2.5 biological membranes

Fluid-mosaic model described

Fluid- phospholipid bilayer, (membrane has flexible shape and individual phospholipids can move

Mosaic- extrinsic & intrinsic proteins of different sizes and shapes are imbedded

Active transport definition

An active process in which ATP is released to be used with a phosphate group that binds to a carrier protein, causing it to change shape

How are cells adapted for transport across membranes

Many carrier and channel proteins

Folded membrane increases surface area

Simple diffusion

A passive process that requires no energy from ATP hydrolosis

Facilitated diffusion

A passive process specific to channel and carrier proteins down a concentration gradient

5 factors that effect the rate of diffusion

Temperature

Diffusion distance

Surface area

Size of molecules

Steepness of concentration gradient

Osmosis in or out of plant cells

Into - protoplasm swells = cell is turgid

Out- protoplasm shrinks = cell is flaccid

Osmosis in or out of animal cells

Into-lysis

Out-crenation

Water potential

Pressure created by water molecules

Pure water=0

Lots of solute =-10

Role of cholesterol

Cholesterol- connects phospholipids by bonding to their tails, also stabilises bilayer which regulates fluidity of bilayer

Role of glycolipids

Glycolipids - cell signalling & cell recognition

Role of extrinsic vs intrinsic proteins

Extrinsic protiens- binding sites, receptors, only inhabit half of membrane

Intrinsic protein- inhabits whole membrane, used as either carrier or channel proteins

Functions of membranes in cells

provide internal transport systems

Selectivity permeable to regulate passage of molecules

Provides a reaction surface

Isolates organelles from the cytoplasm

Functions of the cell surface membrane

Isolates cytoplasm from extracellular environment

Selectively permeable membrane to regulate transport

Involved in cell signalling recognition

3 factors effecting membrane permeability

Temperature ( can denature protiens)

PH (changes tertiary structure of protiens)

Solvent (may dissolve membrane)

Colorimeter to investigate permeability

Water would read at o

Therefore the higher the absorbarce of coloured Solution into the membranes, the less will be left over and therefore the weaker the remaining Solution will be causing the reading to be lower

Osmosis definition

When water diffuses across a semi-permeable membrane from an area of higher water potential to an area of lower water potential until a dynamic equilibrium is established.