Energy Respiration

Energy and respiration: lesson outline

• Introduction

• Significance of energy production; why do cells need ATP, what do they need it for

• Structure (related to function) of ATP and mitochondria

• Various methods by which ATP can be produced

• Substrates, raw materials, and factors essential for ATP production

• Glycolysis

• Link reaction

• Krebs cycle

• Electron transport chain

• Anaerobic respiration

• Oxygen debt

• Adaptations of rice plant for respiration

Introduction • Respiration is one of the essential characteristics of living things

• It basically involves the production of energy in living cells from substrates such as carbohydrates, proteins and lipids

• Energy produced for cell activities is in the form of chemical energy within a molecule called ATP.

• ATP is the energy currency of the cell; it serves as the intermediary molecule between energy yielding reactions and energy consuming reactions.

The need for energy

• Living organisms require energy for various metabolic activities

• The energy must be provided promptly, and in sufficient levels• Anabolic reactions: like DNA replication and

protein synthesis • Active transport: transport of sodium and

potassium ions by Na+ /K+ pump, etc • Movement: movement of organelles within the

cell, contraction of contractile proteins, muscle contraction, etc

• Maintenance of body temperature:

outline the need for energy in living organisms, as illustrated by anabolic reactions, such as DNA replication and protein synthesis, active transport, movement and the maintenance of body temperature

Active transport

Structure of ATP• ATP is a phosphorylated nucleotide

made up of a ribose sugar a nitrogenous base called adenine

and 3 phosphate groups

• It is produced by adding Pi to ADP; a process called phosphorylation

and energy is used up

• Other features that make ATP suitable as the universal energy

currency• It is readily formed within the cell from ADP and inorganic phosphate

• It is soluble and readily transported within the cell

• It diffuses rapidly within the cell

• It is readily hydrolysed to release energy (30.6kJ)

describe the features of ATP that make it suitable as the universal energy currency

describe the universal role of ATP as the energy currency in all living organisms;

ATP production

• ATP is formed from ADP and inorganic phosphate

• ATP can be formed in two major ways; • Substrate level phosphorylation; this occurs during the processes of

glycolysis and Krebs cycle. Two substrate molecules react together, thereaction is catalysed by an enzyme, energy is released and that energy iscoupled into the production of ATP

• Electron transport chain; this is a series of reactions occurring on themembranes of the mitochondria or chloroplast. Energy for the mitochondrialphosophorylation comes from the chemical energy locked within FAD andNAD, energy for the choroplast phosophorylatioin comes from sunlight thus itis also called photophosphorylation

•explain that ATP is synthesised in substrate-linked reactions in glycolysis and in the Krebs cycle

•explain that the synthesis of ATP is associated with the electron transport chain on the membranes of mitochondria and chloroplasts (see 12.2g)

Substrate Level Phosphorylation

ExamplesSynthesis of pyruvate

during glycolysis

Synthesis of intermediates during

Kreb’s cycle

Respiratory Substrates• A respiratory substrate is an organic substance that can

be used for respiration • Carbohydrates: glucose, fructose, starch, glycogen, sucrose • Fats; when carbohydrates are exhausted, fats are used as

respiratory substrate • Proteins; used under starvation

• Lipids have the highest energy value. This is becausethey contains fatty acids which possess more hydrogenatoms per unit mass than carbohydrates. Thus they cancontribute more hydrogen atoms to the process ofoxidative phosphorylation and yield greater amount ofenergy

explain the relative energy values of carbohydrate, lipid and protein as respiratory substrates and explain why lipids are particularly energy-rich

Respiratory QuotientRespiratory quotient is the volume of carbon dioxide produced divided by the volume of oxygen used during respirationRQ = number of moles of carbon dioxide produced/number of moles of oxygen used up

define the term respiratory quotient (RQ) and determine RQs from equations for respiration

The Mitochondrion describe the relationship between structure and function of the mitochondrion using diagrams and electron micrographs

Aerobic Respiration

• Aerobic respiration occurs in four stages: • Glycolysis: the first stage which occurs in the cytoplasm

• Link reaction; the second stage which occurs in the matrix of the mitochondria

• Krebs cycle: the third stage which occurs also in the matrix

• Oxidative phosphorylation: which occurs in the inner membrane of the mitochondria

list the four stages in aerobic respiration (glycolysis, link reaction, Krebs cycle and oxidative phosphorylation) and state where each occurs in eukaryotic cells

36ATP

Glycolysis• Glycolysis is the first stage in cellular

respiration and it occurs in thecytoplasm

• It involves 3 major steps• Phosphorylation of glucose to get glucose

activated and• Hexose phosphate is unstable and it is split

to produce two unstable compounds whichare then converted to triose phosphate

• Oxidation of triose phosphate to produce 4 molecules of ATP (substrate level phosphorylation), pyruvate and 2 molecules of reduced NAD

