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132 Cards in this Set
- Front
- Back
unique feature of eukaryotic cells
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compartmentalized cytoplasm
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significance of membranes in eukaryotic cells (3)
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1. barrier between the cell and the external environment
2. subdivide cell into compartments 3. allow each type of organelle to maintain novel ionic and enzymatic interior environments |
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three things membranes are composed of
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1. lipids
2. proteins 3. carbohydrates |
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Can membranes be visualized in a light microscope? Why or why not?
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No.
1. Too thin (~7nm) 2. do not stain with H&E |
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Can membranes be seen in an electron microscope?
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Yes, when stained with osmium tetroxide.
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Membrane lipids have _________ tails and __________ heads.
This makes them _________. |
uncharged, hydrophobic
polar, hydrophilic amphipathic |
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Because of their amphiphatic nature, membrane lipids form a lipid bilayer _____________.
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spontaneously
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The key to the organization of the membrane is the presence of the hydro______ center which acts as an ___________ to membrane proteins that can move within the lipid bilayer.
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phobic
anchor |
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The membrane is highly permeable for ____________ that cross the membrane by simple diffusion.
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small, uncharged molecules
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2 different classifications of membrane protein structure
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integral and peripheral
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integral proteins
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Membrane proteins which have a hydrophobic region which is embedded into the hydrophobic core of the membrane
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transmembrane proteins
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integral membrane proteins that extend all the way through the membrane
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peripheral proteins
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not embedded within the lipid bilayer. (attach to integral proteins or hydrophilic heads of the membrane lipids)
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3 functional classifications of membrane proteins
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1. transport proteins
2. receptors 3. structural proteins |
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transport proteins
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allow charged and polar molecules to enter cell and bypass impassible lipid bilayer
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3 types of transport proteins
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1. channel proteins
2. carrier proteins 3. pumps |
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channel proteins
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form ores in the membrane which are either open or closed to certain molecules
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carrier proteins
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drag other molecules through the membrane by hiding them in cleft in the protein
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pumps
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use ATP energy to pump ions through the membrane
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receptor proteins
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bind to specific molecules in the extracellular matrix, resulting in conformational change that serves as a signal that allows the cell to adapt to its environment
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structural/anchoring proteins
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attach cell to its surroundings
use cytoplasmic domains to like to elements of the cytoskeleton use extracellular domains to link to extracellular proteins |
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carbohydrates
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oligosaccharides attached to extracellular domains of membrane proteins and lipids (glycoproteins & glycolipids)
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glycocalyx
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fuzzy coating visualized in electron microscope due to large amount of carbohydrates attached to proteins and lipids on the external surface of cells.
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ribosome
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RNA/protein particles
bring together mRNA and tRNA to synthesize a polypeptide large and small subunit |
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size of a ribosome
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15-25 nm
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3 types of ribosomes in eukaryotic cells
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1. free ribosomes
2. mitchondrial ribosomes 3. RER ribosomes |
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free ribosomes
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majority of cellular proteins synthesized here
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RER ribosomes (4)
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proteins in
1. Golgi apparatus 2. lysosomes 3. secretory granules 4. plasma membrane |
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mitochondrial ribosomes
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20% of mitochondrial proteins
(the rest synthesized on free ribosomes) |
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polysomes
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string of ribosomes connected to single mRNA molecule
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glycogen
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storage form of polysaccharides
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endoplasmic reticulum
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series of membrane-formed anastomosin tubules and cisternae
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smooth ER
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no ribosomes, more tubular appearance
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functions of the smooth ER (4)
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1. lipid and steroid metabolism (membrane synthesis and recycling)
2. detoxification (well developed in liver cells, enzymes break down toxins) 3.glycogen metabolism 4.sarcoplasmic retculum (storage and transport of Ca 2+ in muscles, regulate contraction) |
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rough ER
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ribosomes bound to surface, formed mostly of cisternae
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roles of the RER
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principle cite of synthesis of proteins destined for export out of the cell, into Golgi apparatus , lysosomes, and plasma membrane
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4 targets of RER protein synthesis
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1. out of the cell
2. Golgi apparatus 3. lysosomes 4. plasma membrane |
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structure of Golgi apparatus
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series of stacked, flattened, membrane limited of POLARIZED cisternae and tubular extensions
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cis Golgi
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cisternae which receive vesicles from the RER
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medial Golgi
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middle cisternae
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trans Golgi
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cisternaefrom which the mature proteins are transported
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function of Golgi apparatus (3)
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postranslational
1. modification 2. sorting 3. packaging of proteins |
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modification of proteins in the Golgi
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adding/removing sugar residues, sulfate, phosphate groups
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location of protein modification in the Golgi
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early stages- cis Golgi
intermediate steps-medial Golgi final modifications- trans Golgi |
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location of sorting and packaging of proteins in the Golgi
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trans Golgi
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3 main destinations of proteins from Golgi
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1.secretory vesicles
2.lysosomes 3.constitutive pathway |
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secretory vesicles
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vesicles which undergo maturartion process in which secretory proteins are retained within the vesicle.
