Week 1

Question 1

spermatogenesis vs oogenesis

Answer 1

• sperm continuously produced in adult humans
• eggs however not produced after birth
• oocytes complete meiosis after fertilisation
• number of oocytes declines dramatically with age

Question 2

Human sperm structure

Answer 2

• Acrosome - contains enzymes that digest proteins and complex sugars that make up the egg coat: acrosmal process is a region of globular actin between the acrosome and the nucleus
• haploid nucleus contains highly compacted DNA
• centriole will form one of two spindle poles at first division
• mitochondria lie behind centriole at base of flagellum

Question 3

Egg cell summary

Answer 3

• egg cytoplasm is rich in proteins (yolk), ribosomes, RNA and other components required for embryogenesis
• egg nucleus which may be haploid or diploid, contains nutrtive proteins
• egg cortex is speciallised part of cytoplasm lying under the egg
• egg membrane encloses egg cytoplasm and regulates ion flow during fertillisation
• vitelline membrane is a thin glycoprotein meshwork surrounding eggs that attracts or activates sperm

Question 4

MAIN steps of fertilisation

Answer 4

1. chemoattraction of sperm to egg
2. exocytosis of sperms acrsomal vesicle
3. binding of sperm to extracellular structures
4. passage of sperm through extracellular structures
5. fusion of egg and sperm membranes

Question 5

Acrosome reaction (sea urchin)

Answer 5

• initiated by species - specific interation between sperm head and glycoproteins in egg jelly
• opens ion channels, causing calcium influx, exocytosis of acrosomal vesicle
• prteolytic enzymes from acrosome digest through egg jelly

Question 6

activating egg after fertilisation

Answer 6

• fertilisation triggers wave of calcium signalling throughout egg
• calcium triggers cortical granule exocytosis
• DAG and calcium activate a NA/H+ pump on membrane, leading to h+ outflow and alkalinsation of cell > dna synthesis
• calcium inactivates MAP kinase, restating cell cycle

Question 7

Intracellular calcium wave (sea urchin )

Answer 7

• immediately after fertilisation triggers cortical granule reaction
• as sperm and egg pronuclei meet and fuse leading to cell cycle restarting