Cell Bio Exam 3

Cytoskeleton Functions— what is it made up of

Made up of protein fibers.

Helps keep cell shake and helps with the ability to move things around and divide.

The cytoskeleton is not BLANK. it is able to assemble and dissassemble

fixed

What is the purpose of the cytoskeleton not being fixed

a not fixed structure lets the cells change shape, move, and separate chromosomes during cell division.

Intracellular transport

motor proteins that move along the cytoskeleton tracks carrying cargo like vesicles

Signal transduction

mechanical signals in the cytoskeleton that can help sense physical forces like stretching or pressure— which can then cause a cell response.

intermediate filaments(IF)

stable support cables

10nm diameter

gices the cell mechanical strength and helps resist stretching

often attatched to cell junctions

Lamins- IF’s under the nuclear envelope

Microtubules (MTs)

Diamter: 25nm

Made of tubulin

Location: start at centrosome near the nucleas and radiates out

functions: vesicle transport, helps separate chromosomes during cell division, cilia/flagella movement

Actin filaments(AF)

Diameter 7-8nm

location: cell cortex- directly under the plasma membrane

function: cell shape, movement, muscle contraction

Largest to smallest diameters of the three fibers in the cytoskeleton.

Microtubules, Intermediate filaments, actin filaments

What does it mean for the cytoskeltal structures being dynamic

Means the cytoskeleton can quickly change shape, move, and divide .

Name the subunits for each polymer: MT, AF, IF

Alpha and Beta tubulin

Made of actin

IF proteins

Purpose of microtubules

help move chromosomes apart during anaphase

purpose of actin

helps pinch cells apart during telophase

Microtubule structure

hallotube

has 13 protofilaments

subunit- tubulin apha and beta dimer

has polarity a + end and a - end

+end is ussually denotes with beta

-end is ussuallly denoted by alpha

polarity determines the direction of MT growth

Where do MT’s start growing

MTOC Microtubule organizing center

In animals the MTOC is located in the centrosome which is near the nucleus.

what does the centrosome contain

2 centriolwa

surrounding matrix proteins— which are where MT’s begin to grow

Where do MT’s grow out of

surround matrix proteins in the centrosome

what is a nucleation site

starting point where MT’s start to assemble

Y tubulin ring complex

acts as a nucleation site for MT’s—- helps start the microtubules

provide a template for alpha beta dimers so they can start attatching to their correct arrangment.

at the minus end the y tubulin ring complex anchors the - end allowing the + end to face outword from the centrosome for polymerization.

Are microtubules fixed?

No they have dynamic instability can move back and forth between growing and shrinking

GTP tubulin vs GDP tubulin

GTP tubulin- assembly and growth

GDP tubulin- dissassembly

How does GTP add to the microtubules? what happens when GTP is hydrolyzyzed

Tubulin dimers carrying GTP add on to the + end of the microtubule

If that GTP is hydrolyzed to GDP, then it takes away from the - end

Where do MT’s start growing out of

The MTOC microtubule organizing center

In a animals the MTOC is located in the centrosome

What is located in the centrosome

in the centrosome contains 2 centioles

and surrounding matrix proteins which start MT’s

in animals the centrosome is the MTOC

Microtubules can move back and forth between growing a shrinking what causes growth and dissassembly

GTP tubulin causes assembly-growth

GDP tubulin causes dissasembly

GTP Tubulin and GDP Tubulin process

tubulin dimers carry GTP on the + end of the MT— has a GTP Cap-which stabalized the MT and allows it to keep growing

If that cap is removed by hydrolysis GTP-GDP, dissassembly then occurs with the GDP Cap

Eb Protein

protein that binds to the + end used as a marker for a growing MT end

What process occurs during GDP tublin MT dissassembly

without the GTP Cap MT is less stable

Profilaments peel away

MT starts to shrink

GTP tubulin is released back into the cytosol

Define the dynamic instability of microtubules

The MT is not just steadily growing all of the time

it can suddently grow then shrink

it is constantly exploring the cell

Catastrophe

Rescue

Catastrophe

growth—-shrinkage

rescue

shrinkage—-growth

What does random exploration mean in context of MT’s

random exploration denotes MT’s growing out in many direction

they are constantly growing and searching(due to their dynamic instability)

What does it mean for MT’s to have selective stablization

If MT’s grow to the right place at the right length the MT can be stabalized by:

a capping GTP Protein

Cell Cortex

Another Cell Structure

Taxol

Drug affecting MT dynamics

Binds and stabalizes MT

Colchicine/colemid

drug that affects MT dynamics-

Binds to tubulin dimers and prevents polymerization

drug that stops cell division

interferes with the mitotic spindle(which are MT’s) during separation of chromosomes during mitosis

If spindle doesnt work, cells cannot divide properly— cells die

without MT’s Er collaspes around the nucleus

golgi would break down into fragments

Proves that MT’s are required to keep position of organelles

vinblastine/vincristine

Drug affecting MT dynamics

binds to tubulin dimers and prevent polymerization

Kinesin

MT’s

Outward transport, away from the cell body, goes to the + end

Dyenein

Backward transport, to the cell body, towards the minus end

What does the MT system help with?

