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Anatomy & Physiology I
Lecture 2
Chapter 3: Cells
The Cell
• Cell - structural and functional unit of life
– Biochemical activities dictate their shape and
function
• Organismal functions depend on individual
and collective cell functions
• Continuity of life has cellular basis
The Diversity of cells
• Each cell has the same genomic information
• Over 200 different types of human cells
– differ in size, shape, and functions
Figure 3.1 Cell diversity.
Erythrocytes
Fibroblasts
Epithelial cells
Cells that connect body parts, form linings, or transport
gases
Skeletal
muscle
cell
Smooth
muscle cells
Cells that move organs and body parts
Macrophage
Fat cell
Cell that stores nutrients
Cell that fights disease
Nerve cell
Cell that gathers information and controls body functions
Sperm
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Cell of reproduction
Figure 3.2 Structure of the generalized cell.
Nuclear envelope
Chromatin
Nucleolus
Nucleus
Plasma
membrane
Smooth endoplasmic
reticulum
Cytosol
Mitochondrion
Lysosome
Centrioles
Rough
endoplasmic
reticulum
Centrosome
matrix
Ribosomes
Golgi apparatus
Cytoskeletal
elements
• Microtubule
• Intermediate
filaments
© 2013 Pearson Education, Inc.
Secretion being released
from cell by exocytosis
Peroxisome
Fundamental Structures of most cells
• Plasma membrane—flexible outer boundary
• Cytoplasm—intracellular fluid containing
organelles
• Nucleus— “control center”
compartmentalizes DNA (the genome)
The Plasma Membrane
• Lipid bilayer and proteins in constantly
changing fluid mosaic
• Plays dynamic role in cellular activity
• Separates intracellular fluid (ICF) from
extracellular fluid (ECF) (Interstitial fluid)
Figure 3.3 The plasma membrane.
Extracellular fluid
(watery environment
outside cell)
Polar head of
phospholipid
molecule
Nonpolar tail
of phospholipid
molecule
Cholesterol Glycolipid
Glycocalyx
(carbohydrates)
Lipid bilayer
containing
proteins
Outward-facing
layer of
phospholipids
Inward-facing
layer of
phospholipids
Cytoplasm
(watery environment
inside cell)
Integral Filament of Peripheral
proteins cytoskeleton proteins
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Glycoprotein
Function of Membrane Proteins
• Control movement in and out of cells
• Receptors for signal transduction
– the communication signal from outside the cell to
inside the cell
• Attachment to cytoskeleton and extracellular
matrix
– Cellular movement
Figure 3.4a Membrane proteins perform many tasks.
Transport
• A protein (left) that spans the membrane
may provide a hydrophilic channel across
the membrane that is selective for a
particular solute.
• Some transport proteins (right) hydrolyze
ATP as an energy source to actively pump
substances across the membrane.
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Figure 3.4b Membrane proteins perform many tasks.
Signal
Receptor
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Receptors for signal transduction
• A membrane protein exposed to the
outside of the cell may have a binding site
that fits the shape of a specific chemical
messenger, such as a hormone.
• When bound, the chemical messenger may
cause a change in shape in the protein that
initiates a chain of chemical reactions in the
cell.
Figure 3.4c Membrane proteins perform many tasks.
Attachment to the cytoskeleton and
extracellular matrix
• Elements of the cytoskeleton (cell's internal
supports) and the extracellular matrix
(fibers and other substances outside the
cell) may anchor to membrane proteins,
which helps maintain cell shape and fix the
location of certain membrane proteins.
• Others play a role in cell movement or bind
adjacent cells together.
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Functions of Membrane Proteins
• Enzymatic activity
• Intercellular joining
• Cell-cell recognition
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Figure 3.4d Membrane proteins perform many tasks.
Enzymatic activity
Enzymes
• A membrane protein may be an enzyme
with its active site exposed to substances in
the adjacent solution.
• A team of several enzymes in a membrane
may catalyze sequential steps of a metabolic
pathway as indicated (left to right) here.
