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LS1 Metabolism > Energy production: carbohydrates > Flashcards

Energy production: carbohydrates Flashcards

1
Q

List the two reactions in glycolysis, in which the reactants are phosphorylated compounds with high energy of hydrolysis bonds and therefore are coupled to substrate level phosphorylation

A
  1. Step 10:
    phosphoenolpyruvates + ADP –> pyruvate + ATP
  2. Step 7:
    1,3-bisphosphoglycerate + ADP –> 3-phosphoglycerate + ATP
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2
Q

What is the general formula for carbohydrates?

A

(CH2O)n

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3
Q

What functional groups do carbohydrates contain?

A
  1. Aldehyde or keto group

2. Multiple hydroxyl groups

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4
Q

Name three monosaccharides

A

Glucose
Fructose
Galactose

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5
Q

What monosaccharides make up the disaccharide sucrose?

A

glucose and fructose

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6
Q

What monosaccharides make up the disaccharide lactose?

A

glucose and galactose

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7
Q

Name two digestible polysaccharides

A

Starch

Glycogen

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8
Q

Name an indigestible polysaccharide

A

Cellulose

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9
Q

Why does the body contain relatively little carbohydrate, in spite of its large intake?

A

Most is used as fuels by tissues and is oxidised to CO2 and H2O.
A small amount is stored as glycogen and as a component of cellular polymers such as nucleic acids, glycolipids and glycoproteins

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10
Q

What happens to excess carbohydrate in the diet?

A

Coverted to glycogen for storage and once the glycogen stores are full to triacyglycerols for storage in adipose tissue

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11
Q

Why can all monosaccharides, except for dihydroxyacetone, exist as stereoisomers?

A

Because they contain asymmetric C-atoms (four different groups attached to a C-atom)

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12
Q

What is the natural form of monosaccharide steroeisomer found in the body?

A

D-enantiomer

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13
Q

Describe the structure of glucose

A

It is a hexose (contains 6 carbon atoms). 5 of these carbons and 1 oxygen make a six-membered ring. Each carbon atom has one hydroxyl group.

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14
Q

Glucose can exist in two forms alpha- and beta- which enzymes can distinguish between and preferentially use one or the other. What is the difference between these two forms?

A

Beta-D-glucose has all the neighbouring hydroxyl groups opposite sides of the ring to each other. Alpha-D-glucose has the hydroxyl group next to the oxygen in the ring on the same side of the ring as the next hydroxyl group

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15
Q

What concentration is glucose maintained at in the blood?

A

Approximately 5mM

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16
Q

When does fructose and galactose appear in the blood?

A

For short period after the consumption of fruit and dairy products

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17
Q

High concentration of galactose in the blood are associated with what clinical problem?

A

Galactosaemia

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18
Q

High concentration of fructose in the blood is associated with what clinical problem?

A

Fructose intolerance

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19
Q

List two important physico-chemical properties of sugars

A
  1. Hydrophilic - water soluble, do not cross cell membranes

2. Partially oxidised - need less oxygen than fatty acids for complete oxidation

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20
Q

Name the bond that links monosaccharides together to form disaccharides and polysaccharides

A

glycosidic bond

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21
Q

What are most polysaccharides made from

A

One type of monosaccharide (homo-polymers)

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22
Q

What two types of glycosidic bonds are found in glycogen?

A

alpha-1,4
alpha-1,6
(10:1)

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23
Q

Glycogen is the major store of glucose in the body. Where is glycogen found?

A

Liver and Skeletal muscles - stored as granules

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24
Q

What is glycogen made from?

A

Highly branched, glucose polymer

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25
Q

Where does starch come from?

A

Plants

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26
Q

What is starch made from?

A

Polymer of glucose. It is a mixture of amylose (alpha-,4 linkages) and amylopectin (alpha-1,6 linkages)

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27
Q

Digestive enzymes in the human GIT hydrolyse starch into…

A

Glucose and maltose (glucose-glucose)

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28
Q

Where does cellulose come from?

