Chapter 7: A View of the Cell
7.1. The Discovery of Cells
The Cell Theory (History)
• The microscope was invented
by Anton van Leeuwenhoek.
• The first person to see a cell
(in cork) was Robert Hooke.
• Matthias Schleiden
concluded that all plants
have cells
• Theodore Schwann observed
that animals were also
composed of cells
The Cell Theory
• 3 main ideas:
– All living things are composed of one or more
cells
– The Cell is the basic unit of organization of
organisms
– All cells come from cells
The Light Microscope
• Uses light and lenses
• The Simple light
Microscope used one
lens and natural light
(Leeuwenhoek)
• The Compound light
microscope: Uses
multiple lenses
– Magnifies up to 1500
times
The Electron Microscope
• Invented in the 1940s
• Uses a beam of electrons
• Magnifies up to 500,000
times
• Two Kinds:
– Scanning electron
microscope (SEM): Scans the
surface of cells.
– Transmission electron
microscope (TEM): Allows for
study of structures inside
cells.
The Electron Microscope
SEM
TEM
Two Basic Cell Types
• Prokaryotes: Cells lacking internal membrane-bound
structures
• Eukaryotes: Cells containing internal membrane-bound
structures
– The membrane-bound structures are called organelles
– Contains a nucleus: organelle that manages cellular function.
First observed by Robert Brown. Rudolf Virchow concluded that it
was responsible for cell division.
Chapter 7: A View of the Cell
7.2 The Plasma Membrane
Maintaining a Balance
• The Plasma membrane is the boundary between
the cell and it’s environment
• Needs to let the good stuff (e.g. nutrients) in and
the bad stuff (waste) out
• The plasma membrane maintains homeostasis.
Plasma Membrane
The Plasma Membrane
• Maintains Homeostasis: regulates internal
environment [Good in (but not too much),
Bad Out]
• Selective permeability: Allows some
molecules into the cell and keeps some
out.
• Some molecules can cross the plasma
membrane (i.e. water). Others must go
through channels (i.e. Na, Ca, etc)
Structure of the Plasma Membrane
• Composed of a
phospholipid bilayer.
– A Lipid with a phosphate
group attached
– Has only 2 fatty acid tails
– Forms a sandwich
• The phosphate group
forms the polar head
• The fatty acid tails form
the nonpolar tail
Fluid Mosaic Model
• The membrane is fluid: It is flexible and
phospholipids can move in the membrane like
water in a lake.
• The membrane is mosaic: There are proteins
embedded in the membrane that also move
(like boats in the lake)
Other components
• Cholesterol: Helps stabilize the plasma membrane, and
prevents the phospholipids from sticking together.
• Transport Proteins: Proteins that span the entire
membrane and form channels for specific molecules to
enter and leave (like a door).
• Other Proteins and carbohydrates on the external
surface: Helps with identification.
• Proteins on internal surface: Provides flexibility by
attaching the plasma membrane to the cell’s internal
structure.
Chapter 7: A View of The Cell
7.3 Eukaryotic Cell Structure
Cellular Boundaries
• Plasma membrane
surrounds the cell
• In plants, fungi, most
bacteria and some
protists, the cell wall
surrounds the plasma
membrane
– Fairly rigid
– Provides support and
protection
– Made up of the
carbohydrate cellulose
– Has pores to allow
molecules through
Nucleus and cell control
• The Nucleus is the
leader of the cells
– Gives directions for the
making of proteins
• The master set of
directions is in
chromatin
• During cell division,
chromatin condenses
to form chromosomes.
Nucleus and Cell Control
• Inside the nucleus there is also the
nucleolus
– Makes ribosomes
• Ribosomes are sites where proteins and
other enzymes are made, according to
instructions from DNA
• Ribosomes leave the nucleus, into the
cytoplasm in order to make proteins
• Cytoplasm: The fluid inside the cell
Nucleus and cell control
• The Nuclear envelope
is a double membrane
that surrounds the
nucleus.
– Made up of 2
phospholipid bilayers
– Contains small nuclear
pores
Assembly and Transport
• The endoplasmic reticulum: A
series of highly folded
membranes
– Where cellular chemical
reactions take place
– Like a large workspace
• Some parts have ribosomes
attached (rough endoplasmic
reticulum - RER)
• Others don’t (smooth
endoplasmic reticulum – SER)
Assembly and Transport
• RER: Proteins made in
the RER may:
– form part of the plasma
membrane
– be released from the
cell
– transported to other
organelles
• SER: involved in
production and
storage of lipids.
Assembly and Transport
• The Golgi apparatus:
flattened system of
tubular membranes
and vessicles
– Modifies proteins
– Sorts and packages
proteins
• It’s kind of like the
post office: Sorts the
mail and sends it to
the right place
Assembly and Transport
RER
Golgi apparartus
vessicles
Vacuoles
• A vacuole is a sac surrounded by
membrane
• Used for temporary storage of
– Food
– Enzymes
– Waste
• Plant cells usually have one large vacuole,
animal cells have many smaller ones
Lysosomes and recycling
• Lysosomes are organelles
that contain digestive
enzymes
– They digest food particles,
organelles and engulfed
viruses or bacteria
• Can fuse with vacuoles and
digest the contents.
• Can also digest cells that
contain them.
– i.e. tadpole’s tail
Energy Transformers
• For all the cellular processes to happen,
energy is needed
• Two organelles provide that energy:
– Choloroplasts (in plants)
– Mitochondria (in animals and plants)
Chloroplasts
• Chloroplasts are
organelles that captures
light energy and produces
food to store for later
• Has a double membrane
(like the nucleus)
• The inner membrane folds
in to form stacks of
membranous sacs called
grana/thylakoids.
Chloroplasts
• In the thylakoid
membrane there is the
green pigment called
Chlorophyll
– Traps light energy
– Gives leaves and stems
their green color
Mitochondria
• Mitochondria
produces energy in a
form that can be used
by the cell when
necessary.
• Has an outer
membrane and a
highly folded inner
membrane.
– Provides large surface
area.
Structures for Support and Locomotion
• Cytoskeleton: forms the
framework of the cell
– Maintains shape
– Composed of:
• Microtubules: thin hollow cylinders
made of protein
• Microfilaments: thin, solid protein
fibers
Structures for Support and Locomotion
• Cilia and flagella : Structures that aid in
locomotion and feeding.
– Composed of pairs of microtubules, with
a central pair surrounded by 9 additional
pairs.
– Cilia are short, numerous, hair-like
projections that move in a wavelike
motion
– Flagella are longer projections, move in
a whip-like motion.