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Biochemistry Flashcards

1
Q

what is glycogenesis?

A

the synthesis of glycogen from glucose

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2
Q

what is glycogenolysis?

A

the breakdown of glycogen to form glucose

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3
Q

when is liver glycogen broken down?

A

between meals

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4
Q

from which organ can glycogen be converted back to glucose to maintain blood glucose levels?

A

liver

hepatic glycogen

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5
Q

what is glycogen within muscles used for?

A

production of ATP

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6
Q

during bursts of physical activity what pathway does glycogen go down to produce ATP?

A

glycolysis and the TCA cycle (citric acid cycle)

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7
Q

what type of breakdown is glycogenolysis?

A

phosphorolysis

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8
Q

what is the primary way of maintaining glucose concentrations overnight?

A

gluconeogenesis

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9
Q

what is gluconeogenesis?

A

the synthesis of glucose from non-carbohydrate precursors

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10
Q

what are the 3 sources of blood glucose within the body?

A

dietary glucose
glucose produced from glycogenolysis
glucose produced from gluconeogenesis

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11
Q

what is glycogen?

A

a polymer consisting of glucose monomers

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12
Q

what links join the straight chains of glucose monomers within glycogen?

A

a1-4 glycosidic bonds

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13
Q

what links introduce branches into the glucose monomers within glycogen?

A

a1-6 glycosific bonds

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14
Q

what does the extensive branching of glycogen allow?

A

increases speed at which glucose can be cleaved/added

as this happens at the ends of the polymers

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15
Q

what is the protein at the centre of glycogen?

A

glycogenin

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16
Q

what is the function of glycogenin?

A

can bind to up to 4 glucose molecules in order to create a primer for glycogenesis

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17
Q

what is the enzyme which adds extra glucose monomers to the existing glycogen?

A

glycogen synthase

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18
Q

why is a primer needed for glycogenesis?

A

because glycogen synthase can only add glucose molecules to existing glycogen so needs some way to start

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19
Q

before glucose can be used for any metabolic pathway what must be done to it?

A

glucose first has to be phosphorylated

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20
Q

what is the first step of glycogen synthesis from glucose?

A

phosphorylation of glucose to glucose-6-phosphate

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21
Q

what enzyme catalyses the formation of glucose-6-phosphate from glucose?

A

hexokinase

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22
Q

once glucose has been phosphorylated to glucose-6-phosphate, where does it become trapped?

A

in the cell

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23
Q

if a cell requires energy, what happens to the glucose-6-phosphate?

A

glycolysis for ATP

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24
Q

if a cell doesn’t require energy, what happens to the glucose-6-phosphate?

A

glycogenesis (conversion into glycogen)

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25
Q

if a cell doesn’t require energy, and so goes through the glucogenesis route, what is the glucose-6-phosphate converted to?

A

glucose-1-phosphate

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26
Q

what enzyme converts glucose-6-phosphate to glucose-1-phosphate?

A

phosphoglucomutase

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27
Q

what type of reaction is the conversion of glucose-6-phosphate to glucose-1-phosphate?

A

reversible reaction

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28
Q

how does the glucose-1-phosphate become activated?

A

by forming UDP-glucose

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29
Q

what enzyme uses the substrates UDP-glucose and glycogen to make a longer chain of glycogen + UDP?

A

glycogen synthase

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30
Q

what happens to the UDP left over after the formation of a 1-monomer-longer-glycogen?

A

UDP gets phosphorlyated to UTP

requires ATP

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31
Q

how many molecules of ATP net does glycogenesis require?

A

1 ATP molecule

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32
Q

what type of bonds does glycogen synthase introduce into the glycogen polymer?

A

a1-4 glycosidic bonds

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33
Q

what enzyme removes a glucose monomer from the glycogen in glycogenolysis?

A

glycogen phosphorylase

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34
Q

what does glycogen phosphorylase do to the glucose it has removed from glycogen?

A

phosphorlyates it to glucose-1-posphate

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35
Q

what enzyme converts glucose-1-phosphate to glucose-6-phosophate in the process of glycogenolysis?

A

phosphoglucomutase

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36
Q

what is the difference between glucose-6-phosphate in a liver cell and in a muscle cell?

