Cell Structure
Organelles
Recall the
Characteristics of Life
• All Living things share the following:
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Cells
Organization
Energy use
Homeostasis
Growth/Development
Reproduction
Organization
• 2 levels: Molecular and Cellular
• Molecular:
– Macromolecules are organized into structures
called organelles. Organelles working together
make up a cell.
– 4 macromolecules: proteins, carbohydrates,
lipids, and nucleic acids
• Cellular: a multi-celled organism has cells grouped
as a tissue, tissues into organs, etc.
Cells
• Cell Theory:
– All living things are made of one or
more cells.
– Cells are the basic unit of life.
• The organelles in a cell can perform all of
the functions for life.
– Cells come from the reproduction of
existing cells.
How is a single, tiny little cell able
to do so much?
• Each organelle in the cell performs a specific
function.
– Organelles: small structures that
carry out specific functions in a cell.
• Remember, all cells have
– A cell membrane
– DNA (genetic information)
– Cytoplasm (contains the organelles)
• Only eukaryotic cells have a nucleus and other
membrane-bound organelles.
Cell Membrane
• The cell membrane is the boundary
between the inside of the cell and the
external environment.
• Cells must acquire nutrients and get rid of
wastes.
• The membrane controls traffic of
substances into/out of the cell.
• Analogy: security guard or border
control
Cell membrane vs. Cell Wall
• The cell membrane is mostly made
of lipids (phospholipids) with some
proteins as well.
• All cells have cell membranes, but
only some cells (plant/bacteria)
have cell walls.
– The wall is rigid and helps support and
protect the cell.
– The cell wall is mainly made of cellulose,
a complex carbohydrate.
Phospholipid bilayer
“Quiz”: What
cell is this?
Cell Membrane
Cell Wall
Cell membrane
Cell Wall
“Quiz”: What
cells are these?
These cells have a cell membrane, it’s just not
visible next to the thicker cell wall.
The cytoplasm contains the
organelles of a cell
• The cytoplasm is the region of
the cell between the membrane
and the nucleus. It consists of
a gelatin-like fluid which
“bathes” the organelles.
– It is a solution with dissolved salts,
minerals, etc.
• Region where most of the cell’s
activities are carried out.
cytoplasm
Organelles provide
compartments for specialized
activities to occur
• Mitochondria (or mitochondrion)
– Transfers energy from organic compounds
(food) to ATP (a molecule that provides
energy for the cell to do “work”).
– Analogy: Power Plant- converts energy to a
usable form.
– Think of ATP as a cell’s “energy bank”
– Structure: surrounded by 2 membranes; a
smooth outer membrane and a folded inner
membrane. The folds allow for a lot of space
for chemical reactions to occur.
Mitochondrion
“Membrane-bound” = found only in eukaryotes
(plant and animal cells)
Ribosomes
• DNA contains the instructions that control
growth and development of an organism.
However, it is only like the blueprints for a new
house. A contractor is needed to build the house
according to the plans in the blueprint.
• Growth and development depends on the
production of proteins.
– Ribosomes make (synthesize)
proteins
• Analogy: Construction workers.
Ribosomes
More on Ribosomes
• Structure: made up of proteins and RNA.
– They are not membrane-bound so they are
found in both prokayotic and eukaryotic
cells. (i.e.: ALL cells)
• Some are attached to the endoplasmic
reticulum; others float freely in the
cytoplasm.
“Dots”
Endoplasmic Reticulum
• It’s an “intracellular highway”; molecules
move from one part of the cell to another
through the ER.
• Rough ER: studded with ribosomes; plays a
role in protein synthesis. (connects to
nuclear membrane)
• Smooth ER: synthesizes lipids, breaks down
toxic substances.
• Structure: membranous tubules and sacs
• Analogy: factory; conveyor belts, machines,
etc.
Endoplasmic Reticulum
Golgi Apparatus
• Works closely with the ER. It processes,
packages, and helps release substances
made by the cell (ex: proteins).
– A protein made by a ribosome on the ER will be
transported to the golgi where it is processed
and given a “shipping label” before being
secreted (released) from the cell.
• Analogy: shipping department, Post
Office
• Structure: flattened membranous sacslike pancakes.
Golgi Apparatus
Lysosomes
• Contain enzymes (a special type of
protein) that digest (break down)
molecules, old organelles, viruses, and
bacteria.
• Analogy: garbage/waste disposal.
• Structure: spherical, single membrane
– Note: rare in plant cells
Lysosomes
Cytoskeleton
• Provides support for the cell, may
allow for movement of the cell or
within the cell.
• Analogy: frame of a car/house.
• Made of microfilaments and
microtubules; strands of protein.
• Not surrounded by membrane.
Cytoskeleton
Nucleus
• Besides the cytoplasm the nucleus is the other
major region of a cell.
• Stores hereditary (genetic) information-DNA.
It also synthesizes RNA.
• Analogy: county office that stores the original
building blueprints. “Brain”, stores info and
sends out messages.
• Inside the nucleus is an area called the nucleolus
which is where ribosomes are made.
• Structure: surrounded by a double membrane =
nuclear envelope. Membrane has pores that
allow molecules to pass through.
Nucleus
4 = nucleolus
3 = nuclear membrane
(with pores)
5 = chromatin (DNA)
Nuclear
membrane
Nucleus
Cilia and Flagella
• Both are extensions of the cell
membrane; cylindrical in shape. Made of
microtubules.
• They can be used to propel a single cell,
or to move fluid or materials past cells.
• Cilia = short extensions, many per cell
• Flagella = long extensions, one or few per
cell.
Flagella
Cilia
_______________
Plant and Animal Cells have
many organelles in common
Animal
Plant
Plant cells and Animal cells have
some key differences
• A cell wall
• Vacuole: stores salts, minerals,
nutrients, water, etc., may sequester
harmful substances. Plays an important
structural role for the plant
• Large compartment, surrounded by a
membrane
• Analogy: Warehouse
Chloroplasts
– A type of plastid
– transfer energy from the sun to make
organic compounds (food)
– surrounded by double-membrane,
contain chlorophyll (green pigment).
– Analogy: solar panels
Chloroplast
Plant cell organelles