unit 2 biology

12th grade ap biology

cells

- basic structural and functional unit of every organism
- bound by a plasma membrane
- contain cytosol (like cytoplasm except it's liquid)
- contain chromosomes
- contain ribosomes
- evolutionary/ancestry connection
- prokaryotes and eukaryotes

prokaryotes

- domains bacteria and archaea
- DNA is in the nucleoid region
- generally smaller in size than eukaryotes

eukaryotes

- protists, fungi, animal, plants
- DNA is in the nucleus
- contain membrane bound organelles

organelles

- membrane bound structures in eukaryotes
- endomembrane organelles
- energy organelles

endomembrane organelles

- has own membrane
- nuclear envelope/nucleus, er, golgi, lysosome, vesicles/vacuoles, plasma membrane

energy organelles

- ATP producers
- mitochondria, chloroplasts

compartmentalization

- allows for different metabolic reactions to occur in different locations
- increases surface area for reactions to occur (large surface area to volume ratio = more efficient)
- prevents interfering reactions from occurring in the same location

unique plant components

- chloroplasts
- central vacuole
- cell wall
- plasmodesmata

unique animal components

- lysosomes
- centrosomes
- flagella

nucleus

- contains chromosomes (genetic information)
- enclosed by the nuclear envelope: double membrane
- has pores which regulate entrry and exit of materials from the cell
- contains a nucleolus

nucleolus

- ribosomal RNA is synthesized
- makes ribosomes

ribosomes

- comprised of rRNA and protein
- make proteins
- found in cytosol: makes proteins that stay in cell ("free ribosomes")
- found in rough er: makes proteins that exits cell

endoplasmic reticulum

- network of membranous sacs and tubes
- synthesizes membranes
- compartmentalize the cell to keep proteins formed in the rough er separate from those of the free ribosomes
- rough and smooth er

rough er

contains ribosomes bound to the er membrane

smooth er

- contains no ribosomes
- synthesizes lipids
- metabolizes carbohydrates
- detoxifies the cell

golgi complex/apparatus

- cisternae: flattened membranous sacs
- separate the sacs from the cytosol
- each cisternae is not connected
- has directionality: cis and trans face
- function: receives materials from er, modifies, sorts, add molecular tags, and packages materials into new transport vesicles that exit the membrane through exocytosis

cis face

receives vesicles from the er

trans face

sends vesicles back out into the cytosol to other locations or to the plasma membrane for secretion

lysosomes

- membranous sac with hydrolytic enzymes
- hydrolyzes macromolecules in animal cells
- autophagy: can recycle their own cells organix materials (allows the cell to renew iteself)

peroxisomes

- similar to lysosomes
- membrane bound metabolic compartment
- catalyze reactions that produce H₂O₂
- enzyme then break down H₂O₂ to water

vacuoles

- large vesicles that stem from the er and golgi
- selective in transport
- types: food, contractile, and central

food vacuole

form via phagocytosis (cell eating) and then are digested by lysosomes

contractile vacuole

maintain water levels in cells

central vacuole

- found in plants
- contain inorganic ions and water
- important for turgor pressure

endosymbiont theory

- explains the similarities mitochondria and chloroplasts have to a prokaryote
- an early eukaryotic cell engulfed a prokaryotic cell
- prokaryotic cell became an endosymbiont (cell that lives in another cell)
- became one functional organism
- evidence: double membrane, ribosomes, circular DNA, capable of functioning on their own

mitochondria

- site of cellular respiration
- structure: outer membrane is smooth, inner membrane has folds (cristae)
- intermembrane: space between inner and outer membrane
- mitochondrial matrix: enclosed by inner membrane; location for krebs cycle; contains enzymes that catalyze cellular respiration and produce ATP, mitochondrial DNA, and ribosomes
- number of mitochondria correlates with metabolic activity (ex: high metabolic activity = more mitochondria)

chloroplast

- specialized organelles in photosynthetic organisms
- site of photosynthesis
- contains chlorophyll (green pigment)
- double membrane: thylakoids and stroma

thylakoids

- membranous sacs that can organize into stacks called grana
- light dependent reactions occur in grana

stroma

- fluid around thylakoids
- location for calvin cycle
- contains chloroplast DNA, ribosomes, and enzymes

