Energy production- Carbohydrate Flashcards
What common product are glucose, fatty acids and alcohol broken down into?
Acetyl CoA
What is glucose converted into prior to Acetyl CoA?
Pyruvate
What else can be converted into Acetyl CoA?
Keto-acids
Where do keto-acids come from?
The break down of amino acids
What is the advantage of amino acids, glucose, fatty acids and alcohol all being capable of conversion into Acetyl CoA?
It allows for interconversion
What is acetyl CoA ultimately converted too?
CO 2
Other than keto-acids, what can amino acids be converted into?
NH 3
What is NH 3 ultimately converted into?
Urea
What are the 4 stages of catabolism?
- Breakdown to building block materials
- Breakdown of metabolic intermediates
- TCA (Kreb’s cycle) and release of reducing power and energy
- Oxidative phosphorylation and conversion of reducing power into ATP
What is the purpose of breaking food down into building block materials?
To convert nutrients to a form that can be taken up by cells
Where does breaking down of substances into building blocks occur?
Extracellular, in the GI tract, technically outside of the body
How do the building block materials get into the body?
They are absorbed by epithelial cells in the GI tract
What happens to building block materials once they have been absorbed by epithelium in the GI tract?
They are bought into circulation for use
What is necessary for absorption of building block materials by the GI tract?
Transport mechanisms in the membrane
Does breaking down into building block materials release energy?
No
What bonds are broken when producing building block materials?
C-N and C-O
No C-C
Isbreakdown into metabolic intermediates and release of reducing power intracellular or extracellular?
NAME?
What cells does breakdown into metabolic intermediates and release of reducing power occur in?
Cells at target organs
Is breakdown into metabolic intermediates and release of reducing power a cytosolic or mitochondrial process?
Can be both
What is the result of some reactions in the breakdown into metabolic intermediates and release of reducing power being packaged away?
Gives control over synthesis and catabolism
Isbreakdown into metabolic intermediates and release of reducing power oxidative or reductive?
NAME?
What is the result ofbreakdown into metabolic intermediates and release of reducing power being oxidative?
It requires coenzymes
What happens to to coenzymes used inbreakdown into metabolic intermediates and release of reducing power after?
They are reduced
Is energy produced duringbreakdown into metabolic intermediates and release of reducing power?
A small proportion is
How is ATP produced duringbreakdown into metabolic intermediates and release of reducing power?
Direct phosphorylation of ADP to ATP
What bonds are broken inbreakdown into metabolic intermediates and release of reducing power?
C-C
Where does the TCA occur?
In the mitochondria
Is the TCA oxidative or reductive?
NAME?
What is the result of TCA being oxidative?
It requires NAD + and FAD
Is energy produced in the TCA cycle?
A small proportion is produced directly
What happens to acetyl in the TCA cycle?
It is converted to 2CO 2
What has happened in the conversion of acetyl to 2CO 2 ?
Carbon has been oxidised
What happens to the CO 2 produced in the TCA cycle?
It is put back in circulation, then breathed out at lungs
What does the TCA produce?
Precursors for biosynthesis
What is the advantage of the TCA producing intermediates?
It’s a way of interconnecting pathways
Where does oxidative phosphorylation occur?
In the mitochondria
What happens in oxidative phosphorylation?
Electron transport and ATP synthesis
What happens to NADH and FADH 2 in oxidative phosphorylation?
They are re-oxidised
Why are NADH and FADH 2 re-oxidised in oxidative phosphorylation?
The energy within them in used to drive ATP synthesis
What is required for oxidative phosphorylation?
Oxygen
What happens to oxygen in oxidative phosphorylation?
It is reduced to H 2 O
Why is O 2 reduced in oxidative phosphorylation?
Needed to oxidise H carriers
Does oxidative phosphorylation produce energy?
Yes, large amounts of ATP are produced
What is the general formula of carbohydrates?
(CH 2 O) n
What are the two types of sugars?
- Aldose
- Ketose
What is an aldose sugar?
One that contains a aldehyde group
What is a ketose sugar?
One that contains a ketogroup
Are sugars hydrophilic or hydrophobic in nature?
Quite hydrophilic
Why are sugars quite hydrophilic in nature?
They have multiple -OH groups
What is a monosaccharide?
A single unit
How many C’s are in a monosaccharide?
03-Sep
What is a triose sugar?
A 3 carbon sugar
What is a pentose sugar?
A 5 carbon sugar
What is a hexose sugar?
A 6 carbon sugar
How do monosaccharides with more than 5 carbons generally exist?
In a ring structure
Why do monosaccharides with more than 5 C atoms generally exist in a ring structure?
Because keto/aldehyde group at one end comes round and interacts with the other end, which cyclises the molecule
What reaction is occurring when a ring is formed in a sugar?
Carbonyl reacts with alcohol group
Give 3 features of hydrophilic molecules
- Attract water
- Water soluble
- Don’t pass across the cell membrane without transporters
What is meant by sugars being partially oxidised?
They have H on them
What is the result of sugars being partially oxidised?
They need less oxygen than fatty acids for complete oxidation
What is a disaccharide
A molecule composed of two monosaccharides
What is oligosaccharide?
A molecule with 3-12 monosaccharides
Give an example of a group of oligosaccharides
Dextrins
What are polysaccharides?
Molecules with 10-100 monosaccharide units
What kind of bond is formed between monosaccharides?
