Fertilization Flashcards
Sequence of events:
1.) Attraction and Activation of sperm
2.) Contact and recognition between sperm and egg
3.) Sperm entry
4.) Preventing Polyspermy (and polyploidy)
5.) Fusion of egg and sperm (nuclear fusion)
What is the average size of sperm?
5.1um by 3.1um and the flagellum is 50um (flagellum is the longest part)
Sperm can survive and are capable of fertilization up to______ days?
7
What is the motion time for sperm?
1-3mm per minute
Sperm ejaculation stats
1.5-5ml per ejaculation
Sperm per milliliter
20-150 million
Where are sperm released in the vaginal canal?
Cervix
Within how many hours can the sperm reach the oviduct?
1/2 to 2 hours
Prep Sperm for environment and encounter with egg
1.) The sperm are immobile until they reach the epididymis
2.) Seminal fluids add + strip of carbohydrates and proteins at the head of the sperm because with all of these materials attached to the sperm it will not be able to fertilize an egg
3.) The female reproductive tract contains enzymes and lower pH levels that also help to strip off the sperm’s surface glycoproteins
The sperm are immobile until they reach which structure?
Epididymis
Why do seminal fluids add + strip of carbohydrates and proteins at the head of the sperm?
Because with all of these materials attached to the sperm, it will not be able to fertilize an egg
The female reproductive tract contains enzymes and ______ pH levels that also help to strip off the sperm’s surface glycoproteins
Lower; acidic
What is the average size of an egg?
0.1mm
Egg mobility
“floating” to and thru oviduct
Egg viability
within 12-24 hours after ovulation
Where is the egg fertilized?
Within oviduct
What is the protective layer of the egg?
Zona Pellucida (Vitelline Membrane)
- glycoproteins
- increase surface area
________ cells cover and accompany the egg
Granular cells
The egg is covered with_________
Microvilli
Approximately how many eggs lost each month?
1000
Role of microvilli
Increases surface area and receptors (they do not move though)
Approach of sperm to egg for what?
FUSION (union)
Human sperm travel in this order
cervix –> uterus –> oviduct
Positive retroactive response
sperm in the oviduct have to orient themselves against the ciliated current
(swimming upstream)
Capacitation
Enhancement of sperm to allow penetration of the egg’s membrane
Fertilization occurs within what part of the oviduct?
Upper 1/3 of oviduct
Gametes– haploid + haploid
= diploid
Species gene barrier
Sperm will only fertilize with its own species
- genetic material has to match receptors
Life span of gametes
Females: shorter, roughly 12-24 hours
Males: longer lived, typically 1-2 days
Sperm released
ejaculated
Chemoattraction
Sperm find the egg by detection of soluble chemoattractant
- immune cells releasing chemical sirens and communicating via chemical signals
What happens during chemoattraction?
- human sperm are activated and attracted by fluids in the female reproductive tract
- follicular fluid
- Corona Radiata - Granular cells
- “Sperm Chemotropic Factors”
What is the fluid called that attracts the sperm?
Follicular fluid
Contact and Recognition between sperm and egg
a.) Docking
b.) Acrosome Bursting
Docking (Specific Recognition)
- “lock and key” idea for it to activate
- the sperm bind to a glycoprotein (ZP2) found on the zona pellucida (ZP1-ZP4)
Acrosome bursting
ZP3 binding and Ca++ surge in sperm initiates acrosome rupture and allows for next cellular process to begin
Acrosome projecting
cytoskeleton within the sperm is synthesized and pushes acrosome and sperm into the ovum
The exocytosed acrosome enzymes drill through the egg’s_______
zona pellucida
Within acrosome =
Hydrolytic enzymes
Acrosome enzymes triggers_______
sperm tail to whip faster pushing into the egg’s Zona Pellucida
- many sperm attach but only one makes it in!
Sperm entry
1.) Acrosome reacts with Zona Pellucida space
2.) Sperm membrane fuses with egg membrane
3.) membrane fusion and Calcium surge triggers egg to complete Meiosis II and is now mature Oocyte (and polar body)
4.) A fertilization cone powered by the ovum’s actin filaments rise up out of the egg engulfing sperm
5.) Cortical Granules fuse with egg membrane which renders the Zona Pellucida impenetrable to OTHER sperm
What happens when acrosome reacts with Zona Pellucida space?
Encounters more egg proteins
Sperm specific protein
IZUMO1
Egg specific protein
JUNO
IZUMO1 and JUNO_____
bind
Calcium surge
Triggers egg to complete Meiosis II and is now mature oocyte (and polar body)
A ______ ______ powered by the ovum’s actin filaments rise up out of the egg engulfing sperm
fertilization cone
______ fuse with egg membrane which renders the Zona Pellucida impenetrable to OTHER sperm
Cortical Granules
Preventing Polyspermy (and polyploidy)
a.) Fast block
b.) Slow block
The FAST block (1-3 seconds)
- Slam the door!
- Sperm entry causes the egg membrane to depolarize by opening sodium channels and Na+ is pumped into the egg cell
- The electrical potential of a cell swings from negative -70mV to positive +20mV
- This only lasts one to two minutes but long enough to prevent sperm binding
- The sperm ZP2 receptor proteins change shape and detaches the other sperm
The electrical potential of a cell swings from________ to _________
Negative -70mV to positive +20mV
The Slow block (30 sec to 1 minute)
- lock and bolt the door!
- sperm entry triggers a intercellular wave of calcium ions to radiate over egg membrane (Calcium tsunami)
- *Cortical Granules Reaction
Calcium tsunami releases what?
1000s cortical granules
Cortical Granules Reaction
Granules beneath cell membrane “pop” and release their contents into the space between the plasma membrane an the next outmost layer
- cortical proteases digest other partially attached sperm
- HydroPHILIC (loving) mucopolysaccharides (+ water) push away the outer layer creating a FERTILIZATION ENVELOPE that sperm cannot cross (increases volume) and pushes out other sperm!
Fertilization envelope
Sperm cannot cross
What initiates the cortical granule reaction?
A wave of calcium ions that begins where the single sperm has entered the egg; this calcium wave flowing across the egg takes on average about 30 seconds (slow block)
Nuclear fusion of sperm and egg
1.) The sperm nucleus breaks down
2.) Chromatin is unwound and exposed to the maternal cytoplasm
3.) Microtubules extending of the male and female pronuclei together
4.) All chromosomes unite and lineup right away for the first mitotic division
- 1 cell = zygote
- 23+23 = 46 chromosomes
- Onward to the 1st cell division
Generalized acrosomal process
1.) sperm makes contact with egg
2.) Acrosome reacts with zona pellucida
3.) Acroome reacts with perivitelline space
4.) Plasma membranes of sperm and egg fuse
5.) Sperm nucleus enters egg
6.) Cortical granules fuse with egg plasma membrane, which renders the vitelline layer impenetrable to sperm
