Metabolism Flashcards
What is the daily energy expenditure for a 70kg male?
12000kJ
What does the daily energy expenditure consist of?
Three components
Basal metabolic rate- energy required to support basal metabolism to maintain life at physical digestive and emotional rest (= weight in kg x 24)
Voluntary physical exercise- energy required by the skeletal and cardiac muscle for voluntary physical exercise
Diet induced thermogenesis- energy required to process the food we eat (digest absorb distribute and store) (=10% of energy of ingested food)
What is the daily energy expenditure for a 58kg female?
9500kJ
What are the essential components of the diet?
Carbohydrate Protein Fat Vitamins Minerals Water Fibre
Why are carbohydrates essential?
Supply energy
Why are proteins essential?
Supply energy
Supply amino acids which can’t be made by the body
Maintain a nitrogen balance in the body- N loss = N intake
Why are fats essential?
Supply energy (2.2 x as much as carbohydrates and proteins)
Fat soluble vitamins- assist in their distribution (DAKE)
Supply essential fatty acids which can’t be made in the body (linolenic acid)
Why are vitamins essential?
Assist in metabolic functions of the body
Required for synthesis of fibres- vitamin C required for fibroblast function
Required in blood clotting cascade- vitamin k required to synthesise blood clotting factors
Vitamin D required for calcium serum concentration regulation
Why are minerals essential?
Na, K - muscle and nerve functions
Ca- co factor of body reactions
Mg, I, Cu- enzyme and gland functioning
Why is water essential?
Maintain hydration- (50-60% of body weight); loss of 2.5l/day
Why is fibre essential?
Maintain normal GI function (cellulose)
What are the clinical consequences of protein and energy deficiencies in humans?
Marasmus
Kwashiorkor
What is marasmus?
Protein and energy (carbs) deficiency, low fluids No oedema (due to low plasma protein and fluids) Thin bony child
Usage of fat stores- ketone body synthesis to supply brain
Use of glycogen stores and then protein breakdown= Muscle wastage
Cardiovascular and brain muscle wastage in severe cases= death
What is kwashiorkors?
Protein deficiency, normal energy (carbs), normal fluids
Oedema (due to lower plasma protein than marasmus, and normal fluids)
Thin child with a pop belly
Hepatic dysfunction due to insufficient proteins to synthesise lipoproteins= fat accumulates in liver- fatty liver = HEPATOMEGALY!
Oedema formation due to low plasma protein concentration= low oncotic pressure in plasma= causes fluid shifts (ascites, ankle oedema)
How does reintroduction of food affect marasmus and kwashiorkors patients? Refeeding syndrome?
Marasmus- no serious effect but reintroduction of food needs to be slow
Kwashiorkors- unable to deal with protein rich foods in large amounts due to down regulation of certain enzymes involved in the metabolism and excretory process of proteins normally
Leads to build up of ammonia in blood as a by product of metabolism= toxicity (hyperammonaemia); therefore small amounts of protein at regular intervals are required
How do you calculate BMI?
Weight (kg) / (height)squared (m)
What are the value ranges for BMI?
35 severely obese
Define obesity
Condition in which excess body fat has accumulated as a result of energy intake exceeding energy expenditure, where BMI > 30, which may have an adverse effect on health, resulting in a reduced life expectancy or other comorbidities (heart disease- atherosclerosis, gall bladder disease, hypertension, type 2 diabetes)
What are the factors involved in the regulation of body weight?
Daily energy intake and daily energy expenditure
Define homeostasis
Control of internal body environment within set limits- dynamic equilibrium
What is the clinical relevance of failure of homeostasis?
Homeostasis underpins physiology and failure of homeostasis Results in DISEASE
Define cell metabolism
Set of processes which derive energy and raw materials from food stuff and uses them for support, repair, growth and activities of the tissues of the body to support life
Cells metabolise nutrients to provide…?
Energy for cell function and synthesis of cell components
Building block materials for cell components
Organic precursor molecules to allow interconversion of building block molecules
Biosynthetic reducing power used in synthesis of cell components
What are the origins of cell nutrients?
Diet
Storage in body
Synthesis in body
What are the fates of nutrients in the body?
Degraded to release energy in all tissue
Synthesis of cell components in all tissues except RBCs
Storage in liver muscle or adipose tissue
What is catabolism?
Break down of large molecules into smaller molecules Exergonic Oxidative Produces intermediate cell metabolites Stimulated by low energy signals
What is anabolism?
Synthesis of large molecules from smaller molecules Endergonic Reductive Uses metabolites from catabolism Stimulated by high energy signals
Why do cells need a s continuous supply of energy?
METBO
Mechanical (muscle contraction) Electrical (nerves) Transport (active) Biosynthesis (e.g. Protein) Osmosis (kidneys, large intestine etc)
If insufficient energy intake- body uses stores
Describe ATP?
