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The Gastrointestinal System 2023 > Biochemistry > Flashcards

Biochemistry Flashcards

1
Q

Which two parts compose glycogen metabolism?

A
  1. Glycogenesis
  2. Glycogenolysis
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2
Q

What is glycogenesis?

A

Formation of glycogen from glucose

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3
Q

What is glycogenolysis?

A

Breakdown of glycogen to form glucose

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4
Q

Where is glycogen present in the body?

A
  • Liver
  • Muscle cells
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5
Q

What is the name given to any pathway that generates new glucose from non-carbohydrate precursors?

A

Gluconeogenesis

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6
Q

When in the day may gluconeogenesis occur in the body and why?

A

In the morning

Liver glycogen stores may have deplated and glucose must be obtained from other sources (fat or muscle)

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7
Q

Glucose molecules are joined by which linkages in a glycogen molecule?

A

α1-4 glycosidic links

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8
Q

Which molecule is found at the centre of a glycogen molecule?

A

Glycogenin

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9
Q

Why is glycogenin required?

A

It has catalytic activity and can add glucose to itself

This is useful because glycogen synthase (makes glycogen) cannot make glycogen from scratch and glycogenin allows for a starting glycogen point

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10
Q

What is the first step of glycogenesis?

A

Glucose is phosphorylated (using ATP) to glucose-6-phosphate

This uses hexokinase as a catalyst

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11
Q

When glucose-6-phosphate is produced as part of glycogenesis, which two paths can it take?

A
  1. Breakdown by glycolysis for energy
  2. Storage as glycogen
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12
Q

During the storage pathway in glycogenesis, what is the function of phosphoglucomutase?

A

Glucose-6-phosphate is converted to glucose-1-phosphate

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13
Q

When glucose-1-phosphate is produced during the storage pathway of glycogenesis, what is it then converted to and by which catalyst?

A

UDP-glucose

UDP-glucose pyrophsphorylase

(UTP is first phosphorylated to UDP and then added)

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14
Q

When UDP-glucose is formed, how is it incorporated into a glycogen molecule?

A

Glycogen synthase will take the glucose part of the molecule and allow it to bind to the ends of existing glycogen

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15
Q

What happens to the UDP part of the molecule once glucose is incorporated into glycogen?

A

UDP can be phosphorylated bact to UTP

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16
Q

Which enzyme allows branches to be added to a glycogen molecule?

A

Transglycosylase

It can intoduce α1-6 glycosidic branches approximately every 10 glucose residues

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17
Q

Which process is catalysed by glycogen phosphorylase?

A

Glycogenolysis

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18
Q

How is glucose-1-phosphate produced from glycogen during glycogenolysis?

A

Glycogen has one glucose cleaved

The glucose is combines with a phosphate

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19
Q

During glycogenolysis, how is glucose-6-phosphate produced?

A

Phosphoglucomutase

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20
Q

Where in the body will glucose-6-phosphate be dephosphorylated and released into the blood, and by which enzyme?

A

Liver

Glucose-6-phosphotase

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21
Q

Which transporter transports glucose produced from glycogen in the liver into the blood?

A

GLUT2

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22
Q

What happens to glucose-6-phosphate produced during glycogenolysis in skeletal muscle?

A

Glucose-6-phosphate cannot be dephosphoryated in skeletal muscle

It is used to provide energy via glycolysis and the TCA cycle

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23
Q

Which enzymes regulate the breakdown and reformation of glucose?

A

Glycogen phosphorylase - cleaves glucose from glycogen

Glycogen synthase - adds glucose (UDP glucose) to glycogen

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24
Q

Which hormones regulate the activity of both glycogen phosphorylase and glycogen synthase?

A

Insulin and glucagon

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25
Q

Which enzyme does insulin activate and which hormone does insulin inhibit?

A

Glycogen synthase

Glucagon

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26
Q

Which other hormones may stimulate glucagon?

A

Cortisol and adrenaline

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27
Q

What is glyconeogenesis?

A

The synthesis of glucose from non-carbohydrate precursors when liver glycogen is depleted and no dietary glucose is present

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28
Q

What are the three classes of precursors for gluconeogenesis?