O-glycosidic bond
What happens when an O-glycosidic bond is formed?
Water is eliminated
What are the two kinds of O-glycosidic bonds?
NAME?
What is the difference between alpha and beta glycosidic bonds?
The alpha bond sticks up, and the beta bond goes down
Why is wether you have an alpha or beta glycosidic bond important?
Because enzyme function depends on bond type
What is the main storage polysaccharide in animals?
Glycogen
Where is glycogen stored?
Liver and muscles
What is the purpose of glycogen?
It is a rapidly mobilisable energy store
What bonds are found in glycogen?
- Alpha 1-4
- Alpha 1-6
Why are the two different bond types in glycogen?
It produces branches
How are glucose molecules organised in glycogen?
They are largely lined up end on end
Why is glycogen used as the store, not glucose?
Takes highly osmotic glucose effectively out of the solution
What is the main glucose polymer in plants?
Starch
What is starch made up of?
A mixture of amylose and amylopectin
What is the bond type in amylose?
Alpha 1-4
What are the bond types in amylopectin?
- Alpha 1-4
- Alpha 1-6
How does starch differ from glycogen?
Less highly branched
What is starch broken down into in the GI tract?
NAME?
What is cellulose?
A structural glucose polymer in plants
What bonds are present in cellulose?
Beta 1-4
What is the difference between beta 1-4 and alpha 1-4 linkages?
Beta are more stable
Why can’t cellulose be digested?
There are no GI enzymes to digest ß1-4
What is cellulose important for?
GI function
Why is cellulose important for GI function?
Provides substrate for other molecules to stick to, to be acted on my other enzymes
What is the body content of dietary carbohydrate?
1%
Other than dietary, what are the other sources of carbohydrate?
It can be synthesised from amino acids
Where does carbohydrate digestion occur?
GI tract (extracellular)
What happens in the digestion of carbohydrate?
Hydrolysis of glycosidic bonds
Give 3 places that produce enzymes that are required for carbohydrate digestion
- Salivary glands
- Pancreas
- Small intestine
What enzyme is present in saliva?
Amylase
What does amylase do?
Breaks down starch and glycogen into dextrins by cleaving alpha1-4 glycosidic bonds
What enzyme for carbohydrate digestion does the pancreas produce?
Amylase
Is pancreatic amylase the same as salivary amylase?
No, but has same function
What does pancreatic amylase do?
Breaks carbohydrates down into monosaccharides
What enzymes for carbohydrate digestion does the small intestine have?
It has the disaccharidases lactase, sucrase, pancreatic amylase and isomaltase
Where are the enzymes in the small intestine?
Attached to the brush border membrane of epithelial cells
What does lactase break down?
Lactose
What does sucrase break down?
Sucrose
What does isomaltase break down?
Alpha1-6 branches
What happens in absorption?
Active transport into intestinal epithelial cells
How do monosaccharides get to the target tissues?
Via the blood supply
Why does absorption need active transport?
Because the concentration in the cells is greater than that in the lumen
How is glucose uptaken into the cells?
Facilitated diffusion
What allows facilitated diffusion of glucose?
The transport proteins GLUT1-GLUT5
What is the difference between each GLUT?
They have different tissue distribution and affinities
How can GLUT transporters be controlled?
Hormonally
Which cells can metabolise glucose?
All
Why can all cells metabolise glucose?
They all have the glycolytic pathway
Which tissues have an absolute requirement for glucose?
- RBC
- WBC
- Kidney medulla
- Lens of eye
What does the uptake of glucose to tissues with an absolute glucose requirement depend on?
The concentration of glucose in the blood
When are obligate glucose uses susceptible?
In starvation
What happens in starvation conditions?
The body goes to great lengths to maintain glucose in these tissues, so they have a continuing substrate supply
What tissues prefer glucose as their substrate supply?
CNS (brain)
However, they are not obligated
Which tissues need glucose for specialised functions?
NAME?
Why do the liver and adipose tissue require glucose for specialised functions?
They require carbohydrate backbone for more complex lipid molecule synthesis
What is the central pathway in CHO metabolism?
Glycolysis
Where does glycolysis occur?
In the cytoplasm of all cells
What are the functions of glycolysis?
- Oxidise glucose
- NADH (reducing equiv.) production
- Synthesis of ATP from ADP
- Produce C 3 and C 6 intermediates
Is glycolysis exergonic or endergonic?
Exergonic
Is glycolysis oxidative or reductive?
Oxidative
Is there any loss of C in glycolysis?
No, it’s just cut in half
Can glycolysis operate anaerobically?
Yes, with one additional enzyme
When will glycolysis need to operate anaerobically?
When blood supply does not keep up with metabolic need for O 2
Give the overall equation for glycolysis
Glucose (C6) + 2Pi + 2ADP + 2NAD + → 2 Pyruvate (C3) + 2ATP + 2NADH + 2H + + 2H 2 O
What is required for each step of the glycolytic pathway?
Specific enzymes
What is the first step of glycolysis?
Phosphorylation of glucose to form glucose-6-phosphate
What happens in the phosphorylation of glucose?
Phosphate is transferred from ATP to glucose
Why does glucose need to be phosphorylated in glycolysis?
It needs to be activated, otherwise glucose is a stable molecule
What is the result of the phosphorylation of glucose?
NAME?
How much ATP does step 1 of glycolysis use?
2 moles per mole of glucose
What happens in step 2 of glycolysis?
