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
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