Synthesis of ATP is anabolic/ endergonic
Breakdown of ATP is catabolic/ exergonic (used by cells)
Terminal phosphate bond contains large amount of energy- which is released in hydrolysis
Adenine and three phosphates
How can ATP be stored in muscle?
Creatine + ATP = creatine phosphate + ADP
So ATP can be quickly regenerated when required
CREATINE KINASE
What is the clinical importance of creatinine (formed from creatine)?
Measured of muscle mass
Determinant for kidney function
Comparison for other nutrient measurements
What are the hydrogen carriers and their function?
NAD+ (niacin) FAD (flavin) NADP (niacin) CARRIERS OF BIOSYNTHETIC REDUCING POWER Change between oxidised and reduced form
Obtained from vitamin B ()
How do hydrogen carriers become reduced?
By the addition of 2 H
What happens to the total concentration of carriers at all times?
Remains constant
What is oxidation?
Loss of electrons and H+
Exergonic
What is reduction?
Gain of electrons and H+
Endergonic
What are some high energy signals?
ATP, NADPH, NADH, FADH2
activates anabolism
What are some low energy signals?
AMP, ADP, NADP, FAD, NAD+
What do carbohydrates consist of?
C H O
Polysaccharide chain made up of monosaccharides joined together by glycosidic bonds in condensation reactions
Contain aldehyde or ketone groups
What are monosaccharides?
Monomer unit for carbohydrates
Asymmetric carbon atom (stereoisomers)
Natural form = d form (not l)
Usually 3-9 carbon atoms
What are disaccharides?
Two monosaccharides units joined by a glycosidic bond
What are some examples of disaccharides?
Lactose (galactose and glucose)
Sucrose (fructose and glucose)
Maltose (glucose and glucose)
What are oligosaccharides?
Carbohydrates with 3-12 monosaccharide units
What are polysaccharides?
Carbohydrates with 10-100 monosaccharide units
What are some examples of polysaccharides?
Glycogen-polymer of glucose, animals, alpha 1,4 and 1,6 bonds, highly branched
Starch-polymer of glucose, plants, mixture of amylose and amylopectin, alpha 1,4 and 1,6 bonds, less branched than glycogen, broken down to glucose and maltose by GI tract enzymes
Cellulose- structural polymer of glucose, plants, beta 1,4 bonds, no GI enzymes exist to digest these bonds, dietary fibre important for normal GI function
What enzymes in the body digest carbohydrates?
Salivary amylase (digest alpha 1,4) Pancreatic amylase (digest alpha 1,4) Maltase Lactase Sucrase Isomaltase (digest alpha 1,6)
How are monosaccharides absorbed into the blood?
Actively transported into the intestinal epithelial cells
Facilitated diffusion out of epithelial cells into the blood (using GLUT1-5 transport proteins)
What are GLUT1-5?
Glucose transport proteins which alter their affinity for glucose according to the differences in requirements of tissues for glucose
E.g glut 4 sensitive to presence of insulin in skeletal muscle and adipose tissue (high insulin increases glucose uptake by these cells by increasing number of transport proteins in plasma membrane)
Why is the concentration of glucose in the blood normally held relatively constant?
Some tissues have an absolute requirement of glucose and the amount of glucose uptake by these tissues is dependent on the concentration in the blood
RBCs, kidney medulla, lens of eye, WBCs, peripheral nerves
Brain and CNS prefers glucose
What is the minimum amount of glucose required by a healthy adult on a normal diet
180g/day
40g/day by RBCs WBCs kidney medulla lens of eye
140g/day by CNS
Various amounts required by tissues for specialised functions (e.g. Synthesis of tags in adipose tissue requires glucose as it needs glycerol phosphate)
Outline how carbohydrates catabolised in the body
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
Outline how proteins are metabolised in the body
Amino group is removed by deamination
Amino group goes to urea cycle or undergoes ammonia detoxification
Carbon skeleton-
– glucogenic: glycolysis (pyruvate) or Krebs cycle (oxaloacetate, fumerate or alpha ketoglutarate)
– ketogenic: ketone body synthesis (acetyl coA)
Amino group is transferred to a keto acid using amino transferase enzymes
Keto acid generated can be metabolised in the Krebs cycle (glucogenic and ketogenic as above)
aa1 + ka2 –> ka1 + aa2
What happens in the transamination of alanine (glutamate)?
Alanine + alpha ketoglutarate = pyruvate + glutamate
What enzyme is used in the transamination of alanine?
Alanine amino transferase
What happens in the transamination of aspartate (glutamate)?
Aspartate + alpha ketoglutarate = oxaloacetate + glutamate
What enzyme is used in the transamination of aspartate?
Aspartate amino transferase
What are the main (rate limiting step) enzymes involved in glycolysis?
Step 1 hexokinase and glucokinase (exclusively found in the liver)
Step 3 phosphofructokinase 1
Step 10 pyruvate kinase
What enzyme is involved in the link reaction?