A

glucose-6-phosphate in the liver can be dephosphorylated and then the free glucose released into the blood stream
glucose-6-phosphate in a muscle cell can’t be dephosphorlyate and so it can only be used to produce ATP for itself through glycolysis

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37
Q

what type of bonds does glycogen phosphorlyase break in the glycogen polymer?

A

only straight chain a1-4 glucosidic bonds

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38
Q

what branching enzyme introduces a1-6 glycosidic branches into glycogen?

A

transglycosylase

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39
Q

what is the rate limiting step of glycogenolysis?

A

getting glucose-1-phosphate from glycogen by the action of glycogen phosphorlyase

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40
Q

what transporter allows glucose to leave the liver and enter the blood?

A

GLUT2

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41
Q

what 3 hormones up regulate glycogen phosphorylase?

and so increase rate of glycogenolysis

A

glucagon
adrenaline
cortisol
(hormones of hungry state)

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42
Q

what hormone down regulates glycogen phosphrolase?

and so decreases rate of glycogenolysis

A

insulin

hormone of fed state

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43
Q

what 3 precursors can be used for gluconeogenesis?

A

lactate
amino acids
glycerol

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44
Q

when is lactate synthesised in the body?

A

by muscle under anaerobic conditions

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45
Q

how are amino acids produced?

A

proteolysis of muscle protein

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46
Q

how is glycerol produced?

A

lipolysis of triglycerides in adipose tissue

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47
Q

where does gluconeogenesis occur?

A

mainly in the liver

small amounts in the kidneys

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48
Q

what does gluconeogenesis obtain its energy from?

A

from oxidation of fatty acids released from adipose tissue

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49
Q

what is gluconeogenesis essentially the reverse of?

A

glycolysis

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50
Q

what is the end product of glycolysis?

A

pyruvate

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51
Q

most of the reactions in glycolysis are reversible, what are the 3 irreversible reactions in glycolysis which need different enzymes for the reverse to occur? (for gluconeogenesis)

A

glucose to glucose-6-phosphate by hexokinase

fructose-6-phosphate to fructose-1-6-biphosphate by phosphofructokinase

phosphoenolpyruvate to pyruvate by pyruvate kinase

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52
Q

how many unique liver enzymes are needed to do the reverse of the 3 irreversible reactions within glycolysis?
(for gluconeogenesis)

A

4

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53
Q

in gluconeogenesis what is the substrate?

A

pyruvate

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54
Q

what is the first step within gluconeogenesis?

A

pyruvate to oxaloacetate

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55
Q

for each glucose formed by gluconeogenesis how many pyruvates and how many ATPs (or equivalents) are used?

A 
2 pyruvates
6 ATP (or equivalents)
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56
Q

how many ATPs are generated for each glucose that is oxidised through glycolysis? (net)

A

2 ATP

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57
Q

how is lactate produced in muscle cells transported to the liver?

A

blood stream

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58
Q

why can the Cori cycle (the cycle of glucose-lactate in liver and muscle) not go on forever?

A

because it generates less ATP than it consumes

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59
Q

what are the 2 classes of amino acids?

A

ketogenic amino acids

glucogenic amino acids

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60
Q

which class of amino acid can be used as a precursor for gluconeogenesis?

A

glucogenic amino acids

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61
Q

what are the 2 ways that glucogenic amino acids can form oxaloacetate? (The first step in gluconeogenesis)

A
  1. conversion into pyruvate which gets converted into oxaloacetate
  2. entering the TCA cycle by joining with an intermediate which results in the eventual formation of oxaloacetate
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62
Q

through what molecule do ketoamino acids enter the TCA cycle as?

A

acetyl CoA

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63
Q

what molecule needs to be present for acetyl CoA (made from ketogenic amino acits) to enter the TCA cycle?

A

oxaloacetate

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64
Q

oxaloacetate accepts acetyl CoA thus adding it into the TCA cycle, what is the product that is formed?

