Cell SizeCell Size: is governed by : is governed by several factors: The size of several factors: The size of

the cell is controlled by the cell is controlled by metabolic requirements.metabolic requirements.

DNA must be available to DNA must be available to produce the enzymes and produce the enzymes and proteins needed for proper proteins needed for proper

functioning. functioning.

A too small cell will not have A too small cell will not have enough DNA to support life enough DNA to support life

and a cell too large will need and a cell too large will need an enormous amount of DNA an enormous amount of DNA

to carry on its functions. to carry on its functions.

Surface area to volume Surface area to volume ratio:ratio: As the cell increases in As the cell increases in

size, the volume increases size, the volume increases geometrically while the geometrically while the surface area increases surface area increases

arithmetically. arithmetically.

Eukaryotic cells cope with Eukaryotic cells cope with these problems in that they these problems in that they contain membrane bound contain membrane bound

organelles. organelles.

These organelles break up the These organelles break up the volume of the cell performing volume of the cell performing distinct functions which cuts distinct functions which cuts down on the raw materials down on the raw materials

needed. needed.

Each part of the cell does not Each part of the cell does not need the same material to need the same material to

function. function.

CytoskeletonCytoskeleton: contains : contains microtubules and microtubules and microfilaments.microfilaments.

MicrotubulesMicrotubules: straight hollow : straight hollow rods measuring about 25 nm. rods measuring about 25 nm.

thick .thick .

            They are constructed They are constructed from a and b tubulin. They from a and b tubulin. They

shape, support and help move shape, support and help move organelles around the cell. organelles around the cell.

            They form centrioles, They form centrioles, which are not found in plants. which are not found in plants. They have a "9 + 2 " pattern. They have a "9 + 2 " pattern.

MicrofilamentsMicrofilaments: are : are constructed of 2 interwoven constructed of 2 interwoven pieces of actin about 7nm. in pieces of actin about 7nm. in

diameter. diameter.

            They function in muscle They function in muscle contraction, cytoplasmic contraction, cytoplasmic

streaming, ameboid streaming, ameboid movement, and changes in movement, and changes in

cell shape. cell shape.     

Cell WallCell Wall: From the cell : From the cell membrane out the cell wall is membrane out the cell wall is

as follows: Primary wall, as follows: Primary wall, secondary wall, and a sticky secondary wall, and a sticky area between adjacent cells area between adjacent cells

called the middle lamellacalled the middle lamella

. In animal cells a fuzzy coat . In animal cells a fuzzy coat called the called the glycocalyxglycocalyx is is

found. This is made of sticky found. This is made of sticky oligosaccharides that act as oligosaccharides that act as

glue to keep the cells glue to keep the cells together. together.

  

Intercellular JunctionsIntercellular Junctions: :

1. 1. Tight junctionsTight junctions. bind cells . bind cells together in such a way that no together in such a way that no material can pass through the material can pass through the intercellular spaces. Epithelial intercellular spaces. Epithelial cells are held together by tight cells are held together by tight

junctions. junctions.

2. 2. DesmosomesDesmosomes: These bind : These bind the cells together like rivets. the cells together like rivets.

They let material pass through They let material pass through the intracellular spaces. the intracellular spaces.

3. 3. Gap JunctionsGap Junctions: They : They connect cells but allow connect cells but allow

material to pass from one cell material to pass from one cell to another through the to another through the

opening in the center of the opening in the center of the joint. They are analogous to joint. They are analogous to

the plasmodesmata in plants. the plasmodesmata in plants.   

Cell Membrane ProteinsCell Membrane Proteins: : The proteins are of two types The proteins are of two types

            Integral ( passing through Integral ( passing through the width of the membrane, the width of the membrane, act as transport channels) act as transport channels)

  

            Peripheral ( act as Peripheral ( act as recognition sites ). recognition sites ).

These peripheral proteins These peripheral proteins contain carbohydrates to help contain carbohydrates to help

in cell to cell recognition. in cell to cell recognition. These carbohydrates are These carbohydrates are called oligosaccharides.called oligosaccharides.

If they bind to proteins they If they bind to proteins they become glycoproteins, if they become glycoproteins, if they bind to lipids , they become bind to lipids , they become

glycolipids. glycolipids.

            Cholesterol molecules Cholesterol molecules are found in animal are found in animal

membranes to help add membranes to help add support to its structure. The support to its structure. The majority of the phospholipids majority of the phospholipids

contain unsaturated fatty contain unsaturated fatty acids to keep it fluid.acids to keep it fluid.

  

Traffic of molecules across Traffic of molecules across the membranethe membrane: :

1. 1. Hydrophobic moleculesHydrophobic molecules (Hydrocarbons and Oxygen) (Hydrocarbons and Oxygen) can cross with ease because can cross with ease because they can dissolve in the lipid they can dissolve in the lipid

bilayer. bilayer.

2. 2. Small polar (uncharged) Small polar (uncharged) moleculesmolecules will pass ( water will pass ( water

and carbon dioxide). and carbon dioxide).

3. 3. Large polar (uncharged) Large polar (uncharged) moleculesmolecules will not pass will not pass

( sugar). ( sugar).

4. 4. IonsIons will not readily pass will not readily pass ( H+, Na+, Cl-). ( H+, Na+, Cl-).

Transport ProteinsTransport Proteins: :

1.1. UniportUniport - one molecule - one molecule moves in only one direction. moves in only one direction.

2. 2. Symport Symport - Two different - Two different molecules moving in only one molecules moving in only one

direction. direction.

