Question: Other than as carrier proteins state two function - PowerPoint Presentation

Slide1

Question: Other than as carrier proteins state two functions of membrane bound proteins (2).

ReceptorsEnzymesStructural (attached to microtubules)Click here to hide answers

Click to reveal answersSlide2

Cholesterol in cell membranes

Cholesterol is a type of lipid with the molecular formula C27H46O.

Cholesterol is also important in keeping membranes stable at normal body temperature – without it, cells would burst open.

Cholesterol is very important in controlling membrane fluidity. The more cholesterol, the less fluid – and the less permeable – the membrane.Slide3

Proteins in membranes

Proteins typically make up 45% by mass of a cell membrane, but this can vary from 25% to 75% depending on the cell type.

integral protein

Peripheral

(or

extrinsic

) proteins are confined to the inner or outer surface of the membrane.

Integral

(or

intrinsic

, or

transmembrane

) proteins span the whole width of the membrane.

peripheral protein

Many proteins are

glycoproteins

–

proteins with attached carbohydrate chains.

carbohydrate chainSlide4

Integral proteins

Many integral proteins are

carrier molecules

or

channels

.

These help transport substances, such as ions, sugars and amino acids, that cannot diffuse across the membrane but are still vital to a cell’s functioning.

Other integral proteins are receptors for hormones and neurotransmitters, or enzymes for catalyzing reactions.Slide5

Extrinsic proteins

Extrinsic (or Peripheral)

proteins may be free on the membrane surface or bound to an

intrinsic (or integral)

protein.

Extrinsic

proteins on the extracellular side of the membrane act as receptors for hormones or neurotransmitters, or are involved in cell recognition. Many are

glycoproteins.

Extrinsic

proteins on the

cytosolic

side of the membrane are involved in cell signalling or chemical reactions. They can dissociate from the membrane and move into the cytoplasm.Slide6

Exchanging Substances

Facilitated Diffusion, Osmosis and Active TransportSlide7

Passive Transport

Learning Objectives- explain what is meant by passive transport - compare diffusion and facilitated diffusion Identify the role of membrane proteins in transportSuccess Criteria

Construct definitions of diffusion, facilitated diffusion and osmosis

Create a comparison table

Draw and annotate diagrams to show how the

processes differSlide8

Transport across the cell membrane

All cells are surrounded by a partially-permeable membrane that controls what substances can enter and exit the cell.

A cell needs to be able to import the substances it needs to survive, and to export waste materials and substances that are needed outside the cell.

There are several methods by which substances (molecules and ions) can cross the cell membrane:

diffusion

osmosis

active transport

.Slide9

What is diffusion?

Diffusion is the net movement of particles down a

concentration gradient

: from a region of high concentration to a region of low concentration.

No metabolic energy is expended during diffusion so it is an example of

passive

transport.

One example of diffusion is gas exchange across respiratory surfaces, such as the lungs of mammals and birds, and the gills of fish.

net movement

of particlesSlide10

The rate of diffusion

The rate of diffusion in a given direction across an exchange surface can be summarized by Fick’s law, which states that:

rate of diffusion is proportional to:

surface area × difference in conc.

length of diffusion path

(membrane thickness)

Increasing the surface area across which the particles diffuse, or increasing the size of the concentration gradient will increase the rate of diffusion.

Increasing the distance (or thickness of the membrane) over which diffusion takes place will decrease the rate.Slide11

Plasma Membrane

Plasma membranes form boundaries between cells and their environment.But substances need to cross membranes because:Nutrients need to get in

.

Waste/hormones etc. need to

get out

.

OUTSIDE

INSIDESlide12

Exchange Mechanisms

Plasma membranes are partially permeable – they let some things through, but not others.The substances that can’t get through, need help crossing membranes.

The ways in which substances can

cross membranes

are:

Diffusion

Facilitated Diffusion Osmosis

Active TransportSlide13

diffusionSlide14

Diffusion Recap

All particles that make up liquids and gases are in random motion – they’re moving around very fast.

Because of this, they move from:

a region of

high concentration

to a region of low concentration

High conc. Low conc.Slide15

Diffusion Recap

The molecules will diffuse both ways, but the net (overall) movement will be to the area of low concentration.

There is a

concentration gradient

..... particles move

down

it

Diffusion is PASSIVE! There is NO energy involved.

