CELLS
CHAPTER 4
CELLS
• Cells are the
smallest unit of life.
• Because they are so
small, no one
observed them until
the microscope was
invented. Robert
Hooke was the first
to describe a cell in
1665.
CELL THEORY
• Cell Theory – idea
that all organisms
are composed of
cells.
• All organisms
composed of 1+
cells within which
life processes occur.
• Cells are the smallest living things.
• Life evolved only once, 3.5 billion years ago.
• Cells arise only by division of a previously existing
cell.
TINY CELLS
• Cells are usually
very small
because larger
cells can’t
function as
efficiently.
• Larger cells have
a smaller surface
area to volume
ratio.
CELL STRUCTURE
• Cells have a
delicate cell
(plasma)
membrane
surrounding them
that controls
permeability to
water and dissolved
substances.
• A semi-fluid matrix called cytoplasm fills the
inside of the cell.
Phospholipids
Polar
hydrophilic
heads
Nonpolar
hydrophobic
tails
Polar
hydrophilic
heads
Cholesterol
Polar areas
of protein
Nonpolar areas
of protein
Phospholipid
Protein channel
Cholesterol
Receptor protein
Cell identity
marker
PLASMA MEMBRANE
• Plasma membrane is made up of a variety
of proteins in a lipid framework – the fluid
mosaic model.
• All cells have the same basic type of outer
membrane.
http://www.youtube.com/watch?v=Qqsf_UJcfBc
PHOSPHOLIPIDS
• The lipid layer is
composed of
phospholipids.
• Polar phosphate
group on one end.
• Two nonpolar fatty
acid chains on the
other.
PHOSPHOLIPID BILAYER
• When lots of phospholipids are placed in
water, they form a bilayer with fatty acid
tails pointing in together – away from water.
• Note that the layer is double – no fatty acid tails in
contact with water.
• Polar molecules can’t pass through nonpolar area
without assistance.
MEMBRANE PROTEINS
• Proteins float in
the lipid bilayer
and provide
channels that
will allow certain
molecules to
pass through.
CELL SURFACE PROTEINS
• Cell surface proteins project up from the
membrane surface and may have
carbohydrates or lipids attached to them.
• Identify type of cell.
• Binding sites for particular hormones or proteins.
TRANSMEMBRANE PROTEINS
• Transmembrane
proteins span the
entire lipid bilayer
providing channels
for polar ions and
molecules.
PROKARYOTIC CELLS
• Cytoplasm is not compartmentalized.
• Prokaryotes include the two kingdoms of
bacteria.
• Bacteria are the simplest cellular organisms.
• Ribosomes for protein construction are
present. They are not organelles – no
membrane.
PROKARYOTIC CELLS
• Bacteria have a
plasma
membrane like all
cells.
• Cell wall
(different than
that found in
plants or fungi)
• Capsule encloses
cell wall
sometimes.
PROKARYOTIC CELLS
• Bacteria have
diverse array of
shapes.
• They can
adhere in chains
and masses,
although the
cells remain
separate.
EUKARYOTIC CELLS
• Eukaryotes include all protists, fungi, plants,
and animals.
• Much larger than prokaryotic cells –
complex internal compartmentalization.
• Membrane bound organelles – specialized
structures where particular cell processes occur.
• Largest organelle is usually the nucleus.
• Cells Alive!
CYTOSKELETON
• Cytoskeleton – a
dense network of
protein fibers
which supports
the shape of the
cell and anchors
organelles in
place.
CYTOSKELETON
• Three types of protein
fibers make up the
cytoskeleton.
• Long, slender
microfilaments made
of actin.
• Hollow tubes called
microtubules made of
tubulin.
• Thick ropes called
intermediate fibers.
CYTOSKELETON
• Cytoskeleton is important in determining the
shape of an animal cell (no cell wall).
• Filaments can form and dissolve quickly so
the shape of an animal cell can change
rapidly.
NUCLEUS
• The nucleus is
the control
center of the
cell and genetic
library where
hereditary
information is
stored.
NUCLEUS
• The nuclear envelope is actually 2
membranes.
• Nuclear pores are depressions where the
two membranes pinch together.
• The pores contain many embedded proteins that
permit proteins and RNA to pass into or out of the
nucleus.
NUCLEUS
• In bacteria and eukaryotes, all hereditary
information is encoded in DNA.
• In eukaryotes, the DNA is divided into
several segments and is associated with
protein, forming chromosomes.
• The protein allows the condensing of the
chromosomes during cell division.
• Uncoiled, threadlike strands of DNA are called
chromatin.
NUCLEUS
• The darkest region of the nucleus is called
the nucleolus.
• Ribosomal subunit assembly.
• Subunits leave through nuclear pores –
ribosomes are assembled in cytoplasm.
RIBOSOMES
• Ribosomes read the RNA copy of a gene
and uses the information to construct a
protein.
• Ribosomes are made up of several special forms
of RNA – ribosomal RNA (rRNA) bound up with
proteins.
