CELLSCell Theory,

Microscopy,Prokaryotes, Eukaryotes, Animal Cell, Plant Cell

CELL THEORY1. All living things are composed of cells

and their products.

1. New cells are formed only by the division of existing cells.

1. The cell is the functioning unit of life; the chemical reactions of life take place within cells.

Microscopy

Compound light microscopes

Use visible light and a combination of lenses to magnify objects up to 1000 times.

Electron microscopesUse a beam of electrons, instead of light, to produce image

Transmission Electron Microscope (TEM)

• Extremely thin sections• Electrons pass through

some parts of specimen and not others, forming image

• Good for organelle structure

• Magnifies up to 250,000 times

TEM image

LE 6-41 µm

1 µm

Scanning electronmicroscopy (SEM) Cilia

Longitudinalsection ofcilium

Transmission electronmicroscopy (TEM)

Cross sectionof cilium

Scanning Electron Microscope• Scans sample with a

beam of electrons.

• Magnifies up to 100,000 times

SEM image

Advantages of light microscopes

• Easy, inexpensive sample preparation

• Allows examination of live material (movement; no artificial structures)

• Colors can be seen (natural and stains)

• Field of view is relatively large (1.8 mm at 100X magnification)

Advantage of electron microscopes• Excellent resolution, allowing for

extremely high magnification–This permits examination of very

small objects and details of cell structure

Prokaryotic Cells

Prokaryotic Cells (Bacteria)• Pro – before

• Karyon – nucleus

Prokaryote = Before Nucleus

Electron microscope views of prokaryotic cells

The outer layer has 2 parts• Cell wall – forms protective outer

layer which prevents damage from outside and bursting if internal pressure is high

• Plasma membrane – controls entry and exit of substances, some by active transport

CELLSEukaryotic Cells

Prokaryotic vs. Eukaryotic Cells• Cells are prokaryotic or eukaryotic• Prokaryotic cells are Bacteria• Protozoa, Fungi, Animals, and Plants

all consist of eukaryotic cells

Prokaryotic vs Eukaryotic Cells• Similarities

– Plasma membrane– Semifluid substance called the cytoplasm– DNA - Chromosomes (carry genes)– Ribosomes (make protein)

Differences• Prokaryotic cells have no nucleus• Prokaryotic cells lack membrane-bound organelles• Eukaryotic cells have DNA in a nucleus that is bound by a membrane

(nuclear envelope)• Eukaryotic cells have membrane-bound organelles

– Organelle: one of several formed bodies with specialized functions, suspended in the cytoplasm of eukaryotic cells

LE 6-7

Total surface area(height x width xnumber of sides xnumber of boxes)

6

125 125

150 750

1

11

5

1.2 66

Total volume(height x width x lengthX number of boxes)

Surface-to-volumeratio(surface area volume)

Surface area increases whileTotal volume remains constant

• The plasma membrane is a selective barrier that allows passage of oxygen, nutrients, and waste

Plasma membrane must have sufficient surface area to service the volume of the cell

A Panoramic View of the Eukaryotic Cell

• A eukaryotic cell has internal membranes that partition the cell into organelles

• Plant and animal cells have most of the same organelles

LE 6-9aFlagellum

Centrosome

CYTOSKELETON

Microfilaments

Intermediate filaments

Microtubules

Peroxisome

Microvilli

ENDOPLASMIC RETICULUM (ER

Rough ER Smooth ER

Mitochondrion Lysosome

Golgi apparatus

Ribosomes:

Plasma membrane

Nuclear envelope

NUCLEUS

In animal cells but not plant cells: •Lysosomes•Centrioles•Flagella (in some plant sperm)

Nucleolus

Chromatin

LE 6-9bRoughendoplasmicreticulum

In plant cells but not animal cells:•Chloroplasts•Central vacuole•Cell wall•Plasmodesmata

Smoothendoplasmicreticulum

Ribosomes(small brown dots)

