Chapt 6 ppt

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6.1 Photosynthesis and cellular respiration

provide energy for life

•

Life requires energy.

•

In almost all ecosystems, energy ultimately comes

from the sun.

•

In photosynthesis,

• some of the energy in sunlight is captured by chloroplasts,

• atoms of carbon dioxide and water are rearranged,

and

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6.1 Photosynthesis and cellular respiration

provide energy for life

•

In

cellular

respiration

,

• sugar is broken down to carbon dioxide and water

and

• the cell captures some of the released energy to make ATP.

•

Cellular respiration takes place in the mitochondria

of eukaryotic cells.

(3)

Figure 6.1

Sunlight energy

ECOSYSTEM

Photosynthesis in

chloroplasts _Organic molecules Cellular

respiration in mitochondria

ATP powers most cellular work

CO₂ + H₂O + O₂

(4)

6.2 Breathing supplies O

₂

for use in cellular

respiration and removes CO

₂

•

Respiration, as it relates to breathing, and cellular

respiration are not the same.

• Respiration, in the breathing sense, refers to an exchange of gases. Usually an organism brings in oxygen from the environment and releases waste CO₂.

(5)

Figure 6.2-0

Lungs

Transported in bloodstream

Muscle cells carrying out Breathing

Cellular Respiration O₂

O₂

CO₂

(6)

6.3 Cellular respiration banks energy in ATP

molecules

•

Cellular respiration is an exergonic (energy-

(7)

Figure 6.3

Glucose Oxygen Carbon

dioxide

Water

Heat ATP

H₂O 6

CO₂ 6

(8)

6.5 Cells capture energy from electrons

“falling” from organic fuels to oxygen

•

How do your cells extract energy from glucose?

•

The answer involves the transfer of electrons

(9)

6.5 Cells capture energy from electrons

•

During cellular respiration,

• electrons are transferred from glucose to oxygen

and

• energy is released.

•

Oxygen attracts electrons very strongly.

(10)

•

Energy can be released from glucose by simply

burning it.

•

This electron “fall” happens very rapidly.

(11)

•

Cellular respiration is a more controlled descent of

electrons and like rolling down an energy hill.

(12)

•

The movement of electrons from one molecule to

another is an oxidation-reduction reaction, or

redox

reaction

. In a redox reaction,

• the loss of electrons from one substance is called

oxidation,

• the addition of electrons to another substance is called reduction,

• a molecule is oxidized when it loses one or more

(13)

6.5 Cells capture energy from electrons

•

A cellular respiration equation is helpful to show

the changes in hydrogen atom distribution.

• Glucose loses its hydrogen atoms and becomes

oxidized to CO₂.

• Oxygen gains hydrogen atoms and becomes

(14)

Figure 6.5a

Loss of hydrogen atoms (becomes oxidized)

Gain of hydrogen atoms (becomes reduced) (Glucose)

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6.5 Cells capture energy from electrons

•

An important player in the process of oxidizing

glucose is a coenzyme called

NAD

+

, which

• accepts electrons and

(16)

Figure 6.5b

Becomes oxidized

+ 2 H

+ 2 H Becomes reduced

NAD+ NADH H+

(carries) 2 electrons)

+

(17)

6.5 Cells capture energy from electrons

•

NADH delivers electrons to a string of electron

carrier molecules, which moves electrons down a

hill.

•

These carrier molecules constitute an

electron

transport

chain

.

•

At the bottom of the hill is oxygen (1/2 O

₂

), which

• accepts two electrons,

• picks up two H+, and

(18)

Figure 6.5c

NAD+

H+

NADH

Energy released and available for making 2

2

O₂

2

H₂O −

2 1

(19)

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6.6 Overview: Cellular respiration occurs in

three main stages

•

Cellular respiration consists of a sequence of steps

that can be divided into three stages.