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Figure 3.4d
Figure 3.4e Membrane proteins perform many tasks.
Intercellular joining
• Membrane proteins of adjacent cells may
be hooked together in various kinds of
intercellular junctions.
• Some membrane proteins (cell adhesion
molecules or CAMs) of this group provide
temporary binding sites that guide cell
migration and other cell-to-cell interactions.
CAMs
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Figure 3.4f Membrane proteins perform many tasks.
Cell-cell recognition
• Some glycoproteins (proteins bonded to
short chains of sugars) serve as
identification tags that are specifically
recognized by other cells.
Glycoprotein
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Cell Junctions
• Cells adhere to one another for higher order
function (tissues)
– create a barrier between sides
• Three ways cells are bound:
– Tight junctions
– Desmosomes
– Gap junctions
Figure 3.5a Cell junctions.
Plasma membranes Microvilli
of adjacent cells
Intercellular
space
Basement membrane
Interlocking
junctional
proteins
Prevent fluids and most
molecules from moving
between cells
Intercellular
space
Tight junctions: Impermeable junctions
prevent molecules from passing through
the intercellular space.
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Figure 3.5b Cell junctions.
Plasma membranes
of adjacent cells
Microvilli
Intercellular
space
Basement membrane
Intercellular
space
Plaque
"Rivets" or "spot-welds"
that anchor cells together,
thickens plasma membrane
Linker
proteins
(cadherins)
Intermediate
filament
(keratin)
Desmosomes: Anchoring junctions bind adjacent cells
together like a molecular “Velcro” and help form an
internal tension-reducing network of fibers.
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Figure 3.5c Cell junctions.
Plasma membranes Microvilli
of adjacent cells
Intercellular
space
Basement membrane
Intercellular
space
Transmembrane proteins form
pores that allow small molecules
to pass from cell to cell
Channel
between cells
(formed by
connexons)
Gap junctions: Communicating junctions
allow ions and small molecules to pass
for intercellular communication.
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The Controlled Cell Barrier
• Plasma membranes are selectively permeable
• They control what comes in and what goes
out.
Tonicity
• The ability of solution to alter cell's water volume
• Isotonic
– Solution with same non-penetrating solute concentration as
cytosol
• Hypertonic
– Solution with higher non-penetrating solute concentration than
cytosol
• Hypotonic
– Solution with lower non-penetrating solute concentration than
cytosol
Figure 3.9 The effect of solutions of varying tonicities on living red blood cells.
Isotonic solutions
Cells retain their normal size and
shape in isotonic solutions (same
solute/water concentration as inside
cells; water moves in and out).
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Hypertonic solutions
Cells lose water by osmosis and shrink
in a hypertonic solution (contains a
higher concentration of solutes
than are present inside the cells).
Hypotonic solutions
Cells take on water by osmosis until they
become bloated and burst (lyse) in a
hypotonic solution (contains a lower
concentration of solutes than are
present inside cells).
Membrane Transport
• Passive transport
– No cellular energy (ATP) required
– Substance moves down its concentration gradient
• Active transport
– Energy (ATP) required
– Substance can move up its concentration gradient
Figure 3.7a Diffusion through the plasma membrane.
Extracellular fluid
Lipidsoluble
solutes
Cytoplasm
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Simple diffusion of
fat-soluble molecules
directly through the
phospholipid bilayer
Figure 3.7b Diffusion through the plasma membrane.
Lipid-insoluble solutes
(such as sugars or
amino acids)
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Carrier-mediated facilitated
Diffusion via protein carrier specific
for one chemical; binding of substrate
causes transport protein to change
shape
Figure 3.7c Diffusion through the plasma membrane.
Small lipidinsoluble
solutes
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Channel-mediated
facilitated diffusion
through a channel
protein; mostly ions
selected on basis of
size and charge
Figure 3.7d Diffusion through the plasma membrane.
