Biology Quiz Review

Cellular Membranes:

Cell membrane is semi-permeable
Only lets certain things in
H2O small molecule…starch is huge

CM is a Mosaic
Mixture of two types of molecules, lipids and proteins
Movement within the membrane of these molecules
Fluid mosaic model: cell membrane very dynamic, not static
Phospholipid bilayer
Cholesterol
Oligosaccharides proteins 1. Two layers of lipids: phospholipid bilayer is amphipathic
A. Hydrophilic head-interacting with water
B. Hydrophobic tails-minimizing contact with water.

Phospholipid Bilayer

Polar heads interact with water
Non-polar tails have no way to interact-thus face inward
Water excludes non-polar molecules
Saturated fatty acids
Warm temps-straight saturated f.a. tails reduce fluidity
Unsaturated fatty acids
Introduces kinks reducing tightness
Enhances lipid mobility in membrane at cold temps
2. Cholesterol
A. Cholesterol embeds in bilayer and controls membrane fluidity
Cold temps-can’t pack-increases spaces
High temps-patch spaces
B. Cholesterol is amphipathic: consists of polar and non polar regions
3. Oligosaccharides

Glycolipids
Carbohydrate chain associated with phospholipid
Acts as recognition site for specific chemicals
Maintains stability of membrane by attaching cells to one another forming tissues
Glycoproteins
Carbohydrate attached to a protein
Play a crucial role in cell to cell interactions
Attach to integral proteins
4. Proteins associate with cell membrane in many different ways
Transporters-move ions
Channels
carriers
Receptors-allow cells to receive signals
Enzymes-catalyze reaction
Support & structure-anchor by attaching to other proteins
A. Peripheral
Temporarily associated with lipid bilayer or integral proteins
Internally
externally
Easily separated, leaving structure in tact
B. Integral
Permanently associated
Cannot be separated without destroying the structure
Can be transmembrane

Membrane Transport
Membrane structure/chemistry impacts transport
Phospholipid bilayer is primarily hydrophobic and semi-permeable
Hydrophobic due to fatty acid tails-majority of thickness
Semi-permeable because only some things get across easily
Small, non-polar, lipid soluble molecules travel readily
Gas exhange-CO2, O2
Ions and polar molecules inhibited
Na+, H+, glucose
Transported via proteins (encoded in DNA)
Many different types of proteins, not one single gatekeeper
Na+, glucose
Passive Transport: NO energy required (ATP)
Diffusion: random movement of molecules
If gradient (difference in concentration): net movement from highest concentration to lowest
Moves directly through lipid bilayer “with” or down gradient
May reach dynamic equilibrium
Permeate phospholipid bi (simple) or protein/channel (facilitated

Passive Transport
Facilitated Diffusion: random movement of molecules; from highest to lowest concentration
Moves through channel protein or carrier
In lab-plastic tubing with laser pores, but real cells need a transporter

Movement of Molecules

Osmosis: diffusion (passive!) of water across a semi-permeable membrane from area of high concentration to area of low concentration
Can occur at the same time as diffusion of solutes
Osmosis
H2O sometimes moves faster
Looking at movement of water=osmosis
Looking at movement of solutes= diffusion
More solute=hypertonic
Less solute=hypotonic
Equal=isotonic
Water may diffuse easily between phospholipids BUT more often facilitated transport via aquaporins
Water is polar and needs help getting through the fatty acids

Impact of Osmosis on cells

Net movement of water in response to differences in solute [] between cytosol and extracellular fluid (ECF)
Moving water much faster rate than solutes
LOTS of aquaporins

Active Transport: requires energy (ATP)
Transport from Low [ ] to high [ ]
Pump
Requires proteins and energy ( ATP or ion/electrochemical gradient)
Active transport: requires energy (ATP)