A
  1. Lactate - synthesised by skeletal muscle under anaerobic conditions
  2. Amino acids - derived from muscle protein by proteolysis
  3. Glycerol - derived from triglycerides by lipolysis in adipose tissue
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29
Q

Which two locations in the body are the locations of gluconeogenesis?

A

Mainly the liver, also the kidneys

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30
Q

Why is gluconeogensis not the exact opposite of glycolysis?

A

There are three irreversible reactions in glycolysis mediated by three different enzymes

  1. Hexokinase - glucose to glucose-6-phosphate
  2. Phosphofructokinase - fructose-6-phosphate to fructose-1,6-biphosphate
  3. Pyruvate kinase - phosphoenolpyruvate to pyruvate
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31
Q

How much energy is required for gluconeogenesis to proceed?

A

4ATP

2GTP

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32
Q

During gluconeogenesis, where will lactate travel when it is produced?

A

Liver

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33
Q

How many ATP are required for gluconeogenesis?

A

6 ATP

(there is a net loss of 4 ATP as anerobic respiration provides 2 ATP)

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34
Q

Why is it useful to the muscle tissue and blood when the liver resynthesises glucose from lactate?

A

It prevents acidification of the blood

It takes away some of the metabolic burden from muscle tissue allowing them to function for longer

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35
Q

Which two classes can amino acids be grouped depending on whether they can make glucose or not?

A

Ketogenic - cannot be used for making new glucose

Glucogenic - can be used for making new glucose

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36
Q

Which points in the aerobic respiration pathway can glucogenic amino acids enter to form new glucose?

A
  • TCA cycle (oxaloacetate must already be present for the cycle to function)
  • They can form pyruvate
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37
Q

Regardless of the way amino acids enter the aerobic respiration pathway, what is the outcome in terms of glucose formation?

A

Oxaloacetate is produced either way

This produces glucose via phosphoenol-pyruvate

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38
Q

Gluconeogenesis is regulated at which two levels?

A
  1. Systemic by hormonal control (insulin and glucagon)
  2. Local at the level of individual cells
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39
Q

Describe the systemic regulation of gluconeogenesis involving glycagon

A

Gluconeogenesis is stimulated

Fructose-1,6-biphosphate is stimulated and glycolysis and phosphofructokinase are inhibted

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40
Q

Describe the systemic regulation of gluconeogenesis involving insulin

A

Insulin stimulates glycolysis

Phosphofructokinase is stimulated and gluconeogenesis and fructose-1,6-biphosphate are inhibited

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41
Q

In terms of local regulation of glycolysis and gluconeogenesis, what is responsible for control of these processes?

A

Allosteric effectors

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42
Q

What will stimulate glycolysis and inhibit gluconeogenesis at a local level?

A

High AMP, ADP or ATP will stimulate glycolysis

Fructose-2,6-biphosphate will also stimulate glycolysis when in high concentrations

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43
Q

What will stimulate gluconeogenesis and inhibit glycolysis at a local level?

A

High concentrations of citrate, alanine and acetyl-CoA will inhibit glycolysis and promote gluconeogenesis

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44
Q

What is the most dense energy source?

A

Fat

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45
Q

Why is fat essential to take in through diet?

A
  • It is a key form of energy
  • Some fatty acids are essential fatty acids and can only be obtained through diet
  • Some vitamins are fat solube so require fat for their uptake
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46
Q

What are the three main types lipids?

A
  • Simple lipids - fatty acids, triglycerides and waxes
  • Compound lipids - associated with other compound groups e.g. lipoproteins
  • Steroids - cholesterol, steroid hormones
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47
Q

What is the main energy form within adipose tissue?

A

Triglycerides

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48
Q

Fatty acids have three classifications depending on the structure of the molecule - what are these?

A
  1. Saturated - no double bonds
  2. Unsaturated - one double bond between carbons
  3. Polyunsaturated - several double bonds between carbon atoms
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49
Q

Double bonds are usually in what configuration?

A

Cis

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50
Q

Trans fats are usually in which structural configuration?

A

Trans

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51
Q

What is the consequence of trans fats having a trans molecular structure?

