Cell membrane and transport

Objectives To learn the structure of the cell

membrane To learn how structure and function of

the cell membrane are linked To learn about different forms of

transport across the cell wall.

Cell Membrane Cell is bound by a fluid membrane It regulates movement of chemicals in

and out of the cell; It is involved in recognition and

identification It facilitates the function of the cell It protects the cell It keeps the cell together It interacts with the membranes of other

cells

Cell membrane http://www.youtube.com/watch?v=ow

Egqrq51zY

Structure of the cell membrane

What it comprised of 1 A phospholipid bilayer which allows

the passage of lipids across the membrane

2. Bilayer of phospholipid molecules with water loving heads on the inner and outer surface and water hating tails pointing into the membrane.

We describe our understanding of it as the ‘Singer and Nicholson’ fluid mosaic model.

Inclusions Included in the phospholipid bilayer are: Integral proteins (carrier proteins) Peripheral proteins Cholesterol Carbohydrate chains Glycolipids (lipids with attached

carbohydrate chains) Glycoproteins (proteins with attached

carbohydrate chains) These inclusions can move around the fluid

phospholipid bilayer.

Carbohydrate chains Carbohydrate chains Give the cell a sugar coat or

glycocalyx which protects the cell. These carbohydrate chains are

unique to individuals, tissue types and blood groups.

They are what our immune system uses to recognise our cells and invading ones.

Fluidity Allows rapid movement of carrier

proteins around; Gives flexibility to cells, so e.g. your

nerve cells don’t crack when you bend.

Membrane proteins move freely. Has been demonstrated by merging

human and mouse cells. In 40 minutes membrane proteins from two cells completely mixed.

Proteins Channel proteins: allow molecules to

move across the membrane through a channel;

Carrier proteins: combine with chemicals to transport them across the membrane;

Cell recognition proteins are glycoproteins which allow us to recognise our own cells and invaders and therefore facilitate an immune response.

More proteins Receptor proteins: Have a shape that

allows one type of molecule to bind to it.

Once the molecule is bound to it, it changes shape altering the properties of the cell.

E.g. insulin binding to liver cells causes them to store sugar.

Enzymatic proteins carry out metabolic functions.

Plenary activity 1. make a model of the plasma

membrane 2. Explain how your model shows its

different parts and functions 3. Marking rubric same as for cell

model.

Movement of substances Known as cell transport covers the

movement of substances in and out of the cell membrane.

Will include both the different types of transport

And the structure and function of the cell membrane

Diffusion E.g. H2O, CO2 and O2 in and out of the cell. What is diffusion? http://www.youtube.com/watch?v=H7QsD

s8ZRMI

Across the cell membrane it is helped by protein

http://www.youtube.com/watch?v=OV4PgZDRTQw

This is called facilitated diffusion An idea of random particle movement:

http://ccl.northwestern.edu/netlogo/models/DLA

Key points about diffusion 1. It happens because of the natural

movement of the particles of liquids and gases;

2. It does not need an organism to use energy;

3. It can only happen down a concentration gradient from higher to lower concentrations;

4. Across cell membranes it is assisted by carrier proteins.

Osmosis The diffusion of water across a semi-

permeable membrane; http://www.youtube.com/watch?v=sdiJtDRJQE

c Important in enabling plant cells to absorb

water to maintain their turgor pressure; Results in dilution of the solution Water moves from weak solutions where

there is lots of water to strong solutions where there is less water.

Does not require energy Does require semi-permeable membrane.

Investigating in lab

Key terms Hypotonic solution is weaker than the

solution in the cell; Isotonic solution is equal to that in the cell; Hypertonic solution is stronger than that in

the cell; Lysed means split Turgid means full and firm Flaccid means limp, droopy Plasmolysed means cell membrane and

contents have shrunk away from the cell wall in plants.

Facilitated transport This does not require energy All chemicals pass down a concentration

gradient. It is necessary for the transport of materials like

glucose and some amino acids across the cell membrane because they are not lipid soluble;

It uses carrier molecules which are proteins crossing the cell membrane

Each carrier molecule is specific to one molecule to be transported

http://phet.colorado.edu/en/simulation/membrane-channels Open this simulation and try to show what is happening in a cell in different osmotic conditions

Active transport This does require energy http://www.youtube.com/watch?v=ST

zOiRqzzL4 To summarise both facilitated and

active transport. http://www.youtube.com/watch?v=1Z

FqOvxXg9M&NR=1

Active: Endocytosis endocytosis & exocyctosis are ways to

transport large molecules across a membrane

In some cases, receptor sites on the surface of the cell bond with the large molecule

Endocytosis takes in material from the cell by pockets or in-foldings of the cell membrane itself • this happens by phagocytosis (solids) &

pinocytosis (liquids)

See how this works!

Active: Exocytosis release of large amounts of material

from the cell• The membrane of the vacuole surrounding

the material joins with the cell membrane, forcing the contents out of the cell. Large amounts of water may be removed from a

cell in this way.

Active: Phagocytosis type of endocytosis this means “eating cell” cytoplasm surrounds a particle &

package it within a food vacuole next, the cell engulfs it (surrounds it)

• Amoebas use this to take in their food this uses A LOT of energy= form of

active transport http://www.youtube.com/watch?v=_A

ASYGG7mrw&feature=related

Active: Pinocytosis the taking up liquid from a cell’s

surrounding environment tiny pockets form along the cell

membrane, fill with liquid, and pinch off to form vacuoles within the cell

vitamins, nutrients and hormones may be absorbed into a cell using pinocytosis

Example of how it works The sodium potassium pump. http://

www.youtube.com/watch?v=GTHWig1vOnY

Watch the video and write your own voice over. You may work in pairs. Submit video with your voice over recorded.

Video Time!

Homework: Structure and function of the plasma membrane

Describe the structure of the plasma membrane. Say how its structure affects the transport of materials across it. Think about how chemicals are imported and exported from the

cell. Describe how the structure of the cell membrane allows other

functions. You must also describe the types of transport and say which parts

of the cell membrane they use and how they actually occur. Give examples of each.

¼ of a mark to be deducted for each mistake spelling technical words up to 2 marks

½ marks deducted for each time sentences are not correctly separated with punctuation or joined appropriately and meaningfully – up to 2 marks.

All information must be referenced. You may quote sections of articles but must show this with quotation marks and you must reference the information in the text. Minimum length 1000 words.

You must include labeled diagrams (2 marks). Content 14 marks (total 20marks)