Metabolism Flashcards
What’s the significance for biological systems of the first law of thermodynamics?
Living organisms can convert chemical energy into mechanical energy and heat, but cannot destroy it.
- Thus, excess energy intake can only be stored as fat.
What are the units of energy?
Joule, but usually expressed as MJ or kJ
How can you measure the energy content of foods?
- Inc. steps taken to do this
By oxidising food samples in a bomb calorimeter.
- A measured amount of dry food is placed inside the calorimeter in an atmosphere of oxygen, and ignited
- The amount of heat released is measured by the increase in temperature of the water jacket and thus the heat of combustion is calculated
What are the Atwater Factors of the 4 fuel sources?
- Fat = 38kJ/g
- Carbohydrate = 17kJ/g
- Protein = 17kJ/g
- Ethanol = 29kJ/g
What are the 2 ways of measuring energy expenditure?
- How do they work?
- What do they use?
- Direct calorimetry
- Relies on measuring heat output from a person in a whole-body calorimeter - Indirect calorimetry
- Based on Oxygen consumption and CO2 Production
(certain amount of energy associated with every litre of O2 consumed)
- Measured using a respirometer
- Can calculate RER
What is RER?
- Equation
- Allows determination of?
- RER of carbs and fatty acids
- Respiratory exchange ratio
- CO2 produced / O2 consumed
- Allows determination of which fuel the body is using
- Carbs: RER = 1
- Fatty acids: RER = 0.7
What is basal metabolism?
What does it differs b/w individuals depending on?
- Energy required for maintenance of life; energy expenditure at rest
- Differs b/w individuals depending on:
Gender
Age
Body size/composition
Genetics
Hormonal status
Stress levels
Disease status
Certain drugs
Factors affecting basal metabolism?
Increased by: - Athletic training - Late pregnancy - Fever - Drugs (e.g. caffeine) - Hyperthyroidism Decreased by: - Malnutrition - Sleep - Drugs (i.e. B-blockers) - Hypothyroidism
Function of salivary glands
Produce saliva, which contains mucous and amylase which STARTS THE DIGESTION of CARBOHYDRATES
Functions of the stomach
- incl. what it secretes
- Storage and mixing of food w/ gastric juices
- Slow release of chyme into intestine
- Secretes acid (denaturing), pepsinogen (protein digestion) and mucous (protection)
Function of the pancreas
Secretes most digestive enzymes, incl. amylase, lipase, proteases
Function of the liver
Synthesis of bile salts/acids important for fat digestion
Function of small intestine
Final stage of digestion and absorption
2 general phases of digestion
- Hydrolysis of bonds connecting monomer units in food macromolecules (glycosidic, peptide, ester)
- Absorption of products from gut into body
Carbohydrate digestion process
- Intake of carbohydrates
- Salivary amylase catalyses the hydrolysis of the glycosidic bonds
- Pancreatic amylase completes the digestion of the starch molecule
- Enzymes hydrolyse disaccharides into monosaccharides (in SI) to be absorbed by intestinal epithelial cells
- Maltose and isomaltose —> glucose x2
- Sucrose —> glucose + fructose
- Lactose —> glucose + galactose - Fibre is excreted as faeces
Carbohydrate absorption process
- Glucose is absorbed through apical surface via symport with Na+ (secondary active transport)
- Glucose moves through basal membrane via facilitative transporter (conc. gradient)
The intracellular conc. of Na+ is kept low by Na+/K+ ATPase
Lactose intolerance:
- What is it?
- Caused by?
- What does it cause? why?
- How to manage
- Disorder affecting carbohydrate digestion
- Caused by a lactase deficiency
- Causes bloating, flatulence and diarrhoea, due to fermentation of lactose by intestinal bacteria
- Need to avoid lactose in diet
Coeliac Disease:
- What is it?
- Where in the body does it affect?
- Cause?
- Symptoms?
- Disorder affecting carbohydrate digestion
- SI
- Body reacts against gluten (wheat protein); antibodies react w/ transglutaminase; villi flattened, nutrients not absorbed
- GI symptoms (variable)
Why do we need dietary protein?
