Unit 1 Communication, Homeostasis and Energy. What is aerobic respiration? What is anaerobic...
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Transcript of Unit 1 Communication, Homeostasis and Energy. What is aerobic respiration? What is anaerobic...
Unit 1Communication, Homeostasis and Energy
What is aerobic respiration?What is anaerobic respiration?Which organelle carries out most of
the stages of respiration in eukaryotic cells?
What are the products of aerobic respiration?
What is the universal energy currency molecule?
Outline why plants, animals and microorganisms need to respire, with reference to active transport and metabolic reactions.
In order to maintain life, organisms need a source of energy.
In most organisms this is provided by the oxidation of organic molecules.
Autotrophic nutrition Synthesise organic materials from
inorganic sources e.g. photosynthesisHeterotrophic nutrition
Obtained in organic form
Energy is the ability to do workEnergy exists in two states
Kinetic energy▪ Energy of motion
Potential energy▪ Stored energy
Energy facts Cannot be created or destroyed Can be converted from one form to
another Takes a variety of forms Measured in joules or kilojoules
Metabolism All reactions that take place within the
organism Anabolism▪ Build up of larger, more complex molecules
from smaller, simpler ones Catabolism▪ Breakdown of complex molecules into
smaller, simpler ones▪ Releases energy
“Work” Synthesis of complex substances Active transport e.g. sodium-potassium
pump Movement Bioluminescence Maintenance of body temperature Production of electricity Maintenance, repair and division Activation of chemicals
Energy is defined as the ability to do ________________.
The energy of motion is known as ___________ energy, whereas _________ energy is stored energy.
Living organisms need energy for many reasons __________ reactions in which simple
molecules are built up into complex ones The movement of material by __________
against a concentration gradient.
1. Fireflies can produce light in a process called bioluminescence. Outline the energy transformations that occur in fireflies as they use energy from their food to produce luminescence.
2. Comment on the statement below. Respiration produces energy to form
ATP.
Describe, with the aid of diagrams, the structure of ATP.
State that ATP provides the immediate source of energy for biological processes.
ATP is a phosphorylated nucleotide. Adenosine▪ Adenine▪ Ribose sugar
Three phosphate groups
Covalent bonds between phosphate groups are unstable and easily broken releasing energy
▪ ATP ADP = 30.6kJmol-1 (energy)▪ ADP AMP = 30.6kJmol-
1(energy)▪ AMP Adenosine = 14.2kJmol-1
(energy)
As ATP is hydrolysed energy is immediately available to the cell in small, manageable amounts.
ATP is described as the universal energy currency.
ATP is continually being hydrolysed and resynthesised.
What type of base is adenine?ATP is a nucleic acid / nucleotide
derivative. Is it derived from DNA or RNA
nucleotides? Give reasons for your answer
Explain why ATP is known as the universal energy currency.
explain the importance of coenzymes in respiration, with reference to NAD and coenzyme A;
state that glycolysis takes place in the cytoplasm
outline the process of glycolysis;
The oxidation of food to obtain free energy (ATP)
Respiration of glucose can be summarised in four stages Glycolysis The link reaction Krebs cycle Oxidative Phosphorylation
Oxidation Loss of electrons Loss of hydrogen atoms
Reduction Gain of electrons Gain hydrogen atoms
If one substrate becomes oxidised another becomes reduced.
OIL RIG
During respiration, hydrogen atoms are removed from substrate molecules in oxidation reactions.
This is catalyzed by dehydrogenase enzymes
Co enzymes are required to activate the oxidation reactions in respiration Hydrogen atoms becomes attached to co
enzymes e.g. NAD
Nicotinamide adenine dinucleotide (NAD Is reduced when it has accepted two
hydrogen atoms with their electrons Operates in glycolysis, link reaction, the
Krebs cycle and the anaerobic pathways.
Function To carry ethanoate (acetate) groups
made in the link reaction, onto the Krebs cycle
To carry acetate groups made from fatty acids or amino acids onto the Krebs cycle
Ancient biochemical pathwayGlucose (6C) is broken down into two
molecules of pyruvate (3C), with a net gain of 2 ATP molecules.
