11Bio - Cell membranes

List all the structures in the cell membrane

1. Phospholipid bilayer

2. Cholesterol

3. Transport protein

4. Integral protein

5. Peripheral protein

6. Glycolipid

7. Glycoprotein

What are the properties of the phospholipid bilayer?

• Hydrophobic (water-hating) fatty acid tails

  • Due to the presence of these hydrophobic tails, only small uncharged molecules can diffuse freely through phosopholipid bilayers

  • Charged molecules, such as ions, are unable to diffuse through a phospholipid bilayer regardless of size

• Hydrophillic (water-loving) head

  • Attracted to water molecules due to its polar nature and negative charge - allows the head to interact with the aqueous environment both and in and out the cell

What are proteins?

• Proteins are the other major component of cell membranes, making up 25-75% of the mass of the various cell membranes.

• Proteins carry out the specific functions of different cell membranes

  • Act as transporters, enzymes, receptors and structural components

What are the two types of proteins found in the cell membrane?

• Peripheral proteins

  • more loosely attached to the phospholipid bilayer

  • act as enzymes

  • attaching the membrane to the cytoskeleton, providing structural support and maintaining cell shape

• Integral proteins

  • their potential to cross the membrane are often involved in transportation (e.g. glucose) across the membrane, signalling molecules and providing structural support

What are the classifications of protein functions?

• Transport

  • transports needed compounds into the cell that aren’t permeable acorss the membrane

    • faciltated diffusion

    • active transport

• Receptor

  • detect hormones, neurotransmitters or other messages from outside the cell

    • helps the cell know what to do: grow, divide, or stop

  • coordinate with other cells

• Adhesion

  • the tendency of unlike molecules cells sticking together

    • form tissues and organs

    • clotting for a wound

• Recognition

  • allows cells to distinguish between their own cells and foreign cells

    • ensures proper immune system function so white blood cells can identify the difference between pathogens (viruses, bacteria) your own cells

What is the function of the phospholipid bilayer?

Phospholipid bilayer

• Forms the membrane’s basic structure

• Selective permeaability - allows small, non-polar and lipid-soluble substances (e.g. gases) to pass through. Barrier to water-soluble substances, large molecules and ions

• Fluidity - enables cell movement, needed for cell divide or white blood cells enfulfing pathogens

What is this?

1. Phospholipid bilayer

What is the function of cholesterol?

Cholesterol

• Maintains fluidity and stability (structure) of the membrane in hot and cold temperatures

  • cholesterol’s rigid structure interacts with the phospholipid fatty acid tails, restricting their movement and preventing the membrane from becoming too fluid at high temp

  • at lower temp, cholesterol prevents fatty acids from packing together too tightly and becoming rigid

What is this?

2. Cholesterol

What is the function of the channel (transport) protein?

Channel protein

• Creates hydrophillic pores to transports specific compounds into the cell that AREN’T PERMEABLE across the membrane

  • Facilitated diffusion (high → low concentration)

  • Active transport (low → high concentration)

• Allows larger molecules (e.g. glucose), ions and polar substances to move across the membrane

What is this?

3. Channel protein

What is the function of integral (receptor) proteins?

Integral proteins

• Detects hormones, neutransmitters, or other messages from outside the cell

  • Receptors on the outer part of the protein detect signals and communicate messages to proteins inside the cell

  • Helps the cell know what to do: grow, divide or stop

What is this?

4. Integral protein

What is the function of the peripheral protein?

Peripheral proteins

• Attached to the membrane’s surface, either inside or outside, but does not cross it

• Inside membrane - recieves messages from integral protein and passes them to the cell

• Outside membrane - involved in adhesion (cells sticking together)

  • Forms tissues and organs

  • Clotting for a wound

What is this?

5. Peripheral protein

What is the function of the glycolipid?

Glycolipid protein

• Glycolipid: a lipid (fat molecule) with one or more sugar chains (carbohydrates) attached. This lipid part anchors it to the membrane

• Sugar chain - cell recognition

What is the function of the glycoprotein?

Glycoprotein

• Glycoprotein: proteins that have sugar chains (carbohydrates) attached to them

• Protein - helps with adhesion

• Sugar chain - helps with recognition

What are these

6. Glycolipid

7. Glycoprotein