A

They can be packed less tightly

52
Q

What are the main naturl fatty acids?

A

Palmitic acid - saturated 16 carbons

Stearic acid - saturated 18 carbons

Oleic acid - same as steric acid but includes a doube bond

53
Q

How can essential fatty acids be recognised?

A

The body can only synthesise polyunsaturated fatty acids with double bonds up to nine carbons away from the carboxyl group

Any fatty acid that exceeds this rule is an essential fatty acid

54
Q

What are the two methods for naming fatty acids?

A
  1. The carboxyl group can be counted as carbon 1
  2. The carbon furthest from the carboxyl group is counted as carbon 1 (or the omega (ω) carbon) an the carbon closest is the α carbon
55
Q

Expain what is meant by an omega 3 fatty acid

A

There is a double bond 3 carbons away from the omega carbon

56
Q

Why are plant fats generally oils at room temperature, whilst animal fats are solids?

A

Plant fats are much more unstaurated so their melting point is much lower

57
Q

What are the products of fat digestion in the small intestine?

A
  • Glycerol - readily absorbed into the intestinal epithelium
  • Fatty acids
  • Monoglycerides
58
Q

How does the absorption of short and long chain fatty acids differ?

A

Short chains can enter the portal blod directly

Long chains (and monoglycerides) are first resynthesised into triglycerides, coated with phospholipids, protein and cholesterol to form chylomicrons - they can then enter the lymphatic system

59
Q

What can happen to free fatty acids in the blood?

A
  1. They can be resynthesised to triglycerides for storage
  2. They can be oxidised to produce a huge amount of energy
60
Q

What is lipolysis?

A

The breakdown of lipids stored in adipose tissue

61
Q

What must fatty acids be converted into in order for them to slot into the TCA cycle?

A

CoA derivatives

62
Q

Where does the conversion of fatty acids to CoA derivatives fit into the TCA cycle within the cell?

A

Cytoplasm

(Fatty acid + CoA → Acyl-CoA)

63
Q

After oxididation in the cytoplasm of fatty acids, where does further oxidation take place?

A

Mitochondrial matrix

64
Q

By which process is acyl-CoA carried into the mitochondria?

A

Carnitine shuttle

65
Q

How is acyl-CoA transported into the mitochondrial matrix via the Cartinine shuttle?

A
  1. Fatty acid transferred from CoA to cartinine
  2. Acyl-cartinine transported actoss membrane to matrix
  3. Acyl group cleaved off in matrix
  4. Acyl group recomines with a CoA
  5. Cartinine is moved out and the cycle can start again
66
Q

Where does β oxidation occur?

A

Mitochondrial matrix

67
Q

What are the products of β oxidation?

A
  • Acetyl-CoA
  • Acyl-CoA (shortened by 2 carbons)
  • FADH2
  • NADH
  • H+
68
Q

What happens to the shortened acyl-CoA molecule after β oxidation?

A

It can re-enter the β oxidation cycle to produce more acetyl-CoA

69
Q

Subsequent to β oxidation, what is the yield from one acetyl-CoA molecule in the TCA cycle?

A
  • 1 FADH2
  • 3 NADH
  • 3 H+
  • 1 GTP
70
Q

What is the P/O ratio?

A

Phosphate/oxygen ratio

This is the amount of ATP produced from the movement of two electrons through a defined electron transport chain donated by the reduction of an oxygen atom to water

71
Q

What is the P/O ratio for FADH2?

A

1.5

72
Q

What is the P/O ratio for NADH?

A

2.5

73
Q

How much ATP, in total, will be produced from steric acid which can be cleaved 8 times to produce 9 acetyl-CoA

A
  • 9 GTP
  • 27 + 8 = 35 NADH
  • 27 + 8 = 35 H+
  • 9 + 8 = 17 FADH2

(9 (GTP + ( 35x 2.5) + (17 x 1.5) - 2 (activation)) = 120 ATP

74
Q

Where can glycerol be activated and what will it be activated to?

A

Liver and kidneys (not present in adipose tissue)

Glycerol-3-phosphate (by glycerol kinase)

75
Q

When gycerol-3-phosphate is produced what is it converted to in order for it to begin glycolysis?

