Respiration Flashcards
Why organisms need energy
-Active transport
-exocytosis/endocytosis
-synthesis of molecules eg. proteins
-DNA replication
-cell division
-movement
-activation of chemicals
Role of ATP
-standard intermediary between energy releasing reactions eg. respiration and energy consuming reactions eg. active transport
-energy produced in respiration is used to synthesise ATP from ADP + Pi which can release the energy when needed
-universal energy currency as occurs in all living cells and is a source of energy that can be used by cells in small amounts
Structure of ATP
-adenine bonded to ribose sugar
-ribose bonded to 3 phosphates by phosphodiester bond
-3 phosphates bonded to each other by phosphoanhydride bonds
4 stages of respiration
-glycolysis
-link reaction
-Krebs cycle
-oxidative phosphorylation
Glycolysis
- 2ATP hydrolysed to 2ADP + 2Pi. 2Pi added to glucose to make hexose biphosphate
-this splits into triose phosphate
-Pi in cytoplasm is added to triose phosphate to produce triose biphosphate - 2ADP removes the Pi from the triose biphosphate
-dehydrogenase enzymes, aided by coenzyme NAD, remove hydrogens from triose biphosphate
-the NAD accepts hydrogens and is reduced
-this changes the structure of the triose sugar, forming 2pyruvate for every one glucose molecule
Products from glycolysis
-Net gain of 2 ATP
- 2 reduced NAD
-2 pyruvate for link reaction and Kreb cycle
How pyruvate is transported
-transported across mitochondrial envelope via pyruvate/H symport, which is a transporter protein that transports 2 molecules in the same direction
Where the link reaction and Krebs cycle takes place
mitochondrial matrix
Link reaction
- carboxyl group (COOH) is removed from pyruvate producing CO2
- this decarboxylation together with dehydrogenation produces acetyl group
- the dehydrogenation of pyruvate reduces NAD
- acetyl group combines with CoA producing acetyl CoA
2pyruvate + 2NAD + 2CoA -> 2CO2 + 2 reduced NAD + 2 acetyl CoA
-No ATP is produced
Krebs cycle
-acetyl group (2C) from acetyl CoA combines with oxaloacetate (4C) to form citrate (6C)
-citrate decarboxylated and dehydrogenated, producing 5C compound, CO2 and reduced NAD
-5C compound is decarboxylated and dehydrogenated producing 5C compound, CO2 and reduced NAD
-4C compound temporarily combines with CoA and then released. This is substrate level phosphorylation and produces ATP
-4C compound dehydrogenated producing different 4C compound and reduced FAD
-atoms in 4C compound are rearranged by enzyme isomerase, followed by dehydrogenation, to regenerate oxaloacetate
Other substances that can be respired aerobically
-fatty acids, broken down to acetate which enters Krebs cycle via acetyl CoA
-glycerol converted to triosphosphate
-amino acids deaminated and enters the cycle directly or changed to pyruvate or acetyl CoA
Oxidative phosphorylation
-red. NAD and FAD reoxidised when they deliver H to electron transport chain
-H split into proton and electron
-protons go into solution of mitochondrial matrix
-electrons pass through electron carriers (Fe) which are reduced and reoxidised producing energy
-energy is used to pump protons from matrix into intermembrane space
-proton gradient generates chemiosmotic potential/ proton motive force
-protons can’t diffuse through bilayer easily as outer membrane has low permeability and inner membrane impermeable
-this means protons diffuse through ATP synthase, causing a conformational shape and the formation of ATP
-oxygen final electron acceptor as combines with electrons from transport chain and protons producing water
4H+ + 4e- + o2 -> 2H2O
Oxidative phosphorylation definition
formation of ATP using energy released from electron transport chain in the presence of oxygen
How many molecules of ATP produced, why theoretical yield hardly achieved
-oxidative phosphorylation produces 28ATP
-glycolysis produces 2ATP
-total 32 ATP
-some ATP used to actively transport pyruvate from cytoplasm to matrix
-some ATP used to transport red. NAD into mitochondria
-some protons leak out through outer mitochondrial membrane
Chemiosmosis definition
flow of protons, down conc. gradient, across a membrane, through ATP synthase
Mitochondria structure
-inner and outer membrane making envelope
-inner membrane folded into cristae for large SA
-in inner membrane there’s electron transport system and ATP synthase
-between 2 membranes is the intermembrane space
-inner membrane impermeable to protons
-outer membrane partially permeable
Matrix contains
-enzymes to catalyse stages of reactions
-NAD + FAD
-oxaloacetate
-mitochondrial DNA
-mitochondrial ribosomes
Respiration in absence of oxygen
-oxygen can’t be final electron acceptor, so protons can’t combine with electrons and oxygen to produce water
-the conc. of H+ in matrix increases, reducing proton gradient
-oxidative phosphorylation stops
-red. NAD and FAD can’t donate H atom and be reoxidised
-therefore stopping krebs cycle and link reaction
Anaerobic respiration in plants and fungi
Yeast fermentation pathway
-pyruvate is decarboxylated by pyruvate decarboxylase to produce ethanal
-ethanal accepts H atoms from red. NAD forming ethanol catalysed by ethanol dehydrogenase
-in the process red. NAD is reoxidised and therefore can accept more H from glycolysis
Anaerobic respiration in animals
Lactate fermentation pathway
-pyruvate accepts H from red. NAD
-this is catalysed by lactate dehydrogenase producing lactate
-reoxidised NAD can accept more H from glycolysis
Fate of lactate
-convert to pyruvate to enter link reaction
-recycled to glucose and glycogen
ATP produced from anaerobic respiration
-ethanol and lactate fermentation don’t produce ATP, they only allow glycolysis to continue
-as only glycolysis is occurring, only a net gain of 2ATP
Respiratory substrate-
-organic substance that can be oxidised by respiration, releasing energy to synthesise ATP
Glucose as respiratory substrate
-chief respiratory substrate
-RBC and brain cells only respire using glucose
-glucose is produced by hydrolysing disaccharides or monosaccharides eg. fructose can be changed into glucose via isomerase
