Question

What happens after a sperm has penetrated the extracellular coat of the egg?

Answer 1

Fertilization happens when the nuclei of a sperm and an oocyte (egg) unite. Because each of these reproductive cells is a haploid cell that contains half of the genetic material required to make a human being when they are combined, a diploid cell is formed. A zygote is a new single cell that includes all of the genetic material needed to make a human, half from the mother and half from the father.

Complete answer:
When a sperm penetrates the egg's extracellular coat, it binds to the egg plasma membrane, which covers the tips of microvilli on the egg's surface. The neighbouring microvilli elongate fast, and a ring of microvilli around the sperm guarantees that it is firmly attached so that it may fuse with the egg. Because microvilli are resorbed, the entire sperm is brought head-first to the egg after it fuses.

During the acrosome reaction, fertilising, a transmembrane protein, is exposed to the surface of the sperm in mouse sperm. This helps the sperms attach to the egg's plasma membrane and may play a part in the two plasma membranes joining together. A sperm interacts with the egg plasma membrane atop the tips of microvilli on the egg surface after penetrating the egg's extracellular coat.

Fertilization is a math problem. Hundreds of millions of sperm (spermatozoa) are discharged into the vaginal canal during ejaculation. Almost immediately, the acidity of the vagina (pH 3.8) overcomes millions of these sperm, and millions more may be stopped from entering the uterus by thick cervical mucus. Thousands of those who do get in are killed by phagocytic uterine leukocytes. As a result, the race into the uterine tubes, which is the most common location for sperm to meet an egg, is reduced to a few thousand competitors.

Their voyage, which is believed to be aided by uterine contractions, takes anywhere from 30 minutes to 2 hours. If the sperm do not meet an oocyte right away, they can survive for another 3–5 days in the uterine tubes. If intercourse occurs a few days before ovulation, conception can still occur. An egg, on the other hand, can only live on its own for about 24 hours after ovulation. Intercourse that occurs more than a day after ovulation is unlikely to result in conception.

Fluids in the female reproductive system prepare the sperm for fertilisation during the voyage through a process known as capacitation, or priming. Spermatozoa motility is improved by the fluids. They also deplete cholesterol molecules contained in the membrane of the sperm head, weakening the membrane and making it easier for lysosomal (digestive) enzymes to be released, allowing the sperm to penetrate the oocyte's surface once contact is achieved. To have the “capacity” to fertilise an egg, sperm must go through a process called capacitation. They will be unable to penetrate the oocyte's thick outer layer of cells if they arrive before capacitation is complete.

Note: When the head of a sperm adheres to the zona pellucida surrounding the egg in a species-specific manner, mammalian fertilisation occurs. This causes the sperm to undergo the acrosome reaction, releasing the contents of its acrosomal vesicle and exposing enzymes that assist the sperm digest its way through the zona to the egg plasma membrane, where it will merge with it.