Endoplasmic Reticulum – The Transportation
System
• Endoplasmic
Reticulum “Little net within
the cytoplasm”
- an extensive
system of internal
membranes.
• Sometimes forms
membrane
enclosed sacs
called vesicles.
ENDOPLASMIC RETICULUM
• Carbohydrates and lipids are manufactured
on the surface of the ER.
• Manufacture of proteins intended for export
occurs on ER that is studded with ribosomes
and called rough ER.
• ER with few ribosomes is called smooth ER.
Golgi Complex – The Delivery System
• New molecules made on the ER surface are
passed through the ER membrane and into
flattened stacks of membranes called Golgi
bodies.
• Function – collection, packaging, and distribution
of molecules manufactured in the cell.
• Collectively Golgi bodies are called the Golgi
complex.
GOLGI COMPLEX
• Proteins & lipids manufactured on ER
membranes are transported through the
channels of the ER or as vesicles budded off
of it and passed into Golgi bodies.
• Inside Golgi bodies, carbohydrates may be
attached.
GOLGI COMPLEX
• Vesicles pinch off
the Golgi and
carry molecules to
other parts of cell
or to the plasma
membrane so
they can be
released outside
the cell.
Lysosomes – Recycling Centers
• Lysosomes arise from the Golgi complex
and contain a concentrated mix of
powerful enzymes that break down
macromolecules.
• They act as recycling centers by digesting
worn out cell components to make way for
newly formed ones while recycling the
proteins of the old components.
LYSOSOMES
• They also eliminate particles engulfed by the
cell.
• Enzymes that occur inside a lysosome digest
cell parts that are engulfed – if not confined
to the lysosome, they would digest the cell!
ORGANELLES THAT CONTAIN DNA
• Eukaryotic cells contain some organelles
derived from ancient bacteria assimilated
by ancestral eukaryotes.
• Mitochondria – occur in all but a few eukaryotes.
• Chloroplasts – occur only in plants & some protists
(algae).
• Centrioles – relict organelles with no membrane
that occur in all animals & most protists.
Mitochondria – Powerhouses of the Cell
• Eukaryotic organisms extract energy from
food through a complex series of chemical
reactions called oxidative metabolism
which takes place in mitochondria.
MITOCHONDRIA
• Mitochondria have two membranes
• Outer membrane is smooth
• Inner membrane bent into numerous folds called
cristae.
• Cristae partition mitochondrion into two
compartments, an inner matrix and an outer
compartment – the intermembrane space.
MITOCHONDRIA
• Mitochondria still have some of their original
genes, contained in a circular, closed
molecule of DNA (mtDNA).
• This DNA loop contains genes that code for
proteins essential to oxidative metabolism.
Chloroplasts – Energy Capturing Centers
• All photosynthesis
in plants and
algae takes place
within
chloroplasts.
• Likely derived from
an ancient
symbiotic
bacteria.
CHLOROPLASTS
• Two membranes, as in mitochondria.
• Inner membranes are fused to form stacks of
closed vesicles called thylakoids.
• Light powered reactions of photosynthesis
take place within thylakoids.
• Stacks of thylakoids are called grana.
• Interior fluid is called the stroma.
CHLOROPLASTS
• Like mitochondria, chloroplasts contain a
circular DNA molecule containing genes
that code for proteins essential to the
process of photosynthesis.
CENTRIOLES
• Centrioles
assemble
microtubules
from tubulin
subunits in
animals and
most protists.
CENTRIOLES
• Centrioles occur in pairs in the cytoplasm.
• Often at right angles
• Usually near nuclear envelope
• Cilia and flagella are anchored by a type of
centriole called a basal body.
CENTRIOLES
• Centrioles lack a membrane, but contain a
circular DNA molecule involved in the
production of structural proteins.
• They resemble a type of bacteria.
• May have originated as symbiotic bacteria.
CELL MOVEMENT
• Cell motion is tied to movement of actin
filaments, microtubules, or both.
• Actin filaments form and dissolve quickly.
CELL MOVEMENT - CRAWLING
• The arrangement of actin filaments in the
cell cytoplasm allow a cell to crawl.
• Motion essential to inflammation, clotting, wound
healing, and the spread of cancer.
• White blood cells move this way.
• Produced in bone marrow, released in
circulatory system, they crawl out of capillary
into tissue to destroy pathogens.
CELL MOVEMENT
• During animal cell reproduction,
chromosomes move to opposite sides of a
dividing cell because they are attached to
shortening microtubules.
• Cells pinch in two because the belt of actin
filaments contracts.
• Also essential for muscle contraction.
FLAGELLA
• Flagella are long, threadlike organelles
protruding from the cell surface.
• Each flagellum is anchored at a basal body
and consists of 9 microtubule pairs
surrounding 2 central microtubules (9+2
arrangement).
• 9+2 arrangement is fundamental feature of
eukaryotes.
• Examples: human sperm cell, many single celled
organisms - used for locomotion.
CILIA
• When flagella are very numerous and
organized in dense rows they are called
cilia.
• Cilia have the same structure as flagella, but are
usually short.
