Reproduction 3: Fertilisation Flashcards
L4
What is fertilisation?
Union of 2 hapliod gametes, producing diploid offspring
Why is fertilisation not as simple as you might think? Give some examples of obstacles that occur.
- Sperm must make it to the ovum
- Gametes must recognise each other
- Sperm must penetrate ovum
- Haploid egg nucleus & sperm nucleus must fuse to from diploid zygote (syngamy)
- Ovum must block entry of additional sperm (polyspermy) to avoid polyploidy (pathologic in mammals) (>diploid)
List the structure of an egg cell
Germinal vesicle
Germinal spot
Ooplasm
Vitelline membrane
Zona Pellucida
Corona Radiata
What is the germinal vesicle in en egg cell?
nucleus containing DNA
What is the germinal spot in an egg cell?
nucleus
What is the ooplasm in an egg cell?
cytoplasm - contains nutrients
What is the Vitelline membrane in an egg cell?
cell membrane surrounding the ooplasm
What is the Zone Pellucida in an egg cell?
extracellular matrix containing glycoproteins
What is the function of the Zone Pellucida in an egg cell?
protects and plays vital role in fertilisation
What is the Corona Radiata in an egg cell?
layer of follicle cells
List the 4 structures of a sperm cell
- Head
- Neck - contains centriole
- Midpiece
- Tail / Flagella
Describe the head of a sperm cell
Contains nucleus with DNA, capped with acrosome
What does the sperm acrosome contain?
contains enzymes that help penetrate the egg membrane
Describe the neck of a sperm cell
contains centriole (important for tail formation and movement)
Describe the midpiece of a sperm cell
contains many mitochondria = energy for movement
What is the function of a sperms tail?
Drives sperm forward
What is external ferilisation?
fusion occurs outside either parent (must be aquatic)
What is internal fertilisation?
Sperm can only move through liquid → terrestrial organisms inseminate using seminal fluid (and oviductal fluid in the female reproductive tract)
Human fertilisation: How does the pH of the vagina affect fertilisation?
The acidity kills lots of sperm, however some are protected by seminal fluid
Human fertilisation: What happens to the sperm when they enter the cervix?
- Some killed by cervical mucus
- Others by immune system cells
- Others are trapped in folds
Human fertilisation: What happens to the sperm when they reach the uterus?
They must choose 1 fallopian tube
- Many swim up the inactive tube (only 1 active per month)
What effect do cilia in the fallopian tube have on sperm?
They waft the egg from the fimbrae
= sperm swim against the current
Describe the process of internal fertilisation in mammals (5 steps)
- Sperm penetrate cumulus cell layer using burrowing movement
- Acrosomal reaction
- Penetrates zona pellucida
- Once acrosome cap has dissolved → ZP proteins in new membrane on sperm is recognised by the plasma membrane of the egg = fusion of plasma membranes (mediated by recognition/ attachment proteins)
- Sperm enters egg cytoplasm.
Which class uses internal ferilisation
Mammals
Describe the acrosomal reaction in sperm
acrosome cap on sperm head fuses with the plasma membrane exposing enzymes that allow it to penetrate the zona pellucida
After one sperm has entered the egg, why does the egg membrane and ZP block more sperm from entering?
To avoid polyspermy
Describe the process of external fertilisation in sea urchins.
- Protective jelly coat (replaces ZP) has protein receptors with (species specific) chemoattractants = attracts sperm through the water
- Acrosome breaks down, releases enzymes to penetrate jelly coat
- Sperm binds through plasma mem fusion (requires species specific bindin protein)
- Rapid cortical reaction: e potential of egg mem changes (more rapid than mammal) to block polyspermy
Give 4 features of an egg of an externally fertilising species and why they are necessary
- Protein receptors on protective jelly coat are species specific = to avoid other species sperm penetrating
- Species specific bindin protein
- Jelly coat tougher than internal fertilisers
- Rapid cortical recation faster than internal = due to large amounts of sperm still surrounding egg
Gametogeneis is highly _________
Conserved
= most animals have the same process
Mating is extraordinarily _______
Diverse
