AP Biology Unit 2 - Cell Structure and Function

surface to area volume ratio

this ratio must be kept large so that there is plenty space to do these exchanges

* smaller cells have a higher ratio, allowing for ore efficient exchange of materials with their surroundings through specialized exchange surfaces.
* greater volume, less ratio, the exchange of materials becomes less efficient

nucleoid

the genetic material in a prokaryote is continuous circular DNA molecule that is found free in the cell.

cell wall

composed of peptidoglycans the surrounds a lipid layer called the plasma membrane.

* made of cellulose
* support for the cell
* plant cells, protists, fungi, and bacteria
* important for protection against osmotic changes, made of chitin (in fungi), modified polysaccharide
* possesses chloroplasts which have a double outer membrane, light capturing pigment

flagella

projections used for motility

plasma membrane

outer envelope, double-layered structure made up of mostly phospholipids and proteins.

* hydrophobic fatty acid tails face inward
* hydrophilic phosphate heads face outward
* phospholipid bilayer
* regulates the movements of substances in and out of the cell
* semipermeable membrane
* peripheral proteins

phospholipid bilayer

two lipid layers are forming a hydrophobic sandwich

semipermeable

only certain substances, small hydrophobic molecules O2 and CO2 pass through its unaided

* any large thing or hydrophilic can pass through the membrane only via special tunnels

peripheral proteins

located in the inner or outer surface of the membrane, amphipathic

transmembrane proteins

integral proteins which extend all the way through the membrane

fluid-mosaic model

arrangement of phospholipids and proteins.

* each layer of phospholipids is flexible
* mosaic as it is peppered with different proteins and carbohydrate chains
* phospholipids in one side should never flip-flop to the other side of the membrane (would require their polar heads to pass through the hydrophobic area)

some plasma membrane proteins

* membrane proteins (adhesion proteins), form junctions between adjacent cells
* receptor proteins, serve as docking sites for arrivals at the cell
* transport proteins, form pumps that use ATP to actively transport solutes across the membrane
* channel proteins, form channels that selectively allow the passage of certain ions or molecules
* cell surface makers, exposed on the extracellular surface and play a role in cell recognition and adhesion

carbohydrate side chains

attached to the surface of some proteins, found only on the outer surface of the plasma membrane

* cholesterol molecules are also found in the phospholipid bilayer because they help stabilize membrane fluidity in animal cells

nucleus

usually the largest organelle in the cell, directs what goes on in the cell, is responsible for the cell’s ability to reproduce, home for DNA

* nucleolus

chromosomes

large structure sin which DNA is organized into

nucleolus

where rRNA is made and ribosomes are assembled

ribosomes

sites of protein synthesis, manufacture all the proteins required by the cell or secreted by the cell.

* round structures with large subunit and small subunit.
* ribosomal RNA and proteins
* free floating in the cell or attached to the ER

endoplasmic reticulum

ER, continuous channel that extends into many regions of the cytoplasm, provides mechanical support while aiding in intracellular transport

* rough er (rer): attached to the nucleus and studded with ribosome, compartmentalizes the cell.
* proteins generated in the rough ER are trafficked to or across the plasma membrane, or used to build Golgi bodes, lysosomes, or the ER.
* smooth er (ser): lacks ribosome, makes lipids, hormones, and steroids, breaks down toxic chemicals.

golgi complex

participate in the processing of proteins, once the ribosomes on the rough ER have completed synthesizing proteins the Golgi complex modify, process, and sorts the products.

* packaging and distribution centers for materials destined to be sent out of the cell
* vesicles

vesicles

little sacs which carry products to the plasma membrane

mitochondria

the powerhouse of the cell, the most common energy molecule in the cell is ATP (adenosine triphosphate)

* cristae: the inner mitochondria membrane forms these fold and separates the innermost area (matrix) from the inter membrane space
* the outer membrane separates the intermembrane space from the cytoplasm
* production of ATP is done on the cristae

lysosomes

small, membrane-enclosed structures, carry digestive enzymes, which they used to break down old, worn-out organelles, debris, or large ingested particles

* contain hydrolytic enzymes that function at acidic pH, enclosed inside the lumen of the lysosome
* made when vesicles containing specific enzymes from the trans golgi fuse with vesicles made during endocytosis
* are essential during programmed cell death (apoptosis)

centrioles

small, paired, cylindrical structures that are often found within microtubule organizing (MTOCs)

* most active during cellular division
* when a cell is ready to divide, centrioles produce microtoblues, which pull the replicated chromosomes apart and move them to opposite ends of the cell
* not found in plant cells

vacuoles

fluid-filled scar that store water, food, waste, salts, or pigments

* plant cells

perixomes

organelles that detoxify various substances, producing hydrogen peroxide H2O2 as a byproduct