A

Dihydroxyacetone phosphate

(by glycerol phosphate dehydrogenase)

This can then be converted into one of the intermediates of gycolysis

76
Q

Where do ketone bodies originate?

A

β oxidation of fatty acids

Formed in liver mitochondria

77
Q

What are the three ketone bodies?

A
  1. Acetoacetate
  2. Acetone
  3. Hydroxy-butyrate
78
Q

How are ketone bodies useful for energy production?

A

They can enter the TCA cycle in peripheral tissues and heart muscle and be resyntheised into acetyl-CoA

79
Q

Why and when may ketone bodies become dangerous?

A

During periods of starvation

Much oxaloacetate is used up for gluconeogenesis, this means ketone bodies are produced from excess acetyl-CoA

Ketone levels rise in the blood and this can cause acidosis affecting the CNS and heart

Acidotic coma or death may occur

80
Q

What is the treatment for ketosis in starvation or diabetes?

A

Administration of insulin to prompt glucose breakdown

(glucose may also me given)

81
Q

What is lipogenesis?

A

When new fatty acids are synthesised when there is surplus energy

82
Q

In which tissues can lipogenesis occur?

A

Liver, kidneys, mammary glands and brain

83
Q

By which protein are free fatty acids transported into the plasma?

A

Albumin

84
Q

Excess carbohydrate is used to form fatty acids and triglycerides in the liver, what is used to transport these triglycerides to adipose tissue for storage?

A

Low density lipoprotein

85
Q

What can happen to fatty acids when they are produced? (2)

A
  1. Esterified with glycerol to form triglycerides
  2. Oxidised to allow acetyl-CoA to be resynthesised again
86
Q

Lipogenesis occurs in th cytoplasm of which cells?

A

Liver

87
Q

What is the substrate for lipogenesis?

A

Acetyl-CoA

88
Q

Where is acetyl-CoA produced and by action of which enzyme?

A

Mitochondrial matrix

Pyruvate dehydrogenase

89
Q

How does acetyl-CoA cross the inner mitochondrial membrane for lipogenesis?

A

It bind to citric acid allowing it to cross the membrane

90
Q

Which regulatory enzyme controls how much fatty acid is synthesised at any one time?

A

Acetyl-CoA carboxylase

(found in liver and adipose tissue)

91
Q

When effect does acetyl-CoA carboxylase have on acetyl-CoA?

A

It converts acetyl-CoA to malonyl-CoA by adding bicarbonate

This uses 1 ATP

92
Q

What is the purpose of malonyl-CoA in terms of fatty acid synthesis?

A

It will donate the addition carbon (from bicarbonate) to the fatty acid

93
Q

Which enzyme catalyses fatty acid synthesis?

A

Fatty acid synthase

94
Q

Describe how fatty acid synthase facilitates fatty acid synthesis

A
  • There are two acyl binding sites - one for acetyl-CoA and one for malonyl-CoA
  • 2 carbons are transferred from malonyl-CoA to acetyl-CoA
  • The second acyl binding site becomes free and a new malonyl-CoA is added and the cycle repeats
  • The fatty acid chain develops 2 carbons at a time and remains attaced to fatty acid synthase
95
Q

As well as acetyl-CoA and malonyl-CoA, what else does fatty acid synthase require in order to function?

A

NADPH

An electron donor (this is a reductive process)

96
Q

At what chain length is the fatty acid released from fatty acid synthase and what is the name of this fatty acid?

A

Palmitic acid

(this is th maximum chain length fatty acid synthase can synthesise)

97
Q

Which enzyme confers control of fatty acid metabolism?

A

Acetyl-CoA carboxylase

98
Q

Which hormones can influence acetyl-CoA carboxylase and what will their effects be on it?

A

Insulin - stimulate

Glucagon - inhibit

Adrenaline - inhibit

(fatty acid synthesis ony occurs in times of plentiful resources)

99
Q

What can antagonise acetyl-CoA carboxylase when its levels are high?

A

Palmitoyl CoA

(abundant when fatty acids are in excess)

100
Q

If glycerol-3-phosphate is required for triglyceride synthesis, how may it be synthesised?

