BIO 302 Unit 4 Flashcards

Intermediate filaments – why are they the strongest

they have the ropelike structure that is best for withstanding mechanical strength

Structure of intermediate filaments

intermediate filament proteins twist together to form these ropelike structures. Some forms of the individual filaments come together to make meshlike network as polymers. Some extend across cell to connect cell-cell junctions

What filaments make u pthe cell cortex

actin filaments and actin polymers

What kind of filaments are in the nuclear lamina

intermediate filaments, specifically lamin proteins

Which of the following cytoskeletal structures grows out from a centrosome toward the cell periphery?

microtubules

Intracellular transport filaments? Transport what?

microtubles – transport vesicles, organelles, and other cell components

Dynamic instability

switch back and forth between polymerization and depolymerization

Mechanism behind dynamic instability

when the β-tubulin hydrolyzes its bound GTP shortly after a dimer is added to a growing microtubule, leaving it with GDP, which is less stable than GTP

The end of a growing microtubule is rich in which type of tubulin subunit?

GTP-associated tubulin subunits

Kinesin which direction does it travel

• end of a microtubule (out of cell)

Dynein which direction does it travel

• end of the microtubule (into cell)

Which motor protein transports the GA

dynein – pulls it in toward the nucleus

gamma-tubulin ring complex function

nucleation sites from which new microtubules are assembled.

Centrosome composition

a pair of centrioles in the center, surrounded by a matrix of proteins

Does a flagellum contain actin and myosin?

NO

what drives the bending of flagellum

Ciliary dynein generates a sliding force between two parallel microtubules. The linking proteins then help to make this a bending motion

actin filament structure

twisted chain of identical globular actin monomers, all of which “point” in the same direction along the axis of the chain.

In eukaryotic cells, the cell cortex is made of a network of what type of protein filament?

actin filaments

Cell crawling depends on?

actin filament polymerization - Actin filaments grow at the leading edge of a cell, pushing the membrane out and moving the cell forward.

What does myosin 1 do

which cells are they present in

How does myosin 1 move along the actin filaments

The head domain binds to an actin filament and has the ATP-hydrolyzing motor activity that enables it to move along the filament in a repetitive cycle of binding, detachment, and rebinding.

Treadmilling

simultaneous gain of monomers at the plus end of an actin filament and loss of monomers from the minus end; hence, actin filaments tend not to undergo drastic changes in length. This means NO CHANGE IN LENGTH

Lamellipodia actin filament composition

has actin but no myosin

***Intermediate filaments are found in what structure?

nuclear lamina

***Which of the following describes the structure of an actin filament?

It is a twisted chain of actin molecules.

Were are actin most highly concentrated

in the cytoplasm just beneath the plasma membrane.

Which filament type provideds the shape of cell

actin

Which type of filament has Keratin

intermediate

Which type of filament has tensile strength of cell

intermediate filaments

Do intermediate filaments deform under stress

yes

Keratin

intermediate filaments that span epithelial cells and indirectly connect to keratins in other epithelial cells via desmosomes

Which filament can lead to premature aging when disrupted

intermediate filaments

Size comparison of intermediate and actin filaments

the intermediate are wider than actin filaments.

cross-linking, stabilizing proteins

what does microtubule depolymerizes mean

because GDP-bound tubulin subunits associate less tightly, hydrolysis of GTP generally causes a microtubule to disassemble.

If GTP hydrolysis occurs on a tubulin molecule at the plus end of a microtubule protofilament before another tubulin molecule is added, what typically happens?

The microtubule depolymerizes

Which motor proteins pull on the ER

kinesins – pull them outward to the plus ends at the edge of the cell

Imagine that you add a non-hydrolyzable analog of ATP to the cell. What would you see occur as you continued to video the cell?

ATP hydrolysis is required for both kinesin and dynein function so a non-hydrolyzable ATP analog would inhibit both motor proteins, which transport organelles and vesicles

retrograde transport

backward transport to cell body using microtubules

ADP-containing actin filaments in tredmilling

these are the older actin filaments that were added on at the beginning and are making their way to the end of the actin chain

ATP-containing actin filaments in tredmilling

Rho proteins

group of closely related monmeric GTPases that Triggers actin filament bundling to promot fillapodia formation, Activates nucleation promoting factors (lamella formation), and Bundles actin filaments with myosin motor proteins

****Blocking rho proteins results in

Block organization of the actin filaments required for phagocytosis of the pathogen by the host macrophage.

Rho, Rac, and Cdc42 do what

responsible for controlling the organization of the actin cytoskeleton responsible for cell crawling and phagocytosis

Rho family examples

Rho, Rac, and Cdc42

Myosin I

motor proteins that has one head domain, moves along actin toward the plus end, and is found in all cell types?

Which direction does myosin II go

plus end

How could you increase the level of muscle contraction

addition of a leaky Ca2+ channel to the sarcoplasmic reticulum, blockage of the Ca2+ pump

How would you decrease the level of muscle contraction

mutation in troponin such that it no longer binds tropomyosin or addition of a molecule to bind free Ca2+

At a cellular level, what is the mechanism behind rigor mortis?

ATP binding to myosin releases myosin from actin, allowing muscle relaxation. In the absence of ATP, muscles remain in a locked, contracted state.

In the myosin ATPase cycle, the binding of ATP leads to

the release of myosin from interaction with the actin filament.

the release of the ATP hydrolysis products (phosphate and ADP)

lead to the binding of myosin to the actin filament and the power stroke, respectively.

Ch 18

The basic organization and machinery of the cell cycle is similar among…

all eukaryotes

Which molecule fluctuates across the cell cycle

cyclin

Is cyclin a “skeleton key” (one size fits all) or is it specific to different Cdks

Different cyclins are expressed during the phases of the cell cycle and bound by the appropriate cyclin.

