Cellular Respiration

Cellular Respiration

Nelson Biology Chapter 7

Pages 204 - 228

General Learning Outcome

• Explain the role of cellular respiration in releasing potential energy from organic compounds

Focusing Questions

• How is the energy in organic matter released for use by living systems?

• How do humans in their application of technologies impact photosynthesis and cellular respirations

Importance of Cellular Respiration

• Cellular respiration is the process where – cells break down glucose into

carbon dioxide and water, releasing energy

C6H12O6(s) + O2(g) CO2(g) + H2O(l) + energy

Importance of Cellular Respiration

• When cells require energy it is supplied by ATP– This is the role of cellular respiration

• Both plant and animal cells release energy– Energy is stored in bonds of glucose

Electron Carriers

• NADH– Donates electrons in cellular processes

• NAD+– Accepts electrons in cellular processes

• FADH2

– Donates electrons in cellular processes

• FAD+– Accepts electrons in cellular processes

L.E.O. goes G.E.R.

• Loss Electrons Oxidation

• Gain ElectronsReduction

• The transfer of electrons releases energy

• This energy can be used to make ATP

STOP!! Practice Questions

• What is the primary function of cellular respiration?

• How do redox reactions in electron transfer help to form ATP?

Energy, Cells & ATP

Energy, Cells & ATP

• Energy for most cellular processes are supplied by:

ATP• Typical human cell estimated to contain

1.0x109 molecules ATP– Continually broken down to ADP + Pi

– Release energy to do work– Reformed to be used again

Active Transport

• Used to move substances into or out of the cell

• Is against a concentration gradient

– Often referred to as “pumps”• Utilizes membrane-bound carrier proteins

and energy from ATP

Sodium-Potassium Pump

Large Scale Motion

• Critical use of ATP– Energy from ATP

used for movement of muscle

Glucose & ATP

• ATP not abundant in food– Provide relatively small amounts of

energy per molecule

Carbohydrates - They are Good!

• Most useable source of energy– Notably in the form of glucose

• Along with oxygen is a substrate of cellular respiration

– Some energy in glucose is converted into ATP

ATP is like GOLD

• The cell is like a Western amusement park– Operates off gold

coins– Stores only accept

gold coins

Bars vs. Coins

• Glucose is like bars of gold– Contains 100x more energy

than an individual ATP coin– Have to exchange the bars

for coins to be useful

• Virtually all process conducted require ATP– ATP is immediate source of

energy

STOP!! Practice Questions

• How do carrier proteins use ATP to transport molecules across the membrane?

• One glucose molecule has 100x more stored energy than one ATP molecule.– Why can’t cells use

glucose to run their processes?

Breaking the Bonds, Releasing the Energy

• Respiration - chemical bonds of food molecules are broken down– New bonds form in resulting chemical

products• ALWAYS takes energy to break

chemical bonds• Energy is ALWAYS released when

new bonds form• More energy is released than

consumed

Starting

Substance

Exchange Rate

• Food molecules such as glucose have high energy content– Trade in one $100 gold bar for individual

coins• Exchange rate is at best 36%• For every 1 gold bar, will only receive $36 in

gold coins– 64% is lost as heat

2 Types of Cellular Respiration

• Aerobic Cellular Respiration– Takes place in presence of oxygen– Complete oxidation of glucose

• End products: CO2, H2O, 36 ATP molecules

• Anaerobic Cellular Respiration– Takes place in absence of oxygen– Glucose not completely oxidized

• Broken into 2 main types

Aerobic Respiration

• Stage 1: glycolysis• Stage 2: pyruvate oxidation• Stage 3: the Krebs cycle• Stage 4: ETC and chemiosmosis

C6H12O6 + 6O2 +36ADP +36Pi 6CO2 + 6H2O + 36 ATP

Anaerobic Cellular Respiration

• Stage 1: glycolysis• Stage 2: fermentation

C6H12O6 + 2 ADP + 2 Pi 2C3H6OH + 2CO2 + 2 ATP

ethanol

C6H12O6 + 2 ADP + 2 Pi 2C3H6O3 + 2 ATP

lactic acid

Glycolysis• Greek for “Sugar

splitting”• Glucose molecule (6

carbon sugar) breaks down to two pyruvate molecules (3 carbon sugar)

