Unit 4: Lecture 17

What are the three reasons why cells divide to make identical copies of themselves?

1) asexual reproduction

2) growth and development

3) wound repair

What are the steps of binary fission?

1. circular chromosome attaches to the plasma membrane
2. the chromosome is duplicated
3. the cell grows and fibers for a contractile ring
4. fibers contract to pinch the cell into two

What is mitosis?

asexual reproduction that results in two identical cell s

What are the three primary stages of the eukaryotic cell cycle?

1. Interphase
2. Mitosis (M-phase)
3. Cytokinesis

What are the three stages of Interphase and their function?

1. G-1: first growth phase and is used to grow the cell and create more organelles for later division
2. S phase: chromosomes are duplicated or “synthesized”
3. G-2: second growth phase in order for last minute protein synthesis and a checkpoint

What were the 2 major steps in DNA replication?

1. unwind the parental strands
2. synthesize the new daughter strands

When chromosomes are duplicated in S-phase what do they create?

sister chromatids

What are sister chromatids connected at?

a centromere

What is the main function of mitosis?

to separate sister chromatids into their respective daughter cells

What are G0 cells?

cells that are not preparing for division

What are the stages of Mitosis?

1. prophase
2. prometaphase
3. metaphase
4. anaphase
5. telophase
6. cytokinesis

What occurs during prophase?

1. duplicated chromosomes begin moving to opposite poles
2. nuclear membrane and nucleolus both begin breaking down


1. centrosomes move to opposite poles

What occurs during Prometaphase?

1. the nuclear envelope is completely broken down
2. chromosomes are easily visible
3. centrosomes begin moving via spindle fibers

What does the mitotic spindle do?

organizes and separates the replicated chromosomes

What is the mitotic spindle comprised of?

1. Centrosomes (organize the spindle)
2. microtubules (form the spindle)

What are kinetichores?

regions of the centromere where microtubules attach to sister chromatids

Define Centromere

region that holds the sisters together

Define centrosome

where microtubules grow out of

Define chromosome

condensed DNA

What occurs during Metaphase?

1. sister chromatids are lined up at the equatorial plate
2. centrosomes are at the poles of the cell

What occurs during Anaphase?

1. sister chromatids are pulled apart at the centromere

How are sister chromatids pulled apart during Anaphase?

1. motor proteins move the daughter chromosomes toward the pole using ATP hydrolysis
2. the kinetochore microtubules are shortened towards the poles

What occurs during telophase?

1. cleavage furrow develops
2. nucleolus returns
3. nucelar envelopes reform

What occurs during cytokinesis of an animal cell?

the cleavage furrow creates a contractile ring which separates the two cells

What occurs during cytokinesis of a plant cell?

vesicles form a cell plate which separates into two new cells

Where are cell cycle checkpoints?

1. G1
2. G2
3. M

What is the role of cell cycle check points?

they detect errors in order to stop the cell cycle

How is the cell cycle regulated?

protein kinases (cyclin-dependent kinases). cyclin is accumulated throughout the cell cycle and is degraded during M phase. Cdk must be at a lower concentration for a cell to go back through the cycle

Does replication change the ploidy of a cell?

No it does not, chromosomes are duplicated and then split in half during cytokinesis.

What is the restriction point of the cell cycle?

The restriction point of the cell cycle is G1. If a cell moves past this stage they will go through the entire cell cycle. its the “point of no return”

What checked at the first check point in G1?

size, nutrients, molecular signals, and DNA integrity is checked to see if the cell is capable of division later on

What is checked at the second check point in G2?

DNA damage and DNA replication completeness in order to see if repairs are needed before division

What is checked at the third check point in M?

chromosome attachment to the spindle at metaphase in order to ensure that division goes smoothly