Chapter 17: The Cytoskeleton

Question 1

Cytoskeleton

Answer 1

intricate network of protein filaments that extends throughout the cytoplasm

dynamic, continuously reorganizes as cells change shape, move, or divide

Question 2

Importance of cytoskeleton

Answer 2

• significant for cellular shape, mitosis, intracellular traffic or organelles, motility for sperm mobility(endothelial, white blood cells), contractility of muscles cells, and extension of axons from neurons

Question 3

Intermediate Filaments

Answer 3

• rope-like fibers(many strands for durability)
• for mechanical strength, resistance to shear stress that occurs when cells become twisted or deformed
• most durable (survive when other cells are destroyed)
• fibrous proteins
• found in most animal cells and some nuclei

Question 4

Intermediate Fiber four major classes

Answer 4

Cytoplasmic: keratin filaments, vimentin and vimentin-related filaments, and neurofilaments

Nuclear: nuclear lamins (lamina singular)

Question 5

Nuclear lamins/lamina

Answer 5

• intermediate filaments proteins called lamins
  -break and reforms at each cell division
• controlled by phosphorylation(breaking) and dephosphorylation(reassembly)
• reinforce nuclear envelope

Question 6

Neurofilaments

Answer 6

• in nerve cells
• along axons of vertebrate neurons, provide strength/stability
• relatiosn to Lou Gehrig’s disease

Question 7

Lou Gehrig’s Disease

Answer 7

• excess of neurofilaments
• build up can contribute to neuronal degeneration and muscle weakness

Question 8

Vinmentin and vimentin-related filaments

Answer 8

• in connective-tissue cells, muscle cells, and glial cells
• critical role in regulating cell mechanics
• required to coordinate transduction, signaling pathways, motility, and inflammatory responses

Question 9

Keratin filaments

Answer 9

• in epithelial cells(in skin, distribute applied forces to prevent shear/tears)
• forms nails and hair
• forms outer layer of skin(epidermis) and keeps it healthy

Question 10

Progeria

Answer 10

• premature aging disorders, causes individuals to have wrinkled skin, lose hair and teeth, develop severe cardiovascular disease by teens for kids
• defects in the nuclear lamin
• caused by cells division instability, becomes impaired
• has increase in cell death and decrease in tissue repair

Question 11

microtubules

Answer 11

• long hollow cylinders made from tubulin
• positions organelles, directs intracellular transport
• grow from centrosomes or basal bodies
• not permanent, assemble and dissassemble in cell division to form mitotic spindle
• can form tube cilia or flagella

Question 12

Formation/structures of microtubules

Answer 12

• build from subunites(molecules of tubulin), dimer
• composed of two globular proteins (alpha- tubulin and beta-tubuin), noncovalent
• tubulin dimers stack to make microtubule
• hollow tube consists of 13 parallel protofilaments, alternating alpha and beta units(has polarity with beta as plus end and alpha as minus end; can grow from either end by plus side is faster

Question 13

Centrosome

Answer 13

• major microtubule-organizing center in animal cells
• has pair of centrioles surrounded by gel matric of proteins
• matric contains ring-shaped structures called g-tubulin

Question 14

Basal bodies

Answer 14

• major microtubule-organizing center for cilia and flagella
• centrioles nucleate growth of microtubules here

Question 15

Cilia

Answer 15

• hairlike structures, covered by plasma membrane, that extend from surface of many kinds of eukaryotic cells
  -contains bundle, core of stable microtubules
  (grows from basal bodies!!)
• move liquid over a cell surface or move single cell through fluid (respiratory tract cilia removes mucus into throat to be swallowed and eliminated)

Question 16

g- tubulin

Answer 16

• ring complexes that are the nucleation site (starting point) of one microtubule

Question 17

centrioles

Answer 17

• made up of short microtubules
• do not serve purpose in animal cells!
• serve purpose in cilia and flagella!!

Question 18

Tubulin polymerization

Answer 18

• from nucleation sites on the centrosome
  -nucleating sites: y-tubulin ring complexes
• minus end(alpha) of each microtubule is embedded in centrosome (grown from ring complex), whereas plus end of each microtubule extends into cytoplasm
• (can build and disassemble mitotic spindle)

Question 19

Microtubules organization- special cell types

Answer 19

• in specialized cell types, dynamic instability of micro tubules can be suppressed by proteins; will then serve to maintain organization of differentiated cell
• differentiated cells display polarity(two ends structurally different, example is nerve cells having axons out one end, dendrites out other)
• organelles and other vesicles carrying proteins and other macromolecules move along microtubules

Question 20

Motor Proteins

Answer 20

• in microtubules, drive intracellular transport
• use energy derived from repeated cycles of ATP hydrolysis to travel steadily along microtubule (or actin filament) in a single direction
• Two families of motor proteins are kinesins and dyenins; two globular ATP binding heads and one tail that move along microtubule by bind, release, and rebind(tail determines cargo it can transport)

Question 21

kinesins

Answer 21

• motor protein
• move toward plus end microtubule (outward from cell body)

Question 22

dyenins

Answer 22

• motor protein
• move toward minus end microtubule (in towards cell body)

Question 23

Motor protein movement process

Answer 23

• move along microtubules using their globular heads
• ATP hydrolysis lossens attachment of head 1 to microtubule
  -ADP release and ATP binding change conformation of head 2, which pulls head 1 forward
• 2 heads bind and hydrolyze ATP, interact with microtubules
• tail interacts with cargo directly or indirectly with adaptor proteins (“walks hand-over-hand”)

Question 24

Microtubule transport

Answer 24

• microtubules in axon point in same direction (plus end, beta, towards axon terminals)
• oriented tracks allow organelle vesicle and macromolecules transport
• cell body to axon route and opposite
  -polarized system of microtubules help position organelles in required location and guide traffic within cells

Question 25

Dyenin motor protein transport

Answer 25

• transport toward minus end by cytoplasmic dyenin, ALWAYS uses adaptor proteins to interact with selected cargo

Question 26

Kinesin motor protein transport

Answer 26

• transport of vesicles, organelles, or molecules toward plus end of microtubules carried out by kinesin
• different adaptor proteins can allow same type of kinesin to carry different cargos

Question 27

Flagella

Answer 27

• propel sperm and many protozoa, longer than cilia(since designed to move entire cell)
• move fluid over tissue
• in respiratory tract
• circular shape of 9+2 arrangement
• share similar structures with cilia

Question 28

9+2 arrangement

Answer 28

• nine doublet microtubules arranged in ring around pair of single microtubules
• shared by nearly all eukaryotic cilia and flagella (protozoans to humans)

Question 29

Flagella sperm

Answer 29

• composed of acrosome(digestive enzymes)
• nucleus(contains 23 chromosomes)
• collar(containing many mitochondria)
• flagellum (causes sperm to swim)

dyenins allow flagellum to bend(slide against each other or flexible protein links to cause bending)