P2- Plasma MembraneStructure and FunctionMovement of Substances

Key KnowledgeThe structure and function of the plasma membrane and the movement of substances across it The fluid-mosaic model The packaging, transport, import and

export of bio macromolecules The role of ribosomes, endoplasmic

reticulum, Golgi apparatus and associated vesicles in the export of proteins

Plasma membrane This is the insoluble boundary of the

living cell that maintains the contents of the cell and regulates the movement of substances in and out of the cell.

ALL cells have a plasma membrane.

The plasma membrane is differentially or selectively permeable.

The plasma membrane is composed of two layers of phospholipids.

Fluid mosaic modelThe lipid component of the membrane allows flexibility and the membrane has the ability to repair itself.

Glycoprotein Sugar attached to a

protein

Often a marker or receptor

molecule that identifies ‘self’ from ‘non self’

Important in cell recognition and communication

Glycolipid

Sugar attached to a lipid

Their role is to provide energy for the cell and

also as a marker.

Membrane Proteins

Important for: Regulation of cell behaviour

Organisation of cells in tissues

Cellular communication: receptor sites detect hormone and other chemical

molecules to control transmission of messages within and

between cells.

Plasma membrane – the Sieve Small particles can pass through openings or

pores between the phospholipids easily – eg: H20, CO2, O2 and other small, non polar particles.

Within the membrane are channels made by proteins – these allow a variety of larger or polar substances in and out eg: glucose.

Large proteins cannot pass through the membrane.

Plasma membrane – the Sieve

Copy diagram into your workbook

Diffusion The net or overall movement of particles (molecules

or ions) from a region where they are at a relatively high concentration to a region where they are at a relatively low concentration.

Concentration gradient = difference between the two regions.

Diffusion continues until an equilibrium is reached and there is the same concentration of particles on either side of the membrane.

Passive process – no energy is required.

Diffusion is quicker if greater concentration gradient.

http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

Diffusion

What determines the rate of diffusion?There 4 factors:

1. The steepness of the concentration gradient. The bigger the difference between the two sides of the membrane the quicker the rate of diffusion. 2. Temperature. Higher temperatures give molecules or ions more kinetic energy. Molecules move around faster, so diffusion is faster.3. The surface area. The greater the surface area the faster the diffusion can take place. This is because the more molecules or ions can cross the membrane at any one moment.4. The type of molecule or ion diffusing. Large molecules need more energy to get them to move so they tend to diffuse more slowly. Non-polar molecules diffuse more easily than polar molecules because they are soluble in the non polar phospholipid tails.

OsmosisTerms

Solute: a substance dissolved into another substance (the solvent) to create the solution.

Solvent: a substance in which other substances (solutes) can be dissolved to create a solution. E.g. Water is a solvent because it is polar and many

other polar solutes can dissolve in it.

Osmosis High concentration solution: High solute concentration and low solventconcentration. Low concentration solution:Low solute concentration and high

solventconcentration.

IsotonicSame concentration of solvent and solute HypotonicLower concentration (low solute and high solvent) HypertonicHigher concentration (high solute and low solvent)

Osmosis continued... If a vacuole swells and

pushes the plasma membrane against the cell wall it is called turgid

The pressure on the cell is called turgor pressure keeps cell firm & maintains shape.

Opposite of turgid is a process called plasmolysis.

Water diffuses out of the cell and the plasma membrane is withdrawn from the cell wall making the cell limp or flaccid.

Transport across the membrane

Crenated

Osmosis continued...

Osmosis Animation: http://highered.mcgraw-hill.com/sites/00724958

55/student_view0/chapter2/animation__how_osmosis_works.html

Osmosis: establishing an equilibrium: http://www.stolaf.edu/people/giannini/flashanim

at/transport/osmosis.swf

Facilitated Diffusion

Substances are helped across the cell membrane by carrier molecules. Their diffusion is facilitated (helped).

Facilitated Diffusion Transport proteins in

membrane assist in movement of simple sugars, amino acids, nucleotides, charged ions and other nutrients.

http://highere.mcgraw-hill.com/sites.0072495855/student_view0/chapter3/animation_how_facilitated _diffusion_works.html

Carrier Proteins Assist the passage of other molecules across the

membrane in facilitated and active transport. Carry some molecules to other side of

membrane.Channel Proteins Form pores in membrane that fill with water. Lining of protein = hydrophilic Particles that are able to dissolve in water move

through membrane this way. Selective Open only when correct signal received.

Active Transport Requires input of energy

Cells that undergo lots of active transport of substances have lots of mitochondria to provide energy.

Involves a carrier protein attached

to a source of energy. Function in one direction

Bulk Transport Large molecules also need to

move in and out of cells. E.g. hormones, mucus, enzymes etc.

Sometimes this is not as easy as facilitated diffusion.

Endocytosis and exocytosis is then required.

Endocytosis Inward movement of

particles into a cell. The membrane engulfs the

substance and forms a endocytic vesicle which stores and transports the substance throughout the cytoplasm.

Phagocytosis – encloses solid material e.g. food

Pinocytosis – encloses droplets of liquid.

Exocytosis Movement of particles out of a cell via the plasma membrane. Small membrane bound vesicles move

throughout the cytoplasm to the plasma membrane where it fuses and releases its contents to the external environment.

http://www.youtube.com/watch?v=K7yku3sa4Y8 http://highered.mcgraw-hill.com/olc.dl.120068.bio02.swf

Synthesis and transportInvolves the coordinated activity of a number of organelles, including nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus and vesicles.

STEP 2-Polypeptide produced on ribosome

STEP2-Polypeptide enters ER tubule

STEP 3-Polypeptide modified in ER tubule environment

STEP 4-Polypeptide enclosed in transport vesicles

STEP 5-Further modification of polypeptide in Golgi complex. Finally ready for export

STEP 6-Protein placed in protein transport vesicle

STEP 7-Protein transport vesicle fuses with plasma membrane. Exocytosis: Protein product secreted

STEP 1- mRNA made in nucleus enters cytoplasm

STEP 2- The mRNACodes for proteinBeing made atribosome

QuestionsQuiz http://www.hbwbiology.net/quizzes/ch8-cell-m

embrane.htm

Complete the following QuestionsHeinemann Biology 2 Textbook:

Chapter 1 Review QuestionKey Questions 20-25 page 25

18 – 21 page 44