Respiration

What is respiration?The process whereby energy stored in complex

organic molecules is used to make ATP. It occurs in living cells.

ATP is a phosphorylated nucleotide and it is the universal energy currency.

Energy is the ability to do work.All living things need energy to drive their biological

processes, all reactions that take place within an organism are known collectively as METABOLISM.

Anabolic reactions (build up small to large molecules)Catabolic reactions (break down large to small)

Metabolic processes?The ones which require energy are:Active Transport – moving ions across a

membrane against a concentration gradient. (Much of an organisms energy is used for this)

Secretion – large molecules that need to be exported by exocytosis.

Endocytosis – bulk movement of large molecules into cells.

MovementReplication of DNA.

Where does the energy come from?Plants, protoctists and some bacteria =

PHOTOAUTOTROPHS.They use sunlight energy in photosynthesis to

make large, organic molecules that contain chemical potential energy. The plants are eaten by consumers, and the energy can be released in respiration.

The energy released is used to phosphorylate ADP, making ATP which contains lots of energy.

The role of ATPPhosphorylated nucleotide.High-energy intermediate compound found in

both prokaryotic and eukaryotic cells.Each molecule = adenosine + 3 phosphate

groups.It can be hydrolysed to ADP + Pi = 30.6Kj

energy per mol.So energy can be released in small, manageable

amounts = cells will not be damaged and energy will not be wasted.

ATP = UNIVERSAL ENERGY CURRENCY.

Stages of respirationGlycolysis – happens in the cytoplasm of all

cells, it can take place with or without oxygen. It breaks down glucose (6C sugar) into 2 x Pyruvate (3C sugar).

The link reaction – happens in the matrix of mitochondria, pyruvate is dehydrogenated, decarboxylated and converted to ACETATE.

Krebs Cycle – happens in the matrix of mitochondria, acetate is decarboxylated and dehydrogenated.

Oxidative phosphorylation – takes place on cristae of mitochondria. ADP is phosphorylated to ATP.

CoenzymesDuring the first 3 stages of respiration,

substrate molecules are OXIDISED (H atoms removed).

These reactions are catalysed by DEHYDROGENASE enzymes, but the enzymes are not very good at catalysing oxidation or reduction reactions.

So COENZYMES are needed to help them (e.g NAD)

They carry the H atoms to the inner membranes of mitochondria (for oxidative phosphorylation later).

NADOrganic molecule.Helps dehydrogenase carry out oxidation

reactions.Made of two linked nucleotidesWhen it accepts 2 H atoms, it is reduced,

when it loses them, it is oxidised.Operates in the first 3 stages of respiration.

Coenzyme AIts function is to carry ETHANOATE, made

from pyruvate during the link reaction, onto the Krebs cycle.

Simple really!

GLYCOLYSIS – Stage 1Phosphorylation1 ATP molecule is HYDROLYSED and the Pi group

released is attached to glucose at carbon 6, so it is now FRUCTOSE 6-phosphate.

Another ATP is hydrolysed and the Pi is attached to fructose 6-phosphate at carbon 1, so it is now called fructose 1,6-BISPHOSPHATE.

The energy released activates the hexose sugars and prevents it from being transported out of the cell. It is now known as HEXOSE 1,6-bisphosphate.

Note that 2 ATP molecules have been used in this stage.

Glycolysis – Stage 2Splitting of hexose 1,6-bisphosphateEach molecules of hexose 1,6-bisphosphate is

split into 2 x TRIOSE PHOSPHATE.It is a 3 carbon sugar with a phosphate group

attached.

Glycolysis – Stage 3Oxidation of triose phosphateAnaerobic process – each triose phosphate

molecule is oxidised.This involves dehydrogenase enzymes, aided

by NAD.NAD = hydrogen acceptor, so becomes rNAD.At this stage, 2 molecules of NAD are

reduced per molecule of glucose.2 x ATP molecules are also formed =

SUBSTRATE LEVEL PHOSPHORYLATION.

Glycolysis – Stage 4Conversion of triose phosphate to pyruvate4 enzyme-catalysed reactions convert each

triose phosphate molecule to a molecule of pyruvate (3C).

Another 2 molecules of ATP are produced.

Products of glycolysis?2 x ATP2 x rNAD2 x pyruvate

MitochondriaThe MatrixSite of link reaction and Krebs cycle.Contains catalytic enzymes, NAD,

oxaloacetate.The outer membraneContains proteins (forms channels or

carriers)The Inner MembraneFolded into many cristae (large SA)Many electron carriers and ATP synthase

enzymes embedded in it.

The Link ReactionConverts pyruvate to acetate. NAD is

reduced.2pyruvate+2NAD+2CoA2CO₂+2rNAD+2ace

tylCoANAD becomes reduced, CoA accepts acetate

to be acetyl CoA, CoA carries acetate to Krebs cycle.

No ATP producedHowever each rNAD will take a pair of H

atoms to inner mitochondrial matrix to make ATP during oxidative phosphorylation.

The Krebs CycleAlso takes place in mitochondrial matrix.1. Acetate of offloaded from CoA and joins oxaloacetate to

form citrate.2. Citrate is decarboxylated and dehydrogenated to form a

5C compound. 1 x rNAD is reduced.3. The 5C compound is decarboxylated and

dehydrogenated to form a 4C compound + 1 x rNAD.4. The 4C compound is changed into another 4C

compound = x ATP produced = SUBSTRATE LEVEL PHOSPHORYLATION

5. “ “ = x rFAD6. The 3rd 4C compound is dehydrogenated and

regenerates oxaloacetate + 1 x rNAD produced

KC Continued…1 turn of the cycle = 1 x acetate so…2 turns of the cycle = 1 x glucoseYay…

ChemiosmosisAs electrons flow along the electron transport

chain, energy is released and used to pump protons across the intermembrane space.

This builds up a proton gradient (also a pH gradient) and an electrochemical gradient.

So potential energy builds up in the intermembrane space.

H ions cannot diffuse through the lipid part of the inner membrane but can diffuse through ion channels.

The flow of H ions is known as chemiosmosis.

Oxidative PhosphorylationFormation of ATP by the addition of PI to ADP

in the presence of oxygen:AS protons flow through an ATP Synthase

enzyme, they drive the rotational part of the enzyme which joins ADP and Pi to form ATP.

The electrons are passed from the last electron carrier in the chain to molecular oxygen, which is the final electron acceptor!

H ions also join so that oxygen is reduced to water.

And that, my friends, is RESPIRATION!All you have to do know is learn it all

(mwahahaha)