A

Plants - glucose polymer which has a structural role

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29
Q

Why can cellulose not be digested?

A

Glucose units are linked with beta-1,4 glycosidic bonds which can’t be hydrolysed by human GI tract enzymes

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30
Q

Why is cellulose important in our diet?

A

It is a major component of dietary fibre, that is important for normal GI tract function

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31
Q

What is the name of the glycosidase enzyme secreted in the mouth?

A

Salivary amylase

starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)

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32
Q

What is the name of the glycosidase enzyme secreted into the duodenum?

A

Pancreatic amylase

starch&glycogen –> glucose, maltose and smaller polysaccharides (dextrins)

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33
Q

What are the names of the gyocosidase enzymes which break down dietary disaccharides (maltose and sucrose), maltose and dextrins in the duodenum and jejunum, releasing the monosaccharides glucose, fructose and galactose?

A

lactase
glycoamylase
sucrase/isomaltase

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34
Q

Where are the glyocsidase enzymes lactase, glycoamylase and sucrase/isomaltase found in the gut?

A

They are large glycoprotein complexes attached to the brush border membranes of the epithelial cells lining the duodenum and jejunum

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35
Q

What happens to the activity of lactase throughout life?

A

It is high in infants but decreases in childhood in most populations except Northern Europeans

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36
Q

What is low activity of lactase associated with?

A

Reduced ability to digest the lactose present in milk products and may produce the clinical condition of lactose intolerance

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37
Q

How does lactose intolerance cause the clinical symptoms of diarrhoea, bloating and discomfort?

A

In individuals with a low level of lactase, if lactose is digested then it will persist into the colon where bacteria can break it down. The presence of lactose in the lumen of the colon increases the osmotic pressure of the contents and draws water into the lumen, causing diarrhoea. Colonic bacteria can produce hydrogen, carbon dioxide and methane gases from lactose, causing feelings of bloating and discomfort

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38
Q

How is glucose, fructose and galactose transported into the epithelial cells lining the gut?

A

Active transport (against their concentration gradient)

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39
Q

How are glucose, fructose and galactose transported from epithelial cells into the blood and from blood into tissues?

A

Facilitated diffusion (down a concentration gradient) using a family of glucose transport proteins (GLUT1-5)

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40
Q

How do the family of glucose transport proteins (GLUT1-5) differ?

A

In their affinity for glucose and relative activities. They reflect differences in the requirement of tissues for glucose

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41
Q

How does the glucose transport protein GLUT-4 function and why is this important?

A

GLUT-4 is found in skeletal muscle and adipose tissue. It is sensitive to insulin. High levels of insulin increase the uptake of glucose into these tissues by increasing the number of glucose transport proteins in the plasma membrane

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42
Q

Which tissues can metabolise glucose, fructose and galactose?

A

All tissue can remove glucose, fructose and galactose from the blood.
All tissues can metabolise glucose but the LIVER is the major site of fructose and galactose metabolism

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43
Q

Why is the concentration of the glucose in the blood kept relatively constant?

A

Some tissues have an absolute requirement for glucose and the rate of glucose uptake into these tissues is dependent on the concentration in the blood

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44
Q

Which tissues have an absolute requirement for glucose?

A

red blood cells, white blood cells, kidney medulla, lens of the eye, (brain and CNS prefer glucose)

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45
Q

What is glucose required for?

A
  1. Tissues which have an absolute requirement
  2. Tissues which prefer glucose (brain and CNS)
  3. Variable amounts for specialised functions e.g. synthesis of triacylglycerol in adipose tissue requires glycerol phosphate
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46
Q

What substrate from glycolysis is used by adipose tissue to help synthesis TAGs?

A

DHAP is used to form glycerol phosphate which is combined with fatty acyl-CoA to form triacylglycerol

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47
Q

List some pathways that glucose can enter once in tissues?

A

Glycolysis
Pentose phosphate pathway (from G-6-P)
Glycogen for storage (from G-6-P)
Conversion to other sugars e.g. galactose
The importance of these pathways varies from tissue to tissue

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48
Q

Which tissues use glycolysis?