cytoskeleton

- network of fibers throughout the cytoplasm
- gives structural support and mechanical support
- allow for movement of vesicles and organelles and/or the whole cell (movement occurs when the cytoskeleton interacts with motor proteins)
- types of fiber: microtubules, microfilaments, intermediate filaments

microtubules

- hollow, rod-like structures made of protein tubulin
- grow from the centrosome
- function: structural support for the movement of organelles that are interacting with motor proteins, assist in the separation of chromosomes during cell division, cell motility (cilia, flagella)

microfilaments

- thin, solid rods made of the protein actin
- functions: maintain cell shape, assist in muscle contraction and cell motility (actin works with a protein called myosin to cause a contraction), division of animal cells (contractile ring of the cleavage furrow)

intermediate filaments

- fibrous proteins made up of varying subunits
- permanent structural elements of cells
- functions: maintain cell shape, anchor nucleus and organelles, form the nuclear lamina (lines the nuclear envelope)

cell size

- cellular metabolism depends on cell size
- cellular waste must leave
- dissipate thermal energy
- nutrients and other resources/chemical materials must enter
- at a certain size, it begins to be too difficult for a cell to control what enters and exits the plasma membrane

surface area to volume ratio

- size of cell will dictate function
- cells need a high surface area to volume ratio to optimize the exchange of material through the plasma membrane
- cells tend to be small

small cells

- high SA:V ratio
- optimizes exchange of materials at the plasma membrane

larger cells

- lower SA:V ratio
- lose efficiency exchanging materials
- cellular demand for resources increases
- rate of heat exchange decreases

plasma membrane

- separates internal cell environment from external environment
- comprised primarily of phospholipids, which are amphiphatic
- forms a bilayer

amphiphatic

has both hydrophobic and hydrophilic regions

selective permeability

ability of membranes to regulate the substances that enter and exit

easy passage through selective permeability

- small, nonpolar, hydrophobic molecules
- ex: hydrocarbons, CO2, O2, N2

difficult/protein assisted passage through selective permeability

- large, polar, hydrophilic molecules, ions
- ex: sugars, H2O, Na+, amino acids

fluid mosaic model

describes the structure of cell membranes

fluid

- membrane is held together by weak hydrophobic interactions and can therefore move and shift
- temperature affects fluidity
- unsaturated hydrocarbon tails help maintain fluidity at low temps (kinked tails prevent tight packing of phospholipids)
- cholesterol helps maintain fluidity at high and low temps

high temp (cholesterol)

reduces movement

low temp (cholesterol)

reduces tight packing of phospholipids

moasic

comprised of many macromolecules

membrane proteins

integral and peripheral

integral proteins

- embedded into lipid bilayer
- amphiphatic
- transmembrane proteins

peripheral proteins

- not embedded into the lipid bilayer
- loosely bonded to the surface

membrane carbohydrates

- important for cell-to-cell recognition
- glycolipids and glycoproteins

glycolipids

carbohydrates bonded to lipids

glycoproteins

- carbohydrates bonded to proteins
- most abundant

cell wall

- plants have a cell wall that cover plasma membranes
- extracellular structure provides shape/structure, protection, and regulation of water intake
- composed of cellulose
- thicker than plasma membranes
- contain plasmodesmata

plasmodesmata

hole-like structures in the cell filled with cytosol that connects adjacent cells

passive transport

- does not require energy from the cell
- solute moves with it concentration gradient (HIGH -> LOW)
- involved in the import of materials and export of waste
- diffusion, osmosis, facilitated diffusion

diffusion

- spontaneous process resulting from the constant motion of molecules
- molecules diffuse directly across the membrane
- different rates of diffusion for different molecules (affected by particle size, amount, and extracellular conditions)
- membrane is still selectively permeable

osmosis

- diffusion of water down its concentration gradient across a selectively permeable membrane
- areas of low solute concentration -> areas of high solute concentration

facilitated diffusion

- diffusion of molecules through the membrane via transport protein
- increases rate of diffusion for small ions, water, and carbohydrates
- transport proteins: channel and carrier

channel protein

- provides a hydrophilic channel for molecules and ions to pass
- many are gated channels which only allow passage when there is a stimulus
- specific channel protein: aquaphorins

aquaphorins

- specific channel protein for water
- water can still go in without it but it makes it easier

carrier protein

undergo conformational changes for substances to pass

active transport

- requires energy
- solute moves against its concentration gradient (LOW -> HIGH)
- pumps, cotransport, exocytosis, endocytosis