A

citric acid

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65
Q

what do AMP/ADP stimulate? (gluconeogenesis or glycolysis)

A

glycolysis

inhibit gluconeogenesis

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66
Q

what does ATP stimulate? (gluconeogenesis or glycolysis)

A

gluconeogenesis

inhibit glycolysis

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67
Q

what does fructose 2,6-biphosphate stimulate? (gluconeogenesis or glycolysis)

A

glycolysis
(inhibits gluconeogenesis)
[this is because fructose 2-6 biphosphate is high in the fed state, so no more blood glucose is needed]

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68
Q

what do citrate, alanine and acetyl-CoA stimulate? (gluconeogenesis or glycolysis)

A

gluconeogenesis
(inhibits glycolysis)
[these substances are high when intermediates or building blocks are abundant]

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69
Q

what are essential fatty acids?

A

fatty acids that can not be made in the body

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70
Q

what are the 4 major fat-soluble vitamins? (absorption of these is closely linked to that of fat and they are stored in body fat)

A

A, D, E, K

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71
Q

what is the main energy storage form in adipose tissue?

A

triglycerides

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72
Q

what do triglycerides consist of?

A

glycerol + 3 fatty acids

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73
Q

fats are aliphatic, what does this mean?

A

their structure contains no rings

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74
Q

what type of structures within fatty are rare?

A

branched chain fats

odd numbers of carbons

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75
Q

what are the 3 types of fatty acids?

A

saturated
unsaturated
polyunsaturated

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76
Q

what is a saturated fatty acid?

A

there are no C=C double bonds within the chain

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77
Q

what is an unsaturated fatty acid?

A

there is 1 C=C double bond within the chain?

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78
Q

what is a polyunsaturated fatty acid?

A

there are several C=C double bonds within the chain

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79
Q

compare the cis formation of a C=C double bond to a trans formation?

A

cis C=C double bond: both R chains are on the same side

trans C=C double bond: R chains are on dopposing sides

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80
Q

describe the structure of palmittic acid?

A

16:0
16 carbon chain, 0 C=C double bonds
-saturated

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81
Q

describe the structure of stearic acid?

A

18:0
18 carbon chain, 0 C=C double bonds
-saturated

82
Q

describe the structure of oleic acid?

A

18:1
18 carbon chain, 1 C=C double bonds
-unsaturated

83
Q

describe the structure of linoleic acid??

A

18:2
18 carbon chain, 2 C=C double bonds
-polyunsaturated

84
Q

what is the difference between stearic, oleic and linoleic acid?

A

all have 18 carbons in the chain
stearic acid has 0 C=C double bonds
oleic acid has 1 C=C double bond
linoleic acid has 2 C=C double bonds

85
Q

in a fatty acid, which carbon is C1?

A

the carbon of the carboxyl roup

86
Q

in a fatty acid which carbon is a-carbon? (alpha carbon)

A

the carbon adjacent t the carboxyl group

87
Q

in a fatty acid which carbon is a w-carbon? (omega carbon)

A

the furtherst away carbon from the carboxyl group

88
Q

how long does a fatty acid chain have to be to be a solid at room temperature?

A

> 8 carbons

89
Q

what do C=C double bonds do to the melting point of the fatty acid?

A

lower the melting point

90
Q

what type of fatty acids are contained within plant fats?

A

unsaturated fatty acids

liquid at room temp

91
Q

what type of fatty acids are contained within animal fats?

A

saturated fatty acids

solid at room temp

92
Q

what are the 3 main products of fat digestion?

A

glycerol
fatty acids
monoglycerides

93
Q

what happens to short and medium length fatty acids once absorbed into the enterocytes of the intestine?

A

enter portal blood system

94
Q

what happpens to the longer chain fatty acids and monoglycerides once absorbed into the enterogytes of the intestine?

A

re-sythensised into triglycerides, form chylomicrons and enter lymphatic system

95
Q

where is fat stored in the body?

A

adipose tissue

96
Q

what type of lipases cleave the fat into free fatty acids and glycerol?
(lipolysis)

A

hormone sensitive lipases

97
Q

what has to happen before fatty acids can be oxidised to generate energy?

A

fatty acids must be converted to CoA derivatives

acyl-CoA

98
Q

where does the conversion of fatty acids into CoA deriviatives occur?

A

cytoplasm

99
Q

how much ATP is required for the conversion of fatty acids to CoA derivatives?

A

2 ATP

100
Q

where does oxidation of the fatty acid derived acyl-CoA occur?