Anaphase-prompting complex, or cyclostome (APC/C)

large enzymes that abruptly degrade M- and S-cyclins partway through M phase. It does this by separating sister chromatid and orchestrating the carefully timed destruction of proteins controlling the cell cycle.

How does APC/C work

it tags cyclins – how? By adding chains of ubiquitin. These cyclin undergo ubiquitylation and degradation , turing Cdk inactive

How does tagging of cyclin by APC/C cause degradation of cyclins

the ubiquitylated ubiquitin causes the cyclin to be destined for the proteosome

Ubiquitination

when you add the ubiquitin on a molecule

The inactivation of M-Cdk leads to which of the following?

exiting mitosis

Example of Cdk inhibitory proteins

p27

What’s the “job” of Cdk inhibitory proteins

arrest the cell cycle at specific transition points by delaying progression through the cell cycle

How does the contractile ring pinch a cell to form 2

causes the plasma membrane to pinch, which eventually results in the formation of two separate cells.

How does a Cdk inhibitory protein do its job

binding to active cyclin-Cdk complexes and preventing Cdk from phosphorylating its target proteins.

The cell-cycle control system initiates chromosome segregation only after which of the following has occurred?

duplicated chromosomes are correctly aligned on the mitotic spindle

Why does the cell-cycle control system initiates chromosome segregation only after chromosome alginment

duplicated chromosomes are correctly attached to kinetochore proteins that interact with the microtubules of the mitotic spindle.

Which protein activates DNA replication

S-Cdk

How does S-Cdk do its job

activation of the DNA helicases in the prereplicative complex, promoting the assembly of the proteins that form the replication fork.

pre-replication complex (pre-RC) is a multi-protein structure that assembles on DNA during the late M to early G1 phase of the cell cycle to "license" replication origins, ensuring DNA is replicated only once

ORC

bind to replication origins and recruit Cdc6

Cdc6

What happens when Cdc6 degrades

re-replication is prevented

When do cells grow and duplicate organelles.

G1 and G2 phases

Condensins

proteins that assemble along the sister chromatids at the start of M phase and help them coil up into a more compact form.

The shortening and thickening of chromosomes in M phase depends on which of the following?

condensins

What triggers the assembly of condensin complexes onto the DNA

phosphorylation of condensins by M-Cdk.

When does centrosome duplication begin

S phase

When does mitotic spindle formation begin

initial stage of mitosis once interphase has completed

What happends to dynamic instanbility of microtubules at the beginning of mitosis and why

it increases due to M-Cdk phosphorylating mitrocutule-associated proteins that invluence microtuble stability

Result of changed dynamic instability behavior of mitotic spindles

they rapidly frow and shrink and extend in all directions from 2 centrosomes + new microtubules branch from sides of old microtubules

How do the 2 poles of the spindles form

this is with the help of astral and interpolar microtubulesformation

What does the random growth of mictrotubles from the centrosome allow for

astral and interpolar microtube

How do interpolar microtubules form

the centrosome starts to have more dynamic instability, causing more random growth of microtubles. When two microtubules from opposite centrosomes come into contact, their interaction is stabilized by motor and other proteins, which prevents their depolymerization.

Why does the nuclear envelope break down at the start of prometaphase?

Proteins that form the nuclear pores and nuclear lamina become phosphorylated by M-Cdk, which triggers the breakdown of the nuclear envelope.

Where do Kinetochore proteins assemble

at the centromere of each condensed chromosome.

Name three things that help the cell pull the duplicated chromosome apart/ to opposite poles in anaphase

1. Dynein proteins attach to ell cortex and pull poles apart 2. Kinesins push spindle poles apart 3. Kinetochore microtubules shorten by dypolymerization

Contractile ring – transient or stable

transient - this structure disassembles after cytokinesis is complete.

How do Mitogens function

by way of receptor-mediated signal transduction.

Mitogens

a ligand that triggers an intracellular signaling pathway that release molecules that overcome/ stop molecular brakes that block entry into the cell cycle/ S phase. In other words they help make the transition from G1 to S phase

Initiator caspases

An initiator caspase is activated by the stimulus, then cleaves an executioner caspase to activate it.

Apoptotic signal cascade

caspase cascade that uses a bunch of proteolytic cleavages.

What does Activated M-Cdk trigger

entry into M phase, where the replicated chromosomes will be distributed into two daughter cells.

What Activated S-Cdk initiate

DNA replication

What does Activated G1-Cdks and G1/S-Cdks do

help drive cells through G1 into S phase.

What happens if you inhibit APC activation

Without APC activation, the sister chromatids will remain glued together and anaphase cannot begin. In addition, inhibiting APC activation will block the destruction of M cyclin, preventing the exit from mitosis. So you’ll stay stuck in the mitosis

Growth factors

help to enlarge the cell so that daughter cells don’t shrink. They activate RTKs tha activate PI 3 kinases to activate Akts that activate Tor proteins. These Tor proteins then increase synthesis rates and decrease degradation rates

4 steps in apoptosis

1. cytoskeleton collapses, 2. Nuclear envelope disassembles 3. DNA breaks down (fragments) 4. CELL SURFACE ALTERED TO ATTRACH PHAGOCYTIC CELLS (macrophages)

Executioner caspases

activated by initiator caspases, they dismember numerous key protein

Bcl2

regulate activation of caspases and therefor apoptosis (inhibit or stimulate caspase processes). it has has both pro-apoptotic and anti-apoptotic members. Balanced activity dictates whether cell induces apoptosis or not.