Reproduction

Question 1

Cumulus cells

Answer 1

create an intracellular junction with the oocyte cell membrane. And they penetrate the zona pellucida

Question 2

Which species has the largest sperm cells?

Answer 2

Drosophilla (fruit fly)

Question 3

The spermatozoon are divided into 3 bits:

Answer 3

the head, mid piece and the tail

Question 4

Sperm can be prevented from reaching the ova from

Answer 4

the vaginal area (acidic env/ leaking out), the cervix, and the fallopian tube

Question 5

Fertilisation involves a number of selective barriers

Answer 5

1. swim from vagina to oviduct
2. penetrate the cumulus layer
3. bind to and penetrate zona pellucida
4. bind to and fuse with the plasma membrane

Question 6

Three stages of fertilisation include

Answer 6

1. Sperm preparation
2. Sperm binding and fusion
3. cortical reaction

Question 7

Capacitation

Answer 7

• takes place in the oviduct
• mature sperm need to acquire capacity to fertilise
• lose cholesterol, phospholipids, and glycoproteins on surface
• sperm becomes less stable

Question 8

Acrosome reaction

Answer 8

is the fustion of sperm plasma membrane and outer acrosomal membrane- creates pores

• this is induced by progesterone
• enzymes are released
• exposes acrosin
• exposes surface molecules for sperm binding

Question 9

Sequence of events in fertilisation

Answer 9

1. hyaluronidase from sperm breaks down hyaluronic matrix between cumulus cells (aided by whiplash movements)
2. acrosome reaction occurs in cumulus cells
3. sperm binds to zona pellucida
4. …

Question 10

Immediately after the sperm fuses with oolemma…

Answer 10

the tail stops beating

Question 11

The microvilli on the oocyte plasma membrane…

Answer 11

engulf the sperm, starting at the equatorial segment

Question 12

Swelling (fertilisation cone)

Answer 12

forms ….

Question 13

Cortical reaction…

Answer 13

cortical granules fuse with the plasma membrane. Contents released into perivitelline space

Question 14

Polyspermy is blocked via

Answer 14

Zona reaction - zp2 cleaved, oligosaccharides removed from ZP3) - this is a slow block
Membrane block- Juno receptor is gradually shed from the plasma membrane so other sperm cannot bind

Question 15

Sperm contribution to the zygote

Answer 15

in most mammals, whole sperm enters oocyte, sperm mitochondria are destroyed,

Question 16

Formation of zygote

Answer 16

In the pronucleate zygote, there is a male pronucleus (which forms once the sperm enters the oocyte) and a female pronucleus,

Question 17

The zona pellucida does not need to be removed

Answer 17

before fertilisation

Question 18

Cleavage is

Answer 18

a series of rapid cell divisions without cell growth

divisions are reductive - form a blastomeres

Question 19

Blastomeres are

Answer 19

totipotent- the ability to form the placenta is a defining feature of totipotent cells

Question 20

Cleavage timings differ between species

Answer 20

mouse have a gestation period of 19-20 days. Humans take 270-290 days.

Question 21

Compaction and polarisation occurs at

Answer 21

the 8-cell stage. Spherical cells become flattened, E-cadehrin and B- cadherin are essential. Embryo becomes a closely bonded single entity.

Question 22

Polarisation includes

Answer 22

forming a apical surface (microvilli), apical region (organelles), inner basal region (nucleus), and tight junctions form.

Question 23

How is the blastocyst formed?

Answer 23

energy dependant pump system, Na+ pumped into blastocyst cavity, water is drawn into cavity by osmosis, cavity expands.

the blastocyst hatches from the zona pellucida 1-2 days after cleavage.