Isomerisation- G-6-P is rearranged to form fructose-6-P
What happens in step 3 of glycolysis?
F-6-P phosphorylated to form F-1,6-bisP
What is the purpose of the phosphorylation of F-6-P?
It activates the molecule, so it becomes much more energetic
Which steps in phase 1 of glycolysis (steps 1-3) are committing?
1 and 3
Why are steps 1 and 3 of glycolysis committing?
They have a large negative ∆G
At what step is glucose committed to metabolism via glycolysis?
3
What is the result of step 3 committing glucose to metabolism by glycolysis?
It can be used as a regulatory step
What happens in reaction 4 of glycolysis?
Cleavage of C 6 to C 3
What is formed in the cleavage of C 6 to C 3 ?
DHAP and G-3-P
What is reaction 5 of glycolysis
DHAP ↔ G-3-P
What happens in reaction 6 of glycolysis?
A small amount of reducing power is captured in NADH
How is reducing power captured in reaction 6 of glycolysis?
By coupling to oxidation reactions
What happens in reaction 7-10 of glycolysis?
ATP synthesis
Why can ATP synthesis occur in stages 7-10 in glycolysis?
Because the molecules are now energetic enough to give up energy
What kind of phosphorylation occurs in steps 7-10 of glycolysis?
Substrate level phosphorylation
How does substrate level phosphorylation occur in steps 7-10 of glycolysis?
1,3-BPG and ADP are bought together in an enzymes active site, where direct phosphate transfer occurs
Which reaction of 7-10 of glycolysis is irreversible?
10
Why is reaction 10 of glycolysis irreversible?
Because it has a large negative ∆G
What does the body want to do in times of starvation?
Make glucose
What can be used to make glucose in times of starvation?
Some of the enzymes in the glycolytic enzymes
What must be done to use the glycolytic pathway to produce glucose?
Must find ways of bypassing steps 1,3 and 10
Why must steps 1, 3 and 10 by bypassed when making glucose using the glycolytic pathway?
Because the reactions are so energetically committed
How much ATP is synthesised during glycolysis?
Net 2 moles of ATP per mole of glucose- 2 moles are invested to get it going, and 4 moles are produced per mole of glucose (C 3 x 2)
Why does glycolysis occur in small steps?
- Chemistry easier in small steps
- Efficient energy conversion
- Gives versatility
- Can be controlled
Why does smaller steps mean more efficient energy conversion?
If large, complex molecules used, more energy is wasted as heat
Why does smaller steps give more versatility in glycolysis?
NAME?
Where is DHAP formed in glycolysis?
In step 4, when C 6 is cleaved into 2 x C 3 , one of which is DHAP
What is DHAP converted into?
Glycerol phosphate
Give the equation for the conversion of DHAP to glycerol phosphate
DHAP + NADH→ Glycerol Phospate + NAD +
What enzyme is required for the conversion of DHAP to glycerol phosphate?
Glycerol 3-phosphate dehydrogenase
What kind of molecule is glycerol phosphate?
A 3 carbon phosphorylated alcohol
Where is glycerol phosphate important?
In triglyceride and phospholipid biosynthesis
Why is glycerol phosphate important in triglyceride synthesis?
It forms the backbone
Where is glycerol phosphate produced?
- Adipose tissue
- Liver
What is the result of DHAP being required for lipid synthesis in liver?
Lipid synthesis in liver requires glycolysis
Can the liver phosphorylate glycerol directly?
Yes
What is 1,3-bisphosphoglycerate converted into?
2,3-bisphosphoglycerate
What enzyme is required for the conversion of 1,3-BPG to 2,3-BPG?
Bisphosphoglycerate mutase
What can 2,3-BPG interact with?
Haemoglobin
Why can 2,3-BPG interact with haemoglobin?
Because it is negatively charged, so can interact with positive charges within haemoglobin
How is 2,3-BPG produced in red blood cells?
From 1,3-BPG
Why is 2,3-BPG important?
Important regulator of oxygen affinity in haemoglobin- produces the tense form
What concentration is 2,3-BPG present in red blood cells?
5mM- same as haemoglobin
What does transfusion blood contain to provide the 2,3-BPG required?
Glucose
How long can transfusion blood be kept for?
120 days
Why can transfusion blood only be kept for 120 days?
Any longer and the 2,3-BPG all gets metabolised
What are the 2 regulation methods for glycolysis?
NAME?
How does metabolic regulation of glycolysis occur?
If high [NADH] (therefore low [NAD + ], signals high energy levels, which causes product inhibition at step 6, which thereby inhibits glycolysis
How does high [NADH] cause product inhibition at step 6 of glycolysis?
If the product of the enzyme is high, it will feed back into the equilibrium, pushing the reaction in the opposite direction
How does the product inhibition at step 6 cause an overall inhibition of glycolysis?
If glucose comes in at the top of the pathway, the whole pathway backs up because the concentration of substrates increases, which allows G-6-P to reach a concentration that means it’s fed into glycogen storage
Where would you not use regulation on enzymes?
In a reaction that comes to equilibrium
Why would you not put regulation on a reaction that comes to equilibrium?
It would still come to the same equilibrium, just reach it at a different rate, so no regulation
Which enzymes are potential sites of control in metabolic pathways?
Those catalysing essentially irreversible reactions
What are the two methods of enzymatic regulation in glycolysis?
NAME?
What happens in allostery?