Occurs in the cytoplasm
Pathway can be outlined in four stages Phosphorylation Splitting of hexose 1,6-bisphosphate Oxidation of triose phosphate Conversion of triose phosphate to
pyruvate
Net gain of two ATP moleculesTwo molecules of reduced NADTwo molecules of pyruvate
Enzymes that cause the shape of a molecule to change (without changing in proportions of atoms in that molecule) are called isomerases. At which stage of glycolysis are isomerase
enzymes involved? How does the fact the nearly all living
things use the glycolysis pathway support the theory of evolution?
recall the structure of a liver mitochondrion identify inner and outer membranes and
the inter membranal space state that, during aerobic respiration in
animals, pyruvate is actively transported into mitochondria;
explain, with the aid of diagrams and electron micrographs, how the structure of mitochondria enables them to carry out their functions;
All mitochondria have an inner and outer phospholipid membrane (envelope)
Inner membrane is folded into cristae Intermembrane spaceMatrix
Contains looped DNA Mitochondrial ribosomes enzymes
This is where the link reaction and the Krebs cycle take place
It contains Enzymes Molecules of coenzyme NAD Oxaloacetate Mitochondrial DNA Mitochondrial ribosomes
It contains Protein channels or carriers to allow
pyruvate to pass through Other proteins act as enzymes
Has a different membrane structure and is impermeable to small ions (e.g. hydrogen ions)
Folded into cristae to give a large surface area
Contains electron carriers and ATP synthase enzymes
It has been suggested that mitochondria are derived from prokaryotes. What features of their structure support this suggestion?
Suggest how the structure of a mitochondria from a skin cell would differ from that of a mitochondrion from heart muscle tissue.
state that the link reaction takes place in the mitochondrial matrix;
outline the link reaction, with reference to decarboxylation of pyruvate to acetate and the reduction of NAD;
explain that acetate is combined with coenzyme A to be carried to the next stage;
Pyruvate is actively transported into the matrix of the mitochondria.
Pyruvate is dehydrogenated and decarboxylated to acetate in a series of enzyme controlled reactions.
Enzymes Pyruvate dehydrogenase Pyruvate decarboxylase
NAD accepts the hydrogen ionsCoenzyme A accepts acetate to form
Acetyl CoA, to carry onto the Krebs cycle.
Carbon dioxide is released
state that the Krebs cycle takes place in the mitochondrial matrix;
outline the Krebs cycle, with reference to the formation of citrate from acetate and oxaloacetate and the reconversion of citrate to oxaloacetate
explain that during the Krebs cycle, decarboxylation and dehydrogenation occur, NAD and FAD are reduced and substrate level phosphorylation occurs
Takes place in the mitochondrial matrix
Main stages Decarboxylation ▪ Removal of Co2
Dehydrogenation ▪ reduction of NAD
Substrate-level phosphorylation▪ Production of ATP
For each original glucose molecule there are two turns of the Krebs cycle.
Products 6 reduced NAD 2 reduced FAD 4 carbon dioxide 2 ATP Although oxygen is not used up in these
stages, they can not take place if it is absent – they are aerobic stages
Product per molecule of glucose
Glycolysis
Link reaction
Krebs cycle
Reduced NAD
Reduced FAD
CO2
ATP
Product per molecule of glucose
Glycolysis
Link reaction
Krebs cycle
Reduced NAD 2 2 6
Reduced FAD 0 0 2
CO2 0 2 4
ATP 2 0 2
Moving into the last stage of aerobic respiration 10 reduced NAD 2 reduced FAD
Explain why mature erythrocytes cannot carry out the link reaction or Krebs cycle
The inner mitochondrial membranes are impermeable to reduced NAD. For this reason a shunt mechanism moves hydrogen ions from reduced NAD made during glycolysis, to the matrix side of the inner mitochondrial membrane. The hydrogens are carried in by another chemical than then becomes reoxidised, reducing NAD that is already in the mitochondrial matrix.
Explain why such a shunt mechanism is not required for NAD reduced during the link reaction and Krebs cycle.
Aerobic prokaryotes can carry out the link reaction, Krebs cycle and oxidative phosphorylation.
