Week 4

Question 1

briefly describe the mechanism of cell motility and the involvement of Rho,Rac , location of cell action?

Answer 1

BACK OF CELL
- Rho activation occurs, leads to MLC phosphorylation by Rho kinase, formin upregulation— focal adhesion formation, integrin clustering– inhibits Rac for the moment

Rac ACTIVATION by cdc42– FRONT OF CELL
- Rac phosphorylation leads to removal of capping (via PIP2), filament cross-linking (via PAK), and branching (via Wasp->ARP2/3)
—> LAMELLIPODIA formed

Question 2

what is the result of Cdc42 activation on the the front of a cell (in terms of WASP, actin, and location of impact)

Answer 2

filopodia formation at the front of the cell due to WASP activation of Arp 2/3–> leading to actin polymerization
- activation of Par6 as well–> gives polarity

Question 3

describe the role of cdc42 on front end cell activity and consequences of activation (cdc42-GTP)
- impact on actin polymerization?
- impact on dynein motor protein

Answer 3

cdc42 is Rho family monomeric GTPase whose activation occurs on the inner surface of the plasma membrane
– leads to actin polymerization, and eventual bundling resulting in lamellipodia formation

actin polymerization occurs via
- cdc42-GTP–> WASP, Rac-GTP->WAVE activation–>Arp2/3 complex activation–> nucleation of actin filament

ALSO
activation of Par6 protein induces dynein activation– polarity induction

Question 4

distinguish the difference between formin, Arp2/3 in terms of their role in facilitating actin nucleation

Answer 4

formin– dimeric proteins that nucleate growth of unbranched filaments at focal adhesions.
- Arp2/3— complex that nucleates NEW actin filament growth– binds to sides of existing “mother filaments” and allows branching

Question 5

purpose of oxygenic photosynthesis in terms of
light energy conversion
- ATP
- NADP

Answer 5

• conversion of light energy into chemical
  ATP formation via chemiosmotic means
• reduction of NADP—>NADPh

Question 6

Site of photosynthesis– briefly describe structure
- what structure represents the “cytosol” of the plant cell

Answer 6

thylakoid membrane– site of photosynth
- stroma acts as the plant cytosol– important for ETC

Question 7

Describe PSII in terms of
- function
- relation to PSI

Answer 7

• captures light energy via chlorphyll antenna (P680) and passes electrons to PSI

Question 8

end goal of electron passing from PSII–PSI— down chlorophylls with longer absorption max
(hint: Forster energy transfer)

Answer 8

physical energy i.e. excited, delocalized electron cloud is being transferred DOWN towards reaction center between chlorophylls that are:
- small distances away from one another
- have a small difference in absorption max

Question 9

Purpose of light harvesting complex/ movement of energy towards the reaction center

Answer 9

• goal is to facilitate electron displacement —which will be used in the ETC to generate electrochemical gradient– ATP synthesis

Question 10

role of H2O as the end reducing agent in ETC?

Answer 10

• H2O oxidation into O2— releases electrons– allows replenishing of reaction center electrons

Question 11

importance of pyrrole ring in chlorophyll A,B in terms of
- Mg interaction
- electron organization
- energy movement

Answer 11

having a delocalized electron structure— allows light absorption/passing towards reaction center complex

Question 12

purpose of light harvesting complex

Answer 12

• ensures unidirectional movement of energy towards reaction center

Question 13

displaced electrons from PSI/light reaction are used for what

Answer 13

• H2O oxidation

Question 14

due to energy loss of electrons upon arrival in PSI, how are electrons re-energized/replenished?

Answer 14

Oxidation of P700 reaction center of PSI leads to reduction of NADP to NADPH