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HLTH2210 > Metabolism / Bioenergetics > Flashcards

Metabolism / Bioenergetics Flashcards

1
Q

What are pathways and how are they regulated

A
  • Pathways: Series of related enzymatically catalysed reactions form a pathway
  • Metabolic Pathway: Produces energy or valuable materials
  • Signal Transduction Pathway: Transmits information throughout the body
  • Regulation: Controlled in order to regulate levels of metabolites, feedback inhibition
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2
Q

What is cellular metabolism and respiration

A
  • Sum of all chemical reactions that occur in the body, anabolic (synthesis of molecules) and catabolic (breakdown of molecules)
  • Regulated by enzymatic activity
  • Respiration relates to O2 utilisation and CO2 production by the cellular tissues
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3
Q

What is the role of high energy transporters such as ATP, NADH and FADH2

A
  • Electrons from reduced fuels (carbohydrates, lipids, AA) are transferred to reduced cofactors NADH or FADH2
  • Transport H and E, to mitochondria for ATP generation (aerobic) or convert pyruvic acid to lactic acid (anaerobic)
  • NADH: Produced in glycolysis / TCA to facilitate ATP synthesis (2.5), in ETC, converted back to NAD
  • FADH2: Produced in glycolysis / TCA, 1.5 ATP
  • ETC utilises reduced co-enzymes to produce ATP via oxidative phosphorylation
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4
Q

Why is ATP the universal energy currency of the cell and how is it required

A
  • Frequently the donor of phosphate in biosynthesis of phosphate esters
  • ATP hydrolysis has very high negative ΔG = - 30.5kJ/mol (very favourable)
  • Cellular ATP concentration is usually far above equilibrium concentration, ATP = potent source of = energy
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5
Q

What is anaerobic vs aerobic metabolism

A
  • Anaerobic: Formation of ATP without the use of O2 (ATP-PC and glycolysis), cytoplasm, shorter energy production
  • Aerobic: Production of ATP using O2 as the final electron acceptor (TCA, ETC), oxidative, mitochondria, longer energy production (60sec)
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6
Q

What is the pentose phosphate pathway

A
  • Alternative use to glucose, cells generate pentose phosphates and NADPH
  • Pentose phosphates can be generated into glucose-6-phosphate and inserted into TCA cycle (no ATP required)
  • Or ribose-5-phosphate (precursor for DNA / RNA / coenzyme synthesis)
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7
Q

What is glycolysis and the steps involved

A
  • Anaerobic, ubiquitous, substrate level phosphorylation
  • Sarcoplasm, breakdown of glucose to pyruvate
    Preparatory Phase:
  • Energy investment, phosphorylation of glucose (6C)
  • Glucose-6-phosphate (via hexokinase, use ATP)
  • Fructose-6-phosphate
  • Fructose-1,6-biphosphate (via PFK, use ATP)
  • Glyceraldehyde-3-phosphate (3C)
  • Used: 2 ATP molecules, 1 glucose and 2 NAD+
    Payoff Phase:
  • Energy production, glyceraldehyde-3-phosphate (3C) converted to pyruvate (3C) via pyruvate kinase
  • Glucose + 2 NAD+ + 2 ADP + 2 Pi — 2 Pyruvate + 2 NADH + 2 H+ + 2 ATP
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8
Q

What are the fates of pyruvate

A
  • Pyruvate formed in glycolysis can serve as a precursor in anabolic reactions or become
  • Acetyl CoA: 2 acetyl CoA, aerobic, CAC to produce 4CO2 + 4H2O), animal plant and many microbial
  • Ethanol: 2 ethanol + CO2, anaerobic, fermentation
  • Lactate: 2 lactate, anaerobic, fermentation, via lactate dehydrogenase in vigorously contracting muscle, regenerates NAD for glycolysis to continue, favourable
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9
Q

