Cell Membranes (WIP)

Eduqas spec A Level biology

What are cell membranes made of?

A phospholipid bilayer

What are the main components of phospholipids? 

Hydrophilic polar phosphate head, glycerol, hydrophobic non-polar hydrophobic fatty acid tails

What effect do phospholipids on their own have on hydrophobic and hydrophilic molecules?

Something hydrophilic can pass through the heads but not the tails so can not pass through (without help). Something hydrophobic is able to avoid the heads and pass through the tails so can pass through

What are the two types of protein molecules in phospholipid layers?

Extrinsic- partly embedded

Intrinsic- extend completely across the bilayer

What is the function of intrinsic protein molecules?

Transport through the membrane as Carrier Proteins or Protein Channels for molecules that would otherwise not be able to pass through.

What is the function of extrinsic protein molecules?

used for cell recognition, as enzymes or for cell recognition

What is it when a carbohydrate chain is attached to a phospholipid or protein?

It is a glycocalyx forming a glycolipid/ glycoprotein. It helps with the functions of the protein molecules.

What is the fluid mosaic model?

The model of the arrangement of the membrane. It means that the proteins and phospholipids can change places

What does the cholesterol in ANIMAL membranes do?

bind the phospholipids together meaning there is less movement

What is the function of the plasma membrane?

• regulating intake of nutrients and secretion of chemicals

• cell recognition using glyco(proteins/lipids)

• separating the inside and outside of the cell

• separating one cell from another

How well do differently soluble substances pass through the membrane?

Lipid soluble substances move easily and quicky as they can move through the lipid bilayer.

Water soluble substances move more slowly as they must move through protein channels.

The lipid bilayer is semi-permeable, what things can diffuse across the bilayer?

small nonpolar molecules diffuse rapidly and so do uncharged polar molecules if they are small enough. HOWEVER the bilayer is highly impermeable to ALL charged molecules

What affects the permeability of the cell membrane?

Ethanol- dissolves the lipid components

Temp and pH- when they are above/ different ot the optimum the enzymes denature