- Supplies AAs to make body proteins
- Source if Nitrogen for purines, pyrimidines and haem
- C skeletons can be used as fuel
General function of GI hormones
Control the secretion of digestive enzymes
What are the 3 main GI hormones and their function?
- Gastrin - stimulates the secretion of gastric juices
- Secretin - stimulates secretion of alkaline bile and pancreatic fluids (bicarbonate)
- Cholecystokinin (CCK) - stimulates the release of pancreatic enzymes and release of bile from the gallbladder
What is protease specificity determined by?
In terms of hydrolysis of proteins
AA side chains
Endopeptidases vs exopeptidases
Endo- attack peptide bonds w/in the peptide chain
Exo- attack peptide bonds at the end of the chain
Pepsin
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- Stomach
- Proteins and pepsinogen
- Stomach
- Endo
Trypsin
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- Pancreas
- Polypeptides, chymotrypsin
- SI
- Endo
Chymotrypsin
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- Pancreas
- Polypeptides
- SI
- Endo
Carboxypeptidase
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- Pancreas
- Polypeptides
- SI
- Exo
Aminopeptidase
- What is it
- Source
- Substrate
- Site of action
- Endopeptidase or exopeptidase?
- Enzyme involved in protein digestion
- SI
- Polypeptides
- SI
- Exo
Dipeptidase
- What is it
- Source
- Substrate
- Site of action
- Enzyme involved in protein digestion
- SI
- Dipeptides
- SI
Protein digestion process
- Protein —> peptides in stomach (via HCl + pepsin)
- Peptides —> di- and tripeptides + AAs in SI (via digestive enzymes: trypsinogen, chymotrypsinogen, carboxypeptidases, aminopeptidases)
- Di- and tripeptides —> AAs in SI (via di- and tripeptidases)
- AAs cross intestinal epithelial cells and move into blood
Absorption of AAs
- Absorption thr’ apical membrane of SI by Na+ dependent carriers (symport)
- AA absorption thr’ basal membrane (into portal vein) via facilitated transporter
Intracellular Na+ levels kept low via Na+/K+ ATPase
Cystic fibrosis
- What is it
- What does it cause?
- Leads to?
- Disorder affecting protein digestion
- Causes thick mucous secretions which block the pancreatic duct and thus the secretion of pancreatic enzymes
- Leads to malabsorption
Coeliac disease
- What is it
- How is it caused?
- Leads to?
- Disorder affecting protein digestion
- Body reacts against wheat protein bc antibodies react w/ transglutaminase
- Flattened villi —> malabsorption
Process of nucleic acid digestion
- DNA + RNA undergo acid hydrolysis in the stomach
- Intestinal nucleases hydrolyse the phosphodiester bonds b/w nucleotides
- Individual nucleosides absorbed via nucleoside transporters
Main classes of dietary lipids
- TAG
- Phospholipids
- Cholesterol
Bile acids
- What do they do?
- How do they do this?
- What structural feature allows them to do this?
- Emulsify fats
- Forms micelles w/ TAGs to increase SA for digestion
- Have a hydrophobic side (facing inside micelle) and hydrophilic side (facing outside micelle)
Role of pancreatic lipase/how it does it
- Also what does this allow?
- Within micelle: hydrolyses fatty acids at positions 1 + 3 of glycerol backbone to break down TAGs —> fatty acids + monoacylglycerol + cholesterol
- Smaller micelles formed (w/ bile salts), which can be absorbed across intestinal cell membrane
Process of Micelle/lipid absorption
- Micelles absorbed across intestinal membrane; release contents into cell
- MAG + ffa transported to ER, where they’re resynthesised into TAGs and cholesterol esters
- TAGs + other lipids combine w/ apoB in ER to form chylomicrons
- Chylomicrons secreted from intestinal cells entering the bloodstream via the lymphatic system
What does Xenical do? How?
- Inhibits pancreatic lipase by interacting w/ the OH group in its active site —> leads to inactivation bc can’t hydrolyse fatty acids
- Mimicks a TAG molecule
4 Main classes of lipoproteins
- What do they solubilise?
