prokaryotic cells are characterized by having – no nucleus – dna in an unbound region called the...

• Prokaryotic cells are characterized by having– No nucleus– DNA in an unbound region called the nucleoid– No membrane-bound organelles– Cytoplasm bound by the plasma membrane

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings1

Fig. 6-6

Fimbriae

Nucleoid

Ribosomes

Plasma membrane

Cell wall

Capsule

Flagella

Bacterialchromosome

(a) A typical rod-shaped bacterium

(b) A thin section through the bacterium Bacillus coagulans (TEM)

0.5 µm

2

• Eukaryotic cells are characterized by having– DNA in a nucleus that is bounded by a membranous

nuclear envelope– Membrane-bound organelles– Cytoplasm in the region between the plasma

membrane and nucleus

• Eukaryotic cells are generally much larger than prokaryotic cells


Fig. 6-9a

ENDOPLASMIC RETICULUM (ER)

Smooth ERRough ERFlagellum

Centrosome

CYTOSKELETON:

Microfilaments

Intermediatefilaments

Microtubules

Microvilli

Peroxisome

MitochondrionLysosome

Golgiapparatus

Ribosomes

Plasma membrane

Nuclearenvelope

Nucleolus

Chromatin

NUCLEUS

4

The Endoplasmic Reticulum: Biosynthetic Factory

• The endoplasmic reticulum (ER) accounts for more than half of the total membrane in many eukaryotic cells

• The ER membrane is continuous with the nuclear envelope• There are two distinct regions of ER:

– Smooth ER, which lacks ribosomes • (lipid synthesis, metabolizes carbohydrates)

– Rough ER, with ribosomes studding its surface


Fig. 6-12Smooth ER

Rough ER Nuclear envelope

Transitional ER

Rough ERSmooth ERTransport vesicle

RibosomesCisternaeER lumen

200 nm

6

• Six major functions of membrane proteins:– Transport– Enzymatic activity– Signal transduction– Cell-cell recognition– Intercellular joining– Attachment to the cytoskeleton and extracellular

matrix (ECM)

Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

7

Fig. 7-9

(a) Transport

ATP

(b) Enzymatic activity

Enzymes

(c) Signal transduction

Signal transduction

Signaling molecule

Receptor

(d) Cell-cell recognition

Glyco-protein

(e) Intercellular joining (f) Attachment to the cytoskeleton and extracellular matrix (ECM)

8

Effects of Osmosis on Water Balance

• Osmosis is the diffusion of water across a selectively permeable membrane

• Water diffuses across a membrane from the region of lower solute concentration to the region of higher solute concentration


9

Fig. 7-13

Hypotonic solution

(a) Animal cell

(b) Plant cell

H2O

Lysed

H2O

Turgid (normal)

H2O

H2O

H2O

H2O

Normal

Isotonic solution

Flaccid

H2O

H2O

Shriveled

Plasmolyzed

Hypertonic solution

10

Facilitated Diffusion: Passive Transport Aided by Proteins

• In facilitated diffusion, transport proteins speed the passive movement of molecules across the plasma membrane

• Channel proteins provide corridors that allow a specific molecule or ion to cross the membrane

• Channel proteins include– Aquaporins, for facilitated diffusion of water– Ion channels that open or close in response to a

stimulus (gated channels)


11

Fig. 7-17Passive transport

Diffusion Facilitated diffusion

Active transport

ATP

12

• The change in free energy (∆G) during a process is related to the change in enthalpy, or change in total energy (∆H), change in entropy (∆S), and temperature in Kelvin (T):

∆G = ∆H – T∆S• Only processes with a negative ∆G are

spontaneous• Spontaneous processes can be harnessed to

perform work


13

Fig. 8-5

(a) Gravitational motion (b) Diffusion (c) Chemical reaction

• More free energy (higher G)• Less stable• Greater work capacity

In a spontaneous change• The free energy of the system decreases (∆G < 0)• The system becomes more stable• The released free energy can be harnessed to do work

• Less free energy (lower G)• More stable• Less work capacity

14

• ATP drives endergonic reactions by phosphorylation, transferring a phosphate group to some other molecule, such as a reactant

• The recipient molecule is now phosphorylated


15

Fig. 8-12

P iADP +

Energy fromcatabolism (exergonic,energy-releasingprocesses)

Energy for cellularwork (endergonic,energy-consumingprocesses)

ATP + H2O

16

Substrate Specificity of Enzymes

• The reactant that an enzyme acts on is called the enzyme’s substrate

• The enzyme binds to its substrate, forming an enzyme-substrate complex

• The active site is the region on the enzyme where the substrate binds

• Induced fit of a substrate brings chemical groups of the active site into positions that enhance their ability to catalyze the reaction


17

Fig. 8-17

Substrates

Enzyme

Products arereleased.

