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Mol / Cel Biology > Lecture 9 > Flashcards

Lecture 9 Flashcards

1
Q

Gametogenesis is… (the process)

A

Development of haploid sex cell:

mature oocyte and sperm cell in a diploid organism by meiosis.

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2
Q

Origin of gametes? (timeline)

A

At about 4 weeks of pregnancy.

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3
Q

Sex cell precursors? And where they arise?

A

PGC (primordial germ cells) arise in the yolk sac to genital bridge (bisexual gonads).

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4
Q

When does PGC migrate to genital ridge - bisexual gonads? (timeline)

A

4-6 week of pregnancy

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5
Q

Early migration of PGC’s is dependent on expression of what?

A

The expression of ITProteins 1 and 3.

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6
Q

What is SRY (the male determining pathway)?

A

Sex-determining region on the Y chromosome (obviously males).

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7
Q

What is the main role of SRY?

A

Up-regulating the expression of SOX9 during a very narrow critical time window.

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8
Q

In human SRY is expressed in both (cells)?

A

Sertoli cells and germ cells at fetal and adult stages.

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9
Q

What is SOX9 (protein what)?

A

Gene on autosome, activated by SRY

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10
Q

SOX9 is expressed at low levels in?

A

Bipotential gonads of both sexes under SF1 regulation.

Because the gender is not determined yet.

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11
Q

Some oocyte and sperm genes are imprinted differently because (passage to generations)?

A

Because germ cell genes, but not somatic cell genes, are passed on to the next generation:
- imprinted marks present in the zygote must be erased then -> reset at some point during germ cell development
- in the somatic cells of the developing embryo, these
same imprinted marks must be retained

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12
Q

X-chromosome re-activation?

A

In female’s PGC (2n).

2 X chromosomes are active (inactivated X is
reactivated).

Reduction of Xist RNA levels

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13
Q

Timing of gametogenesis in males and females:

A

In males – starts at puberty and continues
throughout adult life

In females – starts during embryonic life (before birth) and ends for each particular oocyte after
fertilization (menopause).

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14
Q

Oogenesis happens by:

A

Mitosis and meiosis both.

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15
Q

Modified meiosis consists of (oogenesis / what stops)?

A

2 arrests (stops):

In Meiosis I (prophase I -> diplotene)

In Meiosis II (metaphase II)

Meiosis II can be finished only AFTER the fertilization

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16
Q

Periods of oogenesis are?

A

Proliferation period.
Growth period.
Maturation period.

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17
Q

Proliferation period happens (when and what steps involved)?

A

3rd month of embryonic development.
From PGC → oogonia (2n).
Primary oogonia → secondary oogonia.

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18
Q

Growth period happens (when and what steps involved)?

A

4-6 month of embryonic development

Secondary oogonia → Primary oocytes.

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19
Q

Maturation period happens (when and what steps involved)?

A

7-8 month of of embryonic development.

Meiosis I. STOP at diplotene.

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20
Q

Put in real order of oogenesis meiosis I: zygotene, pachytene, leptotene, diplotene and STOP

A

Leptotene, zygotene, pachytene, diplotene and

STOP

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21
Q

Primary oocytes in embryonic ovaries are surrounded by (what cells)?

A

Follicular cells. They form an embryonic follicle

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22
Q

What happens postnatal period (after birth) - at the time of birth:

A

Primary oocytes remain in diplotene till the puberty.

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23
Q

What happens postnatal period - at the puberty:

A

400 000 primary oocytes.
Embryonic (primordial) follicles → primary follicles.
Maturation of primary oocytes.

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24
Q

Primary follicle consists of (?+?):

A

Oocyte I + follicular cells.

