Download Cells

 1665-Robert
Hooke first used the term “cell”
 1670-Anton
van Leeuwenhoek
discovered bacteria and single
celled organisms in pond water
 1830s-Matthias
Schleiden and Theodor
Schwann propose the cell theory.
 Rudolf
Virchow observes cells dividing and
reports cells come from existing cells.
1. A cell is the basic unit of life
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Nothing smaller than a cell is “alive”
2. All living things are made of cells
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Cells may specialize but all cells have certain
structures in common
Organisms may be unicellular or multicellular
3. New cells come from pre-existing cells.
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New cells come from cell division
Cells are small
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Surface area must be large enough to allow
nutrients to enter and wastes to leave
As cells grow their surface area does not grow as
fast as their volume.
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This makes large cells inefficient. Materials cannot
get in and to where they are needed fast enough
Light microscope (LM)
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light passes through specimen and is bent by glass lenses
Object can be magnified up to 1000 times
Resolving power is a measure of the clarity of image.
 LM only resolve to .2 microns
Advantageous for viewing live cells
Stains allow for contrast but usually kill the cells
Electron microscope (EM)—introduced in 1950s
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Uses a beam of electrons to pass through the specimen
Resolution is 100 times better than the LM
You see a picture of the specimen-not the actual
specimen
specimen must be dead to view it—no movement can
be detected
 Transmission
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EM
Electrons pass through the cell
used to study internal structures
 Scanning
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EM
cells coated with thin layer of metal
electrons move back and forth across the surface
This creates a 3-D image of the external
structures
 Prokaryotic
cells lack a membrane bound
nucleus
 Eukaryotic cells have a nucleus as well as
other membrane bound structures
DNA is found in a central area called the nucleoid
 Most have a cell wall
 Flagella may be used for
locomotion
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 Smallest
of all cells
 Found everywhere
 Divided into two domains
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Eubacteria / Bacteria
Archaebacteria
 Cell
membrane
 Cytoplasm
 Ribosomes
 Nucleoid
 Cell wall
 Capsule
 Cause
disease
 Decomposers
 Produce food
 Synthesize molecules
 Larger
in size
 Membrane bound organelles designed to
carry out particular functions
 Can specialize to work together
Nucleus
Contains DNA
a. extended out under normal cell conditions
is called chromatin
b. during cell division it shortens and forms
chromosomes
The nucleus is surrounded by a double
membrane called the nuclear envelope. It has
pores to allow materials to pass in and out.
There is also a darker region called the
nucleolus which makes
ribosomes.
Ribosomes
very abundant structures
made of two subunits, a small and a large one
produces proteins
Endoplasmic reticulum
network of flattened sacs coming from the
nuclear envelope and extending out into the
cell.
The twists and turns create more surface area.
Two types of ER exist:
1. rough ER has ribosomes attached.
proteins made in the ribosomes are
modified as they move through the ER
2. smooth ER has no ribosomes.
makes lipids such as cholesterol and
hormones, produces the enzymes that
detoxify the liver (alcohol and drugs)
Golgi apparatus
Looks like a stack of flattened sacs
Receives, processes and packages proteins to
be sent out of the cell.
Lysosomes
Have a low pH and contain enzymes for
digestion of molecules, bacteria, or worn out
parts
Vacuoles
Sacs for storage of food, water, waste.
Plants usually have one large central one (it
may take up 90% of the cell volume)
Chloroplasts
Contain the pigment chlorophyll
that can absorb sunlight.
Light is used to make sugar in
photosynthesis.
They have a double membrane
with stacks of inner membranes
Mitochondria
Often called the powerhouse of the cell.
These structures carry on cellular respiration
which turns sugars into ATP for energy.
Also has a double membrane with the inner
one having many folds.
Cytoskeleton
Internal network of fibers.
They give support and shape to the cell.
1. Actin filaments are two twisted strands
that support structures and cause
movement.
2. Intermediate filaments are ropelike and
mainly provide strength and support.
3. Microtubules are cylindrical and help cause
motion.
Structures for movement:
Cilia-short, made from
microtubules
Flagella-long, also formed with microtubules
Centrioles
Short barrels made of microtubules
Organize the microtubules that will separate
the chromosomes in cell division.
PLANT CELLS:
Cell walls
Chloroplasts
Large central vacuole
No lysosomes
No centrioles
ANIMAL CELLS:
No cell walls
No chloroplasts
Several small vacuoles
Lysosomes
Centrioles
The idea that a long time ago, aerobic bacteria
entered a larger host cell.
This allowed the host cell to produce energy
giving it an evolutionary advantage.
The two cells became one functioning cell.
Evidence:
1. Mitochondria and chloroplasts have their
own DNA. It is circular, like prokaryotic
DNA
2. They have a double membrane
3. They can reproduce on their own in a
similar way to bacteria
4. They are similar in size to prokaryotes
The plasma membrane is the boundary between
the outside and inside of the cell. It regulates the
passage of molecules into and out of the cell and
allows cells to communicate with each other.
 Fluid
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mosaic model
The cell membrane is fluid-having the
consistency of olive oil, the phospholipids can
move and wiggle
The cell membrane is a Mosaic, having embedded
molecules scattered throughout
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Proteins-some transport materials in and out, others
act as receptors for other molecules to bind to the cell
Cholesterol-gives support to the membrane
Carbohydrate chains-serve as markers
Types of proteins in the membrane
1. Channel-molecules pass through it
2. Carrier-attaches to molecule to move it
3. Recognition-recognized by immune system
4. Receptor–site to bind with another molecule
5. Enzymatic-carry out reactions
6. Junction-involved in forming junctions
between cells
1. Channel
4.Receptor
2. Carrier
5. Enzymatic
3.Recognition
6. Junction
Passive: no energy is used
1. Diffusion
2. Facilitated diffusion
3. Osmosis
Diffusion:
Movement follows the concentration gradient
(from high to low)
Remember, molecules are always in motion
Actually, few molecules can diffuse across the
hydrophobic part of the membrane.
What does?
-Alcohols
-Gases (oxygen, carbon dioxide)
Facilitated diffusion:
Molecules are helped by proteins. They still
flow with the gradient so no energy is used.
The proteins are specific to the molecule they
move.
What moves this way?
-Water
-Glucose
-Amino acids
Osmosis:
The diffusion of water across the membrane.
The solute is unable to pass so the water
moves depending on the solute concentration.
Isotonic solutions-same as cell
Hypotonic solutions-cause cell to gain water
Hypertonic solutions-cause cell to lose water
Active transport-cells must use energy to move
the material. Movement is against the
gradient.
Endocytosis-into cell
phagocytosis-large food particle
pinocytosis-liquid or small particles
receptor mediated-proteins select
Exocytosis-out of cell
Endocytosis
 Extra
cellular material (outside of cell) is
produced by the cell and transported out.
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Cell walls in plants
Fibers in certain tissues
Animal cells:
Tight junctions keep cells closely joined (like a
zipper). This prevents leaking of materials.
Gap junctions form when cell membrane
channels join. Some small molecules may pass
through but mainly it gives strength.
Anchoring or adhering junctions connect with
filaments that allow movement in tissues that
stretch.
Tight
Anchoring
Gap
Plant cells:
Plasmodesmata connect plant cells with
numerous channels allowing exchange of
materials.