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Chapter 2
*Lecture Outline
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Chapter 2 Outline
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The Study of Cells
A Prototypical Cell
Plasma Membrane
Cytoplasm
Nucleus
Life Cycle of the Cell
Aging and the Cell
The Study of Cells
• The study of cells: cytology
– only visible by microscopy
– measured in micrometers (µm)
• 1 cm = 10,000 µm
– sizes vary
• from 7µm (RBC) to 120µm (oocyte)
– shapes vary
• flat, cylindrical, oval, and irregular in shape
Figure 2.1
Types of Microscopy
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Light Microscopy (LM)
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visible light passes through the cell
Transmission Electron Microscopy
(TEM)
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a beam of electrons passes through the cell
can magnify about 100X greater than LM
Scanning Electron Microscopy (SEM)
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beam of electrons bounces off surface of the
cell to provide a 3D study of the cell surface
Comparison of the
Three Types of Microscopy
Figure 2.2
Cellular Functions
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Covering
Lining
Storage
Movement
Connection
Defense
Communication
Reproduction
Cellular Functions
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Table 2.1
Selected Common Types of Cells and Their Functions
Functional
Category
Example
Specific
Functions
Functional
Category
Example
Specific
Functions
Covering
Epidermal cells in skin
Protect outer
surface of body
Connection
(attachment)
Collagen (protein) fibers from
fibroblasts
Form ligaments
that attach bone
to bone
Lining
Epithelial cells in small intestine
Regulate nutrient Defense
movement into
body tissues
Lymphocytes
Produce
antibodies to
target antigens or
invading cells
Storage
Fat cells
Store lipid
reserves
Liver cells
Store
carbohydrate
nutrients as
glycogen
Muscle cells of heart
Pump blood
Skeletal muscle cells
Move skeleton
Movement
Communication
Reproduction
Nerve cells
Send information
between regions
of the brain
Bone marrow stem cells
Produce new
blood cells
Sperm and oocyte cells
Produce new
individual
(left-1): © Ed Reschke/ Peter Arnold; (left-2-4): © The McGraw-Hill Companies, Inc./ Photo by Dr. Alvin Telser; (right-1): © Ed Reschke/ Peter Arnold; (right-2): © The McGraw Hill
Companies, Inc./Photo by Dr. Alvin Telser; (right-3): © Carolina Biological Supply Company/Phototake; (right-4): © Jason Burns/ Phototake
A Prototypical Cell
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A generalized cell (not a real cell in the
body)
Combines features from many different
cells for teaching purposes
Most human cells have three basic parts:
Plasma (cell) membrane
Cytoplasm
Nucleus
A Prototypical Cell
Figure 2.3
Plasma (Cell) Membrane
• An extremely thin outer border on cell
• Serves as a selective physical and
chemical barrier deciding what comes into
and leaves the cell
• It is the “gatekeeper” that regulates the
passage of gases, nutrients, and wastes
between the internal and external
environments of the cell
Composition and Structure
of Membranes
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The plasma membrane and membranes within
the cell have two molecular components:
Lipids
Proteins
Structure of Membranes
Figure 2.4
Membrane Lipids
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Two layers: outer and inner
Insoluble in water . . . prevents cells from
dissolving in water
3 types of lipids in membranes:
Phospholipids
Cholesterol
Glycolipids
Phospholipids
• The majority of lipids in cell membranes
• Each has a polar (charged) region and
nonpolar (uncharged) region
• When exposed to aqueous (water)
environment, they form a phospholipid
bilayer
– polar regions face outside and inside of
the cell
– nonpolar regions face each other (form
internal core of the membrane)
Other Lipids
Cholesterol
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about 20% of all membrane lipids
strengthens and stabilizes membrane against
extreme temperature
Glycolipids
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about 5–10% of all membrane lipids
have carbohydrate (sugar) molecules attached
facing out and forming the glycocaylx
Membrane Proteins
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Lipids are majority of structure but
proteins give membrane functions
Proteins: complex molecules made of
amino acids chains
2 types of membrane proteins:
Integral
Peripheral
Membrane Proteins
Figure 2.4
Integral Membrane Proteins
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Embedded in phospholipid bilayer
Span the entire thickness of the membrane
Exposed to the outside and inside of the cell
Also termed transmembrane proteins
Can have carbohydrates (sugars) attached to
outer surface = glycoproteins
The glycoproteins and the glycolipids form the
glycocalyx on the external surface of the
plasma membrane
Have many varied functions
Peripheral Proteins