Pyruvate dehydrogenase
What is the main (rate limiting step) enzyme in the Krebs cycle?
Isocitrate dehydrogenase
How is hexokinase, glucokinase activity regulated?
Glucose 6-phosphate product inhibition
How is phosphofructokinase-1 activity regulated in the muscle and liver?
Muscle :
By allosteric regulation
Simulated by AMP, ADP, citrate
Inhibited by ATP
Liver :
By hormonal regulation
Stimulated by high insulin: glucagon
Inhibited by low insulin: glucagon
How is pyruvate kinase activity regulated?
Dephosphorylation- covalent modification
Stimulated by high insulin: glucagon ratio
Inhibited by low insulin: glucagon ratio
Where in the cell and the body does glycolysis occur?
Cytoplasm of all body cells
What are the functions of glycolysis?
Oxidise glucose, produce 2 NADH
Synthesise 2 ATP (net)
Produces c6 and c3 intermediates (glycerol phosphate (for fatty acid synthesis) and 2-3BPG)
What are some features of glycolysis?
Exergonic, oxidative (catabolism) C6--> 2C3 no loss of C Operates anaerobic ally Cytoplasm of all cells Irreversible
How does fructose join in on the glycolysis pathway?
Fructose –> Fructose-1-Phosphate –> Glyceraldehyde –> Glyceraldehyde-3-Phosphate –> GLYCOLYSIS
Fructose –> Fructose-1-Phosphate –> Dihydroxyacetone phosphate (DHAP) –> Glyceraldehyde-3-Phosphate –> GLYCOLYSIS
What are the enzymes involved in fructose metabolism?
Fructose kinase (F to F-1-P) Aldolase (F-1-P to glyceraldehyde)
What happens in the deficiency of fructokinase?
Essential fructosuria
What happens in the deficiency of aldolase?
Fructose intolerance
Fructose-1-Phosphate accumulates in liver = liver damage
What are the enzymes involved in galactose metabolism?
Galactokinase (Gal to Gal-1-P)
Galactose-1-Phosphate uridyl transferase (Gal-1-P to G-1-P)
What happens in deficiency of galactokinase?
Build up of galactose
Increased conversion of galactose into galactitol using aldose reductase and NADPH
Depletes levels of NADPH (normally prevents formation of SS bonds) in lens
Formation of disulphide bonds between cysteine residues on proteins in lens= cataracts
What happens in deficiency of galactose-1-phosphate uridyl transferase?
Build up of galactose
Increased conversion of galactose into galactitol using aldose reductase and NADPH
Depletes levels of NADPH (normally prevents formation of SS bonds) in lens
Formation of disulphide bonds between cysteine residues on proteins in lens= cataracts
Build up of galactose-1-phosphate
Damage to liver kidney and brain
Toxic to hepatocytes = liver damage
Bilirubin (which is produced from haem in breakdown of RBCs in the spleen) can’t be conjugated by liver and so is released in to the blood = jaundice
What happens if NAD+ is not regenerated from NADH produced during glycolysis?
Glycolysis would stop due to accumulation of NADH inhibiting some steps
(Normally NAD+ is regenerated in oxidative phosphorylation but in anaerobic conditions this cannot occur)
What happens in anaerobic conditions that stops the regeneration of NAD+?
Oxygen is the final acceptor in the electron transport chain
Lack of oxygen means electron transport chain will stop- oxidative phosphorylation cannot occur - as no free energy is being produced and so no pmf is produced
Therefore no NAD+ is being regenerated
How is NAD+ regenerated under anaerobic conditions or generally in RBCs and keratinocytes?
Glycolysis (anaerobic) +
Pyruvate–> lactate (using lactate dehydrogenase) = reduction reaction
What is important about RBCs and keratinocytes which means that they are constantly undergoing anaerobic catabolism?
They lack mitochondria which are the site of aerobic catabolism
When is lactate produced?
By RBCs all the time and by skeletal muscle under anaerobic conditions
What is the fate of lactate?
Released in the blood
Normally metabolised by LIVER and HEART via LDH back to pyruvate (since liver and heart are generally well supplied with oxygen and so can quickly perform the reaction when anaerobic conditions cease)
What is hyperlactaemia?
Plasma conc 2-5 mM
Below renal threshold
No change in blood pH (buffering capacity)
What is lactic acidosis?
Above 5mM
Above renal threshold- lactosuria
Blood pH lowered (lactate itself does not cause the lowering of pH- the fact that H+ ions, which are released in ATP hydrolysis, are not being reincorporated back into ATP synthesis in oxidative phosphorylation means that H+ concentration increases)
Cramps, pains
What is the normal lactate production rate?
40-50g/day
In strenuous exercise what is the lactate production rate?
30g/5 min
How is lactate utilised?
