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Chapter 4: Cell Structure and
Function
Lecture Outline
Enger, E. D., Ross, F. C., & Bailey, D. B. (2012). Concepts in biology (14th ed.). New York: McGrawHill.
4-1
The Cell Theory
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All living things are made of cells.
A cell
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4-2
The basic unit of all living things.
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The Historical Context of the Cell
Theory
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Robert Hooke coined the
term “cell.”
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Anton van Leeuwenhoek
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4-3
Look at cork cells under a
simple microscope.
Made better microscopes
Used them to look at a variety
of substances and identified
animalcules
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The Historical Context of the Cell
Theory

Mathias Jakob Schleiden
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Theodor Schwann
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4-4
Concluded that all plants were made of cells
Concluded that all animals were made of cells
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Initial Observations of Cells
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Cell wall
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Outer non-living part of
plant cells
Protoplasm
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Interior living portion of the
cell
Nucleus
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Cytoplasm
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Fluid part of the
protoplasm
Organelles
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4-5
Contains the genetic
information of the cell
“Little organs” within the
protoplasm
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Basic Cell Types
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Prokaryotic
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Eukaryotic cells
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Structurally simple cells
Lack a nucleus
Lack most other organelles
Bacteria
More complex
Have a nucleus
Have a variety of organelles
Plants, animals, fungi, protozoa, and algae
Typically much larger than prokaryotic cells
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Major Cell Types
4-7
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Cell Size

Prokaryotic cells
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Eukaryotic cells
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4-8
1-2 micrometers in
diameter
10-200 micrometers in
diameter
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Surface Area-to-Volume Ratio
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Cell size is limited.
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Cells must get all of their nutrients from their environment
through their cell membranes.
Volume increases more quickly than surface area.
Surface area-to-volume ratio must remain small.
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The Structure of Cell Membranes
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Cell membranes
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Thin sheets composed of phospholipids and
proteins
Fluid-mosaic model
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Two layers of phospholipids
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Fluid
Has an oily consistency
– Things can move laterally within the bilayer.
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Mosaic
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4-10
Proteins embedded within the phospholipid bilayer
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The Phospholipid Bilayer
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Phospholipid structure
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Bilayer
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Hydrophobic tails of each
layer associate with each
other.
Hydrophilic heads on the
surface of the bilayer
Cholesterol
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4-11
Hydrophobic tails
Hydrophilic heads
Hydrophobic
Found within the
hydrophobic tails
Keeps the membrane
flexible
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Membrane Proteins
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Some are on the surface
Some are partially embedded.
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Some are completely
embedded.
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Protrude from both sides
Functions
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4-12
Protrude from one side
Transport molecules across
the membrane
Attachment points for other
cells
Identity tags for cells
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Organelles Composed of Membranes
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Plasma membrane (cell membrane)
Different cellular membranous structures serve
different functions
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
Vacuoles and vesicles
Nuclear membrane
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The Plasma Membrane
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Composed of a phospholipid bilayer
Separates the contents of the cell from the external
environment
Important features
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Metabolic activities
Moving molecules across the membrane
Structurally different inside and outside
Identification: Self vs. nonself
Attachment sites
Signal transduction
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The Endoplasmic Reticulum
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Consists of folded membranes and tubes throughout
the cell
Provides a large surface area for important chemical
reactions
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Because it is folded, it fits into a small space.
Two types of ER
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Rough
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Has ribosomes on its surface
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Smooth
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Sites of protein synthesis
Lacks ribosomes
Metabolizes fats
Detoxifies damaging chemicals
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The Golgi Apparatus
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Stacks of flattened
membrane sacs
Functions
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4-16
Modifies molecules that
were made in other
places
Manufactures some
polysaccharides and
lipids
Packages and ships
molecules
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Traffic Through the Golgi
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Vesicles bring molecules from the ER that
contain proteins.
Vesicles fuse with the Golgi apparatus.
The Golgi finishes the molecules and ships
them out in other vesicles.
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Some are transported to other membrane
structures.
Some are transported to the plasma membrane.
Some vesicles become lysosomes.
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Lysosomes
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Vesicles containing enzymes that digest
macromolecules
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Carbohydrates
Proteins
Lipids
Nucleic acids
Interior contains low pH
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These enzymes only work at pH=5.
The cytoplasm is pH=7.
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If the lysosome breaks open, these enzymes will inactivate
and will not damage the cell.
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Functions of Lysosomes
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Digestion
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Destruction
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Of food taken into
the cell
Disease-causing
organisms
Old organelles
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Peroxisomes
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Not formed from golgi membrane, but from
ER membrane
Contain the enzyme catalase
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4-20
Breaks down hydrogen peroxide
Breaks down long-chain fatty acids
Synthesizes cholesterol and bile salts
Synthesizes some lipids
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Vacuoles and Vesicles
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Membrane-enclosed sacs
Vacuoles
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Larger sacs
Contractile vacuoles found in many protozoa
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Vesicles
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4-21
Forcefully expel excess water from the cytoplasm
Smaller vesicles
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Vacuoles and Vesicles
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The Nuclear Membrane
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Separates the genetic
material from the rest of
the cell
Filled with nucleoplasm
Composed of two
bilayers
Contains holes called
nuclear pore complexes
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4-23
Allow large molecules
like RNA to pass through
the membrane into the
cytoplasm
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The Endomembrane System ̶
Interconversion of Membranes
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Membranes are converted from one membranous
organelle to another.
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Energy Converting Organelles
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Mitochondrion
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A small bag with a large
bag stuffed inside
Larger internal bag is
folded into cristae
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Cristae contain proteins
for cellular respiration.
