Cell Bio exam 3

the 3 cytoskeletal fibers- which ones are in all eukaryotes

microtubles (all eukaryotes)

microfilaments (all eukaryotes)

intermediate fibers (animals only)

cytoskeletons 3 main jobs in a cell

• organize the cytosol through coordinating transport of cargo

• provide structure, connectivity and shape to cells

• provide for cell motility

cytoskeletons create “tracks” to support…. and provide transport throguht the ___

organelles, cytosol

the MT are spread like an array/star with the what end on what

• - ends on the inside at the centromere

• + ends spread throughout cytosol

  • bumping into MT can then lead you where you wanna go

  • leads to outter egde of cell then MF takes it from there

the MF are more on the edge of cell where what end is where

• - side more towards cytosol

• + side near the edge/PM

  • short distance transport, they finished their journey on these MF

what are MT and MF made up of

MT- tubulin

MF- actin

the ability of euk cells to move is depnedent on the action of the

cytoskeleton

MT can make up ____ to be motlie while MF can make up ____

MT- cilia

MF- contractile fibers and actin webs

MT are made up of

polymer of αβ-tubulin dimers, these are hollow

B- binds with GDP

a- binds with GTP

has polarity

MT can do more fuctions the more…

beefed up it is, doublets and triplets

both MT and MF are bound to nucleotides, this…

changes the shape and fuction.

IF do not bind to

nucleotides

IF are made up of

polymer of fiber-forming proteins

no polarity.

MF is made up of

polymer of actin

has polarity

all cytoskeletal elemnts shrink and elongate constantly due to

dynamic instability in living cells

(in matter of seconds always changing)

dynamic instability is caused by

the binding of the nucleotides

when do MT and MF want to be a filament/ grow

when its boung to a tri- GTP or ATP

what do the + and - ends mean on MT and MF

• + grows faster

• - still grows just not as fast

why do IF not grow and shrink?

becuase it doesnt bind to a nucleotide so the shape doesnt change

what happens if most of the MT have GDP but have end caps of GTP

as long as there is caps of GTP then it stays filament

once cap removes it shrinks again (catastrophe)

when does catastrophe occur

when the ends lose the GTP gap

it will shorten quickly and disassemble polymers

what is the only things that can save catastrophe

MT can rescue by adding new GTP cap

difference in GDP filaments vs GTP

GTP is linear, GDP curls up

each end of a filament has critical concentration that does what

required to promote assembly
each end has different concentraion

what end has what for a critical concentration

• + end will always be lower then the - end

  • having a lower concentration is better

if the actin ATP is above the CC then

both ends will grow

if actin ATP is below the CC then

the - end will stop growing (may shrink)

the + end will still grow

what is treadmilling

when one end can shrink while the other end will grow making it look like there is movement

different protiens can encouage cells to

stabilize or unstabilize regulating the cytoskeleton

what are the three most important classes of motor protiens carrying cargo along filaments

myosins, kinesins, and dyneins

all euk have all three

myosins

on MF- move toward + ends

kinesins

on MT move to + ends

dyneins

on MT move to - ends

all motor protiens are ____ and use ATP hydrolysis to walk

ATPases

they bind cargo on one end and MT or MF on other end

kinesins and myosins are very similar

common ancestor they look and move similar

myosins come in 3 different types differing in tail domains

monomeric- vesicle transport - hop around

dimeric- organelle transport- walk

bipolar- contraction of MF- motors are fixed to each other

moter fix vs cytoskeleton fix

moter “cargo” is fixed then the cytosk is moving

• pushes - side back while walking to + side

cytoskeltons fix then the cargo walks normally to + side

bipolar myosins

pull + sides to middle beaucse motors are fixed to one another pulling

three types of kinesis

monomeric- organelle transport - hop around

dimeric- organelle + chromosome transport- walk

bipolar- contraction of MT- motors are fixed to each other

the power of the head domain for tubulin and actin is the binding to a

nucleotide - ADP to ATP

dyneins have two forms depending on where they are found

cytoplasmic- organelle transport

ciliary dyneins- cell motility

power stroke of the dyneins comes from the

ATP hydroluysis driving conformational change

walking from the hip

swimming motility is through MT bases appendages

axonemes of doublet MT form the core of the cilia

cilia can either

beat to propel cells thrpough liquid

or

cause liquids to flow across a field of cells

crawling/amoeboid motility on the surface is my MF based appendages

MF form parellel bundles to support

eukaryotes have ____ and prokaryotes have _____ to help move

euk- cilia

prok-flagella

flagella

flagelin, not membrane bound

how many cilia do we have

only 1, the rest has 2

basal body

At the base of the cilium, where it attaches to the cell, there is a structure called the basal body.

• The basal body acts like a foundation or anchor for the cilium.

  • It organizes and starts the growth of the microtubules that form the cilium.

  • inside are triplets of MT

cilia can undergo two different kinds of motions (wave forms)

1. breast stroke -pulls body forward through fluid

   1. sinusodial- swimming sperm pushing cells

how are the cilia moved by doublet MT

one MT slides past another.

