Cells

How big are cells?This is the head of

a pin at 100 µmThis is the same

pin magnified and your view is at 20 µm. What you see are rod-shaped bacteria.

Finally, the bacteria magnified. The view is 0.5 µm

Who discovered cells?Robert Hooke

Hooke was engaged in many aspects of science, including chemistry, physics, mechanics, and his name is attributed to the discovery of the Law of Elasticity.

His most famous discovery however, involves microscopy. In 1665 Hooke published Microphagia. In his book, he

described the first cells, and even coined the word cells.

He was looking at dead plant cells in cork.

Cork cells at 400x magnification

Who discovered cells?Anton Van

LeeuwenhoekVan Leeuwenhoek was

a Dutch trader and scientist, whose knowledge of glass allowed him to create his own microscopes.

He is known as the father of microbiology.

He was the first to describe:ProtozoaBacteriaThe vacuole of the cellSpermatozoa (he called

these animalcules)And muscle fibers

protozoa

Who discovered cells?Matthias

Schleiden ,Theodor Schwann, and Robert BrownIn the 1820’s, improved

lenses brought cells into sharper focus.

BrownFirst to identify plant cell

nucleusSchleiden

First to propose that plant cells may be an independent unit apart from the plant.

SchwannReported that cells and

their products made up both plants and animals.

Onion cells

nucleus

Who discovered cells?Rudolf Virchow

Studied how cells divide (mitosis and meiosis)

Every cell, he decided, must come from a cell that already exists.

Cell division

What is the Cell Theory?All of these discoveries lead

to the cell theory1. Organisms consist of one

or more cells.2. The cell is the most basic

unit of life.3. All cells come from other

cells.

amoeba

neuron binary fission

What is a cell?The cell is the smallest unit

with the properties of life: metabolism, response to environment, growth, and reproduction.

All cells have three things in common.A plasma membrane

separates each cell from the environment, permits the flow of molecules across the membrane, and contains receptors that affects the cell’s activities.

A nucleus localizes hereditary material, which can be copied and read.

All cells have some sort of cytoplasm.

Macrophage (a type of white-blood cell) eating

bacteria

Why aren’t cells bigger?The cell is constrained by

the surface-to-volume ratio.

If a cell expands in diameter during growth, its volume will increase more rapidly than its surface area will.

A cell that is too large will not be able to move materials into and out of the cell interior.

The smaller the cell, the more efficiently materials cross its surface and become disturbed through the interior.

Prokaryotic Cells Prokaryotes are the smallest known

cells and are the most metabolically diverse forms of life on earth.

Two domains of prokaryotes exist: Bacteria and ArchaeaThe term prokaryotic means “before

the nucleus” and indicates the existence of bacteria before the evolution of cells with a nucleus. In fact, prokaryotes don’t have ANY

organelles.Prokaryotes have a rigid cell wall, and

sticky polysaccharides (carbohydrates) help cells attach to surfaces, such as teeth. Many bacteria have the ability to

photosynthesize like plants.The bacterial chromosome is a singular,

circular DNA molecule. All prokaryotes are unicellular.

Eukaryotic CellsEukaryotic cells (true

nucleus) are larger and generally more complex with a nucleus and other membrane-bound organelles.The nucleus contains the

genetic material of the cell.

All multi-cellular organisms are eukaryotic.

Some unicellular organisms are also eukaryotic.

Plasma MembraneIn BOTH plant and animal cells

Lipid bi-layer of plasma membranes forms a boundary between the inside and outside of the cell.

Regulates the entry/exit of substances.Proteins embedded in the lipid bilayer or positioned

at one of its surfaces serve as channels, pumps, or receptors.Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

The NucleusIn BOTH plants and animal cells

Nuclear envelopeA nuclear envelope encloses the

semi-fluid intereior of the nucleus called the nucleoplasm.

The ribosome-bound outer membrane is loaded with pores, and it is continuous with the endoplasmic reticulum.

