Lecture 27 Flashcards Preview

BMS238 Molecular and Cell Biology > Lecture 27 > Flashcards

Flashcards in Lecture 27 Deck (41)
Loading flashcards...

What is the results of microinjection of dominant negative Rho into active cells

Leads to the loss of stress fibres


What changes happen at the molecular level as a result of GTP nucleotide binding to GTPases

This causes a very small conformational change dictated by the presence of a final phosphate that changes the orientation of the switch 1 and switch 2 domains. This leads to an activation of signalling


What is the role of guanine nucleotide dissociation inhibitors

GDIs effectively pull the GDP bound GTPases out of the cycle and hold it in the cytoplasm to create a pool of inactive GTPases


What is the result of microinjection of constitutively active Rho into quiescent cells

Leads to the formation of stress fibres


Why is the actin cytoskeleton not a rigid structure

Rigid structures are unstable whereas tensile cytoskeleton are much more robust. A tensile structure can temporarily adjust the application of forces to maintain its shape


In its inactive state, GTPases are bound to GDP, what is required to activate signalling

Displacement of the GDP by GTP activates the GTPase and initiates signalling


Active Rac activates WAVE proteins, what is the downstream effect of this activation

Activated WAVE proteins bind to Arp2/3 and lead to the formation of actin filaments associated with branching


What is the name of the superfamily to which all small GTPases belong

Ras Superfamily of GTPases


GTPases hydrolyse ATP, T or F

F – they hydrolyse GTP


What is the role of RhoA

RhoA stabilises and consolidates actin filaments into a more rigid skeletal framework known as stress fibres


Nucleotide-free GTPases are extremely energetically favourable, T or F

F – its extremely unfavourable


What is the rough weight of a GTPase



Actin polymerisation occurs at both ends of the filament, T or F

F – actin tends to be added at one end (+ end) and subunits are removed at the other end (- end)


What are the three members of the Rho family of GTPases

RhoA, Rac1 and Cdc42


Give an example of another important actin accessory protein and its role

Gelsolin – involved in capping existing actin filaments as well as capping and nucleation


What is the purpose of the post-translational lipid modifications often seen in GTPases

These hydrophobic lipid groups added to the proteins will target them to specific membrane sites


GTPase activating proteins are responsible for catalysing the hydrolysis of the GTP bound to GTPases, thus do they act as positive or negative regulators of GTPase signalling

GAPs are negative regulators of GTPase signalling as they promote the catalyses of GTP hydrolysis to the inactive GDP-bound form


What is the result of microinjection of constitutively active Rac or Cdc42 into cells

Leads to the formation of membrane ruffles or filopodia respectively


What are GEFs and what is the role of these proteins in the cyclic nature of GTPase activity

Guanine nucleotide exchange factors stabilise GTPases in a transition state so that GTP can then bind after GDP release


What is meant by actin filaments being referred to as polar

Actin filaments have specific ends. The + end or barbed end is the faster growing end of the filament where polymerisation is favoured. The – end or pointed end is the slower growing end where depolymerisation is favoured


Profilin is an important actin-binding/accessory protein, explains its dual roles

Profilin binds to free monomeric G-actin and transports it to the correct end of the microfilament as well as catalysing the exchange of the bound nucleotides. This all acts to promote microfilament assembly


What are the four factors that influence cell shape

Adjacent cells, cell adhesions, extracellular matrix and the function of the cell


What are the two type of actin

Monomeric or globular/G-actin and polymeric or filamentous/F-actin


What is the name of the specific 16 amino acid sequence which activated Rho proteins bind to within effector proteins

Cdc42/Rac1 Interactive Binding (CRIB) sequence


What is the result of the intrinsic nature of GTPases to hydrolyse GTP

Hydrolysis of the bound GTP by the GTPase releases a phosphate and switches it back to an inactive state


Describe a gain of function approach that can be used to elucidate the precise function of GTPases

Create a constitutively active GTPase mutant that is always on and remains in the GTP-bound form. This can be achieved by the substitution of the catalytic glutamine in the switch 2 region which perturbs GTP hydrolysis and creates an always active GTPase


What is the role of Rac1

Rac1 controls the organisation of new actin filaments, particularly branched actin, into dynamic ruffling structures or lamellipodia


What is the role of the Rho family of GTPases

They coordinate actin cytoskeletal organisation, which in turn ultimately controls cell morphology, movement and polarity


Rac activation is required to precede Cdc42 activation, T or F

F – vice versa


GTPases are small monomeric proteins, T or F