Suggest where in the prokaryotic cell these reactions take place.
outline the process of oxidative phosphorylation, with reference to the roles of electron carriers, oxygen and the mitochondrial cristae;
state that oxygen is the final electron acceptor in aerobic respiration;
Formation of ATP by adding a phosphate group to ADP
Takes place in the presence of oxygen
Oxygen is the final electron acceptorTakes place across the inner
mitochondrial membrane
Reduced NAD and reduced FAD are reoxidised when they donate the hydrogen, split into H+ and e-
Electrons are accepted by electron carriers
Protons go into solution in the matrix
Electrons passed along chain of carriers, energy released is used to pump protons across to intermembrane space
building up a proton/ pH / electrochemical gradient
Hydrogens diffuse through ion channels associated with ATPsynthase (chemiosmosis)
As protons flow through ATP synthase Drive the rotation of part of enzyme This joins ADP and Pi to form ATP
Electrons and hydrogen ions combine with oxygen to form water.
outline the process of chemiosmosis, with reference to the electron transport chain, proton gradients and ATPsynthase
evaluate the experimental evidence for the theory of chemiosmosis
The complete oxidation of one molecule of glucose produces a net yield of 32 ATP’s.
Energy required to make ATP comes from: Respiration – energy released by rearranging chemical
bonds The transfer of electrons by electron carriers in
mitochondria H+ ions create a concentration gradient through a
protein channel; this protein channel acts as the enzyme ATP synthase.
3 H+ ions provide the energy to make one ATP molecule, provided that ADP and Pi are available.
Build of hydrogen ions on one side of membrane is a source of potential energy
Movement of ions across the membrane down an electrochemical gradient – provides energy to form ATP from ADP and Pi.
Inner mitochondrial membrane = energy transducing membrane
Kinetic energy of the flow of ions = proton motive force
On the hand out – write out how each piece of evidence supports the chemiosmosis theory put forward by Mitchell in 1961.
pH gradient across the membranes in involved in ATP production The pH on one side of the membrane is
higher than the other This suggests hydrogen ions are being
actively moved across the membraneMembranes make ATP even if there
is no electron transport taking place, as long as a pH gradient is produced.
Explain why was it important to keep the thylakoids in the dark?
Explain why the pH inside and outside the thylakoid membranes becomes equal when they are left in pH4 buffer for some time.
Does a pH4 buffer contain a greater or smaller concentration of H+ than a pH8 buffer?
In which direction was there a pH gradient when the thylakoids were place in the pH8 buffer?
Explain why and how the thylakoids were able to make ATP when they were placed in the pH8 buffer solution.
Chemicals that prevent hydrogen ions being transported across the membrane also stop ATP being produced. Dinitrophenol is a chemical that acts as
a hydrogen carrier across membranes. If Dinitrophenol is added – no hydrogen
ion gradient is built up.
The hydrogen ion gradient is responsible for making ATP not the electron transport.
explain why the theoretical maximum yield of ATP per molecule of glucose is rarely, if ever, achieved in aerobic respiration;
Summary aerobic respiration Glucose is oxidised to pyruvate in
glycolysis Pyruvate is oxidised in Krebs Cycle Hydrogen ions removed are passed
along the electron transport chain▪ For every two hydrogen donated to the ETC
by reduced NAD – 3 ATP molecules are made▪ For every two hydrogen donated to the ETC
by reduced FAD – 2 ATP molecules are made
Some energy has been put in to these processes. For every two hydrogen donated to the
ETC by reduced NAD – 2.5 ATP molecules are made
For every two hydrogen donated to the ETC by reduced FAD – 1.5 ATP molecules are made
processATP used
ATP produced
Glycolysis
Phosphorylation of glucose
Direct phosphorylation of ADP
From reduced NAD
Link reaction
From reduced NAD
Krebs cycle
Direct phosphorylation of ADP
From reduced NAD
From reduced FAD
Totals
Net yield
processATP used
ATP produce
d
Glycolysis
Phosphorylation of glucose 2
Direct phosphorylation of ADP
4
From reduced NAD 5
Link reaction
From reduced NAD 5
Krebs cycle
Direct phosphorylation of ADP
2
From reduced NAD 15
From reduced FAD 3
Totals 2 34
Net yield 32
Transport ADP into mitochondria from the cytoplasm
Transport ATP from mitochondria into the cytoplasm
Protons could “leak” across membrane reducing the number to generate the proton motive force.