Places organelles in the right locations— Move ER outwards from the center of the cell. (kinesin)——-Pull Golgi inwards toward the center of the cell(dyenin)

moves vesicles and proteins where theyre needed

maintains cell polarity

supports neuron functions over long distances

Parts of a MT Motor protein

Tail- binds and caries the cargo(vesicles, organelles, materials)

Two heads: that attatch to the MT’s and walk along it step by step through ATPase activity —— ATP hydrolysus provides the energy for movement

Heads determine moving direction

Tails determine cargo

Cilia and flagella 9+2 structure

9 outer MT doubles and 2 central single MT’s(structure of one flagella)

Purpose of the 9 + 2 structure

The 9 outer doubles are where dyenin motors fenerate force(the doublets slide together)— causes energy through ciliary dyenin

the 2 central microtubules help organize and regulate the flagella so that movement is coordinated

Nexin

The clilium/flagella the MT’s are held to gether by nexin a linking protein

Basal Bodies

In cilia and flagella they are build from MT’s which are anchored to basal bodies(its own MTOC)

Basal bpdies sit at the base of each cilia/flagella

they are anchor the MT’s and build MTs from inside out

kartagerner syndrom

hereditaty defects in ciliary dyenon causing no movement in cilia

this causes non motile sperm

paralyzed cilia in respitory track causing a higher risk of respitory infections

Where are actin filaments located

they are flexible proteins which are mainly concentrated in the cell cortext under the plasma membrane

functions of actin filaments

cell shaping

intracellular transport- help organize inside of the cell

cell migration: pushed the membrane foward during movement

animal cell divitions: cleaves off during telophase

Muscle contraction

Actin fiber subunits

actin monomers

How is actin polymerized

through treadmilling: which end grows faster or looses faster

Actin has a + end and a - end

+end grows faster

-end grows slower and often looses subunits first

Treadmilling

In actin with the +end gains and -end looses at the same time which happens in immediate ATP actin concentration

the filiament may appear to be the same length byt actin subinits are constantly moving through it.

What happens dyring high, intermediate, and low ATP Actin Concentration

High: Both ends(+ and -) adds subunits

Intermediate: + end adds, - end looses at the same time

Low: both ends lose subunits

Cell Cortext/Actin Cortext

Thin meshwork of actin filaments which sit under the plasma membrane

Helps control the shape, stiffness, and cell movement

ARP Complex

starts new actin filaments off of existing ones

creates a branced web of actin filaments

branchint network pushes against plasma membrane which helps the cells move

Branched structure is regulated by capping proteins which stop the growth at a certain filament— controls where the branched network goes

How actin helps cells crawl

• front of the cell moves first, actin polymerization occurs at the + end of the ARP complex and pushes the membrane outwards

• ARP builds networks in the lamellipodium

• Cell attatches to the surface/substratum using integrins

• Integrin attatchments form focal contacts

• myosin dependent actin contraction helps pull the cell body foward

• at the rear of the cell actin dissasembles

• actin myosin contraction helps retract the rear

• deadhesion happens back and releases its attatchement to the surface

• Overall sequence- PUSH- ATTATCH- PULL- Release

Why is cell migration important

Development: cells have to move to correct places as an embryo forms

Immune system: white blood cells have to migrate to sides of injury or infection

cancer: cells can migrate and spread

metatasis

cancer cells

Filamin

protein that cross links actin filaments

builds a strong flexible 3D actin network

network helps cells change shape and move

if filamen is mutated cells cannot migrate normally

RHO GTPases what is it and what is the purpose

RHO GTPases regulate actin dynamics

they act as a molecular sqitch which trigger changes in actin in the cytoskeleton-changes shape, tension, movement

ACTIN MOVEMENT

What happens during RHO activation

causes formations of stress fibers

thick actin bundles in the cell that help with contraction and strong cell attatchment

What happens during RAC Activation

causes the lamellipodia to polymerize ARP complex, helps the cell PUSH foward during migration

CDC42 Activation

Causes Flipopofia— Spike like protrusions that help the cell sense its environment.

Phoalloidin

drug affecting AF

Binds and stabalizes filaments

filaments are locked in place and cannot move

Commonly used as a toxic stain imaging tool in lab.

Fixes cells

Cytochalasin

Drig affecting AF

Caps filaments at + end preventing polymerization at + end

Latrunculin

Binds actin monomers and prevent entire polymerization

Myosins

Motor proteins that move on actin filaments

Myosin heads: bind to actin

Most myosin heads walk towards the + end

Use ATP—-ADP+PI— Hydrolyzyes of ATP

Functions of myosins

Transports, cell shape changes, contraction

myosin 2 purpose and function

Myosin used in contraction

2 myosin 2’s bundle their tails together and form a biopolar myosin filament.