A

All of them!

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49
Q

What is unique about glycolysis?

A

It is the only pathway that can generate ATP under anaerobic conditions?

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50
Q

What does glycolysis generate?

A

ATP for cell function
NADH from NAD+
Building blocks for anabolism
Useful intermediated for specific cell functions

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51
Q

What is the overall equation for the 10 steps of aeorbic glycolysis?

A

glucose + 2Pi + 2ADP + 2NAD+ –>

2 pyruvate + 2ATP + 2NADH + 2H+ + 2H2O

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52
Q 
Glycolysis can be broken down into 2 phases:
Phase 1 (steps 1-3)
Phase 2 (steps 4-10)
What is the name of each phase and the net synthesis/usage of useful carriers in each phase?
A

1 - preparative phase: Loss 2xATP

2 - ATP-generating phase: Gain 2x NADH and 4xATP

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53
Q

What is the first step in glycolysis and how is it catalysed?

A

Glucose + ATP -> glucose-6-phosphate + ADP

Enzyme: hexokinase (all tissues), glucokinase (liver)

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54
Q

What is the purpose of phosphorylating glucose?

A
  1. Makes the sugar anionic - can’t cross membrane
  2. Increases reactivity of sugar - so it can be metabolised by several pathways (glycolysis, pentose P, glycogen s.)
  3. Allows formation of compounds with high phophoryl-group transfer potential that can transfer their phosphate group to ADP->ATP (substrate level phosphorylation)
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55
Q

What is the purpose of glycolysis reactions 2 and 3?

A

They isomerise glucoe-6-phosphate into a sugar phosphate that can be split into two C3 units following further phosphorylation using ATP

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56
Q

Which reactions in glycolysis are irreversible and why?

A

Reactions 1,3 and 10 because they have large negative delta-G values

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57
Q

Reaction 3 is the first step unique to glycolysis. Why is it known as the committing step?

A

It is irreversible and therefore commits glucose to metabolism via glycolysis

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58
Q

What is notable about reaction 6 of glycolysis?

A

It is the only reaction in glycolysis which produces NADH (x2)

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59
Q

What happens to glycolysis if NADH is not oxidised back to NAD+?

A

Glycolysis stop as there is a lack of NAD+ for step 6 of glycolysis

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60
Q

How is NADH oxidised back to NAD+?

A
  1. In cells with mitochondria and an adequate oxygen supply, this occurs in the electron transport chain
  2. In cells that lack mitochondria (e.g. RBCs) or in the absence of adequate oxygen (vigorously exercising muscle) it is converted back by lactate dehydrogenase reaction
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61
Q

What does lactate dehydrogenase catalyse?

A

pyruvate + NADH + H+ lactate + NAD+

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62
Q

Why is the lactate dehydrogenase reaction so important?

A

It recycles NADH –> NAD+ in anaerobic conditions and in cells without mitochondria so that glycolysis (step 6) is not inhibited and ATP (substrate level phosphorylation) can continue to be produced

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63
Q

In which reactions of glycolysis does substrate level phosphorylation occur?

A

Steps 7 and 10

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64
Q

What is substrate-level phosphorylation?

A

Substrate-level phosphorylation is a type of metabolic reaction that results in the formation of adenosine triphosphate (ATP) or guanosine triphosphate (GTP) by the direct transfer and donation of a phosphoryl (PO3) group to adenosine diphosphate (ADP) or guanosine diphosphate (GDP) from a phosphorylated reactive intermediate. Note that the phosphate group does not have to come directly from the substrate. By convention, the phosphoryl group that is transferred is referred to as a phosphate group.

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65
Q

Does loss of CO2 occur in glycolysis

A

NO

66
Q

Overall how is the delta-G for glycolysis

A

Negative - it is overall an exergonic process

67
Q

Why does the storage of lipid in adipose tissue depend on an adequate rate of glycolysis?

