5.1.6 Respiration Flashcards
What is respiration and why does it occur?
-energy stored in glucose is transferred to ATP, which provides immediate energy source for biological processes (by breaking C-H bonds in glucose to release energy used in synthesising ATP during chemiosmosis)
-one glucose molecule= net 32 ATP molecules
Why do plants and animals need to respire?
-animals require energy for muscle contractions, cytokinesis, homeostasis etc
-plants require energy for active transport, photosynthesis, DNA replication, cell division etc
Explain the structure of a mitochondrion
- outer mitochondrial membrane= separate the contents of the mitochondrion from the rest of the cell–} cellular compartment with ideal conditions for aerobic respiration
- inner mitochondrial membrane= contains electron transport chains and ATP synthase, folds of the membrane are cristae(increases SA available for oxidative phosphorylation)
- inter membrane space = proteins are pumped into it via ETC, small area so conc builds up quickly
- matrix= granular area, contains enzymes for Krebs cycle + link, contains mitochondria DNA
- ribosomes= protein synthesis
- mitochondrial DNA(contains 37 genes which are maternally inherited)
What are the 4 stages of aerobic respiration?
-glycolysis= in the cytoplasm of the cell, also anaerobic as it doesn’t require oxygen
-link reaction= in the matrix of mitochondria
-Krebs cycle= in the matrix
-Oxidative phosphorylation= inner mitochondrial membrane
Summary of what happens in glycolysis
-hexose, 6C glucose is split into 2 smaller, 3C pyruvate molecule
-ATP and reduced NAD also produced
Glycolysis: Activation of glucose by phosphorylation
-2 phosphate molecules are released from 2 molecules of ATP–} attach to glucose to form hexose bisphosphate
(prvents glucose from being transported to plasma membrane and leaving cell= HB is more reactive than glucose)
-ATP is reduced to ADP and inorganic phosphate in this step
Glycolysis: Lysis of the phosphorylated hexose
-hexose bisphosphate(6C) is very unstable
-causes it to split into 2 molecules of triose phosphate/TP(3C)
Glycolysis: Phosphorylation of TP
-another phosphate group is added to to each molecule of TP to form two molecules triose bisphosphate
-the phosphate groups are free inorganic phosphate ions from the cytoplasm
Glycolysis: Dehydrogenation and formation of ATP
-two TP molecules are oxidised by the removal of hydrogen atoms to from two pyruvate molecules
-hydrogen atoms are transferred to NAD coenzymes which then become reduced NAD
-two phosphate groups(from TP molecules) are transferred to ADP to form ATP–} substrate level phosphorylation(formation of ATP without ETC)
What are the net and gross product and why are they different?
-the gross product of glycolysis is 4 ATP molecules but the overall net product is 2 ATP molecules
-because two ATP molecules are used to activate glucose at the beginning of glycolysis
What is the link reaction?
-first step in aerobic respiration that links glycolysis(anaerobic) to the Krebs cycle(aerobic)
The link reaction: pyruvate transporting
-pyruvate enters mitochondrial matrix through active transport via specific carrier proteins
-undergoes series of reactions catalysed by multienzyme complex pyruvate dehydrogenase
The link reaction: Decarboxylation
-CO2 is removed from pyruvate(3C)
The link reaction: Dehydrogenation
-hydrogen atoms are removed
-accepted by NAD, which becomes reduced to NADH
The link reaction: combination with coenzyme A
-the resulting 2 carbon acetyl group is combined with coenzyme A to form 2 AcetylCoA
What are the products of the link reaction for 1 glucose molecule?
-2 AcetylCoA molecules–} to the Krebs cycle to deliver acetyl group
-2 CO2–} released as waste product
-2 reduced NAD–} goes to oxidative phosphorylation stage
What is the importance of AcetylCoA?
-CoA is an enzyme that is used as a carrier for acetyl group(from pyruvate to Krebs)
-most respiratory substances can be converted into AcetylCoA:
- carbohydrates
-fats-} fatty acids-} glycerol-} glycerol-3-phosphate
-fatty acids-} 2C fragments
- reactions are reversible
What is the Krebs cycle?
-series of oxidation-reduction reactions that produces reduced coenzymes(NAD + FAD) + ATP
-takes place in the matrix of mitochondria
-cycle happens twice for every glucose molecule(once for every pyruvate molecule)
Krebs cycle: formation of citrate
-Acetyl CoA(2C) enters Krebs cycle + combines with Oxaloacetate(4C) to form Citrate(6C)
-loses coA in the process
Krebs cycle: Formation of 5-C compound
-citrate molecule undergoes decarboxylation + loses a carbon in the form of CO2
-dehydrogenation occurs–} hydrogen is transferred to produce reduced NAD from NAD
-5C compound produced i.e Ketoglutarate
Krebs cycle: Regeneration of oxaloacetate
-5C compound undergoes another decarboxylation to form oxaloacetate
-NAD reduced to NADH(twice to lose 2 hydrogen atoms)
-FAD reduced to FADH(once to lose 2 hydrogen atoms)–} dehydrogenation produces 4 more hydrogen atoms
-ATP is also produced from ADP and inorganic phosphate(substrate level phosphorylation)
What are differences between NAD and FAD?
