Unit 1 Cell Membrane Structure And Function Flashcards
How can fatty acids vary?
Differ in their hydrocarbon tail, two types - saturated and unsaturated.
Saturated - no double bonds between carbon atoms
Unsaturated - double bonds between carbon atoms causing chain to kink.
What is the structure of a phospholipid?
Phospholipids are pretty similar to triglycerides except one of the fatty acid molecules is replaced by a phosphate group. The phosphate group is hydrophilic and the fatty acid tails are hydrophobic.
How is the presence of a lipid identified?
The emulsion test:
Shake substance with ethanol for a minute
Pour solution into water
Any lipid will show up as a milky emulsion ( more milky, more noticeable the milky colour is)
What is the structure of the cell-surface membrane?
Composed of lipids, proteins and carbohydrates.
Fluid mosaic model was suggested to describe the arrangement of molecules in the membrane
Phospholipid molecule form a continuous, double layer (bi layer), the layer is ‘fluid’ as constantly moving.
Protein molecules are scattered through the layer like tiles in a mosaic.
What are the functions of the various components of the cell-surface membrane?
Controls entry and exit - some proteins in membrane allow passage of large water soluble substances that would otherwise find it difficult to cross the membrane.
Forms barrier against water soluble substances - phospholipids have hydrophilic head and hydrophobic tail, so acts as a barrier to water soluble substances.
Allows cell communication - membranes contain receptor proteins, allows cell to detect chemicals released from other cells. Chemicals signal the cell to respond in some way.
Allows cell recognition - some proteins and lipids in the plasma membrane have short carbohydrate chains attached to them (glycoproteins and glycolipids). These molecules tell white blood cells that the cell is your own.
Is fluid - phospholipids in plasma membrane make belayer fluid, cholesterol molecules fit between to reduce the phospholipids and reduce membrane fluidity (makes more rigid preventing membrane from breaking up).
What is diffusion and how does it occur?
The net movement of particles from a high concentration to a lower concentration. Continues until particles are evenly distributed throughout liquid/gas.
Diffusion is a passive process (down a conc gradient - no energy needed). Particles can diffuse across plasma membranes.
What affects the rate of diffusion?
The concentration gradient (the higher it is the faster the diffusion rate)
Thickness of exchange surface (the thinner the faster diffusion rate)
The surface area (the larger the SA the faster the rate of diffusion)
How does facilitated diffusion differ from diffusion?
Some molecules (larger/charged) can't diffuse directly through membrane - instead diffuse through proteins in membrane. Again is passive process and moves molecules down their concentration gradient. Two types - carrier proteins and protein channels. (Carrier proteins - large molecule attaches to carrier protein, protein changes shape, releases molecule on opposite side) (Protein channels - form pores in membrane for charged particles to diffuse through)
What is osmosis?
The diffusion of water molecules across a partially permeable membrane from an area of high water potential to an area of lower water potential.
If two solutions have the same water potential they’re isotonic, there’s no net movement of water.
Solutions with higher water potential compared to the inside of the cell are hypotonic - net movement of water inside the cell.
Solutions with a lower water potential than the cell are called hypertonic - net movement of water outside of the cell.
What is the water potential of pure water?
Water potential of zero. (Adding solutes to pure water lowers the water potential, so water potential is always negative)
How are triglycerides formed?
They are formed by condensation reactions, an ester bond is between two molecules which releases a molecule of water. (Process happens twice more to form a triglyceride.