NucleolusDark globular mass where

ribosomes are made.Nuclear DNA

Chromatin refers to the cell’s total collection of DNA and associated proteins.

A chromosome is a double-stranded DNA molecule and its associated proteins.

Endoplasmic Reticulum In BOTH plant and animal

cellsThe endoplasmic reticulum

(ER) is a collection of interconnected tubes and flattened sacs that begin at the nucleus and ramble through the cytoplasm.

There are two types of ER distinguished by the presence or absence of ribosomes. Rough ER

Has ribosomes on its surface and looks “rough”

Lipids for use outside the cell (like hormones) are manufactured here

Smooth ER Has NO ribosomes on its

surface and looks “smooth” Lipids for use inside the cell

(like more cytoplasm) are manufactured here.

RibosomesIn BOTH plant and

animal cellsMade in the

nucleolus and located throughout the cytoplasm and on the rough ER.

They help make proteins.They are made of a

small and large subunit that assists in threading protein.

Golgi BodiesIn BOTH plants and

animal cellsIn the golgi bodies

(also golgi apparatus), proteins and lipids undergo final processing, sorting, and packaging.

The membranes of the golgi are arranged in stacks of flattened sacs whose edges break away as vesicles.

LysosomesIn BOTH plant and

animal cellsThey are rare in plant cells

but are there at times.Lysosomes are vesicles

that bud from the golgi bodies.

They carry powerful enzymes that can digest the contents of other vesicles, worn-out cell parts, or bacteria and foreign particles.

They are programmed for cell-death (apoptosis).

PeroxisomesIn BOTH plants and

animal cellsVesicles like

lysosomes that contain enzymes that break down fatty acids and amino acids.

Central VacuoleIn PLANTS ONLY

Accumulates a watery solution of ions, amino acids, sugars, and toxic substances.Vacuoles enlarge during

growth and greatly increase the cell’s outer surface area.The enlarged cell, with

more surface area, has an enhanced ability to absorb nutrients.

MitochondriaIn BOTH plants and animals

Are the primary organelles for making useable energy for the cells.Each mitochondrion has two membranes,

and inner folded membrane (cristae) surrounded by a smooth outer membrane.

Inner and outer compartments formed by the membranes are important in energy transformation.

Mitochondria resemble bacteria in size and biochemistry.Like bacteria they have their own DNA

and divide on their own apart from the cell.

They have ribosomes.Endosymbiosis is a theory that explains

how mitochondria may have once been independent prokaryotic cells that were engulfed by another cell but became permanent.

ChloroplastsIn PLANTS ONLY

Oval or disk-shaped organelle, bound by a double membrane, and specialized for photosynthesis. In the innermost membrane,

stacked disks (thylakoids), pigments and enzymes trap sunlight energy to form ATP and NADPH.

Sugars and starches are formed in the fluid substance (stroma) surrounding the stacks.

Pigments such as chlorophyll (green) confer distinctive colors to the chloroplasts.

ChromoplastsIn PLANTS ONLY

store red and brown pigments that give color to flowers, autumn leaves, fruits, and roots.

Cell WallsIn PLANTS CELLS only

Cell walls are carbohydrate frameworks (cellulose) for mechanical support in bacteria, protistans, fungi, and plants.Cell walls have an inner

and outer wall.It makes plant parts

stronger, more waterproof, and less inviting to insects.

CytoskeletonIn BOTH plant and

animal cellsSupporting matrix of

protein fibersMaintains cell shape and

acts as a scaffold upon which organelles are attached.

Composed of microfiliments, microtubules and many other supportive proteins.

These animal cells are stained to show the cytoskeleton.

microtubules (green), microfilaments (red), and nuclei

(blue).

How do cells move?Cells can move with a variety

of structures.Cilia

These are short, numerous, hair-like extensions of the cell membrane.

Found on free-living cells.Flagella

Long, not usually numerous.Found in one-celled protozoans

and spermatazoa.Pseudopods

“false feet”Temporary lobes that project from

the cell, used in locomotion and cell capture.