Movement of molecules-2013.pptx

8/13/2019 Movement of molecules-2013.pptx

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Learning objectives

At todays lecture we will cover the main

mechanisms through which cells exchangematerials with their environment.

Different types of movement of moleculesthrough the cell membrane will be elucidated

and examples of each discussed.

The importance of each mechanism will also beoutlined.


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Learning outcomes

By the end of todays lecture

you should:

1) Understand the main mechanisms of movementof molecules through the cell membranediffusion; osmosis; facilitated diffusion; active

transport and cytosis.2) Be able to comparethese mechanisms.

3) Understand their requirementsand significance

for the functioning of the cells.


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The state of matter

As the temperature rises the kinetic energy of the

molecules increases and they move faster.


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Second Law of Thermodynamics

All things tend towardsentropy(randomness).

Molecules move (diffuse)

from an area of highconcentration to areas of

low concentration.

Eventually moleculesbecome randomly

distributedunless acted

on by something else.


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Random Movement of Molecules


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Movement along a concentration

gradient

Molecules of water move in every direction.

As a result the lump of salt disappears and the

molecules of salt spread throughout the water.


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Movement down a concentration

gradient


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Movement across cell membrane

Movement of molecules across the cell

membrane has two main features:

Allows uptake and release of molecules

according to the biological needsof the cell

(eg. uptake and release of oxygen by red

blood cells).

Transport can be regulated (eg. increased

transport of glucose into muscles during

physical activity).


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The nature of phospholipid bilayers

Hydrophilic phospholipid heads interact with the

aqueous media inside and outside of the cell.

Hydrophobic tails repel aqueous media and prevent

passage through the membrane.


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The three characteristics of a molecule that

determine the phospholipid bilayerpermeability to that species are . . .

1) polarity - (Hydrophobic vs Hydrophylic)

2) charge - (charged vs uncharged)

3) size - (large vs small)


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Molecules that pass through the phospholipid bilayer

easily

hydrophobic molecules i.e. O2, N2, steroids. Nonpolar - benzene

Small uncharged polar molecules - H2O, Urea, glycerol,

CO2

Molecules that dontpass through the phospholipid bilayer

easily...

Large uncharged - Glucose

Polar molecules - Sucrose

Ions (charged) - H+, Na+, HCO3-, K+, Ca2+ , Cl-, Mg2+


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The cell membrane is more than just

a phospholipid bilayer


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Control of molecule transport in and

out of the cell

Cell membrane is selectively permeableallows the passage of certain substances but

not that of others.

Property depends on both protein andphospholipid components of membrane

Mechanisms of movement include:

1. Diffusion.

2. Osmosis.

3. Facilitated Diffusion.

4. Active Transport.

5. Cytosis.


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Diffusion

A physical process characterised by the net

movement of particles from a place of high

concentration to a place of lower concentration.


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The rate of diffusion

depends on a number of factors such as:

Particle sizeinversely proportional

Temperaturedirectly proportional

Concentration gradient sizedirectlyproportional

Path lengthinversely proportionalSurface areadirectly proportionalDensityinversely proportional


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Ficks Law

In many living organisms

temperatureand densityare constant.

Cells and tissues adapt to

diffusion by short pathlengths, large surface

areas and high

concentration gradients.


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The rate of exchange of substances

depends on the organism's surface area

that's in contact with the surroundings. Requirements for materials depends on

the volumeof the organism.

The ability to meet the requirementsdepends on the surface area : volume

ratio.

Surface area and volume


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The problem of getting large

As organisms get larger their volume andsurface area both increase, but volume

increases much more than surface area.

ORGANISM LENGTH SA (M) VOL. (M) S/A:VOL

bacterium 1 mm 6 x 10-12 10-18 6,000,000:1

amoeba 100 mm 6 x 10-8 10-12 60,000:1

fly 10 mm 6 x 10-4 10-6 600:1

dog 1 m 6 x 100 100 6:1

whale 100 m 6 x 104

106

0.06:1


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Osmosisdiffusion of water through

a partially permeable membrane
http://www.google.kz/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&docid=wf_GGFUAVhoF_M&tbnid=A1NjleX7nfEZzM:&ved=0CAUQjRw&url=http://keepinapbiologyreal.wikispaces.com/Osmosis&ei=lTtVUta6EceJ4ATo0YDoAg&bvm=bv.53760139,d.bGE&psig=AFQjCNE-XLqslF3M2a3Bi1nKeiAZwK8bIA&ust=1381403875243652


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Water potential

The force pushing water to move from one side of amembrane to another is measured by the water

potential which has the units of pressure

The water potential () of pure water is 0.The pressure on a cell will increase its .

cell = s+ p

ssolute potential

ppressure potential


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Animal cells and osmosis

cell < outside cell = outside cell > outside


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Plant cells and osmosis


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Facilitated diffusion


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Passive diffusion of glucose -

permease


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Active transport - principles

Creates internal environment different from theexternal one. Different from diffusion where theend state is equilibrium between internal andexternal environment.

Represents the movement of particles across thecell membrane often from an area of low to anarea of high concentration.

Would not be possible according to 2ndLaw of

Thermodynamics unless cellular energy (ATP) isexpended to transport against concentrationgradient.


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Types of active transport


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Uniportproton pumps


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Antiportsodium/potassium pump


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Co-transport


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Secondary active transport


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Cytosis

Some things are too big to diffuse fast enough

or pass through a pore or a pump. These are

moved in vesicles via cytosis.

Vesicles and other large complexes are moved

around the cell by motors attached to

microtubules (dynein and kinesins) or

microfilaments (myosins).

Import of particles is endocytosisexport of

particles is exocytosis.


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Phagocytosis


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Pinocytosis


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Clathrin (receptor) mediated

endosytosis


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Exocytosis - secretion


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2013 Nobel prize in Physiology or

Medicine

Awarded jointly to James E. Rothman, RandyW. Schekman and Thomas C. Sdhof "for their

discoveries of machinery regulating vesicle

traffic, a major transport system in our cells".


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Summary

The following mechanisms of transport through thecell membrane were elucidated:

1. Diffusion.

2. Osmosis.3. Facilitated diffusion.

4. Active transport.

5. Cytosis.The subtypes and their importance for the cellswere also discussed.

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Movement of molecules-2013.pptx