Cytoskeleton and Organelles Flashcards
Rigid, hollow cylinders of tubulin. Organized into curvy structures that radiate from MTOC
Microtubules
Flexible, contractile filaments of actin. Organized into linear bundles beneath plasma membrane
Microfilaments
Intermediate filaments
Ropelike fibers of keratin, lamina, or vimentin. Provide mechanical strength and carry stresses
Functions of cytoskeleton
maintain cell shape; stabilize cell adhesion and placement; facilitate movement(organelle motility/ chromosome separation/cilia and flagella-Microtubules)(muscle contraction/cell migration-Actin)
Long cylinders composed of tubulin heterodimer of α and β tubulin
microtubules
All tubulin monomers bind ___
GTP
Which end of the polarized microtubules binds GTP
Plus end of microtubule binds GTP (promotes polymerization)
Hydrolyzed GDP at which end of microtubule
Minus end (favors dissociation)
Tubulin subunits form long rows called
protofilaments
How many protofilaments associate to form the tubule?
13 protofilaments
Half life averages of microtubules are around __ mins
10 minutes
Faster growing end of microtubule
Plus End
Basal bodies have what type of arrangement of microtubules
9 x 3 arrangement
Microtubules occur as ______ in cilia and ______ in basal bodies
doublets; triplets
More stable: microtubules or microfilaments
microfilaments
F-actin
Filamentous actin
G-actin
globular actin monomers
In microfilaments, one complete turn involves how many monomers
Fourteen
Microfilaments
helical actin filaments
Invagination of cell surface during cytokinesis
Cleavage furrow
Cleavage furrow provides contractile apparatus to “pinch off”
daughter cells
Stress fibers
Actin bundles along basal cell surface terminate at focal adhesions; stabilize integrin adhesions
Actin organized by
α-actinin, talin
Actins role in integrin adhesion
Provide tension for migration and adhesion; provide scaffold for intracellular signal transduction
Adhesion belts
Circumferential actin near apical cell surface
– Stabilize cadherin-mediated adherens junctions
• Organized by catenins, -actinin - Provide scaffold for intracellular
signal transduction
Lamellapodia
outward projections of cytoplasm the leading edge of migrating cells
Microvilli
Fingerlike extension at cell surface; Increases cell surface area
Where is membrane skeleton (spectrin) most prominent
erythrocytes (but spectrin is ubiquitous)
Sickle cell anemia involves modification of
spectrin skeleton
______ links spectrin to Band 3 and Glycophorin
Ankyrin
Intermediate filaments size relative to microfilaments and microtubules
“intermediate”
Assembly and disassembly of intermediate filaments are regulated by
phosphorylation of proteins
How many basic types of intermediate filaments
Six basic types
Rope-like polymers of long, fibrous protein
Intermediate filaments
One of the most common markers for neoplasia
Change in cytokeratin expression
Type I intermediate filament
acidic keratin
Type II intermediate filament
neutral to basic keratin
Type III intermediate filaments
vimentin, desmin, glial fibrillary acid protein, peripherin
Type IV intermediate filaments
neurofilaments (axons and dendrites)
Rod shaped organelles- have an outer bounding membrane and inner membrane that invaginated to form cristae
Mitochodrion
Name of area between the outer and inner membranes of mitochondria
intermembrane space
Inner matrix compartment of mitochondria contain granules that bind…
(Mg +2 and Ca +2)
Matrix granules increase in number when
cations increase in cytoplasm. (may help regulate cytosolic ion concentration)
Mitochondrion matrix contains all the enzymes of the TCA cycle except
succinate dehydrogenase (located on the inner mitochondrial membrane)
Elementary particles contain
ATP synthase
enzyme involved in coupling oxidation to phosphorylation of ADP to form ATP
ATP synthase
Mitochondria have their own genetic apparatus composed of
circular DNA, mRNA, tRNA, and rRNA
Most mitochondrial proteins are encoded by
nuclear DNA
Mitochondrial Energy Generation
Energy produced by oxidation of fatty acids, glucose, and amino acids using Krebs cycle
ATP in mitochondrial energy generation is generated by
chemiosmotic coupling
Two types of Endoplasmic reticulum
Rough(granular ER) and smooth (agranular ER)
Endoplasmic reticulum is the site of
noncytosolic protein synthesis
The interior ER region is called the
cisterna (or lumen)
ER is abundant in cells synthesizing
secretory proteins
Phospholipids for new membranes are produced in
cytosolic half of ER
Where is cholesterol produced?
Endoplasmic reticulum
Ceramide is produced in the
ER
Many proteins in the ER have what sugars attached?
N-linked (Asn) oligosaccarides . (further modified in the Golgi)
Irregular network of membrane-bound channels which lack ribosomes
Smooth ER
Where are smooth ER found in abundance?
