AP BIO UNIT 2: cell structure and function

topic 5.

**CELL ORGANELLES, MEMBRANES, AND TRANSPORT**

**OVERVIEW:**

* **cell organelles and their functions**
* **endosymbiosis hypothesis**
* **the advantages of compartmentalization**
* **the importance of surface area to volume ratios**
* **structure of the plasma membrane**
* **what can (and cannot) cross the plasma membrane**
* **passive transport**
* **active transport**

ribosomes

function in protein synthesis and are found in both prokaryotic and eukaryotic cells.

* made of proteins and ribosomal RNA (rRNA).

endoplasmic reticulum

is a series of membrane channels in eukaryotic cells.

* **rough endoplasmic reticulum:** has ribosomes bound to its membranes and functions in protein synthesis.

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* **smooth endoplasmic reticulum:** does not contain ribosomes and functions in the synthesis of lipids and the detoxification of harmful substances in the cell.

golgi complex

is a stack of flattened membrane sacs (called cisternae).the interior of each cisternae is called the lumen and contains the enzymes necessary for the golgi complex to function. the golgi complex controls the modification and packaging pf proteins for transport.

lysosomes

are membrane-bound sacs, containing hydrolytic enzymes, that function in variety of cell processes. lysosomes can help digest macromolecules, break down worn-out cell parts, function in apoptosis, or destroy bacteria and viruses that have entered the cell.

vacuole

a membrane-bound sac in eukaryotic cells. vacuoles function in food or water storage, water regulation in a cell, or waste storage until the waste can be eliminated from the cell.

mitochondria

produces energy for the cell. the mitochondria have double-membranes, with a smooth outer membrane and a folded inner membrane. mitochondria also contain their own mitochondrial DNA (mtDNA).

* **matrix:** an enzyme-containing fluid located in the center of the mitochondria.

chloroplasts

are found in plants and algae that carry out photosynthesis. like mitochondria, chloroplasts also have a double-membrane structure.

* **thylakoids:** a smooth outer membrane and pancake-shaped membranous sacs.
* **grana:** stacked thylakoids.


* **stoma:** the liquid inside the chloroplast that surrounds the grana.

centrosome

is found in animal cells and helps the microtubules assemble into the spindle fibers needed in cell division.

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**fun fact:** defects in centrosome function have been associated with dysregulation of the cell cycle in some cancers.

amyloplasts

plant cells may contain amyloplasts. excess glucose produced by photosynthesis is stored as starch molecules in the amyloplasts. amyloplasts are frequently found in the root and tubers of starchy vegetable, such as potatoes!

peroxisome

helps oxidize molecules and break down toxins in the cell.

nucleolus

it is not a membrane-bound organelle; that term refers to the region in the nucleus where ribosomes are assembled.

cytoskeleton

are fibers that help give cells their shape and can be used to move items in the cell.

endosymbiosis hypothesis

states that membrane-bound organelles, such as mitochondria and chloroplasts, were once free-living prokaryotes that were absorbed into other larger prokaryotes.

surface area to volume ratios

as the radius *increases*, the surface area to volume ratio will *decrease*. *(the amount of surface are available per unit volume for exchange of materials gets smaller and smaller.)*

plasma membrane

are selectively permeable, which means that some materials can cross the membrane while other materials cannot.

bilayer

the plasma membrane is made of a bilayer of phospholipids. phospholipids have a hydrophilic (or polar) phosphate “head” and two hydrophobic (or nonpolar) “tails.”

glycoproteins & glycolipids

membrane, modified proteins that are embedded in the phospholipid bilayer. these components of the membrane are mobile and can flow throughout the surface of the plasma membrane, allowing the cell to adapt to changing environmental conditions.

**proteins in the plasma membrane have many functions:**

* transporting materials
* participating in cell signaling processes
* anchoring the cell to its surroundings
* catalyzing chemical reactions

aquaporins

are specialized proteins that allow for most of the passage of water in and out of the cell.

cell wall

are composed of large carbohydrates (cellulose in plants, glucans in fungi, and peptidoglycan in prokaryotes). the cell walls provide rigidity to the cell and are an additional barrier to substances entering or exiting the cell.

*plants, fungi, and prokaryotic cells are surrounded by a cell wall.*

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passive transport

the movement of molecules from areas of higher concentration to areas of lower concentration.

*molecules move “down” their concentration gradient.*

diffusion

the movement of molecules down their concentration gradient without the input of energy.

facilitated diffusion

the process of passive transport that uses a membrane protein.

*ex.) the specialized membrane proteins called aquaporins that allow large quantities of water to move down their concentration gradient.*

channel proteins

can allow the passive transport of ions, such as Ca^+2 or Cl^-1, down their concentration gradients.

active transport

moves molecules from areas of low concentration to areas of high concentration.

*ex.) Na^+/k^+ pump. this membrane protein requires the input of ATP to pump Na^+ ions from their lower concentration outside the cell to an area with higher concentrations of k^+ ions inside the cell.*

***3 Na^+ pumped out of the cell, 2 k^+ions are pumped into the cell***

this movement of molecules “against” their gradient requires the input of energy.

endocytosis

is used bu the cell to take in water and macromolecules by enfolding them into vesicles formed from the plasma membrane.

exocytosis

vesicles (that contain molecules to be expelled) are fused with the plasma membrane, which then allows these molecules to be expelled from the cell. this movement of large molecules into or out of the cell requires the input of energy.

topic 6.

**MOVEMENT OF WATER IN CELLS**

**OVERVIEW:**

* **water potential**
* **osmolarity and its regulation**

hypotonic solution

has a lower concentration of solute.

hypertonic solution

has a higher concentration of solute.

isotonic solution

has the same concentration of solute as that of another solution.

water potential

can be defined as the potential energy of water in a solution, or the ability of water to do work.

osmolarity

the total concentration of solutes in a solution.