A

Glycerol phosphate is required for the synthesis of triacylglycerols and is synthesised from the glycolysis intermediate DHAP

68
Q

Why is the liver less dependent on the glycerol phosphate produced by glycolysis to produce triacylglycerol than adipose tissue?

A

The liver can phosphorylate glycerol directly using glycerol kinase and ATP but this enzyme is not found in adipose tissue

69
Q

What is the glycolysis intermediate 1,3-bisphosphoglycerate an important substance for?

A

It is converted into 2,3-bisphosphoglycerate in red blood cells. 2,3-BPG is an important regulator of oxygen affinity of haemoglobin

70
Q

What is the role of myokinase in muscles?

A

It enables the high energy of hydrolysis phosphate bond in ADP to drive ATP synthesis under emergency conditions:
2ADP ATP + AMP

71
Q

Why is not necessary to regulate the activity of all the enzymes in a metabolic pathway, only the rate limiting steps?

A

Most of the reactions in a metabolic pathway are close to equilibrium and the flow of material through the pathway is determined by a small number of rate-determining reactions

72
Q

What is the most important rate limiting step in glycolysis?

A

Step 3 catalysed by phosphofructokinase (PFK)

73
Q

What is the role of phosphofructokinase (PFK)?

A

It is the most important rate-limiting step of glycolysis and catalyses:
fructose-6-phosphate + ADP –> fructose 1,6-bisphosphate + ADP
This commits glucose to glycolysis

74
Q

How is PFK regulated?

A

Muscle- allosteric regulation: inhibited by high [ATP], stimulated by high [AMP]
Liver - hormonal regulation: inhibited by insulin, stimulated by glucagon

75
Q

By what high and low energy signals is glycolysis regulated?

A

Inhibited by high energy signals: high [ATP], low [AMP], {ADP]
Stimulated by low energy signals: low [ATP]. high [AMP], [ADP]

76
Q

What is the overall equation for glycolysis under anaerobic conditions?

A

glucose + 2Pi + 2ADP –> 2 lactate + 2ATP + 2H2O

77
Q

What happens to all the lactate produced by red blood cells, skin, brain, skeletal muscle and the gastrointestinal tract?

A

It is released into the circulation, transported to the liver and heart muscle (and kidney), where it is converted back to pyruvate and oxidised to CO2 (heart muscle) or converted to glucose (liver and kidney)

78
Q

Under normal physiological conditions what is the rate and utilisation of lactate?

A

Equal, therefore the plasma concentration remains relatively stable

79
Q

In what physiological and pathological conditions is a high level of lactate seen?

A 
Strenuous exercise
Hearty eating
Shock
Congestive heart disease
Increases due to decreased utilisation occur in:
Liver disease
Thiamine deficiency
During alcohol metabolism
80
Q

What causes lactic acidosis?

A

When plasma levels of lactate exceed the renal threshold and begin to affect the buffering capacity of plasma.

81
Q

Galactose is used for the biosynthesis of which molecules?

A

Glycolipids and glycoproteins, such as blood group antigens

82
Q

Which enzyme hydolyses dietary lactose so its products can be absorbed into the bloodstream?

A

Lactase

lactose –> glucose and galactose

83
Q

Where is galactose largely metabolise?

A

Liver (some in kidney and gastrointestinal tract)

84
Q

In the liver what is the overall reaction of galactose that soluble enzymes catalyse?

A

galactose + ATP –> glucose-6-phosphate and ADP

85
Q

Why is it important that the epimerase reaction in galactose metabolism is reversible?

A

It means that galactose can also be synthesised from glucose via UDP-galactose. This is important during lactation when breast tissue is synthesising large amounts of lactose for milk production

86
Q

Name two clinical conditions that affect galactose metabolism

A

Lactose intolerance

Galactosaemia

87
Q

In galactosaemia individuals are unable to utilise galactose obtained from the diet because of a lack of which enzymes?

A

Galactokinase of Galactose-1-P transferase

88
Q

What is the role of the galactokinase enzyme?