Active transport of pyruvate into mitochondria
Read the information supplied at the top of the practical sheet.
Set up the three test tubes as shown below.▪ 10ml glucose▪ 10ml yeast▪ 5 ml dye
Shake tubes vigorously for 20 seconds, and place in a water bath set at 37oC.
Leave for a few minutes
Write up the experiment using the back of the sheet.
Tube A Colour change from blue via pink to
colourless. Hydrogen has been rapidly released and
has reduced the dye. For this to happen – dehydrogenase
enzymes present in yeast cells must have acted on the glucose, the respiratory substrate, and oxidised it.
Tube B Change from blue – pink – colourless Reaction is slower since no glucose was added. Dehydrogenase could only act on any small
amount of respiratory substrate already present in the yeast cells.
Tube C Boiling has killed the yeast and denatured the
dehydrogenase enzymes.
explain why anaerobic respiration produces a much lower yield of ATP than aerobic respiration;
compare and contrast anaerobic respiration in mammals and in yeast;
Occurs when free oxygen is not available
oxygen is no longer the final hydrogen acceptor
Reduced NAD cannot be recycled to NAD
The stages of respiration inside the mitochondrion can not take place
Two other pathways recycle the reduced NAD formed during glycolysis Alcoholic fermentation▪ Conversion of pyruvate to ethanol
Lactate fermentation▪ Conversion of pyruvate to lactate
Both pathways are inefficient and provide a net gain of two ATP molecules per glucose molecule
Pyruvate is decarboxylated to form ethanal
Ethanal accepts hydrogen from reduced NAD to form ethanol
The alcoholic fermentation pathway is irreversible
Pyruvate accepts the hydrogen and is converted into lactate
The lactate pathway is reversible by the Cori cycle in the mammalian liver
Lactate causes a fall in pH which may stop the muscles from contracting.
define the term respiratory substrate;
explain the difference in relative energy values of carbohydrate, lipid and protein respiratory substrates
Molecules from which energy can be liberated to produce ATP in a living cell.
Below are 3 respiratory substrates and their energy value Glucose 16kJg-1 Lipid 39kJg-1 Protein 17kJg-1
Fatty acids enter the Krebs cycle after being broken down into two Acetyl CoA molecules
Amino acids are deaminated Converted either into pyruvate and enter
the link reaction or acetate and enter the Krebs cycle
Glycogen or starch
Glucose
Pyruvate
Acetylcoenzyme A
Krebs cycle
Protein
Amino Acids
Lipid
fatty Acids
The more hydrogens there are in the structure of a molecule, the greater the energy value
Revise the structure of glucose, amino acids and fatty acids from the AS course.
The respiratory quotient (RQ) is the ratio of the volumes of oxygen absorbed and carbon dioxide given off in respiration.
RQ = Volume of carbon dioxide given off
Volume of oxygen taken in
Calculate the RQ for the aerobic respiration of Glucose.
Calculate the RQ for the fatty acid oleic acid, when respired aerobically. C18H34O2+ 25.5O2 18 CO2 + 17 H2O
C6H12O6 2C2H5OH + 2CO2
A high RQ value suggests that anaerobic respiration is taking place.
No RQ can be calculated for the lactate pathway as no carbon dioxide is given off.
The respiratory quotients of different respiratory substrates are well documented from previous investigations. Carbohydrate 1.0 Protein 0.9 Fat 0.7
It is possible to deduce which substrate is being used by the metabolism at a specific time. NB if a mixture of substrates is being used then the
figure will be different from those above.
Sodium hydroxide absorbs all CO2 from the air in the apparatus from the beginning.
As the germinating seeds use oxygen and the pressure reduces in tube A so the manometer level nearest to the seeds rises.
Any CO2 excreted is absorbed by the sodium hydroxide solution.
The syringe is used to return the manometer fluid levels to normal.
The volume of oxygen used is calculated by measuring the volume of gas needed from the syringe to return the levels to the original values
If water replaces the sodium hydroxide then amount of carbon dioxide given off can be measured
The respiratory quotient can be measured.RQ = x + y or x - z
x x where
x is the oxygen consumption y is the increase in volume of air (if more CO2 is
produced than oxygen taken in) z is the decrease in the volume of air (if less
CO2 is produced than oxygen taken in)