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Cells
Structures and Functions of
Prokaryotic and Eukaryotic
cells
All cells have:
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Plasma membrane
Cytosol (semifluid substance in which the
organelles are suspended) / Cytoplasm
Chromosomes (DNA)
Ribosomes
Prokaryotic Cell
Prokaryotic cells
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Prokaryotic = “before nucleus”
No nucleus or membrane-bound organelles
DNA floats freely in cytoplasm (in nucleoid region)
– DNA is in the form of a loop
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Very small
(in general, 10x smaller than eukaryotes)
 Cell wall made of peptidoglycan surrounds the cell
membrane
 Contain 70s ribosomes (smaller than 80s)
 Thought to have appeared on Earth first
Prokaryotic Cell
Prokaryotic cell structures and functions
Cell wall – forms a protective outer layer that prevents damage
from outside (made of peptidoglycan)
Plasma membrane – controls entry and exit of substances,
pumping some of them out or in by active transport.
Cytoplasm – contains enzymes that catalyze chemical reactions
and contains DNA in a region called nucleoid.
Pili – hair-like structures projecting from cell wall; when connected
to another bacterial cell, they can be used to pull cells together
Flagella – used for locomotion in some prokaryotes
Ribosomes (70s) – small granular structures which
synthesize proteins
Nucleoid – region of cytoplasm that
contains “naked loop of DNA” (single,
long, continuous circle of DNA)
Reproduction in bacteria:
most bacteria can reproduce asexually or sexually
Asexual =
Binary Fission
(1 bacterium splits into 2)
Sexual = Conjugation
bacteria exchange
genetic material with
other bacteria thru cellto-cell contact.
- Increases genetic
diversity of bacteria
Binary fission
See Binary fission (p. 227)
Eukaryotic Cells
Diagram
of an
animal
cell
Liver
Cell
Ultrastructure of a
liver cell.
1:Nucleolus; 2:Chromatin;
3:Dense Chromatin; 4:Nuclear
Pores; 5:Mitochondria;
6:Rough Endoplasmic
Reticulum; 7:Ribosomes;
8:Golgi Apparatus; 9:Smooth
Endoplasmic Reticulum;
10:Peroxisomes;
11:Lysosomes; 12:Bile
Capillary; 13:Desmosomes;
14:Microvilli.
Diagram of
a plant cell
Plant cell
The cell
nucleus
Nucleus
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Large spherical structure
surrounded by a double membrane
with pores (called the nuclear
envelope)
Contains nucleolus and
chromosomes (DNA) (Uncoiled
chromosomes are called chromatin)
Control center of the cell.
Controls the cell’s
f
functions through
the expression of genes.
Nucleolus
Ball-like mass of fibers
inside nucleus
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Makes ribosomes
Plasma membrane
Selectively-permeable: controls which substances can enter and
exit a cell. It is a fluid structure that can radically change shape
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The membrane is a double layer of phospholipids
(phospholipid bilayer)
Receptors in the outer surface detect signals to the cell and relay
these to the interior
The membrane has pores that run from the cytoplasm to the
surrounding fluid
Cell (Plasma) Membrane
Cytoplasm
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Entire region of cell between membrane and nucleus
Semi-fluid substance; contains salts, minerals and organic molecules
Holds organelles which have membranes around them
Actual fluid portion of cytoplasm is referred to as cytosol)
Endoplasmic Reticulum (ER)
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An extensive network of membrane tubules or channels that
extends thru the cell, outwards from the nucleus
Two types:
– Smooth Endoplasmic Reticulum
– Rough Endoplasmic Reticulum
Smooth Endoplasmic Reticulum
Lacks ribosomes
Functions
 Synthesizes phospholipids (and other lipids)
 Storage of calcium ions (needed for contraction in
muscle cells)
 Detoxification of drugs in liver cells
 Transportation of lipid-based compounds
 Synthesizes sex hormones: testosterone and estrogen
Rough Endoplasmic Reticulum

Covered with ribosomes
Functions
 protein synthesis
 Proteins made here are generally
inserted into membranes or
secreted out of the cell
 Also a “membrane factory” for the
cell: adds membrane proteins and
phospholipids to its own
membrane
Ribosomes
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Found attached to Rough ER
and also floating free in the
cytoplasm
Composed of rRNA
(ribosomal RNA) and protein
Made of 2 subunits
Function: Protein synthesis!