Normally metabolised by LIVER and HEART via LDH back to pyruvate (since liver and heart are generally well supplied with oxygen and so can quickly perform the reaction when anaerobic conditions cease)
Heart–> CO2
Liver –> glucose (gluconeogenesis)
—— impaired in liver disease, thiamine vitamin B1 deficiency, alcohol consumption (NAD+ –> NADH), enzyme deficiencies
What is lactose intolerance?
Low activity of lactase
Lactose can’t be broken down in the gut so remains and lowers wp in the large intestine so increased water loss = diarrhoea and dehydration
Bacteria colonise indigested lactose and ferment it to produce organic acids that irritate the GI= stomach cramps
What is the pentose phosphate pathway?
2 stage (multistep) pathway, break from glycolysis!
- oxidative decarboxylation of G-6-P by G-6-P dehydrogenase
G-6-P + NADP+ –> C5 sugar + CO2 + NADPH
-rearrangement back to glycolytic intermediates
3C5 sugars ~~~~> 2-fructose-6-phosphate + 1-glyceraldehyde-3-phosphate
What are some features of the pentose phosphate pathway?
No ATP production
Loss of CO2 therefore irreversible
Controlled by NADP+/NADPH ratio at G-6-P dehydrogenase
What enzyme is involved PPP?
Glucose-6-Phosphate dehydrogenase
What is the purpose of PPP?
Produces NADPH in cytoplasm- Biosynthetic reducing power (for fatty acid synthesis so high activity in liver and apipose) and maintain free S-H on cysteine residues in certain proteins/ prevent oxidation to S-S (disulphide bond)
Produces C5 sugars for nucleotides needed for nucleic acid synthesis (so high activity in dividing tissues e.g. Bone marrow)
What tissues have high activity of ppp?
Liver and adipose tissue- fatty acid synthesis
Dividing tissues (bone marrow)- c5 nucleotides
RBC and lens of eyes- need NADPH to prevent formation of S-S bonds
What two things does the ppp produce?
NADPH C5 sugars (ribose)
What are the symptoms of a deficiency in galactokinase?
Cataracts
Galactosuria
What are symptoms of a deficiency in galactose-1-phosphate uridyl transferase?
Cataracts
Galactosuria
Liver damage
Jaundice
How does galactose join in on the glycolytic pathway?
Galactose –> Galactose-1-Phosphate –> Glucose-1-Phosphate –> Glucose-6-Phosphate –> GLYCOLYSIS
What happens in a glucose-6-phosphate dehydrogenase reaction?
Reduction in NADPH causes:
Reduction in fatty acid synthesis
Less maintenance of SH residues in lens of eyes= formation of disulphide bonds= CATARACTS in lens of eye
Less maintenance of SH residues in RBCs= formation of disulphide binds between haemoglobin molecules= Heinz bodies= increased breakdown of RBCs by spleen= ANAEMIA = increased amount of bilirubin in liver= liver can’t conjugate all the bilirubin= some released back into blood= JAUNDICE
Oxidised form of glutathione (with disulphide bonds) stabilised= so reduced glutathione is not available to detoxify/ reduce hydrogen peroxide and other ROS’s = oxidative stress
What is the side effect of using anti malarials on glutathione?
Anti malarials have the side effect of oxidising glutathione (disulphide bridges formed)
Reduced Glutathione (and NADPH) both prevent the formation of disulphide bonds between haemoglobin molecules
So when an anti malarial oxidises glutathione, it is no longer able to present formation of disulphide bonds- which consequently form
= Heinz bodies
What is the refeeding syndrome?
Occurs in anorexic patients, cancer patients, post surgery, alcoholics
Unclear cause- occurs from reintroduction of calories to malnourished
Metabolic disturbance due to shift away from predominantly fat metabolism
Need to closely monitor electrolytes and treat disturbances carefully
Risks include confusion, coma, convulsions and death
Where does the link reaction Krebs cycle and oxidative phosphorylation occur?
In the mitochondrial matrix
What enzyme is used to convert pyruvate into acetyl coA?
Pyruvate dehydrogenase
What is pyruvate dehydrogenase?
5 enzyme complex- different enzymes require different cofactors (FAD, thiamine pyrophosphate, lipoic acid= all provided by vitamin B)
Pyruvate –> acetyl coA
How is pyruvate converted to acetyl coA?
Pyruvate + NAD+ + coA –> acetyl coA + NADH + CO2
Irreversible!
Using PDH
What is important about the conversion of pyruvate to acetyl coA?
IRREVERIBLE AS CO2 IS LOST = key regulatory step
How is PDH regulated?
Stimulated by coA, NAD+, ADP, (pyruvate and insulin)
Inhibited by acetyl coA, NADH, ATP
What vitamin deficiency affects the actin of PDH and why?
Vitamin B1 (thiamine) - provides the cofactors (FAD, thiamine pyrophosphate and lipoid acid) needed by the different enzymes in the PDH enzyme complex
What does a deficiency in PDH result in?
Lactic acidosis as lactate dehydrogenase pathway is stimulated
What are some key features of the Krebs cycle?