- Chylomicrons (high lipid:protein ratio)
- VLDL
- LDL
- HDL (low lipid:protein ratio)
solubilise lipids for transport
Functions of apoproteins
- Structural for assembly of lipoproteins (apoB)
- Ligands for cell surface receptors (apoE + apoB)
- Enzyme cofactors (apoCII for lipoprotein lipase)
What are the 2 lipid transport pathways? What type of fat do they transport?
- Exogenous chylomicron pathway - dietary fat
2. Endogenous VLDL/LDL pathway - endogenously synthesised fat
What apoprotein activates lipoprotein lipase?
apoCII
Familial Hypercholesterolemia (FH)
- What is it
- Caused by?
- Leads to?
- Treated with?
- Common form of hyperlipidaemia, which leads to premature atherosclerosis
- Caused by a defect in LDL receptor gene
- Leads to LDL build up in the blood
- Treated w/ statins, which lower LDL
Key characteristics of vitamins
- “vital to life”
- Essential, individual, ORGANIC molecules
- Don’t provide energy when broken down
- If absent/low in the diet –> symptoms of deficiency
- Required in the diet in small amounts (mg or µg)
What is bioavailability?
Amount absorbed and used
What are the 4 components used to ascertain if someone is consuming enough vitamins/minerals to meet their requirements?
- Clinical examination - look for symptoms
- Anthropometry - energy balance/growth
- Biochemical tests
- Dietary assessment (compare nutrient intake w/ Nutrient Reference Values)
Roles of vitamins
- Coenzymes: allow metabolic reactions to occur (transport molecules)
- Cofactors: allow metabolic reactions to occur (directly participate/assist in catalysis)
- Other roles:
Structural
Antioxidants
DNA/RNA
Thiamin - role? - Deficiency Causes Diseases
- Part of coenzyme; role in nerve cells and converting pyruvate —> acetyl-CoA
- Glucose can’t be converted into energy; increased pyruvate and lactate (vasodilators)
- -> Beriberi (heart failure due to venous pooling)
- -> Wernicke-Korsakoff (cerebral beriberi + psychosis)
Characteristics of minerals
- Essential NON-ORGANIC elements
- Don’t provide energy
- If absent or low in the diet, symptoms of deficiency MAY appear
- Required in the diet in small amounts (mg or µg)
Minerals vs. trace elements
Minerals: >5g in the body
Trace elements: <5g in the body
Roles of minerals
- Cofactors
- Structural role (hydroxyapatite crystal)
- Key constituent of molecules (i.e. Fe)
- Transfer of electrons (redox reactions)
- Nerve impulse + muscle contraction
- Fluid + electrolyte balance
Why do we need Mg? (i.e. roles)
- Cofactor for >300 enzymes involved in cellular processes
- Stabilises proteins, nucleic acids, membranes
- Bone metabolism + remodelling
- Nerve impulse + muscle contraction
Why do we need Selenium? (i.e. roles)
- Antioxidant (works w/ vitamin E)
- Cofactor for other enzymes (e.g. thyroid hormone)
2 diseases caused by Selenium deficiency
- Occurs in who?
- Caused by?
- White muscle disease
- occurs in pasture-fed animals
- low levels of Selenium in soils - Keshan’s disease
- Humans develop cardiomyopathy
- Influenced by diet
Why is ATP a central energy intermediate?
Bc energy from energy-releasing reactions is converted to ATP and can subsequently used to drive energy-requiring reactions
What does Gibbs free energy tell us about a reaction?
The amount of work that can be done (+ve △G) or that is required (-ve △G)
What is energy coupling?
When an energetically favourable reaction drives an energetically unfavourable reaction by making the overall △G -ve.
Role of reducing equivalents in redox reactions
Interact w/ enzymes to accept and donate reducing equivalents, which allows fuel molecules to become oxidised
Characteristics of coenzymes
- Carrier molecules (of H atoms)
- Exist in 2 forms (oxidised + reduced)
- Low conc. in cell
4 .Usually derived from vitamins
Coenzyme A (CoA)
- What is the functional group involved in binding acyl groups?
- Carrier of what?
- 2 forms
- SH group
- Carrier of acyl groups
- Free CoA = CoASH
- acyl group attached = Acetyl-CoA
Which cell types use glucose as a fuel? Why?