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25
Primary follicle structure:
``` Oocyte I: - Plasmatic membrane - Nucleus - Cytoplasm - Zona pellucida One layer of follicular cells. ```
26
What happens to the oocyte at the puberty?
Every month 5-15 oocytes I start maturation. Only one will mature in the end. Primary follicles → secondary (developing) follicles.
27
Secondary follicle structure? (2nd follicle developed from the 1st)
- Oocyte I - Zona pellucida - Several layers of follicular cells - Anthrum enlarges
28
Mature follicle structure? (developed from 2nd follicle)
- Oocyte I - Zona pellucida - Differentiation of follicular cells: »Corona radiata »Cumulus oophorus - Anthrum is enlarged more
29
What happens in maturation period of oocytes?
Only one oocyte I finishes meiosis I and develops to: One oocyte II (n), that continues with meiosis II and stops in metaphase II and one first polar body (n).
30
Cytokinesis happens by help of? (Oogenesis)
Actin – myosin contractile ring. Cytokinesis is UNEQUAL, but COMPLETE. In Meiosis I: one large cell – oocyte II (n) and one small cell – polar body (n)
31
Regulation of meiosis in oogenesis is controlled by:
MPF complex of Cdk2 and cyclin B.
32
After fertilization? (Oogenesis)
Oocyte II continues in meiosis II. | One large cell: mature oocyte II (egg) and small cell – polar body (n).
33
What happens in absence of fertilization?
Oocyte II stays in metaphase II of meiosis II. Secreting hormones, promotes development of the next oocyte.
34
Follicular cells consists of? (2)
Granulosa cells. Theca cells.
35
Granulosa cells:
Produce sex hormones – estrogen and progesterone. | Produce different growth factors.
36
Theca cells:
Internal – Theca interna – produce androgenes and progesterone. External – Theca externa – connective tissue, important in the ovulation.
37
Result of oogenesis is in a nutshell:
One mature oocyte II (n) and polar bodies, which are not used in fertilization.
38
The main function of polar bodies is:
To reduce the chromosome number.
39
Oogenesis occurs:
From 3rd month of embryonic life till the menopause
40
Spermatogenesis starts at:
Puberty and continues through life time. One cycle last +- 70 days.
41
Spermatogenesis occurs:
In testes (semineferous tubules).
42
Why don’t spermatogonia enter meiosis?
In human fetal testis, CYP26B1 does not seem to be expressed. During embryonic life Sertoli cells produce inhibitor of meiosis – PG D2
43
At the time of birth sex cells are located in?
Sex cords.
44
Sertoli cells: Tall columnar epithelial cells structures? Aika jolloin sperma ilman häntää :)
- with large nucleus, - abundant in euchromatin, - well developed Golgi complex - many mitochondria (Mt) - extended smooth ER
45
Sertoli cells functions:
- Surround developing sperm cells. - Secrete proteins and fluids, growth. - Trophic function - Synchronize the events of spermatogenesis.
46
Spermatogenesis periods:
Proliferation. Growth. Maturation. Spermiogenesis.
47
Proliferation period (when and what steps involved)? (Spermatogenesis)
Begins in embryonic life and continues through life time. During embryonic life Sertoli cells produce inhibitor of meiosis – PG D2. PGC → primary (A) spermatogonia (2n). Primary spermatogonia → secondary (B) spermatogonia (2n).
48
Growth period (when and what steps involved)? (Spermatogenesis)
Begins in puberty. Secondary spermatogonia grow → primary spermatocytes (2n)- Growth period is weak comparing to oogenesis
49
Maturation period (when and what steps involved)? (Spermatogenesis)
Two meiosis. | Lasts for 22-24 days.
50
Role of syncytium: (Cytoplasmic bridges)
Akap82 protein – important in tail formation. | Akap82 gene is located on X chromosome.
51
What is different in cytokinesis of spermatogenesis?
Cytokinesis is EQUAL, but INCOMPLETE. - Two cells of identical size - Male’s sex cell precursors remain joined by cytoplasmic bridges.
52
Steps of spermiogenesis? (Not periods)
- Formation of an acrosome - Nuclear morphogenesis - Formation of tail structures - Rearrangement of organelles - Sheding most of the cytoplasm
53
Formation of an acrosome:
Formed from Golgi complex. Enzymes allow sperm to penetrate oocyte.
54
Nuclear morphogenesis:
Changes in shape (from round to oval). Becomes more dense. Chromatin condensation. Sperm specific histones are produced.
55
Formation of tail structures:
Elongation of microtubules. | Distal centriole elongates.
56
Rearrangement of organelles:
Mitochondria fuse and form spiral around of the tail.
57
Sperm functions:
To deliver its set of genes to the egg. | To activate the egg.
58
Abnormal sperm and sperm production syndromes:
Azoospermia: » no sperm in semen (ejaculate) Oligozoospermia: »low sperm count (< 20 million spermatozoa per ml of ejaculate) Sertoli cell only syndrome: » in seminiferous tubules only Sertoli cells
59
Beginning and ending: (Spermatogenesis vs. oogenesis)
Begins at puberty, ends at death. Vs. Begins before birth, ends at menopause.
60
Encompass how many stages? (Spermatogenesis vs. oogenesis)
4 stages: proliferation, growth, maturation, spermiogenesis. Vs. 3 stages: proliferation, growth, maturation.