The activator/inhibitor binds at ‘another’ site
What two sites do proteins have?
- Catalytic site
- Regulatory site
What happens at the catalytic site?
The substrate is converted to products
What happens at the regulatory site?
The binding of a specific regulatory molecule
What effect does the binding of a specific regulatory molecule have?
It can change the conformation of a protein, changing the catalytic activity
Does the binding of allosteric molecules have a inhibitory or activating effect?
Can be either
What happens in covalent modification of enzymes?
Phosphorylation or dephosphorylation
What enzymes are affected in the allosteric regulation of glycolysis?
NAME?
How is hexokinase affected by allosteric inhibition?
Decreased by G-6-P
How does allosteric inhibition using hexokinase in glycolysis work?
Hexokinase has a second, allosteric site that recognises G-6-P, so when G-6-P levels increase, causes product inhibition.
What is the significance of phosphofructokinase-1?
It is the enzyme that is responsible for the committing step in glycolysis
How is phosphofructokinase-1 affected by allosteric regulation in the muscle?
It is decreased by high ATP:AMP ratio
How does allosteric activation using phosphofructokinase-1 in the muscle work?
The enzyme is stimulated by AMP as it binds as a positive allosteric regulator
What is the importance of AMP being a positive allosteric regulation onphosphofructokinase-1?
AMP is the low energy signal, as ATP is converted to ADP and AMP, so activates enzyme to make more energy when it’s low
What happens tophosphofructokinase-1 in times of high energy?
There is feedback inhibition from ATP, so negative feedback on committing enzyme
How is phosphofructokinase-1 affected by allosteric regulation in the liver?
It is increased by high insulin:glucagon ratio
How is pyruvate kinase affected by allosteric regulation?
Increased by high insulin:glucagon
Why is pyruvate kinase increased by high insulin:glucagon
It tells the cell that there is lots of glucose present, so the high ratio means that the enzyme can be switched on to use the glucose
How is pyruvate kinase switched on?
Dephosphorylation
What would happen if NAD + was not regenerated from NADH produced during glycolysis?
Glycolysis would stop due to product inhibition at step 6
How many moles of NADH are produced per mole of glucose?
2
What is NAD + essential for?
The continuation of the glycolytic pathway
How does the cumulative level of NAD + and NADH change?
It doesn’t, it remains constant
When is NAD + usually regenerated from NADH?
In stage 4 of metabolism
When can stage 4 of metabolism not occur?
NAME?
Why can’t RBC’s regenerate NAD + from NADH?
Because they have no stage 3 and 4 of metabolism
Where is the oxygen supply often reduced?
To the gut and the muscles
How can NAD + be regenerated when stage 4 of metabolism cannot occur?
Using lactate dehydrogenase (LDH)
Give the equation for the regeneration ofNAD + using LDH
NADH + H + + pyruvate ↔ NAD + + lactate
What is the problem with the regeneration ofNAD + using LDH?
It produces an acid
What must be done to the lactate?
It must be removed
Why must the lactate be removed?
Otherwise muscles would fatigue
Where is lactate predominantly produced?
NAME?
What happens to the lactate produced in tissues?
It is released into blood
Where is lactate normally metabolised?
Liver and heart
How is lactate usually metabolised?
Using LDH, processed by the reverse reaction
What must happen in the liver and heart for efficientNAD + regeneration?
Must be well supplied with oxygen
In what 3 ways is lactate utilised?
NAME?
Give the equation for the conversion of lactate into pyruvate
NAD + + lactate → NADH + H + + pyruvate
Where is lactate used directly for energy production?
In the heart
How is lactate used directly for energy production in the heart?
Through the Krebs cycle and oxidative phosphorylation
What is the ultimate product from the use of lactate to produce energy directly?
CO 2
Where does the conversion of lactate to glucose occur?
The liver
What is the process of converting lactate to glucose called?
Gluconeogenesis
Give 4 situations where the conversion of lactate to glucose is impaired
- Liver disease
- Thiamine deficiency
- Alcohol
- Enzyme deficiencies
Why is gluconeogenesis inhibited after alcohol?
Because alcohol is metabolised by alcohol dehydrogenase, which takesNAD + and converts it to NADH, thereforeNAD + can’t be used for reconverting to lactate
How is lactate produced via pyruvate?
Using glucose and alanine
How much lactate is produced without major exercise?
40-50g per 24hrs
How much lactate is produced with strenuous exercise?
30g within 5mins
What can lactate production in pathological situations lead too?
Shock or congestive heart failure
When may pathological lactate production occur?
When circulation is compromised to normally oxygenated tissues
What 3 factors determine the plasma concentration of lactate?
- Production
- Utilisation
- Kidneys
Which tissues utilise lactate
Liver, heart and muscle
What disposes of lactate?
Kidneys
At what plasma concentration of lactate would a patient have hyperlactaemia?
2-5mM
Is hyperlactaemia above or below the renal threshold?
Below
Does hyperlactaemia cause a change in blood pH?
No
Why does hyperlactaemia not cause a change in blood pH?
Because there is sufficient circulating protein to buffer blood pH
At what plasma concentration of lactate would a patient have lactic acidosis?
Above 5mM
Is lactic acidosis above or below the renal threshold?
Above
What happens to the blood pH in lactic acidosis?
It decreases
What is fructose converted to in the body?
2 molecules of G-3-P
What is galactose converted to in the body?
