UNIT 2 AP BIO

2.1 Cell Structure and Function
Ribosomes - cellular structures made of rRNA and proteins. PRODUCES PROTEINS BASED ON MRNA SEQUENCES. IN ALL CELLS.

Endomembrane System: Modifies packages and transports cellular products in vesicles.

-ER: Helps maintain cell shape and ship cellular
Smooth ER - detoxifies cells, synthesizes lipids
Rough ER - embedded with ribosomes, separates cell parts, helps with protein synthesis

-Golgi Complex
flattened membrane sac that folds and modifies newly made celullar products , packages proteins in vesicles for shipping. SHIPPING CENTER

-Mitochondria - Synthesizes ATP

-Lysosomes
Breaks down waste, aids apoptosis (which is telling cell to kill itself)

-Vacuoles
Sac that stores material. (Big one in plant cells. maintains turgor pressure and stores nutrients and water.

Chloroplast - found in plants and algae. Location in photosynthesis. Thylakoid

2.2 Cell Size
All living things must:
obtain nutrients
eliminate wastes
and DISSIPATE HEAT

More surface area = more interaction with environment

More volume = greater nutrient requirement and waste/heat elimination

More surface area per unit of volume THE BETTER because cells that have higher surface area to volume ratio have more EFFICIENT exchange with their environment.

SA of a cube = 6s^2

V of a cube = S^3

SA of sphere = 4pir^2

V of a sphere = 4/3 pi (4)^3

INCREASED VOLUME means DECREASED SA/V RATIO

So. THE LARGER A CELL IS, THE LOWER ITS SA/V RATIO IS which means its less efficient at exchanging materials with its environment.
REQUIRES MORE RESOURCES THAN A SMALLER CELL.

Rate of heat exchange DECREASES in larger cells as well.
—> Doesn’t dissipate heat as well
Smaller cells EXHANGE proportionally more heat.

Smaller organisms have higher metabolic raters per unit of body mass than larger organisms.
Large cells have specialized structures to increase surface area for material exchange.
Folded, extending structures.
—> Membrane folds INCREASE surface area without increasing VOLUME.

2.3 Plasma Membrane
Plasma membrane is the part of the cell that interacts with external environment.
—> Controls what comes in/out and receives cellular messages.

Phospholipid bilayer
—> embedded with proteins, steroids, glycoproteins, and glycolipids. FLUID MOSAIC MODEL.
PROTEINS AND LIPIDS CAN MOVE AROUND THE SURFACE OF THE CELL.
Its like bubble. can move around.

Hydrophilic heads. Hydrophobic tails.

Sterol controls membrane fluidity

2.4 Membrane Permeability
Membranes are SELECTIVELY permeable because of phospholipids and how they are arranged.

Small nonpolar molecules can freely pass through bilayer.

Large polar molescules like IONS pass through CHANNELS and transport proteins

Transport Protein:
Every protein that helps go something go through.

Channel Protein:
Passive Transport. Tunnel shapped. For large polar molecules and ions

The nonpolar tails is what BLOCKS charged molecules (ions) and polar molecules from passing.

Small, polar uncharged molecules can pass through in SMALL AMOUNTS. (they struggle to get through but are small enough)

Cell walls provide both STRUCTURE and a BARRIER for some substances. Also prevents cell from bursting —> osmosis

2.5 Membrane Transport
Cells form CONCENTRATION GRADIENTS. More of something on either inside or outside of cell.

Diffusion: Tendency of particles to move from an area of high conc to low conc.

Passive Transport is when there is a net movement of molecules from a high conc to a low conc region.
HIGH —> LOW CONC

NO ENERGY!!

Active Transport is the movement of particles across a membrane using ENERGY.
Use to move molecules that cannot normally cross or AGAINST a conc gradient.

LOW —> HIGH CONC

Endocytosis - type of active transport where large molecules and particles are taken in by the membrane folding in and forming a vesicle

Exocytosis - type of active transport where vesicles release materials from the cell by fusing with the plasma membrane

2.6 Facilitated Diffusion

Facilitated diffusion - passive transport that requires a channel protein
K+ and Na+ require channel proteins, as well as large molecules

Membranes can become polarize based on movement of ions across membranes.

Aquaporin channel proteins that transport large quantities of water.

2.7 Tonicity and Osmoregulation
Cells need to balance how much water they absorb and lose to their external environment
—> water and other molecules are constantly moving across membrane

Diffusion of water is called OSMOSIS
Water moves from a HIGH WATER POTENTIAL TO LOW WATER POTENTIAL

Water moves from HYPO to HYPER
Water moves from low to high solutes

Water moves to where theres MORE SOLUTES cuz it wants to spread it around

Cells will have a net loss of water when in a HYPERTONIC ENVIRONMENT

Cells have a net GAIN of water when in a HYPOTONIC environment

Cells have NO net gain of water when in an ISOTONIC environment.

Hypotonic is GOOD IN PLANT CELLS - TURGID

Water moves from a high water potential to low water potential.

PURE WATER in an OPEN CONTAINER has a water potential of 0 since it has no solute and no pressure.

Solute potential (osmotic potential)
Solute Potential = -iCRT
i (ionization. 1 IF SUGAR. 2 IF SALT)
C = solute concentration (M)
R = pressure constant (0.0831)
T = temperature (K)

2.8 Mechanisms of Transport
Some cells require their membrane to be polarized to carry out their function
-nerve and muscle cells

A difference in charge across a membrane is called MEMBRANE POTENTIA.

Membrane potentials are established through the distribution of IONS across the MEMBRANE

CUZ ions cant pass through the bilayer, electrochemical gradients are established through active transport. (WORK DONE TO MAKE SURE IT STAYS LIKE THAT)

cells use electrochemical gradients to accomplish tasks

SODIUM-POTASSIUM PUMP —> pumps 3 NA+ and brings in 2 K+
Maintain resting membrane potential (-70mV)

Potassium on inside, Sodium outside

2.9 + 2.10 Cell Compartmentalization + Origins
Membranes separate cells internal environments from their external environments

Prokaryotic cells DO NOT have internal membranes that separate processes out.
NOT COMPARTMENTALIZED.

Eukaryotic cells have internal membranes that keep cellular processes separate.
Comparmentalized!

INTERNAL MEMBRANES MAKE CELLULAR PROCESSES MORE EFFICIENT
—> DECREASES COMPETING INTERACTIONS
—> INCREASE SURFACE AREA FOR REACTIONS TO OCCUR

Chloroplasts and Mitochondria's have 2 membranes.

Big Prokaryote swallowed (PHAGOCYTOSIS) Small prokaryote that was good at aerobic respiration
Small prokaryote provides ATP and big provides stable environment.

Big prokaryote swallowed cyanobacteria.
Cyanobacteria does photosynthesis and big proka provides a stable environment.

Evolved into mitochondria and chloroplasts through endosymbiosis. Resulting organisms evolved into eukaryotes.