Chapter 7: A View of the Cell
Objectives
• Relate advances in microscope technology to
discoveries about cells and cell structure.
• Compare the operation of a compound light
microscope with that of an electron microscope
• Identify the main ideas of the cell theory
The History of the Cell Theory
• Cells- the basic units of living organisms
• Compound light microscope uses a series of
lenses to magnify objects in steps
▫ Magnify by up to 1500 times
▫ Beam of light to magnify an
object
The Cell Theory
• Van Leeuwenhoek was the first to describe living
cells seen through a simple microscope
• Studied with a simple microscope
• The research on cells was halted for 200 years
until the compound light microscope was
created
• Robert Hooke studied cork, dead cells of oak
bark
• Called them cells because it reminded him of the
small rooms monks lived in at a monastery
Cell Theory
• 3 Main ideas
1. All organisms are composed of one or more
cells
1. Some organisms just have one, plants and
animals multicelluler
2. The cell is the basic unit of structure and
organization of organisms
3. All cells come from preexisting cells
1. The cell divides to form identical cells
Electron Microscopes
• Uses a beam of electrons instead of light to
magnify structures up to 500 000 times their
actual size
▫ See structures inside the cell
▫ Electrons can collide with air particles and scatter,
specimens must be examined in a vacuum
• 2 basic types
1. Scanning electron microscope (SEM)- learn 3D shape
2. Transmission electron microscope (TEM)study structure contained in a cell
Two Basic Cell Types
• Organelles- small, specialized structures inside
the cell that help the cells function
• Each organelle has a specific function in the cell
• 2 broad types of cells
▫ Contain membrane bound organelles
▫ Do not contain membrane bound organelles
Prokaryotic Cells
• Don’t contain any membrane-bound organelles
• Prokaryotes- unicellular organisms, bacteria,
do not have membrane bound organelles
Eukaryotic Cells
• Cells that contain membrane bound organelles
• Eukaryotes- most of the multicellular organisms
we know are made up of eukaryotic cells
▫ Some eukaryotes are unicellular
▫ Amoebas, some algae, and yeast
Nucleus
• Eukaryotic cells contain a prominent structure
• Responsible for cell division
• Nucleus- the central membrane bound organelle
that manages or controls cellular functions
Objectives
• Describe how a cell’s plasma membrane
functions
• Relate the function of the plasma membrane to
the fluid mosaic model
Maintaining a Balance
• All living things cells must maintain a balance
regardless of inter and external conditions
• Plasma membrane- flexible boundary between
the cell and its environment
▫ Allows a steady supply of nutrients to come into
the cell
• Maintaining the balance of an environment is
called what?
▫ Homeostasis
Selective Permeability
• A process in which a membrane allows some
molecules to pass through while keeping others
out
▫ Some molecules freely enter and leave through the
cell membrane
▫ Others must be allowed into the cell only at
certain times, amounts, and channels
Structure of the Plasma Membrane
• Phospholipids have a glycerol backbone, two
fatty acid chains, and a phosphate group
• Membrane is composed of a phospholipid
bilayer
▫ Two layers of phospholipids back-to-back
The Phospholipid Bilayer
• Phosphate group is critical in the formation and
function of the plasma membrane
• Two fatty acid tails are nonpolar
• The head, containing the phosphate, is polar
• Polar heads allow the cell membrane to interact
with its water environment because water is
polar
• The tails avoid water, form the interior of the
membrane
• Water soluble molecules do not easily move
through the membrane because they are stopped
by water-insoluble layer in the middle
• The phospholipid bilayer is a fluid mosaic model
because the phospholipids move within the
membrane just as water molecules move with
the currents in a lake
• Proteins also move
▫ Create “mosaic” or pattern on the surface
• Cholesterol is also in the membrane
▫ helps prevent fatty acid tails from sticking
together
▫ Necessary for diet
• Proteins help transport molecules through the
membrane that can’t normally pass
▫ Such as water-soluble substances
• Transport membranes- move needed substances
or waste materials through the plasma
membrane
• Other proteins and carbohydrates identify
molecules
Objectives
• Identify the structures and function of the parts
of a typical eukaryotic cell.
* Not all cells look like the cells we will be looking
at, but these cells are a model for how the majority
of the cells are organized
• Explain the advantages of highly folded
membranes in cells.
• Compare and contrast the structures of plant
and animals cells.
