Fertilisation Flashcards
what is fertilisation?
fusion of male and female gametes
What does meiosis produce in humans?
Two segregation phases and cell divisions generate haploid germ cells (eggs and sperm)
How is sperm production characterized in adult humans?
Sperm is continuously produced.
When are eggs produced in females?
Eggs are not produced after birth.
When do oocytes complete meiosis?
Oocytes only complete meiosis after fertilization.
What happens to the number of oocytes with age?
The number of oocytes declines dramatically with age.
what does having a limited amount of oocytes mean for female fertility?
Female fertility declines with age
what causes greater risk of improper chromosomal segregation
longer oocytes paused before meiosis II
what complication increases with maternal age
fetal aneuploidy
What is fetal aneuploidy?
chromosomally abnormal
What is a risk factor of increased mutation in sperm?
Age
What does sperm mutation link to?
neurodevelopmental disorders
implications for evolution
What did Anton von Leeuwenhoek believe abt sperm?
sperm are parasites
What did Herman Fol and Oscar Hertwig find out abt sperm.
Only one sperm was seen to enter each egg,and all nuclei of the resulting embryo werederived mitotically from the nucleus createdafter fertilisation”
What is the function of the acrosome in human sperm?
The acrosome contains enzymes that digest proteins and complex sugars that make up the egg coat.
What is the acrosomal process in some species of human sperm?
The acrosomal process is a region of globular actin between the acrosome and the nucleus.
What type of nucleus does human sperm have?
The haploid nucleus contains highly compacted DNA.
What role does the centriole play in human sperm?
The centriole will form one of the two spindle poles at the first division.
Where are mitochondria located in human sperm?
Mitochondria lie behind the centriole at the base of the flagellum.
What is the axoneme in human sperm?
The axoneme is the central core of the flagellum composed of a superstructure of tubulin protein.
What is the classic arrangement of microtubules in the axoneme of human sperm?
The classic arrangement is a ‘9 + 2’ microtubule doublet arrangement.
What is the composition of the egg cytoplasm?
The egg cytoplasm is rich in proteins (yolk), ribosomes, RNA, and other components required for embryogenesis.
What does the egg nucleus contain?
The egg nucleus contains nutritive proteins, ribosomes, tRNA, mRNAs, morphogenetic factors, and protective chemicals.
What is the function of the egg cortex?
The egg cortex is a specialized part of the cytoplasm lying just under the egg membrane containing cortical granules.
What is the role of the egg cell membrane?
The egg cell membrane encloses the egg cytoplasm and regulates ion flow during fertilization.
What is the vitelline membrane?
The vitelline membrane is a thin glycoprotein meshwork surrounding the egg membrane, often involved in sperm/egg recognition.
What is the jelly layer in relation to the egg cell?
The jelly layer is a second glycoprotein meshwork surrounding the egg that attracts or activates sperm.
Where is the vitellinne envelope in the sea urchin egg cell
Extracellular
Where is the Cortical granules in the sea urchin egg cell
Under the plasma membrane
What is the first step of fertilisation
Chemoattraction of the sperm to the egg
What is the second step of fertilisation?
Exocytosis of sperm’s acrosomal vesicle (acrosomal reaction)
What is the third step of fertilisation?
Binding of sperm to extracellular structures (e.g. vitelline envelope, zona pellucida)
What is the fourth step of fertilisation?
The passage of sperm through extracellular structures
What is the fifth step of fertilisation?
Fusion of egg and sperm membranes
What protein coats the inner membrane of the acrosomal vesicle in sea urchins?
Bindin protein
What is the role of bindin in sea urchin fertilization?
Bindin interacts with receptors on the egg surface to mediate interaction between the egg and sperm membranes.
What limits the number of sperm that can bind to the egg in sea urchins?
Limited receptor numbers on the egg surface.
What happens when the sperm acrosomal process contacts the egg microvillus?
It binds to the bindin receptor and forms a fertilization cone.
What is formed when the sperm binds to the egg in sea urchins?
A fertilization cone.
What occurs after the fertilization cone is formed in sea urchin fertilization?
