Metabolism ew Flashcards
What the diagram that summarises metabolism?
What type of reaction mainly are the breakdowns of protein, fat and carbohydrates?
Oxidative processes= reactions that involve the transfer of 1 or more electrons from an electron donor (reductant) to an electron acceptor
What is ATP mainly used for?
Ion pumping
Biosynthetic reactions
Muscle contraction
Where is ATP produced?
Mainly through the electron transport chain, TCA cycle (respiration), amino acid breakdown, fatty acid oxidation and glycolysis (glucose breakdown)
What is the actual and effective free energy of hydrolysis of ATP?
Hydrolysis of ATP= releases energy
Actual= 60 kJ/mol but ATP is not 100% effective so effective= ~40 kJ/mol
Where is NADPH produced from?
Produced in the pentose-phosphate pathway from NADP+
What is NADPH used for?
Fatty acid synthesis, ribonucleitode reduction and cholesterol synthesis
At what stage of life do you need the most energy per kg?
Baby, then slowly decreases, unless are an athlete
What energy source has the biggest energy yield?
What are the different energy stores in the body?
Glucose (plasma, liver, muscle)
Triacylglycerol (adipose and muscle)
Protein
What are the pros and cons of the different glucose stores?
Plasma- very small store, used by all cells
Liver- highly hydrated so heavy and not efficient storage
Muscle- can be mobilised rapidly in fight and flight and provide glucose anaerobically, store can only be used for muscle and also heavy
What are the pros and cons of triacylglycerol energy storage?
Not hydrated- less heavy and big energy yield
However, fat oxidation requires oxygen and free fatty acids cannot be used by the brain as fuel
What are the pros and cons of protein energy storage in the body?
It is convertible to both glucose and ketone bodies
All protein is functional however, there is no excess storageq
What are the different fuels present in the blood?
Glucose, fatty acids, ketone bodies, amino acids and lactate (breakdown product of glucose in anaerobic respiration)
What are ketone bodies made of?
Breakdown of fatty acids or proteins in starvation
What parts of the body require glucose as a fuel?
Brain- mainly uses glucose cannot use fatty acids
Erythrocytes- metabolise only glucose as they do not have mitochondria
Some other tissues e.g. renal medulla
What can amino acids be broken down into?
Some are glucogenic- can be broken down into glucose
Some are ketogenic- broken down into ketones
Some are both
How is fat metabolised? (diagram)
Triacylglycerol in diet converted to chylomicrons then stored as TG in adipose and be broken down when needed to FFAs in the plasma
FFA taken up by muscles (for energy) and in the liver (for energy and to be converted to ketone bodies for brain)
What are the differences between fast twitch and slow twitch muscles?
Red=fast twitch, white= slow twitch
What is a source of ATP in muscle?
Creatine phosphate can be converted to creatine by creatine kinase and in the process ATP is produced
When energy is not needed, creatine can be rephosphorylated back
What fuels are used for muscle contraction (in anaerobic and aerobic exercise)?
Anaerobic e.g. sprinting= muscle ATP, creatine phosphate and muscle glycogen
Aerobic e.g. marathon running- fatty acids, ATP, glycogen, creatine P, and plasma glucose
What is the pathway of glucose metabolism in muscle in aerobic and anerobic conditions?
What is the cori cycle?
Where the liver converts lactate back to glucose, however comes at an ATP cost
What fuel is used in different times of moderate exercise?
Firstly running on muscle glycogen, but runs out
Plasma glucose not initially a big contributor but increases as liver glycogen breaks down
Fatty acids are major fuel towards end of exercise
How is ATP produced during exercise?
Once existing ATP runs out, ADP can be rephosphorylated by creatine phosphate
Once creatine P runs out, 2 ADP can be converted to AMP and ATP
This is why AMP slowly increases during exercise
How are enzymes controlled by phosphorylation?
An addition of a phosphate by kinases causes activation of degredative pathways
Phosphatases hydrolyse off the phosphate in the oppsite reaction, causes activation of biosynthetic pathways
What are the metabolic effects of AMP activated protein kinase?
AMP= produced in sustained exercise
What is the nitrogen balance in the body based on?
Nitrogen balance = total nitrogen ingested - total nitrogen excreted
What is the diagram that summarises nitrogen balance in the body?
What are essential and non-essential amino acids?
