2.1 - Mitosis and Cell Cycle

Question 1

What is typically the goal of cell division?

Answer 1

The goal of cell division typically is to equally partition two more-or-less identical copies of genetic material between two daughter cells

Question 2

Who has an easier time with cell division: Eukaryotes or Prokaryotes?

Answer 2

Prokaryotes are comparatively simple, with only one chromosome, so have a relatively easy time sorting daughter chromosomes to daughter cells

Eukaryotes, with their longer DNA and multiple chromosomes, don’t have it nearly so easy

Question 3

What are chromosomes?

Answer 3

• Chromosomes are tightly packaged DNA
• They are found only during cell division
• DNA is not being used for macromolecule synthesis (creation of polymers)

Question 4

What is chromatin?

Answer 4

• Chromatin is unwound DNA
• It is found throughout interphase
• DNA is being used for macromolecule synthesis (creation of polymers)

Question 5

How is DNA organized?

Answer 5

DNA is organized in chromosomes
- Double helix DNA molecule wrapped around histone proteins like thread on spools
- DNA-protein complex = chromatin organized into long thin fiber condensed further during mitosis

Chromatin = long strand of spaghetti (gets squished even smaller during mitosis)

Question 6

What is a chromatid?

Answer 6

Each of the two threadlike strands into which a chromosome divides during cell division. Each contains a double helix of DNA.

Chromosome contains two sister chromatids (lines) that look like this: II

The two sister chromatids are held together by a centromere, making the chromosome look like an X

Question 7

What is a telomere?

Answer 7

A telomere is a compound structure at the end of a chromosome (the tip)

Question 8

What is a centromere?

Answer 8

Centromeres are small round segment that holds two chromatids together.

It is also the region of a chromosome to which the microtubules of the spindle attach, via the kinetochore, during cell division.

Question 9

What is a centrosome?

Answer 9

The centrosome is the centre of the microtubule production in a cell. It consists of 2 centrioles.

Question 10

What is a centriole?

Answer 10

A centriole consists of microtubules, and a pair of centrioles makes up a centrosome.

Question 11

What is a kinetochore?

Answer 11

A kinetochore is a protein structure in eukaryotes which assembles on the centromere and links the chromosome to microtubule polymers from the mitotic spindle during mitosis and meiosis.

• Protein structure near centromere/middle of chromosome where microtubules attach

Question 12

What is a nucleus?

Answer 12

• Control center of the cell
• Holds the cell’s genetic material (DNA)
• Regulates cell activities

Question 13

What are nucleoli?

Answer 13

• Found inside the nucleus
• Involved in making components for protein production (ribosomes)
• Not a separate membrane-bound structure

Question 14

What are the 4 phases of the cell cycle (in mitosis)?

Answer 14

G1, S, G2, mitosis

• Note: G1, S, and G2 are grouped together as ‘interphase’

Question 15

What occurs during interphase (general description)?

Answer 15

During G1, S, and G2 cell grows and continues to make proteins and organelles

Only replicates DNA during S phase

Question 16

What are the 2 different kinds of cell life cycle?

Answer 16

• Cell grows/matures to divide again
• Cell grows/mature to never divide again

Question 17

What kinds of cells divide multiple times?

Answer 17

• Epithelial cells
• Blood cells
• Stem cells

Question 18

What kinds of cells divide only once?

Answer 18

• Brain/nerve cells
• Muscle cells

Question 19

What occurs during G1 phase?

Answer 19

Beginning of a cell’s life:
- Follows Cytokinesis
- Cell begins growing to full size
- Transcription and Translation occur
- DNA only in single strands now

Question 20

What occurs during S phase?

Answer 20

DNA replicates itself (makes 2 double stranded DNA molecules):
- No more RNA will be made BUT leftover RNA (translation) can still be used for repairs etc.
- Centrosomes replicate
- Cells which do not go through this phase – can’t divide. (Eg. brain cells, some nervous tissue)*

• Research with this might help cancer

Question 21

What occurs during G2 phase?

