mod 3. cytoskeleton and motility

what are the three types of filaments?

IF

actin

MT

describe IF

strong to combat mechanical stress

describe the sturcture of IF’s

each monomerhas a pair of globular terminal domains seperated by long fibrous alpha helical region that is polar

pairs of monomers are parallel

monomers form dimers

dimers form non polar tetramers

tetramers form 8unit lengths IF filament

what are the types and functions of IF?

cytoplasmic; keratin, neurofilaments, vimentin filaments.

nuclear; nuclear filaments

explain what keratin filaments serve to do?

act as the structural protein of epithelial cells

radiate through cytoplasm thethered to nuclear envelope anchored to outer edge of cell. and also connect to MT and F actin via plecton

e

explain neurofilaments

bundles of IF located in cytoplasm of mature neurons, parallel to axon for sztrength and stability.

describe the assembly and disassembly of IF

doesnt directly require ATP/GTP

assembly is controlled by subunit phosphorylation and dephosphorylation.

once assembeled subunits are not incorporated end to end just along.

what is the function of linker proteins?

cross links other IF and desmosomes for reinforcment and stabilization. each plectin dimer has two binding sites for its respective filament binding.

what are actin filaments for?

maintain cell shape movement and cell division 

what is the sturcture of actin filaments?

thin flexible helicla filament made of actin monomers free form in the ctyoplasm

F-actin; polar filament for higher order structure.

describe the assembly and disassembly of actin filaments

grow by the addition of actin at both ends but fvaster at positive end. ATP is hydrolyzed to ADP is encorporated into growing end that is dedpolymerizing ( if conc of atp-actin monomers is very high subunits are added to both ends).

at the point where addition=loss the actin filament doesnt grow.

treadmilling is the addition of monomers at olne end with equal loss at the other, generating movement.

what are the actin binding proteins?

1. nucleating; to form seeds

2. monomer-sequestering; binding individual actin to prevent spontaneous assembly

3. bundleling;pushes cell forward

4. cargo movement

5. end blocking; stops hrowth

6. cross linking; gives stren gth

7. filament severing; stop smovement

8. actin filament depolymerization

describe cell motility

cell sends out protrusions at its front edge by actin polymerization. 

protrusions adhere to surface over which the cell is crawling by formation of focal adhesions.

the rest of the cell drags behind deploymerization olf focal adhesion

what are myosins described as?

motors of f actin

what are the two types of mysosin?

unconventional-myosin 1

conventional myosin 2

how do the two types of myosin work?

1- hand a repetitive cylce of binding, release, reattachment

2- muscle contraction, sliding filamentmodel.

what are the three layers of mucle fibers?

muscle fibers→myofibrils→sarcomeres

describe the sliding filament model steps

1. attachment

2. release

3. cocked

   1. rebinding/power stroke

what are MT’s functions?

cell shape, cell division, cell motility, provide tracks

describe the structure of MT

tubular structures alpha tubulin(-) and beta tubulin(+) form a polar heterodimer.

explain the assembly of MT

each tubulin dimer contains GTP tightly bound to beta tubulin.

added to + end of MT

GTP is hydrolyzed= GDP

GDP remains bound to beta tubulin

if tubulin dimers are added faster than it is hydrolyzed the MT grows

how is MT disassembled?

if the GDP bounds less tightly it tips in favour of disaszsembly.

what are the MAPs?

1. nucleation

2. branching

3. link other MTs

4. polymerization

5. stability

6. severing

   1. motor proteins

intracellular motility

requies ATP through motor proteins

list the three motor proteins included in intracellular motility

myosins; actin filaments move to + end

kinesins; MT move to + end

dyneins; MT move to negative end

all move unidirecionally

how do kinesis move?

hand over hand model

how do dyneins move?

pull the golgi inwardly along the MT and towards centrosomes

what is the mechanism of ciliary/flagellar locomotion
?

the dynein anchored along the tubule attached to an adjacent binding site and flexible linker proteins cause bending when the tubules power stroke.