Studying cells and cell surface membrane

Light microscope

Passes into the condenser lens of the microscope and the object into the objective lens, uses light source

Advantages :

Uses live speciments

Easy to use

Provide coloured images

Relatively cheap

Disadvantages :

Low resolution

Low magnification

Transmission electron microscope (TEM)

Electron beam through a sample called a photomicrograph

Denser tissue appears darker and lighter tissue appears brighter

Very high magnification and resolution as electrons have shorter wavelength

Disadvatages :

Must be used in a vacuum

Expensive and requires a lot of training

Only black and white images

Artefacts may be present

Scanning electron microscope (SEM)

Electrons are directed across a specimen

Secondary electrons captured by a cathode ray tube

Advantages :

Produces 3D images

Can used on thick specimens

Can scan the surface of a specimen and capture all textures

Disadvantages :

Lower resolution and magnification compared to a TEM

Dead materials only

Expensive, tranining required

Cell fractionation

Place tissue sample in an ice-cold, buffered, isotonic solution

Homogenisation : Break open the cell by using a blender to disrupt the plasma membrane and release organelles into solution

Filter the solution through a gauze that’s placed in a filter funnel to filter large debris

Ultracentrifugation : Spins the solution in a centrifuge at different speeds to separate organelles. Heaviest organelles form pellet first.

Side notes cell fractionation

Ice-cold temperature —> slows enzyme activity

Buffered —> remain constant pH to prevent damaging the cell

Isotonic —> same water potential as the tissue sample

Cell surface membrane

Comprised of phospholipids where the hydrophilic heads point outwards and the hydrophobic tails point inwards. This allows lipid soluble molecules to pass through but not water soluble molecules. The fluidity of the membrane and the mosaic arrangement of the protein gives the name fluid mosaic model.

Proteins

Intrinsic protein are integrated throughout the membrane, include carrier proteins which allows substances to cross th membrane

Extrinsic protein are on the surface

Proteins provide mechanical support and act in conjunctions with glycolipids as receptors

Cholesterol

Provide rigidity

Reduce lateral movement of the phospholipids

Prevents the leakage of water and dissolved ions

Very hydrophobic

Glycolipids

Made up of carbohydrate that is bound to lipids

Acts as a cell surface receptors

Allow the cells to form tissue

Glycoproteins

Carbohydrates that attach to extrinsic proteins

Acts as cell surface receptors and neurotransmitters

Allow cells to attach and form tissue