Structure of the Gametes Gilbert Ch. 7 pp

Structure of the Gametes: Sperm Parts of mature sperm: Head –Haploid nucleus –Little cytoplasm –Acrosome Neck/Midpiece –Mitochondria –Centriole Tail (or propulsion system) –Some species - ameboid motion –Most sperm are propelled by flagella Formed by microtubles Highly Specialized Cell Type!

Gilbert - figure Sperm maturation

Figure 7.2(1) The Modification of a Germ Cell to Form a Mammalian Sperm

Figure 7.2(2) The Modification of a Germ Cell to Form a Mammalian Sperm

Figure 7.2(3) The Modification of a Germ Cell to Form a Mammalian Sperm

Flagella structure Must allow sperm to travel long distances, using plenty of energy Axoneme: motor portion –Microtubules in a 9+2 configuration 2 central microtubules, 9 doublets Made up of the protein tubulin Dyenin molecules attach to microtubules and provide motor activity by hydrolysis of ATP Allows filaments to slide and flagellum to bend

Sperm Capacitation Upon release, mammalian sperm are able to move, but do not yet have the capacity to bind an egg Must enter the female reproductive tract to complete the last step of the maturation process (Capacitation) and acquire the ability to bind the egg

Structure of Gametes: The egg Ovum (mature egg) stores all material for beginning of growth and development Unlike sperm, the egg conserves and acquires more cytoplasm as it matures Synthesizes and stores proteins (like yolk) as reservoirs for the developing embryo The components of the egg vary from species to species

Structure of the gametes: The egg PARTS OF THE EGG: Cytoplasm - many components Haploid nucleus Cell membrane – will fuse with sperm plasma membrane Vitelline envelope –Contains glycoproteins essential for species specificity & sperm binding Zona pellucida (mammals) extra coating made of Extracellular matrix

Structure of the Gametes: The egg (cont’d) Cumulus (mammals): layer of cells that nurture the egg –Innermost layer is called Corona Radiata Cortex –Beneath the cell membrane –Gel-like cytoplasm - may help sperm entry into the cell Cortical granules –Inside cortex –Membrane bound vesicles (like the acrosome in sperm) –Help prevent polyspermy Egg jelly (some species) –Attract/activate sperm

Sea urchin egg at fertilization

Eggs are protected by elaborate envelopes Vitelline envelope: a glycoprotein layer covers the plasma membrane of all eggs. This acts to protect the egg. Eggs that are deposited in water have a jelly-like coating that surrounds the egg (frogs eggs) Eggs that are deposited on land have particularly elaborate envelopes. The eggs of birds have a vitelline envelope, a fibrous layer, an outer layer of albumin (egg white), and a shell composed of calcium carbonate. The outer envelopes are synthesized in the oviduct after the egg has been fertilized.

Egg Cytoplasm Proteins: energy, amino acids mRNA –To provide early instructions for development Ribosomes and tRNA –To aid in protein synthesis early in development Morphogenetic factors –Molecules that effect differentiation of various cell types (can be localized to specific areas of the cell) Protective Chemicals –UV filters, DNA repair enzymes, antibodies (birds)

Egg maturation at the time of fertilization in various species

HUMANS

Hamster Eggs Before Fert.