Cell adhesion Flashcards by Solene Sagna

Define a cell

cells are the fundemental units of life

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Types of cells and examples

Prokaryotic cells : Do not contain a membrane bound organelles or nucleues and only contains DNA eg) Bacteria and unicellular oragnanisms
Eukaryotic cells : They contain membrane bound organelles, a nucleus

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Describe all the components of the cell and state their functions

1) Cell-membrane: Seperates the inside of the cells from its external environment ( ECM) and controls the movement of molecules into and out of the cells.

2) Cytoplasm: Jelly -like fuid

3) DNA|: Located in the nucleus and stores genetic information necessary for the synthesis of proteins

4) Nucleus: Control centre of the cell that contains DNA

5) Endoplasmic Recticulum : Smooth ER contain zero Ribosomes. Transports materials in the cell
Rough ER conatins ribosomes which play a role in protein synthesis
6) Golgi Apparatus : Receives proteins in vesicles

7) Mitochondrion: Power house of the cell

8) Lysosome: Carries out wastes in the cell( An enzyme)

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Define a tissue and explain how cells organise themselves in an organism

Tissues are a set of cells arising from the same type of progenitor or stem cell

cell -> tissues -> organs -> systems

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List all the system in the human body

Skeletal system
Muscular system
Nervous system
Reproductive system
Digestive system
Respiratory system
Circulatory system

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Define cell adhesion

Cell adhesion refers to the interaction of the cells with each other and with the extracellular matrix ( ECM)

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Define adhesion proteins

Adhesion proteins are the proteins that mediate the cell-cell interaction and cell interaction with the ECM

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Define Cell cytoskeleton

The cytoskeleton refers to the network of filaments and proteins that accounts for the cell’s mechanical strength, shape , mobility and its ability to divide .

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Cytoskeleton contains 3 filaments list them

1) Actin filaments / microfilaments
2 ) Microtubules
3) Intermediate filamaments

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1) Actin filaments: Define and list some key structural components

Actin filaments are helical polymers made up of globular actin subunits
* Head to tail assembly
* contains two protofilaments forming a right handed helix
* Subunits ( Actin) is binded to ATP ( adenosine triphosphate)

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1) Actin Filaments : State the function

The actin filament allows for cell mobility and cell movement. The polymerisation of the actin filaments against the membrane drives the movement of the cell while the hydrolysis of ATP-ADP reugulates the filament growth.

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Define polymerisation of Actin Filaments list the stages

Actin polymerisation is the formation of the actin filaments. As the actin polymerizes against the membrane it results in movement of the cell.
1) Filament Nucleation
2) Filament Elongation
3) Equilibrium phase( steady state)

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Describe Filament Nucleation

The actin submunits assemble into an initial aggregate(Nucleus). forms a “seed” usually 3 sub-units

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Describe Filament Elongation

Subunits are added quickly to the ends

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Describe the equilibrium phase/steady state

This invloves the addition and dissociation of subunits. ie: As the actin subunits come to the plus end the subunits leave on the minus end.

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What is an ongoing process that happens during polymerisation

ATP hydrolysis
The actin subunits are bound to ATP (Adensosine Triphosphate )

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Describe the process of ATP hydrolyis in the stages of polymerisation.

Filament Nucleation : No ATP hydrolysis yet. Nucleus is barely stable.

Filament Elongation : During filament elongation ATP-Actin starts adding to the filaments specifically the plus end. ATP slowly starts hydrolysing into ADP at this stage.

Steady state/ equilibrium phase : At this stage the rate of actin additon = rate of actin dissociation. In the plus end you have more ATP-actin units and this is where growth is favorable. The minus end contains the already hydrolysed ADP-actin units and rate of dissociation is favorable.

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Why is ATP actin added to plus end and ADP actin dissociate at the minus end

ATP-actin is attracted to the plus end of the filament and is more stable at that end.

As the ATP-actin filament hydrolys to ADP it’ll form the ADP-actin filament but it will find itself at the minus.

On the plus end additon is faster and favorable due to change in monomer conformation in the polymer.

On the minus end addition is slower and less favorable aand this accounts for the loss of ADP-actin.

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list and explain the types of actin filaments

T form: ATP-Actin units and grows favorably
-D Form: ADP-Actin units and dissociates favorably

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Polarity of Actin filament: What are the ends called

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Plus end = Barbed end -> Favors addition due to change of monomer conformation in the polymer
minus end = pointed end - > Favors dissociation

Polarity of Actin Filament : what happens in the following scenario
C = Conc of actin subinuts
Cc= critical concnetration
C>Cc
C=Cc
C<=Cc

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C>Cc There is addtion at both ends but more on plus end. Elongation faster than disscoiation .

C=Cc This would be in the equilibrium state where rate of addition = rate of dissiociation. filament length is the same.

C<Cc The rate of dissociation is faster and there will be hydrolysis at both ends

Define Actin- Binding proteins

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These are proteins that regulate the dynamics of actin filaments in various location in the cell.

