Cell membranes 2

What is The Fluid Mosaic model of a cell membrane?

Success criteria

• I can describe the fluid mosaic model of the cell membrane structure with the aid of diagrams.

• I can describe the roles of the components of the cell membrane– Phospholipid– Cholesterol– Glycolipids– Proteins– glycoproteins

Components of the fluid mosaic.What do you know about this?

Key words – what are these things?

–Glycolipids–glycoproteins– Cholesterol– Proteins

Glycoproteins and glycolipids

• Glyco – carbohydrates (sugars)

• So these are carbohydrate chains attached to proteins(glycoprotein)

• or attached to phospholipids (glycolipid).

These are used for signalling

Key words – what are these things?

– Glycolipids– glycoproteins

–Cholesterol– Proteins

Cholesterol

• Cholesterol is very important in SOME EUKARYOTIC cells for providing stability.

• IT is a steroid molecule that fits between the fatty acid tails forming a barrier and meaning water molecules and ions cannot pass easily through the membrane.

Key words – what are these things?

– Glycolipids– glycoproteins– Cholesterol

–Proteins

Proteins

• Extrinsic and intrinsic – what do these mean?

Role of proteins

• They may act as enzymes eg carbohydrase enzymes are found in the cell membranes of intestinal epithelial cells.

• They act as receptors for hormones.• They act as carrier proteins, controlling what

enters and leaves the cell.• Carbohydrates and lipids attached to proteins

(forming glycolipids and glycoproteins) , allow cells to recognise one another.

The fluid mosaic model of the plasma membrane:

The proteins can move freely through the lipid bilayer.

The ease with which they do this is dependent on the number of phospholipids with unsaturated fatty acids in the phospholipids.

Fat-soluble organic molecules can diffuse through the bilayer but polar molecules require proteins

Extracellular space

Cytosoplasm (aqueous)

Fat-soluble molecules Polar molecules

hydrophilic pore

There are different types of carrier proteins in the membrane:

ATP

Channel proteinGated-channel proteinCarrier protein(passive)

Carrier protein(active)

Channel proteins

These provide a pathway for polar or large particles to move through the membrane.

Carrier proteins

• These actively pump molecules into cells.• These use ATP energy

• E.g pumping Mg2+ ions into root hair cells,

Question 4: How can polar and non-polar molecules pass through the membrane (2).

•Polar molecules require proteins to enable them to pass through the membrane

•Non-polar molecules can diffuse directly through the phospholipid bilayer

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The membrane contains many types of protein:

glycoprotein

carbohydrate chain

integral proteinperipheral protein

carrier protein

Glycocalyx: For cell recognition so cells group together to form tissues

Receptor: for recognition by hormones

Enzyme or signalling protein hydrophilic channel

Receptor proteins Receptor: for recognition by hormones

These allow hormones / drugs to bind to cells and cause a response to happen inside the cell.

Question: Label the diagram (11marks)1

2 10

3

4

5 6

8

9

11

Note: label the proteins based on location or structure, e.g. you do not need to identify receptors and enzymes.

1) carbohydrate; 2) glycoprotein; 3)integral protein; 4) peripheral protein; 5) carrier protein 6) hydrophilic channel; 7) phosphate group; 8) fatty acid; 9) phospholipid; 10) glycocalyx; 11) phospholipid bilayer click to cover answers

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Question: Explain why the model for membrane structure is known as the fluid mosaic model (3).

• The phospholipid molecules can move freely laterally and makes the membrane fluid.

• The proteins are distributed throughout the membrane un evenly and in a mosaic pattern.

• The agreed structure is based upon experimental and chemical evidence and so is classed as a model.

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Question: Describe the structure and function of the glycocalyx (a glycoprotein) (2)

• Consists of glycoproteins• Which are proteins with added carbohydrate chains• Used for cell recognition/receptors• Click here to hide answersClick to reveal answers

Internal membranes

• The inner membranes of the mitochondria and chloroplasts contain enzymes and co enzymes. These allow respiration and phs to take place respectively.

• This is why the cristae and thylakoids exist.