A

mitochondrial matrix

101
Q

how is the acyl CoA transferred from the cytoplasm to the mitochondrial matrix?

A

carnitine shuttle

102
Q

describe the carnitine shuttle?

A
  1. fatty acids are transferred from acyl-CoA to canitine: acyl carnitine
  2. acyl-carnitine transporter facilitates the transport of acyl-carnitine into the mitochondrion
  3. fatty acids are transferred from the acyl-carnitine to CoA: acyl-CoA
  4. acyl-carnitine transporter facilitates the tranport of canitine out of the mitochondrion

[CoA itself doesn’t get tranported across, 2 separate pools of CoA]

103
Q

what is beta-oxidation?

A

the catabolism of fatty acids into products that can be used in the TCA cycle or oxidative phosphorylation

104
Q

how many steps are in each cycle of beta-oxidation?

A

4

105
Q

what are the products of 1 beta-oxidation cycle?

A

1 acetyl-CoA
1 FADH2
1 NADH + H+
1 fatty acyl-CoA (shortened by 2 carbon atoms)

106
Q

how do you calculate the number of beta-oxidation cycles needed for a specific fatty acid?

A

(number of Carbons/2) -1

eg stearic aicd
(18/2) -1 = 8 cycles

107
Q

what is acetyl-CoA (produced from beta-oxidation of fatty acids) oxidised in the TCA cycle to produce?

A

1 FADH2
3 NADH + 3H+
1 GTP
2 CO2

108
Q

compare the yield of FADH2 in saturated fatty acids compared to unsatruated fatty acids?

A

unsaturated fatty acids yield less FADH2 than saturated fatty acids because they are already partially oxidise

109
Q

in the last cycle of beta oxidation of an odd-chain fatty acid instead of yielding 2 acetyl Co-As what is yielded?

A

acetyl CoA (2 carbon)
+
propionyl-CoA (3 carbon)

110
Q

how does propionyl-CoA enter the TCA cycle?

A

converted to succinyl-CoA which enters the TCA cycle directly

111
Q

where are ketone bodies formed?

A

in the liver mitochondria

112
Q

what are ketone bodies formed from?

A

acetyl CoA from beta oxidation

113
Q

what is the function of ketone bodies?

A

diffuse into peripheral tissues and then can be converted back into acetyl CoA which enters the TCA cycle

114
Q

how many carbons are in oxaloacetate?

A

4

115
Q

in starvation or diabetes why can acetyl CoA from the ketone bodies not convert back into acetyl CoA and enter the TCA cycle?

A

because to enter the TCA cycle there needs to be oxaloacetate

in starvation nor diabetes, gluconeogenesis has used up the oxaloacetate and so acetyl-CoA can’t enter the TCA cycle and accumulates in tissues instead

116
Q

what blood gas result does starvation or diabetes cause due to the accumulation of ketone bodies?

A 
metabolic acidosis
(diabetic ketoacidosis due to hypoglycaemia)
117
Q

where does de novo synthesis of fatty acids mainly occur?

A

in the liver, kidney, mammary glands, adipose tissue and brain

118
Q

lipoenesis is a reductive process, what does this mean?

A

electrons are required

119
Q

what is the precursor molecule in the synthesis of fatty acids?

A

acetyl CoA

120
Q

where does synthesis of fatty acids from acteyl-CoA occur?

A

cytoplasm

121
Q

why can acetyl-CoA not easily transfer between mitochondrial matrix and cytoplasm?

A

inner mitochondrial membrane is impermeable to acetyl-CoA

122
Q

what transports the acetyl made in the matrix (by beta oxidation) to the cytoplasm for lipogenesis?

A

citrate

123
Q

how is citrate formed?

A

condensation of acetyl-CoA with oxaloacetate

first step of TCA cycle

124
Q

why would citrate leave the mitochondria to allow lipogenesis to take place instead of carrying on with the TCA cycle?

A

if the cirrate concentrations are very high

125
Q

what is the first step in lipogenesis?

A

activation of acetyl-CoA to malonyl-CoA

126
Q

what enzyme converts acetyl-CoA to malonyl-CoA

A

acetyl-CoA carboxylase

127
Q

what is the function of fatty acid synthase?

