(3) Fertilization: Beginning a New Organism Part 1

Question 1

4 major events of fertilization

Answer 1

1. contact and recognition between the sperm and the egg (ensures species specificity)
2. regulation of sperm into the egg (only 1 sperm can penetrate)
3. fusion of genetic material from sperm and egg
   4, activation of egg metabolism to begin development

Question 2

how does a sperm come about, and is it diploid or haploid?

Answer 2

sperm arise by meiotic cell division in testes; it is haploid (1 complete set of chromosomes; n)

Question 3

function of the sperm

Answer 3

1. deliver haploid nucleus to the egg
2. activate egg’s metabolism so that development can proceed

Question 4

sperm: form fits function! (explain)

Answer 4

1. not much more than a highly motile nucleus
2. it is comprised of a haploid nucleus, propulsion system, specialized plasma membrane to recognize egg of same species, and a sac of digestive enzymes to digest through protective layers of egg

Question 5

spermiogenesis: plasma membrane

Answer 5

specialized to recognize and bind to egg of same species

Question 6

spermiogenesis: acrosome

Answer 6

specialized vescile derived from golgi apparatus; contains digestive enzymes that help sperm penetrate egg

Question 7

spermiogenesis: haploid nucleus

Answer 7

contains the paternally derived chromosomes

Question 8

spermiogenesis: 2 centrioles

Answer 8

one becomes one of the mitotic poles in the first mitotic division of zygote; one becomes the organizing center for the outgrowth of microtubules within the flagellum

Question 9

spermiogenesis: axoneme

Answer 9

the motor portion of the flagellum; comprised of a 9+2 configuration of microtubules coursing down the length of the flagellum and dynein motor proteins that hydrolyze ATP to cause sliding of microtubules along each other to whip the flagellum

Question 10

spermiogenesis: mitochondria

Answer 10

surround the axoneme in midpiece to provide ATP for flagellar movement

Question 11

describe the egg/ovum

Answer 11

arise by meiotic cell division in ovaries; haploid; much larger than sperm; contains organelles and other cytoplsmic constituents missing from sperm that are required for embryonic development

Question 12

describe egg maturation

Answer 12

1. meiosis produces 1 haploid ovum from 1 diploid primary oocyte; other 3 daughters are polar bodies, which degenerates

Question 13

why is it advantageous to produce only 1 egg, sacrificing 2 polar bodies?

Answer 13

b/c we need the cytoplasm and organelles that sperm is missing

Question 14

cytoplasmic constituents of the egg (name them)

Answer 14

1. nutritive proteins
2. ribosomes and tRNA
3. maternal messenger RNAs
4. morphogenetic factors
5. protective chemicals

Question 15

cytoplasmic constituents: nutritive proteins

Answer 15

source of energy and amino acids for developing embryo; usually in form of yolk proteins

Question 16

cytoplasmic constituents: ribosomes and tRNA

Answer 16

protein synthesizing machinery; a burst of translation occurs soon after fertilization

Question 17

cytoplasmic constituents: maternal messenger RNAs

Answer 17

stored but not translated until after fertilization

Question 18

cytoplasmic constituents: morphogenetic factors

Answer 18

transcription factors or signaling molecules that direct early axis formation in embryo

Question 19

cytoplasmic constituents: protective chemicals

Answer 19

found in species that develop externally; protect developing embryo from UV irradiation, microbes, predators

Question 20

egg plasma membrane and external protective layers! (sea urchin egg)

Answer 20

jelly coat –> vitelline envelope –> egg cell membrane
(sperm has to penetrate through all three layers in order for fertilization to occur!)

Question 21

describe the sea urchin egg (membrane and cortex)

Answer 21

1. plasma membrane is microvilliated; they increase surface area of egg for binding of sperm
2. cortex: 5 um layer of gel-like cytoplasm directly underneath the PM; contains actin microfilaments and cortical granules (needed for fertilization)

Question 22

mammalian egg: zona pellucida (ZP)

Answer 22

layer of extracellular matrix (lots of fibers) outside the egg PM; equivalent of the sea urchin vitelline layer

Question 23

mammalian egg: cumulus

Answer 23

a “cloud” of follicle cells that surround the ZP; equivalent of sea urchin jelly coat

Question 24

how do sea urchins (phylum echinodermata) reproduce

Answer 24

they reproduce by broadcast spawning into sea water and external fertilization

Question 25

5 steps of sperm/egg recognition in sea urchins

Answer 25

1. chemoattraction of sperm to egg (species-specific) 2. acrosomal reaction 3. digestion of jelly layer by released acrosomal enzymes 4. sperm binding to vitelline membrane (species-specific) 5. fusion of egg and sperm plasma membranes

Question 26

chemoattraction

Answer 26

secreted from egg attract sperm; chemotaxis also activate sperm by increasing respiration and motility

Question 27

species specific sperm activating peptides

Answer 27

resact speract

Question 28

acrosomal reaction: 2 components

Answer 28

1. fusion of acrosomal vesicle with sperm plasma membrane and exocytosis of acrosomal enzymes that digest jelly coat 2. protrusion of acrosomal process from sperm head that binds egg to vitelline layer and tethers sperm to the egg

Question 29

species specific interaction between sperm and egg jelly coat triggers acrosomal reaction

Answer 29

1. jelly coat of different species contains different sulfated polysacchardies 2. sperm PM has proteins that bind only to the sulfated polysacchardies from the same species 3. once boud to jelly coat, acrosomal reaction is triggered in sperm

Question 30

digestion of jelly and binding of sperm to vitelline layer

Answer 30

1. release of acrosomal enzymes into jelly coat (digestion of jelly coat) 2. polymerization of actin to produce acrosomal process 3. acrosomal process is studded by bindin proteins 4. bindins bind with species-specificity to proteins in vitelline layer surrounding the egg

Question 31

sperm binding to vitelline layer

Answer 31

bidnin binds to species-specific receptors on egg vitelline membrane agglutination: in same species; can bind to each oher

Question 32

ensuring species specificity of fertilization

Answer 32

1. species-specific chemoattractants (correct egg to correct sperm) 2. species-specific interation between sperm and sulfated polysaccharides of egg jelly coat 3. species-specific interaction between sperm bindins and receptors of vitelline membrane

Question 33

fusion of egg and sperm plasma membranes

Answer 33

1. sperm and egg plasma membranes fuse, forming cytoplasmic bridge 2. bridging of actin filaments in acrosomal process and egg to form a fertilization cone 3. actin filaments widen cytoplasmic bridge 4. sperm nucleus, centriole, and tail enter egg (sperm centriole will divide and form two poles of the mitotic spindle for first mitotic division of zygote (fertilized egg))