ACROSOME REACTION

Information Only. You will not be able to observe this happening yourself.

1.Unreacted sperm. Cannot fertilize an egg until reacted. 2. Surface receptors on the sperm react to egg jelly causing the acrosome to fuse with the plasma membrane and start the g-actin to polymerize into f-actin |||. 3. The process continues as the polymerizing actin pushes out from the sperm. 4. Actin extension is complete and the bindin molecules from within the acrosome coat the surface of the sperm. Bindin will be needed later to bind with the egg surface.

This entire process takes only a few seconds to complete.

EARLY EVENTS

TIME EVENT COMMENTS DRAWING

The sperm acrosome reacts with the egg jelly -30s Acrosome causing the acrosome reaction.

The acrosome reacted sperm binds with the 0 Binding egg. This causes an electrical change in the

egg helping prevent other sperm from binding.

The successful sperm's membrane fuses with 30s Fusion the egg's plasma membrane

The cortical granules release causing the 1-2m Cortical Rx fertilization membrane to rise, also helping to

prevent further sperm entry.

Fertilization A cone of actin forms around the sperm 5m Cone nucleus, pulling it into the egg.

10- The sperm and egg haploid nuclei fuse to Nuclei Fuse 15m become a diploid sea urchin nucleus

20- The beginnings of the mitotic spindle force the Centering 30m nucleus into the center of the embryo

50- The centrosome replicates causing a spread of Streak 60m microtubules resembling a clear streak.

80- The chromosomes line up in the center of the Metaphase 90m embryo ready for cell division.

90- First Cytokinesis, cell division occurs. The embryo 120m Division becomes 2 cells.

FERTILIZATION 1. Water currents in the ocean are much stronger than any sperm. How do sperm and egg find each other?

2. In humans there are no water currents and the volume of the female reproductive tract is relatively limited. Then, why does the male have so many sperm?

3. Why do sea urchins have external fertilization?

4. Then why don't the parents take care of the young?

5. Because the urchin life involves two or more ecological niches, they are more susceptible to predation and exposure to environmental toxins. What environmental conditions, predators and toxins might they be exposed to at each stage?

General Lab Report Layout

(name, period, date):

TITLE OF REPORT

PROBLEM OR QUESTION:

HYPOTHESIS:

MATERIALS & PROCEDURES (summary if following guide)

DATA & OBSERVATIONS:

charts, tables, graphs, drawings

IMPLICATION QUESTIONS ASSIGNED:

INTERPRETATIONS & CONCLUSIONS:

SUGGESTIONS FOR FURTHER STUDY:

 What would you change about how you did the experiment?  Given this new knowledge, what next?

NEATNESS COUNTS, OTHER SCIENTISTS HAVE TO BE ABLE TO READ YOUR WORK