• Takes place without the presence of oxygen

• Occurs in the cytosol of the cell

• Pyruvate (pyruvic acid) moves into the mitochondria via a transport protein

• Uses a hydrogen carrier NADH– Photosynthesis

uses NADPH

• Produces a net of 2 ATP molecules– Also produces two

NADH molecules

Key Steps in Glycolysis

1. Two ATP molecules are used - an investment of energy

2. Redox reactions occur - 2 positive NAD+ ions remove H+ from the pathway to form 2 NADH molecules

3. Enough energy is released to join 4 ADP molecules with 4 Pi molecules this forms 4 ATP molecules

Glycolysis

• When complete, cell has• consumed

– one glucose molecule and

• produced – two ATP molecules, two

NADH molecules and two pyruvate molecules

– These ATP molecules are available for cellular functions (the gold coins)

REACTANTS PRODUCTS

Glucose 2 pyruvate

2 NAD+ 2 NADH

2 ATP 2 ADP

4 ADP + Pi 4 ATP

Glycolysis

1 glucose + 2 ADP + 2Pi + 2 NAD+ 2 pyruvate + 2 ATP + 2 NADH + 2 H+

• Alone glycolysis is not a highly-efficient energy-harnessing mechanism– Transfers only ~2.2% of free energy in glucose to ATP

• Some energy released as thermal energy• Majority is trapped in pyruvate and NADH molecules

• ALL organisms carry out glycolysis - either as only ATP source or as first step in more energy-productive process– EX. Cellular Respiration

RECALL: Aerobic Respiration

• Stage 1: glycolysis– 10 step process in cytoplasm

• Stage 2: pyruvate oxidation– 1 step process in mitochondria

• Stage 3: the Krebs cycle– 8 step cyclical process in mitochondria

• Stage 4: ETC and chemiosmosis– Multi-step process in inner mitchondrial

membrane

C6H12O6 + 6O2 +36ADP +36Pi 6CO2 + 6H2O + 36 ATP

Mitochondria

- Round or sausage-shaped organelles in cell’s cytoplasm

- Specialize in large production of ATP

- Cannot proceed without free oxygen

Mitochondrial Powerhouse

• Cristae– Folds in inner

membrane– Increases surface

area– Site of ATP

synthesis

• Mitochondrial Matrix– Site of the Citric

Acid Cycle

Stage 2: Pyruvate Oxidation

• By the end of Stage 1 cell has formed 2 ATPs, 2 NADHs, and 2 pyruvate molecules

Stage 2: Pyruvate Oxidation

• Pyruvate oxidation is a chemical pathway connecting glycolysis in cytoplasm with the Kreb’s cycle in the mitochondrial matrix– The 2 pyruvate molecules must be

transported through the two mitochondrial membranes into the matrix

Key Steps in Pyruvate Oxidation

1. One CO2 is removed from each pyruvate - released as a waste product

2. Remaining 2-carbon portions are oxidized by NAD+

1. Gains 2 H+ (2 protons and 2 electrons) from pyruvate1. Remaining 2-C compounds become an acetic acid

group1. High energy hydrogens are transferred to NAD+

3. Coenzyme A (CoA) attaches to acetic acid group - forms acetyl-CoA

1. This acetyl-CoA can enter the Krebs cycle

Stage 3: the Krebs Cycle

Key Features of the Krebs Cycle

1. Krebs cycle occurs twice for each molecule of glucose processed

2. Acetyl-CoA enters and releases the CoA, which is recycled for the next pyruvate

3. During one cycle1. three NAD+s and one FAD are reduced

forms three NADHs and one FADH22. one ADP + Pi combine to form one ATP3. two CO2 molecules are produced and

released as waste

• ALL 6 carbon atoms of glucose have been oxidized to CO2

– Released from cell as metabolic waste• All that remains is some free energy in form