• Not embedded in the lipid bilayer
• Loosely attached to the external or internal
surface of the plasma membrane
• Have many varied functions
General Functions of the
Plasma (Cell) Membrane
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Communication
Intercellular connection
Physical barrier
Selective permeability
Protein-Specific Functions of the
Plasma (Cell) Membrane
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Transport
Intercellular connection
Anchorage for the cytoskeleton
Enzyme activity
Cell–cell recognition
Signal transduction
Crossing the Membrane
2 general types of membrane transport:
Passive:
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does not require energy from the cell
materials move from area of higher
concentration “down” to area of lower
concentration = diffusion
Active:
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requires energy from the cell
materials are moved up or against
concentration gradient
Passive Transport
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All involve diffusion
None require energy from the cell
4 types of diffusion:
Simple diffusion
Osmosis
Facilitated diffusion
Bulk filtration
Types of Diffusion
Simple diffusion
• small and/or nonpolar (uncharged)
molecules
– examples
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movement of O2 out of lungs (higher
concentration) into blood (lower concentration)
movement of CO2 from blood (higher
concentration) into lungs (lower concentration)
Types of Diffusion
Osmosis
• applies only to movement of H2O
– same principle as simple diffusion
– H2O moves from region of higher
concentration to region of lower
concentration
Types of Diffusion
Facilitated diffusion
• for large and/or polar (charged)
molecules
• requires a specific transport protein
(integral membrane protein) that will bind
to the molecule being transported
Bulk Filtration
• diffusion of both liquids (solvents) and
dissolved molecules (solutes)
Active Transport
• Movement of a molecule against the
concentration gradient
– opposite of passive transport
• Requires energy from the cell
• May involve a transport protein
– example is an ion pump
– Na+ and K+ are moved in opposite directions
against their concentration gradients
Active Transport by Ion Pump
• Na+ is
pumped out
of cell and K+
is pumped
into cell
• Requires
energy
Figure 2.5
Bulk Transport
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Moves large molecules or bulk structures
across the plasma membrane
Requires energy from the cell
Can go in either direction:
1. Exocytosis: out of the cell
2. Endocytosis: into the cell
Bulk Transport
Exocytosis
• materials to be secreted out of cell and
are packaged into vesicles
• vesicles fuse with plasma membrane
and materials are released
Endocytosis
• opposite of exocytosis
• materials are taken into the cell
packaged into vesicles
Exocytosis
Figure 2.6
Endocytosis
Types of Endocytosis
Phagocytosis
nonspecific uptake of particles by formation of
membrane extensions (pseodopodia) that
surround particles to be engulfed
Figure 2.7
Types of Endocytosis
Pinocytosis
nonspecific uptake of extracellular fluid
Figure 2.7
Types of Endocytosis
Receptor-mediated endocytosis
engulfing of specific molecules bound to
receptors on the surface of the plasma
membrane
Figure 2.7
Cytoplasm
• All materials (solid and liquid) between
plasma membrane and nucleus
̶ Cytosol
̶ Inclusions
̶ Organelles
Figure 2.8
Cytosol
• A viscous, syruplike fluid containing many
different dissolved substances such as:
– Ions
– Nutrients
– Proteins
– Carbohydrates
– Amino acids
Inclusions
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Large storage aggregates of complex
molecules found in the cytosol
Examples:
Melanin: brown pigment in skin cells
Glycogen: long chains of sugars in the
liver and skeletal muscles
Organelles
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Means “little organs”
Many types, each perform different function
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A type of division of labor
The type and number of organelles within a cell is a
reflection of the cell’s function
Organelles can be classified in two types:
Membrane-bound
Non-membrane-bound
Membrane-Bound Organelles
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Biochemical activity in organelle is
isolated from cytosol and other
organelles
Examples are:
Endoplasmic reticulum
Golgi apparatus
Lysosomes
Peroxisomes
Mitochondria
Endoplasmic Reticulum (ER)
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A network of intracellular membrane-bound
tunnels
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enclosed spaces are called cisternae
2 types of ER:
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Smooth endoplasmic reticulum (SER)
Rough endoplasmic reticulum (RER)
Endoplasmic Reticulum
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Nucleus
Cisternae
Ribosomes
Ribosomes
Rough ER
Smooth ER
TEM 12,510x
Functions of Endoplasmic Reticulum
Figure 2.8
1. Synthesis: provides a place for chemical reactions
