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Prokaryotic vs. Eukaryotic Cells
• Why would it benefit a cell have to membrane-bound organelles?– Different “compartments” for specific reactions– Allows incompatible reactions to occur at the
same time
Limits to Cell Size
• Surface Area to Volume Ratio– As a cell increases in size, the volume increases
faster than the surface area (SA:V ratio also becomes smaller)
• Why is this significant?– If ratio is too small flow of nutrients (in) &
flow of wastes (out) aren’t fast enough to keep up with metabolic activities of the cell
– Larger cells also have more trouble moving materials through cytoplasm
Protein Traffic in a Cell
• Secretory Protein = protein that is going to leave the cell
• Pathway:– Ribosome Rough ER
vesicle Golgi Apparatus vesicle Plasma (Cell) Membrane
Movement within a cell
• Involves specialized proteins “walking” across microtubules or other proteins
• Requires ATP as an energy source
• Examples include:– Vesicle movement within a cell– Cilia and flagella movement– Muscle contraction
Membrane Properties
• fluid = phospholipids move a lot laterally but not much flip-flopping
• Membranes need to stay fluid to function properly. Fluidity of the membrane can be adjusted by– Temperature– Amount of cholesterol
Fluidity of the membrane• Effect of temperature
– the higher the temperature, the more fluid the membrane will be
– At a certain temperature, each membrane will become more solidified (less fluid)• This depends on the types of fatty acids in the
membrane (saturated or unsaturated)
Fluidity of the membrane
• Effect of cholesterol– At medium temperatures
- reduces fluidity
- prevents lateral movement of phospholipids– At low temperatures
- prevents solidification -- lowers the temperature at which a membrane solidifies
- Prevents phospholipids from being packed closely
Membrane Properties• Mosaic = proteins, carbohydrates
embedded in membrane• Integral/Transmembrane proteins
often have both hydrophilic and hydrophobic regions.
• Membrane proteins have many different functions.
• Carbohydrates are often involved in cell-cell recognition.
hydrophobichydrophilic
Why must a plasma membrane be selectively permeable?
• To control what enters the cell
• Maintain a certain environment within the cell (Dynamic Homeostasis– things constantly moving in and out to maintain certain concentrations, conditions)
Passive Transport• Require NO energy
• Small, nonpolar molecules, O2, CO2
• Moves with the concentration gradient– From high to low concentrations
• Osmosis (diffusion of water)– occurs across the membrane and
through aquaporin (channel proteins)
Passive Transport
• Facilitated Diffusion– Channel Proteins– Carrier Proteins
• What would you expect the amino acid composition to be on the channel portion of the protein?– Polar and hydrophilic (so
that polar/hydrophilic molecules can get across)
Active Transport
• Requires energy• Ions, larger molecules• Moves against the
gradient – From low to high
concentrations
• Ex. Sodium-Potassium pump– Requires ATP to work
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