A

Converts:

galactose + ATP –> galactose-1P + ADP

89
Q

What is the role of the galactose-1-P uridyl transferase enzyme?

A

Converts:
galactose-P + UDP-glucose –> glucose-1P + UDP-galactose
Glucose-1P can then be converted to glucosose-6-P and therefore enter glycolysis or the pentose phosphate pathway

90
Q

The lack of which enzyme in galactosaemia is more common and more serious?

A

Galactose-1-P uridyl transferase

91
Q

Why is lack of Galactose-1-P uridyl transferase more serious than lack of galactose kinase?

A

It causes a build up of galactose and galactose-1P. In addition to the depletion in NADPH this causes, it also depletes inorganic phosphate stores leading to liver damage

92
Q

What is the effect of a build up of galactose on NADPH stores?

A

The enzyme aldose reductase catalyses:
Galactose + NADPH –> Galacitol + NADP+
Depleting NADPH stores

93
Q

Why does depletion of NADPH compromise defences against oxidative damage?

A

Key cellular defence mechanisms again oxidative damage require NADPH for function:

  1. Glutathione - glutathione reductase uses NADPH as electron donor
  2. Thioredoxin system - thioredoxin reductase used NADPH as electron donor
  3. Thioltransferase system - uses gluathione as cofactor
94
Q

How can ROS damage proteins?

A

ROS react with either the side chain or backbone:

  1. Backbone -> fragementation -> protein degradation
  2. Modified amino acid -> change in protein structure -> protein degradation/ loss of function/ gain of function
95
Q

How does ROS damage to proteins in galactosaemia cause cataracts?

A
  1. ROS takes electrons from cysteine residues in crystallin protein of eye
  2. Inappropriate disulphide bonds form -> misfolding -> cross-linking and disruption of function
  3. Aggregation of denatured crystallin protein in the eye form cataracts
96
Q

What are the clinical symptoms of galactosaemia?

A 
Hepatomegaly + cirrhosis
Renal failure
Vomiting
Seizure + brain damage
Cataracts
Hypoglycaemia
97
Q

What else can cause cataracts in galactosaemia, other than inappropriate disulphide bond formation?

A

Non-enzymatic glycosylation of lens proteins

98
Q

What can be the cause of glaucoma in galactosaemia?

A

Accumulation of galactose and galactitol in the eye may lead to intra-ocular pressure (glaucoma) which if untreated may lead to blindness

99
Q

What is the effect of a build-up of galactose-1-phosphate in tissues?

A

Causes damage to liver, kidney and brain and may be related to the sequestration of Pi making it unavailable for ATP synthesis

100
Q

What enzyme hydrolyses dietary sucrose -> glucose and fructose?

A

Sucrase

101
Q

How is fructose metabolised in the liver?

A

By soluble enzymes which ultimately convert it to glyceraldehyde 3-phosphate an intermediate of glycolysis

102
Q

Glucose-1-phosphate is made from glucose-6-phoshate. What pathways is it an intermediate in?

A

Galactose pathway and glycogen pathway

103
Q

Which pathways is glucose-6-phosphate an intermediate in?

A

Glycolysis
Pentose phosphate pathway
Galactose synthesis/conversion to glucose
Glycogen synthesis/break-down

104
Q

What are the main functions of the pentose phosphate pathway?

A
  1. Produce NADPH in the cytoplasm

2. Produce C5-sugar ribose

105
Q

In which tissue is the pentose phosphate pathway particularly important?

A

Liver
Red blood cells
Adipose tissue

106
Q

Why is NADPH production important in liver and adipose tissue?

A

NADPH provides reducing power for anabolic processes such as lipid synthesis

107
Q

Why is NADPH production important in red blood cells?

A

It is important in the defence against oxidative damage - maintains reduced glutathione which can maintain free -SH groups on cystein residues in certain proteins

108
Q

How is NADPH involved in the protection of cells against toxic chemicals?