a. Smooth ER is the site of lipid synthesis and carbohydrate metabolism
b. Rough ER synthesizes proteins for secretion, incorporation into the
plasma membrane, and as enzymes within lysosomes
2. Transport: Move molecules through cisternal space from one part of
the cell to another; sequestered away from the cytoplasm
3. Storage: Stores newly synthesized molecules
4. Detoxification: Smooth ER detoxifies both drugs and alcohol
(bottom): © Dennis Kunkel/ Phototake
Smooth Endoplasmic Reticulum
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Walls have a smooth appearance
Continuous with RER
Functions include:
1. Synthesis, transport, and storage of lipids
including steroid hormones
2. Metabolism of carbohydrates
3. Detoxification of drugs, alcohol, and poisons
Rough Endoplasmic Reticulum
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Walls appear rough due to attachment of
ribosomes on outside of the RER membrane
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ribosomes synthesize proteins
The RER functions to synthesize, transport, or
store proteins for:
1. Secretion by the cell
2. Incorporation into the plasma membrane
3. Creation of lysosomes
Golgi Apparatus
• Stacked cisternae whose lateral edges
bulge, pinch off, and give rise to small
transport and secretory vesicles
• Function to receive proteins and lipids
from the RER for modification, sorting, and
packaging
– Receiving region is the cis-face
– Shipping region is the trans-face
Golgi Apparatus
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Functions of Golgi Apparatus
1. Modification: Modifies new proteins destined for lysosomes, secretion,
and plasma membrane
2. Packaging: Packages enzymes for lysosomes and proteins for secretion
3. Sorting: Sorts all materials for lysosomes, secretion, and incorporation
into the plasma membrane
Transport
vesicle
Vacuole
Vacuole
Shipping
region
Secretory
vesicles
Shipping
region
Vacuole
Receiving
region
TEM17,770x
(a)
Transport
vesicle
Cisternae
Rough endoplasmic
Transport vesicle
reticulum
Golgi apparatus
Transport
vesicle
Lumen of cisterna filled
with secretory product
Protein incorporation
in plasma membrane
6c
Membrane protein
transport vesicles
Shipping
region
Lysosomes
Plasma
membrane
4
Secretory
vesicles
Exocytosis
2
3
Figure 2.9
Extracellular
fluid
6a
5
1
RER proteins in transport vesicle
2 Vesicle from RER moves to Golgi apparatus
5
Receiving
region
1
Transport
vesicles
5
Cytoplasm
6b
(b) Movement of materials through the Golgi apparatuss
a: © DennisKunkel/ Phototake
3
Vesicle fuses with Golgi apparatus receiving
region
4
Proteins are modified as they move through Golgi
apparatus
5
Modified proteins are packaged in shipping region
6
Vesicles become either (a) lysosomes,
(b) secretory vesicles that undergo exocytosis,
or (c) plasma membrane
Protein Flow through the
Golgi Apparatus
1. Proteins synthesized in RER get packaged into
transport vesicles.
2. Transport vesicles pinch off from RER and
fuse with the receiving cis-face of the Golgi
apparatus.
3. The proteins move between and are modified
in the cisternae of the Golgi apparatus.
4. Modified proteins are packaged in secretory
vesicles.
5. Secretory vesicles either participate in
exocytosis or become lysosomes in the cel.l
Protein Flow through the
Golgi Apparatus
Figure 2.9
Lysosomes
• Vesicles generated by the Golgi apparatus
• Contain enzymes used to digest and
remove waste products and damaged
organelles within the cell (autophagy)
• When a cell is dying it releases lysosomal
enzymes that digest the cell (autolysis)
Lysosomes
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Lysosomes
TEM 16,000x
Lysosome
Functions of Lysosomes
1. Digestion: Digest all materials that enter cell by endocytosis
2. Removal: Remove worn-out or damaged organelles and cellular
components (autophagy); recycle small molecules for resynthesis
3. Self-destruction: Digest the remains (autolysis) after cellular death
Figure 2.10
(top left): © David M. Phillips/ Visuals Unlimited
Peroxisomes
• Vesicles smaller than lysosomes
• Use O2 and an enzyme (catalase) to
detoxify harmful molecules taken into the
cell
Peroxisomes
Figure 2.11
Mitochondria
• Bean-shaped organelles with double
membrane
– inner membrane folded into shelf-like cristae
– internal fluid: matrix
• Function to produce a high energy
containing molecule called ATP on the
cristae
• Cells that require more energy have more
mitochondria than cells requiring less
energy
Mitochondrion
Figure 2.12
Non-Membrane-Bound Organelles
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In direct contact with the cytosol
Examples are:
Ribosomes
Cytoskeleton
Centrosomes and centrioles
Cilia and flagella
Microvilli
Ribosomes
• Comprised of a large and small subunit
• Responsible for protein synthesis
• Free ribosomes float unattached within
the cytosol
• Fixed ribosomes are attached to the
outer surface of RER
Ribosomes
Figure 2.13
Cytoskeleton
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Proteins organized in the cytosol as solid
filaments or hollow tubes
