Post on 24-Feb-2016
description
Unit L Energy and Respiration
What is Energy?
In science, the ability to do work Energy = force x distance Measured in Joules 1J = 1N x 1m 1 kJ = 1000J
Energy has many forms
Kinetic contraction of muscle fibres Chemical energy stored in food Heat energy lost to surroundings Sound vibrations of vocal cords Light energy trapped by
photosynthesis Electrical impulses transmitted along a
neurone
Chemical Energy
Energy is transferred from one form to another
Energy is never created or destroyed (the law of conservation of energy)
All chemicals contain energy within their bonds
This energy is transferred during a chemical reaction
Combustion of ethanol
C2H5OH + 3O2 2CO2 +3H2O Products contain less energy than reactants 1400kJ per mole released as heatExergonic reaction – releases energyExothermic reaction – releases heat Many metabolic processes are Endergonic
and need energy to drive them, e.g. protein synthesis
Respiration releases energy for processes which require it.
ATP
Combustion reactions release energy as heat
Too much heat would damage cells Intermediate source of chemical
energy, ATPAdenosine triphosphate Phosphorylated nucleotide Has universal role of immediate
energy source in cells Cannot be transported or stored Must be made continuously
Structure of ATP
ATP
ATP + H2O ADP + PiHydrolysis releases 30.6 kJ per mole
A metabolically active cell may require up to2 million ATP molecules every second
Formation of ATP
ATP Animation Formation of ATP
Uses of ATP
1) Anabolic processes (building macromolecules from components)- formation of polysaccharides- protein synthesis- DNA replication
2) Movement- muscle contraction- ciliary action- spindle movement in cell division
Uses of ATP
3) Active transport (movement of molecules against the concentration gradient)- ion pumps
4) Secretion- formation of vesicles
5) Activation of chemicals(making chemicals more reactive)- phosphorylation of glucose at start of glycolysis
Metabolic Pathways
A series of reactions in a cell Product of one reaction is substrate for
next Each reaction catalysed by a specific
enzyme
A enzyme 1 B enzyme 2 C enzyme 3 D enzyme 4 E
Enzymes often arranged close to one another bound to membranes in cells
Multi-enzyme complex
Advantages of Metabolic Pathways Direct conversion may require a
large amount of energy Intermediates may be useful
products or form the start of other metabolic pathways
Final products may act as inhibitors – feedback or end product inhibition
Allosteric inhibitor
Anabolic or Catabolic
Anabolic reactions - involve build up of small, simple molecules into larger ones- require energy input- protein synthesis and photosynthesis
Catabolic Reactions- break down of large molecules into smaller ones- release energy- hydrolysis of starch
Co-factors and Co-enzymes
Inorganic ions – combine with enzyme or substrate making E-S complex form more easily e.g. salivary amylase and Cl- ions
Prosthetic groups – non protein organic co-factors permanently attached to an enzyme e.g. catalase has organic haem group
Co-enzymes – small non protein organic molecules which binds temporarily with enzymes when it forms E-S complex and acts as a carrier e.g. NAD (nicotinamide adenine dinucleotide)
NAD Nicotinamide adenine dinucelotide
Works with dehydrogenase enzymes which catalyse removal of hydrogen
Accepts H atoms and passes to another carrier
In cell exists as NAD+ Carries hydrogen as NADH and a proton
2H 2H+ + e-
NAD+ + 2H+ +2e- NADH + H+
Structure of NAD
Redox
Oxidation ReductionAddition of oxygen Removal of
oxygenRemoval of hydrogen Addition of
hydrogenRemoval of electrons Addition of
electrons
Anaerobic Respiration
Four stages 1) Glycolysis
6C glucose 2 x 3C pyruvate
2) Links Reaction3C pyruvate 2C acetyl
CoA 3) Kreb’s Cycle
2C acetyl CoA CO2 4) Electron Transport Chain
Most ATP made here
Overview of Aerobic Respiration
Glycolysis
“Sugar splitting” Takes place in cytosol Glucose is phosphorylated (requires
ATP) Phosphorylated glucose split into 2
triose phosphate molecules Triose phosphate loses phosphate
group to ADP making ATP Triose oxidised by losing H atoms to
co-enzyme NAD
Glycolysis
Overall
Pyruvate (pyruvic acid) formedATP producedReduced NAD made (NADH + H+) 2ATP used for phosphorylation 4 ATP made during glycolysis Net gain of 2ATP Reduced NAD passes into electron
transport chain and can generate 6ATP per glucose
Glycolysis
Overall
Link Reaction If oxygen available pyruvate enters matrix
of mitochondria Each pyruvate is decarboxylated and loses
C as CO2 2C fragment = acetyl group Picked up by coenzyme A Oxidised by NAD2C +CoA + NAD+ acetyl CoA + CO2 +
NADH + H+
Acetyl Co A enters Kreb’s cycle
The Link Reaction
Mitochondria
Mitochondria
Structure and Function Rod shaped structure with double membrane Outer membrane - permeable to nutrient
molecules, ions, ADP and ATP due to presence of porins
Inner membrane site of electron transport chain and permeable only to CO2, O2 and H2O. Cristae, folds on inner surface which increase surface area for ATP production.
Matrix – mixture of enzymes for ATP production, mitochondrial ribosomes, tRNA and DNA.
