Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Structure of the Gametes Gilbert Ch. 7 pp. 175-180 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 19.19 - 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.