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87 Cards in this Set

  • Front
  • Back

3 kinds of protein filaments

Intermediate


Microtubules


Actin

What are the different filaments composed of?

Intermediate: various fibrous proteins


Microtubules: tubulin


Actin: actin

Intermediate filaments

Rope like, strong, provides mechanical strength to cells to withstand stress

Where are intermediate filaments

A network in the cytoplasm, around the nucleus and radiating out


In the nucleus as a meshwork called the nuclear lamina under the inner membrane of the envelope

Desmosomes

Cables connecting intermediate filaments between cells in tissues to increase structure strength

Epidermolysis bullosa simplex (EBS)

Rare mutation that prevents proper keratin filament assembly

Structure of intermediate filaments

Ropes made of multiple stands that are made of filament proteins. All proteins have N-terminus globular head, C-terminus globular tail, with an alpha helical region connecting them

Subunits of intermediate filaments

2 protein units wind as a coiled coil. 2 coils line up head to tail as tetramer. Tetramers line up end to end as protofilaments. 8 protofilaments wind together to form intermediate filament

Intermediate filament assembly/breakdown

Regulated by phosphorylation of the filament proteins

Microtubules

Long, cylindrical, hollow rods, made of tubulin, help determine cell shape, provide tracks for vesicle movement, positioning of organelles, separation of chromosomes during cell division

Where are microtubules

Animal cells: originate from the centrosome and extend out

Subunits of microtubules

Tubulin subunit with an alpha and beta unit, Chains of tubulin alternating alpha and beta form protofilaments (one end is beta +, the other is alpha -), 13 protofilaments around holow core make microtubule

Centrosomes

Initiation of microtubulal assembly, - end attaches to gamma tubulins in centrosome

Dynamic instability

Alternating building and breakdown of microtubules quickly to allow remodeling of the cytoskeleton as needed

Microtubule associated proteins

MAPs proteins that help stabilize microtubules, the interactions give the cell shape and organization

Antimitotics

Drugs that fight cancer by preventing cell division through stopping assemby/breakdown of microtubules

Motor proteins

Kinesins and dyneins. Attach to cargo to pull along microtubule track. Nrg provided by ATP. Also keep organelles correctly positioned


Kinesins: towards +


Dyneins: towards -

Actin filaments

Most abundant, long fibers, cell movement, phagocyctosis, cell division, cell shape, intracellular traffic, muscle contraction

Subunits of actin filaments

Globular proteins, 3 bind as trimer, have plus and minus end, form similar to microtubules

Where are actin filaments

Just inside plasma membrane as the cell cortex

Cell movement

Actin network changes shape by growing, making protrusions that help the cell crawl/perform phagocytosis

Signal transduction

The transformation of info in the signal from one form to another

Signals that cross the cell membrane

Small, hydrophobic, steroid hormones (lipid molecules), bound by receptors inside cell

What happens when a steroid binds it's receptor?

The receptors are dormant transcriptional activator that bind to enhancers and cause transcription once bound

Stages of interphase

G1: growth phase 1


S: DNA synthesis


G2: growth phase 2

When do cells decide to divide?

Late G1. If they don't want to divide they drop out into the G0 nondividing state. This point is called START

When do cells decide to divide?

Late G1. If they don't want to divide they drop out into the G0 nondividing state. This point is called START

Factors influencing cell division

Is there sufficient food for new cells, is there the signal, how crowded is it

Cell checkpoints

Mechanisms that allow the cell to proceed from one stage to another only after the previous one is confirmed as completed correctly

Controlling cell cycle progression

Controlled by special protein kinases called Cdks, cyclin dependent kinases, that must be bound to a cyclin protein to be active

What happens to the cyclin after the cdk does its job

It is sent out of the nucleus and destroyed

Factors that regulate cdk activity

Phosphorylation on 1 binding site, none on the other 2


Cdk inhibitors: bind to Cdk to inactive thrm

What happens if a cell has damaged dna

Levels of the transcriptional protein p53 increase, increasing gene expression of p21. P21, a Cdk inhibitor, binds the S-Cdk and stops it from entering S phase until the damage is fixed

What if the damaged dna can't be fixed

P53 triggers cell death

How is DNA only copied once

Licensing factors: proteins that bind near origins of replication only during G1. They allow the initiation of replication. Once replication is started the factors are removed from the nucleus

M-Cdk/MPF

Kinase that starts mitosis


Cytoplasm of cell in M sent interphase cells into M. Each proteins was tested until the correct one was isolated


Cdk 1: constant throughout cycle cyclin B: high only before/during mitosis


How does M-Cdk work

Transfers phosphate from ATP to target proteins which activates cell pathways, triggering many of the events in mitosis

Prophase

Chromosomes condense when Condensins are phosphorylated by M-Cdk

Prometaphase

Nucleur envelope breaks down when M-Cdk phosphorylates lamins (lamina proteins)

Metaphase

Mitotic spindle forms when M-Cdk causes the phosphorylation of microtubule associated proteins. This stabilizes the microtubules so they can attach to the kinetochores of the chromosomes and align them at the metaphase plate

Anaphase

The breakdown of regulatory proteins triggers the separation of the Chromosomes

APC

Anaphase promoting complex, adds ubiquitin to regulatory proteins to start anaphase.