Mitochondrial
Single pathway- central pathway in catabolism of sugars, fatty acids, ketone bodies amino acids and alcohol
Acetyl converted to 2CO2
Oxidative/exergonic/ requires NAD+ and FAD
Produces lots of NADH FADH2 - used to drive ATP synthesis in ox phos
Some energy produced as ATP/GTP
Produces precursors for biosynthesis (amino acids, haem, glucose and fatty acids)
Occurs twice for every molecule of glucose entering glycolysis
Only functions in presence of oxygen
What key enzyme is involved in Krebs cycle
Isocitrate dehydrogenase
How is isocitrate dehydrogenase regulated?
Regulated by energy availability
ATP/ADP ratio and NADH/ NAD+ ratio
Stimulated by ADP (low energy signals)
Inhibited by NADH (high energy signals)
What two things does stage 4 of catabolism consist of?
Electron transport- electrons in NADH and FAD2H transferred through a series if carrier molecules to oxygen; releases energy in steps
ATP synthesis by Oxidative phosphorylation- free energy released used to drive ATP synthesis
Where does stage 4 of catabolism occur?
Inner mitochondrial membrane
What is the process of stage 4 of catabolism? C p e f I p a o
NADH and FAD2H carriers transfer their electrons to carrier molecules in the mitochondrial membrane, which transfer electrons to molecular oxygen and are organised into a series of 4 highly specialised protein complexes spanning the entire mitochondrial membrane
3 complexes (I, III AND IV) act as proton translocation complexes
Free energy from electron transport is used to move protons from the inside to the outside of the inner mitochondrial membrane via the proton translocation complexes
The mitochondrial membrane itself is impermeable to protons and as electron transport continues, concentration of protons outside the inner mitochondrial membrane increased
Proton translocation complexes transform chemical bond energy of electrons into an electrochemical gradient of protons across the membrane = proton motive force
ATP synthesis requires 31kJ/mol energy from pmf to drive the reaction
Protons renter the mitochondrial matrix bis ATP synthase complex (V) driving the synthesis of ATP from ADP and Pi
Oxygen acts as the final electron acceptor of the electron transport chain
How many proton translocating complexes do NADH and FAD2H use?
NADH uses 3 whereas FAD2H uses 2
Because electrons in NADH have more energy than in FAD2H
What is the relation between proton motive force and ATP synthesis?
The greater the pmf the more ATP synthesis
How much ATP is produced per mole of NADH?
2.5 ATP/ mole of NADH
How much ATP is produced per mole of FAD2H?
1.5 ATP / mole FAD2H
How is oxidative phosphorylation regulated?
Mitochondrial concentration of ATP
What describes the relationship between electron transport and ATP synthesis?
Tightly Coupled
When ATP concentration in mitochondria is high, what happens to ox phos?
When ATP: ADP ratio is high = no substrate for ATP synthase = inward flow of protons stops = increase in conc of protons in inner mitochondrial space= prevents further pumping of protons= stops electron transport
Name three uncouplers
Dinitrophenol
Dinitrocresol
Fatty acids
How do uncouplers affect ox phos?
Uncouplers work by uncoupling electron transport and ATP synthesis
Uncouplers penetrate the inner mitochondrial membrane
Uncouplers increase permeability of inner mitochondria membrane for protons
Protons reenter the mitochondrial matrix
ATP synthase not activated so no ATP synthesis
Pmf is dissipated as heat
Electron transport and thus NADH/FAD2H oxidation continues
Free energy is released as heat
Respiration continues to bring more NADH and FAD2H to mitochondria and uses up fuel molecules (fatty acids, glucose etc)
More and more heat production
What inhibits ox phos and how does this happen?
Cyanide and carbon monoxide Binds to IV (ptc) Stops electron transport Blocks NADH and FAD2H oxidation No free energy is produced No pmf No ATP synthesis Cell death
What are ox phos diseases?
Genetic defects in proteins encoded by mtDNA (some subunits of the PTCs and ATP synthase) which cause a decrease in electron transport and ATP synthesis
Which is more common to occur transamination or deamination?
Transamination
What hormone stimulates the production of aminotransferases in the liver?
Cortisol
Which keto acid is mostly used in transamination?
Alpha keto glutarate- always produces glutamate when an amino group is added
What amino acid is produced when alpha keto glutarate undergoes transamination?
Glutamate
What amino acid is produced when glutamate undergoes transamination?
Aspartate
Why is aspartate a useful product in the catabolism of proteins?
Important intermediate in the synthesis of urea
What enzymes are involved in deamination and where are they found?
L and D amino acid oxidases in the liver (D has a higher activity)
Describe the two step process of deamination of glutamine
Glutamine is converted into glutamate and ammonia by glutaminase
Glutamine –> glutamate + NH3 (glutaminase)
Produced glutamate is then converted to alpha ketoglutarate and an ammonium ion by glutamate dehydrogenase
Glutamate + NAD + H2O –> alpha ketoglutarate + NADH + H+ + NH4+ (glutamate dehydrogenase)
Why do the Krebs and urea cycle lack defects?