Water
molecules
Lipid
bilayer
Aquaporin
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Osmosis, diffusion of a
solvent such as water
through a specific
channel protein
(aquaporin) or through
the lipid bilayer
Active Transport
• Two types of active processes
– Active transport
– Vesicular transport
• Both require ATP to move solutes across a
living plasma membrane because
Sodium (Na) – Potassium (K) Pump
• Na+-K+ ATPase
• Located in all plasma membranes
• Remember action of ATP
– convert chemical energy to mechanical energy
– Phosphate group (neg charge) changes shape of
proteins allowing “action”
Figure 3.10 Primary active transport is the process in which solutes are moved across cell membranes against
electrochemical gradients using energy supplied directly by ATP.
Extracellular fluid
Na+
Na+–K+ pump
Na+ bound
K+
ATP-binding site
Cytoplasm
Three Na ions bind channel
P
K+ released
ATP binds and repeats process
Binding Promotes ATP Hydrolysis
Na+ released
K+ bound
P
Pi
Binding opens channel
on opposite end,
releasing phosphate
K+
Phosphorylation opens channel on
Opposite end, releasing Na ions
P
2 Extracellular K ions bind channel
© 2013 Pearson Education, Inc.
Slide 1
Figure 3.11 Secondary active transport is driven by the concentration gradient created by primary active
transport.
Extracellular fluid
Slide 3
Glucose
Na+-K+
pump
Na+-glucose
symport
transporter
loads glucose
from extracellular
fluid
Na+-glucose
symport transporter
releases glucose
into the cytoplasm
Cytoplasm
1 Primary active transport
The ATP-driven Na+-K+ pump
stores energy by creating a
steep concentration gradient for
Na+ entry into the cell.
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2 Secondary active transport
As Na+ diffuses back across the membrane
through a membrane cotransporter protein, it
drives glucose against its concentration gradient
into the cell.
Vesicular Transport
• Exocytosis—transport out of cell
• Endocytosis—transport into cell
– Phagocytosis, pinocytosis, receptor-mediated endocytosis
• Transcytosis—transport into, across, and then out of
cell
• Vesicular trafficking—transport from one area or
organelle in cell to another (exocytosis)
Resting Membrane Potentials
• Resting membrane potential (RMP)
• Produced by separation of oppositely charged
ions across cellular membranes
– polarization
• Creates voltage (electrical potential energy) at
membrane
• Ranges from –50 to –100 mV in different cells
Figure 3.15 The key role of K+ in generating the resting membrane potential.
1 K+ diffuse down their steep
concentration gradient (out of the cell)
via leakage channels. Loss of K+
results in a negative charge on the
inner plasma membrane face.
Extracellular fluid
+
+
–
+
+
+
+
+
–
–
Slide 1
–
–
Potassium
leakage
channels
Cytoplasm
© 2013 Pearson Education, Inc.
–
–
+
–
Protein anion (unable to
follow K+ through the
membrane)
2 K+ also move into the cell
because they are attracted to the
negative charge established on the
inner plasma membrane face.
3 A negative membrane potential
(–90 mV) is established when the
movement of K+ out of the cell equals
K+ movement into the cell. At this
point, the concentration gradient
promoting K+ exit exactly opposes the
electrical gradient for K+ entry.
Diffusion of Ions set RMP
• In many cells Na+ affects RMP
– Attracted into cell due to negative charge RMP
• K+ primary influence on RMP
– more permeable to K+ than Na+,
• Cl– does not influence RMP
– concentration and electrical gradients balanced
Action Potentials
Role of ions on Action Potentials
Action
potential
Plateau
20
2
0
Tension
development
(contraction)
–20
–40
3
1
–60
Absolute
refractory
period
–80
0
150
Time (ms)
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300
Tension (g)
Membrane potential (mV)
Figure 18.13 The action potential of contractile cardiac muscle cells.
Slide 4
1 Depolarization is due to Na+
influx through fast voltage-gated Na+
channels. A positive feedback cycle
rapidly opens many Na+ channels,
reversing the membrane potential.
Channel inactivation ends this phase.
2 Plateau phase is due to Ca2+
influx through slow Ca2+ channels.