List the requirement for Actin Polymersation

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1) Actin Monomer availability
2) Filament Nucleation
3) Filament Elongation

Actin Binding proteins:
1) Thymosin
- Function

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think “timeout”

Thymosin binds to free actin monomers ( ATP-actin) and prevents polymerization.

This enables the cell to control when it builds these filaments,

Actin Binding protein: Profilin - Function - Describe how it performs its function {Mechanism}

think "pro" Profilin binds to free actin monomers and promotes polymerisation. - This is the protein the makes atp-actin attracted to the plus end beacuse profilin binds to one side of the of the monomer resulting in a conformational change of the actin monomer in the polymer thus binding to the plus end.

ATP-Binding proteins: Nucleating proteins - Function - list the proteins and their unique functions

Actin nucleating proteins initiate the filament nucleation in Actin polymerisation. 1) Arp2/3 complex : It creates branched actin filaments 2) Formin: creates unbranched actin filaments

Actin Binding proteins: Tropomyosin

Trpopmyosin binds to the side of the filament and stabalizes polymerisation

Actin Binding proteins: Capping proteins( CapZ) trigger word " lin"

Binds to the plus end of the filament and prevents addition.

Actin Binding protein: Tropomodulin

Binds to the minus end of the actin filament and stablizes the filament

Actin Binding proteins: Severing proteins

1) Gelsolin: Cuts the the filaments into shorter segments. Triggered by high Ca2+ levels 2) Cofilin: Binds to ADP- actin and promotes dissociation

2) Microtubles define and list its basic structure.

Microtubles are long hollow tubes made of globular subunits called tubulin. The are the stiffest cytoskeleton - Tubulin is a heterodimer that is formed by two globular proteins. ( alpha tubulin ) and (beta tubulin) - Tubulin subunits are binded to GTP ( Guanine Triphosphate) which hydrolyses to GDP.

Describe the function of microtubules

Microtubules account for the organisation of the organelles in the cells as well as guiding intracellular transport. Microtubles also form spindle fibres during cell devision.

Describe the polarity of microtubules

- The tubulin subunits are in a head-tail formation forming protofilaments - There are 13 protofilaments that are aligned side by side - This forms a hollow cylinder - There is a plus end which is Beta tubulin exposed ( faster grwoing end) - plus end which is beta tubulin exposed ( slower growing end) - The alpha tubulin is anchored to the centrosome

Why are microtubules so dynamic and what drives their dynamic behaviour

They constantly grow and shrink - GTP hydrolysis

Describe the process of GTP Hydrolysis

1) The Tubulin beta dimers which are bound to GTP add to the plus end as this complex is more stable. 2) Beta tubulin is hydrolysed to form GDP 3) Because of the difference in conformation of GDP it'll be less stable on the plus end causing the microtubles to shrink( Fold backwords) 4) When there are several GTP-tubulin beta it forms a GTP cap making the filament more stable 5) Loss of the GTP cap cases a catastrophe- less stable.

What does MTOC stand for and explain what it does

Microtubule- Organising centre aka Centromere 1) This is where microtublues nucleate/originate from 2) The MTOC is located near the nucleus 3) The MTOC is rich in gamma- tubulin 4) Gamma tubulin forms a gamma-tubulin ring complex that acts as a template for nucleation.

Structure of MTOC /Centrosome

- contains a pair of centrioles - contains an amorphous( has no clear shape) matrix that conatins gamma tubulin - MTOC is where the minus end of the microtubule is anchored - The plus end grows into the cytoplasm

Describe the function of the MTOC

- Positions the organelles - Helps establish cell polarity - plays a role in spindle fibre formation

List the drugs that affect microtubules

1) Taxol - stabalizing effect 2) Colchicine , Nocodazole - Destabalising effect

List how these drugs carry out their function

1) Taxol binds to the microtubules and stablizes 2) Colchicine and Nocodazole binds too the tubulin subunits preventing polyemerisation these drugs are used to kill dividing cells -> cancer treatments

What are MAPs and what are their functions

These are microtubule Associated proteins and they regulate the dynamics and organisation of microtubules.

MAPs: Stathmin

Binds two tubulin heterdimers preventing addition

MAPs: Katanin

Severs the microtubles fromMTOC promoting depolymerisation

Kinesin-13

The protein that binds to the ends of the microtublues and peels the protofilaments apart. This is the protein that caused GDP to fade away

XMAP215

The protein that adds the beta GTP tubulin to plus end promoting growth

Intermediate Filaments define

Intermediate filaments are rope- like structures that contain an alpha helical domain.

What is the function of intermediate filaments

The provide mechanical strength

Describe the structure of Intermediate Filaments

- Contains dimers and tetramers - 2 dimers that lie oppsite one another - 8 tetramers/ prtofilamemts that lie side by side laterally - The subunits are small and dissolve easliy into the cytosol - The filaments lines the inner face of the nuclear envolope protecting the DNA - The filaments twist into a cable via hydrophobic forces providing strength

Cell adhesion Flashcards

(48 cards)