Introduction
• There are huge differences between the
forms of life but cells are the basic unit of
life and have many characteristics in
common
Introduction
• Cells are often divided into certain groups
based on major characteristics.
– Two main groups:
• Prokaryotic cells
• Eukaryotic cells
2.2 Prokaryotic Cells
Prokaryotic Cells
• Much smaller and simpler than eukaryotic
cells
– Most are less than 1 um
Prokaryotic Cells
• Features of prokaryotic cells
– Cell wall
– Plasma membrane
– Flagella
– Riboome
– Nucleoid (region containing free DNA)
• Be Sure you can Identify all of these!!!
2.2.1
2.2.2
Prokaryotic Cell
Prokaryotic Cell
Prokaryotic Cells
• Cell Wall and Plasma Membrane
– Protects and maintains the shape of the cell
• Composed of a carbohydrate-protein complex
called peptidoglycan
– Some bacteria have an additional layer of a
type of polysaccharide out the cell wall
• This layer makes it possible for some bacteria to
adhere to structures such as teeth, skin, and food
Prokaryotic Cells
• Cell Wall and Plasma Membrane
– The plasma membrane is just inside the cell
wall and has a composition similar to the
membranes of eukaryotic cells
• Controls the movement of materials in and out of
cells
• Cytoplasm occupies the complete interior of the
cell
Prokaryotic Cells
• Pili and flagella
– Some bacterial cells contain hair-like growths
on the outside of the cell wall
• These are pili and are used for attachment
• However their main function is in joining bacterial
cells in preparation for the transfer of DNA from
one cell to another (sexual reproduction)
– If bacterium has flagella (plural) or flagellum
(singular), they are longer than pili
• Allows cell motility
Prokaryotic Cells
• Ribosomes
– Ribosomes occur in all prokaryotic cells and
function as sites of protein synthesis
• The more protein produced the larger the number
of ribosomes.
Prokaryotic Cells
• The nucleoid region
– Is non-compartmentalized and contains a
single, long, continuous, circular thread of
DNA
– In addition to the bacterial chromosome,
bacteria may also contain plasmids
• These small, circular, DNA molecules are not
connected to the main bacterial chromosome.
• Replicates independently of the chromosomal DNA
• It is not required by the cell under normal
conditions but it may help the cell adapt to unusual
circumstances
Binary Fission
• Prokaryotic cells divide by a very simple
process called binary fission.
– During this process:
• DNA is copied
• The two daughter chromosomes become attached
to different regions on the plasma membrane
• The cell divides into two genetically identical
daughter cells
Prokaryotic Cells divide by binary
2.2.4
fission
2.3 Eukaryotic Cells
The Parts of the Cell
• Each living cell carries out the tasks of taking food,
transforming food into energy, getting rid of wastes,
and reproducing.
• Most eukaryotic cells have three main components:
– Cell Membrane
– Cytoskeleton
– Nucleus
Animal Cell
2.3.1
2.3.2
Now let
Annotate this
picture with all
the functions of
each structure
named
Plant Cell
Now let
Annotate this
picture with all
the functions of
each structure
named
Liver
Cell
2.3.3
Structure and Function of
Organelles
• The Structure and Function of the following
organelles will be discussed:
–
–
–
–
–
–
–
–
Cell Membrane
Nucleus
Cell Wall
Cytoplasm
Cytoskeleton
Ribosomes
Endoplasmic Reticulum
Golgi Apparatus
–
–
–
–
–
–
–
–
Mitochondria
Lysosomes
Peroxisomes
Cilia and Flagella
Basal Bodies
Centrioles
Vacuoles
Plastids
Cell Membrane
• Structure: phospholipid
bilayer with proteins that
function as channels,
markers, and receptors
-also contains cholesterol
which provides rigidity
• Function: selectively
permeable boundary
between the cell and the
external environment
Nucleus
• Structure: the nucleus is a
sphere that contains
another sphere called a
nucleolus
• Function: -storage center of
cell’s DNA
-manages cell functions
Cell Wall
• Structure: rigid wall made
up of cellulose, proteins,
and carbohydrates
• Function: boundary around
the plant cell outside of the
cell membrane that provides
structure and support
Cytoplasm
• Structure: gelatin-like fluid that lies inside the cell
membrane
• Function: -contains salts, minerals and organic
molecules
-surrounds the organelles
Cytoskeleton
• Structure: a network of
thin, fibrous elements
made up of
microtubules (hollow
tubes) and
microfilaments (threads
made out of actin)
• Function: -acts as a
support system for
organelles
-maintains cell shape
Ribosomes
• Structure: consist of two
subunits made of protein
and RNA
• Function: location of protein
synthesis
Endoplasmic Reticulum
• Structure: a system of membranous tubules and sacs
• Function: intercellular highway (a path along which
molecules move from one part of the cell to another)
• Two types:
– Rough Endoplasmic Reticulum
– Smooth Endoplasmic Reticulum
Rough Endoplasmic Reticulum
• Rough Endoplasmic
Reticulum (rER): prominent
in cells that make large
amounts of proteins to be
exported from the cell or
inserted into the cell
membrane
– Covered with ribosomes
Smooth Endoplasmic Reticulum
• Smooth Endoplasmic
Reticulum (sER): involved in
the synthesis of lipids and
breakdown of toxic
substances
– Not covered with
ribosomes
Golgi Apparatus
• Structure: stacked flat sacs
• Function: receives proteins
from the rER and distributes
them to other organelles or
out of the cell
(receiving, processing,
packaging, and shipping)
Mitochondria
• Structure: folded membrane
within an outer membrane
– The folds of the inner
membrane are called
cristae
• Function: -converts energy
stored in food into usable
energy for work
– cellular respiration
Lysosomes
• Structure: spherical
organelles that contain
hydrolytic enzymes within
single membranes
• Function: breaks down food
particles, invading objects,
or worn out cell parts
Peroxisomes
• Structure: spherical
organelles that contain
enzymes within single
membranes
• Function: Degrade
hydrogen peroxide, a toxic
compound that can be
produced during
metabolism.