What is the function of gluconeogenesis

A
  • Allows generation of glucose from AA, lactate and glycerol when glycogen stores are depleted
  • Reverse pathway of glycolysis
  • Pyruvate to oxaloacetate (pyruvate carboylase)
  • Oxaloacetate to PEP (PEP carboxykinase)
  • Fructose 1-6 biphosphate to fructose 6 phosphate (fructose biphosphatase-1)
  • Glucose 6 phosphate to glucose (glucose 6 phosphatase)
  • 2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2 H+ + 4 H2O — Glucose + 4 ADP + 2 GDP + 6 Pi + 2 NAD+
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10
Q

Compare and contrast regulation of glycolysis and gluconeogenesis and key regulatory steps

A
  • Opposing pathways both thermodynamically favourable
  • End product of one is starting product of the other
  • Reversible reactions used in both, prevents futile cycle
  • No ATP generated during gluconeogenesis
  • Different key regulatory enzymes
  • Glycolysis (muscle and brain) and gluconeogenesis (liver)
  • Regulatory enzymes correspond to points that have same substrate and product but different enzyme
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11
Q

What is the role of fats as fuel

A
  • 1/3 of energy comes from triacylglycerols
  • Carry more energy than polysaccharides per C, they are more reduced, complex and carry less water (non-polar)
  • Long term energy needs, good storage, slow delivery
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12
Q

Explain the process of B oxidation of saturated fats

A
  • Mitochondria, small saturated (<12 C) FA diffuse freely across mitochondrial membranes, larger FA transported via carnitine transporter / fatty acyl-adenylate (exergonic)
  • Series of reactions, oxidative conversion of FA chain 2 C units at a time into acetyl CoA
  • Reduce FAD and NAD+
  • Acetyl CoA enters CAC and further oxidises into CO2, makes more GTP, NADH, and FADH2
  • Or acetyl CoA is converted to ketone bodies (oxaloacetate depletion), taken up by heart, muscles, brain
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13
Q

Describe process of fatty acid synthesis

A
  • Occurs when NADPH levels are high (adipocytes / hepatocytes), requires malonyl-CoA and acetyl-CoA
  • Synthesis of fatty acids is a multistep process
  • Step 1: Acetyl-CoA is carboxylated to form malonyl-CoA, catalysed by acetyl CoA carboxylase (ACC)
  • Step 2: FAS1 catalyses sequential addition of 2C units to malonyl CoA
  • Final Product is Palmitate, uses a lot of ATP and NADPH, palmitate can be extended further and also desaturated
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14
Q

How is fatty acid synthesis regulated

A
  • Citrate Anabolism: Excess energy / acetyl CoA is transported into cytosol so FA synthesis can use it up
  • RLE: Acetyl CoA to Malonyl-CoA via acetyl-CoA carboxylase (ACC), palmitoyl CoA inhibits, citrate activates
  • Gene Expression: FA bind to transcription factors
  • Malonyl-CoA: Inhibits FA import into mitochondria, ensure FA synthesis and b oxidation don’t occur simultaneously
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15
Q

What are the fates of nitrogen

A
  • Ammonia: Plants conserve almost all N, aquatic vertebrates release NH3 to environment (passive diffusion from epithelial cells or active transport via gills)
  • Urea: Terrestrial vertebrates / sharks excrete nitrogen in form of urea (less toxic than NH3, high solubility)
  • Uric Acid: Birds and reptiles excrete N as uric acid (insoluble, excretion as paste)
  • Both: Humans excrete both urea (from AA) and uric acid (from purines)
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16
Q

What are the processes of amino acid metabolism

A

NH3 (Ammonia)
- Transfer of one amine to a-ketoglutarate (transamination)
- Transfer of second amine to l-glutamine
- L-glutamine is a temporary storage of N (2 fates)
- 1: Glucose alanine cycle
- 2: Converted to carbamoyl phosphate to enter urea cycle and secreted by sweat / urine
Carbon Skeleton
- Ketogenic AA: Converted to ketone bodies via acetyl CoA
- Glucogenic AA: Converted to glucose and enter glycolysis (pyruvate, acetyl-CoA, α-ketoglutarate, succinyl-CoA, oxaloacetate)