3 main protein types:
Microfilaments
Intermediate filaments
Microtubules
Microfilaments
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7 nm (nanometer) thick filaments
• 1,000 nanometers = 1 micron (µm)
Maintain and change cell shape
Participate in muscle contraction and cell
division
Intermediate Filaments
• 8−12 nm thick filaments
• Provide structural support and stabilize
junctions between apposed cells
Microtubules
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25 nm thick hollow tubes
Radiate from centrosome
Fix organelles in place
Maintain cell shape and rigidity
Direct movement of organelles in the cell
Allow cell motility (in cilia and flagella)
Cytoskeleton
Figure 2.14
Centrosome and Centrioles
• Centrosome: a pair of centrioles at right
angles to each other
• Centriole: nine sets of microtubule triplets
– involved in organizing microtubules
– attached to chromosomes during cell
division causing chromosomal migration
Centrosome and Centrioles
Figure 2.15
Cilia and Flagella
• Projections of the cell containing
cytoplasm and microtubules capable of
movement
• Cilia: grouped on cells that move objects
across their surface (i.e., cells of the
respiratory tree and oviduct)
• Flagella: longer, usually singular, to
propel a cell (e.g., sperm)
Cilia and Flagella
Figure 2.16
Microvilli
• Extensions of cell, not capable of motion
– much smaller than cilia
• Increase the surface area to increase
absorption of food
– found on surface of cells of the small intestine
Nucleus
• Control center for cellular activity
• Contains DNA (deoxyribonucleic acid), a
complex molecule containing
– when not dividing, nuclear DNA is
unwound into fine filaments called
chromatin
– during cell division chromatin coils
tightly to form chromosomes
Chromatin and Chromosomes
Figure 2.17
Figure 2.18
The Nuclear Envelope
• Double membrane structure
• Controls entry and exit of molecules from
nucleus and cytoplasm
• Outer membrane is continuous with
endoplasmic reticulum
• Nuclear pores are selectively permeable
channels that allow some molecules in or
out of the nucleus
Nucleoli
• Dark staining bodies within the nucleus
• Responsible for making the components of
the small and large units of the ribosome
Figure 2.17
Life Cycle of the Cell
• Cells are always in one of two states:
Interphase: maintenance (resting) phase
between cell divisions where the following
activities occur:
• normal activities
• prep for cell division
• cells spend the majority of life in this
Mitotic phase: when the cell divides
Interphase
and Mitosis
Figure 2.20
Interphase Stages
G1 Phase
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Cells grow, replicate organelles, produce proteins
for replication, and centrioles just prior to cell
division
S Phase
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“Synthesis” phase where DNA replicates in
preparation for cell division
G2 Phase
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Centriole replication is complete
Other organelle production continues
Enzymes needed for cell division are synthesized
Interphase Stages
Figure 2.19
Mitotic Phase
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Mitotic cell division is the process by
which two daughter cells are produced
that are genetically identical to the
original (mother) cell
2 distinct events occur in this phase:
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Mitosis: duplication of DNA and division
of the nucleus
Cytokinesis: division of the cytoplasm
and the mother cell
Stages of Mitosis
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Mitosis has 4 consecutive stages
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takes less than two hours to complete all 4
1. Prophase
2. Metaphase
3. Anaphase
4. Telophase
Stages of Mitosis
Figure 2.19
Prophase
• Chromatin supercoils forming
chromosomes.
• Duplicate, identical sister chromatids are
conjoined at a region called the
centromere.
• Elongated microtubules called spindle
fibers begin to grow from each centriole.
• The end of prophase is marked by the
dissolution of the nuclear envelope.
Metaphase
• Chromosomes
line up along the
equatorial plate.
• Spindle fibers
attach to the
centromere of
sister chromatids
and form an oval
structure array
called the mitotic
spindle.
Figure 2.20
Anaphase
• Spindle fibers pull
sister chromatids
apart to opposite
ends of the
dividing cell.
Figure 2.20
Telophase
• The nuclear envelope forms
around each set of
chromosomes.
• Chromosomes begin to
uncoil and the mitotic
spindle disappears.
• A pinched area, the
cleavage furrow, appears
that will complete the
physical division of the
daughter cells.
Figure 2.20
Aging and the Cell
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Aging is a normal and continuous
process
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indicated by changes in number of
organelles or chromatin structure
Cells can die in two general ways:
1. Harmful agents or mechanical damage
2. Programmed cell death or apoptosis
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