There are no known defects in Krebs and ureas cycle that allow life to be sustained as a lack in any enzyme would result in DEATH
What is phenylketonuria?
Phenylalanine–> tyrosine (phenylalanine hydroxylase)
Inherited recessive condition = Defective enzyme: phenylalanine hydroxylase
Phenylalanine accumulates in tissues and is metabolised by their pathways
Phenylketones (phenylpyruvate) are produced in an alternative pathway:
Phenylalanine–> phenylketones
What are some symptoms of phenylketonuria?
Hypopigmentation
If not picked up- it can cause mental retardation as phenylalanine inhibits brain development
Lack of tyrosine (usually involved in synthesis of neurotransmitters, hormones, noradrenaline, adrenaline) leads to decrease in neurotransmitters
Phenyl pyruvate prevents pyruvate uptake into mitochondria- brain energy metabolism
What is the reaction in which phenylalanine is converted into phenyl pyruvate?
Transamination reaction
Phenylalanine + alpha ketoglutarate –> phenyl pyruvate + alpha glutamic acid
What are the clinical consequences of PKU and why should it be detected as early as possible?
Phenylalanine is a large neutral amino acid (LNAA) and so competes with other LNAA’s for transport across the brain blood barrier via LNAAT (transporter)
If excess phenylalanine is present (in the case of PKU) this saturates the LNAAT thereby decreasing the levels of other LNAA’s (essential for neurotransmitters and protein synthesis) entering the brain
As a result phenylalanine builds up hindering the development of the brain and causing MENTAL RETARDATION
What is the test for PKU?
Heel prick test at birth
What enzyme is deficient in PKU?
Phenylalanine hydroxylase
What is homocystinuria?
Homocysteine–> cystathione –> cysteine (cystathione beta synthase) (vitamin B6 and folate)
Inherited recessive condition = Defective enzyme: cystathione beta synthase
Homocysteine accumulates in tissues and is metabolised by other pathways
Methionine is produced in an alternative pathway:
Homocysteine –> methionine (vitamin B12)
What enzyme is defective in homocystinuria?
Cystathione beta synthase
What are some symptoms of homocystinuria?
Affects muscles, CNS and CVS
Fibrillin 1 protein is affected- unstretchy skin
In homocystinuria what amino acid is found in high concentrations in the urine?
Homocystine (oxidised form of homocysteine)
Methionine is not found in the urine because kidneys have a higher renal threshold for methionine than for homocystine and so methionine is reabsorbed into the blood whereas homocystine is not)
What is required for the conversion of homocysteine into methionine?
Vitamin b12
How can PKU be treated ?
Avoiding phenylalanine in diet
Why do the signs and symptoms of homcytsinutia initially resemble Marfan’s syndrome?
Homocysteine affects fibrillin1 production much like in Marfan’s
Results in tall stature, less stretchy skin due to this effect on connective tissue
How do you treat homocystinuria?
Supplement vitamin b6 and folate (increase activity of CBS)
Low methionine diet
Supplements of cysteine
Medication to reduce levels of homocysteine
What is Marfan’s?
Disease in which there is lack of expression of fibrillin 1 protein- affects connective tissues
What is the test for Marfan’s?
Arms length versus height
Why is homocystine (the oxidised form of homocysteine) found in the urine instead of methionine?
Renal threshold for methionine is much higher than it is for homocystine - so methionine is reabsorbed into the blood whereas homocystine remains in urine
What type of inheritance pattern do homocystinuria and phenylketonuria show?
Recessive
Why is homocystinuria associated with an increased risk of cardiovascular disease?
Homocysteine is a sulphur containing compound which increases its potential for oxidative stress
This results in increased atheroma formation in coronary arteries a a younger age
High risk of artery rupture due to defective fibrillin 1 formation (elastin) so high pressure in arteries OR oxidative stress (high sulphur content)
What is non shivering thermogenesis and where is it found?
Example of uncoupling process
BAT in babies and mice
In response to cold noradrenaline activates lipase to release fatty acids from TAGs
Fatty acids activate UCP1 and themselves undergo oxidation to produce NADH and FAD2H for electron transport
UCP1 transports H+ back into mitochondria
So electron transport and ATP synthesis are uncoupled and pmf is captured as extra heat
Outline the metabolism of lipids
Broken down into fatty acid and glycerol (breakdown and recombination occurs a lot throughout)
Fatty acid undergoes beta oxidation- combined with coA using fatty acyl coA synthase to make fatty acyl coA; taken into mitochondria using the carnitine shuttle; beta oxidation then occurs- 2 C lost in every cycle, using FAD/NAD+ and H2O
Acetyl coA is formed as a result–> Krebs cycle or ketone body synthesis
Glycerol–> glycerol phosphate (glycerol kinase)
- -> Dihydroxyacetone phosphate (DHAP)
- -> 2-Glyceraldehyde-3-phosphate
- -> GLYCOLYSIS
Outline the synthesis of fatty acids
A Acetyl coA molecule is converted into Malonyl coA: Acetyl coA(2) + CO2 + ATP ---> Malonyl coA(3) + ADP + Pi (acetyl coA carboxylase) Malonyl coA(3) is combined with another acetyl coA(2) using NADPH in repeat cycles- in each cycle a CO2(1) is lost - so at the end if each cycle a molecule is produced with 2 more carbons than the original eventually producing fatty acyl coA (~C16) (fatty acid synthase) Fatty acyl coA is elongated and desaturated in the ER and combined with glycerol 3 phosphate to produce a TAG
What are tags?
