Transport across Transport across membranesmembranes

By the end of this lesson you should be able to describe how the components of

a membrane allow both passive and active transport of molecules into and

out of cells

Metabolism and cell survivalMetabolism and cell survival

• Reactions in living cells require molecules to be transported into the cells.

• Some reactions make useful products that need to be transported out of the cells

• Many reactions produce waste products that need to be removed from the cells.

• All molecules that need to pass into or out of a cell will have to pass across a membrane.

• How do you think this happens?

Types of transport

• Simple Diffusion• Facilitated diffusion through “channel”

proteins• Facilitated diffusion through “carrier” proteins• Facilitated diffusion through “gated” proteins• Active transport which requires energy in the

form of ATP

Diffusion

• The NET movement of molecules from an area of high concentration to an area of low concentration

• This means that molecules are moving randomly in all directions but the final outcome appears to be in one direction.

Factors that affect Rate of Diffusion Factors that affect Rate of Diffusion across a membraneacross a membrane

• Temperature• Concentration gradient• Surface area of the membrane• Distance/thickness of the

membrane• Size of molecules

Diffusion in cellsDiffusion in cells

Passive (simple) Diffusionhttp://www.youtube.com/watch?

v=s0p1ztrbXPY&feature=related

Simple diffusion through the phospholipid bilayer

• Lipid based molecules can slip through the hydrophobic core and passively move down the concentration gradient

• Very small or non-polar molecules E.g. Oxygen, carbon dioxide and water can easily pass through the bilayer

• Larger or charged molecules cannot pass between the phospholipids, so they require help through facilitated diffusion

• Channel proteins: gated or ungated ‘pores, Ungated pores are always open, Gated pores need another substance to bind to them to open the gate.

• Carrier proteins: These are “molecule-specific” carriers that change shape when activated to allow passage through the membrane

Which Which is is

which?which?

http://www.stolaf.edu/people/giannini/flashanimat/transport/channel.swf

Copy blue box bottom of page 23

Gated and non gatedGated and non gated

Active TransportActive Transporthttp://www.stolaf.edu/people/giannini/fhttp://www.stolaf.edu/people/giannini/f

lashanimat/transport/channel.swflashanimat/transport/channel.swf

When concentration gradients can’t help!

Find 2 examples

•‘Pump’ like carrier protein•Complementary shape to molecule•Require ATP•Go against concentration gradient•Can transport at a faster rate than diffusion•Molecules can be accumulated on either side of a membrane

See how Active Transport happens!

• YouTube - Active Transport

Endo- and Endo- and ExocytosisExocytosis

Used for bulk transport

Complete notes by reading through

p25

See how Endocytosis and Exocytosis happen

YouTube - Cell Membrane, Exocitosis & Endocitosis

Cell signallingCell signalling• Signalling and receiving signals is vital for cell survival and

communication• When looking at the bilayer, chains ‘sticking out’ from the

surface are visible (called?)• These allow for ‘self’ recognition of cells by the immune

system, to prevent auto immune responses• The surface also has membrane bound receptors

associated with these projections that are modified protein molecules.

• They receive ‘messages’ about cell activities via chemical messengers (called?)

• Like jigsaw pieces a hormone and receptor will only bind with their complementary partner causing the target cell to respond. (similar idea to enzyme active site and substrate)

For cover work:For cover work:Research in as much detail as you can the communication and cell signalling involved with:

• Insulin• AIDS• BOTOX and• Beta blockers

Please use p20-21 to help guide you and help you begin your research