Multicellularity 1

Question 1

How many times has multicellularity evolved?

Answer 1

• 6 times in plants
• 3 times in fungi
• 1 time in animals (metazoa)

Question 2

What is the closest single celled relative to animals?

Answer 2

Choanoflagellates

Question 3

Explain the structure of choanoflaggelates

Answer 3

• flagella
• collar

Question 4

What do choanoflaggelates eat?

Answer 4

Bacteria

Question 5

What is the presence of actin and tubular in choanoflagellates?

Answer 5

• actin - the colar
• tubulin - the flagella

Question 6

What is the animal that choanoflaggelates relate to?

Answer 6

sponges

Question 7

What is a choanocyte?

Answer 7

• cell type of the sponge
• has a flagellum and collar

Question 8

What are 2 cell types that sponges don’t have?

Answer 8

• nerves
• muscle

Question 9

What are the 2 types of tyrosine kinases?

Answer 9

• receptor tyrosine kinases (RTK)
• cytoplasmic tyrosine kinases (CTK)

Question 10

Explain tyrosine kinases in choanoflagellates and sponges / animals

Answer 10

• cytoplasmic ones found in the common ancestor to choanoflagellates and animals
• receptor ones found only in choanoflagellates and animals, not in choanoglagellates precursor

Question 11

Explain cadherins in choanoflagellates

Answer 11

• they are present (23 of them)
• contained SH2, IgG and Hh domains which animal cadherins don’t normally have
  -they don’t have the section that would bind cadherin to actin
• most common in the collar
• thinking they evolved not for cell-cell adhesion but to bind bacteria for food

Question 12

explain the interactions of Src and Csk

Answer 12

• Csk phosphorylates tyrosine in the tail of Sir
• will fold only SH2 domain
• shuts down Src
• Csk is a negative regulator

Question 13

explain the interactions of Src and Csk in chanoflaggelates

Answer 13

• negative inhibition doesn’t happen, but phosphorylation does