80s in eukaryotes
cis
Golgi
Apparatus
trans
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Flattened sacs called cisternae which are stacked on top of each other
Function: receives proteins from the rER and distributes them to other
organelles or out of the cell
Collects, modifies, packages, and ships
Side closest to rough ER is cis side (it receives products from the ER).
Movement then continues through to the trans side. Small sacs called
vesicles can be seen coming off the trans side carrying materials.
Secretory Pathway
Secretory Pathway
Lysosomes
Lysosomes
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Membrane-bound sacs that contain digestive enzymes!
Function: digestion of old or non-working organelles, food
particles, bacteria and virus invaders!
Mitochondria
(singular:
Mitochondrion)
Mitochondria
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Structure: folded membrane within
an outer membrane
– The folds of the inner membrane
are called cristae
Site of cellular respiration
The amount of mitochondria in cells
is correlated with amount of
energy the cell needs (ex. muscle
cells- Lots of mitochondria!)
Peroxisomes
spherical organelles that contain enzymes
Function: Breaks down hydrogen
peroxide (a toxic compound that can be
produced during metabolism) into water,
rendering the potentially toxic substance
safe for release back into the cell
the Cytoskeleton
Cytoskeleton
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Structure: a network of thin,
fibrous elements made up of
microtubules (hollow tubes),
intermediate filaments, and
microfilaments (threads made
out of actin)
Function: -acts as a support
system for organelles
-reinforces cell shape
-functions in cell movement,
Components are made of protein
Centrioles
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Structure: composed of
nine sets of triplet
microtubules arranged in a
ring
– Exist in pairs
Function: centrioles play a
major role in cell division
(mitosis)
Cilia and Flagella
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Hair-like organelles that extend from the surface of cells
– (Both are composed of nine pairs of microtubules arranged
around a central pair.)
Function: cell motility
Cilia: numerous, short, move together like oars in water
Flagella: usually only one, propels cells through water (ex.
Sperm tail)
Cilia
Flagella
http://programs.northlandcollege.edu/biolog
y/Biology1111/animations/flagellum.html
Vacuoles
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Structure: a sac of fluid surrounded
by a membrane
– Very large in plants (Large Central
Vacuole)
Function: used for temporary storage
of wastes, nutrients, water, pigments,
etc.
In some freshwater protists, there is a
contractile vacuole which pumps out
excess water out of the cell
Chloroplasts
Only in plant and algae cells
Site of photosynthesis:
(conversion of light energy
to chemical energy)
Double membrane around stacks of
flattened sacs (thylakoids)
Chloroplast
Pigment Chlorophyll makes them green
Cell Wall
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In plant cells only: rigid wall made
up of cellulose, proteins, and
carbohydrates
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Function: boundary around the
plant cell outside of the cell
membrane that provides structure
and support
Comparison of plant and animal cells
Animal cells
Plant cells
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Cell wall outside
plasma membrane
makes cells rigid
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Chloroplasts
Large central vacuole
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No cilia or flagella
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Store carbohydrates
as starch
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No cell walls, only
plasma membrane,
which makes cells more
flexible
No chloroplasts
Vacuoles are much
smaller
Some have cilia or
flagella
Store carbohydrates as
glycogen
Extracellular Matrix
Animal cells lack a rigid cell
wall, but most are embedded
in a sticky layer of
glycoproteins called the
"Extracellular Matrix“
(ECM).
It is an elaborate matrix of
glycoproteins and collagen
which forms strong fibers
outside the cell.
The ECM functions to hold
cells together and can also
have a protective and
supportive function.
Extracellular Matrix