25.3
수정
수정(fertilization) 중에 난자와 정자가 융합해 새로운 이배체(diploid) 구조를 만듭니다. 인간의 경우, 이 과정은 난소(ovary)에서 난자가 방출되고 나팔관(fallopian tube) 안으로 이동한 뒤 발생합니다. 수정엔 몇 가지 주요 단계가 필요…
인간에 있어서 수정은 난자와정자 세포가 결합하여 새로운 개체를 만드는 것이다수정 전에, 투명대라는 내부 단백막으로둘러싸인 반수성 난자와지원 난구 세포의 외부 행렬이난소를 나와서 수란관으로 이동한다동시에, 단수 정자는생식관에 있어야 하고부분적으로는 자궁 수축 때문에비슷하게 수란관으로 밀려간다거기에서, 수정 능력 획득이라는성숙 과정에 들어가는데, 난자 융합 단백질이정자 머리로 전송된다여기서, 정자는 꼬리 또는 편모 움직임을보여주기 시작한다그러면 세포가 난자를 향하게 되고난자 복합체가 분비하는 황체 호르몬 같은화학 신호를 감지하여 그 위치를 찾아낸다도착하면, 정자는 첨단체 반응을 겪는데이 때 정자의 꼭지인 첨체에 있는 소화 효소를 가진소낭이 내용물을세포 밖으로 풀어 놓는데세포는 투명대를 통하여 비집고 들어간다일단 첫 정자가 단백막에 완전히들어가면, 그것과 난자 세포의 막이 합쳐진다이것이 난자를 변화시키고, 구명대가 굳어지면서다른 세포가 들어가는 것을 막아버린다수정은 정자가 난자에 내용물을 방출하면서끝난다그 결과로 생긴 2배체 구조물은 이제 두 부모의유전 물질을 포함하고 있어서 결국 새로운 개체를생성하게 될 것이다
View the full transcript and gain access to JoVE Core videos
Q1: What happens to sperm cells before they can fertilize an egg?
Sperm undergo capacitation, a maturation process where egg-fusing proteins transport to the sperm head and flagellum movements increase. Sperm then locate the egg by sensing chemical signals like progesterone released by cumulus cells. Finally, they undergo the acrosome reaction, expelling digestive enzymes that allow them to burrow through the zona pellucida surrounding the egg.
Q2: How does the zona pellucida prevent multiple sperm from entering the egg?
After the first sperm penetrates the zona pellucida and fuses with the egg, calcium signaling triggers cortical granules beneath the egg's membrane to release enzymes. These enzymes cleave sperm-binding proteins on the zona pellucida's surface, hardening it and blocking additional sperm entry. This polyspermy block ensures only one sperm fertilizes the egg.
Q3: What role does calcium signaling play in egg activation after fertilization?
Sperm-egg fusion initiates calcium ion waves pulsing through the egg cytoplasm. These Ca2+ oscillations activate kinases in the egg that restart meiosis, which was arrested when the egg was released from the ovary. Calcium signaling essentially awakens the egg, allowing it to resume division and prepare for embryonic development.
Q4: What happens to the egg's chromosomes during meiosis completion after fertilization?
After fertilization triggers meiosis resumption, the egg divides into a large mature ovum containing most cytoplasm and a smaller polar body that dissolves. The mature egg's nucleus, called the egg pronucleus, contains one set of unduplicated chromosomes. This haploid nucleus will soon fuse with the sperm pronucleus to form a diploid embryo.
Q5: How do the sperm and egg pronuclei combine to form a diploid nucleus?
When the sperm nucleus enters the egg, its membrane dissolves and chromosomes unpack. A new nuclear membrane forms around the loosened sperm material, creating the sperm pronucleus. The sperm's centrosome orients between both pronuclei, forming microtubules that draw them together. Their membranes dissolve, chromosomes mingle, and mitosis begins, combining both parents' genetic material.
Q6: What structures guide sperm toward the egg in the fallopian tube?
Sperm are driven into the fallopian tubes partly by uterine contractions. Once there, they sense chemical signals like progesterone released by the cumulus cell complex surrounding the egg. These chemical cues guide sperm toward the egg, enabling them to locate and approach it for fertilization.
Q7: What happens after the sperm and egg membranes fuse during fertilization?
Once sperm and egg membranes fuse, the sperm releases its contents—including its nucleus and centrosome—into the egg's cytoplasm. The zona pellucida hardens, blocking other sperm from entering. The diploid structure now contains genetic material from both parents and will undergo embryogenesis cleavage and blastulation to eventually generate a new individual.