nucleus - largest organelle in a eukaryote 

• 1st descried by Robert Brown in 1831
• surrounded by cytoplasmic filaments in some cells
• some cells have multiple nuclei
• erythrocytes - mammalian red blood cells; lose nuclei as they mature
• nucleolus - dark region where synthesis of ribosomal RNA takes place

nuclear envelope - 2 phospholipid bilayers surrounding the nucleus 

• outer membrane continuous w/ the endoplasmic reticulum
• nuclear pores - shallow depressions scattered over the surface; contain proteins that determine what substances can enter or leave the nucleus
• 2 types of molecules allowed to pass through nuclear envelope:
  • proteins moving into the nucleus for nuclear structures, catalyze reactions
  • RNA, protein-RNA complexes made in the nucleus

chromosomes - extended into strands called chromatin except when the cell divides 

• histones - packaging proteins which DNA wraps around
• nucleosomes - clusters of histones
• more extended form allows RNA copies to be made from the DNA
• condenses into tight rods when the cell divides

endomembrane system - divides the cell into compartments 

• endoplasmic reticulum - largest internal membrane; made of lipid bilayer embedded w/ proteins
  • cisternal space - inner region of ER
  • cytosol - exterior region of ER
  • rough endoplasmic reticulum - surface studded w/ ribosomes; used for protein synthesis
  • proteins made here eventually sent out from the cell
  • signal sequences - special amino acid sequences found on proteins about to be exported
  • proteins go from the cisternal space to the Golgi apparatus to the plasma membrane
  • smooth endoplasmic reticulum - organizes internal activities w/ enzymes
  • abundant in cells that carry out lots of lipid synthesis
  • endocytosis - process where plasma membrane forms vesicles by budding inward; some move in to the cytoplasm and fuse w/ smooth ER
• Golgi apparatus - named for Camillo Golgi, 19th century Italian physician
  • abundant in glandular cells (manufacture/secrete substances)
  • contains 1 to a few hundred Golgi bodies
  • cis face - front, receiving end; located near the ER
  • trans face - back, discharging end; substances sent into secretory vesicles
  • modifies proteins/lipids traveling through it by adding sugar chains (making glycoproteins/glycolipids)
  • cisternae - stacked membrane folds where newly formed glycoproteins/glycolipids gather; periodically pinches off small vesicles containing the substances
• lysosomes - digestive vesicles; break down old organelles, recycle component molecules
  • function best in acidic environments
  • keeps a low internal pH by pumping protons inside
  • primary lysosome - does not maintain an acidic internal pH
  • secondary lysosome - forms when primary lysosome fuses w/ food vesicle to activate hydrolytic enzymes
  • phagocytosis - engulfing foreign cells
• microbodies - enzyme-bearing vesicles
  • found in all eukarytoes
  • glyoxysome - plant microbody containing enzymes that convert fats into carbohydrates
  • peroxisome - contains enzymes that catalyze removal of electons/hydrogen; would short-circuit cell metabolism if oxidative enzymes weren't isolated

ribosomes - where protein synthesis takes place  

• large RNA-protein complexes outside the nucleus
• consist of 2 subunits that only join when attached to messenger RNA (mRNA)
• proteins that function in the cytoplasm are formed by free ribosomes not found in the ER
• nucleolus - where ribosomes are assembled in the nucleus

mitochondria - bacteria-sized organelles that produce energy 

• bounded by smooth outer membrane and cristae (inner/folded membrane)
• matrix - area within the inner membrane
• intermembrane space - area between inner/outer membranes
• proteins on the surface of the inner membrane carry out oxidative metabolism
• contains DNA that codes for proteins needed for oxidative metabolism in mitochondria
• cannot grow/split by themselves, still need proteins coded by DNA in the nucleus

chloroplasts - where photosynthesis takes place in plants 

• contain chlorophyll, gives plants their green color
• have inner/outer membranes like mitochondria
• grana - stacked membranes lying inside the inner membrane; contain thylakoids (disk-shaped structures on which photosynthetic pigments are located) surrounded by liquid stroma
• also contain DNA like mitochondria, lacks DNA for self-replication
• plastid - organelle acting as storage; includes chloroplasts, leucoplasts, amyloplasts; produced only through division of existing plastids
• amyloplast - leucoplast (simple plastid) that stores starch

endosymbiosis - claims that eukaryotic organelles evolved when 1 prokaryote lived inside another 

• symbiosis - close relationship between organisms of different relationships that live together
• mitochondria thought to come from bacteria capable of oxidative metabolism, chloroplasts thought to come from photosynthetic bacteria
• supported by size, membrane, cristae, DNA, replication procedures of mitochondria/chloroplasts

cytoskeleton - network of protein fibers 

• support cell shape and keep organelles in fixed locations
• polymerization - spontaneous assembly of identical protein subunits into long chains
• actin filaments - long fibers responsible for contraction, crawling, pinching during cell division, formation of cellular extensions
• many enzymes and ribosomes bind to actin filaments
• microtubules - hollow tubes consisting of a ring of 13 protein protofilaments
  • extends from nucleation centers (-) at the center of the cell to the periphery (+)
  • move materials within the cell
  • kinesin - protein that moves organelles towards cell periphery (+)
  • dynein - protein that moves organelles towards the nucleation center (-)
  • help move chromosomes to opposite sides of the cell during replication
• intermediate filaments - most durable part of the cytoskeleton
  • twined together in overlapping arrangement
  • vimentin - most common type; provides cellular structural stability
  • keratin - found in epithelial cells that line organs/body cavities
  • neurofilaments - found in nerve cells
• centrioles - barral-shaped organelles
  • occur in pairs; each composed of 9 triplets of microtubules
  • centrosome - region surrounding a pair of centrioles in animal cells
  • help assemble microtubules