ATP

- energy source used by cells
- can transfer the terminal phosphate group to the transport protein, which changes the shape of the transport to better move a substance

pumps

- maintain membrane potential (pump protons out of the cell)
- ex: electrogenic, sodium potassium, proton

membrane potential

- unequal concentrations of ions across the membrane results in an electrical charge (electrochemical gradient)
- cytoplasm is relatively negative in comparison to the extracellular fluid
- energy is stored in electrochemical gradients

electrogenic pumps

proteins that generate voltage across membranes, which can be used later as an energy source for cellular processes

sodium potassium pumps

- animal cells will regulate their relative concentrations of Na+ and K+
- 3 Na+ get pumped out and 2 K+ get pumped into the cell
- results in a +1 net charge to the extracellular fluid

proton pump

- integral membrane protein that builds up a proton gradient across the membrane
- used by plants, fungi, and bacteria
- pumps H+ out of the cell to maintain pH

cotransport

- the coupling of a favorable movement of one substance with an unfavorable movement of another substance
- uses the energy stored in electrochemical gradients (generated by pumps) to move substances against their concentration gradient
- plants use cotransport for sugars and amino acids
- favorable movement = downhill diffusion
- unfavorable movement = uphill transport

exocytosis

- the secretion of molecules via vesicles that fuse to the plasma membrane
- vesicles can fuse to the membrane by forming a bilayer
- once fused, the contents of the vesicles are released to the extracellular fluid
- transport of large molecules
- ex: nerve cells releasing neurotransmitters

endocytosis

- the uptake of molecules from vesicles fused from the plasma membrane
- transport of large molecules
- phagocytosis, pinocytosis, receptor mediated endocytosis

phagocytosis

- when a cell engulfs particles to be later digested by lysosomes (brings in solids)
- cell surrounds particle with pseudopodia
- packages particles into a food vacuole
- food vacuole fuses with a lysosome to be digested
- ex: white blood cell engulfing bacteria

pinocytosis

- nonspecific uptake of extracellular fluid containing dissolved molecules
- cell takes in dissolved molecules in a protein coated vesicle
- protein coat helps to mediate the transport of molecules

receptor mediated endocytosis

- specific uptake of molecules via solute binding to receptors on the plasma membrane
- allows the cell to take up large quantities of a specific substance
- when solute bind to the receptors, they cluster in a coated vesicle to be taken into the cell

tonicity

- the ability of an extracellular solution to cause a cell to gain or lose water
- depends on the concentration of solutes that cannot pass through the cell membrane
- cells can be hypertonic, hypotonic, or isotonic (ideal)

osmoregulation

- cells must be able to regulate their solute concentrations and maintain water balance
- animal cells will react differently than cells with cell wall (plants, fungi, protists)

isotonic solutions

- cells immersed in this solution have no net movement of water
- the concentration of nonpenetrating solutes inside the cell is equal to that outside the cell
- water diffuses into the cell at the same rate water moves out of the cell

hypertonic solutions

- high solute solution
- cells immersed in this solution lose water to their extracellular surroundings
- the concentration of nonpenetrating solutes is higher outside the cell
- water flows to the extracellular fluid
- cell shrivels and dies
- plasmolysis: vacuole shrinks and plasma membrane pulls away from the cell wall

hypotonic solutions

- low solute solution
- cells immersed in this solution gain water
- the concentration of nonpenetrating solutes is lower outside the cell
- cell gains water
- animal cells swell and lyse
- plant cells work optimally (maintain turgor pressure)

water potential

- a physical property that predicts the direction water will flow
- includes the effects of solute concentration and physical pressure
- water potential: ψ = ψs + ψp
- solute potential: ψs = -iCRT

ionization

- sucrose: 1
- NaCl: 2

direction of water flow (water potential)

high to low

direction of water flow (solute)

low (lots of water) to high

direction of water flow (pressure)

high to low