cellular metabolism biol 105 lecture 6 read chapter 3 (pages 63 – 69)

Cellular Metabolism

Biol 105

Lecture 6

Read Chapter 3 (pages 63 – 69)

Copyright © 2009 Pearson Education, Inc.

Metabolism

Consists of all of the chemical reactions that take place in a cell


Metabolism

Animation—Breaking Down Glucose For Energy

http://wps.aw.com/bc_goodenough_boh_4/177/45509/11650544.cw/index.html


Cellular Metabolism

Aerobic cellular respiration – requires oxygen, produces carbon dioxide

Anaerobic Fermentation – does not require oxygen


Summary of Cellular Respiration

Figure 3.27

Bloodvessel

Carrierprotein

Glucose

Oxygen

Extracellular fluid

Plasmamembrane

Glycolysisglucose pyruvate

Mitochondrion

CitricAcidCycle

ElectronTransport

Chain

TransitionReaction

Electronstransferredby NADH

Cytoplasm


and FADH2


+32 ATP 36 ATP+2 ATP +2 ATP


Aerobic Cellular respiration

In aerobic cellular respiration cells take in sugar (glucose) and breaks it down to 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 of aerobic cellular respiration:

1. Glycolysis

2. Transition Reaction

3. Citric Acid Cycle (Krebs Cycle)

4. Electron Transport Chain


NADH and FADHNADH and FADH22 are important carriers of are important carriers of electronselectrons


Cellular Respiration - Glycolysis

Phase 1: Glycolysis

Occurs in the cytoplasm Splits one glucose into two pyruvate molecules Generates a net gain of 2 ATP and 2 NADH

molecules Does not require oxygen


Cellular Respiration - Glycolysis

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-yieldingphase

2 ATP

The two molecules of pyruvate then diffusefrom the cytoplasm into the inner compartmentof the mitochondrion, where they pass througha 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 preparingglucose for splitting.

2 Pyruvate

Two molecules of nicotine adenine dinucleotide (NADH), a carrier of high-energy electrons, also are produced.

In Cytosol


Cellular Respiration – Transition Reaction

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

Start with: 2 pyruvate (3 carbon molecules) 2 Coenzyme A

End with: 2 CO2

2 NADH 2 Acetyl CoA (2 carbon molecule)


Transition Reaction

Figure 3.24

NADH

(electron passesto electrontransport 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.


Cellular Respiration – Citric acid cycle

Phase 3: Citric acid cycle

Occurs in the mitochondria Acetyl CoA enters the citric acid cycle Releases 2 ATP, 2 FADH2 and 6 NADH, 4

CO2 molecules

Requires oxygen


Citric Acid Cycle

Also called the Krebs Cycle

Start with 2 Acetyl CoA

End with: 4 CO2

2 ATP 6 NADH and 2 FADH2


Citric Acid Cycle

Figure 3.25

Acetyl CoA

CoA

Citrate

CO2

leavescycle

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


Cellular Respiration

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 carriers of electrons

They donate electrons to the electron transport chain

At the end of the chain oxygen accepts the electrons.


The Big Pay Off – Electron Transport Chain

Electron Transport Chain produces ATP using the ATP synthase protein molecule

The Electron Transport Chain produces 32 ATP


Electron Transport Chain

Figure 3.26

The molecules of NADH andFADH2 produced by earlier phasesof 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

Membraneproteins

H2O

2 H+ + O2Energy released is used

for synthesis of ATP

FADH2

NADH

Electron Transport Chain (inner membrane of mitochondrion)

FAD

12

Po

ten

tial

en

erg

y

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


How is ATP made using the ETC

1. In the mitochondria, the NADH and FADH 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 the concentration gradient, transporting them from the lumen of the mitochondria to the intermembrane space.


How is ATP made using the ETC

4. The ATPsynthase transports the H+ back to the lumen of the mitochondria.

5. The H+ falling through the ATPsynthase provides the energy for the ATPsynthase to catalyze the reaction of ADP + P →ATP



Table 3.5



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: Starts the process by taking in glucose. Produces 2 ATP

The Transition Reaction produces CO2 and NADH

The Citric acid cycle: Produces 2 ATP but also produces lots of NADH and FADH2. Produces CO2.



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



Complex Complex Carbohydrates Carbohydrates must first be must first be broken down into broken down into glucose before glucose before entering glycolysisentering glycolysis

Fats and proteins Fats and proteins enter the process enter the process at different stepsat different steps


Oxygen

Cellular respiration requires oxygen – this is aerobic cellular respiration

Sometimes organisms, including humans, need to produce energy without using oxygen

When you need energy quick, or if there is not enough O2 then the cell will use only glycolysis


Anaerobic Fermentation

Breakdown of glucose without oxygen

Takes place entirely in the cytoplasm

It is very inefficient - results in only two ATP


Anaerobic Fermentation

Anaerobic Fermentation: Anaerobic pathway to produce ATP from glycolysis without the Krebs and ETC


Fermentation in Animals

When cells need energy quick 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


What is the starting molecule of glycolysis?

1. Acetyl CoA

2. Protein

3. Glucose

4. Pyruvate (pyruvic acid)


Which stage produces CO2

1. Glycolysis


3. Transition

4. Citric acid Cycle

5. Both 3 and 4


Which stage uses O2

1. Glycolysis

2. Krebs Cycle



Which stage produces the most NADHs

1. Glycolysis

2. Krebs Cycle



Which stage produces the most ATP

1. Glycolysis

2. Krebs Cycle



Important Concepts

Read Ch 4

What is Cellular respiration and Anaerobic Fermentation and 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 is ATP made using the electron transport chain

What is the role of ATPsynthase, 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, what steps produce carbon dioxide

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


Definitions

Aerobic cellular respiration, anaerobic fermentation , ATP synthase, metabolism

cellular metabolism biol 105 lecture 6 read chapter 3 (pages 63 – 69)

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