mature secretory vesicles eventually fuse with the plasma membrane to release the secretory product into the extracellular space |
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lysosomes
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spherical organelles of variable size produced by the Golgi, characterized by low pH and presnence of hydrolytic enzymes
digest senescent organelles and material take up from outside the cell |
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hydrolytic enzymes found in lysosomes
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proteases, lipases, glucosidases
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mannose-6-phosphate
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principle sorting signal which direct proteins from the trans Golgi network to the lysosome
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I-cell disease
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mutation of enzymes that signal lysosome maturation causing lysosomal proteins to be secreted into the intercellular space
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3 types of lysosomes
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1.primary lysosomes
2.secondary lysosomes.phagosome 3.lupofuscin granules |
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primary lysosome
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lysosomes which have not yet received substrates for digestion
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secondary lysosomes
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(phagosomes)
fusion of primary lysosome with target |
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lupofuscin granules
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(residual bodies)
senescent, non-functioning lysosomes with indigestible material |
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constitutive pathway
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small vesicles which are transported directly to the plasma membrane because they are not destined for lysosomes or secretory granules
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examples of proteins in consitutive pathway
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integral membrane proteins, continuosly secreted proteins
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peroxisomes
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0.5 µm, small membrane bound organelles containing catalase and other oxidative enzymes used to oxidize a wide range of organic substances such as very long fatty acids to convert ethanol to acetaldehyde.
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catalase
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oxidative enzyme, breaks down long chain FAs.
degrades toxic hydrogen peroxide, a byproduct of oxidation |
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Lysosomes and peroxisomes have ________ precursors.
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different
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adrenoleukodystrophy
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inherited X-linked disorder
accumulation of lipid in brain/adrenals progressivebrain damage, failure of adrenal glands, death |
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Zellweger syndrome
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congential disease
mtations in proteins responsible for transport of peroxisomal enzymes from cytoplasm --> nonfunctioning peroxisomes improper formation of myelin sheath, affect brain development, die before 6 mo age |
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mitochondria
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produce ATP through oxidation of pyruvate and FAs
present in virtually all cells, esp. where large amounts of energy are used |
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cells which do not contain mitochondria
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red blood cells and terminal keratinocytes
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evidence of symbiosis theory of mitochondria
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1. contain seperate genome
2. posses dual membrane 3.increase number by division |
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mitochondrial matrix
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space enclosed within inner mitochondrial membrane
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Mitochondria are able to....
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migrate from one area of the cell to another to supply energy where needed.
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outer mitochondrial membrane
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contacts the cytoplasm on outer side
contacts intermembrane space on inner side contains pores/anion channels which allow passage of small molecules, proteins, ions, etc |
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inner mitochondrial membrane
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thinner than outer membrane
highly folded into cristae contains many enzymes involved in energy production |
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composition of intermembrane space
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pH and ionic composition similar to cytoplasm
protein composition is unique, enzumes that use ATP are generated here cytochrome C located here |
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cytochrome C
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initaites apoptosis
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mitochondrial matrix
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enclosed in inner mitochondrial membrane
contains soluble enzymes for Krebs cycle, DNA/RNA transcription/translation mitochondrial DNA, ribosmes and RNAs electron dense granules |
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electron dense granules
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store Ca 2+, reflect role in metabolism of ions
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Approximately ______ of the proteins involved in oxidative phosphorylation are encoded by mitochondrial DNA.
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1/5
(Therefore mitochondrial myopathies [ex. lactic acidosis, cardiomyopathy] can have nuclear OR mitochondrial origin.) |
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nucleus
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5-10 µm
large membrane bound contains genome |
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chromatin
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DNA bound to histones
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nuclear envelope
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consists of two membranes, perinuclear space between them, nuclear lamina and nuclear pores
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outer nuclear membrane
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closely resembles the membrane of the RER, continous with chambers of the RER
ribosomes attached to cityplasmic surface |
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perinuclear space
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continous with lumen of RERE. can transport proteins fro RER to nucleus.