This keeps the cell depolarized
because few K+ channels are open.
3 Repolarization is due to Ca2+
channels inactivating and K+
channels opening. This allows K+
efflux, which brings the membrane
potential back to its resting voltage.
Cell – Environment Interactions
• Cells interact directly or indirectly by
responding to extracellular chemicals
• Contact signaling
– touching and recognition of cells
• Chemical signaling
– interaction between receptors and signal (ligand)
Figure 3.16 G proteins act as middlemen or relays between extracellular first messengers and intracellular second messengers that cause
responses within the cell.
Slide 1
Ligand (1st Receptor G protein Enzyme
messenger)
1 Ligand* (1st messenger) binds to the receptor.
The receptor changes shape
and activates.
2 The activated receptor
binds to a G protein and activates it. The G protein changes
shape (turns “on”), causing it to
release GDP and bind GTP (an
energy source).
2nd
messenger
3 Activated G protein
activates (or inactivates)
an effector protein by
causing its shape to
change.
Extracellular fluid
Effector protein
(e.g., an enzyme)
Ligand
Receptor
G protein
GDP
Inactive 2nd
messenger
Active 2nd
messenger
Activated
kinase
enzymes
* Ligands include
hormones and
neurotransmitters.
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4 Activated effector enzymes
catalyze reactions that produce
2nd messengers in the cell.
(Common 2nd messengers include
cyclic AMP and Ca2+.)
5 Second messengers
activate other enzymes or ion
channels. Cyclic AMP typically
activates protein kinase enzymes.
6 Kinase enzymes activate
other enzymes. Kinase enzymes
transfer phosphate groups from ATP
to specific proteins and activate a
Cascade of cellular responses series of other enzymes that trigger
(The amplification effect is
various metabolic and structural
tremendous. Each enzyme
catalyzes hundreds of reactions.) changes in the cell.
Intracellular fluid
Signal Transduction Pathways
• Cellular signaling strategies that transmits a
signal from outside the cell to inside the cell
• Generally results in gene transcription to
synthesis the proteins/enzymes necessary to
carry out the desired effect
• Enzymes responsible are “kinases” phosphorylation
Nucleus
• Largest organelle
– contains are DNA (genome)
• Most cells uninucleate
• Skeletal muscle, some bone and liver cells are
multinucleate
• red blood cells are anucleate
Figure 3.29a The nucleus.
Nuclear
envelope
Chromatin
(condensed)
Nucleolus
Cisterns of
rough ER
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Nuclear
pores
Nucleus
DNA Facts
• There are 3 billion letters in your DNA code in every cell
of your body.
• This would fill a stack of books 200ft high.
• At 1 base/second, this would take you 100yrs to finish
• If you and a friend read your own DNA code, it would
take 8.5 seconds before you found a difference!
• Human DNA is 98% identical to Chimpanzee
DNA
Condensation
Chromatin
Mitotic
Chromosome
All this DNA
into this
Chromsome!
=
50,000X package!
Area= 195ft x 300ft
= 58,500 ft2
58,500 ÷ 50,000 = 1.17ft2
1.17ft2 ÷ 2 = 0.59ft
= 7 in x 7 in
= smaller than
a piece of
paper!
Figure 3.29b The nucleus.
Surface of nuclear envelope.
Fracture
line of outer
membrane
Nuclear
pores
Nucleus
Nuclear pore complexes. Each
pore is ringed by protein particles.
Nuclear lamina. The netlike lamina
composed of intermediate filaments
formed by lamins lines the inner surface
of the nuclear envelope.
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The Endomembrane System
• Produce, degrade, store, and export biological
molecules
– Degrade potentially harmful substances
• Includes ER, Golgi apparatus, secretory
vesicles, lysosomes, nuclear and plasma
membranes
Endoplasmic Reticulum
• Network of tubules continuous with rough ER
• Functions include
– Lipid/fat metabolism and synthesis and absorption
– Detoxification of drugs (chemicals)
– Storage and release of calcium
– Transport of proteins destined to the cell surface
or out of the cell
Figure 3.18 The endoplasmic reticulum.