Triacylglycerols- three fatty acids and one glycerol
How are TAGs formed?
Esterification of glycerol and 3 fatty acids
How are TAGs broken down?
Lipolysis of TAG with 3 water molecules
What are the three classes of lipids?
- Fatty acid derivatives- TAGs (storage and insulation), phospholipids (cell membrane and plasma lipoproteins), eicosanoids (local mediators)
- Hydroxy-methyl-glutaric acid derivatives- ketone bodies (water soluble fuel molecules- can cross blood brain barrier; substitute for glucose can be made from fatty acids), cholesterol (membranes and steroid hormone synthesis), cholesterol esters (storage of cholesterol), bile acid and salts (lipid digestion)
- Vitamins- DAKE
Can fatty acid metabolism occur anaerobically?
NO as it requires NAD+ and FAD which need to be regenerated in the aerobic stage 4 of metabolism- so without oxygen fatty acid metabolism CANNOT OCCUR
What are the three main ketone bodies?
Acetoacetate
Acetone
Beta hydroxy butyrate
How are ketone bodies synthesised?
In the liver under conditions of starvation or type 1 diabetes
TAGs (storage)–> Fatty acids –> Acetyl coA–(HMGcoA synthase)–> HMG coA –(HMG coA lyase)–> acetoacetate –> acetone (spontaneous decarboxylation of acetoacetate) OR beta hydroxy butyrate
How is cholesterol produced?
TAGs (storage)–> Fatty acids –> Acetyl coA–(HMGcoA synthase)–> HMG coA –(HMG coA reductase)–> mevalonate –> cholesterol
What drug inhibits cholesterol synthesis and how does it work?
Statins inhibit cholesterol synthesis by inhibiting the enzyme HMG coA reductase
How is ketone body synthesis regulated?
Ketone bodies are produced in conditions of starvation or in type 1 diabetes when an alternative source of fuel is required for organs like the brain! Lyase enzyme Hormone regulation Stimulated by glucagon Inhibited by insulin
Regulated by the availability of carbohydrates for the body cells - so when no carbohydrates are available in starvation and type 1 diabetes- ketogenesis occurs
What enzymes are key in the production of ketone bodies?
HMG coA synthase and lyase
What enzymes are key in the production of cholesterol?
HMG coA synthase and reductase
How is alcohol metabolised?
Alcohol–(alcohols dehydrogenase and CYP2E1)–> acetaldehyde –(aldehyde dehydrogenase)–> acetic acid/ acetate
Alcohol –> acetaldehyde step requires NAD+ so can only occur in aerobic conditions (since NAD+ has to be regenerated in stage 4 of metabolism which can only occur in the presence of oxygen)
What enzymes are involved in the metabolism of alcohol?
Alcohol dehydrogenase
CYP2E1 (form of cyp450)
Aldehyde dehydrogenase
Explain the effects of excessive alcohol consumption on the liver?
The intermediate metabolite of alcohol metabolism, acetaldehyde, is toxic to liver cells. The increased availability of acetyl-CoA affects liver metabolism. The conversion of alcohol to acetaldehyde by alcohol dehydrogenase also produces NADH. The decreased NAD+/NADH ratio favours the formation of triacylglycerols which accumulate in the liver cells, leading to ‘fatty liver’.
What drug can be used to stop alcoholism?
Desulfiram - inhibits aldehyde dehydrogenase leading to an accumulation of acetaldehyde which gives symptoms of a long lasting headache
PUTS YOU OFF ALCOHOL FOR GOOD!
Danger is it could cause liver damage
What is pharmacodynamics?
What the drug does to the body - the effect of the drug on the body
What is pharmacokinetics?
What the body does to the drug- how the body metabolises the drug
What is pharmacokinetics the study of? Adme
Absorption
Distribution
Metabolism
Elimination of a drug
What is the two phase process of drug metabolism?
Phase 1 - hydrolysis, oxidation and reduction; make drug more reactive before it enters phase 2; CYP450; sometimes NADPH
Phase 2 - glucuronidation, glutathione conjugation, sulphate conjugation; attaches a water soluble group to the drug so that the whole drug molecule is made water soluble, so that it can be excreted in the urine; cytosolic enzymes in liver
What three reactions are common to phase 1 of drug metabolism?