• Overall, one molecule of glucoseundergoing glycolysis results in theformation of 2 molecules of ATP, 2molecules of reduced NAD

Outline glycolysis as the phosphorylation of glucose and the subsequent splitting of Fructose 1,6-bisphosphate(6C) into two triose phosphate molecules, which are then

further oxidised to pyruvate with a small yield of ATP and reduced NAD

The Link reaction • Pyruvate enters matrix of mitochondrion for further reaction

• It is first decarboxylatedand one molecule of Carbondioxide is formed

• It is then dehydrogenated and one molecule of reduced NAD is formed

• It is then combined with coenzyme A to form acetyl coenzymeA

Explain that, when oxygen is available, pyruvate is converted into acetyl(2C) coenzyme A in the link reaction

Krebs Cycle

•Outline the Krebs cycle, explain that oxaloacetate (a 4C compound) acts as an acceptor of the 2C fragment from acetyl coenzyme A to form citrate (6C), which is reconverted into oxaloacetate in a series of small steps

•Explain that reactions in the Krebs cycle involve decarboxylation and dehydrogenation and the reduction of NAD and FAD

• Krebs cycle occurs within the matrix of the mitochondrion

• It begins when oxaloacetate(4C) accepts acetyl group(2C) from acetyl coenzyme Ato form citrate(6C).• Coenzyme A is reformed and free to form

another molecule of acetyl coA

• The citrate is then converted back to oxaloacetate in a series of small steps involving decarboxylation and dehydrogenation.

• The carbondioxide formed duringdecarboxylation is removed and givenoff as gas

Krebs Cycle• Step1: acetyl groups from acetyl

coA combines with a 4 carbon oxaloacetate to form a 6 carbon compound called citric acid.

• Step 2: the 6C citric acid is then decarboxylated to form a 5C α-ketoglutarate. Dehydrogenation also occurs and reduced NAD is formed.

• Step 3: The 5C α-ketoglutarate is decarboxylated to form a 4c oxaloacetate.

• Dehydrogenation also occurs during this stage and reduced NAD and reduced FAD are formed.

• A substrate level phosphorylation also occurs and ATP is formed

Kreb’s Cycle

• The hydrogen released duringdehydrogenation reactions areused to form reduce NAD andreduced FAD

• One molecule of ATP is alsoformed during a substrate-levelphosophorylation reactionoccurring during Krebs cycle

• Overall, one molecule ofglucose results in the formationof 6 molecules of reduced NADduring Krebs cycle and 2molecules of reduced FAD inaddition to 2 molecules of ATPand 4 molecules of CO2

NAD and FAD • NAD (and FAD) is a coenzyme

that functions as carrier

molecules to receive hydrogen

atoms during glycolysis and

Krebs cycle and transport the

hydrogen atoms into the inner

membrane of the mitochondria

for the final phase of

respiration.

• Coenzyme A functions as a

molecule that carries acetyl

group produced during the link

reaction into the Krebs cycle

phase of respiration. Outline the roles of the coenzymes NAD, FAD and coenzyme A in respiration

Oxidative phosphorylation

• Oxidative phosphorylation occurs on and within the inner membrane of the mitochondrion.

• During this series of reactions, the hydrogen atoms attached to reduced NAD and FAD are released and passed

to hydrogen carriers within the membrane.

• Each hydrogen atom is then split into hydrogen ion and electron

• The electrons pass along a series of electron carriers, each of which is at a lower energy level than its predecessor,

while the hydrogen ions remain in solution.

• The final electron acceptor is oxygen. When oxygen accepts an electron, a hydrogen ion from the solution combines

with the oxygen to form water.

• The transfer of electrons along the series of electron carriers makes energy available for the synthesis of ATP

from ADP and Pi by creating a proton gradient across the inner mitochondrial membrane: this is chemiosmosis

outline the process of oxidative phosphorylation, including the role of oxygen as the final electron acceptor (no details of the carriers are required)

Three steps of oxidative phosphorylation• during oxidative phosphorylation:

• energetic electrons release energy as they pass through the electron transport system

• the energy released during the transfer of electrons is used transfer protons across the inner mitochondrial membrane

• This active transport of proteins into the intermembranespace results in the build up of a gradient across the inner membrane. This inner membrane is impermeable to protons (hydrogen ions)

• The protons then return to the mitochondrial matrix by facilitated diffusion through ATP synthase and as they are transported, energy is released and used for ATP synthesis