But because the microtubules are connected to each other, they can’t slide very far, so instead the structure bends.

what powers the cilia to move from the doublet MT

potor protien dynein

uses ATP to walk along one MT causing the bending

what is cilia also used for

signaling and sensing the enviorment

some are so deticated they stop being motile

difference in motile cilia and non motile

motile have the middle doublet MT that spin around to hit the signaling

so the signiling on the non motile is broken not the dynein

how is Amoeboid motility accomplished (crawling)

non-ciliated cells

by protusion, attachment, traction/pull

protrution for non ciliated cells

actin grows on + end pushing PM out

lamellipoda- flat 2-D (actin webs)

pseudopodia- shorter 3-D (actin webs)

filopodia- thin and flat (actin bundles)

podia is the (protrusion/feet)

podia then attached to the surface using what

focal adhesion attaching to the outside

then to pull the non ciliated cell it uses traction by

cortical actin network contracts (tightens). pulling the + ends together

what controls actin network? how does it move

g-protiens

the Rho family

on GTP off GDP

these trigger actin filament growth

cells can soometimes switch between swimming or amoeoid movement depending on

their enviorment

if the cells want to crawl they usually retract their cilia to move it out of the way

can divide euk organelles into 3 groups based on how connected each is to the cytosol

1. nuclus is connected to cytosol by large channels so small molecules can easily diffuse btw them

2. endomembrane org. cross one membrane to get to cytosol

3. endosymbiotic org. cross two membranes (ex mitoch.)

gating

the nucleus is connected to the cytosol by large aqueous channels, small things can diffuse in and out, large things

need a pore that can open or close (i.e., a “gate”)

translocation

to cross a membrane, proteins need a translocon that can pass the proteins across the lipid bilayer (i.e.,

“translocate” those proteins across the membrane)

transcription occurs in

nuclues

transaltion occurs in

cytosol

vesicle trafficking

not all compartments have translocons; to access these compartments we need to use transport vesicles

which leave one compartment and then fuse with another.

nuclear envelops is a domain of the

ER

it is almost completley closed by two lipid bilayers

think balloon-

outide- cytosol, balloon- ER, and inside air is- ER lumen

ER has two different kinds of protien transporting channels

• Nuclear pore complex (NPC)

• ER translocon

both are channels (holes)

Nuclear pore compec NPC

gatway to nucleus, massive gated pore, always open

found in nuclear pores

how does the NPC work

small protiens- diffuse in and out through aqueous pore

large protiens- need nuclear localization signals (NLS) to enter and (NES) nuclear export signals to exit

(protien will be in tert or quant strucutr, does not need to unfold with NLS)

how are NLS and NES signals bound

by the nuclear cargo receptors (importins or karyopherins) which help escort the cargo through the gate.

what controls nuclear targeting of cargo- Nuclear Cargo Receptor (NCR)

small G protiens Ran

ran protien is kept in different states depending on

the different side of the NPC its on

Ran GEF is only found in the nucleus, so any Ran in the nucleus will be in the form of

Ran-GTP

Ran GAP is only found in the cytosol, so any Ran in the cytosol will be in the form of

Ran-GDP

ran gap is too big for nucleus

explain nuclear import

NLS is recognized and bound by the NCR which then escorts the cargo in,

once in the nuclues, binding to Ran GTP cause the NCR to release NLS containing cargo

the NCR can only bind to an NLS if what is present

Ran GDP

can no bind to ran GTP and NLS at same time, drops one and picks the other up after in nucleus

expalin how nuclear transport outside (exit)

NES is recognized by NCR Ran-GTP complex which then escorts cargo out of NPC, once in the cytosol ran GAP trigger ran GDP form now dissociating from the complex leaving the cargo in cytosol

All protein targeting requires signals encoded in the primary sequence of the proteins

hese signals are recognized by cargo receptors that mediate transport of the cargo proteins that have those signals. Behavior

of the cargo receptors is generally regulated by G-proteins!

• Proteins carry built-in destination signals

• Cargo receptors read those signals and transport the proteins

  • G-proteins control when and how this transport happens

In protein targeting, translocation is the process of

physically moving a protein across a lipid bilayer (a membrane) like threading a needle.

secration

delivering things outside the cell

bSec translocon found on the

PM

eSec translocon moved to the ____ and is now the start of

ER, start of vessicle trafficking t

translocon requires protiens to be

unfolded

becuase it is too small of a space for big folded protiens, needs to maintain the seal

what does eSec use to complete the secretion of protiens and get it out of the cell

vessicle traffiicking

if sec translocon is hinged, then the protiens inside can

choose to stay in hydrophillic env or leave to the lipid tails in hyrophobic env

compare TMD vs ER signal peptides

both hydrophobic regions favoring lipid part of membrane, as well as both inserted into membrane by ER translocon

BUT ER signal peptide is at the N terminus where TMD is found anywhere

signal pepties are recognized by

ER SRP made up of rna and GTPase

two G protiens that help control ER translocation

SRP and SRR

SRP g protien

detecting signal peptide on protien then pauses translation

SRR g protien

lives on ER membrane and detects SRP GTP now trying to find translocation

once the SRR and SRP find the translocon

GTP triggers opening of translocon and needs to fold so hydropobic part ( the signal peptide ) can go through membrane

once the signal peptide (hydrophobic) goes through membrane this is the

start of the start transfer seq, once N term is through, it transfers everything else after it into the ER lumen

only the ER has a translocon, so other organelles use what to get their proteins transported to them from the ER

vessicle traficking, allows you to move the protiens without crossing PM everytime

all organelle protiens must start at the

ER

Vessicles can allow pathways by 2 main ways

automatic or signal mediated

The automatic pathways represent:

1. Secreation (going outside) - exocytosis

2. Endocytosis (going inside cell)

what are the three coated vesicles

COP-I COP-II and clathrin

how do coated vesicles work

grab piece of membrane with a little of the inside now coated with protiens

to make a vesicale the remodleing works from the what side

cytosol side