Kreb’s Cycle Tricarboxylic acid or citric acid cycle Involves 2 types of reactionDecarboxylation Catalysed by decarboxylase enzymes Involves removal of C atoms from
intermediates and formation of CO2Dehydrogenation Oxidation of intermediate followed by
removal of H atoms, catalysed by dehydrogenase enzymes
Hydrogen taken up by acceptor molecules NAD and FAD (flavinadenine dinucleotide)
Kreb’s Cycle Cont’d 2C Acetyl CoA combines with a 4C compound
to form a 6C compound 6C compound undergoes a series of reactions
eventually losing 2C to regenerate the 4C compound
The C atoms are lost as CO2 The 6C compound is oxidised by removal of H
atoms H atoms pass to hydrogen acceptor molecules
3 molecules of reduced NAD and 1 molecule of reduced FAD (FADH2)
1 ATP synthesised
Kreb’s Cycle
Electron Transport Chain
C6H12O6 + 6O2 6CO2 + 6H2O
The story so far: Glucose has been used up in glycolysis CO2 was produced in the Link Reaction
and Kreb’s cycle But we have not yet seen the use of O2 or
production of water These happen in the electron transport
chain (ETC)
Electron Transport Chain Electrons from NADH or FADH2 are passed
through a chain of carrier molecules At the end of the chain molecular oxygen is
reduced to water Electron transport is coupled to the formation
of ATP from ADP and Pi The 2 processes occur simultaneously Electron carriers are large protein complexes
on the inner membranes of mitochondria arranged in order of electron affinity
flavoproteins, quinones and cytochromes
Electron Transport Chain
Start of chainNADH + H+ NAD+ + 2H+ + 2e-
Electrons are passed from carrier to carrier down the chain
At the end of the chain molecular oxygen accepts electrons and protons produced from oxidation of NADH at the start1/2O2 + 2H+ + 2e- H2O
This takes places at the final electron carrier cytochrome oxidase
Electron Transport Chain
As electrons pass along the chain they lose energy
This energy is used to pump protons through the inner mitochondrial membrane setting up a concentration gradient.
As protons re-enter ATP synthases use their energy to make ATP from ADP and Pi.
Mitchell’s chemiosmotic theoryOxidative phosphorylation
Summary of Respiration
Overview of Respiration
Source of ATP How Many Molecules?Glycolysis 22 x NADH + H+ (glycolysis) 6 (or 4)2 x ATP in Kreb’s 22 x NADH + H+ (Link) 66 x NADH + H= (Kreb’s) 182 x FADH2 (Kreb’s) 4Total 38 (or 36)
Efficiency
Car engine 20% efficient Complete combustion of o2 releases
2870 kJ 38 moles ATP = 38 x 30.6 = 1162.8
kJ 1162.8/2870 x 100 = 40% efficiency
Which part of respiration?
ETC animation and quiz
ATP producedCO2 formed6C into 3CMitochondriaNAD reduced to NADH + H+
Anaerobic Respiration Used by organisms in O2 deficient
environments or to maintain supplies of ATP when temporarily deprived of O2
e.g bacteria in stagnant water e.g muscles during continuous
exercise Different processes in yeast and
mammals.
Yeast
Single celled fungus found on surface of fruits
C6H12O6 2C2H5OH + 2CO2
Glycolysis takes place as normal
2ATP 2ADP + Pi
Glucose 2 x pyruvate NAD NADH + H
+
Anaerobic Respiration in Yeast Pyruvate is then decarboxylated
forming CO2 and ethanal Ethanal is reduced to ethanol by
NADH + H+
Regeneration of NAD+ enables glycolysis to continue
Only 2 ATP produced as NADH + H+ doesn’t enter mitochondria for oxidative phosphorylation
Muscles During vigorous exercise not enough O2 for
anaerobic respiration Pyruvate is converted to lactateCH3COCOO- + NADH + H+ CH3CHOHCOO- +NAD+
Lactate is 3C compound No decarboxylation CO2 not produced Build up causes muscle fatigue. After exercise oxidised in liver to pyruvate then
respired aerobically to CO2 and H2O
Oxygen Debt
Oxygen needed to fully oxidise the lactate produced during anaerobic repiration
Respiration of other Substrates
Energy from other Substrates Hydrolysis of polymers e.g.
starch/glycogen into glucose Fructose/galactose chemically
modified to enter glycolysis Lipids/proteins also oxidised to yield
energy Substrate Energy (kJ/g)
Carbohydrate 17Lipid 39Protein 23
Respiration of Lipids
When energy demands are great or carbohydrates in short supply triglycerides stored in fatty tissue are respired
Hydrolysed to glycerol and fatty acids
Glycerol (3C) converted to triose sugar dihydroxyacetone phosphate which is converted to glyceraldehdye 3- phosphate an intermediate in glycolysis
Produces 19 ATP per molecule
Respiration of Lipids Cont’d Fatty acids are oxidised and fed into
Kreb’s cycle as Acetyl Co A Energy yield depends on length of
hydrocarbon chains Up to 150 ATP per molecule
Respiration of Proteins
Only respired in cases of severe starvation
Hydrolysed to amino acids Amino acids deaminated Amino group converted to urea and
excretedCarbon backbone fed into
glycolysis or Kreb’s cycle directly or after modification
Respiratory Quotients
RQ = Volume of CO2 producedVolume of O2 used
C6H12O6 + 6O2 6CO2 + 6H2O
RQ = 6/6 = 1 (as one mole of any gas occupies the same volume)
Question
Respiration of stearic acid
C18H36O2 + 26O2 18CO2 + 18H2O + ATP
Calculate the RQ value.
RQ values of different substrates Lipids 0.7 Proteins 0.8/0.9 Carbohydrates 1.0
Organisms rarely respire just one type of substrate
Can be calculated by measuring volume CO2 produced and volume O2 used over period of time using a respirometer
Respirometer
Respirometer set up
Revision Questions
Questions 1 Questions 2