3. 3. AntiportAntiport - Two molecules - Two molecules moving in opposite directions. moving in opposite directions. These transport proteins work These transport proteins work

in the following ways:in the following ways:

provide a tunnel to allow provide a tunnel to allow material to flow through, bind material to flow through, bind

to the substance and to the substance and physically move it, they are physically move it, they are

specific for the substance they specific for the substance they move. move.

Diffusion and Passive Diffusion and Passive TransportTransport::

Concentration gradientConcentration gradient: is a : is a regular concentration change regular concentration change over a distance in a particular over a distance in a particular

direction. direction.

The net directional movement The net directional movement is away from the center of is away from the center of

concentration. concentration.

            Diffusion is the net Diffusion is the net movement down the movement down the

concentration gradient. concentration gradient.

Diffusion is caused by the Diffusion is caused by the following natural occurrences: following natural occurrences: thermal motion ( movement thermal motion ( movement caused by the loss of heat ), caused by the loss of heat ),

random molecular movement, random molecular movement, and an increase in entropy of and an increase in entropy of

the system.the system.

In a solution of many different In a solution of many different substances each substance substances each substance

diffuses down its own diffuses down its own concentration gradient concentration gradient

independent of the others.independent of the others.

Diffusion is a passive type of Diffusion is a passive type of transport, it requires no transport, it requires no

additional energy to make it additional energy to make it work. work.

            Osmosis is diffusion of Osmosis is diffusion of water across a biological water across a biological

membrane. membrane.

. . Types of Aqueous Solutions: Types of Aqueous Solutions:

1.1. HyperosmoticHyperosmotic: solution : solution with the greater with the greater

concentration of solute concentration of solute ( salt water compared to ( salt water compared to

fresh water).fresh water).

1.1. If a cell from a salt water If a cell from a salt water fish is placed in a beaker fish is placed in a beaker of fresh water, the cell is of fresh water, the cell is

said to be hyperosmotic to said to be hyperosmotic to the water. the water.

1.1.2. 2. HypoosmoticHypoosmotic: solution : solution with a lesser concentration of with a lesser concentration of solute ( fresh water compared solute ( fresh water compared

to salt water). to salt water).

1.1.If a cell from a fresh water If a cell from a fresh water fish is placed into a beaker of fish is placed into a beaker of salt water, the cell is said to salt water, the cell is said to

be hypoosmotic to the water. be hypoosmotic to the water.

1.1.3. 3. IsosmoticIsosmotic: solutions of : solutions of equal solute concentrations equal solute concentrations

are said to be isosmotic. are said to be isosmotic.

1.1.Water balance in a living Water balance in a living cellcell: :

1.1.1. Cells placed in a 1. Cells placed in a hyperosmotic environment hyperosmotic environment ( salt water) animal cells ( salt water) animal cells

crenate (shrivel). Plant cells crenate (shrivel). Plant cells plasmolyze (shrivel). plasmolyze (shrivel).

1.1.2. Cells placed in a 2. Cells placed in a hypoosmotic environment hypoosmotic environment

( fresh water) animal cells lyse ( fresh water) animal cells lyse ( explode) and plant cell ( explode) and plant cell

become turgid (firm). become turgid (firm).

1.1.3. Cells placed in an 3. Cells placed in an isosmotic solution animal cells isosmotic solution animal cells

are normal, plant cells are are normal, plant cells are flaccid (limp). flaccid (limp).

            Facilitated DiffusionFacilitated Diffusion: : Passive form of transport Passive form of transport

caused by the help of carrier caused by the help of carrier proteins specific for the proteins specific for the

molecules they transport.molecules they transport.

Movement is always down Movement is always down the concentration gradient. the concentration gradient.

Polar molecules and ions are Polar molecules and ions are usually moved in this fashion. usually moved in this fashion.

            Active TransportActive Transport: : Movement of molecules up Movement of molecules up the concentration gradient. the concentration gradient.

The cell must expend its own The cell must expend its own energy to move the energy to move the

substances. substances.

            Sodium-Potassium Sodium-Potassium PumpPump: Antiport type molecule. : Antiport type molecule. It takes 3 sodium ions out of It takes 3 sodium ions out of

the cell for every 2 potassium the cell for every 2 potassium ions it takes into the cell. ions it takes into the cell.

Since sodium is more Since sodium is more abundant outside the cell and abundant outside the cell and potassium inside the cell, the potassium inside the cell, the

cell is working against the cell is working against the concentration gradient.concentration gradient.

In order for the protein to In order for the protein to work, it must be energized by work, it must be energized by

ATP. ATP.

As this occurs the cytoplasm As this occurs the cytoplasm generates an over all negative generates an over all negative charge 2K as opposed to 3Na charge 2K as opposed to 3Na

on the outside, giving the on the outside, giving the extracellular fluid a positive extracellular fluid a positive

charge.charge.

            Another example is a Another example is a Proton pumpProton pump that transports that transports

Hydrogen ions. Hydrogen ions.

These are called electrogenic These are called electrogenic pumps, since they produce pumps, since they produce mild currents of electricity.mild currents of electricity.

Chloroplasts and mitochondria Chloroplasts and mitochondria use this to perform energy use this to perform energy

creating products from creating products from sunlight and macromolecules. sunlight and macromolecules.

  

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