10 21 09 Lecture

Copyright © 2009 Pearson Education, Inc.

Active Lecture Questions forBiology: Concepts & Connections, Sixth EditionCampbell, Reece, Taylor, Simon, and Dickey

Chapter 6Chapter 6 How Cells Harvest Chemical Energy


Concept CheckSome prokaryotic and all eukaryotic cells use oxygen to harvest energy from food molecules? In what form is that energy available to power cell work?

1) Heat and light.

2) Glucose molecules.

3) Fat molecules.

4) ATP molecules.


AnswerSome prokaryotic and all eukaryotic cells use oxygen to harvest energy from food molecules? In what form is that energy available to power cell work?

4) ATP molecules.


Concept Check

The figure above represents an overview of the different processesof cellular respiration. Which of the following correctly identifies thedifferent processes?

1) 1. Glycolysis; 2. Electron transport chain; 3. Krebs cycle

2) 1. Glycolysis; 2. Krebs cycle; 3. Electron transport chain

3) 1. Krebs cycle; 2. Electron transport chain; 3. Glycolysis

4) 1. Electron transport chain; 2. Glycolysis; 3. Krebs cycle


Answer

The figure above represents an overview of the different processesof cellular respiration. Which of the following correctly identifies thedifferent processes?

2) 1. Glycolysis; 2. Krebs cycle; 3. Electron transport chain


Cytoplasm

Glucose

FADH2

Mitochondrion

Maximum per glucose:

OXIDATIVEPHOSPHORYLATION

(Electron Transportand Chemiosmosis)

CITRIC ACIDCYCLE

Electron shuttleacross membrane

2 NADH

2 NADH

2 NADH

6 NADH 2(or 2 FADH2)

2 AcetylCoA

GLYCOLYSIS2

Pyruvate

About38 ATP

about 34 ATP

by substrate-levelphosphorylation

by oxidative phosphorylation

2 ATP

by substrate-levelphosphorylation

2 ATP


6.13 Fermentation enables cells to produce ATP without oxygen

Fermentation is an anaerobic (without oxygen) energy-generating process

– It takes advantage of glycolysis, producing two ATP molecules and reducing NAD+ to NADH

– The trick is to oxidize the NADH without passing its electrons through the electron transport chain to oxygen




Your muscle cells and certain bacteria can oxidize NADH through lactic acid fermentation

– NADH is oxidized to NAD+ when pyruvate is reduced to lactate

– In a sense, pyruvate is serving as an “electron sink,” a place to dispose of the electrons generated by oxidation reactions in glycolysis


Animation: Fermentation Overview


Glucose

NADH

NAD+

2

2

NADH2

NAD+2

2 ADPP

ATP2

2 Pyruvate

2 Lactate

GL

YC

OL

YS

IS

Lactic acid fermentation

2



The baking and winemaking industry have used alcohol fermentation for thousands of years

– Yeasts are single-celled fungi that not only can use respiration for energy but can ferment under anaerobic conditions

– They convert pyruvate to CO2 and ethanol while oxidizing NADH back to NAD+



2 ADP

P

ATP2 GL

YC

OL

YS

IS

NADH

NAD+

2

2

NADH2

NAD+2

2 Pyruvate

2 Ethanol

Alcohol fermentation

Glucose

CO22

released

2

Wine- grapes, water, yeast

Beer- water, malted barley, hops and yeast

Grains make liquors from mashing and yeast

To Yeast, EtOH is toxic and secreted to the extracellular

space. If you ferment too much, the yeast die and this limits the proof of what you

are drinking.


Fermentation vats for wine- have one-way valves to release the CO2 but keep out the oxygen. Fermentation needs to happen without Oxygen.


