The cell #8 (pt 2: cell components - Plasma membrane)

Plasma membranes

• Location: found on the outside of both prokaryote and eukaryote cells

  • found on the inside of eukaryotic cells as components of various organelles

• Composition: Primarily made up of phospholipid bilayers

  • as well as steroids, carbohydrates, & proteins

• Function: control what enters and what leaves the cell with its semi-permeable barrier btw the outside and inside of the cell

  • they sense and then tell the cell to responds to its environment

  • protect themselves and maintain their internal environment

  • generate electrochemical gradients

    • convert chemical or light energy to biological energy

they are found on the outside of both prokaryote and eukaryote cells & only on the inside of eukaryotic cells as components of organelles

Where are plasma membranes located?

plasma membranes are primarily made up of phospholipid bilayers as well as some steroids, carbohydrates, and proteins

What are plasma membranes composed of?

Phospholipids

• _______ naturally assemble into a fluid bilayer

  • hydrophilic heads on the outside

  • hydrophobic tails on the inside

• individual molecules are constantly moving around (not locked in place)

• by changing the fatty acid (hydrophobic) tails, the properties of the membrane can change

• are mobile within the lipid bilayer

Phospholipids are mobile within the lipid bilayer: they turn on their axis, move laterally, and rarely flip across the membrane

Remember: Phospholipids are mobile within the lipid bilayer: they turn on their axis, move laterally, and rarely flip across the membrane

the membrane would be more fluid because the kinks in the unsaturated fatty acids would prevent them from packing closely together (too fluid = too permeable)

What would happen if a plasma membrane included mostly unsaturated fatty acids?

the membrane would be more solid (solid at room temp) because saturated fatty acids are able to pack tightly together

What would happen if a plasma membrane included mostly saturated fatty acids?

The steroid Cholesterol

• within plasma membranes

• amphipathic

• Function: helps maintain the integrity of membranes by preventing them from becoming either too fluid or too rigid

Amphipathic means it has both hydrophobic and hydrophilic parts

What is the definition of Amphipathic:

cholesterol helps maintain the structural integrity of plasma membranes by preventing them from becoming either too fluid at high temperatures or too rigid at low temperatures

Function of the steroid cholesterol in plasma membranes:

Heating or cooling a phospholipid membrane will change its fluidity and ability to function correctly, so cells modify the biochemical components of their membranes to maintain optimal fluidity

Remember: Heating or cooling a phospholipid membrane will change its fluidity and ability to function correctly, so cells modify the biochemical components of their membranes to maintain optimal fluidity

increase the amount of unsaturated fatty acids, the amount of cholesterol, and the proportion of shorter-chain fatty acids, all of which will increase fluidity

In colder conditions what will the cell do to maintain optimal fluidity of the plasma membrane?

decrease the amount of unsaturated fatty acids, increase the amount of cholesterol, and the proportion of longer-chain fatty acids, all of which will decrease fluidity and increase solidity

In hotter conditions what will the cell do to maintain optimal fluidity of the plasma membrane?

Carbohydrates

• within plasma membranes

• Function: cell-to-cell recognition

  • act as “keys” fitting into matching protein “locks” on other cells to help cells recognize one another

• Types:

  • Glycolipids- carbohydrates covalently bonded to lipids

  • Glycopeptides- carbohydrates covalently bonded to proteins

carbohydrates covalently bonded to proteins

Glycopeptides definition:

carbohydrates covalently bonded to lipids

Glycolipids definition:

Proteins

• within plasma membranes

• Functions:

  • Transporters

  • Receptors

  • Enzymes

    • ATP synthesis

  • Anchors

only Non-polar molecules can be exchanged through the membrane easily, and O2 and CO2 can only pass through freely when there is a concentration gradient

Remember: only Non-polar molecules can be exchanged through the membrane easily, and O2 and CO2 can only pass through freely when there is a concentration gradient

Polar molecules need assistance from special transport proteins in order to get through the membrane

Remember: Polar molecules need assistance from special transport proteins in order to get through the membrane

Diffusion gradient

• Def: molecules in an area where they are highly concentrated will diffuse (spread out) to areas where they are less concentrated)

Concentration gradients

• Def: molecules try to balance themselves out across a permeable membrane

Transport proteins

• within the plasma membrane

• aid polar molecules

• Def: protein molecules that san the lipid membrane and provide a pathway for other molecules to enter or leave the cell

  • hydrophilic tips & hydrophobic centers

• Types:

  • passive

  • active

Aquaporins

• common passive transport protein

• Def: protein channels allowing water molecules to move in and out of the cell

• diffusion of water across concentration gradients = osmosis

Osmoregulation

• the regulation of the amount of water within the cell

  • maintain the cells integrity

• Diffusion:

  • if concentration of solute is higher inside - water flows in

  • if concentration of solute is higher outside - water flows out

Active membrane Transport proteins

• Def: transport proteins that work against concentration gradients (require energy to be added to the protein to work against the pressure)

  • gets this energy from the expansion of a molecules of ATP

• common ______ protein: Na+/K+ pumps

  • push Na+ ions out of cell, and bring K+ ions into cell

  • 30% of ATP spent of these pumps