• Two types of eukaryotes
▫ Animal
▫ Plant
• Schleiden was the scientist who discovered that
all plants are made up of cells
• Schwann was the scientist who concluded that
all animals are composed of cells
Cellular Boundaries
• Plasma membrane is a fluid mosaic model that
describes a flexible boundary of a cell
• Plant cells, fungi, bacteria, and some protists
have an additional boundary
• Cell wall- a fairly rigid structure located outside
the plasma membrane that provides additional
support and protection
Cell Wall
• Function- forms an inflexible barrier that
protects the cell and gives support
• Cell wall is composed of cellulose
• Forms a thick tough mesh of fibers
• Very porous and allows molecules to enter
• Does not select which molecules can enter into
the cell
The Nucleus and Cell Control
• Nucleus
• Function- gives direction to make proteins
• Every part of the cell depends on proteins to
function
• The nucleus contains the blueprint to form
proteins
• Controls the activity of the organelles
• “Control center”
• Chromatin- strands of genetic material, DNA
• Master set of directions
• When the cell divides, the chromatin condenses
to form chromosomes
• Nucleolus- organelle inside the nucleus
• Function- makes ribosomes
• Ribosomes• Function- the sites where the cell produces
proteins according to the directions of DNA
▫ Not bound by a membrane
▫ Made of RNA and protein
• Cytoplasm- clear gelatinous fluid inside a cell
• Function- suspends the cell’s organelles
• Ribosomes and translated RNA are transported
to the cytoplasm through the nuclear envelope
• Nucelar envelope
• Function- separates the nucleus from the
cytoplasm
▫ Double membrane made up of two phospholipid
bilayers containing small nuclear pores for
substances to pass through
▫ Ribosomes and translated RNA pass into the
cytoplasm through these pores in the nuclear
envelope
Assembly, Transport, and Storage
•
•
•
•
Endoplasmic reticulum (ER)Function - site of cellular chemical reactions
Takes up tremendous space
Folds and pleats fit into compact units
▫ Increases surface area
• Ribosomes are attached to the surface called
rough endoplasmic reticulum
▫ Where they carry out the function of protein
synthesis
▫ Proteins go to other organelles
• Also found floating in the cytoplasm
• Area of the ER that are not studded with
ribosomes are known as smooth ER
• Function: Produce and store lipids
Golgi apparatus
• After proteins are made, they are transferred to
the Golgi apparatus
• Function- sorts proteins into packages and packs
them into membrane-bound structures to be
sent to the appropriate destination
• Vesicles- the membrane –bound structures
• Like mail being sorted at the post office
• Vacuoles- membrane bound compartment
• Function- temporary storage of materials
▫ Stores food, enzymes, and other materials
▫ Some store waste
• Animals cells usually don’t contain vacuoles, if
they do the vacuoles are much smaller
Lysosomes
• Lysosomes- organelles that contain digestive
enzymes
• Function- digest excess or worn out organelles,
food particles, and viruses or bacteria
▫ “Garbage disposal”
• Lysosomes can fuse with vacuoles and dispense
their enzymes into the vacuole, digesting its
contents
• https://www.youtube.com/watch?v=ekdIEpSf1I
Energy in a cell
• Protein production, modifications,
transportation, and digest all require energy
• Chloroplasts and mitochondria provide energy
Chloroplasts
• Function: cell organelles that capture light
energy and convert it to chemical energy
• Only found in plant cells
• Located in green plants and some protists
• Has a double membrane
• Thylakoid trap energy from sunlight
• Stacked in grana, resemble stacked coins
• The fluid that surrounds them is called stroma
• Chloroplast belongs to a group of plant
organelles called plastids, used for storage
• Some store starches or lipids
• Other contain pigments, molecules that give off
color
• Named according to their pigment or color they
contain
• Chloroplasts contain green pigment chlorophyll
• Chlorophyll trap light energy and give leave
and stem their green color
Mitochondria
• Mitochondria- membrane-bound organelles in
plant and animal cells
• Function- transform energy for the cell
• “Power house”
• Energy is stored in the bonds of other molecules
that cell organelles can access easily and quickly
when energy is needed
• Folded inner membrane
• Occur in varying numbers depending on the
function of the cell
Cytoskeleton
• Function- support structure for the cell within
the cytoplasm
• Forms a framework for the cell
• Constantly changing
• Microtubules- thin, hollow cylinders made of
protein
• Microfilaments- smaller, solid protein fibers
• Centrioles- occur in pairs and made up of
microtubules
• Important in cell division
Cilia and Flagella
• Cilia- short, numerous projections that look like
hairs
• Flagella- longer projections that move with a
whip-like motion
• Usually one or two flagella
• Unicellular organisms, cilia and flagella are the
major means of locomotion
Cell Part
Prokaryotic Cell
Eukaryotic Cell
Plasma Membrane
Present
Present
Cell wall
Present
Present in plants
Ribosome
Present
Present
Chloroplast
Absent
Absent
Cytoskeleton
Absent
Present
Endoplasmic reticulum
Absent
Present
Golgi apparatus
Absent
Present
Lysosome
Absent
Present in some
Mitochondria
Absent
Present
Nucleus
Absent
Present
Vacuole
Absent
Present