Cell Structure
By: J. Quigley
9/2013
Discovery of Cells
• All life forms on the
planet are made from
cells
• The bacteria that live in
our gut and the cells that
make up are body are
built from the same
machinery
• Cells need to obtain and
use energy, respond to
their environment and
reproduce
Discovery of Cells
• Microscope
observations of
organisms led to the
discovery of the basic
characteristics common
to all living things.
• In 1665, Robert Hook,
an English scientist,
created the first
microscope
Cell Theory
• There are three rules of cells:
– All living things are made up of one or more cells
– Cells are the basic units of structure and function
in organisms
– All cells arise from existing cells
Looking at Cells
• A cell’s shape reflects the
cells function.
• Cells may be flat, round
or rectangular. Some cells
have irregular shapes
while others constantly
change shapes… these
differences enable cells to
perform highly specific
functions in the body
Cell Size
• All substances that enter or leave a cell must pass
through the surface of the cell. As a cell gets larger, it
takes up more nutrients and releases more wastes.
These substances must move farther to reach their
destination in a larger cell
• Cell size is limited by the cell’s surface area to volume
ratio
• Scientists can estimate a cell’s ability to exchange
materials by calculating the cell’s surface area to
volume ratio… cells with greater surface area to
volume ratio exchange substances more efficiently
• Smaller is better.
Cell Shape
• Larger cells often have
shapes that increase
the surface area
available for exchange…
such as being broad and
flat
Cell Features
• All cells from a bacteria to an apple to a
human share common structural features. All
cells have:
– A cell membrane
– Cytoplasm
– Ribosomes
– DNA
Cell Features
• Cell membrane is the
cells outer boundary. It
acts as a barrier
between the outside
environment and the
inside of the cell
Cell features
• Cytosol- the fluid inside
the cell that is full of
dissolved particles
• Cytoplasm- includes the
fluid cytosol and most
of the structures that
are suspended in the
fluid
Cell Features
• Ribosomes are cellular
structures that make
proteins.
• All cells also have DNA,
the genetic material
that provides
instructions for making
proteins, regulates
cellular activities and
enables cells to
reproduce
Prokaryotic Cells
• A prokaryote is/has:
– Only one cell
– Quite simple in
organization
– Genetic material is a
single loop of DNA which
looks like a tangled string
in the center of the cell
– Ribosomes and enzymes
share the cytoplasm
with the DNA
Prokaryotes
• Scientists think that the
first prokaryotes may
have lived 3.5 billion
years ago or more! For
millions of years,
prokaryotes were the
only organisms on earth.
• They were/are very
simple and small and they
live in a wide range of
habitats
Eukaryotes
• A eukaryote is organism that is made up of one or
more eukaryotic cells
• Some are single cells, most are multicellular
• Because of their complex organization, eukaryotic
cells can carry out more specialized functions
than prokaryotic cells can
• Their DNA is housed in an internal compartment
called the nucleus
• Eukaryotes have organelles. Organelles are
structures that carry out specific
activities/functions within the cell
Eukaryotes
• Primitive eukaryotes
first showed up about
1.5 billion years ago and
have evolved into the
multicellular organisms
of today
Framework of the Cell
• The cytoplasm of a
eukaryotic cell is packed
with all sorts of
structures and
molecules.
• The cytoskeleton has a
web of protein fibers
that help the cell move,
keep its shape and
organize its parts
Directing Cellular Activity
• Almost all cellular activity
depends on the proteins the
cell makes.
• The instructions for making
proteins is in the DNA
• The DNA in eukaryotes is
inside the nucleus
• DNA instructions are copied as
RNA messages, which leave
the nucleus. In the cytoplasm
ribosomes use the RNA
messages to assemble
proteins.
Nucleus
• The nucleus stores the cell’s
DNA.
• The nuclear envelope is a
double membrane that
surrounds and protects the
nucleus
• Within the nucleus is the
nucleolus.
• The nucleolus is the region
in the nucleus that makes
ribosomes. The ribosomes
pass through the nuclear
envelope and into the
cytoplasm.
Ribosomes
• Each ribosome is made of
RNA and many proteins.
• Some ribosomes are
found in the cytosol.