• Stage 1: Glycolysis

• _{Stage 2: Pyruvate oxidation and the citric acid cycle}

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6.6 Overview: Cellular respiration occurs in

three main stages

•

Stage 1:

Glycolysis

• occurs in the cytosol,

• begins cellular respiration, and

• breaks down glucose into two molecules of a

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6.6 Overview: Cellular respiration occurs in

three main stages

•

Stage 2: Pyruvate oxidation and the

citric

acid

cycle

• take place in mitochondria,

• _{oxidize pyruvate to a two-carbon compound, and}

• supply the third stage with electrons.

(23)

6.6 Overview: Cellular respiration occurs in

three main stages

•

Stage 3:

Oxidative

phosphorylation

• NADH and a related electron carrier, FADH₂, shuttle electrons to an electron transport chain embedded in the inner mitochondrial membrane.

• Most ATP produced by cellular respiration is

generated by oxidative phosphorylation, which uses the energy released by the downhill fall of electrons

from NADH and FADH₂ to oxygen to phosphorylate

(24)

6.6 Overview: Cellular respiration occurs in

three main stages

•

Stage 3:

Oxidative

phosphorylation

• As the electron transport chain passes electrons down the energy hill, it also pumps hydrogen ions (H+) across the inner mitochondrial membrane, into the narrow intermembrane space, and produces a concentration gradient of H+ across the membrane.

(25)

Figure 6.6-0

Electrons carried by NADH FADH2

Glycolysis

Glucose Pyruvate _OxidationPyruvate Citric Acid Cycle

Oxidative Phosphorylation (Electron transport and chemiosmosis)

(26)

Figure 6.6-1

Electrons carried by NADH FADH₂

ATP

Glycolysis

Glucose Pyruvate _OxidationPyruvate Citric Acid Cycle Substrate-level phosphorylation Substrate-level phosphorylation Oxidative phosphorylation Oxidative Phosphorylation (Electron transport and chemiosmosis)

(27)

6.7 Glycolysis harvests chemical energy by

oxidizing glucose to pyruvate

•

In

glycolysis

,

• a single molecule of glucose is enzymatically cut in half through a series of steps,

• two molecules of pyruvate are produced,

• two molecules of NAD+ are reduced to two molecules of NADH, and

(28)

Figure 6.7a

Glucose

2 ADP

ATP 2

NADH NAD+

+2 H+

+2

(29)

6.7 Glycolysis harvests chemical energy by

•

ATP is formed in glycolysis by

substrate-level

phosphorylation

during which

• an enzyme transfers a phosphate group from a

substrate molecule to ADP and

• ATP is formed.

•

The compounds that form between the initial

(30)

Figure 6.7b

Enzyme Enzyme

ADP

Substrate Product

P

P P

(31)

6.7 Glycolysis harvests chemical energy by

•

The steps of glycolysis have two main phases.

• In steps 1–4, the energy investment phase, energy

is consumed as two ATP molecules are used to

energize a glucose molecule, which is then split into two small sugars.

• _{In steps 5–9, the energy payoff phase, two NADH}

molecules are produced for each initial glucose molecule and four ATP molecules are generated.

(32)

Figure 6.7c-1-2 Glucose 1 3 1 2 3 4 4 Glucose 6-phosphate Fructose 6-phosphate Fructose 1,6-bisphosphate ENERGY INVESTMENT PHASE Step P ATP ADP

Step A six-carbon

intermediate splits into two three-carbon intermediates. ATP ADP P P P

Steps – Glucose

(33)

Figure 6.7c-2-2 5 5 5 6 9 7 8 8 7 6 6 Glyceraldehyde 3-phosphate (G3P) ATP ADP P ATP ADP ADP ADP

H₂O H₂O

NAD+ NAD+

NADH NADH

+ H+ ₊_H+

P

P P

P P P P

P P P P P P ENERGY PAYOFF PHASE 1,3-Bisphosphoglycerate 3-Phosphoglycerate 2-Phosphoglycerate Phosphoenolpyruvate (PEP)

Step A redox reaction generates NADH.