A

catalyses synthesis of saturated long-chain fatty acids from malonyl-CoA, acetyl-CoA and NADPH

128
Q

what is teh function of NADPH within lipogenesis?

A

donates electrons

129
Q

how many acyl-carrier proteins does fatty acid synthase carry?

A

2 per dimer

130
Q

what is the longest fatty acid that can be created by fatty acid synthase?

A

palmitic acid (16:0)

131
Q

what does each lipogenesis cycle do to the growing acyl-CoA?

A

2 carbons are added to the acetyl-CoA on the first cycle from maloynyl-CoA
and this cycle continues until a 16 carbon molecule is made

132
Q

what derivative of glycerol is needed for the synthesis of triglycerides?

A

glycerol-3-phosphate

133
Q

what does the liver produce glycerol-3-phosphate from?

A

glycerol

134
Q

what does adipose tissue produce glycerol-3-phosphate from?

A

glucose

135
Q

when are fats synthesised de novo?

A

when there are times of excess carbohydrates

causing excess citrate

136
Q

where is the main site of amino acid degradation?

A

liver

137
Q

what are the 4 major nitrogen-containing excretory molecules?
(remember nitrogen comes from amino acids)

A

urea
uric acid
creatinine
ammonium ion

138
Q

where is urea produced?

A

liver

139
Q

what are the 3 steps in the synthesis of urea?

A

transamination
de-amination
urea cycle

140
Q

where does the transamination phase of urea synthesis occur?

A

all cells

141
Q

what happens in the transamination phase of urea synthesis?

A

production of glutamic acid from the transfer of an amino group from amino acid to ketoglutarate

142
Q

what enzyme catalyses the transmination phase of urea synthesis?

A

amino transferase

143
Q

where does the de-amination phase of urea synthesis occur?

A

liver cells

144
Q

what happens in the de-amination phase of urea synthesis?

A

amino group is removed from glutamatic acid

and NADH + NH4+ is formed

145
Q

what 2 amino acids are the main transporter molecules of nitrogen to the liver?

A

alanine
glutamate
(glutamic acid is converted to these for transport to the liver, once in the liver they are converted back)

146
Q

what is the overall process of the urea cycle?

A

ammonium ion + CO2 + aspartic acid = urea

147
Q

how many high energy phosphate bonds are used in the urea cycle?

A

4

3ATP to 2 ADP + AMP

148
Q

what biproduct is made in the urea cycle?

A

fumerate

149
Q

once the amino group has been removed, what are the 2 options for ketogenic amino acids?

A
  1. degraded to acetyl-CoA which can be oxidised in the TCA cycle
  2. give rise to ketone bodies
150
Q

once the amino group has been removed, what are the 2 options for glucogenic amino acids?

A
  1. degraded to pyruvate or TCA cycle intermediates

2. converted into phosphoenolpyruvate and then into glucose (gluconeogenesis)

151
Q

what is alcaptonuria?

A

an inherited disorder where the degradation of phenylalanine and tyrosine is blocked

152
Q

what is mable syrup urine disease?

A

an inherited disorder where degradation of valine, isoleucine and leucine is blocked

153
Q

what is phenylketonuria?

A

an inherited disorder where phenylalanine cant be broken down

154
Q

how do you treat urea cycle disorders?

A

low-protein diet

drugs which remove nitrogen

155
Q

why are urea cycle disorders so dangerous?

A

accumulation of ammonia in the blood (toxic)

156
Q

what are the 6 principle roles of the liver?

A
  1. destination of most nutrients and xenobiotics absorbed from the GI tract
  2. bile production
  3. elimination of unwanted molecules
  4. secretion of plasma proteins
  5. storage of important molecules
  6. regulation of metabolism
157
Q

what are the 6 main classes of liver-derived plasma protein?

A 
albumin
alpha 1 globulins
alpha 2 globulins
beta 1 globulins
beta 2 globulins
gamma globulins
158
Q

what are gamma globulins more commonly known as?

A

immunoglobulins

159
Q

describe the relative concentrations of liver-derived plasma proteins?

A

albumins are present at high concentrations

alpha, beta and gamma globulins are present at lower concentrations

160
Q

list the liver-derived plasma proteins in terms of molecular weight?
(heaviest to lightest)

A

gamma globulins
beta 1 + 2 globulins
alpha 1 + 2 globulins
albumin

161
Q

what are the 5 main function of plasma proteins?