Nucleus
Smooth ER
Nuclear
envelope
Rough ER
Ribosomes
Diagrammatic view of smooth and rough ER
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Electron micrograph of smooth and rough
ER (25,000x)
Golgi Membranes
• Stacked and flattened membranous sacs
• Glycosylates packages proteins and lipids from
ER
– carbohydrates serve as delivery tags for
destination
Figure 3.19a Golgi apparatus.
Transport vesicle
from rough ER
Cis face—
“receiving” side of
Golgi apparatus
Cisterns
New vesicles
forming
Transport
vesicle
from
trans face
Secretory
vesicle
Trans face—
“shipping” side of
Golgi apparatus
Many vesicles in the process of pinching off
from the Golgi apparatus.
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Figure 3.20 The sequence of events from protein synthesis on the rough ER to the final distribution
of those proteins.
1 Protein-conta- Rough ER
ining vesicles
pinch off rough
ER and migrate
to fuse with
membranes of
Golgi apparatus.
ER
Phagosome
membrane
Proteins in
cisterns
2 Proteins are
modified within
the Golgi
compartments.
3 Proteins are
then packaged
within different
vesicle types,
depending on
their ultimate
destination.
Vesicle
becomes
lysosome
Golgi
apparatus
Pathway A:
Vesicle contents
destined for
exocytosis
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Secretory
vesicle
Secretion by
exocytosis
Slide 1
Plasma
membrane
Pathway C:
Lysosome
containing acid
hydrolase
enzymes
Pathway B:
Vesicle membrane
to be incorporated
into plasma
membrane
Extracellular fluid
Mitochondria
• Double-membrane structure with inner cristae
• Provide most of cell's ATP via cellular respiration
• Contain their own DNA, RNA, ribosomes
• Capable of cell division called fission
– thought to be an endosymbiotic relationship for the
modern cell
Figure 3.17 Mitochondrion.
Outer
mitochondrial
membrane
Ribosome
Mitochondrial
DNA
Inner
mitochondrial
membrane
Cristae
Matrix
Enzymes
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Cytoskeleton
• Elaborate series of rod-like structure dispersed
throughout cytosol giving structural support
and “highways” for intercellular movement
• Three types
– Microfilaments (actin)
– Intermediate filaments
– Microtubules
Figure 3.23a Cytoskeletal elements support the cell and help to generate movement.
Microfilaments
Strands made of spherical protein
subunits called actins
Actin subunit
7 nm
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Microfilaments form the blue network
surrounding the pink nucleus
in this photo.
Figure 3.23b Cytoskeletal elements support the cell and help to generate movement.
Intermediate filaments
Tough, insoluble protein fibers
constructed like woven ropes
composed of tetramer (4) fibrils
Tetramer subunits
10 nm
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Intermediate filaments form the purple
batlike network in this photo.
Figure 3.23c Cytoskeletal elements support the cell and help to generate movement.
Microtubules
Hollow tubes of spherical protein
subunits called tubulins
Tubulin subunits
25 nm
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Microtubules appear as gold networks
surrounding the cells’ pink nuclei in
this photo.
Figure 3.24 Microtubules and microfilaments function in cell motility by interacting with motor molecules powered by
ATP.
Vesicle
Receptor for
motor molecule
Motor molecule
(ATP powered)
Microtubule
of cytoskeleton
Motor molecules can attach to receptors on
vesicles or organelles, and carry the organelles
along the microtubule “tracks” of the cytoskeleton.
Motor molecule
(ATP powered)
Cytoskeletal elements
(microtubules or microfilaments)
In some types of cell motility, motor molecules attached to one
element of the cytoskeleton can cause it to slide over another
element, which the motor molecules grip, release, and grip at a
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new site. Muscle contraction and cilia movement work this way.
Centrosomes and Centrioles
• Generates microtubules; organizes mitotic
spindle
– Contains paired centrioles
• Barrel-shaped organelles formed by
microtubules
• Centrioles form basis of cilia and flagella
Figure 3.25a Centrioles.