A

It is involved in various detoxification mechanisms

109
Q

Why is there a high activity of the pentose phosphate pathway in dividing tissue (e.g. bone marrow)?

A

It produces the C5 sugar ribose which is required for the synthesis of nucleotides, the building blocks of DNA and RNA

110
Q

The pentose phosphate pathway can be considered in two phases. What happens in the first phase?

A

glucose-6-phosphate is oxidised and decarboxylated by the enzymes glucose 6-phosphate dehydrogenase and 6-phosphgluconate dehydrogenase in reactions that require NADP+ - producting a C5-sugar phosphate

111
Q

The pentose phosphate pathway can be considered in two phases. What happens in the second phase?

A

In phase 2 a complex series of reactions convert any unused C5-sugar phosphates to intermediates of glycolysis (fructose 6-phosphate or glyceraldehyde 3-phosphate)

112
Q

How is the pentose phosphate pathway regulated?

A

By controlling the activity of glucose 6-phosphate dehydrogenase, the first enzyme in the pathway.
NADP+/NADPH ratio controls the enzyme
NADP+ stimulates
NADPH inhibits

113
Q

What is the inheritance pattern in glucose 6-phosphate dehydrogenase deficiency (G6PD) ?

A

X-linked

114
Q

Which population is G6PD more commonly found in?

A

Mediterraneans and black USA males

115
Q

Why are red blood cells particularly affected by oxidative damage in G6PD?

A

The pentose phosphate pathway is the only source of NADPH in red blood cells and their roles as oxygen carriers puts them at increased risk of oxidative damage

116
Q

Why do Heinz bodies occur inside red blood cells of individuals with G6PD deficiency?

A

Due to the depletion in NADPH, oxidative damage to haemoglobin and other proteins cause them to cross-link with each other, forming insoluble aggregates called Heinz bodies

117
Q

Why does G6PD deficiency cause an increase in oxidative damage in cells?

A

G6PD is an enzyme of the pentose phosphate pathway which reduces NADP+ –> NADPH. Therefore a lack of this enzyme reduces the concentration of NADPH inside cells. NADPH is used to reduce oxidised gluathione. Reduced gluathione donates electrons to radicals in cells caused by oxidative damage and therefore protects the cell against protein modification that can cause protein degradation, loss of function and gain of function

118
Q

Why is haemolysis increased in individuals with G6PD deficiency?

A

Damage to the red blood cells causes them to be prematurely destroyed.

119
Q

Why are acute haemolytic episodes of G6PD deficiency precipitated by chemicals such as: antimalarials, sulphonamides and certain glycosides found in broad beans?

A

These chemicals reduce the level of NAPH

120
Q

Pyruvate is converted into acetyl-CoA by which enzyme?

A

Pyruvate dehydrogenase

121
Q

What is the overall reaction for the conversion of pyruvate into acetyl-CoA and why is it reversible?

A

pyruvate + CoA + NAD+ –> acetly-CoA + NADH + H+

The reaction is irreversible because it produces a gas CO2, which is lost through diffusion

122
Q

Why can acetyl-CoA not produce glucose by gluconeogenesis?

A

Because pyruvate dehydrogenase reaction is irreversible due to the loss of CO2

123
Q

PHD is a multi-enzyme complex that enables a complicated reaction to occur in a controlled manner. Which four B vitamins does it require as cofactors?

A

CoA - pantothenic acid
NAD+ - niacin
FAD - riboflavin
thiamine pyrophosphate - thiamine

124
Q

Why is PHD very sensitive to Vitamin B deficiency?

A

Four Vitamin Bs are cofactors in this enzyme complex

125
Q

Why would acetyl-CoA be synthesised from fatty acids rather than glucose, in some conditions?

A

To preserve glucose in times of starvation for glucose-dependent tissues such as RBCs, kidney medulla and the brain and CNS

126
Q

Which molecules inhibit pyruvate dehydrogenase?

A

Allosterically - acetly-CoA, NADH, ATP

127
Q

Which molecules activate pyruvate dehydrogenase?

