Cellular Respiration

Energy for life’s activities

Overview of Cellular Respiration

The life processes of ALL organisms require energy.

The potential energy held in the bonds of food molecules CANNOT be used directly by the cell.

Energy from food must be converted to the ONLY energy source that cells can use … ATP!

Review of ATP Adenosine Triphosphate Result of the bonding of a free

phosphate w/free ADP molecule The bond between the phosphates is

where the actual energy is stored

Review of ATP, cont.

When the bond between the phosphates is broken, energy is released

Cellular Respiration Defined

Respiration is the process by which the energy in the bonds of nutrients are used to synthesize ATP.

Respiration occurs continuously in all cells of all organisms.

The energy needed to synthesize ATP comes from an organism’s food

Summary of Cell Respiration

ATP

ADP + P

energy (out)

energy (in)

cellular respiration

cell activities

ATP

energy (out)

cellular respiration

cell activities

The whole process is an enzyme controlled reaction.

Aerobic Respiration

Aerobic Respiration – respiration with oxygen

C6H12O6 + 6O2 6CO2 + 6H2O

energy

(to make ATP)

Aerobic Respiration, cont.

Happens in 2 stages: Stage 1 – Glycolysis glyco – glucose lysis – splitting In glycolysis, a glucose molecule is broken

into 2 pyruvic acids This requires the input of 2 ATP molecules as

activation energy

energy released to make small quantity of ATP(2 molecules)

series of enzyme controlled reactions

pyruvic acid

glucose

Glycolysis does not require oxygen

Aerobic Respiration, cont.

Stage 2 – Breakdown of pyruvic acid The pyruvic acid made in glycolysis still

contains a lot of energy It can only be broken down to release

the rest of the energy in the presence of oxygen

energy released to make largequantity of ATP(34 molecules)

series of enzyme controlled reactions

pyruvic acid

carbon dioxide + water

Summary of ATP production

Stages 1 and 2 release all the chemical energy in one molecule of glucose to make a total of 36 molecules that can be used by the organism

There is actually enough energy in a glucose molecule to make ~90 ATP, but the rest is lost as heat

ATP production – summary

34 ADP + 34 P =34 ATP

glucose

pyruvic acid

carbon dioxide + water

2 ADP + 2 P =2 ATP

~56 ATP (heat)

The Mitochondrion

The Role of the Mitochondrion

In order for the cell to capture as much energy as it possibly can from it’s food, a series of controlled reactions requiring the input of oxygen is necessary

These reactions are directed by the mitochondrion

The Role of the Mitochondrion, cont.

Glycolysis occurs in the cytosol (cytoplasm) of the cell

The aerobic reactions occur in the mitochondria of the cell and are divided into 2 stages

The Role of the Mitochondrion, cont.

Stage 1 – The Krebs (Citric Acid) Cycle Discovered by Hans Krebs in 1937 Pyruvic acid is broken down into CO2 in

a series of energy-extracting reactions The first compound formed in this series

of reactions is citric acid This is the stage that is the source of all

the CO2 that you exhale

KrebsCycle

The Krebs Cycle occurs in the matrix of the mitochondrion

The Role of the Mitochondrion, cont.

Stage 2 – The Electron Transport Chain The Krebs Cycle generates many high-

energy hydrogen atoms Oxygen is added as an electron carrier

at this stage When the oxygen binds with the

hydrogen, energy is released to form ATP and water is made

Electron TransportChain

The electron transport chain occurs in the cristae of the mitochondrion.

Anaerobic Respiration

Also called fermentation Happens in low/no oxygen conditions 1 Glucose only partially broken down to

form waste products and 2 ATP

Anaerobic Pathways

Pathway 1- Lactic Acid Fermentation Glucose 2 lactic acid + 2 ATP

– Happens in muscle cells when they run out of oxygen

– Happens in bacteria that make yogurt, cheese, dill pickles

glycolysis still happens as it does not require oxygen

in absence of oxygen pyruvic acid is turned into lactic acid.

pyruvic acid

lactic acid

glucose

2 ADP + 2 P

2 ATP

Anaerobic Pathways, cont. A build up of lactic acid produces muscle

fatigue This makes the muscles ache and contract

with less power A recovery period is needed; during this time

more O2 is taken in which converts lactic acid back into pyruvic acid

The volume of O2 needed is called oxygen debt

Anaerobic Pathways, cont.

Pathway 2 – Alcoholic Fermentation Glucose 2 ethanol + 2 CO2 + 2 ATP

 process in which sugars are converted into alcohol and carbon dioxide by the action of various yeasts, molds, or bacteria

glycolysis still happens, producing 2 ATP molecules

This time in absence of oxygen, pyruvic acid is turned into carbon dioxide and ethanol

glucose

pyruvic acid

ethanol + carbon dioxide

This is irreversible

2 ADP + 2 P

2 ATP

Comparing Aerobic & Anaerobic Cellular Respiration Pathways

Aerobic (needs oxygen)

Anaerobic

(no oxygen)

Occurs in: Most organisms Mostly yeast and bacteria

1 glucose makes:

6 CO2 + 6 H2O Ethanol + CO2

Or

Lactic acid + CO2

Net ATP production:

36 2

Adaptations for Respiration

Bacteria, protists & fungi– Respiratory gases are exchanged by

diffusion Plants

– Respiratory gases are exchanged through leaves, stems, and roots

– Moves in and out of cells by diffusion but leaves and stems also have openings to the environment (stomata)

Adaptations for Respiration in Animals Techniques vary:

– Simple diffusion across cell membranes – Diffusion across moist skin into a

circulatory system– Openings to the environment that can be

flapped open and closed with a circulatory system to transport gases

– Specialized respiratory structures (e.g. lungs) to speed exchange of respiratory gases