Cellular Respiration

Chemical Energy and Food• Food is the energy source for cells. The energy in food is

measured in calories.• A calorie is the amount of energy needed to raise the

temperature of 1 gram of water 1 degree Celsius. There are 3811 calories in one gram of sugar glucose.

• The cell doesn’t burn glucose directly but converts into an energy source, ATP, through a process that begins with the pathway called glycolysis.

Glycolysis• Glycolysis is the process in which one molecule of glucose is

broken in half, producing two molecules of pyruvic acid, a three carbon compound.

• Glycolysis takes place in the cytoplasm of a cell.• In the process of breaking glucose in half two molecules of ATP

are needed but four molecules of ATP are produced creating a net gain of two molecules of ATP

• 4 high energy electrons are also removed and added to NAD+ (nicotinamide adenine dinucleotide) creating NADH, which helps pass energy from glucose to other pathways in the cell.

Glucose

To the electron transport chain

Glycolysis

2 Pyruvic acid

Glucose

Glycolysis Krebs cycle

Electrontransport

Fermentation (without oxygen)

Alcohol or lactic acid

Chemical Pathways After Glycolysis

Fermentation• When oxygen is not present, fermentation follows glycolysis• ● Fermentation releases energy from food molecules by producing ATP in

the absence of oxygen, this is an anaerobic process.• ● There are two main types of fermentation: 1) Alcoholic fermentation2) Lactic acid fermentation• ● Alcoholic fermentation example is yeast which causes carbon dioxide to

form and make bread rise.• ● pyruvic acid + NADH alcohol + CO2 + NAD+

Fermentation

• ● Lactic acid fermentation:• Pyruvic acid + NADH lactic acid + NAD+• ● Lactic acid is produced in your muscles during rapid exercise

when the body cannot supply enough oxygen to the tissues.• ● “FEEL THE BURN” is actually the result of a build up of lactic

acid in the muscles and can become painful and lead to cramps.

Glucose Pyruvic acidLactic acid

Lactic Acid Fermentation

Overview of Cellular Respiration

• If oxygen is present, The Krebs Cycle and electron transport chain follow glycolysis

• Glycolysis, the Krebs Cycle, and the electron transport chain make up the process called cellular respiration.

• Cellular respiration is the process that releases energy by breaking down glucose and other food molecules in the presence of oxygen (an aerobic process).

Cellular Respiration Chemical Equation

GlucoseGlycolysis

Cytoplasm

Pyruvic acid

Electrons carried in NADH

Krebs Cycle

Electrons carried in NADH

and FADH2

Electron Transport Chain

Mitochondrion

Cellular Respiration: An Overview

Mitochondrion

The Krebs Cycle (Citric Acid Cycle)• The Krebs cycle is the 2nd stage of cellular respiration.

(glycolysis is the 1st stage)• During the Krebs cycle, pyruvic acid is broken down into

carbon dioxide in a series of energy-extracting reactions.• The Krebs cycle is also known as the citric acid cycle, because

citric acid is one of its 1st products.

Stages Of The Krebs Cycle1. The Krebs cycle starts when pyruvic acid formed by glycolysis enters the

mitochondrion.2. The pyruvic acid is broken down into carbon dioxide and a 2-carbon acetyl

group.3. The 2 carbons of the acetyl group join a 4-carbon compound to produce

citric acid. The Krebs cycle continues in a series of reactions. In these reactions, two energy carriers accept high-energy electrons. NAD+ is changed to NADH, and FAD is changed to FADH2. These molecules carry high energy electrons to the electron transport chain. The carbon dioxide is released as a waste product.

Citric Acid Production

The Krebs Cycle

Mitochondrion

The Electron Transport Chain (ETC)• The ETC is the 3rd and final stage of cellular respiration.• The ETC uses the high energy electrons to change ADP into ATP.• In the ETC, high energy electrons move from one carrier protein to the

next.• At the end of the chain, oxygen pulls electrons from the final carrier

molecule. These electrons join with hydrogen ions, forming water.• Each transfer along the chain releases a small amount of energy. ATP

synthase uses the energy to produce ATP.

Electron Transport Chain

Electron TransportHydrogen Ion Movement

ATP Production

ATP synthase

Channel

Inner Membrane

Matrix

Intermembrane Space

Mitochondrion

Cellular Respiration Overview

Glucose(C6H1206)

+Oxygen

(02)

Glycolysis KrebsCycle

ElectronTransport

Chain

Carbon Dioxide

(CO2)+

Water(H2O)

ATP Totals For Cellular Respiration• ● The totals for the cellular respiration cycle are as follows:• -Glycolysis: +4 ATP – 2 ATP = Net gain 2 ATP• -Krebs Cycle and ETC: +32 ATP • -Net gain for entire cycle is 34 ATP• Note: remember there are 2 ATP used in glycolysis, therefore

only 34 ATP are realized for the cell’s further needs. • -The total number of ATP molecules formed during cellular

respiration is 36

The Partnership Between Photosynthesis And Cellular Respiration

• The energy flows in photosynthesis and cellular respiration occur in opposite directions.

• On a global level, photosynthesis removes carbon dioxide from the atmosphere and puts back oxygen.

• Cellular respiration removes oxygen from the atmosphere and puts back carbon dioxide.