Answer 21

Nucleus is well defined and still has the membrane
- Centrosomes present
- Chromosomes (DNA) has duplicated but is still a mess of strands
- New RNA transcribed to make proteins necessary for division – spindle fibers
- Leftover RNA (S phase) is used now for repairs

Cells are ready for mitosis

Question 22

By the end of G2 phase, what qualities does the cell have?

Answer 22

• Nucleus is defined
• Nucleoli are present
• Replicated Centrosomes
• DNA is duplicated
• DNA is still chromatin

Question 23

Define mitosis

Answer 23

Mitosis is unicellular reproduction (making 2 cells out of 1)

Question 24

What is mitosis used for?

Answer 24

• Used for repair, growth, and development from a fertilized egg
• Used to produce somatic cells (not sexual cells - gametes)

Question 25

What is the end result of mitosis?

Answer 25

Mitosis yields 2 identical daughter cells (produced asexually)

Question 26

How is mitosis affected by genetic variation?

Answer 26

Genetic variation is comparatively slow in mitosis (MUCH greater in meiosis)

Question 27

What are the 4 stages of mitosis?

Answer 27

- Prophase - Metaphase - Anaphase - Telophase

Question 28

What occurs during prophase (mitosis)?

Answer 28

- Chromatin fibers condense, becoming more coiled - Chromosomes are seen as two identical sister chromatids - Nucleoli vanish, and the nuclear membrane starts breaking down - A mitotic spindle forms from centrioles - Centrosomes move apart to poles - No more RNA is transcribed - The nucleus is still visible, and chromosomes are condensing, becoming thicker and visible

Question 29

By the end of prophase, what has occured?

Answer 29

- Chromosomes condense - Nucleoli vanish - Mitotic spindle forms - Centrosomes move apart

Question 30

What occurs during prometaphase?

Answer 30

In the transition from prophase to metaphase: - Nuclear envelope breaks apart - Microtubules enter the nucleus and engage with chromosomes - Kinetochores (handles for mitotic spindle) form at centromeres

Question 31

What occurs during metaphase?

Answer 31

- Spindle fibers connect with chromosomes - Centrioles are now on opposite sides - Fibers grab onto kinetochore - Chromosomes form a line in the middle of the cell (called metaphase plate) - The nucleus breaks down, and chromosomes line up in the middle

Question 32

By the end of metaphase, what has occured?

Answer 32

- Centrosomes are at opposite poles - Metaphase plate is formed - Chromosomes line up on the plate - Mitotic spindle is in action - Brief, static phase

Question 33

What occurs during anaphase?

Answer 33

- Sister chromatids split, moving to opposite poles of cell - By the end, each pole has a complete set of chromosomes. - Spindle fibers move chromosomes apart (chromosomes split and go to opposite sides).

Question 34

By the end of anaphase, what has occured?

Answer 34

- Starts with "sister" separation - Chromatids become chromosomes - "Sisters" go to opposite ends - All movement led by centromeres - Poles separate even more

Question 35

What occurs during telophase?

Answer 35

- Unconnected microtubules move even farther - New nuclei start to form - Protective membrane around nuclei begins to reappear - Chromatin is now less tightly wound

Question 36

By the end of telophase, what has occured?

Answer 36

- "Sisters" are at opposite ends - Protective layer around nuclei is reforming - Chromosomes are relaxing - Cytokinesis (cell division) is already happening

Question 37

What is cytokinesis?

Answer 37

Cell division ends with cytokinesis in telophase. This is when the cell actually splits into two identical daughter cells.

Question 38

How is cytokinesis different in animals and plants?

Answer 38

- Animals have a tightening middle part (cleavage furrow) like squeezing a water balloon - Plants use a cell plate (a line forms within the cell wall) to divide the cell

Question 39

What is the role of microtubules in mitosis?

Answer 39

Microtubules create spindle fibers that pull and arrange chromosomes, ensuring they separate correctly and go to the right places in daughter cells.