Lab 1 - fertilization in sea urchins

Question 1

What is the egg type and cleavage type of a sea urchin?

Answer 1

Egg type = isolecithal
Cleavage = radial, equal holoblastic

Question 2

Describe how the sperm is attracted to the egg

Answer 2

sperm moves up a resact gradient and contacts the egg

Question 3

Describe the acrosomal rxn

Answer 3

1. polymerization of actin in sperm head
2. formation of acrosomal filament
3. digestive enzymes released by sperm to break down jelly coat

Question 4

What does the acrosomal filament do?

Answer 4

Binds to the vitelline membrane
- specific proteins (bindin) on sperm and vitilline membrane confers species specificity

Filament continues to digest through to p.m. + causes fast block + corticol rxn in egg to prevent polyspermy

Question 5

Describe the fast block to polyspermy

Answer 5

Egg depolarization:

• Na+ in, H+ out –> +ve charged memb, increase pH of egg cytoplasm –> prevents other sperm from making contact
• cannot stay like this for long

Question 6

Describe the slow block to polyspermy

Answer 6

Corticol rxn
- Ca2+ released
- high pH + high [Ca2+] –> egg protein/DNA synthesis –> cell division
- cortical granules bind to the vm –> f.m

Question 7

Where are sperm granules released, what are the protein in the granules and what does each one do?

Answer 7

Where = granules fuse the v.m and are released into space between vitilline membrane and p.m

• proteases –> break down bindin R
• proteoglycans –> changes the osmotic gradient between fertilization membrane and p.m
• peroxidases –> crosslink the fertilization membrane + makes the fertilization a hard shell
• hylain –> protein that forms an impermeable shell + provides support for the blastomeres

Question 8

How is the egg metabolism induced?

Answer 8

• low H+ during fast block –> increase cellular pH
• Ca2+ release –> activation of metabolism
• increase in O2 consumption –> increase protein/DNA synthesis + activatoin of enzymes –> cleavage
• yolk = food supply until free-swimming larva forms

Question 9

Describe the cleave divisions of sea urchins, when does determinate cleavage occur?

Answer 9

1. meridional division
2. meridional but perpendicular to the first
3. equitorial but displaced towards the animal pole (determinal cleavage –> creates animal half and vegetal half)
4. animal half –> mesomeres, vegetal half –> micro and macromeres
5. creation of a blastula with a blastocoel

Question 10

What is gastrulation?

Answer 10

the movement of the blastomeres relative to each other resulting in the formation of the 3 germ layers: ectoderm, mesoderm, endoderm

Question 11

Describe the gastrulation events of sea urchins

Answer 11

1. some blastoderm cells ingress, becoming primary mesenchyme
2. other blastoderm cells invaginate to form the archenteron from the blastopore
3. cells at the sides of the archenteron elongate

Question 12

List the features of a sea urchin larva

Answer 12

• mouth
• feeding arms
• spicules
• anus

Question 13

How is spawning induced in sea urchins

Answer 13

injection of KCl

Question 14

Describe what sea urchin sperm and eggs appear as

Answer 14

sperm = white and cloudy
egg = coloured (yellow or red)

Question 15

Why is DMSO used?

Answer 15

good solvent - can integrate things that are more hydrophobic

Question 16

What is an ionophore?

Answer 16

A substance that is able to transport ions across a membrane