The Cell
& Mitosis
The Cell:
Fundamental Unit of Life
Rudolf Virchow says: • Life as we define it consists
of cells
• All cells arise from previously
existing cells
• Organisms depend upon the
activity of cells to exist
• Subcellular structures are
responsible for specific
cellular biochemical functions
according to the
“complimentarity of structure
& function”
This is Modern Cell Theory!
• There are TRILLIONS of cells in
your body
• Approximately 200 distinct types
• They range in size from about 2
micrometers (sperm) to over a meter
(motor neurons)
Anatomy
of a
Typical
Animal
Cell
Organelle Functions
Organelle Functions
The Plasma Membrane
Functions of
membrane
proteins
More
functions of
membrane
proteins
Subcellular organelles and
other subcellular structures
• Cytosol – the fluid portion of the
cytoplasm
• Cytoplasm – cytosol + subcellular
organelles
• Many organelles are bound by their
own phospholipid membranes
• All have their own unique functions
The
Cytoskeleton
Microvilli
• Increase surface area for absorption
• Attach to cytoskeleton
Centrioles
Cilia
Fig. 03.19
Ribosomes
Endoplasmic reticulum
Golgi
apparatus
Transport Vesicles
• Carry materials to and from Golgi
apparatus
Figure 3–7a
Lysosomes
Mitochondria:
Powerhouse of the Cell
Mitochondrial Function
• Mitochondrion takes chemical energy
from food (glucose):
– produces energy molecule ATP
The Reactions
glucose + oxygen + ADP 
carbon dioxide + water + ATP
• Glycolysis:
– glucose to pyruvic acid (in cytosol)
• Tricarboxylic acid cycle (TCA cycle):
– pyruvic acid to CO2 (in matrix)
• The TCA cycle is more commonly
known as “Krebs Cycle” or the Citric
acid cycle
The Nucleus
Structure of the Nucleus
• Nucleus:
– largest organelle
• Nuclear envelope:
– double membrane around the nucleus
• Perinuclear space:
– between 2 layers of nuclear envelope
• Nuclear pores:
– communication passages
DNA:
Blueprint of
Life
Protein Synthesis
• Transcription:
– copies instructions from DNA to mRNA
(in nucleus)
• Translation:
– ribosome reads code from mRNA (in
cytoplasm)
– assembles amino acids into polypeptide
chain
To produce a protein the DNA must
be “transcribed” into mRNA
Translation
• mRNA moves:
– from the nucleus
– through a nuclear
pore
Figure 3–13
Translation (2)
• mRNA moves:
– to a ribosome in
cytoplasm
– surrounded by amino
acids
Translation (3)
• mRNA binds to
ribosomal subunits
• tRNA delivers
amino acids to
mRNA
Translation (4)
• tRNA anticodon binds
to mRNA codon
• 1 mRNA codon
translates to 1 amino
acid
Translation (5)
• Enzymes join amino
acids with peptide
bonds
• Polypeptide chain has
specific sequence of
amino acids
Translation (6)
• At stop codon,
components separate
Translation
summary
3 letter
“words”
called
codons
code for
amino acids
Summary of protein synthesis
Membrane permeability
• An important function of the membrane
is to control what can enter or leave the
cell
• How easily something passes through is
called “permeability”
• If something cannot pass through the
membrane is said to be “impermeable”
Gradients
• The differential concentrations of
substances leads to the establishment of
gradients
• According to the 2nd LTD, things tend to
move from a high concentration to a low
concentration.
• If there is a gradient across a membrane,
particles will want to flow across that
membrane
Gradients can be
of concentrations
solutes or
charged particles
such as ions.
