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Cellular Respiration. Cellular Respiration: Harvesting Chemical Energy. Life Requires Energy. Living cells require energy from outside sources Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants.

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Cellular respiration

Cellular Respiration

Cellular Respiration: Harvesting Chemical Energy


Life requires energy
Life Requires Energy

  • Living cells require energy from outside sources

  • Some animals, such as the giant panda, obtain energy by eating plants; others feed on organisms that eat plants



ATP heat

  • ATP stands for Adenosine Tri-Phosphate

  • ATP is a molecule that serves as the most basic unit of energy

  • ATP is used by cells to perform their daily tasks


ATP heat

  • ATP can be broken down into a molecule of ADP by removing one of the phosphate groups.

    • This releases energy.

  • ADP can be remade into ATP later when the cell has food that can be broken down (i.e. glucose)


NADH heat

  • NADH is a molecule that can “carry” H+ ions and electrons from one part of the cell to another.

    • NADH is the “energized” version of this molecule that is carrying the H+ ion and two high-energy electrons.

    • NAD+ is the “non-energized” version of this molecule that does not have the ion or the extra two electrons.


Le 8 9

LE 8-9 heat

P

P

P

Adenosine triphosphate (ATP)

H2O

+

P

P

P

+

Energy

i

Adenosine diphosphate (ADP)

Inorganic phosphate


Le 9 2

Light heat

energy

LE 9-2

ECOSYSTEM

Photosynthesis

in chloroplasts

Simple sugars

(Glucose)

CO2 + H2O

+ O2

Cellular respiration

in mitochondria

ATP

powers most cellular work

Heat

energy


Cell respiration and production of atp
Cell Respiration and Production of ATP heat

  • The breakdown of organic molecules (carbohydrates, lipids, proteins) releases energy.

  • Cellular respiration consumes oxygen and organic molecules and yields ATP

  • Although carbohydrates, fats, and proteins are all consumed as fuel, it is helpful to trace cellular respiration with the sugar glucose:

    C6H12O6 + 6O2 6CO2 + 6H2O + Energy


Glycolysis
Glycolysis heat

  • Glycolysis is the first stage of cellular respiration.

  • Occurs in cytoplasm.

  • During glycolysis, glucose is broken down into 2 molecules of the 3-carbon molecule pyruvic acid.

    • ATP and NADH are produced as part of the process.


Atp production
ATP Production heat

  • 2 ATP molecules are needed to get glycolysis started.


Atp production1
ATP Production heat

  • Glycolysis then produces 4 ATP molecules, giving the cell a net gain of +2 ATP molecules for each molecule of glucose that enters glycolysis.


Nadh production
NADH heatProduction

  • During glycolysis, the electron carrier 2 NAD+become 2 NADH.

  • 2 NADH molecules are produced for every molecule of glucose that enters glycolysis.


Glycolysis1
Glycolysis heat

  • Glycolysis uses up:

    • 1 molecule of glucose (6-carbon sugar)

    • 2 molecules of ATP

    • 2 molecules of NAD+

  • Glycolysis produces

    • 2 molecules of pyruvic acid (3-carbon acids)

    • 4 molecules of ATP

    • 2 molecules of NADH


Advantages of glycolysis
Advantages of Glycolysis heat

  • Glycolysis produces ATP very fast, which is an advantage when the energy demands of the cell suddenly increase.

  • Glycolysis does not require oxygen, so it can quickly supply energy to cells when oxygen is unavailable.


Movement to the citric acid cycle
Movement to the Citric Acid Cycle heat

  • Before the next stage can begin, pyruvic acid must first be transported inside the mitochondria.

  • Pyruvic acid is combined with an enzyme called Coenzyme A. This enzyme helps with the transportation.

    • Pyruvic acid + Coenzyme A make Acetyl CoA

    • One more molecule of NADH is produced.

    • This also releases one molecule of CO2 as a waste product.


Le 9 10

LE 9-10 heat

MITOCHONDRION

CYTOSOL

NAD+

NADH

+ H+

Acetyl Co A

CO2

Coenzyme A

Pyruvate

Transport protein


Krebs cycle
Krebs Cycle heat

  • During the citric acid cycle, pyruvic acid produced in glycolysis is broken down into carbon dioxide and more energy is extracted.


Citric acid cycle
Citric Acid Cycle heat

  • Acetyl-CoA from glycolysis enters the matrix, the innermost compartment of the mitochondrion.

  • Once inside, the Coenzyme A is released.


Citric acid cycle1
Citric Acid Cycle heat

  • The molecule of acetate that entered from glycolysis joins up with another 4-carbon molecule already present.

  • This forms citric acid.


Citric acid cycle2
Citric Acid Cycle heat

  • Citric acid (6-carbon molecule) is broken down one step at a time until it is a 4-carbon molecule.

  • The two extra carbons are released as carbon dioxide.


Citric acid cycle3
Citric Acid Cycle heat

  • Energy released by the breaking and rearranging of carbon bonds is captured in the forms of ATP, NADH, and FADH2.

  • FADH2has the same purpose as NADH – to transport high-energy electrons and H+ ions.


Citric acid cycle4
Citric Acid Cycle heat

  • For each turn of the cycle, the following are generated:

    • 1 ATP molecule

    • 3 NADH molecules

    • 1 FADH2 molecule


Citric acid cycle5
Citric Acid Cycle heat

  • Remember! Each molecule of glucose results in 2 molecules of pyruvic acid, which enter the Krebs cycle.

  • So each molecule of glucose results in two complete “turns” of the Krebs cycle.

