Download Cell Size: is governed by several factors: The size of the

Cell Size: is governed by
several factors: The size of
the cell is controlled by
metabolic requirements.
DNA must be available to
produce the enzymes and
proteins needed for proper
functioning.
A too small cell will not have
enough DNA to support life
and a cell too large will need
an enormous amount of DNA
to carry on its functions.
Surface area to volume
ratio: As the cell increases in
size, the volume increases
geometrically while the
surface area increases
arithmetically.
Eukaryotic cells cope with
these problems in that they
contain membrane bound
organelles.
These organelles break up the
volume of the cell performing
distinct functions which cuts
down on the raw materials
needed.
Each part of the cell does not
need the same material to
function.
Cytoskeleton: contains
microtubules and
microfilaments.
Microtubules: straight hollow
rods measuring about 25 nm.
thick .

They are constructed
from a and b tubulin. They
shape, support and help move
organelles around the cell.

They form centrioles,
which are not found in plants.
They have a "9 + 2 " pattern.
Microfilaments: are
constructed of 2 interwoven
pieces of actin about 7nm. in
diameter.

They function in muscle
contraction, cytoplasmic
streaming, ameboid
movement, and changes in
cell shape.
Cell Wall: From the cell
membrane out the cell wall is
as follows: Primary wall,
secondary wall, and a sticky
area between adjacent cells
called the middle lamella
. In animal cells a fuzzy coat
called the glycocalyx is
found. This is made of sticky
oligosaccharides that act as
glue to keep the cells together.
Intercellular Junctions:
1. Tight junctions. bind cells
together in such a way that no
material can pass through the
intercellular spaces. Epithelial
cells are held together by tight
junctions.
2. Desmosomes: These bind
the cells together like rivets.
They let material pass through
the intracellular spaces.
3. Gap Junctions: They
connect cells but allow
material to pass from one cell
to another through the
opening in the center of the
joint. They are analogous to
the plasmodesmata in plants.
Cell Membrane Proteins:
The proteins are of two types

Integral ( passing through
the width of the membrane,
act as transport channels)

Peripheral ( act as
recognition sites ).
These peripheral proteins
contain carbohydrates to help
in cell to cell recognition.
These carbohydrates are
called oligosaccharides.
If they bind to proteins they
become glycoproteins, if they
bind to lipids , they become
glycolipids.

Cholesterol molecules
are found in animal
membranes to help add
support to its structure. The
majority of the phospholipids
contain unsaturated fatty acids
to keep it fluid.
Traffic of molecules across
the membrane:
1. Hydrophobic molecules
(Hydrocarbons and Oxygen)
can cross with ease because
they can dissolve in the lipid
bilayer.
2. Small polar (uncharged)
molecules will pass ( water
and carbon dioxide).
3. Large polar (uncharged)
molecules will not pass (
sugar).
4. Ions will not readily pass (
H+, Na+, Cl-).
Transport Proteins:
1. Uniport - one molecule
moves in only one direction.
2. Symport - Two different
molecules moving in only one
direction.
3. Antiport - Two molecules
moving in opposite directions.
These transport proteins work
in the following ways:
provide a tunnel to allow
material to flow through, bind
to the substance and
physically move it, they are
specific for the substance they
move.
Diffusion and Passive
Transport:
Concentration gradient: is a
regular concentration change
over a distance in a particular
direction.
The net directional movement
is away from the center of
concentration.

Diffusion is the net
movement down the
concentration gradient.
Diffusion is caused by the
following natural occurrences:
thermal motion ( movement
caused by the loss of heat ),
random molecular movement,
and an increase in entropy of
the system.
In a solution of many different
substances each substance
diffuses down its own
concentration gradient
independent of the others.
Diffusion is a passive type of
transport, it requires no
additional energy to make it
work.

Osmosis is diffusion of
water across a biological
membrane.
.
Types of Aqueous Solutions:
1. Hyperosmotic: solution
with the greater
concentration of solute (
salt water compared to
fresh water).
1. If a cell from a salt water
fish is placed in a beaker
of fresh water, the cell is
said to be hyperosmotic to
the water.
1.2. Hypoosmotic: solution
with a lesser concentration of
solute ( fresh water compared
to salt water).
1.If a cell from a fresh water
fish is placed into a beaker of
salt water, the cell is said to be
hypoosmotic to the water.
1.3. Isosmotic: solutions of
equal solute concentrations
are said to be isosmotic.
1.Water balance in a living
cell:
1.1. Cells placed in a
hyperosmotic environment (
salt water) animal cells
crenate (shrivel). Plant cells
plasmolyze (shrivel).
1.2. Cells placed in a
hypoosmotic environment (
fresh water) animal cells lyse (
explode) and plant cell
become turgid (firm).
1.3. Cells placed in an
isosmotic solution animal cells
are normal, plant cells are
flaccid (limp).

Facilitated Diffusion:
Passive form of transport
caused by the help of carrier
proteins specific for the
molecules they transport.
Movement is always down
the concentration gradient.
Polar molecules and ions are
usually moved in this fashion.

Active Transport:
Movement of molecules up
the concentration gradient.
The cell must expend its own
energy to move the
substances.

Sodium-Potassium
Pump: Antiport type molecule.
It takes 3 sodium ions out of
the cell for every 2 potassium
ions it takes into the cell.
Since sodium is more
abundant outside the cell and
potassium inside the cell, the
cell is working against the
concentration gradient.
In order for the protein to
work, it must be energized by
ATP.
As this occurs the cytoplasm
generates an over all negative
charge 2K as opposed to 3Na
on the outside, giving the
extracellular fluid a positive
charge.

Another example is a
Proton pump that transports
Hydrogen ions.
These are called electrogenic
pumps, since they produce
mild currents of electricity.
Chloroplasts and mitochondria
use
.
this to perform energy
creating products from
sunlight and macromolecules.