Movement and Transportation

8/14/2019 Movement and Transportation

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CHAPTER 3

PLASMA MEMBRANE ANDTRANSPORTATION PROCESS


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General Function of Plasma Membrane

Protects the whole cell

1. Separates the cell components from its

environment

2. Regulates transport of molecules in and

out of the cell

3. Controls the intake of foreign moleculesdue to its selective permeable

characteristics.


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Plasma membrane

A model that described the structure of plasma

membrane which consists of various proteinsembedded in or attached to a double layer

(bilayer) of phospholipids.

In 1935, Hugh Davson and James Danielli

suggested a structure of the membrane

- the membrane were coated on both sides withhydrophilic proteins, a sandwich model : a

phospholipid bilayer between two layers of

proteins


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In 1972, S.J. Singer and

G. Nicholson proposed

that membrane proteinsare dispersed and

individually inserted into

the phospholipid bilayer

with only their

hydrophilic regions

protruding far enough

from the bilayer to beexposed to water. This

structure is called The

Fluid Mosaic Model


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The Fluid Mosaic Model - S.J. Singer and G. Nicholson

Proteins that penetrate the

hydrophobic core of the lipid blayer.

Many are transmembrane proteinswhich completely span the membrane

Not embedded in the lipid bilayer;

bound loosely to the surface of the

membrane, the exposed part of theintegral protein.

Carbohydratecovalently

bonded to lipid.

Carbohydrate covalently

bonded to protein.

Main functions: cell-

cell recognition


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Permeability of Plasma Membrane

- Depends on its structure and pore size

4 types of permeability:

a. Permeable

Allows all solutes or molecules to pass through.

b. Semi-permeable

Allows only water molecules and not solutes to pass

through.

c. Selectively permeableAllows selected solutes and water to pass through.

d. Non-permeable

Does not allow solutes or water molecules to passthrou h.


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In transportation across the plasma membrane,

these elements will be discussed:

1. Solution

A liquid that is a homogeneous mixture of two

or more substances

2. Solvent

The dissolving agent of a substance.

Water is the most versatile solvent known.

3. Solute

A substance that is dissolved in a solution


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Transportation processes across plasma membrane

1. Passive transport

Movement of materials or molecules through a

membrane down the concentration gradient,

without the use of energy.

Examples: Diffusion, osmosis and dialysis

2. Active transport

Involved a carrier system (protein or lipoprotein)to transfer materials or molecules against the

concentration gradient, with the use of energy

ATP.

P i t t


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Passive transport

Diffusion

A substance diffuses from where it is more concentrated

to where it is less concentrated the substance will

diffuse down its concentration gradient until it reaches

equilibrium.


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Rate of diffusion depends on several factors:

a. Concentration gradient

The higher the concentration gradient, the higher the rate ofdiffusion

b. Diffusion distance

The shorter the diffusion distance, the higher the rate of

diffusion.

c. Surface area of diffusion

The bigger the surface area, the higher the rate of diffusion.

d. Structure and characteristics where diffusion occurs

Higher number and size of the membrane pores will result inhigher diffusion rate.

e. Size and characteristics of diffused molecules

Lipid-soluble molecules can easily cross the plasma membrane.

The smaller the molecules, the higher the rate of diffusion.


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Osmosis

The diffusion of water across the selectively

permeable membrane from the region of lowerconcentration to the higher concentrations until both

sides are equal

Passive transport no energy neededSame concentrations of sugar

Only allows water molecules topass through the pores.

osmosis


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3 types of environments:

Isotonic the same environment with the cell

- no net movement of water across the

membrane, but at the same rate in both

directions

Hypertonic the environment is more concentratedcompared to the cell

- the cell will lose water to its environment

Hypotonic the environment is less concentratedcompared to the cell

- the water will enter the cell


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Water balance of cells without walls

Water balance of cells with walls

Hemolysis Normal Crenation

Turgid Deplasmolysis Plasmolysis


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Active transport

The movement of substance across a biological

membrane against its concentration gradient with thehelp of energy input and specific transport protein

ATP power active transport by transferring its terminal

phosphate group directly to the transport protein

It could induce the protein to change its shape to help

transfer the solute bound to the protein across the

membrane

Example: Sodium-potassium pump an exchange ofsodium (Na+) for potassium (K+) across the plasma

membrane of animal cells


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Specific transport

protein

Less

concentration

region

High

concentration

region


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Exocytosis

The cell secretes

macromolecules by thefusion of vesicles with the

plasma membrane and

spill them to the outside

of the cell

Many secretory cells use

exocytosis to export their

products

Example:

Cell in pancreas

that secretes insulin.


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Endocytosis

The cell takes in macromolecules and particulate

matter by invagination of the plasma membrane.Involved the formation of vacuole which is

surrounded by plasma membrane.

Two types of endocytosis:1. Phagocytosis (cellular eating)

The intake material is in solid form.

2. Pinocytosis (cellular drinking)

The intake material is in liquid form.


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A cell engulfs a particle by wrapping pseudopodia

around it and packaging it within a membrane-enclosedsac large enough to be classified as a vacuole. The

particle is digested after the vacuole fuses with a

lysosome containing hydrolytic enzymes.


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The cell gulps droplets of extra-cellular fluid into tiny

vesicles. It is not the fluid itself that is needed by thecell, but the molecules dissolved in the droplet.

Because any and all included solutes are taken into the

cell, pinocytosis is nonspecific in the substances it

transport.

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Movement and Transportation