61
Primary cycles form how many? (Spermatogenesis vs. oogenesis)
One primary spermatocycle forms 4 sperm cells. Vs. One primary oocyte forms one egg and polar bodies.
62
Quantity? (Spermatogenesis vs. oogenesis)
Billions of sperm cells are produces at a time. Vs. One oocyte matures monthly.
63
Cytokinesis? (Spermatogenesis vs. oogenesis)
Cytokinesis is not completed until the end of spermatogenesis. Vs. Nuclear division takes place at the very end of oogenesis.
64
Acrosome undergoes exocytosis and what happens then?
Sperm releases digestive enzymes into | the Zona pellucida
65
The sperm migrates through the coat of the ___ ___ (Corona radiata) and binds to a receptor molecule in the ___ ___ of the egg (secondary oocyte)
follicle cells | Zona pellucida
66
Sperm-Egg Recognition & Binding Receptors of Zona pellucida mediators? (3)
ZP3 mediates sperm-specific egg binding. ZP2 mediates subsequent sperm binding. ZP1 important for structural integrity of Zona pellucida.
67
``` With the help of ___ ___ the sperm reaches the egg, and a ______ ____ (ADAM) of the sperm binds to a receptor (ZP2) on the ___ ____ ```
acrosomal reaction membrane protein egg membrane
68
The plasma membranes fuse making it possible for sperm cell to:
enter the egg
69
Cortical reaction:
Enzymes released from corticular granules harden Zona pellucida. Block the polyspermy (allow monospermy)
70
After sperm cell enters the egg:
Basal body of the sperm’s flagellum divides and forms the centrioles of zygote. Male and female pronuclei form synkaryon
71
Significance of fertilization:
Changes in the egg`s cytoplasm are induced. The diploid chromosome number is reestablished. Mixing of paternal and maternal chromosomes takes place.
72
What determines the sex?
SRY (-> Presence of Y-chromosome.) -> if present -> activates SOX9 -> Presence of Y-chromosome.
73
What happens to PAR1 in chromosomes during meiosis?
Crossing over
74
If Y-chromosome is present ->
Spermatogenesis
75
In which period of oogenesis does the crossing over occurs?
During meiosis I in prophase I IN maturation period.
76
In which periods of oogenesis the non-disjunction of chromosomes can occur?
During the maturation period of oogenesis in anaphase I. Non-disjunction occurs in anaphase I/II. The first non-disjunction could happen in the anaphase I of the proliferation phase in the mitosis. The second non-disjunction could happen in anaphase I of the meiosis I. The thrid non-disjunction could occur in the anaphase II after the fertilization.
77
What is zona pellucida?
Zona pellucida is a glycoprotein layer surrounding the plasma membrane of mammalian oocytes.
78
What does zona pellucida consists of?
Zona pellucida is an extracellular matrix composed of three glycoproteins: ZP1, ZP2, and ZP3. Receptors on the sperm plasma membrane attach to ZP3. Binding to ZP3 allows the sperm to adhere to the zona pellucida and is a critical step in fertilization. It triggers the sperm head to undergo the acrosome reaction.
79
What is zona pellucidas function in oogenesis and fertilization?
Zona pellucida supports communication between oocytes and follicle cells during oogenesis, protects oocytes, eggs, and embryos during development, and regulates interactions between ovulated eggs and free-swimming sperm during and following fertilization.
80
What is Corona radiata?
Corona radiata is formed by follicle cells adhering to the oocyte before it leaves the ovarian follicle. Corona radiata is formed when the granulosa cells enlarge and become cuboidal, which occurs during the transition from the primordial to primary stage.
81
What does corona radiata consists of?
Corona radiata is the inner layer of the cells of the cumulus oophorus and is directly adjacent to zona pellucida. Its main purpose in many animals is to supply vital proteins to the cell.
82
What is corona radiatas functions in oogenesis and fertilization?
For fertilization to happen, sperm cells rely on hyaluronidase to disperse the corona radiata from the zona pellucida of the Oocyte II. So, it is permitting entry into the perivitelline space and allowing contact between the sperm cell and the nucleus of the oocyte.
83
What is an acrosome?
Acrosome is an organelle that develops over the head (anteriorly) in spermatozoa (sperm cells) of animals / humans. It is a cap-like structure derived from the Golgi apparatus.
84
What is acrosome significance in fertilization?
The function of the acrosome reaction is to help the sperm get through the egg's protective coat and to allow the plasma membranes of the sperm and egg to fuse. This has three major consequences: the release of proteolytic enzymes, extension of the acrosomal process, and exposure of membrane proteins.
85
What is the role of centrioles of sperm cell in fertilization and what is their impact on meiosis II in oocyte?
Centriole serves as microtubule organizing center (MTOC) after fertilization and accumulates centrosomal components from the oocyte to form the sperm aster, zygote aster, and mitotic apparatus after fertilization.

Mol / Cel Biology (17 decks)

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