2/18/2013

1

THE CELL

History of the microscope and cell

1500’s: Europe

Merchants used magnifying glasses to determine quality of cloth

Mid 1600’s: Holland, development of the microscope and telescope

1665: Robert Hooke (English)

** first to observe DEAD CELLS

1675: Anton van Leeuwenhoek (Dutch)

** first to observe LIVING CELLS

History, cont. 1833: Robert Brown (Scottish)

Discovered nucleus

1838: Matthias Schleiden (German)

Stated “all plants are made of cells”

1839: Theodor Schwann (Dutch)

Stated “all animals are made of cells”

1855: Rudolf Verchow (German MD)

Stated “all cells arise from other cells”

Characteristics of Microscopes

• magnification: ability to make an image larger than

actual size

• resolution: power to show details clearly while enlarged

(if poor, objects seem fuzzy)

Types of Microscopes

I. compound light

- light passes through one or more lenses

- object must be sliced thinly enough to be transparent

- upper limitation is 2000X or 0.5 microns (um) in diameter

II. Electron Microscopes

- limited by physical characteristics of light

- can magnify an image up to 200,000 X, or

2 nm in diameter

- beams of electrons produces enlarged

image

2/18/2013

2

Types of Electron Microscopes

1. transmission electron microscope (TEM)

- transmits a beam of electrons

through very thinly sliced specimen

- dead specimens

- 200,000 X magnification

- black and white only

Plant Cell

2. scanning electron microscope (SEM)

- three dimensional images

- beam of electrons passed over specimens surface

- 100,000 X mag.

- dead specimens only

3. scanning tunneling microscope

- computer tracks movement of probe across object

- produces 3 D images

- can be used on living organisms

CELL THEORY

1. all living things are composed of cells

2. cells are basic units of structure and

function

3. all cells come from pre- existing cells

How cells differ

1. size

- most cells are 5-50 microns

surface area ratio (limits size of cells)

inside of cell grows faster: cubed

(V = L x W x H)

outside of cell grows slower: squared

(A = L x W)

Relationship of Surface Area to Volume

LENGTH OF

SIDE

(CM)

TOTAL

SURFACE

AREA (CM2)

TOTAL

VOLUME

(CM3)

SURFACE

AREA TO

VOLUME

RATIO

1

(1X1X6)= 6

(1X1X1)=1

6:1

2

(2X2X6)=24

(2X2X2)=8

24:8

3:1

3

(3X3X6)= 54

(3X3X3)=27

54:27

2:1

2/18/2013

3

2. shape

- most spherical or cuboidal

- different shapes reflect function

dermal epidermal cells

white blood cells

goblet cell

red blood cells

nerve cell

3. internal organization

- organized by nucleus and organelles

- 2 types cells

1. prokaryotes:

- no nucleus or membrane

bound organelles

- more primitive cells

(bacteria)

- no compartments within

cytoplasm so ribosomes,

enzymes, DNA free floating

- contain cell walls- made of peptidoglycans

(polysaccharides connected by short chains of a. a. )

- flagella: whiplike structures for movement

Types of cells, cont.

2. eukaryotes:

- contain nucleus and membrane

bound organelles

- unicellular eukaryotes have

flagella or cilia for movement

- much more complex cells

Common features of all cells

- cell membrane (plasma membrane)

- cytoplasm: gel like , holds cellular structures

- cytoskeleton: microscopic protein fibers that keep cells shape

- ribosomes: make proteins

- DNA: controls all cell activities

CELL STRUCTURE

Main components of eukaryotic cells

1. cell membrane (outer boundary)

2. nucleus (control center)

3. cytoplasm (material between nucleus

and membrane)

ANIMAL CELLS

Cell Membrane

(plasma membrane)

Functions:

- separates cells from surroundings

- regulates substance movement

(bring in nutrients, remove wastes)

- selectively permeable

- protection and support

- gives shape and flexibility

- signal receptor from other cells

2/18/2013

4

Fluid mosaic model of Cell Membrane

liquid phospholipid bilayer (water insoluble, no movement through)

- polar outside (head- phospholipid, hydrophilic)

- nonpolar inside (tail- two fatty acids, hydrophobic)

- polar outside (head- phospholipid, hydrophilic)

Polar: hydrophilic; attracts other polar and ionic compounds

Non-polar: hydrophobic; will not allow most polar molecules, ions, or large

molecules to pass across the membrane

animation – permeability animation – fluid mosaic

Membrane Proteins 1. transport proteins:

- involved in facilitated diffusion

(water soluble mols. not soluble in fat portion of membrane, so need help)

- go through the entire membrane

2 types

channel: gated pores

move water and ions freely in and out of cell

carrier: substrate binds to site on protein

protein changes shape and exposes substrate to cytoplasm

2. recognition proteins: recognizes substances

(like tips of icebergs emerging from ocean surface)

- Contain carbohydrate antennas (glycoproteins)

- Used as chemical ID markers to differential cell types

***cell/cell recognition (immune response)

***embryo cells tissues organ systems

3. receptor proteins: binds to specific molecules

(neurotransmitters, blood antigens, hormones)

- initiates cell response

4. enzymes: embedded in cell membrane to catalyze biochemical

reactions in cell

called FLUID MOSAIC because:

lipids and protein are liquid in nature and can move around each other

membrane is DYNAMIC (always changing)

