C ELL MEMBRANES & TRANSPORT Biology ATAR Unit 2 Text: Chapter 8 pages

C ODE OF CONDUCT Our classroom community... Our valuesOur responsibilitiesOur words, our actions Is about learningLearning matters Learning well means: ●being prepared ●giving your best effort ●persisting in the face of difficulties Be punctual Bring everything you need to class Know your due dates Complete all tasks to the best of your ability Never give up – mistakes are OK Participate in group discussions Is about peoplePeople matter Treating people well means: ●showing respect ●being kind ●listening Be encouraging – no put downs Help others Always listen well Be accepting of differences and work well with your peers Treat others how you would like to be treated.

Diffusion Osmosis Fluid mosaic model Phospholipid bilayer Hydrophobic Hydrophilic Channel proteins Carrier proteins Carrier mediated transport Facilitated diffusion Active transport Vesicular transport Endocytosis Pinocytosis Phagocytosis Exocytosis Receptor proteins The cells of all living organisms are surrounded by a cell membrane. Cell membranes are made up of lipid (fat) molecules interspersed with protein and cholesterol molecules. The cell membrane is a dynamic system and responds to changes in the environment. KeywordsMaking connections

L EARNING OUTCOMES Understand the structure and function of cell membranes Describe and explain the Fluid Mosaic model Describe and explain passive and active transport processes

Movement of molecules across the membrane is either through passive processes or active processes. Active processes require energy because the molecules are being moved from an area of lower concentration to an area of higher concentration M OVEMENT ACROSS CELL MEMBRANES

C ONCENTRATION GRADIENT When the concentration of a substance is different at two places, the substance will diffuse along the concentration gradient until the concentration of the two areas becomes equal. concentration gradient High concentration Low concentration

Concentration gradient Uniform concentration Equilibrium Rate of diffusion slows Concentration at A Concentration at B High concentration

D IFFUSION Diffusion is the movement of molecules from an area of high concentration to an area of low concentration Diffusion is a passive process and requires no energy input from the cell

O SMOSIS Osmosis is a special case of diffusion. It is the diffusion of water through a semi- permeable membrane. Osmotic flow is simply diffusion of a solvent (water) through a membrane impermeable to the solute molecules (eg. salt) Osmosis is a passive process and requires no energy input from the cell

D EFINITIONS Concentration gradient The concentration gradient is the difference in concentration of ions in a solution Ions will move along the gradient from the area of high concentration to the area of low concentration Osmotic gradient The osmotic gradient is similar to a concentration gradient but involves the difference in concentration across a semi-permeable membrane Water moves across the membrane along the gradient from the area of high concentration to the area of low concentration

R EVIEW : DIFFUSION & OSMOSIS

O SMOSIS High water concentration (dilute solution) Low water concentration (concentrated solution) Semipermeable membrane Net water movement from high concentration to low concentration

The cell membrane is the outer skin of a cell. It surrounds the whole cells and and separates the contents of the cell from the extracellular or interstitial fluid The cell membrane is selectively or differentially permeable – it allows some substances to cross more easily than others. T HE CELL MEMBRANE

F UNCTION OF THE CELL MEMBRANE A physical barrier: separates the cell from the extracellular fluid The regulation of the passage of materials: the membrane controls the movement of materials into/out of cells Sensitivity: the cell membrane is the first part of the cell affected by any changes in the extracellular fluid Support: cell membrane is attached to microfilaments to give cell support

F UID MOSAIC MODEL One model that explains the cell membrane is called the fluid mosiac model The membrane is said to be fluid because the molecules are constantly changing position Its said to be mosiac because it is composed of many kinds of molecules

F LUID MOSAIC MODEL The main structure of the membrane is composed phospholipid molecules, which are lipids that contain a phosphate group The phospholipids are arranged in 2 layers called a bilayer

F LUID MOSAIC MODEL Each phospholipid molecule has a hydrophilic head (water loving) and a hydrophobic tail (water hating) They are arranged so that their heads are on the outside and tails on the inside

F LUID MOSAIC MODEL Embedded in the phospholipid bilayer are cholesterol and protein molecules

M EMBRANE PROTEINS Many of the proteins are involved in the movement of substances through the membrane There are 4 types of membrane proteins, each with a different function: 1. Channel proteins 2. Carrier proteins 3. Receptor proteins 4. Cell-identity markers

M EMBRANE TRANSPORT : C HANNEL PROTEINS & CARRIER PROTEINS Channel proteins are like open doors They allow certain types of molecules (mostly ions) to flow freely in and out of the cell The cell may be able to close these ‘doors’ when required Channel proteins allow passive diffusion across the membrane (osmosis) Carrier proteins are involved in carrier mediated transport These proteins bind to molecules to be transported and help their passage across the membrane They bind to the molecule, change shape and then release the molecule

O SMOSIS : WATER TRANSPORT You would think that water does not cross this membrane easily because of the hydrophobic middle layer. However, considering that... the concentration of water in water is extremely high AND the surface area to volume ratio (membrane to cell) is also very high... water does diffuse across the membrane quite well Transport proteins are also involved in water diffusion

M EMBRANE TRANSPORT : C HANNEL PROTEINS & CARRIER PROTEINS

Facilitated diffusion is a passive process which substances move along the concentration gradient. The protein changes shape and the molecule is released through the membrane M EMBRANE TRANSPORT : C ARRIER MEDIATED TRANSPORT  Active transport requires an energy input as the substance is being transported across the membrane against the concentration gradient There are 2 main types of carrier mediated transport

S IMPLE DIFFUSION & FACILITATED DIFFUSION Diagram created by LadyofHats

A CTIVE TRANSPORT ( SODIUM PUMP ) Diagram created by LadyofHats

M EMBRANE TRANSPORT : C ARRIER MEDIATED TRANSPORT Carrier proteins are specific - they will only bind to a particular molecule Carriers can become saturated. Once all the available carriers are occupied, any increase in the concentration of molecules cannot increase the rate of movement Carrier activity is regulated by substances ie. hormones

M EMBRANE TRANSPORT : V ESICULAR TRANSPORT Vesicular transport is the movement of substances across the cell membrane in membranous bags called vesicles

M EMBRANE TRANSPORT : V ESICULAR TRANSPORT Endocytosis is taking liquids or solids into the cell by vesicular transport Pinocytosis is taking in liquids Phagocytosis is taking in solids Exocytosis is when the contents of a vesicle inside the cell are passed to the outside of the cell

E NDOCYTOSIS Diagram created by LadyofHats

E XOCYTOSIS Diagram created by LadyofHats

M EMBRANE RECEPTORS Membrane receptor proteins are sensitive to certain molecules outside the cell, and when those molecules are present they bind with the receptor protein The receptor and the bound molecule then trigger changes in the cell.

M EMBRANE RECEPTORS Receptor proteins are specific. Each type of receptor protein will bind to only one specific molecule. There are a limited number of receptor proteins in the membrane of each cell, so when each receptor is bound to a molecule there can be no further increase in the rate of the cell’s activity

M EMBRANE RECEPTORS Different cells have different types and numbers of receptor proteins Receptor proteins also function for communication between cells Receptor proteins are binding sites for hormones