Topic 9: cellular respiration Flashcards
Define catabolic pathways
- Energy production = ATP
- Breaking down organic compounds
- E.g. respiration
Define anabolic pathways
- Energy consumption
- Synthesis of organic compounds
- E.g. photosynthesis
What is the energy flow in an ecosystem?
Sunlight > photosynthesis in chloroplast + respiration in mitochondria > heat energy
Explain the catabolic pathways
- Cells must regenerate ATP = in order to keep working
- Produce energy by oxidizing organic molecules = exergonic = releases energy
- Reactants > energy rich than products
PROCESSES
1) Cellular respiration
2) Anaerobic respiration
Describe cellular respiration
- Most efficient catabolic pathway
- Complete degradation of carbohydrates in presence of O2
- Chemical energy in glucose bonds transferred to phosphate bonds in ATP
- Yields highest ATP
- Energy from ATP hydrolysis used to perform endergonic reactions
What is the equation for cellular respiration?
C6H12O6 + Ο2 —-> CO2+ H2O+ ΑΤP
What are the 2 energy production/conversion organelles?
1) Chloroplasts = photosynthesis
2) Mitochondria = 2/3 stages of respiration
3 stages of respiration
1) Glycolysis = anaerobic = cytosol
2) Krebs cycle = aerobic =mitochondria matrix
3) Oxidative phosphorylation =aerobic = inner membrane
Describe the structure of a mitochondria
- Diameter = 1-10 μm
- Outer membrane
- Inner membrane = cristae = ETC complexes + ATP synthase
- Intermembrane space
- Matrix = mitochondrial DNA + free ribosomes
Define redox reactions
- Transfer e- from 1 reactant to another via oxidation/reduction
- Oxidation = lose e-
- Reduction = gain e-
Describe redox in respiration
- Glucose oxidized
- O2 reduced
Describe the ATP production at each stage
- Glycolysis + Krebs = 10% of total = substrate level phosphorylation
- Oxidative phosphorylation = 90% ATP = ATP synthase
Describe how e- energy is transferred and transported
- e- released from oxidation of organic compounds
- Co-transferred with H+
- Transferred to coenzymes FAD + NAD+ = reduced NADH + FADH2
- They transport to ETC
- Transferred to O2 = H2O
What do NAD + FAD stand for?
- NAD = nicotinamide adenine dinucleotide
- FAD - flavin adenine dinucleotide
Define dehydrogenase
- Enzymes that remove e- from organic compounds = transfer them to NAD + FAD
Describe glycolysis
- Breaks down glucose
- Location = cytosol
- Anaerobic
- Products = 2ATP + 2NADH + 2 Pyruvate
PHASES
1) Energy investment
2) Energy payoff
Explain energy investment
- 2 ATP spent
- Substrates phosphorylated = energy-rich = unstable
- Splits glucose
Explain energy payoff
- 4 ADP + 4 Pi = 4 ATP
- 2 NAD + 4e- + 4 H+ = 2NADH
- 2 Pyruvates
Give the net products of glycolysis
- 2 ATP
- 2 NADH
- 2 Pyruvate
Describe the Krebs cycle
- Completes the oxidation of organic molecules
- Location = mitochondrial matrix
- Products = CO2 + energy
Describe the conversion of pyruvate
- Pyruvate is converted into acetyl-CoA before starting Krebs cycle
- Undergoes pyruvate dehydrogenase reaction
- 3 carbon > 2 carbon acetyl-CoA = 1 carbon released = CO2
- NAD+ reduced = NADH
Describe Krebs cycle
- Acetyl-CoA combines with oxaloacetate = citric acid
- NADH + FADH2 produced = transferred to ETC
- Each acetyl-CoA =
> 2 CO2
> 3 NADH
> 1 FADH2
> 1 ATP
How many ATP are produced by 1 NADH + FADH2 in Krebs cycle?
- 1 NADH = 3 ATP
- 1 FADH2 = 2 ATP
Give the net products for Krebs cycle
- 12 molecules ATP
2 Ways that e- enter the ETC
1) NADH oxidation = via complex I = NADH dehydrogenase
2) FADH2 oxidation = via complex II = succinate dehydrogenase
Why is the ETC a stepwise energy transfer?