A

Allosterically - ADP

Promoting dephosphorylation - insulin

128
Q

The citric acid cycle is a central pathway in the catabolism of which metabolites?

A 
Sugars
Fatty acids
Ketone bodies
Alcohol
Amino acids
129
Q

Where in the cell does the citric acid cycle take place?

A

Mitochondrial matrix

130
Q

What does the Kreb’s cycle require to function?

A

NAD+
FAD
oxaloacetate
(acetly-CoA!)

131
Q

What is the main function of the citric acid pathway?

A
  1. Break the C-C bond in acetate (acetly-CoA)

2. Oxidise the C-atoms in acetyl to CO2

132
Q

What is an essential requirement to the Kreb’s cycle - without which it won’t function?

A

Oxygen

133
Q

What useful products are made in the citric acid cycle?

A

Per mole of acetly-CoA:
3NADH
FADH2
GTP

134
Q

In addition to its catabolic role, what anabolic functions does the TCA cycle have?

A

Creates:

  1. C5 and C4 intermediates for the synthesis of non-essential amino acids
  2. C4 intermediates for haem and glucose
  3. C6 intermediates for synthesis of fatty acids
135
Q

What happens to the cycle if intermediates are removed?

A

The cycle will stop until replacements are found. These replacements can be from:
1. Amino acid breakdown –> C5 and C4 intermediates
2. Activity of pyruvate carboxylase (major replacement):
pyruvate + CO2 + ATP + H2O –> oxaloacetate + ADP + Pi + 2H+

136
Q

How is the TCA cycle regulated?

A

Signals feeding info on the rate of utilisation of ATP:

  1. ATP/ADP ratio
  2. NADH/NAD+ ratio
137
Q

Explain how one of the irreversible step enzymes of the TCA cycle is regulated?

A

Isocitrate dehydrogenase is inhibited by NADH (high energy) and activated by ADP (low energy)

138
Q

What has happened by the end of stage 3 catabolism (Kreb’s cycle)?

A
  1. All the C-C bonds have been broken and C-atoms oxidised to CO2
  2. All the C-H bonds have been broken and the H atoms (H+ + e-) transferred to NAD+ and FAD
139
Q

What is the net production of ATP from glycolysis?

A

2

140
Q

How many ATP/ GTP are generated in the TCA cycle?

A

2 GTP

141
Q

Where has all the energy gone from glucose?

A
  1. ATP/GTP generation

2. Chemical bond energy of the e- in NADH and FADH2

142
Q

How is the energy from the high energy electrons in NADH and FADH2 released?

A

Through a series of carrier molecules which are converted from their oxidised to reduced form in the electron transport chain

143
Q

What is the final stage of catabolism?

A

Oxidative phosphorylation

144
Q

Oxidative phosphorylation occurs where?

A

Inner mitochondrial membrane

145
Q

Oxidative phosphorylation involves two processes, electron transport and ATP synthesis. What does the process of electron transport involve?

A

Electrons in NADH and FADH2 are transferred through a series of carrier molecules to oxygen with step-wise release of free energy. This free-energy is used by proton translocating complexes to move protons across the IMM, creating a proton concentration gradient (e.m.f.) across the impermeable membrane. This process therefore requires oxygen as the terminal electron acceptor –> H2O

146
Q

Oxidative phosphorylation involves two processes, electron transport and ATP synthesis. What does the process of ATP synthesis involve?

A

The free energy released in electron transport is used to create a proton motive force. The diffusion of protons down this gradient through ATP synthase complex drives ATP synthesis from ADP + Pi. Thus the greater the proton motive force the more ATP is synthesised

147
Q

Which complexes in the electron transport chain also act as PROTON TRANSLOCATING COMPLEXES?

A

Complexes I,III & IV

148
Q

What do proton translocating complexes do?

A

They use the free energy derived from electron transport to move protons from the inside to the outside of the inner mitochondrial membrane (which is impermeable to protons)
They therefore convert chemical bond energy of the electrons into electo-chemical potential difference of protons.