- RBCs: don’t have mitochondria
- Brain: fats cannot readily cross the blood-brain barrier
- Eye: blood vessels + mitochondria would refract light
- White muscle: fast twitch
General steps for glucose activation
- Addition of phosphate group
- Rearrangement of structure
- Addition of a second phosphate group
- Splitting of carbon skeleton into two 3C sugars
Two types of phosphorylation reactions used for ATP synthesis
- direct/indirect?
- energy source?
- Substrate-level
- Direct
- Energy comes from substrate - Oxidative
- Indirect
- Energy comes form reduced coenzymes
What type of reaction is aerobic metabolism of glucose?
Oxidative decarboxylation reaction
Importance of NAD+ regeneration?
Allows glycolysis + ATP production to continue
Why are fatty acids the preferred fuel for most tissues?
- They release more energy when oxidised bc they’re more reduced than carbohydrates
- Require less space for storage
How are fatty acids delivered to the mitochondria?
- Hydrolysis of stored TAGs in fat cells to ffa + glycerol; conc. gradient formed, diffuse into blood
- ffa bind to albumin, which carries them in the blood to peripheral tissues, where they’re released + transported into cytoplasm
- Bind to FABP (fatty acid binding protein), which allows them to be soluble
How are fatty acids activated for oxidation?
- Energy source?
- Enzyme?
- By attachment to CoA, making a fatty acetyl-CoA
- ATP —> AMP + PPi
- Acyl-CoA synthetase
How is fatty acyl-CoA transported into the mitochondrial matrix?
- Passes through outer membrane via protein carrier
- Converted to fatty acyl-carnitine via carnitine acyltransferase I (in outer membrane)
- swaps CoASH w/ carnitine - Passes through inner membrane via protein carrier
- Converted back to fatty acyl-CoA via carnitine acyltransferase II
- swaps carnitine w/ CoASH
Where does acetyl-CoA arise from?
- B-oxidation of fatty acids
- Pyruvate
- Catabolism of AAs
Main stages of B-oxidation + where they occur
CYTOSOL 1. Activation of fatty acid by adding CoA (ATP --> AMP + PPi) MITOCHONDRIAL MATRIX 2. Oxidation (Each C loses 1 H) 3. Hydration (replaces lost hydrogens and adds O) 3. Oxidation (Beta carbon loses both H) 4. Break bond between alpha + beta carbon, add H from CoA-SH to the alpha carbon (forms acetyl CoA) and CoA-S to the beta carbon (is recycled back to the start)
What does 1080 inhibit? Effect?
- Aconitase
- stops the CAC, bc can’t produce necessary precursors
Overall reaction for CAC
acetyl-CoA + 3NAD+ + FAD + 2H2O + GDP + Pi —> 2CO2 + 3(NADH + H+) + FADH2 + CoA —> GTP
How many H+ ions are pumped through the ETC bc of an NADH molecule?
10
How many H+ ions are pumped through the ETC bc of an FADH 2molecule?
6
What is the co-enzyme required for transamination reactions?
- What does it do?
- Pyridoxal Phosphate
- Transfers the amino group
What are the common AA/α-keto acid pairs?
- Glutamate ⇌ α-ketoglutarate
- Aspartate ⇌ oxaloacetate
- Alanine ⇌ pyruvate
Where can keto acids be fed into?
The CAC
How do transamination reactions remove excess N via the liver
Alanine + Glutamine formed via transamination are transported via the liver, where the N is metabolised into urea
What are the 2 mobile carriers in the ETC?
CoQ and Cytochrome C
What are the 2 pathways of electron transport through the ETC?
- NADH: Complex I –> CoQ –> complex III –> cyt. c –> complex IV
- FADH2: Complex II –> CoQ –> Complex III –> cyc. c –> complex IV
How many protons are pumped at each complex?
Complex I: 4
Complex II: none
Complex III: 4
Complex IV: 2
How does Rotenone inhibit electron flow?
Inhibits the transfer of electrons from Complex I –> CoQ
How does cyanide inhibit electron flow?
Binds to cytochrome a3 in complex IV
How does CO inhibit electron flow?
Decreases conc. of oxygen, which acts as a terminal electron acceptors
What is cytochrome c?
Heme containing protein
What is the proton motive force?