Steroid synthesizing cells and cells involved in synthesis of triglycerides and cholesterol
Golgi complex consist of
several stacks of disk-shaped cisternae(saccules)
Describe cisternae of Golgi
slightly curved, with flat centers and dilated rims
Major functions of Golgi Apparatus (5)
1)modify N-oligosaccharides on Asparagine 2)distribute non-cytosolic proteins to plasma membrane, lysosomes, and secretory vesicles 3)assembles proteoglycans from proteoglycan core proteins 4)adds mannose 6-phosphate to proteins that are targeted for lysosomes 5) sulfates sugars on proteoglycans
Cis (entry) face of Golgi
consists of cis Golgi network and cis cisterna and is the forming cisternae, located at the side of the stack facing the rER, and associated small transfer vesicles
Medial compartment of Golgi
comprises a few cisterna lying between cis and trans faces
Trans (exit) face of Golgi
comprises the maturing cisternae, which are located at the side of the stack facing vacuoles and secretory granules
Trans golgi network
lies apart from the last cistern at the trans face and is separated from the golgi stack
microbodies
membrane-bound ovoid organells
Functions of peroxisomes in human liver
- Breakdown (by oxidation) of excess fatty acids.
- Breakdown of hydrogen peroxide (H2O2), by-product of fatty-acid oxidation. Catalyzed by the enzyme catalase.
- Participates in cholesterol synthesis. One of the enzymes involved, HMG-CoA reductase, is the target of cholesterol-lowering “statins”.
- Participates in the synthesis of bile acids.
- Participates in the synthesis of the lipids used to make myelin.
- Breakdown of excess purines (AMP, GMP) to uric acid.
Disease caused by defective peroxisome assembly
Zellweger syndrome
nonliving components of the cell that do not possess metabolic activity and are not bounded by membranes.
inclusions(pigments, lipid, crystalline, storage and secretory granules, glycogen)
The formation and transport of vesicles within a cell is aided by
vesicle coating proteins
Transport vesicles are coated with either
clathrin or coating protein (COP)
COP coated vesicles transport between
rER ans Golgi (and various Golgi stacks)
Clathrin mediates transport of
vesicles from the trans-golgi network and from the plasma membrane
Lysosomes
dense, membrane bound organelles of heterogeneous morphology. Primary=storage; Secondary=engaged in degradative process
Lysosomes contain
acid hydrolyses to degrade proteins, nucleic acids, oligosaccharides and phospholipids
Lysosome membrane contains proton pump for…
acidifying the lysosome interior
Tubulovesicular structures formed by endocytosis from plasma membrane
endosome
Endosomes usually fuse with
lysosomes
Early endosomes
more electron lucent; may fuse with other vesicles to form CURL(compartment of uncoupling of receptor and ligand)
Late endosomes
more electron dense interior; more acidic pH (5.5); develop via fusion with lysosomes or endosomal “maturation”
Cell drinking via small vesicles
pinocytosis
Pinocytosis is a part of normal cell activities and not a triggered process therefore it is a _________ process
constitutive process
Uptake of microorganisms, cells, and foreign particles by a cell into a phagosome
phagocytosis
Some cells specialized for phagocytosis (degrade proteins and cellular debris)
Macrophages
Phagocytosis may or may not involve
cell-surface receptors
Ingestion and degradation of foreign material taken into cell by receptor mediated endocytosis or phagocytosis
Heterophagy
Digestion of endocytosed ligands may occur in
multivesicular bodies
Digestion of phagocytosed microorganisms and foreign particles may be completed in
phagolysosomes
Segregation of an organelle or other cell component within membranes from the rER to form an autophagic vacuole (autophagosome).
Autophagy
Receptor-mediated endocytosis
specific uptake of a substance (e.g., low-density lipoproteins, EGF) by a cell with plasma-membrane receptors for that substance (ligand).
Process of ligands being endocytosed
(1) Ligand binds to receptor (2). Membrane invagination and endosome formation (3). Proton pump acidifies endosomal compartment (4) Endosome moves along microtubule tracks towards trans Golgi reticulum (TGR).(5) Interaction with TGR determines fate of ligand and receptor.
3 possible fates for ligand in RME
- Ligand degraded in lysosome and receptor recycled (LDL)
- Ligand and receptor recycled (transferrin)
- Ligand and receptor both degraded in lysosomes (Epidermal growth factor)
non-coated pit that has a cholesterol binding protein
caveolin
cholera and tetanus utilize a _______ _______ pathway
clathrin independent
Release of cell material by secretory granule membrane fusion with the plasma membrane
exocytosis
Regulated secretion (exocytosis)
Release of proteins and other materials stored in the cell in response to an extracellular signal
Constitutive secretion (exocytosis)
“continuous” release of material without any storage step or extracellular signal
In immune cells, exosomes carry molecules needed for
adaptive immune response
Exosomes can be captured by other cells and
transfer info to another cell
Where are exosomes formed?
Multivesicular bodies/ endosomes
