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)