Fertilization (*** = emphasized points likely to be tested)

Question 1

Sperm structure

Answer 1

Head (with acrosomal region. Head also contains highly condensed chromatin in nucleus.)
Midpiece
Tail

Chromosomes: haploid (22X or 22Y)

Question 2

What molecule is responsible for keeping chromatin condensed in the nucleus/head of sperm?

Answer 2

***protamine: a specialized histone that tightly wraps DNA by disulfide bonds

Question 3

Acromosome region

Answer 3

• anterior ½ to 2/3 of the sperm head is called the acrosome region (cap on top of sperm)
• a thin-double layered membrane sac.
• The acrosome contains hydrolytic enzymes

Question 4

Structure of sperm tail

Answer 4

-***contains 9 axoneme doublets arranged circumferentially around a pair of microtubules (9+2)
-These doublets are surrounded by a mitochondrial sheath (energy to power sperm)
-The tail is responsible for sperm motility
(Impaired cilia in Kartagener syndrome leads to infertility.)

Question 5

Steps of fertilization

Answer 5

• Ovulation (LH surge) and oviductal collection of the oocytes (via fimbriae)
• Deposition of sperm with sufficient number and motility
• Sperm capacitation (sperm extracted directly from testis WOULD NOT have the ability to fertilize egg. ***Undergoes capacitation in female genital tract).
• Sperm traversing the cumulus oophorus (these are the granulosa cells that have surrounded egg as it matured)
• Sperm interaction with zona pellucida and acrosome reaction
• Sperm penetrate into zona pellucida
• Sperm-oocyte fusion
• Oocyte activation
• Male pronuclei formation

Question 6

Semen Analysis: which features are evaluated? What are normal values?

Answer 6

Color
Viscosity
Volume
pH
Concentration
Motility
Rate of Progression
Morphology

Ejaculate Volume: greater than 2 ml
Sperm Concentration: greater than 20 million / ml
Sperm Motility: greater than 50% motile
Morphology: 14% normal
Progression: greater than 50% normal

Question 7

Sperm capacitation

Answer 7

The process by which spermatozoa acquire the capacity to undergo the acrosome reaction and fertilize eggs.

• see increase in the frequency and amplitude of the flagellar beat of the tail; decrease in progressive movement
• Calcium dependent process and tyrosine kinase driven

Question 8

Primary oocytes are arrested in which phase?

Answer 8

Prophase of meiosis I

Question 9

After ovulatory LH signal, what happens to oocytes? after fertilization?

Answer 9

• completion of first meiotic division and yield first polar body and secondary oocyte.
• secondary oocyte arrests in metaphase of meiosis II until fertilization

-after fertilization, oocyte resumes meiosis II and generates second polar body

Question 10

Where does fertilization normally occur?

Answer 10

ampullary region of Fallopian tube (fimbriae and rhythmic tubal contractions help oocyte get there)

Question 11

Sperm egg interaction

Answer 11

• sperm burrows through cumulus layer (extracellular)
• binds to zona pellucida
• acrosome reaction
• sperm fuses with zona

Question 12

Zona pellucida structure

Answer 12

Shell-like structure that surrounds oocytes

• glycoprotein sheet, several microns thick
• 70% protein, 20% hexose, 3% sialic acid, 2% sulphate
• Composed of three glycoproteins: ZP1, ZP2, ZP3

Question 13

Where does sperm binding occur on the zona pellucida?

Answer 13

***ZP3

Question 14

Acrosome reaction

Answer 14

Outer membrane of the acrosome fuses with the plasma membrane of the sperm, exposing the contents of the acrosome, mainly hyaluronidase and acrosin (digest through zona)

Involve G proteins, voltage-sensitive Ca+2 channels, and intracellular Ca+2 and pH

Question 15

Sperm-oocyte fusion: which components fuse? which protein is responsible for fusion?

Answer 15

• Occurs between the sperm’s plasma membrane in the postacromosomal region and the oolemma
• Fertilin: sperm protein responsible for sperm-oocyte fusion

Question 16

What prevents multiple sperm from fertilizing the egg?

Answer 16

• **Release of cortical granules from the sperm after penetration through the ZP prevents other sperm from fertilizing egg.
• called zona reaction
• forms new glycoprotein ZP3-F which is no longer capable of binding sperm (prevents polyspermy)

Question 17

Oocyte activation

Answer 17

The reawakening of the oocyte in regards to second meiotic division (extrusion of 2nd polar body).

Morphological indicator: exocytosis of cortical granules

Question 18

Male pronuclei formation

Answer 18

Protamine, a DNA-binding protein, keeps chromatin of mature sperm nucleus tightly packed with disulfide bonds.
The disulfide bonds are reduced by the action of oocyte-derived glutathione
Sperm nuclei decondensation
Formation of male/female pronuclei