Diffusion occurs if the molecules involved can pass

freely

through a membrane. So they have to be

small

. If they’re not,

facilitated diffusion is required!Slide16

Rates of Diffusion

The rate at which diffusion occurs is determined by several factors:The size of the concentration gradient. The larger the difference in concentration, the faster diffusion will occur.

The

thickness

of the exchange surface.

The thinner the exchange surface, the faster diffusion will occur.

The

distance between the two areas.

A shorter distance = faster diffusion.The

size of the molecules

.

Smaller molecules such as oxygen will diffuse quicker than large molecules like proteins.Slide17

What is diffusion proportional to?

surface area x difference in concentration length of diffusion pathSlide18

Facilitated diffusionSlide19

Facilitated Diffusion

Facilitated diffusion uses the same principle as ordinary diffusion, except that protein carriers are involved.

Small molecules like

O

2

and CO2

can simply diffuse across a membrane without any help.Larger molecules

like amino acids and

glucose

can’t diffuse directly through the phospholipid bilayer.

They still move down a

concentration gradient

, but because they’re so big, they move through

carrier proteins

or

channel proteins

.Facilitated diffusion is also passive (no energy). Slide20

CARRIER or transmembrane

Proteins

Carrier proteins

move large molecules in or out of the cell down a concentration gradient.

Molecules

attach

to the carrier protein.

The carrier

changes shape

.

It releases the molecule on the

other side

.

OUTSIDE

INSIDESlide21

CHANNEL Proteins

Channel proteins

form

pores

in the membrane for

CHARGED PARTICLES

to move down a concentration gradient.

Only open in response to presence of molecule

OUTSIDE

INSIDESlide22

Facilitated Diffusion

Facilitated diffusion is specific.i.e. A certain type of molecule will have a corresponding carrier or channelGlucose = glucose channelAmino acids = amino acid channelSlide23

Active transportSlide24

Active Transport

Active transport is different from diffusion and facilitated diffusion because it uses ENERGY.Unlike diffusion and facilitated diffusion, molecules move

AGAINST

a concentration gradient

.

This happens in the intestines, where the concentration of nutrients is very high in the cells already.

Active transport uses

carrier proteins too, but they work using ATP (energy).Slide25

Active Transport

OUTSIDE

INSIDE

ATP

Molecule attaches to

carrier protein

.

ATP

molecule provides energy to go

against gradient

.

Carrier

changes shape

and molecule is released on the other side (side with higher concentration).Slide26

Cells like epithelial cells in the intestine have to carry out active transport.

They’re packed with mitochondria to provide the ATP

(energy) needed for transporting nutrients

against a concentration gradient

.Slide27

Summary

Complete a table to show similarities and differences between the different methods of movement across a cell membrane

Simple diffusion

Facilitated diffusion

Active transport

Osmosis

Energy required?

Substances moving

Location within cell membrane

Factors affecting speedSlide28

Summary

Complete a table to show similarities and differences between the different methods of movement across a cell membrane

Simple diffusion

Facilitated diffusion

Active transport

Osmosis

Energy required?

NoNoYes

NoSubstances moving

Oxygen, carbon dioxide, lipid

soluble

mols

Glucose, polar

mols

Many molecules

water

Location within cell membrane

Through

phospho

-lipid bilayerThrough protein carriers or channels

Through protein carriers or channelsThrough phospho-lipid bilayerFactors affecting speed

conc. gradient pathway lengthsurface area, Temp, size of molecule

conc gradientFrequency of carrier molecules, speed of and affinity of binding, Temp

ATP availability, Frequency of carrier molecules, speed of and affinity of binding, Temp

Temp, surface area, water potential gradient, concentration gradient pressure, Slide29

Starter

Name a cellular organelle that possesses a membrane and describe the purpose of the membrane.Describe the purpose of cholesterol in the plasma membraneSuggest why organisms living in polar regions have a high proportion of cholesterol in the membraneList three substances that need to be transported into animal cells in order to survive.

List two substances that need to be transported out of animal cells in order to survive

Golgi, mitochondria, chloroplast, nucleus,

lysosomes

Compartmentalise enzyme reactions/control substances in and out

Prevents

phospholipid

tails from packing close together and preserves fluidity of membrane

To keep membrane fluid and functioning correctly

Oxygen, food, minerals, water

Carbon dioxide, nitrogenous wastesSlide30

Osmosis – transporting waterSlide31

Osmosis

Learning Objectives- Explain what is meant by osmosis, in terms of water potential. (No calculations of water potential will be required);- Recognise and explain the effects that solutions of different water potentials can have upon plant and animal cells.

