Cells

Wassily Kandinsky (1866-1944)

Cells

Figure 4.1x

Cell Theory:

- all organisms are composed of cells

- all cells come from other cells

• Scanning electron microscope (SEM)

Figure 4.1B

TEM

• Cell size and shape relate to function

• Minimum• Maximum

Figure 4.2

• A small cell has a greater ratio of surface area to volume than a large cell of the same shape

30 µm 10 µm

Surface areaof one large cube= 5,400 µm2

Total surface areaof 27 small cubes= 16,200 µm2Figure 4.3

Prokaryotic cells - “before nucleus”

- small, relatively simple cells–Single-celled organisms

2 kinds of cells: prokaryotic and

eukaryotic

- true nucleus

- larger: 10-100 microns

- often multicellular

- organelles surrounded by membranes

- usually need O2

Eukaryotic cells - functional compartments

What do these have in common?

• HIV infection• Transplanted organs• Communication between neurons• Drug addiction• Cystic fibrosis• hypercholesteremia

Plasma membrane

• Contact between cell and environment

• Keeps useful materials inside and harmful stuff outside

• Allows transport, communication in both directions

polarhead

nonpolartails

P –

hydrophobic molecules

hydrophilic molecules

cytosol

1. Phospholipid bilayer

Plasma membrane components

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

Fibers of the extracellular matrix

Figure 5.12

Glycoprotein Carbohydrate (of glycoprotein)

Microfilaments of the cytoskeleton

Phospholipid

Cholesterol

Proteins

CYTOPLASM

Glycolipid

• 2. Cholesterol - adds rigidity

Fluid mosaic model

• 3. Membrane Proteins - span entire membrane or lie on either side

•Structural Support•Recognition•Communication•Transport

How do molecules cross the plasma membrane?

• Passive transport

• Active transport

• Endocytosis and exocytosis

• Diffusion and gradients

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

–Osmosis = diffusion of water across a membrane

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

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

EQUILIBRIUMMolecule of dye

Figure 5.14A & B

Membrane

EQUILIBRIUM

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

• 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

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

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

Water balance between cells and their surroundings is crucial

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

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

• Small nonpolar molecules - simple diffusion

• Many molecules pass through protein pores by diffusion through channels.

• Facilitated diffusion

Passive transport = diffusion across membranes

Figure 5.17

Solutemolecule

Transportprotein

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

• against a concentration gradient

• transport proteins needed

• requires energy (ATP)

Active transport

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

• 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

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

exocytosis = vesicle fuses with the membrane and expels its contents

Exocytosis and endocytosis transport large molecules

Figure 5.19A

FLUID OUTSIDE CELL

CYTOPLASM

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

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

Figure 5.19B

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

human immune system ingests whole bacteria

Receptor-mediated endocytosis

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

• 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