6.14 EVOLUTION CONNECTION: Glycolysis evolved early in the history of life on Earth

Glycolysis is the universal energy-harvesting process of living organisms

– So, all cells can use glycolysis for the energy necessary for viability

– The fact that glycolysis has such a widespread distribution is good evidence for evolution



INTERCONNECTIONS BETWEEN MOLECULAR BREAKDOWN

AND SYNTHESIS



6.15 Cells use many kinds of organic molecules as fuel for cellular respiration

Although glucose is considered to be the primary source of sugar for respiration and fermentation, there are actually three sources of molecules for generation of ATP

– Carbohydrates (disaccharides)

– Proteins (after conversion to amino acids)

– Fats



Food, such aspeanuts

ProteinsFatsCarbohydrates

Glucose

OXIDATIVEPHOSPHORYLATION(Electron Transportand Chemiosmosis)

CITRICACID

CYCLE

AcetylCoA

GLYCOLYSIS

Pyruvate

Amino acidsGlycerolSugars Fatty acids

Amino groups

G3P

ATP


Concept Check

1) The electron transport chain is too deeply embedded in the mitochondria.

2) The electron transport chain only receives electrons carried by reduced electron carrier molecules such as NADH.

3) The electron transport chain only receives electrons carried by oxidized electron carrier molecules such as NAD+.

4) The electron transport chain does not produce ATP.

The figure above represents an overview of the different entry pathways to cellular respiration when different macromolecules are digested for energy production. Why are none of the digestive products entering the electron transport chain, directly?


Answer

2) The electron transport chain only receives electrons carried by reduced electron carrier molecules such as NADH.

The figure above represents an overview of the different entry pathways to cellular respiration when different macromolecules are digested for energy production. Why are none of the digestive products entering the electron transport chain, directly?


6.16 Food molecules provide raw materials for biosynthesis

Many metabolic pathways are involved in biosynthesis of biological molecules

– To survive, cells must be able to biosynthesize molecules that are not present in its foods

– Often the cell will convert the intermediate compounds of glycolysis and the citric acid cycle to molecules not found in food



Cells, tissues, organisms

Proteins Fats Carbohydrates

Glucose

ATP needed to drive biosynthesis

CITRICACID

CYCLE

AcetylCoA

GLUCOSE SYNTHESIS

Pyruvate

Amino acids Glycerol SugarsFatty acids

Amino groups

G3P

ATP


Cytoplasm

GlucoseOxidative

phosphorylation(Electron Transportand Chemiosmosis)

Citricacidcycle

GlycolysisPyruvate

CO2

ATPCO2

ATP

NADH and FADH2

MitochondrionNADH

ATP


ATP (a) glucose andorganic fuels

has three stages

producesome

generates

Cellularrespiration

uses

H+ diffusethrough

ATP synthase

by process called

chemiosmosis

energy for

cellular work

uses

(b) (d)

(c)

(f)

(e)

oxidizes

C6H12O6

to pullelectrons down

to

uses pumps H+ to create

H+ gradient

producesmany


You should now be able toExplain how photosynthesis and cellular respiration are

necessary to provide energy that is required to sustain your life

Explain why breathing is necessary to support cellular respiration

Describe how cellular respiration produces energy that can be stored in ATP

Explain why ATP is required for human activities



You should now be able to

Describe the process of energy production from movement of electrons

List and describe the three main stages of cellular respiration

Describe the major steps of glycolysis and explain why glycolysis is considered to be a metabolic pathway

Explain how pyruvate is altered to enter the citric acid cycle and why coenzymes are important to the process




Describe the citric acid cycle as a metabolic pathway designed for generating additional energy from glucose

Discuss the importance of oxidative phosphorylation in producing ATP

Describe useful applications of poisons that interrupt critical steps in cellular respiration

Review the steps in oxidation of a glucose molecule aerobically




Compare respiration and fermentation

Provide evidence that glycolysis evolved early in the history of life on Earth

Provide criteria that a molecule must possess to be considered a fuel for cellular respiration

Discuss the mechanisms that cells use to biosynthesize cell components from food


Technology

10 21 09 Lecture