Success Criteria

Identify the direction of osmosis using water potential values

Complete a quantitative practical task (practice)Slide32

What is osmosis?

Osmosis is the diffusion of water. It is the net movement of water molecules from a region of high water concentration to a region of low water concentration, through a partially-permeable membrane.

net movement of water molecules

Osmosis is the process by which cells exchange water with their environment, such as in the mammalian kidney.Slide33

Osmosis

Osmosis

is simply the

diffusion of water molecules

.

The definition for osmosis is:

The movement of water across a partially permeable membrane, from an area with a less negative water potential, to an area with a more negative water potential

...so

we need to know what ‘water potential’ is...Slide34

Water Potential

Water is

rarely

pure

–

it is never composed of 100%

H

2

O

molecules.

There are usually

dissolved solutes

in it such as minerals and ions.

Pure water

would have a

‘water potential’ (

Ψ

)

of

zero.But when there are dissolved solutes in water, there’s no longer 100% water molecules – so we say the

water potential is

more negative.

100% water

Ψ

= zero

Ψ

= more negative

Ψ

= even more negativeSlide35

Water Potential

Water potential is measured in

kilopascals (kPa)

.

Water potential of

pure water

= 0 kPa

Water potential of water with a

pinch of salt added

=

-70 kPa

Just remember that the more concentrated water is with solutes (substances), the

more negative the water potential will be

.Slide36

What is water potential?

Pure water has the highest water potential, and has a value of 0 kPa. Solutions have a lower water potential than pure water, and have a negative water potential.

The net movement of water by osmosis is determined by differences in

water potential

between two solutions connected by a partially-permeable membrane.

Water potential is the tendency of water molecules in a system to move. It is denoted by the symbol

Ψ

and is measured in kiloPascals (kPa).

Water molecules always move from a region of high water potential to a region of low (more negative) water potential.Slide37

Cells are affected by the water potential of their surroundings

When you

compare two water potentials

, you can give special names to them in terms of

how different they are

:

Ψ

= -2 kPa

Ψ

= -10 kPa

Ψ

= -2 kPa

Ψ

= -2 kPa

Ψ

= -2 kPa

Ψ

= -10 kPa

Cell is in a

HYPOTONIC SOLUTION

Cell is in a

ISOTONIC SOLUTION

Cell is in a

HYPERTONIC SOLUTIONSlide38

Ψ

= -40 kPa

Ψ

= -36 kPa

Ψ

= -30 kPaSlide39

Annotate your diagram to explain what is happeningSlide40

OsmosisSlide41

Osmosis in an Animal Cell

Copy and complete table – use a red blood cell as the exampleWater potential of external solution compared to cell solution

Higher (less negative)

Equal

Lower (more negative)

Net movement of water

State of cell

Annotated diagramSlide42

Osmosis in an Animal Cell

Water potential of external solution compared to cell solution

Higher (less

negative

)

Equal

Lower (more negative)

Net movement of water

Enters cell

Neither enters nor leaves

Leaves

cell

State of cell

Swells and bursts

No change

Shrinks

Annotated diagram

Contents of cell released

Normal RBC

Cell looks darker, as haemoglobin more concentrated. Cell shrunken

and shrivelled.Slide43

Ψ

= -3 kPa

Ψ

= -5 kPa

Ψ

= -2 kPa

Ψ

= -2 kPa

Ψ

= -1 kPa

Ψ

= -4 kPa

Draw the following diagrams, and

show with arrows

, which way you think osmosis will occur.Slide44

Cells are affected by the water potential of their surroundings

When you

compare two water potentials

, you can give special names to them in terms of

how different they are

:

Ψ

= -2 kPa

Ψ

= -10 kPa

Ψ

= -2 kPa

Ψ

= -2 kPa

Ψ

= -2 kPa

Ψ

= -10 kPa

Cell is in a

HYPOTONIC SOLUTION

Cell is in a

ISOTONIC SOLUTION

Cell is in a

HYPERTONIC SOLUTIONSlide45

PLENARYSlide46

Exam Q’s

Diffusion is a passive transport process. What does this mean?How does the thickness of an exchange surface affect the rate of diffusion across it?

What happens if a cell is placed in a hypotonic solution?