A

Glycerol kinase

(found in the liver)

101
Q

Fat cells do not have glycerol kinase - how do they obtain glycerol-3-phosphate?

A

Via glycolysis

102
Q

In fat cells, why is it virtually impossible to synthesise triglycerides unless there is plenty of glucose in the bloodstream?

A
  • Glycerol-3-phosphate is essential for triglyceride synthesis with fatty acids
  • It can only be obtained in fat cells via glycolysis
  • Glycolysis can only occur if glucose is present
103
Q

Why are amino acids which are not used for protein synthesis degraded and used to provide energy?

A

They are not easily stored

104
Q

Where does amino acid breakdown primarily occur?

A

Liver

105
Q

Which two sources can amino acids be obtained from?

A
  1. Dietary intake
  2. Cellular protein turnover
106
Q

How do tissues which require amino acids access them?

A

Bloodstream

107
Q

What must be removed from amino acids in order to form the intermediates required for them to slot into the TCA cycle?

A

Nitrogen

(from amino groups)

108
Q

What are the breakdown products from amino acids and why is it important that they are excreted?

A

Ammonia and ammonium ions

In high concentrations these can be toxic

109
Q

How are by products containing notrogen mainly excreted from the body?

A

Urea in the urine

110
Q

Where is urea formed?

A

Liver

111
Q

What are the headings for the three stages of urea synthesis?

A
  1. Transamination
  2. De-amination
  3. Urea (Ornithine) cycle
112
Q

Describe the process of transamination

A

The amino group is transferred to a keto acid

This can occur in all tissues and usually forms glutamic acid presuming ketoglutarate is used as the keto acid

113
Q

Describe the process of de-amination

A

The amino group is removed from the glutamic acid reforming the keto acid

The free ammonium ion can now enter the urea cycle

114
Q

Describe the urea cycle

A

Free ammonium ions are converted to urea along with aspartic acid

Urea has two nitrogen atoms and obtains one from each of urea and aspartic acid

115
Q

Where does de-amination occur?

A

Liver

116
Q

How can the amino group of glutamate be transported to the liver for deamination?

A

The amino group is transferred fro glutamate to pyruvate to produce alanine

Alternatively, glutamine synthase can add ammonium ions to glutamate to produce glutamine

Both alanine and glutamine can be transported to the liver

117
Q

Demaination is an energy producing process

True or false?

A

False

It is energy consuming (3ATP)

118
Q

As well as urea, 2 phosphate, 2 ADP and AMP, what else is produced during demaination?

A

Fumarate

It is an intermediate in the TCA cycle

119
Q

What is the resulting structure called when the amino group is removed?

A

Carbon skeleton

120
Q

What is the fate of carbon skeletons? (2)

A
  1. Degraded to glucose
  2. Oxidised in the TCA cycle
121
Q

What are the two types of amino acids that can be broken down?

A
  1. Ketogenic amino acids
  2. Glucogenic amino acids
122
Q

What is a ketogenic amino acid broken down into?

A

Acetyl-CoA or acetoacetyl-CoA

This can give rise to ketone bodies or fatty acids as well as entering the TCA cycle

123
Q

What is a glucogenic amino acid broken down into?

A

Pyruvate or TCA cycle intermediates

They can be converted into phosphoenolpyruvate and then into glucose to allow for glycolysis

124
Q

Alcaptonuria involves a blockage in the degredation of _______________ and ___________

A

Phenylalanine to tyrosine

125
Q

What is maple syrup urine disease and what causes it?

A

The urine is sweet and smells like maple syrup

The degredation of valine, isoleucine and leucine is blocked

Mental and physical retardation can be found in some patients yet this can be controlled through diet

126
Q

What is phenylketonuria?

A

PKU is due to a failure of the degredation of phenylalanine to tyrosine

It causes severe mental retardation if untreated because phenylalanine can build up in all body tissues and fluids

The treatment is a low phenylalanine diet

127
Q

What may happen in a urea cycle disorder where α-ketoglutarate levels become low?

A

Not enough α-ketoglutarate is present to bind to free ammonium ions leading to a rise that is potentially toxic - especially to the nervous system

The Gastrointestinal System 2023 (27 decks)

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