Centrosome matrix
Centrioles
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Microtubules
Figure 3.25b Centrioles.
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Centrioles Create Cellular Extensions
• Cilia and flagella
– Whiplike, motile extensions on surfaces of certain
cells
– Contain microtubules and motor molecules
• Cilia move substances across cell surfaces
• Flagella propel whole cells (tail of sperm)
Figure 3.26 Structure of a cilium.
Outer microtubule
doublet
Dynein arms
Central
microtubule
Cross-linking
proteins between
outer doublets
Radial spoke
TEM
A cross section through the
Microtubules cilium shows the “9 + 2”
arrangement of microtubules.
Cross-linking
proteins between
outer doublets
The doublets
also have
Attached motor
proteins, the
dynein arms.
The outer
microtubule
doublets and the
two central
microtubules are
held together by
cross-linking
proteins and
radial spokes.
Radial spoke
Plasma
membrane
Plasma
membrane
Basal body
Triplet
TEM
A longitudinal section of a
cilium shows
microtubules
running the length of the
structure.
Cilium
TEM
A cross section through the
basal body. The nine outer
doublets of a cilium extend into
a basal body where each
doublet joins another
microtubule to form a ring of
nine triplets.
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Basal body
(centriole)
Figure 3.27 Ciliary function.
Power, or
propulsive, stroke
1
2
3
4
Recovery stroke, when cilium
is returning to its initial position
5
6
7
Phases of ciliary motion.
Layer of mucus
Cell surface
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Traveling wave created by the activity of
many cilia acting together propels mucus
across cell surfaces.
Microvilli
• Minute, fingerlike extensions of plasma
membrane
– made with actin microfilaments
• Increase surface area for absorption
Figure 3.28 Microvilli.
Microvillus
Actin
filaments
Terminal
web
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Cell Theory
• All cells come from living cells
• The Cell Cycle
Figure 3.31 The cell cycle.
G1 checkpoint
(restriction point)
S
Growth and DNA
synthesis
G1
Growth
M
G2
Growth and final
preparations for
division
G2 checkpoint
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Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (1 of 6)
Interphase
Centrosomes (each
has 2 centrioles)
Plasma
membrane
Nucleolus
Chromatin
Nuclear
envelope
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Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (2 of 6)
Early Prophase
Early mitotic
spindle
Aster
Chromosome
consisting of two
sister chromatids
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Centromere
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (3 of 6)
Late Prophase
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Spindle pole
Polar microtubule
Fragments
of nuclear
envelope
Kinetochore
Kinetochore
microtubule
Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (4 of 6)
Metaphase
Spindle
Metaphase
plate
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Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (5 of 6)
Anaphase
Daughter
chromosomes
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Figure 3.33 Mitosis is the process of nuclear division in which the chromosomes are distributed to two daughter
nuclei. (6 of 6)
Telophase
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Cytokinesis
Nuclear
envelope
forming
Nucleolus forming
Contractile
ring at
cleavage
furrow
A Cell Dividing - Mitosis
A Fly Embryo Dividing
From Gene to Protein
• DNA holds the genetic information that
encodes the production of proteins
• RNA is used during protein synthesis
• Two steps
– Transcription (DNA to RNA)
– Translation (RNA to protein)
Figure 3.34 Simplified scheme of information flow from the DNA gene to mRNA to protein structure during
transcription and translation.
Nuclear
envelope
Transcription
RNA Processing
DNA
Pre-mRNA
mRNA
Nuclear
pores
Ribosome
Translation
Polypeptide
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Normal growth is coupled with multiple choices
Senescence
Proliferation
Stem
cell
Apoptosis
Quiescence
Differentiation
Normal cells can respond to stress and act accordingly
Labs for today
• Lab Exercises 4 and 5
• Learning Outcomes:
– Learn the parts of the cell and cellular division
– Learn diffusion, osmosis through membranes
• Passive vs Active

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