Ion gradients are
called electrical
gradients
Types of transport
• Passive
–
–
–
–
Simple diffusion
Facilitated or protein mediated
Filtration
Osmosis
• Active
– ATP driven solute pumps
– Vesicular
• Endocytosis
– Phagocytosis
– Bulk-phase endocytocysis (pinocytosis)
• Exocytosis
Cell transport mechanisms
Diffusion and the Cell Membrane
• Diffusion can be simple or channel-mediated
Simple Diffusion
• Materials which diffuse through cell
membrane:
– lipid-soluble compounds (alcohols, fatty
acids, and steroids)
– dissolved gases (oxygen and carbon
dioxide)
Channel-Mediated Diffusion
• Materials which pass through
transmembrane proteins (channels):
– are water soluble compounds
– are ions
Facilitated Diffusion
• Passive
• Carrier mediated
Fig. 03.09
Gated ion channels control permeability
Fig. 03.10
Facilitated
diffusion:
it’s passive
and controls
permeability
Diffusion rate influences
•
•
•
•
•
•
Slope of concentration gradient
Temperature
Molecular or atomic weight of solute
Density of solvent
Surface area
Diffusion distance
Factors in
Channel-Mediated Diffusion
• Passage depends on:
– size
– charge
– interaction with the channel
Osmosis
• Osmosis is the diffusion of water
across the cell membrane
Tonicity
• Isotonic – same concentration of solute
inside of the cell as outside. No net
movement of water
• Hypotonic – lower concentration of solute
outside than in. Water move into cell
(causes lysis).
• Hypertonic – higher concentration of
solute outside of cell than inside. Watre
moves out of cell (causes crenation).
Effect of tonicity on red blood cells
Active Transport
•
•
•
•
It requires expenditure of cellular energy
Usually involves ATP
Can be primary or secondary
Includes pumps & bulk phase or vesicular
mechanisms
SodiumPotassium
Exchange
Pump
Fig. 03.11
The sodium/potassium pump:
an antiport system
Secondary Active Transport
• Na+ concentration gradient drives
glucose transport
• ATP energy pumps Na+ back out
Vesicular transport
• Endocytosis – taking things in.
– Receptor mediated
– Phagocytosis
– Pinocytosis
• Exocytosis – secreting things.
Fig. 03.13
Receptor mediated endocytosis
Pinocytosis: cellular drinking
Phagocytosis
• Phagocytosis (cell
eating)
– pseudopodia
(psuedo = false,
podia = feet)
– engulf large
objects in
phagosomes
Exocytosis
• Ejects secretory products and wastes
Electrical Charge
• Inside cell membrane is slightly
negative, outside is slightly positive
• Unequal charge across the cell
membrane is transmembrane potential
• Resting potential ranges from —10
mV to —100 mV, depending on cell
type
Mitosis
• Every cell in your body arises from
the process of mitosis
• Before a cell can reproduce itself, it
must first replicate its DNA
Fig. 03.31
DNA Replication
• DNA strands unwind
• DNA polymerase attaches
complementary nucleotides
DNA is
replicated in a
semiconservative
pattern
Fig. 03.32
Then the cell goes through
the following stages
•
•
•
•
•
Prophase
Metaphase
Anaphase
Telophase
Cytokinesis
Prophase
Late
prophase
Metaphase
Anaphase
Telophase:
defined by the
presence of a
cleavage
furrow
&
Cytokinesis
Fig. 03.33
Chemicals Controlling Cell Division
Cancer
Fig. 03.34
Cells can be
highly
specialized.
The structural
specializations
reflect their
function!
SUMMARY (1 of 4)
• Structures and functions of human
cells
• Structures and functions of
membranous and nonmembranous
organelles
SUMMARY (2 of 4)
• ATP, mitochondria, and the process
of aerobic cellular respiration
• Structures and functions of the
nucleus:
– control functions of nucleic acids
– structures and replication of DNA
– DNA and RNA in protein synthesis
SUMMARY (3 of 4)
• Structures and chemical activities of
the cell membrane:
–
–
–
–
diffusion and osmosis
active transport proteins
vesicles in endocytosis and exocytosis
electrical properties of plasma
membrane
SUMMARY (4 of 4)
• Stages and processes of cell division:
– DNA replication
– mitosis
– cytokinesis
• Links between cell division, energy
use, and cancer
Next,
Tissues