Download Cell Theory and Structure

Cell Theory and Cell Structure
Mr. Taylor
Biology
Rainier High School
Originators of the Cell Theory
Mattius Schleiden: Said ALL plants are
made of cells.
Theodor Schwann: Said ALL animals
are made of cells.
Rudolph Virchow: Said ALL cells come
from other living cells.
The Cell Theory
The Cell Theory is composed of 3 ideas:
 All living things are made of one or
more cells.
 Cells are the basic unit of structure and
function in organisms.
 All cells arise from existing living cells.
Cellular Structure
Cells remain little to maintain a favorable
surface area-to-volume ratio.
Cellular Structure

ALL cells have the following structures:

Cell (plasma) membrane: regulates what enters
and leaves the cell.
 Cytoplasm: the mostly liquid interior of the cell
(inside the cell membrane, outside the nucleus if
one present).
 Cytoskeleton: Structural system of microfibers and
microtubules
 Ribosomes: protein manufacturing sites.
 DNA: the genetic code for the cell.
“Cyto” means ‘cell’

Cellular Structure: Prokaryotes
“Pro” means ‘before’, “karyo” means ‘nucleus’.
ALL prokaryotes
 are unicellular.
 contain DNA in a single circular molecule.
Cellular Structure: Prokaryotes
“Pro” means ‘before’, “karyo” means ‘nucleus’.
Modern prokaryotes:
 are bacteria.
 have a cell wall made of polysaccharides
 gives the cell support and shape.

some bacteria also have a cell capsule
 allows the bacteria to cling to almost any surface
… teeth, skin, shoes, leaves, etc.
Cellular Structure: Prokaryotes
Modern prokaryotes:
 many bacteria have one or more flagella
(whip-like structures used for movement.)
Cellular Structure: Eukaryotes

“Eu” means ‘good’, “karyo” means ‘nucleus’.

Eukaryotes
– are unicellular or multicellular.
– have a cytoplasm with various membrane-bound
organelles.
– contain DNA in a nucleus.
– some have flagella or cilia



cilia are small hair-like projections from the cell
membrane.
both can be used for cellular movement
both can be used to move something into or away from
the cell.
Cellular Structure: Eukaryotes
Cellular Structure: Cell Membrane



The cell membrane is a flexible/fluid
membrane and is selectively permeable.
It consists of two lipid layers (fatty
molecules) with proteins embedded in it.
For this reason the membrane is often called
a lipid bilayer.
Cellular Structure: Organelles
1. Ribosomes
The site of protein synthesis
 Some ribosomes float free in the cytoplasm …
those produce proteins that stay in the cell.
 Some ribosomes are attached to the ER … those
produce proteins that leave the cell.
 These are very small organelles and are found in
both prokaryotes and eukaryotes.

Cellular Structure: Organelles
2. Endoplasmic Reticulum
– Has a membrane structure similar to the
plasma membrane.
– Moves substances and organelles around
in the cytoplasm.
Smooth ER: no ribosomes. Produces lipids
and breaks down toxic substances.
 Rough ER: has ribosomes. Contributes to
protein synthesis.

Cellular Structure: Organelles
3. Golgi bodies (apparatus)
– Package and distribute proteins
– These proteins can be useful or waste
products
– Most often these packets are carried to
the plasma membrane where they release
their proteins outside the cell.
Cellular Structure: Organelles
4. Lysosomes (“lyse” means ‘to cut’)
 Contain enzymes that digest proteins,
nucleic acids, carbohydrates, etc.
Cellular Structure: Organelles
5. Mitochondria: the powerhouse of the
cell.
 Mitochondria produce ATP (a high
energy molecule) from organic
molecules (food).
 High energy need cells have many
mitochondria (muscle, lining of
digestive tract, brain)
 Low energy need cells have few
mitochondria (fat cells).
Cellular Structure: Organelles
6. Vacuoles (more in plants than
animals).
 Membrane-bound compartments that
store lipids, carbohydrates, proteins,
and sometimes waste products.
Plant cells have a large central vacuole
that is critical in maintaining the plant’s
shape and giving it support. Loss of
water from the central vacuole will lead to
loss of turgor and the plant wilts.
Cellular Structure: Organelles
7. Plastids: found in plants and algae
ONLY!
 These are storage organelles
– Leukoplasts store food
– Chromoplasts store pigments
– Chloroplasts store chlorophyll and is the site
of photosynthesis.
Cellular Structure: Organelles
Other organelles:
8. Microtubules: provide support and
shape for the cell.
9. Spindle fibers: only present during cell
division.
10. Centrioles: present all the time, but
active only during cell division. (animal
cells only)
11. Cilia and flagella: movement.
Cellular Structure: Plant Cells

Plant cells have some special
structures that help them perform their
activities.
– A cell wall made with cellulose. This
gives the plant support, protection, shape,
and helps attach one cell to its neighbors.
– Chloroplasts: the site of photosynthesis.
– Large central vacuole