Cilia and Flagella
• Structure: hair-like organelles that extend from the
surface of cells
– When they are present in large numbers on a cell
they are called cilia
– When they are less numerous and longer they are
called flagella
– Both organelles are composed of nine pairs of
microtubules arranged around a central pair.
• Function: cell motility
Cillia and Flagella
Basal Bodies
• The microtubule assembly of a cilium or flagellum is
anchored in the cell by a basal body.
• Structurally identical to a centriole
Centrioles
• 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)
Vacuoles
• Structure: a sac of fluid
surrounded by a membrane
– Very large in plants
• Function: used for
temporary storage of
wastes, nutrients, and water
Plastids
• There are three types of plastids in plant cells:
– Chloroplasts (discussed on next slide)
– Chromoplasts: synthesize and store pigments
– Leucoplasts: store food such as starches, proteins,
and lipids
Chromoplasts
Red Pepper
Flower
Leucoplasts
Chloroplasts
• Structure: stacked
sacs (thylakoids) that
contain chlorophyll
surrounded by a
double membrane
• Function:
photosynthesis
(conversion of light
energy to chemical
energy stored in the
bonds of glucose)
Structural Organization of
Eukaryotic and Prokaryotic Cells
2.3.4
2.3.4
Eukaryotes vs. Prokaryotes
• Eukaryotes (animals, plants,
fungi, protists) and
prokaryotes (bacteria) differ
greatly in structure.
Prokaryotic cells
Eukaryotic cells
DNA in a ring form without protein
DNA with proteins as
chromosomes/chromatin
DNA free in cytoplasm
DNA enclosed within a nuclear
envelope
No mitochondria
Mitochondria present
70S ribosome
80S ribosome
Not internal compartmentalization to
form organelles
Internal compartmentalization present
to form many types of organelle
Size less than 10 micrometres
Size more than 10 micrometres
• Similarities between two types of cells:
– Both types of cells have some sort of outside
boundary that always involves a plasma
membrane
– Both types of cell carry out all the functions of
life
– DNA is present in both cell types
Plant cells
Animal Cells
Exterior of cell includes an outer cell
wall with a plasma membrane just
inside
Exterior of cell includes only a plasma
membrane. There is no cell wall
Chloroplasts are present in the
cytoplasm
There are no chloroplasts
Possess large centrally located
vacuoles
Vacuoles are usually not present or are
small
Store carbohydrates as starch
Store carbohydrates as glycogen
Do not contain centrioles within a
centrosome area
Contain centrioles within a
centrosome area
Because a rigid cell wall is present,
this cell type has a fixed, often
angular, shape
Without a cell wall, this cell is flexible
and more likely to be rounded
shape
2.3.5
Plant Cells vs. Animal Cells
• Animal cells are very similar to
plant cells except for the following
major differences:
– Animal cells do not contain
chloroplasts
– Animal cells are not surrounded
by cell walls
– The vacuoles in plants are much
larger than those of animals
Microscope Pictures of a
Plant Cell and an Animal Cell
Elodea
Human Cheek Cells
Extracellular components
• The extracellular matrix (ECM) is
composed of collegen fibers plus a
combination of sugars and proteins called
glycoproteins in many animal cells
– These form fiber-like structures that anchor
the matrix to the plasma membrane. This
strengthens the plasma membrane and allows
attachment between adjacent cells.
Extracellular components
• The ECM allows for cell to cell interaction,
possibly altering gene expression and
bringing about coordination of cell action
within the tissue.
– Many researchers think the ECM is involved
in directing stem cells to differentiate
– Cell migration and movement also appear to
be the result of the interactions between cells
Extracellular components
2.3.6
THE END!