Chapter 22 Part 3
Cells and cell structure
For this part read 22.2 (pg 478) through 22.6 (pg.487)
I. Cell Theory- history
• Anton van Leeuwenhoek- dutch biologist
• Called the ‘father of the microscope’
• Developed first truly usable microscope
• Made detailed drawings of life in pond water
• Robert Hooke- english biologist
• Named ‘cells’ while studying cork
• Opened up the study of cells
• Robert Brown- scottish 1833
• Named ‘nucleus’ as center of cells
Cell Theory Contributors
• Matthias Schleidan- 1838
• All plants made of cells
• Theodor Schwann- 1839
• All animals made of cells
• Rudolf Virchow- 1855
• All cells arise from the division of preexisting
cells
Current Cell Theory
1. All living things are made up of cells
2. Cells are the basic units of structure and
function in living things
3. All cells come from preexisting cells
II. Two Types of Cells
• Prokaryotic- simplistic cells found in
bacteria
• Eukaryotic- more sophisticated cells found
in all other living things
Prokaryotes- original cells
• Have existed on the planet for 3.5-4 billions
years ago and were the only living things
on the planet for several billion years.
• Are single-celled organisms
• All bacteria are prokaryotes
• Are much smaller than eukaryotes
• Have very simplistic structures
Prokaryotes do not have
membrane enclosed organelles
• The main difference between prokaryotes
and eukaryotes is that prokaryotes do not
contain the sophisticated structures that
eurkayotic cells contain.
• **Bacteria cells do not show a nucleus
when you’re looking at them through a
microscope.
More
• They do not contain a nucleus- their DNA is
contained in a single circular chromosome.
• They also do not have structures that are
found in eukaryotic cells: mitochondria,
chloroplasts, endoplasmic reticulum, golgi
apparatus, etc.
• Their structures are much more simple
Very important
• Although they do not contain the
sophisticated structures found in
eukaryotes, prokaryotes carry on all the
functions that eukaryotes do.
• For example: just because they do not
contain a nucleus does not mean that they
don’t have DNA- it is just not contained in a
nucleus.
Typical prokaryote
• Generally prokaryotic cells
have a cell wall and cell
membrane that form their
outside capsule
• They also have a nucleoid
which is a single circular piece
of DNA
• Ribosomes
• Perhaps flagella or cilia which
aid in movement
III Cell Structure
• Enormous variety in the size and shape of
cells
• Smallest cells- the bacteria Mycoplasma - 0.2
micrometers
• Micrometer- one millionth of a meter
• Largest unicellular organisms- amoeba
(protist) Chaos chaos – 1000 micrometers
• Largest single cell- egg yolks of birds
• Average cell size – 5-50 micrometers
Basic Structurescommon to many cells- but not all
• Cell membrane- outer boundary of cell
• Nucleus- control center
• Cytoplasm- material between cell
membrane and nucleus
Cell Membrane
• Function
• Regulates what enters and exits the cell
• Aids in the protection and support of the cell
Cell Membrane
• Structure
• Bilayer of phospholipids with protein
molecules and carbohydrate chains that help
with cell identification and channels through
which molecules pass
Cell Wall – plants, algae and some
bacteria
• Lies outside of cell membrane
• Helps support the cell
• Very porous- allows water, carbon dioxide,
oxygen and other things to easily pass
through
• **You can see a cell wall in a
plant cell when viewed through a
Scope- they also look square/rect.
Cell wall formation
• The first layer to form develops when two plant cells
meet- contains pectin-a gluey substance that helps
hold cells together
• Each cell then forms a primary cell wall made of
cellulose
• In woody cells, a secondary cell wall forms made of
cellulose and lignin
• Lignin makes cellulose more rigid- wood consists
mainly of secondary cell walls
• Note: The cell wall found in prokaryotic bacteria is a
totally different structure
Nucleus- found in eukaryotes
• Eukaryotes- organisms whose cells contain
nuclei and other membrane enclosed organelles
• Protists, fungi, plants, animals
• Prokaryotes- organisms whose cells lack nuclei
and any other membrane enclosed organelles
(mitochondria, chloroplasts, etc)
• bacteria
Nucleus-function
• Information center of the cell
• Contains DNA (deoxyribonucleic acid)
which contains the genetic information to
make thousands of different molecules
• Directs all the cell’s activities
Nucleus- Structure
Nuclear membrane or envelope
• A double layer of membranes that surrounds the
nucleus regulating what enters and exits through the
nuclear pores or openings in the membrane
Nucleolus
• Made up of RNA and protein
• Structure in which ribosomes are made
Chromosomes
• The DNA in the nucleus is attached to special proteins
and forms large structures called chromosomes
• Chromosomes contain the genetic information that
must be passed to each new generation of cells
Cytoplasm
• Function
• Holds organelles (small cell structures) in
place
• Helps with intracell communication and
transport
• Structure
• Gel-like substance
IV. Cytoplasmic Organelles
• Organelle- a tiny structure that performs a
specialized function in the cell
• Types and number of organelles will vary
depending on the type of cell involved and
the function of the cell
Power Stations: Mitochondria and
Chloroplasts
• All living things require a dependable energy
source
• Mitochondria and chloroplasts are key
organelles that change energy from one form to
another
• Mitochondria change the chemical energy in food
into compounds that are more convenient for the
cell to use
• Chloroplasts trap the energy of sunlight and
convert it into chemical energy
Mitochondria
(mitochondrion- singular)
• Two sets of membranes
• An outer membrane
• An inner folded membrane that increases the
inner surface
• of the mitochondria
Chloroplast- only in photosynthetic
cells- plants, algae
• Surrounded by two
envelope-like
membrane and
contains a third kind
of membrane where
the radiant energy of
the sun is actually
changed into
chemical energy
(photosynthesis).
Protein factories- Ribosomes
• Structures in which proteins are made
• Composed of RNA and protein- made in the
nucleolus
• Some are attached to membranes, some
are found free floating in the cytoplasm
• Among the smallest organelles- 25
nanometers (1 nm – 1 billionth of a meter)
ribosome
Packaging and shipping: Endoplasmic
Reticulum and Golgi Apparatus
• Endoplasmic reticulum
(ER)
• A complex network of sacs
that transports materials
through the inside of the
cell
• Two types:
• Smooth ER
• Rough ER – have ribosomes
stuck to its surface
• Golgi Apparatus –named
after Camillo Golgi
• Will modify proteins and
package them for
distribution and shipment
to other parts of the cell
Clean-up Crew: Lysosomes
• Not found in plant cells
• Also called suicide sacs
• Small membrane bordered structures that
contain strong chemicals and enzymes needed to
digest certain materials
• Involved in breaking down old, used up or damage
cell parts
• Don’t work properly in people that have Tay-Sachs
disease
Storage containers: Vacuoles and
Plastids
• Vacuoles- store water, salts, proteins and
carbohydrates
• Plant cells have huge water vacuoles that help give
plant structure when filled up (wilt)
• Plastids- plant storage for pigments and food
• Chloroplast –where photosynthesis occurs
• Leukoplasts- starch storage
• Chromoplasts- contain colored pigment molecules
(tomatoes)
Framework: Cytoskeleton
• Composed of a variety of filaments and fibers that
support cell structure and drive cell movement
• Microtubules-hollow tubules made of protein
• Provide shape for the cell, help move organelles
through the cell, form centrioles in animal cell, can
form cilia and flagella (used in the movement of some
cells)
• Microfilaments- long, thin fibers
• Involved in the moving of the cytoplasm and in
cytoplasmic streaming (amoeba movement)