Biology (Cellular reproduction)

Question 1

Cell cycle

Answer 1

G1—> S—>G2 = interphase (90 % cell cycle)

G1 Phase:

• production of more organelles
• cell size increase
• mRNA proteins produced
• First checkpoint
• May enter G0 if checkpoint is not passed.
  a. If enters permanently called Cellular Senescence
  b. Semi-permanently called Cellular Quiescence ( put on hold and induced to prepare for dividing again).

S phase:

• Genetic material is replicated
• DNA replication results in identical pair of DNA molecules (sister chromatids) attached at centromere.
• Centromeres exist before S phase.

G2 phase

• cell growth and checkpoint for cell damage/ missing proteins
• most microtubules produced, centrosomes duplicate.

Question 2

Cyclic Dependent Kinase of cell cycle

Answer 2

Enzymes important in coordinating cell cycle especially at checkpoints.

• signaling power due to binding with CYCLIN.
• Binding helps add phosphates to other molecules.
• Changes type of communication between cells temporarily.

Question 3

Spermatogenesis

Answer 3

Spermatogonia (2n) —> Mitosis —> Primary Spermatocyte (2n,2n)—> Meiosis I —> Secondary Spermatocyte (1n,1n)—> Meiosis II —> Early Spermatid —> Late Spermatid (1n,1n,1n,1n)—> Spermiogenesis (maturation of Sperm cell)—> Spermatoza

Question 4

Oogenesis

Answer 4

Oogonia (2n)—> Mitosis—>Primary oocyte (frozen in meiosis I until ovulation at puberty)—>Meiosis I —> Secondary Oocyte
—> Meiosis II—> ovum and second polar body.

Question 5

Fertilization

Answer 5

Primary oocyte layers: Zona Pellucida (inner layer), Corona Radiata (outer layer)

Acrosomal Process: penetrates corona radiata and binds to zona pellucida.
- Digestive enzymes break down zona pellucida and reaches oocyte.

Cortisol Reaction: sperm and ovum membranes fuse and calcium is released. Fertilization membrane created around ovum.

Question 6

Embryology

Answer 6

Indeterminate cleavage

• mitotic divisions in early embryo.
• divisions do not differentiate cells into specific types.
• maintain ability to divide.

Determinate is opposite of indeterminate
-e.g becomes neural cell, then part of CNS.

2, 4, 8, 16 cell stage—> morula (solid ball of cells) —> blastocyst (hollow ball of cells). Hollow part called blastocael and bottom part called Inner Cell Mass. outer layer called trophoblast that implants into uterus. —> gastrula

Question 7

Gastrulation

Answer 7

Blastocyst—> Gastrula

Inner Cell Mass divides into Epiblast (top) and Hypoblast (bottom)

Epiblast divides into:

• Epiblast displaces hypoblast
  a. Endoderm is first set of cells to dive through
  b. Mesoderm is second set of cells.
  c. Ectoderm does not dive through and left on top

Question 8

Neurulation

Answer 8

Group of nearby cells cause another nearby group to differentiate caused by notochord.

Question 9

Fetal circulation