Nucleus

- control center of cell: directs all cell activities

- contains chromosomes

- site of DNA and RNA synthesis

- located in center of most cells

2/18/2013

5

Structure:

- nuclear matrix - protein skeleton helps maintain nucleus shape

- nuclear envelope (double membrane)

- contains chromatin: combination of strands of DNA and protein

- nuclear pores: control substance movement

- nucleoplasm: dense, protein rich

- nucleolus: partially assembles ribosomes for protein synthesis

Cytoplasm

(between membrane and nucleus)

- contains cytosol

– gel like material between nucleus and cell membrane

– contains water, salts, organic molecules

– in constant motion (cytoplasmic streaming)

animation

amoeba animation

– holds organelles

Cell virtual tour

Organelles

Organelle: tiny structure that performs

special functions in the cell

to maintain life

Mitochondria

• powerhouse of cell (cell respiration)

• provides energy for cell in form of ATP

• membrane bound

• most numerous in cells which use a lot of energy (muscle)

• self replicating, contain their own DNA

- cristae: greatly enlarge surface area of inner membrane

(more area for chemical reactions of respiration)

Ribosomes

• spherical structures which make proteins

• not surrounded by membrane

• composed of protein and nucleic acids

• site of protein synthesis

Endoplasmic reticulum: (ER) intercellular highway

complex membrane system of folded sacs and tunnels

Rough ER - ribosomes stuck to membrane

surface

- newly produced proteins are

inserted into ER

- can be stored or exported to

smooth ER

- prominent in cells that make a lot

of protein

Smooth ER

- no ribosomes

- also stores and acts as an

intercellular highway for proteins and

enzymes

- involved in:

- synthesis of steroids in gland

- cell regulation of Ca levels

in muscle

- cells break down toxic

substances in liver cells

2/18/2013

6

Golgi Apparatus

• flattened system of membranes and sacs piles on each other

(like pancakes)

• very close to ER

• processes, packages, and secretes proteins

to other parts of cell

Steps of Protein Production and Transport

1. ribosomes make proteins on the rough ER- packaged into vesicles

2. vesicles transport the newly made proteins from the rough to the Golgi

apparatus

3. in Golgi, proteins are processed and then packaged into NEW vesicles

4. vesicles move thru Golgi to cell membrane and release contents outside cell

animation 2

Lysosomes

• small round vesicles that contain digestive enzymes

• formed from Golgi Apparatus

• digest and remove waste from cell (old organelles, byproducts,

bact., viruses)

animation

Peroxisomes

• contain different oxidative enzymes than lysosomes

• break down toxic substances into H2O2

- detox alcohol and drugs

- break down fatty acids

• formed from proteins in cytosol, not Golgi

Cytoskeleton (cell framework)

• maintains shape and size of cell

• composed of network of long protein strands

located in cytosol

• not surrounded by membranes

• provides movement for organelles within

cytosol

Cytoskeleton Structure

A. Intermediate Filaments

- protein fibers coiled into cables

- anchor nucleus and maintain its shape

2/18/2013

7

Cytoskeleton Structure

B. Microtubules

- long hollow coiled protein tubes (tubulin)

- maintain shape and support cells

- internal cell highways – move organelles thru cell

- form centrioles (cell division)

- motility (cilia and flagella)

• flagella: long whip-like structures used for movement

• cilia: short numerous hair like projections

- movement

- transport of substances across cell

ex: ear drum: transmits sound waves

respiratory tract: moves mucus etc.

Internal Organization

9 + 2 Arrangement

animation respiratory system animation

Cytoskeleton Structure

C. Microfilaments

- two strands fine protein (actin) intertwined

- used in cytoplasmic streaming, muscle

contraction

- smallest strands of cytoskeleton

cytoplasmic streaming

PLANT CELLS

Contain the same

organelles as

animal cells plus the

following:

1. cell walls

2. vacuoles

3. plastids

Cell wall

• rigid covering of plant cells, algae, and some bacteria

• composed of long chains of cellulose embedded in

hardened lignin and pectin

• very porous (O, H2O, CO2 easily

pass through)

• function: support & protection

2/18/2013

8

Structure - middle lamella

• laid first, formed from the cell plate during cytokenesis

• pectin: gluey substance holds cells together

- primary cell wall

• forms next, expanded inside the middle lamella

• cellulose: structure and support

- secondary wall

• constructed between the plant cell and primary wall after a maximum size has been reached and stops growing

• lignin: very stiff and hard, in woody plants in bark structure and support

Central Vacuoles

• sac like structures that

store water, salts,

enzymes, and wastes

• usually take up ~ 90% of

cell volume

• push membrane against

wall and responsible for

turgidity

Plastids Convert solar energy into chemical energy to be stored.

3 types (arise from proplastids)

1. chloroplasts- chlorophyll (green pigment)

used in photosynthesis

2. chromoplasts- synthesize and store red, orange, and yellow pigments (give plants unusual colors)

3. leucoplasts- store starches, proteins, and lipids

colorless

Cell Differences

Shape: animal- round

plant- square

Animal cells do not contain:

cell wall

central vacuole

plastids

Plant cells do not contain:

centrioles

lysosomes

Levels of Structure

Cells Tissues Organs Organ Systems

The End