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inner nuclear membrane
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distinct ability to bind chromatin and lamins, supporetd by rigid network of intermediate filaments
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lamin
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provides stability, intermediate filaments, form dense meshwork beneath nucleus
***DISASSEMBLE during mitosis, reassemble after mitosis |
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nuclear lamina
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thin, protein-dense layer, represents skeleon of nucleus formed by lamins
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nuclear pores
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70-80 nm openings through nuclear envelope, allow communication between cytoplasm and nucleus via <9nm particles
complex structure with protein spokes projecting into lumen of the more to the central plug |
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nucleosomes
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smallest unit of chromatin, consists of 8 histones (2 each of H2A, H2B, H3, H4) and 166 DNA base pairs
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beads on a string
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nucleosomes joined by 48 bp DNA segment link
fiber = 11 nm = basic level of DNA packaging |
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intermediate level of DNA packaging
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30 nm fiber
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euchromatin
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loosely packed, lightly stained, transcriptionally active DNA found in metabolically active cells such as neurons
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heterochromatin
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densely packed, dark staining, transcriptionally inactive DNA found in metabolically inactive cells
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3 main locations of heterochromatin
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1. periphery of nucleus, marginal heterochromatin is attached to the nuclear membrane
2.karyosomes 3. in association with nucleolus |
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karyosome
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discrete body of chromatin irregular in shape and size, found throughout nucleus
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chromosomes
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condensed and organized chromatin found in dividing cells
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centromere
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place where two chromatids of a chromosomes are joined together
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kinetochore
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place where each chromosome becomes attached to the microtubles of the mitotic spindle
formed on the centromere |
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nucleolus
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small area within nucleus in which ribosomal RNA is processed and assembled into ribosomal subunits
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3 morphologically distinct regions of nucleolus
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1.fibrillar centers
2. dense fibrillar component (pars fibrosa) 3. granular component (pars granulosa) |
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fibrillar centers
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contain DNA loops with rRNA genes and transcription factors
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dense fibrillar component
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(pars fibrosa)
contains riboslmal genes thate rae being translated and large amounts of RNA |
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granular component
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(pars granulosa)
site for ribosome assembly, made of densely packed custers of pre-ribsomal particles/partially assembled subunits |
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3 functions of cytoskeleton
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1. determines shape of cells
2. provides structural support for organelles 3.plays a major role in cell motility (esp. in mitosis and cytokinesis) |
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3 major types of cytoskeleton filaments
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1.actin filaments
2.microtubules 3. intermediate filaments |
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actin filaments
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thin (6 nm), + and - ends, mostly found in periphery
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3 roles of actin filaments
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1.cell movement
2.cell shape 3. organelle transport |
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2 forms of actin
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1. G-actin
2. F-actin |
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G-actin
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soluble monomeric globular protein, can polymerize into F-actin, polymerization occurs head to tail
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F-actin
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double-stranded helical filament
has head to tail polarity grows faster on one end direction allows for motor protein to travel spontaneous assembly at + end, dissassembly at - end gives effect of movement |
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Actin filaments are also known as
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thin filaments
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2 functions of actin/thin filaments
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1. cortex formation
2. myosin interaction |
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cytoplasmic cortex
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actin filaments form a thin sheath beneath the cytoplasm
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5 functions of the cytoplasmic cortex
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crosslined actin filaments
1. resist cell deformation 2.transmit forces 3. restrict movement of organelles 4. reinforce plasma membrane 3. restrict lateral motion of integral membrane proteins |
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myosin
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interacts with actin to generate force and movement. (motor associated with thin filaments)
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microtubules
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cytoskeletal elements present in all cells (except erythrocytes)
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3 functions of microtubules
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1.organelle and vesicle movement (sometimes over long distances, ie. neuron)
more transport = more microtubules 2.mitotic spindle and chromosome movement 3.beating of cilia and flagella (proteins manipulate microtubules --> movement) |
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structure of microtubules
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stiff, non-branching,cylindrical polymers, made of a-tubulin and ß-tubulin, polymerized side to side and head to tail ---> plus and minus end ---> can have transport
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Plus end of microtubules associated with
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cell periphery
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Minus end of microtubules associated with
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centriole/ microtubule-organizing center
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2 types of microtubule motor proteins
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1. dyneins
2. kinesins |
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function of microtubule motor proteins
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use ATP energy to generate force that moves the motor and materials attached to it along the microtubule
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Dyneins (involved in beating of cilia and flagella) move toward the ______ end of the microtubule.
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minus
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Kinesins move toward the ______ end of the microtubule.
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plus
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4 higher order structures of microtubules
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1.cilia
2.flagella 3.centrioles 4.microtubule-organizing centers |
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axoneme (structure)
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core of cilia and flagella, composed of 9 doublets and a central pair of microtubles
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axoneme (function)
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generates force for the movement of cilia and glagella (dynein arm grabs from one doublet to the other)
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centriole (basal body)
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found at the base of each cilium or glagellum, composed of microtubles arranged into 9 triplets WITHOUT THE CENTRAL PAIR
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microtubule-organizing center (MTOC)
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consists of two centrioles, virtually all cellular microtubules arise from the MTOC, most human cells contain MTOC
(not neurons and red blood cells which ar e incapable of division) |
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function of intermediate filaments
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strong bu flexible polymers that provide mechanical support for cells
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Why don't intermediate filaments have motor proteins associated with them?
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They do not have polarity.
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Lamins
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(Nucleus)
form a meshwork of filamens on the inner side of the nuclear envelope, where they form the nuclear lamina and provide structural support for the nucleus |
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keratins
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(epithelial cells)
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vimentin
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(connective tissue)
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desmin
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(muscle cells)
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glial fibrillary acidic protein (GFAP)
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(support cells of glial cells)
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4 functions of intermediate filaments:
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form bndles between the plasma membrane and nucleus to
1.spread tensile forces 2.maintain cell architecture 3.act as a cocoon when cell is damaged 4.anchor ion channel proteins |