  • Therefore, for each glucose molecule:

    • 6 CO2 molecules,

    • 2 ATP molecules,

    • 8 NADH molecules,

    • 2 FADH2 molecules are produced.


Le 9 11

Pyruvic acid heat

(from glycolysis,

2 molecules per glucose)

LE 9-11

Citric

acid

cycle

Glycolysis

Oxidation

phosphorylation

CO2

NAD+

CoA

NADH

ATP

ATP

ATP

+ H+

Acetyl CoA

CoA

CoA

Citric

acid

cycle

2

CO2

FADH2

3 NAD+

3

NADH

FAD

+ 3 H+

ADP + P

i

ATP


Electron transport chain
Electron Transport Chain heat

  • The electron transport chain occurs in the inner membrane of the mitochondria.

  • Electrons are passed along the chain, from one protein to another.

  • Each time the electron is passed, a little bit of energy is extracted from it.

  • Electrons drop in energy as they go down the chain and until they end with O2, forming water


Electron transport chain1
Electron Transport Chain heat

  • NADH and FADH2 pass their high-energy electrons to electron carrier proteins in the electron transport chain.


Electron transport chain2
Electron Transport Chain heat

  • At the end of the electron transport chain, the electrons combine with H+ ions and oxygen to form water.


Electron transport chain3
Electron Transport Chain heat

  • Energy generated by the electron transport chain is used to move H+ ions (from NADH and FADH2) against a concentration gradient.

  • This creates a “dam” of H+ ions in the outer fluid of the mitochondria.


  • The electron transport chain generates no ATP heat

  • The chain’s function is to break the large free-energy drop from food to O2 into smaller steps that release energy in manageable amounts.

  • The end result is a “reservoir” of H+ ions that can be tapped for energy, much like a reservoir in a hydroelectric dam.


Chemiosmosis
Chemiosmosis heat

  • The electron transport chain has created a high concentration of H+ ions in the outer fluid of the mitochondria.

  • H+ then moves back across the membrane, into the inner fluid.

    • H+ ions pass through a channel protein called ATP Synthase

  • ATP synthase uses this flow of H+ to convert ADP molecules (low energy) into ATP (high energy)


Le 9 14

INTERMEMBRANE SPACE heat

A rotor within the membrane spins as shown when H+ flows past

it down the H+ gradient.

H+

LE 9-14

H+

H+

H+

H+

H+

H+

A stator anchored in the membrane holds the knob stationary.

A rod (or “stalk”) extending into the knob also spins, activating catalytic sites in the knob.

H+

Three catalytic sites in the stationary knob join inorganic phosphate to ADP to make ATP.

ADP

+

ATP

P

i

MITOCHONDRAL MATRIX


Total atp production
Total ATP Production heat

  • During cellular respiration, most energy flows in this sequence:

    glucose  NADH 

     electron transport chain chemiosmosis ATP

  • About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 total ATP

    • Remainder is lost as waste heat


Fermentation
Fermentation heat

  • Cellular respiration requires O2 to produce ATP

  • Glycolysis can produce ATP with or without O2 (in aerobic or anaerobic conditions)

  • In the absence of O2, glycolysis can couples with a process called fermentation to produce ATP.


Types of fermentation
Types of Fermentation heat

  • Fermentation consists of glycolysis + reactions that regenerate NAD+, which can be reused by glycolysis

  • Two common types are alcohol fermentation and lactic acid fermentation


Alcohol fermentation
Alcohol Fermentation heat

  • Yeast and a few other microorganisms use alcoholic fermentation that produces ethyl alcohol and carbon dioxide.

  • This process is used to produce alcoholic beverages and causes bread dough to rise.

Pyruvic acid + NADH → Alcohol + CO2 + NAD+


Lactic acid fermentation
Lactic Acid heatFermentation

  • Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid.

  • Pyruvic acid + NADH  Lactic acid + NAD+


  • In lactic acid fermentation, pyruvate is reduced to NADH, the only end product is lactic acid. No carbon dioxide is released.

  • Lactic acid fermentation by some fungi and bacteria is used to make cheese and yogurt

  • Human muscle cells use lactic acid fermentation to generate ATP when O2 is scarce (out of breath)

    • Result: Soreness!



Le 9 18

Glucose that they can survive using either fermentation or cellular respiration

LE 9-18

CYTOSOL

Pyruvate

O2 present

Cellular respiration

No O2 present

Fermentation

MITOCHONDRION

Acetyl CoA

Ethanol

or

lactate

Citric

acid

cycle


The evolutionary significance of glycolysis
The Evolutionary Significance of Glycolysis that they can survive using either fermentation or cellular respiration

  • Glycolysis occurs in nearly all organisms

  • Glycolysis probably evolved in ancient prokaryotes before there was oxygen in the atmosphere


Other energy sources
Other Energy Sources that they can survive using either fermentation or cellular respiration

  • Catabolic pathways funnel electrons from many kinds of organic molecules into cellular respiration

  • Glycolysis accepts a wide range of carbohydrates

  • Proteins must be digested to amino acids; amino groups can feed glycolysis or the citric acid cycle

  • Fats are digested to glycerol (used in glycolysis) and fatty acids (used in generating acetyl CoA)

  • An oxidized gram of fat produces more than twice as much ATP as an oxidized gram of carbohydrate


Le 9 19

Proteins that they can survive using either fermentation or cellular respiration

Carbohydrates

Fats

LE 9-19

Amino

acids

Sugars

Glycerol

Fatty

acids

Glycolysis

Glucose

Glyceraldehyde-3-

P

NH3

Pyruvate

Acetyl CoA

Citric

acid

cycle

Oxidative

phosphorylation


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