Two energetic gradients across the inner mitochondrial membrane:
- Chemical gradient: different conc.s of H+ on each side (thus acidic side and alkaline side)
- Electrical gradient: due to charge difference across membrane
Experiments supporting the chemiosmotic theory for ATP synthesis
- Isolation of mitochondria + removal of outer membrane; ETC still works but no ATP made
- ATP can be made in an artificial liposome w/ a light-inducible proton pump but no ETC
What do uncouplers do?
Example of one?
- Make the membrane leaky to H+ ions and dissipate the energy as heat
- DNP
How does FoF1-ATP synthase work?
Proton flow drives rotor movement; causes conformational changes in the stator (subunits of F1)
What are the reactions that oxidise ethanol to acetate?
- reducing equivalents?
- Ethanol ————————–> acetaldehyde
alcohol dehydrogenase - Acetaldehyde —————————-> acetate
aldehyde dehydrogenase
Both steps use NAD+ as reducing equivalent
How is ethanol metabolised?
- The acetate produced as a result of alcohol oxidation is converted to acetyl-CoA via acetyl-CoA synthase
- Adds CoA, and converts ATP to AMP + PPi
Effects of ethanol metabolism on other metabolic process in the liver
- Increases NADH and ATP; slows CAC and ETC
- Slows glycolysis by inhibiting phosphofructokinase and pyruvate dehydrogenase
- Impairs fatty acid oxidation by reducing NAD+
- Causes increase in pyruvate –> lactate
- Slows gluconeogenesis
Alternate pathway for ethanol metabolism (i.e. as a toxin)
MEOS:
Ethanol oxidised to acetaldehyde (via oxidase) which is oxidised to acetate
Effects of chronic alcohol metabolism
Toxic acetaldehyde —> fatty liver + inflammation –> alcoholic hepatitis –> necrosis –> cirrhosis –> coma + death
Why do we need to store fuels?
- Bc the body cannot store ATP
- To maintain a supply of glucose b/w meals
- To provide immediate fuel for increased activity
- For long periods when food intake may be inadequate
Why do we have unlimited fat stores?
Bc fat cells are everywhere in the body and they can expand
How are TAGs mobilised?
- Adrenalin (exercise) and/or glucagon (fasting) activates hormone-sensitive lipase
- H-S lipase mobilises the TAGs inside the adipocyte
- Release of glycerol + ffas
Structure of glycogen
Glucose units linked by alpha-1,4 glycosidic bonds, branches introduced at alpha-1,6 glycosidic bonds
Glycogen synthesis:
- where
- when
- inputs
- product
- Enzymes used?
- Mainly in liver and muscle
- Immediately after a meal
- ATP and UDP
- Makes activated high-energy precursor UDP-glucose
- Uses glycogen synthase and branching enzyme
Equation for glycogen synthase
hexokinase mutase
glucose G-6-P G-1-P —–> UDP glucose
ATP–>ADP UTP–>PPi
(add glycogen (n))
————————-> glycogen (n+1)
(lose UDP)
Mobilisation of glycogen: what happens to
- liver glycogen
- Muscle glycogen
- Liver: released as glucose into blood
- Muscle: releases fuel for glycolysis w/in muscle cells
Under what condition is glucose converted to fatty acids?
Occurs where?
Process?
How does it go on to be stored as fat?
- Excess carbohydrate intake, above what can be stored as glycogen
- In liver
- Process
1. Stimulated by insulin
2. Glucose –> acetyl-CoA –> fatty acids
3. Fatty acids –> TAGs –> VLDL –> adipose tissue as fatty acids
Which aerobic tissue cannot use fatty acids as an alternative fuel to glucose?
Brain
How long can the glycogen stores in the liver provide the brain with glucose for?
1 day
Glycogenolysis reaction
+ Pi
Glycogen ————–> G1P ———-> G6P
phosphorylase. mutase
- Pi --------------------------------> glucose glucose-6-phosphatase
What are the substrates for gluconeogenesis?
Stimulated by?
Which tissue uses most of the glucose?
- Lactate from skeletal muscle glycogen
- Alanine from muscle protein
- Glycerol from adipose tissue
- Stimulated by glucagon
- The brain
Structure of lactate
CH3 – CH – COOH
I
OH
Structure of alanine
CH3 – CH – COOH
I
NH2
Structure of glycerol
CH2 – CH – CH2
I I I
OH OH OH
Ketone bodies:
- Used by? As?
