Pt. 2 & Chapter 4

Question 1

what are the four steps of cell differentiation?

Answer 1

1. competence
2. induction
3. commitment (specification, determination)
4. differentiation

Question 2

what is specification?

Answer 2

recieves signal, induced in neutral environment (no signals from neighbors)

Question 3

what are the three types of specification? describe them

Answer 3

autonomous
- dependent on cytoplasmic factors
- knows what to do when separated

conditional / regulative
- dependent on morphogens & induction
- dependent on neighbors if it has them

syncytial
- single cells w/ many nuclei
- act like morphogens & make gradients

Question 4

what is determination?

Answer 4

altered TFs (maintenance processes)
- starting to do the signal
- remain induced in conflicting environment

Question 5

what are morphogens?

Answer 5

threshold gradient (red & blue, in-class demo)
- each level of morphogen determines a specific response

EX: bicoid & nanos

Question 6

what is in each section of sperm? (head, midpiece, tail)

Answer 6

head
- acrosomal vesicle
- cell MB
- nucleus

midpiece
- centriole
- mitochondira

tail
- flagellum

Question 7

what does the acrosomal vesicle do?

Answer 7

bag of enzymes that degrade oocyte jelly coat

Question 8

what is a cumulus?

Answer 8

contains support cells that become corpus lutem
- in mammals

Question 9

why are sea urchins good model organisms?

Answer 9

• complete meiosis before fertilization
• external fertilization (eggs laid)
• transparent egg & embryo
• gametes huge in #
• easy to see fertilization in lab conditions

Question 10

why NOT sea urchins as model organisms?

Answer 10

cannot follow for generations, don’t survive

Question 11

what are the three problems posed with external fertilization? how are the solved?

Answer 11

diluted in entire ocean -> sperm attractant
fertilize wrong species -> bindin binding vitelline en.
multiple fertilization -> fast & slow blocks

Question 12

what is the process of sea urchin external fertilization?

Answer 12

1. egg releases sperm attractant
2. sperm contacts jelly layer
3. actin extends & pushes acrosome
4. acrosome bursts & releases digestive enzymes
5. digestion of jelly coat exposes bindin protein
6. bindin binds vitelline en. (species-species recognition)
7. fusion of acrosomal MB & egg creates a tunnel
8. fast block -> opens ion channels (Na+ IN, Cl- OUT)
9. slow block -> cortical granules burst & release enzymes

Question 13

what are the four enzymes released by the cortical granules? functions?

Answer 13

proteases -> cut vitelline ties
polysaccharides
peroxidases
hyalin -> makes fertilization en. to eject sperm

Question 14

what are the early responses (seconds) of sea urchin fertilization?

Answer 14

• sperm-egg binding
• fast block
• sperm-egg MB fuse
• Ca2+ exocytosis of cortical granules

Question 15

what are the 1min late responses of sea urchin fertilization?

Answer 15

energy & pH
- activation of kinases & energy (NADPH, etc.)
- sperm entry
- acid efflux (increase pH, more basic)

Question 16

what are the 10 min late responses of sea urchin fertilization?

Answer 16

migration & proteins
- DNA decondenses
- migration of gametes
- activation of AA synthesis

Question 17

what are the 20 min late responses of sea urchin fertilization?

Answer 17

cell cycle
- DNA synthesis
- mitosis
- cleavage

Question 18

what is early cleavage? what controls this?

Answer 18

M -> S phase (no cytokinesis)
- Cdc2 / cyclinB (on/off switch)
- allows DNA to double
- made during S-phase, active during M-phase, degraded after M-phase
- activates MPF (mitosis promoting factor) that drives shift from M -> S
- does this 10x

Question 19

what is late cleavage?

Answer 19

full cell cycle
- cells now start to change & differentiate

Question 20

what is holoblastic cleavage? what are the three types?

Answer 20

entire cell divides, including yolk
- radial
- rotational
- displaced radial

Question 21

describe the differences between the three types of holoblastic cleavage

Answer 21

radial: rotate 90 around center
rotational: cut from side at an angle, uneven
displaced radial: yolk parts divide slower

Question 22

what is meroblastic cleavage? what are the two types?

Answer 22

only embryo divides, not yolk
- discoidal
- centrolectihal (syncitium)

Question 23

describe the differences between the two types of meroblastic cleavage?

Answer 23

discoidal: cells divide ontop of yolk
centrolectihal: superficial, many nuclei around outer MB

Question 24

what is invagination?

Answer 24

creates a pore

Question 25

what is involution?

Answer 25

cells move inward to create a new lining of cells

Question 26

what is ingression?

Answer 26

cells leave the layer individually & migrate inward

Question 27

what is delamination?

Answer 27

makes layer thicker, cells remain same type & property

Question 28

what is epiboly?

Answer 28

outer layers thin & stretch to cover entire embryo