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