G-1-P, then to G-6-P, then G-3-P
What happens to all carbohydrate in the diet?
It ultimately goes to glycolysis to be metabolised
Where does fructose in the diet come from?
Cane/beet sugar
What is sucrose a disaccharide of?
Fructose + glucose
Where is fructose metabolised?
In liver
What kind of enzymes metabolise fructose?
Soluble
Describe the metabolism of fructose
- Fructose converted into fructose-1-P, through the action of fructokinase. Requires ATP
- Fructose-1-P is converted into 2-glyceraldehyde-3-P, by action of aldolase.
- 2-glyceraldehyde-3-P goes into glycolysis
What conditions can arise from errors in fructose metabolism?
- Essential fructosuria
- Fructose intolerance
What is missing in essential fructosuria?
Fructokinase
What happens in essential fructosuria?
Fructose levels build in circulation, rising to a level that is greater than the renal threshold
What is the clinical presentation of essential fructosuria?
Fructose in urine, but no clinical signs
What is missing in fructose intolerance?
Aldose
What happens to fructose metabolism in fructose intolerance?
Fructose can feed into the pathway and form F-1-P, but this cannot be metabolised, causing accumulation in the liver
What is the result of the accumulation of F-1-P in the liver?
Causes liver damage
What is the treatment for fructose intolerance?
Remove fructose from diet
Where does galactose come from?
Milk
What is lactose a disaccharide of?
Glucose + galactose
Where is galactose metabolised?
Liver
Describe the metabolism of galactose
- Galactose is converted into galactose-1-P, by action of galactokinase. This requires ATP.
- Galactose-1-P is converted into glucose-1-P, by action of galactose-1-P uridyl transferase. This reaction also causes conversion of UDP-glucose to UDP-galactose, by action of UDP-galactose 4’-epimerase
- Glucose-1-P goes into glycolysis
What does UDP-galactose 4’-epimerase do?
Mutagensies galactose to glucose by moving hydroxyl groups around
What is the role of UDP-glucose in galactose metabolism?
It acts catalytically
What is the clinical importance of galactose metabolism?
Galactosaemia
What can cause an inability to utilise galactose?
- Galactokinase deficiency
- Transferase deficiency
Is galactokinase deficiency rare or common?
Rare
What happens in galactokinase deficiency?
Galactose accummulates
Is transferase deficiency rare or common?
Common
What happens in transferase deficiency?
Galactose and galactose-1-P accumulate
What happens when galactose levels rise?
Can reach concentrations that enter enzymes that have low Km for galactose, and therefore wouldn’t normally metabolise galactose
Give an example that only metabolises galactose when it’s concentrations get too high
Aldose reductase
Give the equation for the effect of aldose reductase on galactose
Galactose + NADPH → Galactitol + NADP +
What is the result of the depletion of NADPH levels?
It damages structures
Why does NADPH depletion cause structure damage?
It prevents maintenance of sulphydryl groups on proteins, leading to inappropriate disulphide bond formation
What is the result of the inappropriate formation of disulphide bonds?
The loss of structural and functional integrity of some proteins that depend on free -SH groups
What can happen to proteins that rely on free -SH groups?
Protein clumping and damage to cells
Give a specific example of problems caused by failure to maintain free -SH groups
In the lens of the eye
What happens in the lens of the eye when free -SH groups not maintained?
Get inappropriate cross linking in the eye, leading to cataracts
What organs does the accumulation of galactose-1-P affect?
Kidneys, liver and brain
When does the pentose phosphate pathway run?
When energy levels are high
Why does the pentose phosphate level only run when energy levels are high?
If glycolysis is running, ATP and NADH levels are high, so there is product inhibition and allosteric inhibition of glycolysis. This causes G-6-P levels to rise, and so can enter pathways it wouldn’t otherwise enter as the enzymes Km is too high- the pentose phosphate pathway
Where does the pentose phosphate pathway occur?
In the cytoplasm
How many stages are there in the pentose phosphate pathway?
2
What are the two stages in the pentose phosphate pathway?
- Oxidative decarboxylation
- Rearrangement to glycolytic intermediates
Give the equation for the oxidative decarboxylation stage of the pentose phosphate pathway
Glucose-6-phosphate + NADP + → C 5 + CO 2 + NADPH
What enzyme is used in the conversion of G-6-P to C 5 ?
Glucose-6-P dehydrogenase
Give the equation for the arrangement to glycolytic intermediates step in the pentose phosphate pathway
3C 5 -sugars → 2 fructose-6-P + glyceraldehyde-3-P
What can happen to glyceraldehyde-3-P?
It can go back into glycolysis
Is the pentose phosphate reversible or irreversible?
Irreversible
Why is the pentose phosphate pathway irreversible?
Because CO 2 is lost
What is the pentose phosphate pathway controlled by?
NADP + /NADPH ratio
How is the pentose phosphate pathway controlled by theNADP + /NADPH ratio?
IfNADP + /NADPH ratio high, less NADPH substrate for pathway to run
What are the functions of the pentose phosphate pathway?
- Produce NADPH in cytoplasm
- Produce C 5 sugars
What is NADPH in the cytoplasm needed for?
NAME?
Give in example of where biosynthetic reducing power is needed
Lipid synthesis
Where is there a high level of lipid synthesis
In liver and adipose tissue
What does the maintenance of free -SH groups on certain proteins prevent?
Oxidation to -S-S- (disulphide) bonds
What are C 5 sugars needed for?
