Cellular Respiration – an overview

Section 9.1

Where do organisms get their energy?

•Unit – calories

•1 calorie = amount of energy required to increase 1 gram of water by 1 degrees Celsius

•1000 calories – 1 Calorie

•Cells can use all sorts of food as energy

Examples

•1 gram of sugar = 3811 calories (3.8 Calories)

•1 gram of beef fat = 8893 calories (8.9 Calories)

•Carbohydrates and proteins – approximately 4000 (4 Calories) calories per gram

• Fats- approximately 9000 calories (9 Calories) per gram

Cellular respiration overview

• It does not happen instantaneously!

Stages of cellular respiration•Cells can use

variety of food sources

•Glucose most important

•Only a small amount of energy is ‘liberated’ during glycolysis

• Pyruvic acid enters in Krebs cycle

• Most energy generated in electron transport chain

Role of oxygen• Oxygen required at the end of the electron

transport chain

• If cell needs energy it needs oxygen

• We need to breathe to respire

• Cellular respiration with oxygen is aerobic• Krebs cycle• Electron transport chain• Occur in mitochondria

• Glycolysis is anaerobic • Occurs in cell cytoplasm• Can continue without oxygen – fermentation

• Keeps glycolysis running

Photosynthesis vs Respiration

• Photosynthesis removes CO2• Respiration replaces CO2• Photosynthesis releases oxygen• Respiration requires oxygen• Virtually all living things respire,

but only plants and some bacteria can photosynthesize

The process of cellular respiration

Section 9.2

Glycolysis

•The first set of reactions

•Means – sugar breaking

•Glucose is transformed through chemical steps

•Pyruvic acid is generated (3 carbons)

•As carbon bonds are broken energy is released

Overview of glycolysis

• Energy is required to break glucose

•Overall net energy gain in the reaction

• NAD+ accepts high energy electrons

• Process is very fast• Thousands of ATP

molecules produced in milliseconds

• Does not require oxygen

Krebs cycle• Pyruvic acid is broken down to carbon

dioxide by a series of energy forming reactions

• Also known as citric acid cycle• Pyruvic acid passes through mitochondrial

membrane into matrix• 1 carbon atom from pyruvic acid becomes

part of CO2 molecule• Remaining carbon form acetic acid• In the Krebs cycle, the acetic acid (acetycl

CoA) combines with a 4-carbon compound• Produces citric acid

Krebs cycle continued….• Citric acid is progressively broken down to a

4 carbon molecule again• Electrons are transported to NADH and

FADH2

• At 5 points around the cycle• Each cycle one molecule of ADP is converted

to ATP• 1 pyruvic acid = 1 ATP• Carbon dioxide is released• ATP can be used straight away• NADH and FADH

2 feed the electron transport

chain

Electron transport and ATP synthesis

• NADH generated from glycolysis enters the mitochondria and joins electron carriers produced by Krebs cycle

• These all feed into the electron transport chain

• In Eukaryotes located in inner membrane of mitochondrion

• In Prokaryotes located in cell membrane• At the end of the chain an enzyme

combines electrons to form water• Oxygen is the final acceptor of electrons

and removes waste H+ ions

• Without oxygen the chain can’t function!

Electron transport and ATP synthesis cont… • The energy from the electrons is used to

pump H+ ions across the membrane• H+ ions build up in intermembrane space• Becomes positively charged relative to

the matrix• Matrix is negatively charged relative to

membrane space• The potential energy from this charge

difference to generate ATP via chemiosmosis

• ATP generated from turbine like ATP synthase

• One pair of high energy electrons can generate 3 ATP molecules

How much ATP does cellular respiration generate?

• Together glycolysis, the krebs cycle and electron transport chain generate 36 molecules of ATP per glucose molecule

• Produces 18 times the amount possible by anaerobic respiration • 36 ATP vs 2 ATP

• We don’t just eat carbohydrates

• Lipids and proteins enter the Krebs cycle or glycolysis at one of many places

• Cells can generate ATP from many things

• 36 ATP is 36 % of total energy of glucose• Remaining 64 % released as heat• Explains why body temp is 37 C• Why you feel warm after exercise

FermentaionSection 9.3

Glycolysis

• Glycolysis can generate energy when oxygen isn’t available

• BUT, in a few seconds all of a cell’s NADP+ ions are full of electrons

• No oxygen means no electron transport chain

• Without NADP+ glycolysis stops

• Fermentation saves the day…..

Fermentation•Cells convert NADH to NAD+ -

high energy electrons are passed back to pyruvic acid

•Glycolysis can continue happening

• Fermentation is anaerobic – occurs in cell cytoplasm

•Two types• Alcoholic fermentation• Lactic acid fermentation

Alcoholic fermentation

• Yeasts and some other microorganisms use alcoholic fermentation to produce ethyl alcohol and carbon dioxide• Used to make bread rise, used to make alcohol

Lactic acid fermentation

•Most organisms can perform lactic acid fermentation • No carbon dioxide is given off• Lactic acid from bacteria can be used to make cheese, yoghurt, sour cream

• Acid = sour taste

• Humans produce lactic acid• Muscles are most adapted to do this, as they often need large supplies of ATP

Energy and exercise•Humans have three sources of

energy for sports• ATP already in muscles

• Enough for a few seconds

• ATP made by lactic acid formation• Enough ATP for 90 seconds (200 –

400 meter sprint…)

• Large amounts of lactic acid builds up, an oxygen debt that must be repaid

Energy and exercise continued

• ATP made from cell respiration• The only way to supply muscles with energy

for a long amount of time• Releases energy slowly – why athletes pace

themselves• Glycogen stored in muscles provides energy

for 20 minutes or so• After that other molecules are broken down

• Help people lose weight• Allow animals to hibernate

• At the beginning of a race muscles use all forms of energy, but stored ATP and lactic acid fermentation can only supply energy for a limited time