Cell Division

Question 1

Chromosomes

Answer 1

Chromosomes are Chromatin, in a more packaged format. First Histones (a protein) start to go around DNA and that forms nucleosomes. Then they condense further into a chromosome. This condensing is very important for mitosis, in fact, chromosomes are usually only there during mitosis.

The cells in the human body tend to have 46 chromosomes. 23 from mom and 23 from dad.

Chromatin: Made of loosely bound DNA and protein.

Question 2

Chromatid

Answer 2

Usually, chromosomes have 1 chromatid or one side of a chromosome. But sometimes, when cells replicate chromosomes end up with two chromatids or two sides of the chromosomes.

Here is an illustration:
https://cdn1.byjus.com/wp-content/uploads/2018/11/biology/2018/07/02064016/Difference-between-Chromosome-and-Chromatid1.png

Question 3

Chromatin

Answer 3

The unwrapped form of DNA found in the nuclease

Question 4

Centromere

Answer 4

Tight ball at the center of the chromosomes, holding the sister chromatids together during cell division.

Diagram:
https://www.genome.gov/sites/default/files/tg/en/illustration/centromere.jpg

Question 5

Interphase

Answer 5

The longest stage (They spend about 90% of the time in this phase), a stage in between mitosis where cells tend to grow, replicate DNA and carry out cell function. During this phase, there is chromatin in the nuclease.

G1-phase (Gap 1): [G1 phase is the longest usually]
→ Make more organelles
→ Synthesize proteins and enzymes for DNA replication
→ Repair damages in the DNA

S-phase (Synthetic Phase):
→ DNA Replication by enzymes called DNA polymerases (Cell now has 46*2=96 chromosomes)

G2 (Gap 2):
→ The cell grows in size by increasing cytoplasm and other things.

Question 6

Centrosomes

Answer 6

A cell structure that, along with protein microtubules called spindle fibers, helps separate the replicated chromosomes into the daughter cells. A centrosome has two centrioles (barrel-shaped proteins).

Question 7

Things before Mitosis

Answer 7

→ Centrosomes Replicate

→ DNA Replicates

Question 8

Prophase

Answer 8

→ Chromatin becomes chromosomes
↑ The Individual chromatids replicate and then are held together with centromeres to form
a chromosome
→ The nucleus completely disintegrates with the nucleolus disappearing and the membrane breaking down
→ The chromosomes start to go to the edges of the cell.
→ The Centrosomes (2 Centrioles) start moving to the “poles” of the cell and microtubules start to form

Question 9

Metaphase

Answer 9

→ The longest phase of mitosis
→ Chromosomes attach to the microtubules or spindle fibres right at the centromere
→ Chromosomes are then moved around by molecules called motor proteins (Attached to each side of the centromere [2 in total]) to line up at the equator of the cell. This is also partly due to the fact that other proteins, called dynein, are tightening the microtubules.

Question 10

Anaphase

Answer 10

→ The motor protein pulls so hard on the chromosomes that they spilt into chromosomes with one chromatid.
→ Once detached, they are pulled to either end of the cell as the spindle fibres shorten.

Question 11

Telophase

Answer 11

→ Nuclear membrane forms
→ Nucleolus starts to form
→ Chromosomes go to a more relaxed state, chromatin
→ The cell starts to pinch in the center, getting ready for the spilt. [This is called cleavage]

Question 12

Cytokinesis

Answer 12

→ The two halves of the cell start to push apart, eventually splitting into two new cells.

Important to note: In a plant cell, instead of pinching off, a new cell wall is created that divides the cell into two new cells.

Question 13

Mitotic Index

Answer 13

The ratio between the number of cells going through mitosis and the total number of cells in the population.

Question 14

What cells cannot divide (undergo mitosis)

Answer 14

→ Skin Cells 
→ Red blood cell
→ Gut lining cells
→ Some muscle cells
→ most neurons

Question 15

What are the reasons cells divide

Answer 15

1) Growth
2) Replace
2) Reproduction

Question 16

Reproduction: Asexual

Answer 16

When cells make identical copies of themselves without the need for another organism. (Think Mitosis for eukaryotic cells or Binary fission for prokaryotic cells).

Question 17

Reproduction: Sexual

Answer 17

Sometimes two organisms need to get two organisms need to come together to form a third organism. Genetic information from both organisms is taken and then combined to make the offspring.