- If e- transfer not stepwise = large release of e- = uncontrolled reaction
- Instead of controlled release of little energy for synthesis
Explain oxidative phosphorylation in the ETC
- e- from NADH/FADH oxidation = transferred to ETC
- e- initially transferred to coenzyme ubiquinone
- e- passed from higher energy carrier > lower energy carriers = down electronegativity
- e- transferred to O2 = most electronegative = H2O
Give the order of complexes in the ETC
1) Complex I / Complex II
2) Coenzyme Q = ubiquinone
3) Complex III = cytochrome oxidoreductase
4) Cytochrome c
5) Complex IV = cytochrome oxidase
Explain chemiosmosis
- ETC causes H+ pumped from matrix > intermembrane space
- H+ concentration gradient created
- pH matrix = 8 / pH IMS = 7
- Higher concentration in IMS
- H+ flow into matrix via ATP synthase down conc grad
- ATP synthase uses energy from H+ = ATP
Define proton motive force
- Proton gradient created by flow of e-
- Drives chemiosmosis
Describe ATP synthase
- Enzyme = synthesizes ATP from ADP + Pi
- Located = inner mitochondrial membrane
- Found in mitochondria + chloroplast + bacteria
- Has a proton pump = uses proton gradient = ATP synthesis
2 PARTS:
1) F0 = transmembrane part = subunits a/b/c
2) F1= matrix part = subunits α/β/γ/δ/ε - Proton though it = changes binding affinity in ATP/ADP
- H+ flowing through = 120° rotation
What is the localization/orientation of ATP synthase?
- Inner membrane
- From intermembrane space to matrix
What is the area of proton accumulation/ATP synthesis?
- Intermembrane space
- Matrix
Describe the number of protons pumped into IMS + ATP production + net gain ATP in NADH/FADH2
- NADH = 10H+ / 3 / 2.5
- FADH2 = 6H+ / 2 / 1.5
Why is the total number of ATP produced not in net total?
1) For each ATP 0.25 = spent for transport to cytosol for cellular work
2) Production depends on type of e- shuttle used to transport from cytosolic NADH > mitochondria = e- passed to mitochondrial NAD+/FAD
3) Energy used for AT of pyruvate from cytosol > mitochondria
What is the total ATP from 1 glucose?
- 38 molecules
What is the difference in ATP production by cytosolic NADH?
- If e- passed to mitocondrial NAD+ = liver cells = 2NADH x 3ATP = 6 ATP
- If e- passed to mitochondrial FAD = 2FADH2 x 2ATP = 4 ATP
Describe anaerobic respiration
- Produces ATP in absence of O2
- 2 molecules of ATP
2 STAGES:
1) Glycolysis
2) Fermentation
Define fermentation
- Lactic acid/alcohol production
- NAD regeneration = can be reused by glycolysis = ATP continue generating
2 Types of fermentation
1) Alcohol: ethanol + CO2 production in yeast
2) Lactic acid: produced in animal cells
Describe alcohol fermentation
- Pyruvate = ethanol + CO2
- Reaction = C6H12O6 → 2 CH3CH2OH + 2 CO2
- Used in = wine/beer + bread making
Explain the uses of alcohol fermentation
- Saccharomyces cerevisiae = yeast = used to produce ethanol in alcoholic drinks + baker’s yeast
- CO2 production = bread rises
Describe lactic acid fermentation
- Pyruvate reduced directly by NADH = lactate
- Reaction = C6H12O6 → 2 CH3CHOHCOOH
- Used in = bacteria convert lactose into lactic acid in yogurt
Why does lactic acid fermentation take place?
- When limited O2 = muscle fatigue under exercise
- Lots of O2 required during exercise = need energy faster than rate of O2 supply via blood
- Therefore fermentation occurs
- However lactate accumulation = muscle cramps + stiffness
Compare aerobic/anaerobic respiration
- Both oxidize glucose > pyruvate in glycolysis
- Different final products
- Aerobic = 38 ATP / Anaerobic = 2 ATP
Describe other catabolic pathway connections
- Proteins = enter respiration after losing amine group
- Glycerol = enter glycolysis
- Fatty acids = enter Krebs as acetyl-CoA
Describe anabolic pathways
- AKA biosynthesis
- Use ATP
- Body used small molecules = synthesize other substances
- Sources = direct from food + glycolysis/Krebs
Explain regulation via feedback mechanism
- Metabolism = regulated according to supply + demand + energy status
- Respiration controlled by allosteric enzymes + feedback inhibition by ATP
Describe control of cellular respiration
- Phosphofructokinase = control point
- Allosteric enzyme
- Stimulated by AMP
- Inhibited by ATP + citrate
Describe the clinical correlations
- Diseases caused by insufficient syntheis of ATP = due to ATP synthase mutation
1) Severe neuromuscular disorders = Leigh + MELAS
2) Cardiomyopathies
3) Leber’s optic neuropathy = due to Complex I mutations