Hydrolysis reduction and oxidation
What three reactions a common to phase2 of drug metabolism?
Glucuronidation
Glutathione conjugation
Sulphate conjugation
How is paracetamol at normal doses metabolised in the body?
Paracetamol is a reactive enough drug so it normally directly enters phase 2 of metabolism
Undergoes glucuronidation or sulphation
How is an overdose of paracetamol metabolised in the body?
Phase 2 of metabolism (glucuronidation and sulphation) tries to happen but it becomes a saturated situation whereby glucuronic acid and sulphate run out, SO:
Toxic paracetamol overdose enters phase 1
Paracetamol –> N-acetyl-p-benzo-quinine-imine (NAPQI)
NAPQI then enters phase 2 with GLUTATHIONE (as opposed to sulphate or glucuronic acid as normal)
NAPQI–> conjugated with glutathione
Outline the four stages of glycogenesis in liver and skeletal muscle
Glucose + ATP –(glucokinase/hexokinase)–> glucose-6-phosphate + ADP
Glucose-6-phosphate –(phosphogluco mutase)–> glucose-1-phosphate
Glucose-1-phosphate +UTP + H2O –> UDP-glucose + 2Pi
UDP-glucose + glycogen (n) –(glycogen synthase/branching enzyme)–> glycogen (n+1) + UDP
What are the 4 key enzymes in glycogenesis and which is the rate limiting enzyme?
Hexokinase/ glucokinase
Phosphogluco mutase
Glycogen synthase (rate limiting)
Branching enzyme
Outline the two stages of glycogenolysis in the muscle
Glycogen(n) + Pi –(glycogen phosphorylase/debranching enzyme)–> glycogen(n-1) + glucose-1-phosphate
Glucose-1-phosphate –(phosphogluco mutase)–> glucose-6- phosphate (GLYCOLYSIS IN Muscle)
Outline the three stages of glycogenolysis in the liver
Glycogen(n) + Pi –(glycogen phosphorylase/debranching enzyme)–> glycogen(n-1) + glucose-1-phosphate
Glucose-1-phosphate –(phosphogluco mutase)–> glucose-6- phosphate
Glucose-6-phosphate –(glucose-6-phosphatase)–> glucose + Pi
What are the 4 key enzymes in glycogenolysis and which is the rate limiting enzyme?
Glycogen phosphorylase (rate limiting)
Debranching enzyme
Phosphogluco mutase
(Glucose-6-phosphatase)
How is glycogenolysis regulated?
Glycogen phosphorylase (stimulated in low glucose conditions)
Hormones
Stimulated by Glucagon/ adrenaline
Inhibited by insulin
How is glycogenesis regulated?
Glycogen synthase (stimulated in high glucose conditions)
Hormones
Stimulated by insulin
Inhibited by glucagon/adrenaline
Outline gluconeogenesis
(Lactate) Pyruvate –(pyruvate carboxylase)–> Oxaloacetate –(phosphoenol pyruvate carboxykinase PEPCK)–> PHOSPHOENOLPYRUVATE –> 2-PHOSPHOGLYCERATE –> 3-PHOSPHOGLYCERATE –> 1,3-BISPHOSPHOGLYCERATE –> (Glycerol, DHAP/ Fructose) GLYCERALDEHYDE-3-PHOSPHATE –> FRUCTOSE-1,6-BISPHOSPHATE –(fructose-1,6-bisphosphatase)–> FRUCTOSE-6-PHOSPHATE –> (galactose) GLUCOSE-6-PHOSPHATE –(glucose-6-phosphatase)–> GLUCOSE
What are the 4 main enzymes involved in gluconeogenesis?
Pyruvate carboxylase
Phosphenol pyruvate carboxykinase (PEPCK)
Fructose-1,6-bisphosphotase
Glucose-6-phosphatase
Which two enzymes in gluconeogenesis are important in the regulation of gluconeogenesis?
Phosphoenol pyruvate carboxykinase (PEPCK)
Fructose-1,6-bisphosphatase
How is gluconeogenesis regulated?
Phosphoenol pyruvate carboxykinase (PEPCK) Fructose-1,6-bisphosphatase Hormone Stimulated by glucagon/ cortisol Inhibited by insulin
In what conditions are ketone bodies produced and why?
Ketone bodies are produced in conditions of starvation and in type 1 diabetes In starvation (no glucose) and in type 1 diabetes (no insulin is being produced so body thinks there is no glucose) and so lipolysis and fatty acid oxidation occur (to provide acetyl coA by an alternative route) and ketone bodies (water soluble) are produced as an alternative fuel for the brain cells as ketone bodies can cross the blood brain barrier
How are lipids transported around the body?
2% with albumin (FFA or NEFA)
98% lipoprotein
What is the structure of TAGs?
3 fatty acids and 1 glycerol
Non polar