• Overall, at the end of oxidative phosphorylation, each molecule of glucose gives a yield of 34ATP (30from NADH, and 4 from FADH)

Explain that during oxidative phosphorylation…

Electron transport chain

Two types of respiration; aerobic and anaerobic

• Aerobic Respiration occurs in the presence of oxygen • C6H12O6 + 6O2 → 6CO2 + 6H2O + energy

• Complete oxidation of an glucose to CO2 and H2O using free O2

• Production of CO2, [NADH + H+] and [FADH + H+], 38ATP

• Anaerobic Respiration occurs in the absence of oxygen

distinguish between

respiration in aerobic and

anaerobic conditions in mammalian tissue and in

yeast cells, contrasting the relative

energy released by

each (a detailed

account of the total yield

of ATP from the aerobic

respiration of glucose is not

required)

Yeast cell Mammalian tissue

Aerobic conditions

Occurs in the presence of oxygen and pyruvate is converted to acetyl CoAIt produces more energy, 36 molecules of ATP

Anaerobic Pyruvate is converted to ethanol Pyruvate is converted to lactic acid

It’s a 2-step reaction that involves the production of ethanol first

It’s a one step reaction

Decarboxylation occurs Decarboxylation does not occur

Occurs in the absence of oxygen, producing 2 ATP, allows regeneration of NAD

Anaerobic respiration in yeast

• During anaerobic respiration, a small amount of ATP is produced (2ATP).

• Absence of oxygen results in unavailability of a suitable molecule to act as the final

electron acceptor of electrons released from; therefore no Krebs cycle or ETC

• Reduced NAD [NADH + H+] reduces (gives off H+ ions to) pyruvate to produce

ethanol, and then the ethanal is then converted to ethanol

• NAD is regenerated and carbondioxide is produced

• NAD can be re-used and it allows glycolysis to continue

explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue, including the concept of

oxygen debt

Anaerobic respiration in mammals

explain the production of a small yield of ATP from respiration in anaerobic conditions in yeast and in mammalian muscle tissue, including the concept of

oxygen debt

• In mammals, pyruvate is converted to lactic acid and 2 ATP are also produced

• The lactic acid accumulates and it eventually causes fatigue when it accumulates above a

certain level

• The excess lactic acid can only be removed by a series of metabolic reactions that require

the availability of oxygen

• This excess lactic acid is taken up from the blood plasma by liver, and converted to

glucose and then to glycogen

• This accumulation of lactic acid causes the mammal to breathe heavily so that the body can obtain the necessary oxygen and oxidise

lactic acid to carbon dioxide and water

How is oxygen debt paid

• The oxygen debt is paid back at the end of the exercise by breathing more deeply than you would normally breath when at rest

• The oxygen inhaled is used to • convert lactate to glucose,• Convert haemoglobin to oxyhaemoglobin• Oxygenate the myoglobin

• The lactate is transport from the muscles to the liver by the blood, and it is then converted back to glucose and broken down to produce energy

Anaerobic respiration and Oxygen Debt

Adaptation of rice for respiration

explain how rice is adapted to grow with its roots submerged in water in terms of tolerance to ethanol from respiration in

anaerobic conditions and the presence of aerenchyma

• Key varieties of rice may be described as ‘swamp plants’.

• As crop plant, it is often grown partly submerged in paddy fields. Fields are flooded,

then ploughed and the young rice plants are planted in the resulting mud.

• Oxygen levels in the mud fall very rapidly as the oxygen is used up by respiration of

bacteria in the mud – and levels remain very low in the flooded paddy fields since oxygen

can only diffuse very slowly through the water.

• Rice plants have a number of adaptationswhich allow them to grow successfully inthese conditions of low oxygenavailability:• The stems and leaves possess very large air

spaces, running the length of the stem –these allow oxygen to get through to theroots from the air.

• The roots are very shallow – this allows themsome access to the higher levels of oxygen inthe surface water.

• When oxygen concentrations fall to very lowlevels, the roots are able to respireanaerobically. This results in the productionof alcohol, which would normally be toxic.

• However, rice root cells produce high level ofenzyme alcohol dehydrogenase which makesthem tolerant to alcohol.

Respirometer Experiments

• Respirometer is a device usedto measure the rate ofrespiration in a living organism

- carry out investigations, using simple respirometers, to determine the RQ of germinating seeds or small invertebrates (e.g. blowfly larvae)

- carry out investigations, using simple respirometers, to measure the effect of temperature on the respiration rate of germinating seeds or small invertebrates

Factors affecting rate of respiration in yeast

carry out investigations to determine the effect of factors such as temperature and substrate concentration on the rate of respiration of yeast using a redox indicator

(e.g. DCPIP or methylene blue)