149
Q

What is the proton motive force (pmf)?

A

It is the force generated by proton translocating complexes pumping protons against their concentration gradient across a membrane impermeable to protons.
It’s a measure of the potential energy stored as a combination of proton and voltage gradients across a membrane (differences in proton concentration and electrical potential).

150
Q

Why does NADH result in more translocated protons than FADH2?

A

NADH has electrons with a greater chemical bond energy than FADH2, therefore NADH electrons have the energy to use all three proton translocating complexes whereas FADH2 only uses two

151
Q

What happens to the energy not conserved in ATP?

A

Lost as heat and help to maintain body temperature at 37oC

152
Q

List some differences between oxidative phosphorylation and substrate level phosphorylation

A
  1. OP requires membrane associated complexes, whereas SLP requires soluble (cytoplasmic and Mt) enzymes
  2. OP has indirect energy coupling through pmf whereas SLP has direct coupling through generation of high energy of hydrolysis bond
  3. OP cannot occur in the absence of O2
  4. OP is major process for ATP synthesis in cells that require large amounts of energy whereas SLP is not
153
Q

How is the coupling of electron transport and ATP synthesis controlled so that one cannot happen without the other?

A

Mitchondrial concentration of ATP plays an important role in regulating both processes. When [ATP] is high:
1. [ADP] is low and ATP synthase stops (lack of substrate), preventing transport of protons back into mitochondria matrix
2. The [H+] outside increases to a level that prevents more protons being pumped
3. In the absence of proton pumping electron transport stops
The reverse occurs when [ATP] is low

154
Q

What is an electron transport uncoupler?

A

A substance, like dinitrophenol, which increases the permeability of the inner mitochondrial membane to protons. This enables protons that have been pumped out of the mitochondrial matrix to reenter without driving ATP synthesis, hence electron transport and ATP synthesis are uncoupled and the p.m.f. is lost as heat.

155
Q

Uncouplers effectively stop ATP synthesis, but what do they do to the electron transport chain?

A

The electron transport chain continues, so excessive heat generation continues

156
Q

How much does proton leak account for the basal metabolic rate?

A

20-25%

157
Q

Where can the natural uncoupling proteins (UCP1-5) be found and what is their role?

A

They are found in the inner mitochondrial membrane of brown adipose tissues and are involved in non-shivering thermogenesis, which enables mammals to survive cold environments

158
Q

How does the sympathetic nervous system drive non-shivering thermogenesis in response to cold stimuli in brown adipose tissue?

A
  1. Releases noradrenaline which stimulates lipolysis which releases fatty acids to provide fuel for oxidation
  2. As a result of beta-oxidation NADH and FADH2 are formed, driving ET and increasing the pmf
  3. Noradrenaline also activates UCP-1, allowing protons back into the mitochondrial matrix without driving ATP synthesis, which dissipate the p.m.f. as heat
159
Q

What substance can inhibit the electron transport chain?

A
  1. Anaerobic conditions

2. CO and various posions (cyanide…)

160
Q

Why do antimalarials such as primaquine precipitate haemolysis in an individual with glucose-6-phosphate deficiency?

A

NADPH levels are limited in these individuals due to the pentose phosphate pathway not being active and therefore they have less protection against oxidative stress due to a lower capacity to recycle oxidised gluathione. Anti-malarials like primquine further deplete the levels of reduced glutathione (they oxidise it) leaving the cells very susceptible to oxidative damage

161
Q

A newborn girl is vomiting after her feeds and has diarrhoea. She becomes jaundiced over the next few days. Her urine is tested and found to contain galactose. She is diagnosed as having galactossaemia. Which enzyme is most likely to be deficient in classical (Type 1) galactossaemia where both galactose and galactose-1-phosphate accumulate in tissues?

A

galactose-1-phosphate uridyl transferase

162
Q

Which rare enzyme deficiency causes a less severe form of galctossaemia characterised by solely build-up of galactose in tissues?

A

Galactokinase

LS1 Metabolism (18 decks)

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