Steps – ATP

(34)

6.8 Pyruvate is oxidized in preparation for the

citric acid cycle

•

The pyruvate formed in glycolysis is transported

from the cytosol into a mitochondrion where the

citric acid cycle and oxidative phosphorylation will

occur.

(35)

6.8 Pyruvate is oxidized in preparation for the

citric acid cycle

•

Pyruvate does not enter the citric acid cycle but

undergoes some chemical grooming in which

• a carboxyl group is removed and given off as CO₂,

• the two-carbon compound remaining is oxidized

while a molecule of NAD+ is reduced to NADH, and

• coenzyme A joins with the two-carbon group to

form acetyl coenzyme A, abbreviated as acetyl

CoA.

(36)

Figure 6.8

Pyruvate

NAD+ NADH + H+

1

2

3

Coenzyme A CO2

CoA

(37)

6.9 The citric acid cycle completes the

oxidation of organic molecules, generating

many NADH and FADH

₂

molecules

•

The citric acid cycle

• _{is also called the Krebs cycle (after the}

German-British researcher Hans Krebs, who worked out much of this pathway in the 1930s),

• completes the oxidation of organic molecules, and

(38)

Figure 6.9a

Citric Acid Cycle

NAD+

NADH

+ 3 H+

CO₂ CoA

CoA Acetyl CoA

2

3 3 FADH₂

(39)

6.9 The citric acid cycle completes the

many NADH and FADH

₂

molecules

•

During the citric acid cycle

• _{the two-carbon group of acetyl CoA is joined to a}

four-carbon compound, forming citrate,

• citrate is degraded back to the four-carbon compound,

• two CO₂ are released, and

• one ATP, three NADH, and one FADH₂ are

(40)

6.9 The citric acid cycle completes the

many NADH and FADH

₂

molecules

•

Remember that the citric acid cycle processes two

molecules of acetyl CoA for each initial glucose.

•

Thus, after two turns of the citric acid cycle, the

overall yield per glucose molecule is

• 2 ATP,

• 6 NADH, and

(41)

6.9 The citric acid cycle completes the

many NADH and FADH

₂

molecules

•

Thus, after glycolysis and the citric acid cycle, the

cell has gained

• 4 ATP,

• 10 NADH, and

• 2 FADH₂.

•

To harvest the energy banked in NADH and

(42)

Figure 6.9b-3

Citric Acid Cycle

NAD+

NADH

+ H+

CO2 CoA CoA Acetyl CoA FADH2 FAD P ADP +

CO2

+ H+

NAD+

NADH

H2O

2 carbons enter cycle

(43)

6.10 Most ATP production occurs by

oxidative phosphorylation

•

The final stage of cellular respiration is oxidative

phosphorylation, which

• involves electron transport and chemiosmosis and

• _{requires an adequate supply of oxygen.}

•

The arrangement of electron carriers built into a

membrane makes it possible to

• create an H+ concentration gradient across the membrane and then

(44)

6.10 Most ATP production occurs by

oxidative phosphorylation

•

Electrons from NADH and FADH

₂

travel down the

electron transport chain to O

₂

, the final electron

acceptor.

• Oxygen picks up H+, which forms water.

• Energy released by these redox reactions is used

(45)

6.10 Most ATP production occurs by

oxidative phosphorylation

•

In chemiosmosis, the H

+

diffuses back across the

inner membrane, through

ATP

synthase

(46)

Figure 6.10a

OUTER MITOCHONDRIAL MEMBRANE

Q

FADH₂ FAD

ATP P

ADP + H+

NAD+

NADH

H₂O O₂ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+ H+

Cyt c

−1₂ + 2

II III I ATP synthase Protein complex of electron carriers Mobile electron carriers Intermem-brane space Inner mito-chondrial membrane Mito-chondrial matrix Electron flow

Electron Transport Chain Chemiosmosis

(47)

Figure 6.10b

INTERMEMBRANE SPACE

Rotor

Internal rod

Catalytic knob

ADP

H+

(48)

6.12 Review: Each molecule of glucose yields

many molecules of ATP

•

Recall that the energy payoff of cellular respiration

involves

1. glycolysis,

2. alteration of pyruvate,

3. the citric acid cycle, and

(49)

6.12 Review: Each molecule of glucose yields

many molecules of ATP

• The total yield is about 36 ATP molecules per glucose

molecule.

