Question

1. The axoneme of a eukaryotic cilium ____________________.

   	a	contains complexes of actin filaments and microtubules
   	b	contains nine (9) central microtubules and two (2) peripheral microtubules
   	c	has a completely different structure than the axoneme of a eukaryotic flagellum
   	d	contains two (2) central microtubules surrounded by nine (9) microtubule pairs

QUESTION 23

1. Receptor tyrosine kinases (RTKs) ____________________.

   a		must be phosphorylated by a separate enzyme (PI3 kinase) before other proteins can dock with them
   b		usually signal through small monomeric GTPases, but some can signal through other pathways
   c		always signal through small monomeric GTPases
   d		usually activate signaling pathways that inhibit growth and antagonize cell survival

QUESTION 24

1. Match each type of actin-binding protein with its function.

   -       A.       B.       C.       D.	Bundling protein
   -       A.       B.       C.       D.	Nucleating protein
   -       A.       B.       C.       D.	Capping protein
   -       A.       B.       C.       D.	Cross-linking protein

   A.	Joins actin filaments side-to-side
   B.	Joins actin filaments into web-like networks
   C.	Initiation site for growth of a new actin filament
   D.	Binds to plus (+) ends of actin filaments and prevents depolymerization

Answer 1

Question 22

The correct answer is option d - contains two (2) central microtubules surrounded by nine (9) microtubule pairs

Explanation: Eukaryotic flagella and cilia are identical in structural organization and contains a pair of central microtubules which remain surrounded by 9 pair of outer microtubules.

Question 23

The correct answer is option b - usually signal through small monomeric GTPases, but some can signal through other pathways

Explanation: RTK is trans autophosphorylated which means when one ligand bind to RTK, they first dimerize and then a tyrosine in the cytoplasmic portion of each receptor monomer are trans-phosphorylated by its partner receptor. No separate kinase is needed. The activated RTK often transform its signal through small GTPase like Ras protein that acts downstream and propagate the signal. Besides these small GTPase, RTK also transduce signal through MAP kinase pathway. So correct answer is option b.

Question 24

The proper matching is shown below:

Binding protein - Joins actin filaments side-to-side (A)

Cross linking protein - Joins actin filaments into web-like networks (B)

Capping protein -  Binds to plus (+) ends of actin filaments and prevents depolymerization (D)

Nucleating Protein -  Initiation site for growth of a new actin filament (C)