Function of a bipolar myosin filaments

2 myosin 2’s bundle their tails together

Both of their heads bind to different actin fimalents

each head walks towards the + end of the actin using ATP

if the different actin filaments are arranched in opposite directions— Myosin 2 pulls them past each other caysing the actin filaments to slide— causing contraction

organization of skeletal muscle

Long multinucleated cell containing myofibrils

each myfibril is made up of repearing units called a sacromere

Sacromere

Contractile unit of muscle

contains actin filaments

myosin filament

z discs which mark the boundries of each sacromere

Z disc to Z disk = one sacromere

in a sacromere actin filaments are anchored at Z discs

Where does the action potential for muscle contraction come from"?

it moves along from the t tubules alond the plasma membrane

what happens when a muscle contraction action poteintial is recieved?

it triggers the sarcoplasmic recticum to release Ca2+ causing binding of Ca2+ to tropomyosin—- causing troponin

to start muscle contraction

What is a t tubule

plasma membrane surrounding each myofibril. Allos action potential to spread inward of muscle fiber

what is the sarcoplasmic recticulum

specific ER surrounding each yofibril containing high Ca2+ content

intermediate filaments function

stregthens cells, protects them from mechanical stress

nuclear strengthening and organizaation(lamin- nuclear lamnia)

strong against stretching

Sub Units for IF’s

dimers! Coiled coil dimers

has central rod domain alpha helical structure

Assembly of iF’s

A single monomer alpha helical

2 monomers wrap together to form a coiled-coil dimer

2 dimers join in a staggered antiparallel way to make a tentramer

more tentramers add end to end laterally to form a roplike filament

How are IF’s held together

non covalent , non polar interactions

What are the types of IF filaments

All are cytoplasmic

Keratin filaments : in epitheial cells- resit stress

Vimetin: in connective tissue, muscle cells, glial cells- muscle related

Neurofilaments: in nerve cells- suports nuerons

Nuclear: nuclear lamnia- in all animal cells

Where are cytoplasmic IF’s not present?

Not in anthropods, echinoderms, or plants

What happens with deffective Keratin

stress is not spread out equally- tearing occurs, cells bcome fragile, causes blistering

Desmosome

Strong cell to cell junction that connects neighboring cells together

is linked to IF filaments inside of the cell

Contains keratin whick helps the tissue resist pulling and stretching

Inside of each cell IF filaments are attatched to cytoplasmic plaqure made of linker proteins— what are the main attatchements

cadherins: in desmosomes- connect one cell to another cell

Integrins: in hemidesmosomes- connect a cell to the basam lamnia or extracellular matrix

What happens when mutations in cadherin and integrin proteins occur?

related metasis due to increase motility in cells.

Tight junctions

seal neighboring cell to prevent leakage

helps polarize cell

Adherins junction

joins actin bundle in one cell to a similar bundle in a neighboring cell

desmosome

joins IF filaments in one cell to those in a neighbor cell

gap junctions:

form channel that allows small molecules to pass from cell to cell

hemidesmosome

anchors IF in a cell to the basal lamnia

nuclear lamnia

netowork of lamin proteins linking the inner side of the nuclear envelope

Maintains nuclear envelope shape

Helps with chromatin organization(where chromatins can attatch)

During mitosis nuclear lamnia is disassembled allowing the nuclear envelope to break down so chromosomes can separate

Progeria

disease related to defective lamins— is a premature aging disorder

what causes the nuclear envelope to break down during mitosis?

phosphoralation of lamins and pores

Lamins act like a bridge between

Chromatin- DNA inside the nuclear

and the cytoskeleton- structure outside the nucleus

The bridge allows for gene expression

How does the lamin bridge held together

Through LINC complex

SUN domain proteins inside nuclear membrane attatch lamins to chromatin

KASH proteins outside nuclear membrane connect cytoskeleton elements

Function of Lamin connection with cytoskeleton

positions the nucleus- structural integrity

Transmits mechanical signals

control chromatin organization + gene expression

Mechanotransduction

How force turns into gene expresison

What does it mean for cell signals to determine cell fate?

combination of specific signals cause specific outcomes of the cell.

SUN domain proteins

KASH proteins

inside nuclear membrane attatch lamins to chromatin— SUN

outside nuclear membrane connect cytoskeleton elements KASH

Order of opps for cell signaling

Extracellular signal molecule—- receptor—- intracellular signaling molecule—- Target protein—- Cell response

What is the difference between Fast Response and Slow response cell signaling

Fast response is protein regulation—- it changes an existing proteins activity

Slow response is gene expression, the signal binds to a transcription factor, making DNA transcription and translation to occur.