* contain enzymes that break down hydrogen peroxide into oxygen and water

cytoskeleton

shape of a cell is determined by a network of protein fibers

* microtubules, made up of the protein tubulin, participate in cellular division and movement
* centirioles, cilia, and flagella
* microfilaments, important for movement, thin godlike structures composed of the protein actin
* actin monomers are joined together and broken apart as needed to allow microfilaments to grow and shrink
* assist during cytokinesis, muscle contraction, and formation of pseudopodia extensions

cilia and flagella

threadlike structures best known for their locomotive properties in single-celled organism

* euglena: uses its whiplike flagellum
* paramecium: covered in cilia

central vacuole

contains the cell sap, most of the cytoplasm within a plant cell is usually taken up by this organelle.

* a full vacuole is a sign that it is not dehydrated and has a healthy amount of turgor pressure

trafic across membranes (transportation)

the ability of molecules to move across the cell membrane depends on two things:

* the semipermeability of the plasma membrane
* the size and charge of particles that want to get through
* as it is composed primarily of phospholipids, small, lipid-soluble substances N2, O2, and CO2 cross the membrane without any resistance
* only hydrophobic things can pass that central zone
* if a substance if hydrophilic, the bilayer won’t let it pass without assistance, called facilitated transport

facilitated transport

a type of passive transport that uses specialized proteins, such as channel proteins and carrier proteins, to help molecules move across a cell membrane

* depends upon a number of proteins that act as tunnels through the membrane
* aquaporins, water specific channels
* although water is polar, there are sufficient aquaporins for water to traverse the membrane whenever it wishes
* glucose and ions such as Na+ and K+ are also transported across the plasma membrane via membrane proteins
* membranes may become polarized as these ions move across

difussion

if there is a high concentration of something in one area, it will move to spread out and diffuse into an area with lower concentration, even if it means entering or exiting the cell (moves down in the concentration gradient)

* simple diffusion: when the molecule that is diffusing is hydrophobic, small nonpolar molecule can just drift right through the membrane without trouble
* facilitated diffusion: when the diffusion requieres the help of a channel protein
* passive transport: anytime that a substance is moving by diffusion, there is no outside energy required to power the movement
* membrane is permeable to solute

osmosis

when water is diffusing, water always wants to move from an area where it is most concentrated to an area where it is least concentrated

* water usually exists as a solution, liquid solvent dissolves solute particles
* water wants to go from where there ice less solute to where there is more solute
* solute concentrations are the same on both sides of the membrane
* membrane is not permeable to solution
* the cell membrane can shrink away from the wall (plasmolysis) if it loses water and can expand and squeeze tightly against the cell wall if it takes in water
* tonicity, describes osmotic gradients
* isotonic (isosmotic), the solute concentration is the same inside and outside the cell
* hypertonic, more total dissolved solutes than the cell
* hypotonic, less
* can cause cells to explode and can overcome gravity

water potential

the measure of potential energy sin water and describes the eagerness of water to flow from an area of high water potential to an area of low water potential

* affected by two factors: pressure potential and solute potential
* solute osmotic potential
* adding a solute lowers the water potential of a solution, causing water to be less likely to leave this solution and more likely to flow into it
* added solution makes it more concentrated and water is now unlikely to diffuse away
* the more solute molecules present, the more negative the solute potential is

active transport

substance wants to move in the opposite direction from a region of lower concentration to a region of higher concentraron, a transport proteins can help usher the substance across the plasma membrane, movement against the natural flow is called active transport

* the protein gets this energy through ATP
* sodium-potassium pump
* primary active transport, ATP is directly utilized to transport something
* secondary active transport, something is actively transported using the energy captured from the movement of another substance flowing down its concentration gradient

endocytosis

when the particles that want to enter a cell are just too large, thece’ll uses a portion of the membrane to engulf the substance, forms either a vacuole or a vesicle.

* pinocytosis, the cell ingests liquids
* phagocytosis, the cell takes in solids
* receptor-mediated endocytosis, cell surface receptors that work in tandem with endocytic pits that are lined with a protein called clathrin, when a particle binds to one of this receptors, the ligand is brought into thece’ll by the folding in of the cell membrane

bulk flow

one-way movement of fluids brought about by pressure

dialysis

diffusion of solutes across a selectively permeable membrane

* special membranes that have holes of a certain size within them can be used to sort substances by using the process of diffusion

exocytosis

large particles are transported out of the cell, a cell ejects waste products or specific secretion products by the fusion of a vesicle with the plasma membrane, which then expels the contents into extracellular space