Cell Organization II Flashcards
phagocytosis
ingestion of large particles and delivery to lysosomes
ingestion of small bits of the plasma membrane with extracellular fluid
three polymer systems of the cytoskeleton
microtubules, intermediate filaments, and microfilaments
microtubules
play a crucial role in organizing cells, major component of the mitotic spindle
formed from subunits containing a dimer of alpha- and beta- tubulin units
thirteen parallel protofillaments, hollow tube
structural polarity with different dynamic behaviors
centrosome
microtubule organizing center or MTOC, containts hundreds of gamma-tubulin rings from which microtubules polymerize
minus end is always embedded in the centrosome
dynamic instability of microtubules
tubulin dimers bound to GTP bind more tightly to one another than those bound to GDP
hydrolysis occurs after a while, so there is a tail of depolymerization towards the minus end
dynein
a motor protein that moves cargo across cilia and flagella, microtubules here have a 9+2 instead of a 13 arrangment
belong to a small family of motors with similar structures to kinesins but move toward the minus end of microtubules - retrograde movement
two groups - cytoplasmic found in all cells and axonemal found in cilia and flagella
intermediate filaments
high tensile strength and can withstand stretching of the cell
ropelike structure with a 10nm diameter made up of filamentous proteins aligned laterally
four classes of cytoplasmic intermediate filament proteins an done class of nuclear intermediate filament proteins
keratin
filaments, eipthelial cells, (also hair and nails)
most diverse group, filaments span the cells and link cells together through intercellular junctions
vimentin
connective tissue cells, muscle cells, neuroglial cells
these filaments help to organize organelles in the cytoplasm and probably act as anchors for proteins and organelles
required for cell locomotion
neurofilaments
found in nerve cells, provide structure to axons and dendrites and are involved in movement of proteins and organelles
nuclear lamins
all cells, provide structural support to the nucleus and a scaffold to assemble complexes for regulating transcription and repliction
plectin
linking proteins that link intermediate filaments to other cytoskeletal systems
actin filaments
has a globular form called g-actin and a filamentous form called f-actin
necessary for the movement of cells and specialized membrane structures
diameter of about 7nm, smallest of the three, usually found in bundles
similar to tubulin in regards to polymerization, uses ATP instead of GTP
cell cortex
a network of actin near the plasma membrane, in motile or muscle cells, actin is arranged in a three-dimsional network that cells use to generate force
Describe the tension and flexibility of each cytoskeletal filament.
microtubules can deform a lot but break easily
actin doesn’t deform much but is resistant to breakage
intermediate filaments form a netowrk, can stretch a lot, strain hardening - harder you pull, harder it gets
basic structure of motor proteins
head domain that contains the motor activity and a cargo binding domain, all utilize ATP for movement and are therefore ATPases
kinesin
belong to a large superfamily with related structure and function, all move on microtubules toward the **plus **end
since microtubules all ahve the same orientation in cells, kinesins move away from the MTOC toward the cell periphery - anterograde movement
myosin
large superfamily of motor proteins that interact with microfilaments or thin filaments in muscle to generate force
all have motor domain at the N terminal and then varying lengths for the rest of the molecule
processive exceptof rones the muscle
Describe the mechanochemical cycles of molecula motors.
In contrast to kinesins and dyneins, myosin head stays attached for only a small time which allows muscle movement
Since each cycle of a head requires a cycle of ATP, very energy intensive process
centrosome
an amorphous mixture of unpolymerized microtubules that is next to the nucleus
γ-tubulin forms small ring that binds to the minus end, only found in centrosome, holds the microtubules
microvilli
place where interaction between cytoskeletal element, associated proteins, and motors are very important for maintaining the structures
Region at the bottom called the terminal web that the actin microfilaments extend into
Crosslinks help the microvili stay rigid
Myosin can move along the actin filaments to transport materials down the microvili