• The number of ATP molecules cannot be stated exactly for

several reasons.

• The NADH produced in glycolysis passes its electrons across the mitochondrial membrane to either NAD+ or FAD. Because

FADH₂ adds its electrons farther along the electron transport chain, it contributes less to the H+ gradient and thus

generates less ATP.

• Some of the energy of the H+_{gradient may be used for work}

(50)

Figure 6.12

NADH FADH2

CO₂

Maximum per glucose:

+ 2

ATP

Glycolysis

Glucose _Pyruvate2

Pyruvate Oxidation 2 Acetyl CoA Citric Acid Cycle

by substrate-level by substrate-level by oxidative

Oxidative Phosphorylation (electron transport and chemiosmosis) CYTOSOL MITOCHONDRION 2 NADH

2 6 NADH + 2

+ 2

ATP +32 aboutATP About

36 ATP O₂

(51)

FERMENTATION:

(52)

6.13 Fermentation enables cells to produce

ATP without oxygen

•

Fermentation is a way of harvesting chemical

energy that does not require oxygen. Fermentation

• uses glycolysis,

• _{produces two ATP molecules per glucose, and}

• _{reduces NAD}+_{to NADH.}

(53)

ATP without oxygen

•

Your muscle cells and certain bacteria can

regenerate NAD

+

through

lactic

acid

fermentation

, in which

• NADH is oxidized back to NAD+ and

(54)

(55)

Figure 6.13a

Glucose

2 ADP

2 NADH

2 NAD+

2 ATP 2 NADH

2 NAD+

+ 2 P

G

ly

co

ly

si

s

(56)

ATP without oxygen

•

Lactate is carried by the blood to the liver, where it

is converted back to pyruvate and oxidized in the

mitochondria of liver cells.

•

The dairy industry uses lactic acid fermentation by

bacteria to make cheese and yogurt.

(57)

6.13 Fermentation enables cells to produce

ATP without oxygen

•

The baking and winemaking industries have used

alcohol

fermentation

for thousands of years.

•

In this process, yeast (single-celled fungi)

• oxidize NADH back to NAD+ and

(58)

Figure 6.13b

Glucose

2 ADP

2 NADH

2 NAD+

2 ATP 2 NADH

2 NAD+

+ 2 P

G

ly

c

o

ly

si

s

2 Pyruvate

(59)

6.13 Fermentation enables cells to produce

ATP without oxygen

•

Obligate anaerobes

• require anaerobic conditions,

• are poisoned by oxygen, and

• live in stagnant ponds and deep soils.

•

Facultative anaerobes

• can make ATP by fermentation or oxidative

phosphorylation and

(60)

Figure 6.15-1

Food

Carbohydrates Fats Proteins

Oxidative Phosphorylation

Sugars Glycerol Fatty acids Amino acids

Amino groups

Glucose G3P Pyruvate Glycolysis

Acetyl CoA

(61)

Figure 6.UN02

Electrons carried by NADH FADH₂

ATP ATP ATP

Glycolysis

Glucose Pyruvate _OxidationPyruvate Citric Acid Cycle

Substrate-level phosphorylation

Oxidative

phosphorylation

Oxidative Phosphorylation (Electron transport and chemiosmosis)

(62)

Figure 6.UN03 Cellular respiration glucose and organic fuels cellular work chemiosmosis ATP _(a) (b) (c) (d) (e) (f) (g)