Cell Organization II

Question 1

phagocytosis

Answer 1

ingestion of large particles and delivery to lysosomes

Answer 2

ingestion of small bits of the plasma membrane with extracellular fluid

Question 3

three polymer systems of the cytoskeleton

Answer 3

microtubules, intermediate filaments, and microfilaments

Question 4

microtubules

Answer 4

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

Question 5

centrosome

Answer 5

microtubule organizing center or MTOC, containts hundreds of gamma-tubulin rings from which microtubules polymerize

minus end is always embedded in the centrosome

Question 6

dynamic instability of microtubules

Answer 6

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

Question 7

dynein

Answer 7

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

Question 8

intermediate filaments

Answer 8

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

Question 9

keratin

Answer 9

filaments, eipthelial cells, (also hair and nails)

most diverse group, filaments span the cells and link cells together through intercellular junctions

Question 10

vimentin

Answer 10

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

Question 11

neurofilaments

Answer 11

found in nerve cells, provide structure to axons and dendrites and are involved in movement of proteins and organelles

Question 12

nuclear lamins

Answer 12

all cells, provide structural support to the nucleus and a scaffold to assemble complexes for regulating transcription and repliction

Question 13

plectin

Answer 13

linking proteins that link intermediate filaments to other cytoskeletal systems

Question 14

actin filaments

Answer 14

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

Question 15

cell cortex

Answer 15

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

Question 16

Describe the tension and flexibility of each cytoskeletal filament.

Answer 16

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

Question 17

basic structure of motor proteins

Answer 17

head domain that contains the motor activity and a cargo binding domain, all utilize ATP for movement and are therefore ATPases

Question 18

kinesin

Answer 18

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

Question 19

myosin

Answer 19

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

Question 20

Describe the mechanochemical cycles of molecula motors.

Answer 20

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

Question 21

centrosome

Answer 21

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

Question 22

microvilli

Answer 22

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