Why organisms need to respire, structure of ATP
Process where energy stored in complex organic mols used to make ATP.
WHY? we need energy to drive biological process+metabolic reactions:
- Active transport- moving ions + molecules across a membrane against a concentration gradient (eg sodium-potassium pumps resting potential)
- Secretion -exocytosis
- Anabolic reactions- building bigger mols from smaller ones- aminos-->proteins
- DNA replication
Energy transfer- photoautotrophs-->chemical pot. energy in organic mols-->heterotrophs-->respiration (chemical pot. in ATP +thermal energy )
- Phosphorylated nucelotide
- consists of adenosine (adenine+ribose sugar), and 3 phosphate groups
- hydrolysed- ADP+P(i)
- releases 30. kj per mol-
- joined by condensation reaction
- constantly hydrolysed and resynthesised
- always coupled with a synthesis reaction eg DNA replication
Importance of coenzymes
Oxidation- loss of electrons
Reduction- addition of electrons
Why are coenzymes needed:
needed to help carry out oxidation and reduction reactions in Glycolysis, link reaction+krebs cycle.
They donate their hydrogen atoms that split into protons and electrons to the intermembrane space in oxidative phosphorylation in order to form ATP.
NAD-nicotinamide adenine dinucleotide- organic, non-protein molecule helps dehydrogenase enzymes carry out oxidation reactions. Made of two nucelotides- one with nicotinamide made in the body+ribose sugar--2phosphates--ribose sugar+adenine.
Made of panthothenic acid, adenosine, cysteine+3phosphates. It carries ethanoate (acetate) from the link reaction or from fatty acids to the krebs cycle.
Phosphorylation of glucose- ATP hydrolysed+ phosphate group added to glucose.
This forms fructose 6-phosphate
Another ATP hydrolysed and phosphate group added to fructose to form fructose 1.6 bisphosphate=hexose 1,6 bisphosphate
Splitting of hexose 1,6 bisphosphate
-each molecule of hexose bisphosphate split into 2 molecules of triose phosphate (3C)
Oxidation of TP: two H+ removed from TP - 2 NAD reduced. +2 ATP made - SUBSTRATE LEVEL PHOSPHORYLATION
Conversion of TP--> pyruvate
-4 enzyme catalysed reactions convert each TP mol into pyruvate- in this 2 more ATP formed
Products= 2xpyruvate, 2xATP, 2xNAD
Structure+function of mitochondria
Matrix- contains mitochondrial DNA, mitochondrial ribosomes +enzymes
Mitochondria in metabolically active cells will have more densely packed cristae so as to have more electron carrier chains + more ATP synthase enzymes. Mitochondria can be moved around the body via the cytoskeleton.
Structure and function of mitochondria
How does structure help them carry out their function:
Matrix-where the link reaction and krebs cycle takes place- contains dehydrogenase enzymes and coenzymes for reactions, contains oxaloacetate which accepts acetate from the link reaction- contains mitochondrial DNA and mitochondrial ribosomes.
Outer membrane- has protein channels that allow the transportation of pyruvate into the organelle
Inner membrane: contains electron transport chains used in oxidative phosphorylation - each electron carrier is an enzyme associated w a cofactor haem group that contains iron, meaning it can be reduced or oxidised- OXIDOREDUCTASE ENZYMES. some have coenzyme that pumps protons from matrix into intermembrane space-inner membrane impermeable to small ions+so buildup.
Also contains ATP synthase enzymes- they are large and allow protons to pass thru them.
Flow down proton gradient thru the enzymes into matrix=CHEMIOSMOSIS. The proton motive force drives the rotation of the enzyme=ADP---ATP!
Link reaction+Krebs Cycle
Link reaction: MATRIX
Decarboxylation of pyruvate-pyruvate decarboxylase
Dehydrogenase of pyruvate- pyruvate dehydrogenase (2 reduced NAD)
Coenzyme A accepts acetate to form acteyl CoA
Products - 2NAD+, 2CO2
Krebs Cycle: MATRIX
- acetate offloaded by Coenzyme A to join w oxaloactate a 4C compound to make citrate 6C.
- citrate decarboxylated and dehydrogenated- 2NAD+=5C
- 5C decarb+dehyd= 2NAD+=4C
- 4C changed into another 4C and a molecule of ATP formed-substrate level
- 4C changed again- dehydrogenated- reduced FAD
- further dehydrogenated to reduce 2NAD+ -oxaloacetate regenerated
- products: 6NAD+, 2FAD+, 1ATP, 4CO2
2 turns of the cycle per glucose - other substrates other than O2 can be used+fatty acids broken down into acetates which can enter Krebs
Occurs in the inner membrane- cristae- large SA available for electron carriers+ ATP synthase enzymes.
Electron transport chain- electrons donated from reduced NAD and reduced FAD pass down the chain - energy is released - pumps protons into the intermembrane space.
Chemiosmosis- build up of protons as innermembrane impermeable to small ions - creates ph gradient and electrochemical gradient- potential energy builds up, and protons flow back thru channels associated w ATP synthase enzyme
Oxidative phosphorylation- formation of ATP by adding phosphate to ADP+P(i)- happens by ATP synthase rotating to form ATP, and by electrons passed down electron transport chain, w oxygen being final electron acceptor. Then O2 reduced to water.
Amount of ATP produced- 26 molecules, as 10 NAD make 26 ATP. +4 made earlier=30
But rarely achieved: pyruvate actively transported into matrix, some protons leak out of intermembrane space, hydrogen from reduced NAD needs ATP to be shuttled into mitochondria.
Evaluating evidence for chemiosmosis in mitochondr
Scientists destroyed outer membrane and found that the remaining mitoblasts did not form ATp- scientists could conclude that the intermembrane space was involved in ATP synthesis.
If the stalked particles removed- no ATP formed
ATP not formed in the presence of oligomycin- anitbiotic that inhibits the flow of protons thru ion channel
In intact mitochondria-
lower pH in intermembrane space
lower PD in matrix than in intermembrane space.
Anaerobic respiration in mammals and yeast
No oxygen- no oxidative phosphorylation as O2 is final electron acceptor-this means no recycling of NAD and FAD and so link+Krebs also stop.
only leaves glycolysis to form ATP and the 2 reduced NAD must be reoxidised so that it can keep going- 2 pathways to reoxidise NAD:
-animals use lactate fermentation
-yeast use ethanol fermentation
-pyruvate accepts hydrogen from reduced NAD, catalysed by lactate dehydrogenase
-forms lactate - lactate transported away from muscle to lvier- reduction in pH is what reduces enzyme activity in muscles +fatigue
pyruvate molecule loses CO2 and becomes ethanal- ethanol dehydrogenase turns it into ethanol and during this NAD is reduced.
Carbohydrate: efficiency is 30%- rest used to maintain body temp
Protein: aa's deaminated- and the rest of the moelcule can be converted into fat-energy source. When organism is fasting, aa's can be respired+ converted into pyruvate/acetate- NAD can accept a higher number of H+ from aa's than glucose= higher energy yield
Lipids: fatty acids are long hydrocarbon chains- lots of H+- lots of ATP formed
Carbs: 15.8 kJ