Nucleic acid synthesis
What tissues have high levels of nucleic acid synthesis?
Ones that divide a lot, e.g. bone marrow
What is the result of a G-6-P dehydrogenase deficiency?
Means that G-6-P can’t be converted into 5 sugar phosphate, therefore no pentose phosphate pathway and no NADPH produced by this pathway
Is G6PDH deficiency common or rare?
Common
What is the result of G6PDH deficiency in RBCs?
The decreased NADPH results in disulphide bonds being formed , which means that haemoglobin is not kept in the reduced form, leading to aggregated proteins called Heinz bodies, which leads to haemolysis, causing anaemia
What is the effect of G6PDH deficiency in the lens of eye?
Get clouding due to inappropriate disulphide bond formation
What must happen to pyruvate at the end of stage 2 of respiration?
It must be acted on my pyruvate dehydrogenase
What is added to pyruvate when it’s acted upon by pyruvate dehydrogenase?
CoA
Give the equation for the reaction between pyruvate and CoA
Pyruvate + CoA + NAD + → acetyl CoA + NADH + H +
What is CoA?
A molecule that, when bonded to another molecule, puts in a reactive bond, therefore activating it
Where is PDH found in the cell?
In the mitochondria
Where does the PDH reaction occur?
In the mitochondrial matrix
How is pyruvate bought into the mitochondrial matrix?
Transported across mitochondrial membrane on a protein
Why does pyruvate need to be transported into the mitochondrial matrix on a protein?
Because it is hydrophilic
How many enzymes are in the PDH complex?
5
How is the PDH complex arranged
Neatly, so that substrates and products are passed around the complex
What do different enzyme activities require?
Various cofactors
Give 4 cofactors that enzymes in the PDH complex requires
NAME?
What provide the cofactors that the PDH complex requires?
B vitamins
What is the result of B vitamins providing the cofactors required for the PDH complex?
The reaction is sensitive to B1 deficiency
Is the PDH reaction reversible or irreversible?
Irreversible
Why is the PDH reaction irreversible?
Because it produces CO 2
What is the result of the PDH reaction being irreversible?
It is a key regulatory step
Can pyruvate be formed from acetyl-CoA?
No
What is the PDH reaction activated by?
NAME?
Give 5 low energy signals that activate the PDH reaction
NAME?
What is the PDH reaction inhibited by?
- High energy signals
- Phosphorylation
Give 4 high energy signals that inhibit the PDH reaction
NAME?
What does a PDH deficiency result in?
Lactic acidosis
How does PDH deficiency cause lactic acidosis?
If the PDH reaction goes wrong, can’t pass substrate into the TCA cycle, so pyruvate builds up, which is then converted into lactic acid by lactate dehydrogenase, which causes lactic acidosis
Where does the TCA cycle occur?
In the mitochondria
Is the TCA cycle a single pathway, or multiple pathways?
A single pathway
What is converted into what in the TCA cycle?
Acetyl (CH 3 CO - ) to 2CO 2
Is the TCA cycle oxidative or reductive?
Oxidative
What does the TCA cycle require as it is oxidative?
NAD + and FAD
Is energy produced in the TCA cycle?
Some, in the form of ATP and GTP
How is ATP and GTP produced in the TCA cycle?
Substrate level phosphorylation
Other than energy, what else does the TCA cycle produce?
Precursors for biosynthesis
What are the key steps in the Krebs cycle?
The oxidative steps, where substrate level phosphorylation occurs, and where CO 2 is released
What has happened to all the reducing power on the original glucose molecule by the end of the TCA cycle?
It has been captured
How is the reducing power of glucose captured in the TCA cycle?
- Substrate level phosphorylation
- On reducing carriers
What is the overall equation for the TCA cycle?
CH 3 CO~CoA + 3NAD + + FAD + GDP + Pi + 2 H 2 O → 2CO 2 + CoA + 3NADH +FADH 2 + GTP
What is the overall yield per mole of glucose from the TCA cycle?
6 NADH
2 FADH 2
2 GTP
How is the TCA cycle regulated?
- By energy availability
- By irreversible steps
What ratios regulate the TCA cycle by energy availability?
- ATP/ADP
- NADPH/NADP +
What steps in the TCA cycle are irreversible?
Ones where CO 2 is removed
In what reactions in the TCA cycle is CO 2 removed?
- Isocitrate + NAD + → α-ketoglutarate (C5) + CO 2 + NADH
- CoA +α-ketoglutarate (C5) +NAD + → succinyl-CoA (C4) +CO 2 + NADH
What is the enzyme for the conversion of isocitrate toα-ketoglutarate?
Isocitrate dehydrogenase
What is isocitrate dehydrogenase regulated by?
- Positively regulated by ADP
- Negatively regulated by ATP and NADH
What is the result of isocitrate dehydrogenase being stimulated by ADP?
If energy levels are low, then it’s stimulated into activity
What is the enzyme of the conversion ofα-ketoglutarate to succinyl-CoA?
α-ketoglutarate dehydrogenase
What isα-ketoglutarate dehydrogenase inhibited by?
It’s product, NADH, and ATP
What 5 intermediates in the TCA cycle supply biosynthetic processes?
NAME?
What biosynthetic processes does citrate supply?
Production of fatty acids
What biosynthetic processes doesα-ketoglutarate supply?
Production of amino acids
What biosynthetic processes does succinate supply?
