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Flashcards in Structure Of The Cell Surface Membrane Deck (12)
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Why are phospholipids important in the cell surface membrane

The hydrophilic heads of both phospholipid layers point to the outside of the cell surface membrane attracted by water on both sides

The hydrophilic tails of both phospholipid layers point into the centre of the cell membrane, repelled by the water on both sides


What are the functions of the phospholipid in the membrane

Allow lipid soluble substances to enter and leave the cell

Prevent water soluble substances entering and leaving the cell

Make the membrane flexible and self sealing


How are proteins imbedded in the phospholipid bilayer

Some proteins occur in the surface of the bilayer and never extend completely across it - act to give mechanical support, or in conjunction with glycolipids as cell receptors

Some are protein channels, which form water filled tubes to allow water soluble joke to diffuse across the membrane. Others are carrier proteins that bind to ions or molecules like glucose and amino acids, then change shape in order to move these molecules across the membrane


What are the functions of proteins in the membrane

Provide structural support

Act as channels transporting water soluble substances across the membrane

Allow active transport across the membrane through carrier proteins

Form cell surface receptors for identifying cells

Help cells adhere together

Act as receptors


What do cholesterol molecules do in the phospholipid bilayer

They add strength to the membranes

Very hydrophobic and therefore ply an important role in prevent water loss and dissolved ions form the cell


What are the functions of cholesterol in the membrane

Reduce lateral movement of other molecules including phospholipids

Make the membrane less fluid at high temps

Prevent leakage of water and dissolved ions from the cell


What are glycolipids

Made up of carbohydrates covalently bonded with a lipid


What are the functions of glycolipids in the membrane

Act as recognition sites

Help maintain the stability of the membrane

Helps attach to one another and so form tissues


What are glycoproteins

Carbohydrate chains are attached to many extrinsic proteins on the outer surface of the cell membrane


Why are the functions of me of glycoproteins in the membrane

Acts as recognition sites

Help cells to attach to one another and so form tissues

Allows cells to recognise one another


Why can most molecules not freely diffuse pass the cell surface membrane

Many are :

Not soluble in lipids and cannot pass through the phospholipid layer

Too large to pass through the channels in the membrane

Of the same charge as the charge on the protein channels and so even if they are small enough to pass through they are repelled

Electrically charged and therefore difficult to pass through non polar hydrophobic tails in the phospholipid bilayer


Why’s it called the fluid mosaic model

Fluid - as the individual phospholipid molecules can move relative to one another. This gives the membrane a flexible structure that is constantly changing shape

Mosaic - as the proteins that are embedded in the phospholipid bilayer vary in shape, size and pattern in the same way as the stones of tiles