The sperm is internalized by the egg.
What initiates the acrosome reaction in sea urchins?
Species-specific interaction between the sperm head and glycoproteins in the egg jelly.
What happens when ion channels open during the acrosome reaction?
Calcium influx occurs, leading to exocytosis of the acrosomal vesicle.
What role do proteolytic enzymes from the acrosome play during fertilization?
They digest through the egg jelly.
What is the effect of calcium influx during the acrosome reaction?
It leads to polymerisation of the actin globule into an extended actin filament, forming the acrosomal process.
What is Polyspermy
the entry of multiple sperm into the egg
What makes polyspermic zygotes different
have multiple centrioles and cleave aberrantly at the first division,leading to embryonic death
How do eggs prevent Polyspermy?
fast block and slow block
Who discovered the fast block to polyspermy?
Ernest Just
What observation did Ernest Just make about the fertilization membrane in 1919?
He observed that cortical changes begin at the point of sperm entry, immunizing the egg to other sperm.
What is the resting membrane potential of an egg before fertilization?
-70 mV
What happens to the membrane potential of an egg after fertilization?
It rises to +20 mV due to an influx of sodium ions.
Why can’t sperm fuse with an egg that has a positive membrane potential?
Because sperm cannot fuse with an egg having a positive membrane potential. Blocks further sperm fusion.
How long does the fast block to polyspermy last?
It lasts only a minute or so.
What is the process that results in the slow block to polyspermy?
The cortical granule reaction.
What happens during the cortical granule reaction?
Cortical granules fuse with the plasma membrane in response to sperm binding.
What do cortical granules contain that is important for preventing polyspermy?
Proteases that cleave the protein bridges linking the vitelline membrane to the plasma membrane.
What does CGSP stand for?
Cortical Granule Serine-protease.
What does MPS stand for?
Mucopolysaccharides.
What does OVOP stand for?
Ovoperoxidase.
What does TG stand for?
Transglutaminases.
What stimulates cortical granule fusion?
An increase in the intracellular free calcium concentration from calcium stores within the egg.
What happens at 10 seconds after sperm addition to the egg?
Sperms surround the egg.
What occurs at 25 seconds after insemination?
A fertilisation envelope is forming around the egg, starting at the point of sperm entry.
What happens at 35 seconds after insemination?
The fertilisation envelope is complete, and excess sperm have been removed.
What triggers a wave of calcium signaling throughout the egg after fertilization?
Fertilization
What process is triggered by calcium signaling that involves the release of cortical granules?
Cortical granule exocytosis
What do DAG and calcium activate on the membrane after fertilization?
A Na/H+ pump
What is the result of the Na/H+ pump activation leading to H+ outflow?
Alkalinization of the cell
What cellular process is initiated by calcium that leads to DNA synthesis?
Alkalinization of the cell
What does calcium inactivate to restart the cell cycle after fertilization?
MAP kinase
What is DAG (Diacylglycerol)?
s a lipid that plays a role in the fusion of sperm and egg during fertilization.
What is the link between calcium and the cell cycle
Molecular link between calcium and control of the cell cycle via calcium-induced cyclin degradation
What happens when the sperm and egg pronuclei meet and fuse in sea urchins?
It leads to the second wave of calcium signaling and the restarting of the cell cycle.
Pronuclear migration (sea urchin)
The pronuclei migrate towards each other on microtubular processes
What happens to the mature unfertilised oocyte during pronuclear migration? (human)
The mature unfertilised oocyte completes the first meiotic division, budding off a polar body.
What occurs when sperm enters the oocyte during pronuclear migration? (human)
Sperm enters the oocyte and microtubules condense around it as the oocyte completes its second meiotic division.
What is observed at 15 hours post-fertilization (hpf) during pronuclear migration? (human)
The two pronuclei have met, and the centrosome splits to organise a bipolar microtubule array.
What happens at prometaphase during pronuclear migration? (human)
Chromosomes from the sperm and egg intermix on the metaphase equator and a mitotic spindle initiates the first mitotic division.