These “free” ribosomes
make proteins that are to
remain INSIDE the cell
• Some ribosomes are
attached to another
organelle. These “bound”
ribosomes make proteins
that are to be exported
OUTSIDE the cell.
Protein Processing
• Proteins produced by cells have many uses. The
proteins that are sent outside the cell must be
kept separate from the rest of the cytoplasm. To
achieve this separation, the cell packages the
protein in vesicles.
• A vesicle is a small, often circular shaped sac that
is formed by a membrane
• The endoplasmic reticulum and the golgi
apparatus are organelles that prepare proteins
for export.
Endoplasmic Reticulum
• The endoplasmic reticulum (ER) is a system of
internal membranes that move proteins and
other substances though the cell. The
membrane of the ER is connected to the outer
membrane of the nuclear envelope
Endoplasmic Reticulum
• Rough ER- ribosomes
are attached to some
parts of the surface of
the ER making it bumpy
in appearance. As
proteins are made they
cross the ER membrane,
entering the ER, which
then pinches off to form
a vesicle around the
protein
Endoplasmic Reticulum
• Smooth ER- Has no
attached ribosomes and
is smooth in
appearance. Enzymes of
the smooth ER perform
various functions such
as making lipids and
breaking down toxic
substances
Golgi Apparatus
• The golgi apparatus is a
set of flattened
membrane-bound sacs
that help make and
package materials to be
transported out of the
cell.
• The golgi also makes
lysosomes.
Storage and Maintenance
• Vesicles have an
important role within
the cell. Some transport
materials within the
cell. Other has
important storage roles.
• Vesicles help maintain
homeostasis by storing
and releasing various
substances as the cell
needs them.
Storage and Maintenance
• Lysosomes are vesicles
that contain specific
enzymes that break
down large molecules.
They digest food
particles to provide
nutrients for the cell
and help recycle
materials in the cell by
digesting old or
damaged organelles.
Storage and Maintenance
• Central Vacuole- many
plants contain a large,
membrane
compartment called the
central vacuole. It is a
large vacuole that
stores water, nutrients
and waste.
Storage and Maintenance
• Vacuoles- Many animal
cells have much smaller
storage vesicles than
plants. They store food
particles for later use.
Energy Production
• Cells need a constant source of energy.
• The energy for cellular functions is produced
by chemical reactions that occur in the
mitochondria and chloroplasts.
• Nearly all eukaryotic cells have mitochondria,
only plant cells have chloroplasts
Energy Production
• Chloroplasts- an organelle
that uses light energy to
make sugar from carbon
dioxide and water.
• Each chloroplast is
surrounded by a pair of
membranes, inside the
membrane are stacks of
flattened sacs. The ATP
producing chemical
reactions take place
inside the sacs.
Energy Production
• Mitochondria- organelle that
uses energy from organic
compounds to make ATP.
• Mitochondrion have a smooth
outer membrane and a folded
inner membrane. ATP
producing enzymes mostly
live in the inner membrane.
• Cells with high energy
requirements have more
mitochondria than cells with
lower energy requirements
Diversity in Cells
• More than 50 million types of organisms live
on earth!!!
• Each organism is made up of different types of
cells.
• Differences in cells enable organisms to adapt
to their natural environments.
Diversity in Prokaryotes
• Prokaryotes vary in
shape, the way they
obtain and use energy,
the make up of their
cell walls and their
ability to move
• Many prokaryotes have
a flagella- a long thread
like structure that
rotates quickly for
movement
Diversity in Eukaryotic Cells
• Eukaryotic cells also vary in structure
according to their function. Some organelles
are more prominent in some cell types. By
varying their internal make up, cells can
become specialized for certain functions.
Diversity in Eukaryotic Cells
• Animal and plant cells
are two types of
eukaryotic cells. Both
have many of the same
organelles, but plants
have chloroplasts, a
large central vacuole
and a cell wall that
surrounds the cell
membrane.
Levels of Organization
• Multicellular organisms,
such as plants and
animals, are made up of
thousands, millions or
even trillions of highly
specialized cells.
• These cells cooperate to
perform specific tasks
• They assemble together
to form structures called
tissues and organs.
Levels of Organization
• Cells make tissues- a
distinct group of cells
that have similar
structure and function
• Tissues make organsspecialized structure
that has a specific
function
• Organs make organ
systems- they carry out
major body functions