BIO1022 Lecture 13: BIO1022 – Lecture 13
30 May 2018
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BIO1022 – Lecture 13
- an organisms development is determined by the genome of the zygote and by
differences that arise between early embryonic cells
- cell differentiation is the specialisation of cells in their structure an function
- morphogenesis the process by which an animal takes shape
- cleavage, gastrulation and organogenesis
- fertilisation
• bring together the haploid nuclei of sperm and egg together to form a
diploid zygote
• contact of the sperm with the eggs surface initiates metabolic reactions
within the effect that triggers onset of embryonic development
•
o two important reactions - preventing polyspermy
o
▪ acrosomal reaction
▪
▪ sperm generates jelly coat - enters the egg
▪ Hydrolytic enzymes released from the acrosome
make a hole in the jelly coat, while growing actin
filaments form the acrosomal process. This structure
protrudes from the sperm head and penetrates the
jelly coat, binding to receptors in the egg cell
membrane that extend through the vitelline layer
▪ recognition of egg and sperm
▪ contact and fusion of sperm and egg membranes
▪
▪ causes dépolarisation of the egg cell
membranes - first block to prevent
polyspermy
▪ A hole is made in the vitelline layer, allowing contact
and fusion of the gamete plasma membranes. The
membrane becomes depolarized, resulting in the
fast block to polyspermy
▪ entry of sperm nucleus
▪ -fast block polyspermy
▪ cortical reaction
▪
▪ slow block polyspermy
▪ Fusion of the gamete membranes
▪ triggers an increase of Ca2+ in the egg’s cytosol,
causing
▪ cortical granules in the egg to fuse with the plasma
▪ membrane and discharge their contents. This leads
to
▪ swelling of the perivitelline space, hardening of the
▪ vitelline layer, and clipping of sperm-binding
receptors.
▪ The resulting fertilization envelope is the slow block
▪ to polyspermy.
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Document Summary
An organisms development is determined by the genome of the zygote and by differences that arise between early embryonic cells. Cell differentiation is the specialisation of cells in their structure an function. Morphogenesis the process by which an animal takes shape. The membrane becomes depolarized, resulting in the fast block to polyspermy: entry of sperm nucleus. Fast block polyspermy cortical reaction slow block polyspermy: fusion of the gamete membranes triggers an increase of ca2+ in the egg"s cytosol, causing cortical granules in the egg to fuse with the plasma, membrane and discharge their contents. In some mammals, the development of the embryo is temporarily suspended at the blastula stage in a process known as embryonic diapause. Holoblastic vs meroblastic cleavage: holoblastic cleavage refers to complete division of eggs and is seen in animals whose eggs contain little or moderate amounts of yolk.