A
  1. maintenance of osmotic pressure in blood vessel
  2. transport of hydrophobic substances
  3. pH buffering
  4. enzymatic
  5. immunity
162
Q

how do plasma protein buffer the pH?

A

by accepting or donating protons

163
Q

what plasma protein binds copper?

A

ceruloplasmin

164
Q

what type of liver-derived plasma protein is ceruloplasin?

A

alpha globulin

165
Q

what type of liver-derived plasma protein is transferrin?

A

beta globulin

166
Q

what type of liver-derived plasma protein is fibrinogen?

A

beta globulin

167
Q

what can loss of transferrin indicate?

A

iron deficiency

168
Q

what happens to transferrin expression when you increase altitude?

A

a rise in transferrin expression (because increasing altitude is an erythopoetic effect)

169
Q

what is fibrinogen?

A

inactive form of fibrin

activated by prothrombin

170
Q

what is the plasma protein which is the determinant of plasma oncotic pressure?

A

albumin

171
Q

what hormone stimulates the production of albumin in the liver?

A

insulin

172
Q

what 3 things cause the decreased levels of albumin?

A

starvation
low protein diet
liver disease

173
Q

albumin also has a transport function, describe affinity albumin has for hydrophobic molecules?
describe capacity albumin has for hydrophobic molecules?

A 
low affinity
high capacity (due to high concentration)
174
Q

what plasma protein carries bilirubin to the liver?

A

albumin

175
Q

what is bilirubin the breakdown product of?

A

haem

176
Q

what form is iron transported as?

A

ferric (Fe3+)

177
Q

what protein is Fe3+ bound to for transport?

A

transferrin

178
Q

what form is iron stored as?

A

ferrous (Fe2+)

179
Q

when stored within cells, what is fFe2+ bound to?

A

ferritin

180
Q

what metal plays the essential role of oxidising Fe2+ to Fe3+ for transport?

A

copper

within ceruloplasmin

181
Q

what is Wilsons disease?

A

an inherited disease where you are deficient in ceruloplasmin leading to the accumulation of copper in organs and tissue

182
Q

how is thyroxine (T4) transported?

A

bound to thyroid-binding globulin

183
Q

how is cortisol transported?

A

cortisol-binding globulin

184
Q

what do binding globulins do to the hormone biological half life?
(how?)

A

extend it

because without binding globulins the hormones would be eliminated rapidly by liver or kidney

185
Q

why does malnutrition (because of vitamin deficiency) take a long time to come into effect?

A

because the liver has stored up many vitamins

186
Q

what does the synthesis of cholesterol require?

A

18 mol of acetyl-CoA
16 mol of NADPH
36 mol of ATP

187
Q

what is the rate limiting step in cholesterol synthesis?

A

the action of HMG-CoA reductase

188
Q

what is the function of HMG-CoA reductase?

A

irreversibly catalyses the formation of mevalonic acid

189
Q

what stimulates the synthesis and activity of HMG-CoA reductase?

A

starving

190
Q

what 2 molecules does vitamin D have a key role in the regulation of their metabolism?

A

calcium

phosphorus

191
Q

what 3 organs are steroid hormones produced from?

A

ovaries
testis
adrenal glands

192
Q

how many carbons are in a corticosteroid?

A

21 carbon atoms

193
Q

how many carbons are in an androgen?

A

19 carbon atoms

194
Q

how many carbons are in an estrogen?

A

18 carbon atoms

195
Q

what is the main metabolic product of cholesterol?

A

bile salts

196
Q

where does fatty acid synthesis take place?

A

cytoplasm

197
Q

where does beta oxidation take place?

A

mitochondrial matrix

198
Q

what is the donor molecule of carbons to a growing fatty acid?

A

malonyl-CoA

199
Q

where does glycolysis occur?

A

cytoplasm

200
Q

what is the P/O ratio?

A

a measure of the number of ATP molecules formed per oxygen atom reduced

201
Q

which has a greater redox potential- NADH + H+ or FADH2?

ie likes to give away electons more

A

NADH + H+

Gastrointestinal (15 decks)

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