Central vacuole

MicrofilamentsIntermediatefilamentsMicrotubules

CYTOSKELETON

Chloroplast

PlasmodesmataWall of adjacent cell

Cell wall

Nuclearenvelope

NucleolusChromatin

NUCLEUS

Centrosome

Golgiapparatus

Mitochondrion

Peroxisome

Plasmamembrane

LE 6-29a

EXTRACELLULAR FLUID ProteoglycancomplexCollagen

fiber

Fibronectin

Integrin Micro-filaments

CYTOPLASM

Plasmamembrane

Extra-Cellular Matrix

MembranesStructure and Function

Plasma Membrane• Also known as “cell membrane”• Surrounds all cells

– In cells with cell walls, the plasma membrane is found inside the cell wall

plasma membrane is a bilayer of phospholipids

Phospholipid molecules have a hydrophilic region and a hydrophobic region

LE 7-2

Hydrophilichead

Hydrophobictail

WATER

WATER

•Most cells have watery environment on both sides of membrane•Water attracts the polar phosphate ends of the phospholipids•Phospholipids align to form double layer membrane, with polar ends on outside of each layer of the membrane•Non-polar tails are inside the bilayer

LE 7-3

Hydrophilic regionof protein

Hydrophobic region of protein

Phospholipidbilayer

LE 7-4

Knife

Cytoplasmic layerExtracellular layer

Cytoplasmic layer

Plasmamembrane

Extracellular layer

Proteins

Membrane Proteins

• A membrane is a collage of different proteins embedded in the fluid matrix of the lipid bilayer

• PeripheralPeripheral proteins are not embedded, they are attached to the membrane surface

• IntegralIntegral proteins penetrate the hydrophobic core and often span the membrane

LE 7-7

Fibers ofextracellularmatrix (ECM)

Glycoprotein

Carbohydrate

Microfilamentsof cytoskeleton

Cholesterol

Integralprotein

Peripheralproteins

CYTOPLASMIC SIDEOF MEMBRANE

EXTRACELLULARSIDE OFMEMBRANE

Glycolipid

LE 7-5c

CholesterolCholesterol within the animal plasma membrane

Functions of Membrane Proteins

• Proteins determine most of the membrane’s functions. They serve as:

1. Hormone binding sites2. Enzymes3. Cell–Cell joining & Communication4. Channels for passive transport5. Pumps for active transport

Transport across the plasma membrane Remember…..

The plasma membrane controls what comes in and out of the cell.

Selective Permeability• Most biologic membranes are

selectively or semi-permeable–This means that they allow some

things through, but not others

Permeability• If substance CAN diffuse across

membrane, membrane is permeable to that substance

• If substance CANNOT diffuse across membrane, membrane is impermeable to the substance

One Way that Some Substances can Cross the Membrane is by Diffusion

• Definition of diffusion:–Movement of particles from area

where they are more concentrated to area where they are less concentrated

• Diffusion is the tendency for molecules to spread out evenly into the available space.

• Substances diffuse down their concentration gradient, that is, from an area where they are more highly concentrated to an area where they are less concentrated.

Diffusion, cont’d.

LE 7-11a

Molecules of dye Membrane (cross section)

WATER

Net diffusion Net diffusion Equilibrium

Diffusion of one solute

LE 7-11b

Net diffusion Net diffusion Equilibrium

Diffusion of two solutes

Net diffusion Net diffusion Equilibrium

Diffusion, cont’d.• Diffusion across plasma membrane

is a form of passive transport, because no work must be done to move substances down the concentration gradient– Passive Transport: transport across

the membrane that requires no energy from the cell.

Diffusion, cont’d.• Hydrophobic, non-polar molecules can

dissolve in and cross a membrane unassisted.– Hydrocarbons– CO2

– O2

Animation: Diffusion

Facilitated Diffusion

• Diffusion of some other substances across the cell membrane is assisted, or “facilitated,” by protein channels within the membrane

• Usually involves large or strongly charged molecules, which cannot dissolve in the lipid bilayer.

Facilitated diffusion• Even though movement is facilitated, it

will still only occur from region of high concentration to region of low concentration.

• Facilitated diffusion is still PASSIVE transport

Examples of molecules moving via facilitated diffusion

• Some ions and polar molecules (e.g. water)

• Aquaporins are channel proteins which greatly speed up the diffusion of water.

Animation: Membrane Selectivity

Osmosis

• DefinitionDefinition: diffusion of water across a selectively permeable membrane

• Water diffuses down its own concentration gradient, which is affected by solute concentration.