Essential= cannot be synthesised within the body so must be supplied in the diet
Non-essential= can be synthesised from other amino acids in the diet
Semi essential (arginine, histidine)= can make them, but not enough to fulfill requirements
What is net protein utilization?
A measure of the ability of a protein to sustain growth, e.g. cow’s milk has an NPU of 81- 81% of amino acids in cow milk can end up as body protein
What are the different conditions associated with protein malnutrition?
Kwashiorkor- adequate energy intake but protein malnutrition, body weight is 60-80% of expected with abdominal bloating due to water retention due to lack of proteins
Marasmus- inadequate intake of protein and energy
What can cause a negative nitrogen balance?
Protein deprivation, essential aminoacid deficiency, trauma, hormones e.g. cortisol and disease
What can cause a positive nitrogen balance?
Growth, pregnancy
How are circulating protein degredaded?
Recognised as damaged/modified and are taken up by receptors and endocytosed
Taken into vesicles which fuse with lysosomes which contain degradative enzymes and produce amino acids
How are intracellular proteins degredaded?
targeted for destruction by attachment of ubiquitin
String of U attaches and this modified protein is recognized by proteasome and it breaks it down to amino acids
Where does protein digestion start?
Starts in the stomach with pepsin enzyme, secreted by chief cells
How does gastric acidification occur by parietal cells?
Cells are pumping protons to stomach and bicarbonate to plasma. Can detect slight alkalization of plasma after a big meal
What secretes and activates pepsinogen?
Chief cells secrete pepsinogen as cannot directly secrete pepsin or it will digest itself
Pepsinogen is activated by H+ ion concentration in the stomach- no enzyme required
What happens to proteins once they leave the stomach?
Pepsin does not fully digest proteins, they enter into small intestine and are cleaved by proteases secreted by the pancreas
The different proteases are selective for what protein they cleave
Examples of proteinases= trypsin, chymotrypsin
What activates pancreatic proteinases?
Trypsin is activated by enteropeptidase from trypsinogen, goes on to auto catalyse that reaction and activate other proteinase precursors
How are amino acids uptaken in the intestine?
Taken through a transporter channel with sodium ions
How are amino acids broken down to ammonia?
Firstly transamination; taking the amino group off to form ketoacid or oxoacid- broken down further for fuel or reconverted
Also forms glutamate, which is converted into ammonia
Why does high levels of ammonia cause toxicity?
In a high ammonia concentration the equilibrium changes and uses up oxoglutamate (TCA cycle intermediate) and slows down TCA cycle- in the brain for example
What is ammonia converted to that is a precursor to the urea cycle?
Carbamoyl phosphate
What is the urea cycle?
Occurs in the liver
Carbamoyl phosphate is converted to urea through various steps
What can cause plasma concentrations of urea to rise and fall?
Rises in renal failure (failure to excrete)
Falls in liver cirrhosis (failure to produce0
What are some properties of urea?
- Toxic, especially to CNS
- Very soluable
- Electrically neutral
- Contains 48% Nitrogen by weight
How does nitrogen from the muscles enter the urea cycle?
Glutamate and pyruvate form alanine. This is the transporter form of amino acids to the liver
What is glutamine?
A transporter form of amino acids. Formed in tissues and kidney and can be excreted directly through kidney
What is the diagram that summarises amino acid breakdown and nitrogen excretion?
Why is folic acid useful in the diet?
It is reduced to tetrahydropholic acid which can carry groups of single carbons and modify their oxidation state- needed for reactions such as DNA synthesis
What are all dietary carbohydrates covertible to?
Glucose
What are the main carbohydrates present in the diet?
Starch
Sucrose
Lactose
Glucose
What is the molecular arrangement of glucose?
Glucose- 6 carbons
Largely in cyclic form (ring structure). The ring is puckered. When ring is formed the hydroxyl group can be above or below the ring- alpha or beta confirmation
That bond is important for enzyme specificity
What are the different structures of starch?
Made entirely of glucose
Amylose= unbranched chains madeof alpha(1-4) links
Amylopectin=branched chains with alpha (1-4) and alpha(1-6) links
What enzymes are involved in starch digestion?
Amylase= present in salvia and also secreted by the pancreas into the duodenum
Glucoamylase= anchored to the intestinal wall
Isomaltose= also intestinal, breaks down isomaltose
What does amylase produce?
