Cellular Metabolism - napavalley.edu 6... · of cellular respiration pass their electrons to a series of protein molecules embedded in the inner ... Slide 1 Author: Stephanie Burns

6/20/2015

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Cellular Metabolism

Biology 105

Lecture 6

Chapter 3 (pages 56-61)

Copyright © 2009 Pearson Education, Inc.

Metabolism

Consists of all the

chemical reactions that

take place in a cell!

Cellular metabolism:

Aerobic cellular

respiration – requires

oxygen, produces

carbon dioxide

Anaerobic fermentation

– does not require

oxygen


Summary of Cellular Respiration

Figure 3.27

Blood

vessel

Carrier

protein

Glucose

Oxygen

Extracellular fluid

Plasma

membrane

Glycolysis

glucose pyruvate

Mitochondrion

Citric

Acid

Cycle

Electron

Transport

Chain

Transition

Reaction

Electrons

transferred

by NADH

Cytoplasm

Electrons

transferred

by NADH

and FADH2

Electrons

transferred

by NADH

+32 ATP 36 ATP +2 ATP +2 ATP

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Aerobic Cellular Respiration

Aerobic cellular respiration:

Cells take sugar (glucose) and break it down into

carbon dioxide and water.

This requires oxygen!

This process produces energy in the form of

ATP.

C6H12O6 + 6O2 → 6CO2 +6H2O + energy


Aerobic Cellular Respiration

There are four steps in aerobic cellular

respiration:

1. Glycolysis

2. Transition Reaction

3. Citric Acid Cycle (Krebs Cycle)

4. Electron Transport Chain

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NADH and FADH2 are important carriers of electrons


Cellular Respiration

Phase 1: Glycolysis

Occurs in the cytoplasm

Splits 1 glucose into 2 pyruvate molecules

Generates a net gain of 2 ATP and 2 NADH

molecules

Does not require oxygen

Starts with glucose

Ends with 2 ATP, 2 NADH, 2 pyruvate


Glycolysis

Figure 3.23

Cytoplasm

2 ADP

Glucose

Energy-

investment

phase

Glycolysis (in cytoplasm)

2 NADH

2 NAD+

4 ATP

4 ADP

Energy-

yielding

phase

2 ATP

The two molecules of

pyruvate then diffuse

from the cytoplasm into the inner compartment

of the mitochondrion,

where they pass through

a few preparatory steps

(the transition reaction) before entering the citric

acid cycle.

During the remaining

steps, four molecules

of ATP are produced.

During the first steps,

two molecules of ATP are

consumed in preparing glucose for splitting.

2 Pyruvate

Two molecules of nicotine

adenine dinucleotide

(NADH), a carrier of high-energy electrons,

also are produced.

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Phase 2: Transition Reaction

Occurs within the mitochondria

Coenzyme A combines with pyruvate, and CO2

is removed from each pyruvate

Forms 2 acetyl CoA molecules

Produces 2 NADH


Transition Reaction

Starts with:

2 pyruvate (which are 3-carbon molecules)

2 Coenzyme A

Ends with:

2 CO2

2 NADH

2 Acetyl CoA (which are 2-carbon molecules)


Transition Reaction

Figure 3.24

NADH

(electron passes

to electron

transport chain)

NAD+

Pyruvate (from glycolysis)

Acetyl CoA

CoA

Coenzyme A

CO2

Transition Reaction (in mitochondrion)

Citric Acid Cycle

A molecule of NADH is

formed when NAD+

gains two electrons

and one proton.

One carbon (in the form

of CO2) is removed

from pyruvate.

The two-carbon

molecule, called

an acetyl group,

binds to

coenzyme A

(CoA), forming

acetyl CoA,

which enters the

citric acid cycle.

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Phase 3: Citric Acid Cycle

Also known as the Krebs Cycle

Occurs in the mitochondria

Acetyl CoA enters the citric acid cycle

Releases 2 ATP, 2 FADH2, and 6 NADH

Generates 4 CO2 molecules

Requires oxygen


Citric Acid Cycle

Starts with 2 Acetyl CoA

Ends with:

4 CO2

2 ATP

6 NADH and 2 FADH2


Citric Acid Cycle

Figure 3.25

Acetyl CoA

CoA

Citrate

CO2

leaves

cycle

NAD+

NADH

-Ketoglutarate

CO2 leaves cycle

NADH

FAD

Succinate

FADH2

Malate

NAD+

ATP ADP

Citric Acid Cycle

NADH

Oxaloacetate

NAD+

Pi +

Acetyl CoA, the

two-carbon compound formed during the

transition reaction,

enters the citric acid cycle. The citric acid cycle also

yields several molecules of FADH2 and NADH, carriers of

high-energy electrons that

enter the electron transport chain.

The citric acid cycle yields

one ATP from each acetyl CoA that enters the cycle,

for a net gain of two ATP.

Citric Acid Cycle (in mitochondrion)

CoA

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Phase 4: Electron Transport Chain

Electrons of FADH2 and NADH are transferred

from one protein to another, until they reach

oxygen

Releases energy that results in 32 ATP

Requires oxygen


The Big Pay Off – Electron Transport Chain!