- Production of amino acids
- Production of haem
What biosynthetic processes does malate supply?
Production of amino acids
What biosynthetic processes does oxaloacetate supply?
NAME?
What is meant by the TCA being a hub?
It’s possible to feed in and out of pathway, and convert one thing into another
What is TCA in a central pathway in?
The catabolism of sugars, fatty acids, ketone bodies, amino acids and alcohol
What strategy does the TCA cycle use?
Produce molecules that readily lose CO 2
What bond is broken in the TCA cycle?
The C-C bond in acetate (acetyl~CoA)
What are carbons oxidised to in the TCA cycle?
CO 2
How many oxidative steps are there in the TCA cycle?
4
What do the oxidative steps in the TCA use?
3 using NAD + , 1 using FAD
Does the TCA cycle function in the absence of oxygen?
No
Why does the TCA cycle not function in the absence of oxygen?
NADH and FADH 2 being stripped off requires oxidative phosphorylation in mitochondria to be running. If there is no oxygen, there is a build up, so the cycle will stop
What happens when the TCA cycle can’t run due to lack of oxygen?
We must rely on the energy from glycolysis and lactate dehydrogenase
How do the intermediates of the TCA cycle act?
Catalytically
Why is it said that intermediates in the TCA act catalytically?
There is no net synthesis or degradation of the intermediates alone (unless if fed in from other substrates)
How much energy does substrate level phosphorylation release?
~124kJmol -1
Where is the remaining energy to be accounted for in a glucose molecule?
In the chemical bonds of NADH and FADH 2
How is the energy in NADH and FADH 2 released?
High energy electrons are transferred to oxygen, releasing large amounts of energy
What is the energy released from NADH and FADH 2 used to do?
Drive ATP synthesis
Where does stage 4 of catabolism occur?
In the mitochondria
What happens in stage 4 of catabolism?
Electron transport and ATP synthesis
What happens to NADH and FADH 2 in stage 4 of catabolism?
They’re reoxidised
What is the purpose of the reoxidation of NADH and FADH 2 in catabolism?
It uses the bond energy released to produce ATP
Why is O 2 required in stage 4 of catabolism?
It picks up electrons released from reduced carriers
What happens to oxygen in stage 4 of catabolism?
It is reduced to H 2 O
Is ATP produced in stage 4 of catabolism?
Yes, large amounts
What processes occur in stage 4 of catabolism?
NAME?
What happens in electron transport?
Electrons on NADH AND FADH 2 are transferred through series of carrier molecules to oxygen
What is the purpose of electron transport?
It releases energy in steps
Why does electron transport release energy in steps?
It allows control of the process, so the most can be got out of it
What happens in oxidative phosphorylation?
Free energy is used to drive ATP synthesis
Describe the structure of a mitochondrion?
- Have outer membrane and inner membrane, folded into cristae
- Between membranes is intermembrane space
- Inside membranes is matrix
Are the mitochondrial membranes permeable?
- The outer membrane is quite leaky
- The inner membrane is very impermeable
What is the inner membrane especially impermeable too?
Hydrogen ions
What does the inner mitochondrial membrane contain?
All machinery for electron transport
What is the significance of proton translocating complexes (PTC) in electron transport?
In a number of steps, electrons are passed between electron transport complexes, with a bit of energy being given up each time
What happens at proton translocating complex (PTC) 1 in electron transport?
NADH gives up an electron to electron transport
Give the equation for what happens at PTC 1
NADH + H + → NAD +
What happens in the mitochondrial membrane once NADH has given up it’s electrons at PTC 1?
2e - pass down as energy level in inner mitochondrial membrane, and 2 H + are pushed out to inter membrane space
What happens at PTC 2?
FAD feeds in
Why does FAD have a lower energy yield?
Because it feeds in halfway down transport chain, so only get 4 H + ions out of inter membrane space
What happens at PTC 3?
2 H + are fed in from matrix, 2e - move down and 2 H + are pushed out
What happens at the end of the electron transport chain?
2H + + O combine with the 2 e - from the inner mitochondrial membrane, on the mitochondrial matrix, forming water
What are electrons transferred through in the electron transport chain?
A series of carrier molecules
Where are the carrier molecules electrons are transferred through mostly found?
Within proteins
How much of the energy is used to move H + across the membrane?
~30%
How is a lot of energy lost in the electron transport chain?
As heat
Why is it important that some energy is lost as heat in the ETC?
To maintain body heat
What is meant by membrane potential?
The [H + ] gradient across the inner membrane of mitochondria
What does the membrane potential create?
Proton motive force
How is the proton motive force induced?
Every time you transfer positive ion out of the matrix, negative anion must be left behind, generating an electrical potential across the membrane, creating a driving force on hydrogen ions that want to come back into matrix
What gradients are now supporting hydrogen ions wanting to come back into the matrix?
NAME?
What does the proton motive force create?
Stored up potential energy
Give the reaction that proton translocating ATPase catalyses
ATP + 2H + (mitochondrial matrix) ↔ ADP + Pi + 2H + (cytoplasm)
What is the energy released by proton translocating ATPase used to do?
Drive H ions out into the inner membrane space
Is the proton translocating ATPase reaction reversible or irreversible?
Reversible
What is the result of the proton translocating ATPase reaction being reversible?
The gradient of H ions set up by electron transport can be used, if we allow H ions to run back into the matrix down their electrochemical gradient, releasing energy
What can the energy released when hydrogen ions come back in through proton translocating ATPase be used for?