Oligosaccharides which are then broken down in the intestine
What are alpha-glucosidase inhibitors?
Alpha-glucosidase inhibitors inhibit the absorption of carbohydrates from the small intestine
Inhibit glucoamylase and isomaltose
Used in treatment of type two diabetes
What is a disaccharide and what are examples?
Disaccharide=any substance that is composed of two molecules of simple sugars
E.g. maltose and isomaltose from starch digestion
Lactose and sucrose from the diet
What causes lactose intolerance?
If lactose is not hydrolysed, passes it into small intestine where bacteria hydrolyse it and produce water and hydrogen.
Lactase gene is shut down later in life however have been mutations which means it does not get switched off and persists- these people can digest lactose
How is glucose uptaken in the intestine and then into body cells?
- Apical side= sodium glucose symport
Sodium ion runs down its conc gradient, ‘drags’ the glucose with it - Sodium ion conc in the cell maintained by ATPase which is found in all cells
- Passive flow to basolateral side (blood)
- Glucose conc in plasma relatively high, rest of body cells is low so it runs in via uniporters
What is the Km of glucose?
Km= concentration of glucose to give you half the max uptake-shows saturation
What is the Km for different uniporters in the body?
Liver kidney, intestine pacreas= high Km, Need higher glucose conc to saturate it. Uptake affected by blood glucose levels
Brain, testes= low Km so usually saturated and takes up glucose at a constant rate, not affected by blood levels
Where are glucose uniporters insulin responsive?
Muscle, adipose and heart
Activity is increased by insulin. Number of transporters increased by insulin. 1 min after meal= 5 fold increase
What are the changes in plasma glucose, insulin and fatty acids after feeding?
Glucose rising= stimulates release of insulin
Insulin promotes uptake of glucose in cells in fat and muscle and glycogen synthesis in the liver
Non esterified fatty acids= After fasting is high but insulin inhibits release of fatty acids from fat and FA have a short half life. Increases when insulin falls
What are the different metabolic fates of glucose?
What enzymes are involved in the breakdown and synthesis of glycogen?
Synthesis= glycogen synthase
Breakdown=glycogen phosphorylase
What are the enzymes involved in glucose phosphorylation?
Hexokinase- all cells in the body has this- saturated at low levels
Glucokinase- in liver and pancreatic b cells. Phosphylation rate increases as the glucose conc rises
What is the structure of glycogen?
Contains just glucose- long chains linked alpha 1-4 and side chains of 1-6
Upto 12 layers of chains.
The addition of glucose or removal takes place at the reducing ends
What does glucose-1-phosphate join onto before it can become glycogen?
UDP- becomes
What causes an increased and decreased synthesis and breakdown of glycogen?
SYNTHESIS
Decrease- adrenalin and glucagon
Increase- insulin
BREAKDOWN
Opposite effects
What ATP is lost/gained turning glucose into pyruvate?
2 ATP needed to convert glucose to glyceraldehyde-3-P
4 molecules to convert that to pyruvate
Net gain of 2ATP in anaerobic respiration
Pyrvuate may go on to be oxidised in mitchondria- 36 molcules made
What is gluconeogenesis?
The reverse of glycolysis- to make glucose
Where does gluconeogenesis occur?
The liver and kidneys
What pathway produces NADPH?
The pentose-phosphate pathway
What is glutathione?
Glutathione is a substance made from the amino acids glycine, cysteine, and glutamic acid. It is produced by the liver
It is an intracellular antioxidant. Lipids that are peroxidised can be reduced by glutathione. It is a protective reaction to destroy peroxides
What is the commonest human genetic disorder?
G6PDH deficiency (glucose-6-phosphate dehydrogenase)
X linked so usually affects males
Can cause hemolytic anemia (low numbers) or possibly red blood cell sequestration (RBC stuck in spleen)
How does metabolism of ethanol occur?
In the liver
Ethanol converted to ethanal by reduction of NAD+ to NADH by alcohol dehydrogenase
Ethanal converted to ethanoic acid also by reduction by aldehyde dehydrogenase
Ethanoic acid -> acetyl-CoA -> TCA cycle or fatty acids and ketones
Why does hypoglycaemia occur in alcohol intake?
Generation of reduced NADH stops glycogenesis in the liver
What drug is used to treat alcohol addiction and what step does it affect?
