Chapter 9 Flashcards
The basics of microtubules structure
- largest of the cytoskeletal components
- 13 straight, hollow, noncovalently bonded globular dimers to form a heterodimer
(a-tublin and B-tublin)
what are MAP’s?
Microtubule Associated Proteins
- increase the stability and promote stability
Energy Source of the Tublin
alpha tublin (NEGATIVE END)
- has a GTP trapped in its monomer that can never be hydrolyzed
Beta tublin (POSITIVE END)
- has a GDP or GTP in its monomer that can be hydrolyzed
What is a microtubules organizing centre and what does it do?
MTOC’s is where they microtubules grow from
they also control these aspects of their assembly
- polarity
-number of MT
- location
- timing
dynamic of microtubules
the process of growing and shrinking is called dynamic instability
- the dislocation rate of GDP tublin dimer is more rapid than GTP tublin dimer
What are motor proteins and what do they do?
they convert ATP into mechanical energy making them able to move unidirectionally on the cytoskeletal track in a stepwise manner
What are the 3 types of molecular motor
- kinesin and dynein move along the microtuble track
- myosin moves along the microtubule track
Function and directionality of Kinesin
-anterograde microtubule motor (moves forward (positive direction))
- walks progressive in a hand over hand manner
- each step is the length of one tublin dimer
Function and directionality of Dynein
retrograde microtubule motor (moves back to nucleus (negative direction))
- walks progressive in a hand over hand manner
- each step is the length of one tublin dimer
How can motor proteins be regulated?
Melanomsome aggregation is done by dynein
Melanosome diapered is done by kinesin
What are the stages the cell cycle
- Go
- G1
- S
- M phase
What is Go phase
the resting phase
What is G1 phase
growth phase: RNA and protein synthesis (6-12 hours)
What is S phase
synthesis phase : DNA synthesis doubles the amount of DNA in the cell and RNA and protein sysnthsis still occur (6-8h)
What is the G2 phase
growth phase 2: more RNA and protein synthesis. DNA synthesis seizes (3-4h)
What is the M phase
Mitosis and Cytokinsis occurs (1h)
What is interphase
The stage when the cell is not dividing (G1, S & G2)
What is cytokinesis
when the cell spilts into 2 daughter cells
What is a centrosome
is the best studied microtubule organization centre and its where they microtubules grow from
What is a centriole
short cylinders of modified microtubules
What is the nucleation of microtubules by gamma TURC
growth of the microtublues: subunits are added to the plus end of them
What are the 3 types of microtubules and roles
- Kinetochores: attach to the chromosomes
- Astral microtubules : orient and stabilize the spindle during cell divison
- polar microtubules: pushing the cells away from each other by pushing on the opposite MT
What are the microtubules doing in prophase?
- the centrosomes form a MTOC and the MT beginning to elongate
- the nuclear envelope dissembles
What are the microtubules doing in prometaphase?
- Kinetochore attach to the centromeres of the chromosomes
one side’s microtubules will grow and the other shrinks
What are the microtubules doing in metaphase?
the kinteochores are equal length on both sides
What are the microtubules doing in anaphase?
the polar MT are pushing apart the cells by a four headed kinesin family motor protein
-tublin is lost at the minus ends to be added to the plus ends
What are the microtubules doing in telophase?
the mitotic spindle disassembles
What’s the characteristics of intermediate filaments
- strong flexible ropelike fibres that give ,mechanical strength to cells that are in physical stress
Role of plectin
they are elongated dimeric proteins that create cross bridges in intermediate filaments
Role of Lamins
to create the nuclear lamina
what regulates the assembly an disassembly of intermediate filaments
they are controlled by subunit phosphorylation and dephosphorylation
What is the structure of G-actin?
globular (when no ATP is present)
What is the structure of F-actin?
filamentous (in the presence of ATP it becomes flexible)
structure of actin
it is polar and it has
- Minus End (pointed end) where the binding cleft is exposed to bind with the plus end
- Plus end (barded end)
Actin Disassembly and assembly
in vitro - plus and minus ends have different polymerization rates
in vivo- polymerization only occurs at the plus ends by ATP-actin (the minus end is probably anchored)
What is myosin?
molecular motor that has a binding spot to ATP and actin
- there’s 2 classes called conventional (found in the muscle cells) and unconventional
Structure of myosin 2
1) pair of globular head with catalytic site
2) a pair of necks each with a pair of light chains
3) 2 intertwining heavy chains
The role of myosin 2 in muscle contraction
conventional, to pull the actin making cross bridges that help the muscle contract
Role and polarity of Cap Z in muscle contraction
caps the act an the plus end
Role and polarity of tropomodulin in muscle contraction
caps the - end of actin and regulates the length of the actin filament
Role and polarity of myomesin in muscle contraction
bundles the myosin filaments
Role and polarity of titan in muscle contraction
extends through the myosin bundle and attaches to the z line (helps prevent tearing)
Role and polarity of nebulin in muscle contraction
binds actin filament to z line
What is the structure of G-actin in vivo
Role and polarity of troponin in muscle contraction
when Ca2= binds on it, it allows it to move tropomyosin off of the myosin binding site.
Role and polarity of tropomyosin in muscle contraction
it covers the myosin binding site on the actin filament when there is not activity in cell
What is the assembly of F-actin in vivo
What is profilin
Polymerization: it functions as adenine nucleotide exchange
- it bind to the plus end of ADP actin changing t into ATP actin so it can join the growing filament
what is cofilin
Depolymerization: it binds to ADP actin and severs filaments promoting depolymerization
what is thymosin
Storage or Pause of Polymerization: binds to ATP actin prevent them from polymerizing
role of the Arp complex
not considered a true actin fitment but shares characteristics of it
it helps polymerize by binding to the side of it along with an activating protein called WASP (Wiskott-Aldrich syndrome protein)
The fundamentals of the branching and elongation of the Arp complex (relation to cell mobility)
1) signal for case to initiate
2) WASP activates Arp and new filaments grow at plus end
3) then causes membrane to put up
4) Coflin depolymerizes old filament
5) Profile will exchange the GDP for GTP
What is Rho
regulates the actin skeleton
What is GDI and its role
guanine nucleotide dissociation inhibitor
- prevent rho from interacting with its GEF
compare and constrast microtubules, actin and intermediate filaments
