Lecture 1 - Gametes&Fertilazation Flashcards
What is meiosis?
Gametes get half the number of chromosomes
Can you explain the steps during meiosis to produce haploid daughter cells? (Telophase)
1) The DNA condenses to become the sister chromatids
2) Metaphase 1 - Sister chromatids move to the centre of the cell by spindle fibres formed by the centrioles. Crossing over genetic information happens.
3) Anaphase 1 - The Sister Chromatids, split into 2 diploid chromosomes because the spindle fibres contract towards the centrioles.
4) Metaphase 2 / anaphase 2- Same as metaphase however, the diploid chromosomes become haploid
5) Produces for gametes
When and where does spermatogenesis begin?
In puberty in the testis
What are spindle fibres made of?
Protein structures.
Can you recall the tissues that Spermatogenesis uses to produce spermatozoa? (5 tissues)
1) Spermatogonia are diploid cells and are progenitor cells for spermatogenesis.
2) Spermatocyte 1 - initiates meiosis, however still diploid cells.
3) Spermatocyte 2 - The cells that go through meiosis and are haploid cells, change shape to form Spermatid
4) Spermatid- finished product of spermatocyte 2, immature spermatozoa
5) Spermatozoa - Released in the lumen as a mature male sex cell.
Can you explain the structure of spermatozoa?
Head - Ancrosomes /Nucleus/ Centriole
Tail - Mitochondria / Tail
What are the three phases in spermatogenesis called?
1) Proliferative phase - Retinoic Acid at puberty induces Spermatogonia to increase by mitosis
2) Meiotic Phase - Produces haploid spermatids
3) Post-meiotic shaping - Post-meiotic shaping called spermiogenesis produces spermatozoa
Where does spermatogenesis take place?
Seminiferous tube
Can you explain how Seprmiogenesis shapes a spermatocyte into spermatozoa?
1) The Golgi apparatus first forms the acrosomal vesicle and granule and then detaches.
2) Centriol attaches to the nucleus and starts forming the flagellum made of tubulin protein
3) The acrosomal vesicle moves towards the wall of the cell, and the flagellum grows larger forming spermatozoa.
Why is the Golgi apparatus important in Spermiogenesis?
Produces the acrosomal vesicle and granules on spermatozoa
Where are spermatozoa collected after they released from the testis?
Epididymis
Can you define Capacitation?
The final maturation of sperm in the female reproductive tract
Can you define Oogenesis?
The formation of the egg
What does Luteneizing hormone due in Oogenesis
Hormone induces the eggs of a female to progress in meiosis
What is an important peculiarity in Oogenesis Meiosis?
1) Only gamete is pronounced an can fertilise, the rest of the cells become polar bodies
2) Fertilisation takes place during second metaphase (In humans)
Explain the structure of the Ooctye
1) Cumulus - nearer the egg is called the Corona Radiata
2) Matrix - Zona pellucida proteins
3) Membrane
4) Nucleus of egg
What is find in the Nucleus of the egg?
1) Mitochondria
2) Nutritive proteins (Yolk Proteins) - produced in liver
3) Ribosomes and tRNA
4) mRNA
5) Morphogenic factors controlling expression
Where is the egg released and fertilisation take place?
Ampulla
Why is the Comulus important in the Ampulla?
For the translocation of the egg
How does sperm travel to the egg?
1) Sperm swims towards the cervical mucus
2) It is then transported by uterine muscle contraction
What is Sperm rheotaxis?
Sperm swim towards the flow of liquid in the oviduct
Why is fertilisation really difficult?
Sperm moving to quickly into the ampulla do not capacitate
Sperm are capacitated for a short period of time in the ampulla
What is done by the female to increase the chances of fertilisation and block polyspermy?
Sperm is released in packets of capacitated sperm to extend fertilisation window
What is capacitation?
The molecular process of capacitation prepare the sperm to the acrosome reaction & enable the sperm to became Hyperactive
How does capacitation accur?
Lipid changes
1) Cholesterol is removed by Albumin in the female
2) Receptors bind the egg Zona Pellucida are exposed
3) Acrosome reaction
Why does Cholesterol removal cause a dramatic change in the sperm membrane?
Signal induces a cascade of modification of many important proteins in the cytoplasm
Where is Sperm temporary stored before it is capacitated?
Uncapacitated Sperm temporarily bind to Isthmus
What does hyper activation of sperm mean?
Capacitated sperm swim with more force and rotate on its axis - this occurs by ion channels opening in membrane of the sperm tails
What is sperm thermotaxis?
Sperm swim towards higher temperature: 2C gradient between isthmus and ampulla
What is sperm chemotaxis?
Oocyte and Cumulus released molecule to attract sperm
Explain the Acrosomal reaction
1) Sperm binds to zona pellucida
2) Acrosome reaction
3) Sperm lyses hole in Zona
4) Sperm and egg membrane fuse
Which proteins does sperm bind in the Zona Pellucida?
ZP2-3 proteins of the Zona Pellucida
Why is Izumu important after achrosomal reaction?
Izumu binds to proteins Juno and CD9 which are expressed on the membrane of the egg fusing the sperm and egg membrane
How does the female egg gamete block polyspermy?
1) Immediately after fusion a layer of cytoplasm release cortical granule
2)enzyme digesting the zona pellucita
3) Zona pellucita matrix ditaches the ZP2 proteins.
Could you recall Genetic Fusion?
1) Male pronucleous produce aster
2) Female oocyte complete second meiotic division
3) Male centriole organises the Zygotic spindle
4) Male and female organised together by spindle