Disulphiram or ‘antabuse’
Stops ethanal being converted to ethanoic acid. Build up of ethanol makes you feel awful
What is the problem with alcohol dehydrogenase and how can it be fixed?
It will oxidise any alcohol even the toxic ones- methanol to formaldehyde and ethylene glycol to oxalic acid which is renally toxic
Can block it by giving ethanol- AD would prefer to oxidise thaty
What enzymes are involved in metabolising fructose so it can become pyruvate?
Fructokinase and to a lesser extend hexokinase. Also F-1-P aldolase
What enzymes are involved in metabolising galactose so it can become pyruvate?
Galactokinase and UDP-galactose
epimerase
(arrow to glycolysis)
What happens if missing enzymes in the pathways of metabolising fructose and galactose?
F-1-P aldolase= missing- fructose intolerance. Can cause hypoglycaemia and lacticaidaemia
Galactokinase or UPD-galactose epimerase= get build up which causes damage to liver and eye. Galactose intolerance
What is the structure of fatty acids?
Straight chain; can be saturated or unsaturated
Carbons are numbered away from the carboxyl group
Unsaturated- natural ones have sis bonds, manufactured (e.g. margarine) have trans bonds
What is the structure of triacylglycerols?
Glycerol with 3 fatty acids attached
How is triacylglycerol digested?
triacylglycerol= insoluable
Mechanical action of stomach breaks it down into small droplets
In the small intestine it meets detergents (bile acid and salts) which breaks them down further. Pancreatic lipase hydrolyses the 2/3 FFA’s off triacylglycerol and leaves moboacylglycerol
Then absorbed by intestinal cells. Once inside cells, reconverted to triacylglycerol. Then to transport around the body, they are packaged into chylomicrons
What is the general structure of chylomicrons?
How are chylomicrons degredated?
Whilst they are circulating, they pick up apoprotein C-II from HDLP which activates lipoprotein lipase.
Lipoprotein lipase is present on the outside of fat, muscle and heart cells. It degrades triacylglycerols to glycerol and free fatty acids
Can fats be synthesised by carbs too?
Yes, acetyl-CoA can be converted to malonyl-CoA (a precusor of fatty acids) by Acetyl-CoA carboxylase
What is acetyl-CoA carboylase activated and inactivated by?
Active form= phosphorylated form
Activated by insulin and citrate
Inactivated by acyl-CoA and glucagon
What is the enzyme that builds up fatty acids?
Fatty acid synthase complex builds up fatty acids adding two carbons at a time, adding acetyl-CoA and malonyl-CoA
Produces fatty acids that are saturated and have an even number of carbons
What promotes fat/triacylglycerol synethsis and what inhibits it?
Insulin and glucagon at different steps of the cycle
How is glucose converted to fat?
Glucose enters the cell and through glycoloysis is converted to pyruvate
It enters the mitochondria, is converted to Acetyle-CoA
In the cytoplasm, this is then converted to malonyl-CoA and this is used to produced fatty acids then triaglycerol
What saturated bonds can be made in fat in the body?
Bond 9,4,5,6
Bonds after 9 cannot be made , have to be supplied in diet as are precursors for prostaglandins, leukotrienes and other molecules
What is the recommended amount of unsaturated fats to have a day?
10-20g
How are fatty acids desaturated?
By a electric transport chain which starts with NADH being reduced to NAD+ and eventually oxidises the saturated bond so 2 hydrogens are given off.
2 hydrogens join oxygen for water- oxygen is required
How is triacylglycerol mobilised from adipose tissue?
Hormone sensitive lipase takes off fatty acids one at a time to glycerol
Hormone sensitive lipase decreased by insulin and increased by adrenalin, glucagon and growth hormone
How are free fatty acids transported around the body?
They are insoluable- transported bound to albumin
How are free fatty acids uptaken and activated in cells?
Taken up by diffusion or more commonly by transporters
Once in cell fatty acid binding proteins will bind them and they are attached to co-enzyme A- means fatty acids are trapped in cells and will be cross the membrane again
What is cholesterol?
Major component of membranes and precursor of steroid hormones and bile acid/salts
How is cholesterol formed?
The liver is the principal site for cholesterol homeostasis maintenance carried out in many mechanisms, such as biosynthesis, via HMG coenzyme A reductase.