Securin and the cyclin component of M-Cdk

Ddgradated by APC


Securin: releases separase, which breaks the cohesins between sister chromotids


Cyclin of M-Cdk: lowering the level starts the cell back to interphase and triggers cytokinesis

Cytokinesis

Animal: Contractor ring of actin and myosin pinch the cell in 2


Plant: formation of a cell plate

Common stem cell properties

Not differentiated


Potential to divide indefinitely


Can undergo differentiation

Pluripotent

Stem cells that have the potential to differentiate into many different kinds of cells

Blastocyst

About 100 cells, has 3 structures


1. Tropoblast, surrounding cell layer


2. Blastocel, a hollow cavity


3. Inner cell mass, the group of cells that develop into the embryo proper

Somatic cell nuclear transfer

Nucleus of somatic cell used to trick oocyte into seeming fertilized and developing. Matches cells to patient

Induced pluripotent stem cells

Inducing adult differentiated cells to express key genes of embryonic cells

Apoptosis

Programmed cell death, a built in cellular process by which cells die via a regulated series of changes within the cell

Why are cells programmed to die?

1. To give form to developing embryos


2. To maintain adult tissues in balance


3. To eliminate cells that might be infected


4. To get rid of cells with lots of dna damage

What happens in cell death?

Cell sheinks, cytoskeleton collapses, nuclear envelope breaks down, DNA fragments. Cell surface signals apoptosis and it's phagocytosed by a healthy neighbor cell for recycling

Caspases

Enzymes that carry out apoptosis

What signals apoptosis

Can be internal, such as p53 causing death when the DNA is too damaged


External through cell death signals

How are caspases activated

Inactive precursors are converted to the active form by being cut by protease. Once active, the caspases can cut other precursors... caspase cascade

Protecting cells from apoptosis

Cellsurvival signals tell cells to express genes that inhibit apoptosis

Metastatis

The process of tumor cells moving to new places in the body

Initiating agents of cancer

Chemical carcinogens, radiation, viruses... it causes damage and/or mutations that can lead to cancer

Cancer cell abnormalities

Proliferation without growth hormone stimulation


Failure to undergo apoptosis


Divide indefinitely/reactivate telomerase

Oncogenes

Genes that promote cancer because when they are mutated they can cause cancer

Proto-oncogene

The original unmutated oncogene that is required for functioning


Often encode proteins that promote proliferation

Ras gene mutations

Causes mutant ras proteins that can't hydrolyzed GTP so they are stuck on and proliferation follows

Tumor suppressor genes

Normally inhibits cell division, if mutated it allows division abnormally

P53 mutations

Removes break during cell cycle between G1 and S


Allows cells with dagamed DNA to divide instead of undergoing apoptosis/repairing damage

Why are mutated p53 genes difficult cancers

Radiation damages DNA to trigger apoptosis, which won't work if p53 isn't working to signal for apoptosis

For a cell to divide it must...

Receive a growth signal


Pass the signal to intracellular molecules


Activate a cascade of protein kinases


Phosphorylate target proteins


Tumor suppressor must approve

Cancer treatments

Block growth factors


Block growth factor receptors


Prevent ras activation


P53 targeted drugs

P53 cancer drug

Virus without E1B that disables host p53 has to attack cells already lacking p53, ie cancer cells, which kills the cancer cells

Signals that can't cross the plasma membrane use

Gated ion channels


G-protein linked receptors


Receptor tyrosine kinase

Gated ion channels

Neutrotransmitters, membrane channels ions travel through, signal binds and opens gate, allowing ion flow

G protein linked receptors

Epinephrine, pass on signal with help of G proteins

Structure of G protein receptors

Polypeptide chain that threads back and forth 7 times through plasma membrane one end is extracellular to bind signal, other end is in the cytosol

G proteins

A protein that can bind GTP/GDP


3 subunits of alpha, beta, and gamma. Alpha binds GTP/GDP


Unstimulated: trimeric, GDP


Stimulated: GTP, alpha with GTP and beta gamma unit

Factors for g protein stimulation length

How long the alpha and beta gamma units bind to their targets


How long the alpha and GTP are associated

G proteins for protein kinase A

Using epinephrine


Epinephrine binds to receptor, g protein is activated, alpha subunit activates adenylate enzyme, producing cAMP a second messenger that spreads the signal

How does cAMP pass the signal on

cAMP levels are mediated by protein kinase A which is composed of 2 catalytic and 2 regulatory subunits, high cAMP activates PKA and binds to release the catalytic subunits to phosphorylate other proteins

How does cAMP pass the signal on

cAMP levels are mediated by protein kinase A which is composed of 2 catalytic and 2 regulatory subunits, high cAMP activates PKA and binds to release the catalytic subunits to phosphorylate other proteins

What happens to cAMP once it's job is done

It is broken down by phosphodiedterase

G proteins for protein kinase C

Alpha subunit activates phospholipase C which produces the second messengers IP3 and DAG

What does IP3 do

Diffuses to the ER membrane where it binds to gated calcium ion channels, releases calcium into the cytoplasm from the ER lumen. This activates protein kinase C

What does DAG do

On the plasma membrane, works with calcium to activate PKC. pkc phosphorylates cell proteins

Receptor tyrosine kinase

A cell surface receptor that also has tyrosine kinase activity. Receptor is on cell surface, kinase is on the cytoplasm

What happens when RTK binds

2 receptor molecules dimerize, bringing tails of the receptor together. The tyrosine kinase activity of the tails is activated and they phosphorylate each other's tyrosine... autophosphorylation

What does phosphorylating the RTK tails do

Triggers the assembly of an intracellular signaling complex on the tails. The tyrosine are binding sites for signaling proteins to pass the message on

RTK ras activation

One of the complex proteins interacts with ras and gives it a GTP, activating it the ras triggers a phosphorylation cascade that distribute the signal

MAP kinases

The 3 kinases activated by ras, Mitogen Activated Protein kinases

What are the common features of signal transduction pathways

Receptor


Intermediates


Target