Plasma Membranes.

STRUCTURE AND FUNCTION

LEARNING AIMS

• To work out the structure of plasma membranes.

• To model the fluid – mosaic theory of plasma membranes.

• To outline the roles (functions) of phospholipids, cholesterol, glycolipids, proteins and glycoproteins in membranes

TASK

• Under the heading Components of Membranes draw a labelled diagram of a phospholipid.

• In groups of 3 or 4 make 6 to 8 bead models of phospholipids.

• Membranes separate one watery fluid from another.

• Now arrange the models on the bench so that hydrophilic phosphates are always next to the imaginary tissue fluid outside the cell and next to the imaginary cytoplasm inside the cell.

Class Fluid – Mosaic Model.

• Phospholipids can be made from plasticine and straws – 6 cm long.

• Transmembrane protein channels can be made from plasticine – 12 cm long.

• Branched chain of sugar molecules (“glyco”) can be made of pipe cleaners.

• Extrinsic surface proteins (6cm), cholesterol (9cm) and lipid and protein components of glycolipids or proteins (6-9cm) can be made from plasticine.

The following site will show you the shape of the components.

• http://www.wisc-online.com/objects/index_tj.asp?objid=AP1101

• Now use the site to check your learning

Fluid – Mosaic Model of a cell (plasma) membrane.

•Now use page 26 to research the roles of membrane components, in order to complete page 3 of your work book and a memory map of names, diagram and function of components.

•Check your learning with the animation quiz.

Roles of Membranes around Cells or Organelles.

Use the key words to write 5 roles of membranes.

Barrier / compartmentalise / cells / organelles / e.g. enzymes / water –soluble particles / large surface area

Selection / partially permeable /enter / leave (what?)

Cell signalling /receptors / hormones / neurotransmitters / self – antigens

Electrical signals /action potentials /CNS /muscleMetabolic molecule attachment /enzymes

/chlorophyll

Cell Signalling.

• Use pages 26/27 to find out:• Two reasons why cells need to

communicate with each other.• Two methods by which they do so.• The general name of the molecule in

the membrane which picks up/responds to the signal.

• A comparison between the shape of the signal and the receptor.

Mechanisms of Cell signalling, i.e. how receptors work.

• Using page 27,(extention page 28) A3 sheets with phospholipid bilayers on, plasticine and beads, make a model of the mechanism given to your pair (15 mins timer)

• Check you can both explain it .• Now student one from each pair moves to

the next model and is taught the new mechanism by the remaining student two.

• Student 2 then moves on and student 1 teaches what they have just learnt.

• Student 1 then moves and so on.

Cell Signalling Animations for Recapping.

• Receptor acts as an ion channel to allow impulse transmission from a nerve to a muscle.

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter45/animations.html#

• Receptor activates a G – protein.• http://images.google.co.uk/imgres?imgurl

=http://www.phschool.com/science/biology_place/biocoach/images/biomembrane2/SigtranC.gif&imgrefurl=http://www.phschool.com/science/biology_place/biocoach/biomembrane2/surface.html&h=184&w=400&sz=112&hl=en&start=10&usg=__khWn9QpwJ_dRPW1_RkhirWwE2A8=&tbnid=UEjeedk7Y2c1bM:&tbnh=57&tbnw=124&prev=/images%3Fq%3Dmembrane%2Breceptors%26gbv%3D2%26hl%3Den%26sa%3DG

• Receptor acts as an enzyme.• http://course1.winona.edu/sberg/ANIMTNS/Recep.htm

Cell Signalling.

• Complete the table on page 6 of your booklet.

• Learn the facts, underline the key words in question ? on page ? and then answer the exam questions.

Transport across Membranes

• http://programs.northlandcollege.edu/biology/Biology1111/animations/transport1.html

• Use the above website and demonstration with ether to remind yourself about…

diffusion.

PASSIVE TRANSPORT

• Passive Transport involves molecules or ions passing down a concentration gradient, from a

HIGH concentration to a LOW concentration,using only the kinetic energy of the

particles themselves.

Passive Transport involves:

• Simple diffusion of small, hydrophobic particles through the phospholipid bilayer, e.g.

oxygen, ethanol, carbon dioxide.

• Small polar molecules diffusing through protein channels e.g.

water, urea.

Passive Transport also involves:

•Facilitated diffusion.

Larger charged molecules diffuse through specific

protein channels.This speeds up the diffusion,

but still only kinetic energy is used.

Comparing passive and active transport.

• Use page ___ of the booklet to find out the mechanisms involved in facilitated diffusion and active transport. The following site shows the sodium pump.

• http://www.brookscole.com/chemistry_d/templates/student_resources/shared_resources/animations/ion_pump/ionpump.html

• Now answer the quiz on page ___

OSMOSIS

• Osmosis is the diffusion of water through a partially permeable membrane from a HIGH to a LOW

WATER POTENTIAL.

Use the following website and plasticine models to understand osmosis.

http://physioweb.med.uvm.edu/diffusion/

What caused Leah Betts to die?

Endo and Exocytosis.

• Membranes can also move substances in bulk across membranes.

• Exocytosis = moving substances out of the cell.

• Endocytosis = moving substances into the cell.

• Use the site on the following slide and page 33 to help you describe the mechanisms.

Endo and Exocytosis

• http://highered.mcgraw-hill.com/sites/0072437316/student_view0/chapter6/animations.html#

• For extension, try this site and quiz.• http://highered.mcgraw-hill.com/sites/

0072495855/student_view0/chapter2/animation__phagocytosis.html

A simple revision quiz!

• http://www.zerobio.com/target_practice_quiz/target_practice_quiz_cells.htm