Releases the energy
from food
– Requires oxygen
– Uses the energy to
make ATP
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4-25
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Energy Converting Organelles
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Chloroplasts
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Sac-like organelle
Contain chlorophyll
Perform photosynthesis
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Contain folded membranes
called thylakoids
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Uses the energy in light to
make sugar
Thylakoids stacked into
grana
Thylakoids contain
chlorophyll and other
photosynthetic proteins.
Thylakoids surrounded by
stroma
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Nonmembranous Organelles
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Ribosomes
Cytoskeleton
Centrioles
Cilia flagella
Inclusions
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Ribosomes
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Made of RNA and proteins
Composed of two subunits
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Are the sites of protein
production
Found in two places
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Large
Small
Free floating in the
cytoplasm
Attached to endoplasmic
reticulum
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Cytoskeleton
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Provides shape,
support, and
movement
Made up of
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Microtubules
Microfilaments
(actin filaments)
Intermediate
filaments
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Centrioles
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Two sets of
microtubules arranged
at right angles to each
other
Located in a region
called the centrosome
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4-30
Microtubule-organizing
center near nucleus
Organize microtubules
into spindles used in
cell division
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Cilia and Flagella
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Hair-like projections extending from the cell
Composed of microtubules covered by plasma
membrane
Flagella
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Cilia
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Long and few in number
Move with an undulating whip-like motion
Small and numerous
Move back and forth like oars on a boat
9 + 2 arrangement of microtubules
Cell can control their activity
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Cilia and Flagella
4-32
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Inclusions
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Collections of miscellaneous materials
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Can be called granules
Temporary sites for the storage of nutrients
and waste
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Nuclear Components
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Contains chromatin
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Surrounded by double layer of
membrane
Nuclear membrane contains
pores to control transport of
materials in and out of nucleus
Contains one or more nucleoli
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Site of ribosome synthesis
Contains nucleoplasm
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DNA + proteins
Becomes condensed during
cell division into chromosomes
Water, nucleic acids, etc.
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Getting Through Membranes
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Diffusion
Facilitated diffusion
Osmosis
Active transport
Endocytosis
Exocytosis
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Diffusion
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Molecules are in constant,
random motion.
Molecules move from where
they are most concentrated
to where they are less
concentrated.
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This is called diffusion.
Involves a concentration
gradient (diffusion gradient)
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4-36
No concentration
gradient=dynamic
equilibrium
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The Rate of Diffusion
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Depends on
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The size of the molecule
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The size of the concentration gradient
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4-37
Smaller molecules diffuse faster.
The greater the concentration difference,
the faster the diffusion.
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Diffusion in Cells
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Diffusion can only happen if there is no
barrier to the movement of molecules.
Can only happen across a membrane if the
membrane is permeable to the molecule
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Membranes are semi-permeable; they only allow
certain molecules through.
Membrane permeability depends on the
molecules size, charge, and solubility.
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The Direction of Diffusion
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Determined solely by
the concentration
gradient
Diffusion that does not
require energy input is
passive.
Example:
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4-39
Oxygen diffusion
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Osmosis
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The diffusion of water
through a selectivelypermeable membrane
Occurs when there is a
difference in water
concentration on
opposite sides of the
membrane.
Water will move to the
side where there is less
water
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Or more solute
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Osmotic Influences on Cells
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If a cell has less water (more solute) than its
environment
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If a cell has more water (less solute) than its
environment
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It is hypotonic to its surroundings.
If a cell has equal amounts of water (and solute) as
its environment
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It is hypertonic to its surroundings.
It is isotonic to its surroundings.
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Osmotic Influences on Cells
4-42
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Osmosis in Animal and Plant Cells
4-43
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Facilitated Diffusion
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Some molecules have
to be carried across the
membrane.
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Still involves diffusion
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Accomplished by carrier
proteins
Follows a concentration
gradient
Is passive transport
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Facilitated Diffusion, Cont.
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Two groups of membrane proteins
involved:
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4-45
Carrier proteins: attaches to the molecule to be
moved across the membrane and the
combination molecule changes shape; this
allows the molecule to be shifted from one side
of the membrane to the other.
Ion channels: Do not really attach to the
molecule being transported through the
membrane, but operate like gates.
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Active Transport
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Opposite of diffusion
Moves molecules
across a membrane UP
their concentration
gradient
Uses transport proteins
in the membrane
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Specific proteins pump
specific molecules
Requires the input of
energy
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Endocytosis
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Moves large molecules or sets of molecules into the
cell
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Phagocytosis
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Pinocytosis
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Cell drinking
Just brings fluid into the cell
Receptor-mediated endocytosis
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Cell eating
Food engulfed by the membrane
Material enters the cell in a vacuole.
Molecules entering the cell bind to receptor proteins first.
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Exocytosis
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Moves large molecules or sets of molecules
out of the cell
Vesicles containing the molecules to be
secreted fuse with the plasma membrane.
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Contents are dumped outside the cell.
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Endocytosis and Exocytosis
4-49
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Prokaryotic Cells
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Two different types
of prokaryotes
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Domain eubacteria
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Domain archaea
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4-50
Contains bacteria
Contains prokaryotes
that live in extreme
environments
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Prokaryotic Cell Structure
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Contain DNA and enzymes
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Able to reproduce
Engage in metabolism
Surrounded by a plasma membrane
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Plasma membrane surrounded by a cell wall
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Cell wall surrounded by a capsule
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Helps them adhere to hosts
Protects them from destruction
Contain ribosomes
May contain flagella
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Maintains the shape of the cell
Facilitates movement
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Different Types of Eukaryotic Cells
4-52
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Summary of Cell
Organelles and
Their Functions
4-53
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