Gametogenesis Flashcards
(14 cards)
What is a gonad ?
An organ that produced gametes
Testes or ovaries
What are primordial germ cells ?
Diploid cells that originate in the extra embryonic tissue and migrate into the embryo via the gut and into the genital ridge.
They divide by meiosis to produce gametes.
What does the genital ridge do ?
It give rise to the somatic cells of the gonad
Describe the stages of spermatogenesis
- PGCs multiply by mitosis during migration to produce spermatogonia that arrest in G1
- Diploid spermatogonia multiply by mitosis to produce spermatocytes
- Spermatocytes undergo meiosis to produce spermatids (haploid)
- Spermatids differentiate into spermatozoa
Each primary spermatocyte gives rise to 4 sperm cells.
Describe spermiogenesis
When spermatids differentiate into spermatozoa.
1. Golgi develops into acrosomal cap
2. Flagellum develops
3. Cytoplasm extruded
4. Mitochondria coalesce near base of flagellum
5. Nucleus condenses
How is the sperm specialised ?
- Acrosome- contains lytic enzymes for protein, carb and lipid digestion. Allows penetration of egg.
- Flagellum- made of microtubules attatched to Dyenin. Dyenin used the energy of ATP hydrolysis to slide the MTs past one another, aiding movement of the sperm.
Describe the stages of Oogenesis
- PGCs multiply by mitosis during migration to generate oogonia
- They differentiate into primary ooctyes
- Primary ooctyes enter meiosis I, but arrest in prophase I
- During each menstrual cycle, one primary ooctyes resumes meiosis I. It divides into a secondary oocyte.
- Secondary ooctyes enter meiosis II, but arrest in metaphase II until fertilisation
- If fertilisation occurs, metaphase II completes, producing an Ovum and 2 polar bodies
Where does spermatogenesis take place ?
Seminiferous tubules
Where does oogenesis take place ?
Ovaries
What is the mammalian oocyte surrounded by ? What does it consist of ?
The Zona pellucida
It consists of 3 glycoproteins: ZP1, ZP2 and ZP3
What is ZP3 ?
The sperm receptor
It’s O-linked polysaccharide determined species specificity
What do cortical granules contain ? What are they derived from ?
Derived from the Golgi
Contain proteases and glycosidases
Describe the steps of fertilisation
- The oocyte is surrounded by cumulus cells in a matrix of hyaluronic acid. Hyaluronidasd activity on the sperm head enables it to penetrate this layer.
- Sperm GaIT recognises ZP3 proteins triggering G protein activation. This causes a change in membrane potential which opens voltage gated calcium channels, increasing intracellular calcium levels. This initiates the acrosome reaction.
- Sperm Izumi binds oocyte Juno, recruiting oocyte CD9, causing the plasma membranes to fuse, and the sperm enters the oocyte.
- Calcium release within the oocyte triggers:
Cortical reaction
Completion of the second meiotic division, producing ovum and second polar body - Sperm and egg pronuclei migrate along MTs towards each other. Their nuclear envelopes break down and the chromosomes align on a shared Mitotic spindle.
- Chromosomes combine, restoring the diploid number
How does the cortical reaction work ?
- Actin polymerises into micro filaments which transport cortical granules to the plasma membrane.
- Cortical granules released by exocytosis.
- Enzymes partially digest ZP2 and remove carb from ZP3.
- ZP hardens