- Used bc?
- Synthesised from? Where?
- Used by starving brain as energy source
- Can cross the blood-brain-barrier
- Synthesised in liver from fatty acids
What are 2 ketone bodies?
Acetoacetate
B-hydroxybutyrate
Formation of ketone bodies
B-oxidation ketogenesis
Fatty acids ———-> acetyl CoA ————> Acetoacetate and B-hydroxybutyrate
R-CO-CoA —–> CH3-CO-CoA —-> CH3-CO-CH2COOH
CH3-CH-CH2COOH
I
OH
How do ketone bodies allow the body to survive longer?
Used by brain, thus brain needs less glucose, thus slows down muscle degeneration (+ less AAs needed for gluconeogenesis)
Anaerobic exercise:
- Intensity?
- Speed of force generation?
- Length of time?
- Uses what energy?
- High intensity
- Rapid force generation
- Short periods
- Uses on-site generation of energy
Aerobic exercise:
- Intensity?
- Length of time?
- Uses which fuels?
- Low intensity
- Prolonged, sustained exercise
- Uses fuels stored in the muscle + circulating in the blood
Phosphocreatine;
- Which type of exercise?
- What type of fuel store?
- What type of compound? Significance?
- Anaerobic exercise
- on-site, fast-fuel store in muscle
- high-energy phosphate compound, can transfer phosphate to ADP to make ATP
- When is glycogen mobilised? Stimulated by?
- Anaerobic glycolysis reaction
- During high-intensity exercise; adrenalin and Ca+
\+Pi ADP-->ATP Glycogen -----> glucose + phosphate --> G6P -------> pyruvate NAD+-->NADH ------------> lactate NADH-->NAD+
How is ATP generated in anaerobic glycolysis?
Substrate-level phosphorylation
Energy production in aerobic exercise:
reaction of oxidation of glucose
glucose –> G6P –> pyruvate –> acetyl CoA –> CAC
Metabolic adaptations of muscle (muscle fibres)
- Type I muscle fibres (red) –> aerobic
- High myoglobin and mitochondria - Type II muscle fibres (white) –> anaerobic
- lack myoglobin, fewer mitochondria
Clinical symptoms of diabetes
Fatigue, weight loss, intense thirst, frequent urination
Biochemical symptoms of diabetes
Hyperglycaemia, glucosuria, ketones
Type 1 diabetes:
- Insulin dependent yes/no?
- Caused by?
- body type of sufferers
- treatment
- Insulin-dependent
- Autoimmune destruction of beta cells
- Usually lean
- Insulin injections
Type 2 diabetes:
- Insulin dependent yes/no?
- Caused by?
- body type of sufferers
- treatment
- No
- Insulin resistance
- usually obese
- diet, exercise, drugs
Range which insulin is regulated b/w?
4-7mmol/L
Actions of insulin
Stops: - gluconeogenesis - glycogenolysis - lipolysis - proteolysis - ketogenesis Stimulates: - glucose uptake (muscle and fat tissue) - glycogen synthesis - TAG synthesis, uptake + storage - protein sythesis
what is phosphofructokinase inhibited by?
ATP, CP, citrate
what is phosphofructokinase activated by?
AMP + Pi
What removes phosphate groups?
phosphatase
What adds phosphate groups?
Kinase
Vitamin associated with NAD
niacin
Vitamin associated with FAD
Riboflavin
Vitamin associated with coenzyme A
pantothenic acid
Vitamin associated with TPP
thiamin
Function of Vitamin K
Blood clotting
Function of Vitamin C
Collagen synthesis
Function of vitamin D
Calcium homeostasis
Function of Vitamin A
Vision
Vitamins used in the CAC?
B2, B3, B5
What is Vitamin B6 used for?
Processing AAs to let them enter the CAC
Main function of selenium
antioxidant
Main function of iron
Haemoglobin oxygen binding
Main function of calcium
blood clotting
Main function of Mg
Kinase reactions
Which coenzyme is a carrier of acyl-groups?
Coenzyme A
