Membrane proteins + Intracellular Transport

Proteins that span a plasma membrane must contain ____ where they cross the membrane

• Hydrophobic amino acids

How does a protein distinguish between a membrane-spanning hydrophobic domain and a hydrophobic domain that is folded into a pocket of the protein?

• It is coded for in the primary sequence

What does the inside of the ER =

• Outside of the cell

What are microtubules?

• They are parts of the cytoskeleton that provide a track for transport

What are the building blocks of microtubules?

• alpha and beta tubulin

  • This gives the dimer polarity, meaning it has distinct ends

What is a tubulin dimer

• alpha and beta tubulins stacked together

  • microtubule subunit

What are protofilaments

• A stack of tubulin dimers

What is the plus end of a microtubule?

• Where new dimers are added more rapidly

• Not charges

What kind of dimers are added to the plus end of a microtubule?

• GTP-bound dimers

What is a B-tubulin

• a GTPase: it hydrolyzes GTP to GDP

What are the differences between GDP and GTP?

• GDP and GTP have different numbers of phophates and thus different charges

• Different charges = different shape

What does hydrolyzing GTP do

• Hydrolyzes to GDP

• adds to the microtubule strand, leads to GTP Cap

What is dynamic instability?

• when b-tubulins hydrolyzes GTP faster than new dimers can be added

• will fall apart

What does the polarity of microtubules allow for

• directional trafficking that can happen along their length

what “motor” moves towards the minus end of a microtubule

• dynein

what “motor” move towards the plus end?

• Kinesin

What do motor proteins do?

• They bind to vesicles and move them

Where do microtubules grow from?

• grow from centrioles that contain gamma tubulin rings

• Nucleating sites increases a the chance microtubules will grow, also stabilizes it

True or false: Microtubules help organelles stay in place

• True