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  • Created by: imanilara
  • Created on: 09-05-16 09:55

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
  • Endocytosis
  • 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 )

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ATP structure

  • 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
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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. 

Coenzyme A:
Made of panthothenic acid, adenosine, cysteine+3phosphates. It carries ethanoate (acetate) from the link reaction or from fatty acids to the krebs cycle. 

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4 stages:

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

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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. 

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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!

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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 

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Oxidative phosphorylation+chemiosmosis

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:
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.

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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.

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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. 

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Respiratory substrates

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
proteins: 17kJ
lipids: 39.4kJ

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