Cell cycle

Mitosis

• Undergone by all somatic cells (body cells)

  • All somatic cells will have a Diploid number of chromosomes

G1 phase, S phase, G2 phase

Stages of interphase

interphase

• Longest cycle in cells life

• Time when cell actually grows and divide

g1 phase

• Starts right after cell division

What happens?

1. Cell growth

2. Organelle duplication

3. Protein synthesis

4. Checkpoint monitoring

5. Preparation for DNA replication

6. Cell differentiation

7. Repair and recovery

s phase

• Where DNA replication occur

• Produces another chromatid after this phase

• X form of chromosome is seen after this phase

g2 phase

• Preparation for cell division

• Nuclear envelope encloses the nucleus

• The nucleus contains one or more nucleoli

• 2 centrosomes have formed by duplication of a single centrosome.

  • Each centrosome contains 2 centrioles.

• Chromosomes, duplicated during S phase, cannot be seen individually because they have not yet condensed.

centrosomes

Are regions in animal cells that organize the microtubules of the spindle.

prophase

• Chromatin fibers become more tightly coiled.

  • condensing into discrete chromosomes

  • observable with a light microscope.

• The nucleoli disappear.

  • To release the chromosomes into the cytoplasm

• Mitotic spindle begins to form

  • Composed of centrosomes and the microtubules that extend from them.

  • The radial arrays of shorter microtubules that extend from the centrosomes are called asters

• The centrosomes move away from each other, propelled partly by the lengthening microtubules between them.

prometaphase

• The nuclear envelope fragments.

• The microtubules extending from each centrosome can now invade the nuclear area.

• chromosomes have become even more condensed.

• A kinetochore, a specialized protein structure, has now formed at the centromere of each chromatid

  • thus, 2 per chromosome

• Some of the microtubules attach to the kinetochores, becoming “kinetochore microtubules,” which jerk the chromosomes back and forth.

metaphase

• All chromosomes are aligned at the center

• centrosomes are now at opposite poles of the cell

• chromosomes have all arrived at the metaphase plate

  • a plane that is equidistant between the spindle’s two poles.

  • The chromosomes’ centromeres lie at the metaphase plate.

• For each chromosome, the kinetochores of the sister chromatids are attached to kinetochore microtubules coming from opposite pole

Anaphase

• is the shortest stage of mitosis, often lasting only a few minutes.

• begins when the cohesion proteins are cleaved.

  • This allows the two sister chromatids of each pair to part suddenly.

  • Each chromatid thus becomes an independent chromosome.

• Two new daughter chromosomes begin moving toward opposite ends of the cell as their kinetochore microtubules shorten.

  • Because these microtubules are attached at the centromere region, the centromeres are pulled ahead of the arms, moving at a rate of about 1 μm/min.

• The cell elongates as the nonkinetochore microtubules lengthen.

• By the end of this phase: two ends of the cell have equivalent—and complete—collections of chromosomes.

telophase

• Two daughter nuclei form in the cell.

• Nuclear envelopes arise from the fragments of the parent cell’s nuclear envelope and other portions of the endomembrane system.

• Nucleoli reappear.

• The chromosomes become less condensed.

• Any remaining spindle microtubules are depolymerized.

• Mitosis, the division of one nucleus into two genetically identical nuclei, is now complete.

cytokinesis

• The division of the cytoplasm is usually well under way by late telophase, so the two daughter cells appear shortly after the end of mitosis.

• In animal cells, this involves the formation of a cleavage furrow, which pinches the cell in two.

checkpoint

when the cell undergoes cell cycle we have what we call the?

• If there is a cell that produced an abnormality, but was not caught at the ________, it will go on and on in the cycle, and that cell maybe abnormal.

• That cell maybe producing harmful proteins, this is one way cancer develops

meiosis

Sex cells undergo?

prophase 1

• Each chromosome pairs with its homologous.

• crossing over also called genetic recombination

  • The DNA molecules of non sister chromatids are broken (by proteins) and are rejoined to each other.

chiasmata

Prophase 1 : Meiosis

Each homologous pair has one or more X-shaped regions called?

• this is where the crossovers have occurred.

chromatids

we count chromosomes by the number of?

tetrad

Prophase 1 : Meiosis

the homologous chromosomes pair up with each other and form a unit called?

• It is called as this because its units have 4 chromatids

synapsis

Prophase 1 : Meiosis

• The process during which the homologous chromosomes pair up with each other is called?

chiasma

Prophase 1 : Meiosis

• In synapsis (pair up of homologous chromosomes), they will get a little closer together and they will be called as?

synaptonemal complex

Prophase 1 : Meiosis

• The protein complex is called as the?

• With the help of this, the 2 chromatids will swap material, and now this is what we call ass crossing over

recombinant

Prophase 1 : Meiosis

• Moving forward to meiosis 2, all the chromatids gets separated into different gametes

  • Everything that is happening in this chromosome is also happening to the others

• Now we can see that we get 4 different gametes

  • 2 of them we call as?

    • because they have a combination of alleles

genetic variability

Genetic recombination increases?

metaphase 1

• The alignment in here is by homologous pairs, unlike in metaphase in mitosis.

• By this time, the spindle fibers are attached to the kinetochores

anaphase 1

• the homologous pairs will be separated

  • but you will not be separating them by chromatids yet.

  • But rather you will be separating them into separate chromosomes.

telophase 1

Meiosis

• same with telophase in mitosis, you form a nuclear envelope.

• since you didin’t actually pull the chromatids apart.

  • you pull them apart to the sides, now after T1;

  • you will only get ONE HALF

  • therefore after this phase, the no. of chromosomes in the cells are just HAPLOID

prophase 2

Meiosis

• nuclear envelope will dissapear

• centromeres and the spindles form

• In late prophase 2, chromosomes are still composed of 2 cromatids

metaphase 2

Meiosis

• chromosomes will line up in the center like mitosis, in a single fine, no longer in homologous pairs anymore

anaphase 2

Meiosis

• breakdown of proteins holding the sister chromatins together

• start moving towards opposite poles as individual chromosomes

telophase 2 and cytokinesis

Meiosis

• 4 new nuclei are made and 4 new haploid cells form

diploid

both egg and sperm cells come form special mother cells that are ______ - meaning they have two sets of chromosomes

oogoniium

Female Side (Egg Cell Development)

• The mother cell of the egg

• still diploid, not ready to divide yet

primary oocyte

Female Side (Egg Cell Development)

• Grows form the oogonium

• gets big because it needs to give most of the cytoplasm to the egg

• now ready for meiosis 1

meiosis 1

Female Side (Egg Cell Development)

• Divides into

  • Secondary oocyte (haploid) - gets most of the cytoplasm

  • First polar body (haploid)- a small cell that wont be used

meiosis 2

Female Side (Egg Cell Development)

• Secondary oocyte divides into:

  • ootid (haploid) - this becomes the ovum (egg)

  • second polar body (haplod)- again wont be used

ovum

Female Side (Egg Cell Development)

• ootid turn into? - the final egg cell

spermatogonium

Male side (Sperm Development)

• The mother cell of sperm

• Each one can produce 4 sperm

• diploid

Primary spermatocyte

Male side (Sperm Development)

• Grows from spermatogonium

• Gets ready for meiosis 1

• diploid

meiosis 1

Male side (Sperm Development)

• Divides into 2 secondary spermatocytes

  • haploid

Male side (Sperm Development)

• Each secondary spermatocyte divides into 2 spermatids

  • haploid

• Totaling = 4 spermatids

spermatozoa

Male side (Sperm Development)

• Spermatids become ?