NADH and FADH2 are important electron carriers.

They donate electrons to the electron transport

chain.

At the end of the chain, oxygen accepts the

electrons.

The electron transport chain produces ATP using

the ATP synthase molecule (a protein).

The electron transport chain produces 32 ATP!


Electron Transport Chain

Figure 3.26

The molecules of NADH and FADH2 produced by earlier phases of cellular respiration pass their electrons to a series of protein molecules embedded in the inner membrane of the mitochondrion.

As the electrons are transferred from one protein to the next, energy is released and used to make ATP. 2e–

2e–

2e–

2e–

2e–

NAD+

High

Low

Membrane

proteins

H2O

2 H+ + O2 Energy released is used

for synthesis of ATP

FADH2

NADH

Electron Transport Chain (inner membrane of mitochondrion)

FAD

1 2

Po

ten

tial e

nerg

y

Eventually, the electrons are passed to oxygen, which combines with two hydrogens to form water.

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How is ATP made using the ETC?

1. In the mitochondria, the NADH and FADH2 donate electrons to the electron transport chain (ETC).

2. Oxygen is the final electron acceptor from the ETC.

3. The ETC uses the energy from the electrons to transport H+ against its concentration gradient, transporting the H+ from the lumen of the mitochondria to the intermembrane space (from the inner compartment to the outer compartment).


How is ATP made using the ETC?

4. The ATP synthase transports the H+ back to the lumen (inner compartment) of the mitochondria.

5. The H+ falling through the ATP synthase provides the energy for ATP synthase to catalyze the reaction of:

ADP + P → ATP

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Summary of Cellular Respiration

Table 3.5


Summary of Cellular Respiration: The Players

One molecule of glucose is broken down and

36 ATP are generated.

Oxygen is used by the electron transport chain

– it accepts electrons from the ETC.

Carbon dioxide is produced by the Transition

Reaction and the Citric Acid Cycle.


Glycolysis: kicks off the process by taking in

one glucose produces 2 ATP

Transition Reaction: produces CO2 and NADH

Citric Acid Cycle: produces 2 ATP, lots of

NADH and FADH2, and some CO2

Summary of Cellular Respiration Summary of Cellular Respiration: The Steps

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Electron Transport Chain

Takes electrons from NADH and FADH2 and

uses them to produce ATP using the ATP

synthase molecule.

Requires oxygen! Oxygen is the final electron

acceptor on the electron transport chain.

One glucose can produce a total of 36 ATP!!!

Summary of Cellular Respiration Summary of Cellular Respiration: The Steps


Complex

carbohydrates must

first be broken down

into glucose before

entering glycolysis.

Fats and proteins

enter the process at

different steps.


A few words about oxygen…

Cellular respiration requires oxygen – this is

why it is called aerobic cellular respiration.

Sometimes organisms, including humans, need

to produce energy without using oxygen.

When you need energy quickly, or if there is

not enough O2, then the cell will use only

glycolysis.

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Anaerobic Fermentation

Breakdown of glucose without oxygen.

Takes place entirely in the cytoplasm.

It is very inefficient and results in only two

ATP.

Anaerobic Fermentation: anaerobic pathway to

produce ATP from glycolysis, without the Citric

Acid Cycle and the ETC.


Fermentation in Animals

When cells need energy quickly, they will use

this pathway for a short time.

2 pyruvic acid + 2 NADH → 2 lactate and 2

NAD+

End result = lactate and 2 ATP produced (from

glycolysis) and NAD+ is regenerated.

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Q: What is the starting molecule of glycolysis?

1. Acetyl CoA

2. Protein

3. Glucose

4. Pyruvate (pyruvic acid)

Q: Which stage produces CO2?

1. Glycolysis


3. Transition

4. Citric Acid Cycle

5. Both 3 and 4


Q: Which stage uses O2?

1. Glycolysis

2. Krebs Cycle


Q: Which stage produces the most NADHs?

1. Glycolysis

2. Krebs Cycle



Q: Which stage produces the most ATP?

1. Glycolysis

2. Krebs Cycle


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Important Concepts

Read chapter 3, pages 56-61

What are aerobic cellular respiration and

anaerobic fermentation? What are the

differences between them?

What are the four steps of aerobic cellular

respiration, what happens in each step, what

are the starting molecules, what comes out of

each step, where in the cell does each step

occur, how many ATP and NADH/FADH2 are

produced in each step?


Important Concepts

Describe in detail how ATP is made using the electron transport chain.

What are the roles of ATP synthase, H+, O2, NADH and FADH2, and the electron transport chain in ATP production?

Know the overall picture of cellular respiration (summary slides).


Important Concepts

What is the role of oxygen in cellular respiration, and which steps produce carbon dioxide?

What is anaerobic fermentation, what steps are involved in fermentation, and what end products are produced in humans? Is oxygen required? If so, when is it used?

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Definitions

Aerobic cellular respiration, anaerobic

fermentation, ATP synthase, metabolism

Cellular Metabolism - napavalley.edu 6... · of cellular respiration pass their electrons to a series of protein molecules embedded in the inner ... Slide 1 Author: Stephanie Burns

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