W1/L1 - Principle of cell function

Question 1

Membrane structure book chapters

Answer 1

Chpt 7

• Concepts 7.1 to 7.5

Question 2

Phospholipds

Answer 2

Abundant in cell membranes

Phospholipds are amphipatic molecules

The fluid mosaic model - membrane is fluid with a mosaic of proteins embedded in it

Question 3

phospholipid movements & fluidity

Answer 3

1. Left to right, happens very often
2. Flip-flop - flip molecule, does not happen often (unlikely)
3. Unsaturated hydrocarbon tails with kinks will move in fluid (double bonds)
4. Saturated hydrocarbon tails make it viscous (single bonds)
5. Cholesterol in cell membranes is really important. Makes the fluidity of the membrane to stay at a certain range. You dont want too much membrane fluidity, cholesterel stops it from becoming too fluid at high temperatures. At lower temperatures cholesterol increases temperature, it works as a buffer basically

Question 4

How do we know protein move around (fluid mosaic)

Answer 4

Fuse two cells with particular proteins only found in mouse to humans

after some time you get mixed up proteins in cell mombrane.

Question 5

What are the six major functions of membrane proteins

Answer 5

1. Transport - Allows things to move across (ion channel or ATP needed to transport from inside to outer membrane)
2. Enzymatic activity
3. Signal transduction (messages within cells) involves receptors, embbeded in cell membrane through protein
4. Cell to cell recognition (have sugars in them) helps cells arrange next to eachother
5. Intercellular joining, interact with eachother to form tissue
6. Attachment to the cytoskeleton and extracellular matrix

Question 6

Lipid bilayers

Answer 6

Impermeable to most essential molecules and ions

Some permeability to water molecules and a few other small, uncharged, molecules like oxygen and carbon
dioxide.
Lipid bilayers are NOT permeable to:
• ions such as K⁺, Na⁺, Ca²⁺, Cl^‐, HCO₃^‐
• small hydrophilic molecules like glucose
• macromolecules like proteins and RNA (Macromolecules are HUGE, NOT GLUCOSE)

Question 7

Passive transport Diffusion of a substance across a membrane with no energy investment

Answer 7

With time – due to random motion molecules become equally distributed i.e. to eliminate concentration gradients – provided molecules can cross the membrane
• Concentration gradient
• No work
• Diffusion across a biological membrane is passive transport (no ATP required)

Question 8

Osmosis

Answer 8

Diffusion of water through a selectively permeable membrane into another aqueous compartment containing solute at a higher concentration
• Water wants to be at equilibrium… same number of molecules in each compartment
• Remember: plasma membrane is semi-permeable!

Why is osmosis impotant? We have lots of water in our bodies and it is very important to have the ability to move them across membranes

Question 9

What are “osmotica”?

Answer 9

things that are osmotically active

• Ions (Na+, K+ , Cl-, etc)
• Sugars
• Proteins
• (Nutrients!!)

Question 10

Osmolarity

Answer 10

1. Does the solute cross the cell membrane by simple passive diffusion?
2. When the solute dissolves, does it remain intact or dissociate into ions?
   Osmolarity (Osm/L) =
   Molar concentration x number of molecules or ions in solution

• *Tonicity** : The ability of a solution to cause a cell to gain or lose water
• *Isotonic solution**: Solute concentration is the same as that inside the cell; no net water movement across the plasma membrane
• *Hypertonic solution**: Solute concentration is greater than that inside the cell; cell loses water
• *Hypotonic solution**: Solute concentration is less than that inside the cell; cell gains water