17
Q

What are the principles of amino acid synthesis

A
  • Synthesised from a-ketoglutarate, 3-phosphoglycerate, oxaloacetate, pyruvate, phosphoenolpyruvate, erythrose 4-phosphate, and ribose-5-phosphate
18
Q

How are amino acids used as precursors for biological macro molecules

A
  • Porphyrin rings (e.g., heme)
  • Phosphocreatine
  • Glutathione
  • Neurotransmitters and signalling molecules
  • Cell-wall constituents
  • Metabolic precursor of nucleic acids
19
Q

What is the role of acetyl CoA in metabolism

A
  • Allows carbohydrates, fats and proteins to enter aerobic metabolism to form ketone bodies or enter TCA / ETC or become FA
  • Glycogen (glycogenolysis) glucose (glycolysis) pyruvate (oxidation) acetyl CoA
  • Triglyceride (lipolysis) FFA (b oxidation) acetyl CoA
  • Protein (proteolysis) AA (deamination / oxidation) acetyl CoA
20
Q

Describe the TCA cycle and high energy carriers

A
  • Priming and oxidation of pyruvate (3 C) to create acetate (2 C), binds with coenzyme A to produce acetyl CoA, CO2 and 2 NADH
  • 1: Acetyl CoA (2 C) combines with oxaloacetic acid (4 C) to produce citrate / citric acid (6 C), favourable, irreversible
  • 2: Isomerisation of citrate to isocitrate, unfavourable, reversible
  • 3-4: Oxidative decarboxylations to produce 2 NADH and CO2, dehydrogenase converts isocitrate to a-ketoglutarate (5C) to succinyl CoA (4C), favourable, irreversible
  • 5: Phosphorylation of succinyl CoA (4C) to succinate (4C) and GTP, favourable, reversible
  • 6: Dehydrogenation to FADH2, reversible, succinate (4C) to fumarate (4C)
  • 7: Hydration of double bond, favourable, reversible, fumarate to l-malate via fumarase
  • 8: Dehydrogenation to NADH, unfavourable, reversible, l-malate (4C) to oxaloacetate (4C)
  • Transfers high energy e- to carriers, harvested e- directed to ETC to drive ATP synthesis
21
Q

Explain the importance of compartmentalisation of metabolic processes and regulation of opposing anabolic / catabolic pathways

A
  • Metabolic processes must be coordinated, opposing pathways are not operating simultaneously, cell must respond to constant changes (external and internal conditions)
  • In multi-cellular organisms cells must co-operate, simplified by division of labour between tissues
  • Different pathways operate in different tissues
  • RBC: Utilises PPP, no mitochondria no TCA
  • Brain: Glucose main fuel
  • Muscle: Glucose, FA, ketone, anaerobic and anaerobic
  • Adipose: FA, affected by insulin / glucagon
  • Liver (G): Glycolysis, gluconeogenesis
  • Liver (FA): Degrade FA, synthesise ketones
  • Liver (AA): Completely oxidised or converted to glucose to ketones
22
Q

What is the ETC and what does it produce

A
  • Inner mitochondrial membrane, series of specialised acceptor / donor molecules (cytochromes)
  • Phase 1 (create proton gradient) phase 2 (chemiosmosis / synthesis of ATP)
  • 1: Reduced coenzymes (NADH and FADH2) deliver e to respiratory complexes I and II
  • 2: E are transferred from one complex to another in membrane, each complex is reduced and then oxidised, releasing energy that is used to pump H+ into inter membrane space
  • 3: Creation of electrochemical gradient between matrix and inter membrane space
  • 4: At respiratory enzymes complex IV, E pairs combine with two protons (H+) and a half molecule of O2 = water
  • 5: Complex V (ATP synthase) harnesses energy of proton gradient
23
Q