• Binding of water molecules to solute particles lowers the proportion of unbound water that is free to cross the membrane.

Osmosis and water balance in cells, parts 1 and 2

LE 7-12Lowerconcentrationof solute (sugar)

Higherconcentrationof sugar

Same concentrationof sugar

Selectivelypermeable mem-brane: sugar mole-cules cannot passthrough pores, butwater molecules can

H2O

Osmosis

• IsotonicIsotonic solution: solute concentration is the same as that inside the cell; no net water movement across the plasma membrane

• HypertonicHypertonic solution: solute concentration is greater than that inside the cell; cell loses water

• HypotonicHypotonic solution: solute concentration is less than that inside the cell; cell gains water

Tonicity is the ability of a solution to cause a cell to gain or lose water

Solutions inside and outside cell are isotonic

10% salt, 90% H2O

10% salt 90% H2O

Solution outside cell is hypertonic to that inside cell

20% salt, 80% H2O

10% salt 90% H2O

20% salt, 80% H2O

Salt sucks.

Solution outside cell is hypotonic to that inside cell

5% salt, 95% H2O

10% salt, 90% H2O

Salt sucks.

Osmotic Pressure

• Created when water diffuses into a cell

• In animals and other organisms without cell walls, cells swell and may burst

• To maintain their internal environment, organisms without cell walls must have adaptations for osmoregulation, the control of water balance

• The protist Paramecium, which is hypertonic to its pond water environment, has a contractile vacuole that acts as a pump

Osmotic Pressure in Cells without Walls, cont’d.

LE 7-14Filling vacuole

50 µm

50 µmContracting vacuole

Video: Paramecium Vacuole

Osmotic Pressure in Cells without Walls, cont’d.• Plasmolysis occurs when water

diffuses out of a cell• Cells shrink

Osmotic Pressure in Cells with Walls

• Cell walls help maintain water balance

• In a hypotonic solution, turgor pressure causes the cell to swell until the wall opposes uptake; the cell is now turgid (firm)

Video: Turgid Elodea

Osmotic Pressure in Cells with Walls, cont’d.• If a plant cell and its surroundings are

isotonic, there is no net movement of water into the cell; the cell becomes flaccid (limp), and the plant may wilt

• In a hypertonic environment, plant cells lose water (plasmolysis); vacuoles collapse, and eventually, the membrane pulls away from the wall.

Video: Plasmolysis

Plasmolysis in Red Onion Cells

Cells in hypotonic solution; water has diffused into cells, creating turgor pressure

Cells in hypertonic solution; water has diffused out of cells, causing them to shrink away from their cell walls

Plasmolysis in Cucumber Cells

Cells in pure water environment; water has diffused into cells, creating turgor pressure

Cells in hypertonic environment; water has diffused out of cells, causing them to shrink away from their cell walls

LE 7-13

Animalcell

Lysed

H2O H2O H2O

Normal

Hypotonic solution Isotonic solution Hypertonic solution

H2O

Shriveled

H2OH2OH2OH2OPlantcell

Turgid (normal) Flaccid Plasmolyzed

Osmosis and water balance in cells, parts 3 and 4

Active Transport• Involves movement of substances

across the cell membrane from area of LOWER concentration to area of HIGHER concentration

• Since movement is against the concentration gradient, it REQUIRES ENERGY from the cell

Active Transport using Membrane Protein “Pumps”

• Active transport of small molecules and ions is usually carried out by membrane proteins that act as energy-requiring pumps

• Changes in the shape of these membrane proteins play an important role

Activity – Active Transport

Active Transport by Endocytosis and Exocytosis

• Endocytosis – Requires Energy!– Materials taken into the cell by means of

infoldings or pockets of the cell membrane– Pocket breaks loose and forms vacuole

within the cytoplasm– Vacuole may fuse with a lysosome, so

material in vacuole can be digested

• http://bio.winona.msus.edu/bates/genbio/images/endocytosis.gif

Exocytosis – Requires Energy!• Way for cell to release large amount of

material from a vacuole to outside of cell

• Membrane surrounding the vacuole fuses with cell membrane

• Contents of vacuole expelled out of the cell

http://www.emc.maricopa.edu/faculty/farabee/BIOBK/endocytosis.gif

Activity – Endocytosis and Exocytosis