• Examples: lining of human trachea to move dust
and mucus out of the respiratory tract to the
throat, protists such as the Paramecium.
PLANT CELL SPECIALIZATIONS
• Vacuoles – a
central storage
compartment for
water, sugars, ions,
& pigments.
• Also functions to
increase surface
area to volume
ratio.
PLANT CELL SPECIALIZATIONS
• Cell walls provide protection & support.
• In plants, cell walls made of cellulose.
• In fungi, cell walls made of chitin.
• Both different from the composition of
bacterial cell walls.
TRANSPORT ACROSS CELL
MEMBRANES
• Food particles, water, and other materials
must pass into a cell, waste must be
eliminated.
• Water can diffuse through a membrane.
• Food particles can be engulfed by membrane
folding around them.
• Proteins in the membrane act as doors allowing
only certain molecules through.
DIFFUSION
• Molecules move randomly.
• Random motion tends to create uniform
mixtures.
• Net movement of molecules toward the area
where they are scarce – down the concentration
gradient.
• Diffusion allows O2, CO2, & nonpolar liquids
to cross plasma membrane.
DIFFUSION
• Diffusion – net movement of molecules from
region of higher concentration to region of
lower concentration.
http://www.youtube.com/watch?v=VY0mZUDvbH4
OSMOSIS
• Water molecules
are small enough to
pass through the
plasma membrane.
• Diffusion of water
across the plasma
membrane toward
the side with more
polar molecules is
called osmosis.
http://www.youtube.com/watch?v=w3_8FSrqc-I
SOLUTIONS
• Solutes are molecules dissolved in a solution.
• Osmotic concentration – concentration of
all molecules dissolved in a solution.
• Hyperosmotic – solution with higher
concentration.
• Hypoosmotic – solution with lower concentration.
• Isoosmotic – solutions with equal concentration.
OSMOSIS
• Movement of water into a cell creates
pressure – osmotic pressure.
• Can cause cell to swell and burst.
• Cell walls protect cells from bursting.
ENDOCYTOSIS
• Endocytosis cells can extend
their plasma
membranes
around food
particles or liquid
engulfing them in
vesicles.
• Phagocytosis –
food
• Pinocytosis – drink
http://www.youtube.com/watch?v=4gLtk8Yc1Zc
EXOCYTOSIS
• Exocytosis – the
process of
ridding a cell of
material by
discharging it
from vesicles at
the cell surface.
SELECTIVE PERMEABILITY
• Endocytosis is energetically expensive.
• It also is not picky – whatever is there gets
engulfed.
• Proteins in plasma membrane can allow
only certain molecules through – selective
permeability.
SELECTIVE DIFFUSION
• Some channels act like open doors – if a
molecule fits, it can pass through in either
direction.
• The concentrations tend to equalize through
the process of diffusion.
• Selective diffusion.
FACILITATED DIFFUSION
• Facilitated diffusion - most diffusion channels
use a special carrier protein.
• These proteins bind only to certain molecules,
binding them on one side of the membrane,
releasing them on the other.
• This process requires no energy.
FACILITATED DIFFUSION
• Net movement is
from region of
higher
concentration to
lower
concentration.
• Just like simple
diffusion, but
facilitated by carrier
proteins.
• Facilitated Diffusion
http://www.youtube.com/watch?v=vKGN_Zhz8AY
ACTIVE TRANSPORT
• Some channels through the plasma
membrane are like closed doors – they
require energy to pass through.
• Active transport channels only work in one
direction.
• Movement of molecules from a region of
lower concentration to a region of higher
concentration.
ACTIVE TRANSPORT
• Two types of active transport channels.
• Sodium-Potassium pump
• Proton pump
SODIUM-POTASSIUM PUMP
• Sodium ions (Na+)
pumped out of
cell. (300/second)
• Potassium ions (K+)
pumped into cell.
• Energy to run
pump derived
from ATP.
• Important in nerve
signal conduction.
http://www.youtube.com/watch?v=yz7EHJFDEJs
PROTON PUMP
• Proton pump – a
complex channel
that expends
energy to +pump
protons (H )
across the
membrane.
• The pump is the
key to cell
metabolism – the
way cells convert
photosynthetic
energy or
chemical energy
from food to ATP.
• This activity is
called
chemiosmosis.
http://www.youtube.com/watch?v=rd1xYSy6s2A
HOW CELLS GET INFORMATION
• Some cells can sense light or pressure
changes.
• Most use chemical or electrical signals.
• Use cell surface proteins embedded in plasma
membrane.
• Cell’s only contact with outside world.
SENSING CHEMICAL INFORMATION
• Cells sense chemical information using cell
surface proteins called receptor proteins.
• Bind to particular molecules – no channel.
• Pass information about concentration of certain
molecules which may indicate the presence of
another cell.
SENSING VOLTAGE
• Voltage sensitive
channels for sodium
or other ions that are
usually closed.
• Open in response to
voltage change.
• Voltage sensitive
“door” contains
charged amino acids.
• Important in muscle &
nerve tissue.
http://www.youtube.com/watch?v=mKalkv9c2iU