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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
slide4

Energy flows into an ecosystem as sunlight and leaves as heat

  • Photosynthesis uses sunlight to generate oxygen and glucose sugar.
  • Cell respiration uses chemical energy in the form of carbohydrates, lipids, or proteins, to produce ATP.
slide5
ATP
  • 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
slide6
ATP
  • 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)
slide7
NADH
  • 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

P

P

P

Adenosine triphosphate (ATP)

H2O

+

P

P

P

+

Energy

i

Adenosine diphosphate (ADP)

Inorganic phosphate

le 9 2

Light

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
  • 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
  • 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
  • 2 ATP molecules are needed to get glycolysis started.
atp production1
ATP Production
  • 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 Production
  • 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
  • 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
  • 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
  • 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

MITOCHONDRION

CYTOSOL

NAD+

NADH

+ H+

Acetyl Co A

CO2

Coenzyme A

Pyruvate

Transport protein

krebs cycle
Krebs Cycle
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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
  • 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

(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
  • 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
  • NADH and FADH2 pass their high-energy electrons to electron carrier proteins in the electron transport chain.
electron transport chain2
Electron Transport Chain
  • 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
  • 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.
slide32

The electron transport chain generates no ATP

  • 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
  • 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

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
  • 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
  • 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
  • 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
  • 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 Fermentation
  • Most organisms, including humans, carry out fermentation using a chemical reaction that converts pyruvic acid to lactic acid.
  • Pyruvic acid + NADH  Lactic acid + NAD+
slide40

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!
slide41

Yeast and many bacteria are facultative anaerobes, meaning that they can survive using either fermentation or cellular respiration

  • Most other organisms cannot survive in the long-run using glycolysis and fermentation, they require oxygen.
    • These are obligate aerobic organisms.
le 9 18

Glucose

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
  • 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
  • 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

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

ad