-NAD takes part in all stages of respiration whereas FAD only in Krebs
-NAD accepts 1 H molecule and FAD accepts 2
-reduced NAD is oxidised at the start of the electron transport chain releasing protons + electrons while reduced FAD is oxidised further along the chain
-reduced NAD results in synthesis of 3 ATP molecules whereas reduced FAD results in 2
Products of one Krebs cycle
(would be double for one glucose molecule)
-2 CO2 molecules(released as waste products)
-1 ATP(used for energy)
-3 reduced NAD(to oxidative phosphorylation)
-1 reduced FAD(to oxidative phosphorylation)
What is oxidative phosphorylation?
-process where the energy carried by electrons, from reduced coenzymes is used to make ATP
-occurs in the inner mitochondrial membrane is highly folded to from cristae(increases SA)
-requires oxygen
Steps of oxidative phosphorylation: protein complexes
-reduced NAD + FAD arrive at mitochondrial membrane(matrix)–} at complex I, reduced NAD is oxidised to NAD and the hydrogen splits into protons and electrons
-the electrons are transferred along the electron transfer chain via series of oxidation-reduction reactions to complex II(2 is reduced and 1 being oxidised)
-as electrons move down the chain, they lose energy–} being transferred to the protein complexes + used to actively transport protons up from matrix to intermembrane space
-at complex II, reduced FAD is oxidised to FAD, which releases 2 H ions
-electrons transferred to complex III and H ions are pumped into intermembrane
-electrons move to complex IV which is reduced(meaning III is oxidised)
Steps of oxidative phosphorylation: forming water
-oxygen acts as the final electron acceptor and combined with protons and electrons to form water
-ee + 2H+ + 1/2 O2 = H2O
Steps of oxidative phosphorylation: chemiosmosis + ATP production
-there is a higher proton conc in the intermembrane space than in the matrix due to protons being pumped there–} forms a proton gradient
-protons move down the gradient, diffusing back into the matrix via ATP synthase
-this movement supplies energy for the synthesis of ATP from ADP and Pi(chemiosmosis)
What is anaerobic respiration?
-respiration that doesn’t require oxygen, resulting in smaller quantities of ATP being produced
-used when O2 cannot be supplied fast enough for respiring cells
-starts with glycolysis like aerobic respiration
What are the 3 different types of respiratory categories?
-Obligate anaerobes= cannot survive in the presence of oxygen, mostly prokaryotes
-Facultative anaerobes= synthesise ATP by aerobic respiration if O2 is present, but can switch in the absence of O2
-obligate aerobes= can only synthesise ATP in the presence of O2
What is fermentation?
-form of anaerobic respiration where complex organic molecules are broken down into simpler organic molecules
-small quantity of ATP produced is through substrate-level phosphorylation
What is lactate fermentation?
-occurs in mammals + some bacteria and produces lactate
-is a survival technique for babies immediately after birth + aquatic organisms in water with fluctuating O2 levels
-lactate is toxic so must be broken down by the liver to CO2 + water for excretion
Lactate fermentation
-pyruvate accepts hydrogen atoms from reduced NAD that was formed in glycolysis
-pyruvate is then converted into lactate and NAD is regenerated*
-catalysed by lactate dehydrogenase
*small quantity of ATP can be produced
What happens to lactate/lactic acid?
-converted back to glucose in the liver via gluconeogenesis
-but oxygen is needed for this process–} oxygen debt
Why can’t lactate fermentation occur indefinitely?
-small quantity of ATP produced would not be enough for vital processes long term
-accumulation of lactic acid causes a fall in pH which leads to proteins denaturing–} respiratory enzymes + muscle filaments will cease to function
Why and where does alcoholic fermentation occur?
-to produce ethanol
-occurs in yeast cells, fungi + some plants
Alcoholic fermentation
-pyruvate is first converted into ethanal via decarboxylation(catalysed by pyruvate decarboxylass)
-reduced NAD from glycolysis transfers hydrogen to ethanal to form ethanol and NAD(catalysed by ethanol dehydrogenase)
-the NAD can be reused in glycolysis
Why is alcoholic fermentation irreversible whilst lactate fermentation is reversible?
-pyruvate is converted into lactate which is catalysed by lactate dehydrogenase—} reversible
-pyruvate is converted into lactate AND CO2–} is lost as waste product which means pyruvate decarboxylase cannot reverse the reaction