of ATP and high-energy NADH and FADH2

• NADH and FADH2 go on to Stage 4– Here much of their energy will be

transferred to ATP

Key Features of the Krebs Cycle

Stage 4: Electron Transport and Chemiosmosis

Stage 4

• Occurs on the inner mitochondrial membranes

• NADH and FADH2 eventually transfer the hydrogen atom electrons through the electron transport chain– The energy associated with the

electrons pumps H+ ions into the intermembrane space

Oxygen - the Final Acceptor

• Oxygen accepts the 2 e- from the final carrier– Also uses 2 H+ ions from the matrix

• Forms water H2O

• This is why all aerobic organisms must obtain oxygen from the environment on a continual basis

Chemiosmosis & Oxidative ATP Synthesis

• The production of ATP in mitochondria is very similar to that which occurs in the thylakoid membranes in photosynthesis

•In photosynthesis, the use of light energy in ATP synthesis is called photosphosphorylation

• In cellular respiration, it is referred to as oxidative phosphorylation, or oxidative ATP synthesis

• Named because the energy used to drive ATP synthesis comes from the energy released in the ETC - from a series of oxidation reactions

Where does the ATP go?

• After ATP molecules are formed by chemiosmosis they are transported through both mitochondrial membranes– Used to drive processes requiring

energy

All in the Family

• The three stages of aerobic cellular respiration - pyruvate oxidation, the Krebs cycle, and ETC & chemiosmosis) are all linked to each other– Dependent on glycolysis for the

production of pyruvate


• Glycolysis changes NAD+ to NADH– Without NAD+ this reaction does not

occur• Cells have a limited supply of NAD+• Without a way to convert NADH to NAD+,

glycolysis will come to a halt– ATP no longer will be produced and cell

death occurs


• Evolved in organisms as a way of recycling NAD+– Allows glycolysis to continue

• One method involves transferring H atoms of NADH to specific organic molecules– Process called fermentation

•Lactic acid fermentation•Alcohol fermentation

• Occur in only 2 stages– Glycolysis: same process as that in

aerobic cellular respiration– Fermentation: products of glycolysis

recycled in 2 different ways•Carbon dioxide and ethanol are final

waste products (alcohol fermentation)•Lactic acid is the final waste product (lactic

acid fermentation)


Alcohol Fermentation

• NADH molecules pass their H atoms to acetaldehyde– This forms ethanol

• Same type of alcohol used in alcoholic beverages

– Recycles NAD+ and allows glycolysis to continue• The 2 ATP produced are enough to satisfy

the organism’s energy needs

Alcohol Fermentation - Application

• Can be carried out by a single-celled fungi– Ex. Saccharomyces cerevisiae

C6H12O6 + 2 ADP + 2 Pi 2C3H6OH + 2CO2 + 2 ATP ethanol

• Under normal conditions, humans obtain energy from glucose by aerobic cellular respiration– During strenuous exercise, the ATP

demand is greater than what can be supplied by aerobic respiration alone

Lactic Acid Fermentation

• NADH transfers its H to pyruvate in the cytoplasm– Regenerates NAD+– Pyruvate changes into lactic acid

Lactic Acid Fermentation

Exercise Phsiology

• Most common problem faced by athletes shortage of energy– Aerobic fitness factor in judging

overall fitness

Exercise Phsiology

• Muscle cells require energy from ATP• ATP production requires oxygen• Thus assume ATP production

increases if more oxygen is absorbed by body cells

Maximum Oxygen Consumption

• VO2 max– Measure of the body’s ability to

generate energy required for activity

• You will develop a concept map indicating the criteria for aerobic and anaerobic respiration. This concept map will indicate:

– Three similarities between the two processes.

– Two types of cells that perform each process.

– Location in the cell where each process occurs.

– Oxygen requirements for each process.

– Reactants and products for each process.

– Energy output for each process.

– Two different types of anaerobic respiration.

• Reactants and products for each.

• Types of cells that perform each process.

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Cellular Respiration