Cell Transport

Cell Membrane: Function:

Maintain homeostasis.This is also called equilibrium.

Allow passage of some molecules while preventing the passage of others This is called being “Selectively

permeable” or “semi-permeable”

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Small molecules and larger hydrophobic molecules move through easily.e.g. O2, CO2, H2O

Semipermeable Membrane

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Ions-hydrophilic molecules larger than water, and large molecules such as proteins do not/ cannot pass through the membrane without help.

Semipermeable Membrane

Membrane structure:• Composed of a

phospholipid bilayer Have a phosphate

head which is polar- does react with water

Have a fatty acid (lipid) tail that is non-polar- does not react with water

Together these make up the membrane

• The inside of the membrane is hydrophobic- which means it does not react with water

• The outside of the membrane is hydrophillic- which means it does react with water

•Contains proteins within its structure1.Integral proteins (transport proteins)-

which allow the passage of molecules too large to pass through the membrane without help

2.Peripheral proteins- aid in signaling for the cell to communicate with other cells

Concentration Gradient Concentration gradients occur

when there is a higher amount of solutes in one area of solution then in another. Molecules will tend to travel from

areas of high concentration to areas of lower concentrations

Passive transport Molecules flow with or down a

concentration gradient No energy required Two types:

Diffusion Ex. Osmosis

Facilitated Diffusion

Diffusion  

Facilitated Diffusion Diffusion for

molecules that are not lipid soluble or are too large to pass through the membrane.

Carrier proteins change shape to aid these molecules across the membrane

No Energy Required.

Example: Glucose, Fructose

Osmosis Diffusion involving water moving from

high water concentration to low water concentration. Water can move freely across the

membrane No energy required.

Osmosis There are three different types of osmotic solutions:

Hypotonic isotonic Hypertonic

Hypotonic Solution Higher concentration

of solutes within the cell More free water

outside the cell Water moves into the

cell The cell becomes

swells or gets larger

Hypo Hippo- it gets big and swells.

Hypertonic Solution Higher concentration of

solute outside the cell More free water in the

cell Water moves out of the

cell Cell shrinks

Isotonic solution Solutions are equal

between the two areas

Water moves both directions to keep the solutions at an equilibrium.

What will happen to water in the cell?

Three Different Osmotic Solutions

Hypotonic- higher concentration of solutes in the cell

Hypertonic- higher concentration of solutes outside the cell

Isotonic – equal amount of solutes inside and outside the cell

Example- Plants: In a hypotonic solution plant cell’s

membrane is pushed against the cell wall Turgor Pressure

In a hypertonic solution a plant cell’s membrane will shrink within the cell wall Plasmolysis Causes wilting when plants

dehydrate

Turgor Pressure

Plant cell becomes engorged with water

Gives plant the stiffness in their stem

Plasmolysis Plant cell membrane shrinks from the cell

wall Causes plant to wilt.

Active Transport Molecules are transported against the

concentration gradient by proteins Requires energy (ATP) Example: Sodium-Potassium Pump

A protein that transfers Na+ and K+ ions up the gradient

Cell has a high Na+ concentration outside the cell and a high K+ concentration inside the cell

http://www.youtube.com/watch?v=GTHWig1vOnY

Active transport Enodcytosis: cells engulf

substances that are too large to enter the cell by passing through the cell membrane

Exocytosis: cellular wastes

are removed from sacs at the cell’s surface

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• Molecules are moved out of the cell by vesicles that fuse with the plasma membrane.

Exocytosis-

moving things out.

• This is how many hormones are secreted and how nerve cells communicate with one another.

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25ExocytosisExocytic vesicle immediately after fusion with plasma membrane.

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Large molecules move materials into the cell by one of three forms of endocytosis.

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Pinocytosis-Most common form of endocytosis.

Takes in dissolved molecules as a vesicle.

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Pinocytosis- Cell forms an

invagination Materials dissolve

in water to be brought into cell

Called “Cell Drinking”

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Example of Pinocytosis

pinocytic vesicles forming

mature transport vesicle

Transport across a capillary cell (blue).

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Receptor-Mediated Endocytosis

Some integral proteins have receptors on their surface to recognize & take in hormones, cholesterol, etc.

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Endocytosis – Phagocytosis

Used to engulf large particles such as food, bacteria, etc. into vesiclesCalled “Cell Eating”

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Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue)

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So to review the three types of Endocytosis are:• Phagocytosis• Pinocytosis• Receptor mediated

Endocytosis.

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Exocytosis The opposite of endocytosis is exocytosis. Large molecules that are manufactured in the cell are released through the cell membrane.

Inside Cell Cell environment

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What are the three different types of active transport? Protein pumps (Na/K) Endocytosis Exocytosis

Cell Transport Passive transport: molecules

travel along/down/with the concentration gradient No energy required

Active Transport: molecules are transported against/up the concentration gradient energy required