What is the physiological relevance of the cori cycle

A
  • Anaerobic glycolysis in muscle, pyruvate → lactate (transported in blood) → liver → pyruvate → glucose / glycogen, reuse lactate and recovery of glucose
  • Re-oxidise NADH and permit continued ATP production from glycolysis
  • Muscles produce ATP via glycolysis but during anaerobic contraction produce lactate
  • Lactate exported into the blood
  • Liver takes up lactate from the blood and then converts it to pyruvate to glucose via gluconeogenesis
  • Glucose then recycled into blood
24
Q

How is metabolism regulated differently in various tissues

A
  • Regulation of metabolism is a coordinated event across the whole organism
  • Availability of substrates, allosteric activation & inhibition of enzymes, covalent modification of enzymes, induction & repression of enzyme synthesis
  • When Glycolysis is switched on GNG is switched off – but may occur in different organs eg Cori Cycle
25
Q

Explain the regulation of movement of fuels during starvation

A
  • Liver makes increased acetyl CoA when fat is mobilised and glucose is decreased
  • Increased acetyl CoA normally causes TAG synthesis but if glucose is low, TAG is also low
  • Excess acetyl CoA to ketones, leads acidosis in starvation
  • The liver maintains glucose output using AA for gluconeogenesis that come from muscle
26
Q

What is the flow chart of catabolism and anabolism

A
  • Energy containing nutrients (CHO, fats, proteins)
  • Use ADP, NAD, FAD to catabolise
  • Produce energy depleted products, ATP, NADH, FADH2, NADPH
  • Precursor molecules for anabolism (AA, sugar, FA)
  • Use ATP, NADH, FADH2, NADPH to undergo anabolism
  • Produce Cell macromolecules (proteins, lipids, nucleic acids), ADP, NAD and FAD
27
Q

Provide an overview of metabolism of lipids proteins and ketones

A
  • Lipids: Triglycerides undergo lipolysis to FFA which undergo β oxidation to acetyl CoA (catabolic), acetyl CoA can also undergo fatty acid synthesis (anabolic)
  • Protein: Undergo proteolysis to AA which undergo deamination / oxidation to acetyl CoA (catabolic), acetyl CoA can also undergo amino acid synthesis (anabolic)
  • Ketones: Acetyl CoA undergoes catabolism to form ketone bodies
28
Q

How are unsaturated fatty acids metabolised

A
  • Contain cis double bonds, not a substrate for enoyl-CoA hydratase and cannot undergo β oxidation, slightly lower yield of FADH2, different enzymes for odd numbered PUFAs
  • Isomerase: Converts cis double bonds starting at carbon 3 to trans double bonds (monounsaturated and polyunsaturated)
29
Q

How is TCA cycle regulated

A
  • Steps 1, 3, 4: Highly thermodynamically favourable and irreversible steps, PDC (pyruvate to acetyl CoA), citrate synthase, IDH and KDH
  • Activated by substrate availability and inhibited by product accumulation
30
Q

What is chemiosmosis and proton motive force

A
  • ATP: ADP + Pi → ATP is highly thermodynamically unfavourable
  • Chemiosmotic Theory: Transfer of electrons down an electron transport system through a series of oxidation-reduction reactions releases energy
  • Chemiosmosis: Movement of ions across semipermeable membrane, down electrochemical gradient, energy needed to phosphorylate ADP provided by flow of protons down electrochemical gradient
  • PMF: The inner mitochondrial membrane separates two compartments of different [H+], resulting in differences in chemical concentration and charge distribution across the membrane
31
Q

What is the glucose alanine cycle

A
  • Similar to cori cycle
  • Pyruvate binds with glutamate to produce a-ketoglutarate and alanine
  • Transfer to liver
  • Binds with a-ketoglutarate to form pyruvate and glutamate
  • Glutamate enters urea cycle
  • Pyruvate undergoes gluconeogenesis to glucose, regenerated for glycolysis

HLTH2210 (9 decks)

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