Fertilization Flashcards
Fertilization is?
when the sperm enters the egg and a zygote is formed in order to propel the 1st stages of development
a complex sequence of chemical cascades
Major steps in fertilization (4)
- Contact and recognition
- Regulation
- Fusion of male and female genetic material
- Activation
Sperm Cell Structure
- Acrosome
- Nucleus
- G-actin
- Centriole
- Axoneme
- Mitochondria
Acrosome
- Contains enzymes that can digest proteins and the egg jelly
- Bindin protein - adhesion of the sperm acrosomal process to the vitelline layer
Nucleus
Haploid - contains 1/2 of the genetic material needed for fertilization
G-actin
Globular actin - in b/w the acrosome and the nucleus, can polymerize and create F-actin microfilaments that can change the cell shape
Centriole
MTOC - microtubule organizing center: long polymers of the tubulin proteins
Axoneme
Structure formed by microtubules connected to the centriole; major portion of the flagellum
Egg Cell Structure
- Egg Cortex
- Cortical Vesicle
- Vitelline Layer
- Jelly Coat
- Follicular cells
- Egg plasma Membrane
Egg Cortex
gel-like, stiffer, contains lots of g-actin f-actin
Cortical Vesicle
membrane bound vesicles inside the egg cortex
contains:
- Glycosaminoglycans (GAGs)
- Enzymes
- can help hold cells together
Vitelline Layer
Fibrous mat close to the egg plasma membrane. Contains bindin receptors
Jelly Coat
Made of GAGs and glyco-proteins, triggers acrosomal rxn in sperm. Can attract sperm / activate sperm
The Cytoplasmic trove includes
- Nutritive proteins
- Ribosomes & tRNA
- mRNA
- Morphogenetic factors
- Protective Chemicals
Nutritive proteins
supply of energy and amino acids
Ribosomes & tRNA
accomplishes protein synthesis
mRNA
accumulates proteins then encodes proteins for the early stages of development
Transcription factors
bind to chromosomes
get into the nucleus of the developing embryo to turn genes on/off
para crine factors
released to the outside of the cell to affect the behavior of neighboring cells
Sperm Mobility
Sperm become active in sea water due to the change in pH that activates Dynein.
Sperm finds the eggs through chemotaxis, direction is provided by resact
Acrosome Reaction
When the sperm membrane comes into contact with the egg jelly:
- Ca++ channels open and calcium ions from SW rush into the sperm
- Sodium/Hydrogen exchange pump opens –> pH rises in the sperm head
- Rise in IP3 –> release of Ca++
Exocytosis
Triggered by the rise in Ca++
A membrane bound vesicle fusing with the plasma membrane to release its contents leading to actin polymerization (g-actin to f-actin)
Egg Response
- Na+ influx
- Change in egg cell electrical potential
- Electrical “shiver” = Fast Block to polyspermy
Fertilization Envelope
Modified vitelline layer, separated from the surface of the egg, no bindin receptors, Slow Block
