Structure of the gametes
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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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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

    • Most sperm are propelled by flagella

      • Formed by microtubles


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 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.


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.


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