Starting molecule is acetyl-CoA
Rate limiting step= reaction controlled by HMG-CoA reductase
What drug can affect the rate limiting step of cholesterol production?
Statins- lower plasma cholesterol
How are bile acids synthesised?
Cholesterol is hydrolated and the side chain is cleaved. This produces primary bile acids which are joined with taurine and glycine to form different bile salts
Bile salts are made in the liver, stored in gallbladder and excreted into the SI
Pass into large intestine and bacteria reduces and hydrolyses them and this produces secondary bile acids which are partly reaborbed
What can inhbit the uptake of cholesterol in the digestive tract?
Plant sterols e.g. those in flora
Cholestyramine
How are fatty acids transported into the mitochondria and what can inhibit this?
Acyl-CoA passes through the outer membrane via a transporter which can be inhibited malonyl-CoA
Once in the inter-membrane space it joins on with carnitine to form Acyl-Carnitine and then is transported to the matrix
How is acyl-CoA formed?
Fatty acids are activated by reaction with CoA to form fatty acyl CoA.
How does beta-oxidation of fatty acids occur?
Occurs in mitochondria
Long chain fatty acids are oxidised (double bond introduced) by reducing uniquinone
It is then hydrated and oxidised for a second time using Nad+ as the reducing agent
Finally, is split into acetyl-CoA and a fatty acid two carbons shorter
What is the comparisons of fatty acid synthesis and degradation? (location, reactions, co-enzymes)
What will happen in the beta oxidation of a odd carbon numbered fatty acid?
Instead of acetyl CoA being produced, there will be a 3 carbon molecules produced called proplonyl-CoA
What happens to proplonyl-CoA to allow it to be fed into the TCA cycle?
3 carbon is converted to 4 carbon by carboxylation and that is isomerized to succinyl-Co-A which is fed into the TCA cycle
Dependant on vitamin B12
What enzyme oxidises pyruvate to acetyl-CoA?
Pyruvate dehydrogenase complex
Uses NAD+ as the oxidising agent
What regulates the active/inactive forms of pyruvate dehydrogenase?
Active form= unphosphorylated
Inactive form= phosphorylated
What is the TCA cycle/ krebs cycle?
Do not need to know all the intermediates
Acetyl-CoA is fed into the cycle, produces CO2 and NADH
There is also production of ubiquinone and GTP
Other intermediates can be fed in- glucogenic amino acids. Used to produce glucose so not just a breakdown pathway
What does one turn of the cycle produce?
3 NAHD
1 ubiquinone
1 GTP
All together these produce ~ 10.6 ATP
When are ketone bodies produced?
When there is excessive breakdown of fatty acids, and the TCA cycle gets saturated so acetyl-CoA gets converted to ketone bodies
When is glucose made?
Gluconeogenesis- glucogenic amino acids fed into the cycle and oxaloacetate is converted to glucose
What ketone bodies are made in starvation?
4 carbon acids are made- 3-hydroxybutyrate which circulates in plasma and can be used for fuel espiecally of the brain
Acetone is a side product produced- can smell it on breath in ketoacidaemia
What is ubiquinone?
Co-enzyme that is reduced in fatty acid oxidation
Very hydrophobic and is dissolved in the membrane
How does the mitochondrial electron-transport chain work?
Series of complexes which pass electrons from one to another
Reduce different substances- firstly NAHD, then succinate
The complexes translocate protons across the membrane- cause pH difference and a different membrane potential.
ATP synthase makes ATP from the protons coming back into the matrix
How many H+ ions enter and exit the mitochondria?
10 H+ produced from electron transport chain
~ 3H + flow back in through ATP synthase
Uncoupler transporters- transport H+ ions back in but do not produce ATP
There is also exchange transporter to get ATP out the cell and ADP and Pi in
What is a P/O ratio and what are the ratios for NADH oxidation and succinate oxidation?
P/O = mols ATP produced / atoms of O reduced
For NADH oxidation, n = 10
P/O = 10 / (~3 + 1) = ~ 2.5
For succinate oxidation, n = 6
P/O = 6 / (~3 + 1) = ~ 1.5
How does muscle contraction control the demand for ATP?
Muscle contraction produces ADP which stimulates ATP synthase, It translocates protons more and decreases the electro gradient more.
ET chain can go faster as does not have as much work. This increases the ratio of NAD+ to NADH which stimulates the TCA cycle