To drive synthesis of ATP
Why is the proton gradient created effectively doing oxidative phosphorylation?
Because the products of oxidation are driving the phosphorylation of ATP from ADP using the proton gradient between two mitochondrial membranes, as the return is highly energetically favourable
What is energetically favoured by the electrochemical potential?
Return of protons across the membrane, from the inner mitochondrial space to the matrix
What is the only way protons can return across the membrane to the matrix?
Via the ATP synthase
Why can protons only return across the membrane through ATP synthase?
Due to the impermeability of the inner mitochondrial membrane
What is the result of protons only being able to return through ATP synthase?
It drives ATP synthesis
What is ATP synthesis coupled to?
Electron transport
How is electron transport coupled to ATP synthesis?
Electrons are transferred from NADH and FADH 2 to molecular oxygen, releasing energy to generate the p.m.f. Energy from the dissipation of p.m.f. is coupled to synthesis of ATP from ADP, further capturing the energy
How many PTC’s does NADH use?
3
How many PTC’s does FADH 2 use?
2
Why does NADH use more PTCs than FADH 2 ?
Because electrons in NADH have more energy
What is the result on p.m.f. of NADH having more energy than FADH 2 ?
More p.m.f. from NADH
What does a greater p.m.f. mean for ATP synthesis?
More ATP synthesised
How is oxidative phosphorylation regulated by ADP?
When [ADP] decreases, no substrate for ATP synthesis, so the inward flow of H + stops. This leads to an increase in [H + ] in the intermitochondrial space, which prevents furtherH + pumping, stopping electron transport. As electron transport and oxidative phosphorylation are tightly coupled, this inhibits both
Give an example of an inhibitor of electron transport (other than ADP)
Cyanide
How do inhibitors such as cyanide block electron transport?
By preventing acceptance of electrons by oxygen
What happens when an inhibitor blocks the acceptance of electrons by oxygen?
The flow of electrons ceases, which means there is no p.m.f. and therefore no oxidative phosphorylation
What structures are electron carriers similar to?
That of haem
What is the result of electron carriers using a similar structure to that of haem?
CO can inhibit
Why can CO inhibit electron carriers?
It binds with a higher affinity that oxygen
What affect does cyanide have on electron transport?
It blocks electron acceptance by oxygen, therefore causing a build up of electrons, so no energy is given up to put H + in inner membrane space, and so decreasing the p.m.f. and consequently ATP.
What do uncouplers do?
Increase the permeability of mitochondrial inner membrane to protons
What is the result of the increased permeability of the inner membrane to protons?
Won’t have to go through ATP synthase
What happens to the p.m.f. because of uncouplers?
Reduces it
Why do uncouplers reduce the p.m.f.?
Because it dissipates the proton gradient
In the presence of uncouplers, what happens to the energy instead of it driving ATP synthesis?
It is released as heat instead
Does electron transport continue when uncoupling has occurred?
Yes
Why does electron transport continue even after uncoupling?
Because there is no inhibition
Give 3 examples of things that can act as uncouplers
NAME?
What are ox/phos diseases?
Generic defects in proteins encoded by mtDNA
What proteins encoded for by mtDNA are defective in ox/phos diseases?
Some sub-units of the PTC and ATP synthase
What is the result of the defective proteins in ox/phos diseases?
Decreased electron transport and ATP synthesis
What is the result of inefficiency in coupling?
Energy lost as heat
What does efficiency of coupling depend on?
Tightness of coupling
Where can the tightness of coupling be varied?
Brown adipose tissue
What is the degree of coupling controlled by in brown adipose tissue?
Fatty acids
What does the control of coupling in brown adipose tissue allow for?
Extra heat generation
What does brown adipose tissue contain?
Thermogenin (UCP1)
What is UCP1?
A naturally occurring uncoupling protein
What happens in response to cold?
Noradrenaline activates lipase and fatty acid oxidation
What is the affect of lipase oxidation?
It released fatty acids from triacylglycerol
What does fatty acid oxidation produce?
NADH and FADH 2
What happens to the NADH and FADH 2 released by fatty acid oxidation?
They go into electron transport
What do fatty acids activate?
UCP1
What does UCP1 do?
Transports H + back into the mitochondria
What happens when UCP1 transports H + back into the mitochondria?
NAME?
Where is brown adipose tissue found?
NAME?
Why is brown adipose tissue found in newborn infants?
To maintain heat, particularly around vital organs
Why is the extra heat from brown adipose tissue needed in newborn infants?
Because they have a small SA to volume ratio
What is the difference in requirements for oxidative and substrate level phosphorylation?
- Oxidative requires membrane-assoicated complexes
- Substrate level requires soluble enzymes
What is the difference between methods of energy production in oxidative and substrate level phosphorylation?
- In oxidative, energy coupling occurs indirectly through the generation and subsequent utilisation of a proton gradient
- In substrate level, energy coupling occurs directly, through formation of high energy hydrolysis bond (phosphoryl-group transfer)
What is the difference in oxygen requirement between oxidative and substrate level phosphorylation?
NAME?
What is the difference in significance of amount of ATP produced between oxidative and substrate level phosphorylation?
- Oxidative is major ATP synthesis process in cells
- Substrate level is minor process for ATP synthesis
When is substrate level phosphorylation the major process for ATP synthesis?
NAME?