Products

Substrates areconverted toproducts.

Active site can lower EA

and speed up a reaction.

Substrates held in active site by weakinteractions, such as hydrogen bonds andionic bonds.

Substrates enter active site; enzyme changes shape such that its active siteenfolds the substrates (induced fit).

Activesite is

availablefor two new

substratemolecules.

Enzyme-substratecomplex

5

3

21

6

4

18

The Principle of Redox

• Chemical reactions that transfer electrons between reactants are called oxidation-reduction reactions, or redox reactions

• In oxidation, a substance loses electrons, or is oxidized

• In reduction, a substance gains electrons, or is reduced (the amount of positive charge is reduced)


Fig. 9-UN1

becomes oxidized(loses electron)

becomes reduced(gains electron)

20

Fig. 9-3

Reactants

becomes oxidized

becomes reduced

Products

Methane(reducing

agent)

Oxygen(oxidizing

agent)

Carbon dioxide Water

21

Fig. 9-UN3

becomes oxidized

becomes reduced

22

The Stages of Cellular Respiration: A Preview

• Cellular respiration has three stages:– Glycolysis (breaks down glucose into two molecules

of pyruvate)– The citric acid cycle (completes the breakdown of

glucose)– Oxidative phosphorylation (accounts for most of

the ATP synthesis)


Fig. 9-6-3

Mitochondrion

Substrate-levelphosphorylation

ATP

Cytosol

Glucose Pyruvate

Glycolysis

Electronscarried

via NADH

Substrate-levelphosphorylation

ATP

Electrons carriedvia NADH and

FADH2

Oxidativephosphorylation

ATP

Citricacidcycle

Oxidativephosphorylation:electron transport

andchemiosmosis

24

• Oxidative phosphorylation accounts for almost 90% of the ATP generated by cellular respiration

• A smaller amount of ATP is formed in glycolysis and the citric acid cycle by substrate-level phosphorylation


Fig. 9-7

Enzyme

ADP

PSubstrate

Enzyme

ATP+

Product

26

Concept 9.2: Glycolysis harvests chemical energy by oxidizing glucose to pyruvate

• Glycolysis (“splitting of sugar”) breaks down glucose into two molecules of pyruvate

• Glycolysis occurs in the cytoplasm and has two major phases:– Energy investment phase– Energy payoff phase


Fig. 9-8

Energy investment phase

Glucose

2 ADP + 2 P 2 ATP used

formed4 ATP

Energy payoff phase

4 ADP + 4 P

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

2 Pyruvate + 2 H2O

2 Pyruvate + 2 H2OGlucoseNet

4 ATP formed – 2 ATP used 2 ATP

2 NAD+ + 4 e– + 4 H+ 2 NADH + 2 H+

28

• The citric acid cycle, also called the Krebs cycle, takes place within the mitochondrial matrix

• The cycle oxidizes organic fuel derived from pyruvate, generating 1 ATP, 3 NADH, and 1 FADH2 per turn


Fig. 9-11

Pyruvate

NAD+

NADH

+ H+Acetyl CoA

CO2

CoA

CoA

CoA

Citricacidcycle

FADH2

FAD

CO22

3

3 NAD+

+ 3 H+

ADP + P i

ATP

NADH

30

An Accounting of ATP Production by Cellular Respiration

• During cellular respiration, most energy flows in this sequence: glucose NADH electron transport chain proton-motive force ATP

• About 40% of the energy in a glucose molecule is transferred to ATP during cellular respiration, making about 38 ATP


Concept 9.5: Fermentation and anaerobic respiration enable cells to produce ATP without

the use of oxygen

• Most 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 couples with fermentation or anaerobic respiration to produce ATP


• Unit 2• C9 10&11, 14&16, 22&25, 27&28, 29&30,

42&43. 64&66• C10 23&28, 37&43, C11 5&6, 9&10, 11&14,

15&18, 21&23, 68&69C12 67/69&70

33

prokaryotic cells are characterized by having – no nucleus – dna in an unbound region called the...

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