Cell membrane structure

What are functions of cell membranes

Acts as selective barriers

Provide surfaces for chemical reactions

Must stay flexible

Enable secretion via endosytosis and executors

Phospholipid structure

Hydrophilic head

Hydrophobic tails

Why does the arrangement of tails on the inside of the bilayer help lipid soluble molecules pass through

The tails are non polar so non polar molecules such as oxygen can dissolve through it

What is the function of cholesterol between the phospholipids

Makes the membrane more rigid and stable and reduces permaebility to small molecules. Influences the fluidity

How do cholesterols between phospholipids act at high temperature

Phospholipids have more kinetic energy

Cholesterol packs phospholipids more closely and reduces fluidity

How do cholesterols between phospholipids acts at low temperature

Phospholipids don’t have much energy

Cholesterols prevents phospholipids from packing to tightly and increases the fluidity

What are the functions of glycoproteins and glycolipids on the surface

Important in cell signalling

Important in cell recognition

What type of peripheral proteins are in the cell membrane

Intrinsic and extrinsic proteins

Intrinsic proteins (integral proteins)

Include channel and carrier proteins and they span the whole bilayer

Intrinsic proteins function

To transport large molecules and ions across membrane

Extrinsic proteins (peripheral proteins)

Only on one side of the bilayer

Extrinsic proteins function

Help with cell signalling or provide structural support

Function of pores/channels

Allow specific modules to move through the membrane

Gated channels function

Channels that can be open or shut depending on charge difference between two sides of the membrane

Active carrier system function

Use energy to move molecules across the membrane

Receptor molecules function

Act as specific receptors for hormones

Davison and Danielli

Proposed a lipid centre coated on each side with protein

Singer and Nicholson

Proposed the fluid mosaic model-proteins floating within a fluid lipid bilayer

How to investigate membrane permeability

Use a beetroot cell which stores red pigment in their vacuole

Use temperature or solvents to increase permeability

When permeability increases, pigment leaks out. Calibrate the calorimeter to test the colour intensity