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Structure of the Gametes

Structure of the Gametes. Gilbert Ch. 7 pp. 175-180. Structure of the Gametes: Sperm. Highly Specialized Cell Type!. Parts of mature sperm: Head Haploid nucleus Little cytoplasm Acrosome Neck/Midpiece Mitochondria Centriole Tail (or propulsion system) Some species - ameboid motion

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Structure of the Gametes

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  1. Structure of the Gametes Gilbert Ch. 7 pp. 175-180

  2. Structure of the Gametes: Sperm Highly Specialized Cell Type! • 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

  3. Gilbert - figure 19.19 - Sperm maturation

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

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

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

  7. 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

  8. 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

  9. 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

  10. 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

  11. 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

  12. Sea urchin egg at fertilization

  13. 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 ajelly-like coatingthat surrounds • the egg (frogs eggs) • Eggs that are deposited on land have particularly elaborate envelopes. The eggs of birds have avitelline 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.

  14. 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)

  15. Egg maturation at the time of fertilization in various species

  16. HUMANS

  17. Hamster Eggs Before Fert.

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