Feb 14, 2005; Biology 2005 Albert Harris

 

1) Important facts omitted from recent lectures:

A) How vaccination works

After the "weeding out" process has either killed on inactivated all the lymphocytes whose (randomly-generated, remember!) binding sites bind to any of the molecules found in your own body, that leaves you with billions of different clones of lymphocytes, each of whose binding sites will fit a certain molecular shape.

Babies start out with small numbers of B lymphocytes and T lymphocytes whose binding sites will exactly fit molecules of the germs that cause polio, smallpox, mumps, hemophilus, diphtheria etc.

When you catch any infection, that stimulates the growth and mitotic division (specifically) of those lymphocytes whose binding sites fit molecules of the particular kind of germ that causes that disease, and if you survive it is because of these lymphocytes produced antibodies and T-cell receptors that killed the germs, and inactivated their molecules.

After you have recovered from an infectious disease, you are protected from catching it again by the increased numbers of lymphocytes whose binding sites fit those germs' molecules.

As time passes, the number of lymphocytes "against" that disease gradually decrease, often enough that you can catch that disease again. But the germs of some diseases are vulnerable enough to a few lymphocytes, so that you are permanently protected (unless something damages your immune system badly enough)

The key idea of vaccination is to use killed germs, weakened germs, inactivated toxins, etc. to stimulate growth and division of the lymphocytes whose binding sites will fit those germs, toxins, etc., so that you get their protection without having to suffer the disease.
Louis Pasteur invented this idea.

As mentioned in the February 11 notes, Pasteur believed in completely false theories about what causes immunity, & invented his vaccines on the basis of those false theories

The textbooks' story about Edward Jenner and the milkmaids is a fiction that each textbook copies from the others.
The truth is more interesting, and if anyone wants to hear about it then I will tell you after class.

B) Apoptosis notes have been added to the February 11 page

Fertilization:

Sperm meets egg ; sperm fuses with egg; egg refuses any other sperm.

Structure of spermatozoa cells

Acrosome Nucleus Mitochondria Flagellum (axoneme)

Compresssion and inactivation of DNA of the sperm nucleus
Most of the cytoplasm separates off from the sperm

. Formation of sperm in the walls of the seminiferous tubules

Species variations in properties of sperm:

    * 2 or more flagella
    * Amoeboid sperm of nematodes
    * Non-motile sperm of many arthropods

Activation of sperm in mammals "capacitation"

Release of acrosomal enzymes

Acrosomal filaments in some echinoderms and other invertebrates
Pushed out by assembly of special forms of the protein actin.

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The world needs new and better methods of contraception! (& you could make a LOT of money if you invented even one!$)

Existing methods of contraception:

    Rubber barriers : condoms and diaphragms
    Sperm-killing (and paralysing) chemicals
    Use of female sex hormones to affect the negative feedback cycle
    (which controls ovulation)

But notice that EVERY event which is a necessary part of fertilization, or spermatogenesis, or oogenesis, could be made a target for inhibition.

Notice differences in the location of fertilization
(in different kinds of animals) (external & internal etc.)

Sea urchins: simply release sperm and oocytes into sea water

Sea squirts: release sperm into sea water; but hold oocyte in body;

    (sperm get sucked in during filter-feeding)

Frogs, most salamanders, & most teleost fish: male and female come together, female releases eggs into the water, and then the male releases sperm onto the eggs.

Some salamanders: Males come to ponds about a week before females, and deposit gooey mucus blobs ("spermatophores").
Then, on the next rainy night, the females come to the pond and pick up the spermatophores with their rear ends and lay eggs past them.

Many fish, & all reptiles birds and mammals: Male inserts sperm into the lower end of the female oviduct, and sperm cells meet the oocytes "coming through the rye", as it were.

(I am listening to "Thistle & Shamrock" on the radio as I type this, and they were playing a song by Robert Burns)

Polyspermy

embryos die if more than 1 sperm fertilizes an oocyte

Blocks to polyspermy

Voltage changes in "resting potential" across oocyte plasma membrane

Release of cortical granules, containing enzymes, etc.

Enzymes digest molecules by which sperm stick to oocyte surface

Formation of a fertilization membrane

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Three important fusions of plasma membranes in fertilization:

Fusion of acrosomal membrane with sperm plasma membrane
Fusion of sperm plasma membrane with oocyte plasma membrane
Fusion of oocyte plasma membrane with cortical granule membranes

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Cytoplasmic rearrangements inside oocytes (after fertilization)

    Sea squirts formation of yellow crescent
      (control muscle cell differentiation)

    Teleost fish cytoplasm forms a lump at the animal pole

    Frogs & Salamanders rotation of cortical cytoplasm relative to
    deeper cytoplasm, forming gray crescent.

      (controls subsequent location of blastopore)

 

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