Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nuclei (yellow) and actin...

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings

• Nuclei (yellow) and actin (red)

Figure 4.6x


• network of protein fibers

The cell’s internal skeleton helps organize its structure and activities

THE CYTOSKELETON

Figure 4.17A


• Microfilaments of actin enable cells to change shape and move

• Intermediate filaments reinforce the cell and anchor certain organelles

• Microtubules

– give the cell rigidity

– provide anchors for organelles

– act as tracks for organelle movement


MICROFILAMENT

Figure 4.17B

INTERMEDIATEFILAMENT

MICROTUBULE

Actin subunit Fibrous subunitsTubulinsubunit

7 nm 10 nm25 nm


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• A cilia or flagellum is composed of a core of microtubules wrapped in plasma membrane

• Eukaryotes have “9+2” structure

How do cilia and flagella move?

Cilia and flagella move when microtubules bend


Figure 4.18A

FLAGELLUM

Outer microtubule doublet

Plasmamembrane

Centralmicrotubules

Outer microtubule doublet

Plasmamembrane

Electron micrograph of sections:

Flagellum

Basal body

Basal body(structurally identical to centriole)


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polarhead

nonpolartails

P –

Phospholipid bilayer

hydrophobic molecules hydrophilic molecules cytosol


Surfaces allow exchange of signals and molecules.

• Plant cells connect by plasmodesmata

Cell surfaces protect, support, and join cells


Figure 4.19A

Vacuole

Layers of one plant cell wall

Walls of two adjacent plant cells

PLASMODESMATA

Cytoplasm

Plasma membrane


• Animal cells - extracellular matrix

– sticky layer of glycoproteins

– binds cells together in tissues

– can also protect and support cells


• Tight junctions can bind cells together into leakproof sheets

• Anchoring junctions link animal cells

• Gap junctions allow substances to flow from cell to cell

TIGHTJUNCTION

ANCHORING JUNCTION

GAPJUNCTION

Plasma membranes ofadjacent cells

ExtracellularmatrixFigure 4.19B


Eukaryotic organelles fall into 4 functional groups

• 1. Manufacture and transport – dependent on network of membranes

- Nucleus

- Ribosomes

- Rough ER

- Smooth ER

- Golgi apparatus


2. Breakdown – all single-membrane sacs

• Lysosomes (in animals, some protists)

• Peroxisomes

• Vacuoles (plants)


3. Energy Processing – involves extensive membranes embedded with enzymes

• Chloroplasts

• Mitochondria


4. Support, Movement, Communication

• Cytoskeleton – includes cilia, flagella, filaments, microtubules

• Cell walls

• Extracellular matrix

• Cell junctions

What do these have in common?

• HIV infection

• Transplanted organs

• Communication between neurons

• Drug addiction

• Cystic fibrosis

• hypercholesteremia


• selectively permeable

• hold teams of enzymes

Membranes organize the chemical activities of cells

Cytoplasm

Figure 5.10

Plasma membrane

• Contact between cell and environment

• Keeps useful materials inside and harmful stuff outside

• Allows transport, communication in both directions

Plasma membrane components


Cholesterol

Proteins

Glycocalyx

polarhead

nonpolartails

P –


hydrophobic molecules hydrophilic molecules cytosol

THE PLASMA MEMBRANE

phospholipids cholesterol

cytoskeletonperipheralprotein

integralprotein

Cholesterol blocks some small molecules, adds fluidity

• Membrane Proteins– span entire membrane or lie on

either side– Purposes

• Structural Support• Recognition• Communication• Transport

• Glycocalyx

– Composed of sugars protruding from lipids and proteins

– Functions

• Binding sites for proteins

• Lubricate cells.

• Stick cells down.


• Many membrane proteins are enzymes

Figure 5.13

• Some proteins function as receptors for chemical messages from other cells

– The binding of a messenger to a receptor may trigger signal transduction

Enzyme activity Signal transduction

Messenger molecule

Receptor

Activated molecule


• The plasma membrane of an animal cell

Fibers of the extracellular matrix

Figure 5.12

Glycoprotein Carbohydrate (of glycoprotein)

Microfilaments of the cytoskeleton

Phospholipid

Cholesterol

Proteins

CYTOPLASM

Glycolipid

• Diffusion and Gradients

– Diffusion = movement of molecules from region of higher to lower concentration.

– Osmosis = diffusion of water across a membrane


• In passive transport, substances diffuse through membranes without work by the cell

EQUILIBRIUMMolecule of dye

Figure 5.14A & B

Membrane

EQUILIBRIUM

free water molecule: can fit through pore

bound water moleculesclustered around sugar:cannot fit through pore

pore

sugar

H2O

bagbursts

selectively permeable membrane

water molecule

pure water

sugar molecule

(a)

selectively permeable membrane

(b)


• water travels from an area of higher concentration to an area of lower water concentration

Osmosis = diffusion of water across a membraneHypotonicsolution

Figure 5.15

Solutemolecule

HYPOTONIC SOLUTION

Hypertonic solution

Selectivelypermeablemembrane

HYPERTONIC SOLUTION

Selectivelypermeablemembrane

NET FLOW OF WATER

Solute molecule with cluster of water molecules

Water molecule


• Osmosis causes cells to shrink in a hypertonic solution and swell in a hypotonic solution

Water balance between cells and their surroundings is crucial to organisms

osmoregulation = control of water balance

isotonic solution hypertonic solution hypotonic solution

10 microns

equal movement of waterinto and out of cells

net water movement out of cells

net water movement into cells

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• Small nonpolar molecules - simple diffusion

• Many molecules pass through protein pores by facilitated diffusion

Passive transport = diffusion across membranes

Figure 5.17

Solutemolecule

Transportprotein


• transport proteins needed

• against a concentration gradient

• requires energy (ATP)

Active transport


• Active transport in two solutes across a membrane

• Na+/K+ pump

• Protein shape changeFigure 5.18

Transportprotein

1

FLUIDOUTSIDECELL

Firstsolute

First solute, inside cell, binds to protein

Phosphorylated transport protein

2 ATP transfers phosphate to protein

3 Protein releases solute outside cell

4 Second solute binds to protein

Second solute

5 Phosphate detaches from protein

6 Protein releases second solute into cell


exocytosis = vesicle fuses with the membrane and expels its contents

Exocytosis and endocytosis transport large molecules

Figure 5.19A

FLUID OUTSIDE CELL

CYTOPLASM


– or the membrane may fold inward, trapping material from the outside (endocytosis)

Figure 5.19B

food particle

particle enclosed in vesicle

phagocytosis

1 32

Phagocytosis, “cell eating”

—How the human immune system ingests whole bacteria or one-celled creatures eat.


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(cytoplasm)

vesicle containing extracellular fluid

pinocytosis

2

extracellular fluid

plasma membrane

vesiclecytosol

receptors captured molecules

coatedpit

vesicle

bacterium pseudopodium

vesicle

Receptor-mediated endocytosis


• Cholesterol can accumulate in the blood if membranes lack cholesterol receptors

Figure 5.20

LDL PARTICLEPhospholipid outer layer

Protein

Cholesterol

Plasma membraneCYTOPLASM

Receptor protein

Vesicle

What do these have in common?

• HIV infection

• Transplanted organs

• Communication between neurons

• Drug addiction

• Cystic fibrosis

• hypercholesteremia

Copyright © 2003 Pearson Education, Inc. publishing as Benjamin Cummings Nuclei (yellow) and actin...

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