267

What formation involves esterification?

Triglyceride fromation

268

Where can all amino acids be completely oxidised?

In the TCA cycle

269

What happens when amino acids cannot be used for protein synthesis?

Degraded, ocurs mostly in liver

270

What do proteolytic enzymes in the stomach and intestine produce?

Single amino acids and di and tri-peptides

271

What initially digests protein?

Proteolytic enzymes in stomach and small intestine

272

Once proteolytic enzymes have made single amino acids or di, tri peptides, what happens to the peptides?

Absorbed into small intestine

273

What is anotehr source, other than diet, for amino acids?

Protein turnover

274

What structures are amino acids?

Tetrahedral structures

275

What does the breakdown of amino acids create, which needs to be removed?

Nitrogen

276

What two things does amino acid breakdown produce?

1. Ammonia (NH3)
2. Ammonium ions (NH4+)

277

What ions, produced from amino acid breakdown, are toxic at high concentrations and a build-up leads to severe problems?

Ammonium ions

278

What is the main molecule used for excreting excess nitrogen?

Urea

279

How is ammonium ion secreted?

In urine

280

Where is urea fromed?

In LIVER

281

Other than urea, what are the other three major nitrogen containing excretory molecules?

Uric acid
Creatinine
Ammonium ion (NH4+)

282

What happens in the first step of urea synthesis?

Amino group of an amino acid is transferred onto a keto acid (occurs in all tissues)

283

What is the keto-acid that normally recieves an amino group from an amino acid in urea synthesis?

Alpha-keto-gluterate

284

What is the step called when amino group of an amino acid is transferred onto a keto acid?

Transamination

285

If keto-glutarate is the keto acid taking part in the transamination reaction, what is the product?

Glutamic acid

286

What is the second step of the syhtesis of urea, and where does it occur?

Occurs in liver
Removal of amino group from glutamic acid

287

What is the removal of an amino group from glutamic acid called?

De-amination

288

What does the removal of amino group from glutamic acid result in formation of?

Alpha-keto-glutamate

289

During the second step of urea synthesis, what happens to the extra ammonium ion produced in de-amination?

Enters a cycle of reactions called urea cycle

290

What is the ornithine cycle?

Urea cycle

291

What is this step: aminotransferases move the amino group from alpha-amino acids to alpha-keto acids. Usually alpha-keto-glutarate, gives glutamate, occurs in all tissues?

Transamination

292

In transamination, for transport to the liver what is the amino group of glutamate transferred to?

Pyruvate, giving alanine

293

In the transport to the liver of transamination, whay is the alternate of amino group of glutamate being transferred to pyruvate making alanine?|

Glutamine synthase adds ammonium ion to glutamate giving glutamine

294

What are two major carriers of nitrogen in blood to liver?

Alanine and Glutamine

295

Where does the urea cycle occur?

In the liver

296

In deamination, what is the amino group of glutamate converted to?

Free ammonium ion

297

In urea cycle, one nitrogen comes from free ammonium, where does the other come from?

Aspartic acid

298

In the urea cycle, where does the carbon come from?

CO2

299

What are the three components that are converted to urea in the urea cycle?

Ammonium ion
Carbon dioxide
Aspartic acid

300

In teh urea cycle what are 3ATP cleaved to form?

2ADP and 1 AMP

301

In urea cycle, how many high energy phosphate bonds are broken?

4

302

What are the two products of the urea cycle?

Fumuerate
Urea

303

What are carbon skeletons?

The remainder when amino groups have been removed from amino acids

304

What are remaining carbon skeletonds converted to?

Intermediate metabolites that can be oxidised in TCA cycle

305

Give three heritable disorders which can derive from probelms with amino acid degradation?

1. Alcaptonuria
2. Maple syrup urne disease
3. Phenylketonuria

306

What is: a disease which results from blockage of the breakdown of phenylalanine and tyrosine. If these two amino acids cannot be broken down alcaptonuria arises

Alcaptonuria

307

What is: derived from a block of degradation of valine, isoleucine and leucine. If it is not treated it can lead to severe mental and physical retardation, prevented by appropriate diet.

Maply syrup disease

308

Whta results from blockage of the breakdown of phenylalanine. If it cannot be broken down it accumulates in all bodily fluids and leads to severe mental retardation if untreated.Therapy involves low phenylalanine diet?

Phenylketonuria

309

Sometimes enzymes in urea cycle become defective and lead to disease, what do these disorders result from?

Accumulation of intermediates of urea cycle

310

What increases in urea cycle disorders?

Glutamine levels

311

If the urea cycle is blocked, what becomes low?

Alpha-keto-glutarate levels

312

If alpha-keto-glutarate levels become low and lead to build-up of free ammonium ions, what can that be?

Toxic

313

Give two ways to treat a defective urea cycle?

1. Low protein diet
2. Drugs which remove nitrogen/gene therapy in hepatocytes