Mitosis and Meiosis

Question 1

What is the role of the ftsZ protein in binary fission?

Answer 1

• ftsZ protein forms the FtsZ ring that constricts the middle of a cell dividing by binary fission
• causes dividing cell to form two new cells

Question 2

What are the stages in a cell cycle?

Answer 2

• M = mitotic phase
• G1 - gap/ growth phase 1
• S - DNA synthesis
• G2 - gap / growth phase 2

Question 3

What is cytokinesis?

Answer 3

• division of a cell’s cytoplasm, separate to the nuclear division

Question 4

Cytokinesis in animal cells

Answer 4

• process also known as cleavage
• furrowing of cell membrane - activity of contractile ring (myosin II and actin)
• plasma membrane constricts in the middle
• eventually 2 daughter cells separate

Question 5

Cytokinesis in plant cells

Answer 5

• cylindrical structure (phragmoplast) forms from remains of spindle microtubules
• a double membrane structure surrounds the early cell plate
• membranes expand and fuse with the surrounding cell to form two daughter cells

Question 6

Chromosome number after mitosis

Answer 6

• mitosis produces two daughter cells which are diploid

- contain the same number of chromosomes as the original cell

Question 7

chromosome number after meiosis

Answer 7

• meiosis produces four haploid daughter cells (half of original cell)

Question 8

Describe G1 phase

Answer 8

• Cells usually spend the most time in this phase
• this phase occurs before S stage (synthesis)
• the cell grows until it is large enough for DNA synthesis to occur

Question 9

What occurs in the S phase of interphase?

Answer 9

• DNA molecules are copied so there are molecules identical to the parent cells

Question 10

Describe the sequence of steps that occur during DNA synthesis?

Answer 10

• single stranded chromosomes where the DNA and proteins are tightly coiled
• enzymes disrupt the hydrogen bonds in the double helix chain and the two strands open, exposing unpaired bases
• using the existing DNA strands as a template, enzymes bring new complementary bases
• replication of one strand is continuous and the other is discontinuous
• the 2 new DNA molecules formed are identical to each other
• the DNA is joined at the centromere
• in the end the chromosomes consist of two identical strands (x-shaped)

Question 11

Describe what occurs in Phase 2 of interphase and when it occurs.

Answer 11

• after S phase
• further prepares the cell for division
• centrosomes outside the nucleus divide
• centrosomes serve as mitotic centres which organise microtubules

Cell maintains a granular appearance due to the loosely coiled DNA.

Question 12

Define mitosis and list the steps involved.

Answer 12

Process where the replicated chromosomes of a single cell are divided into two identical daughter cells.

• prophase
• metaphase
• anaphase
• telophase

Question 13

Prophase

Answer 13

• nuclear envelope breaks down
• chromatin (visible in the cell during interphase) condenses into chromosomes
• the spindle microtubules assemble

*Think of Prophase as preparing

Question 14

Metaphase

Answer 14

• kinetochores develop at the centre of each duplicated chromosome
• chromosomes become arranged equatorially on the mitotic spindle.
• microtubules attached to the kinetochores assist in this alignment

Question 15

Anaphase

Answer 15

• the kinetochore microtubules pull the two sister chromatids towards the opposite poles of the spindle

Question 16

Telophase

Answer 16

• Separated daughter chromosomes arrive at the poles.

* A new nuclear envelope re-forms around each group of daughter chromosomes.

Question 17

What is Meiosis?

Answer 17

• the cell division that occurs in sexually reproducing organisms to produce two haploid daughter cells

Question 18

Kinetochore

Answer 18

Structure that attaches spindle microtubules to chromosomes so that they can be pulled apart (is a protein complex).

Question 19

Prophase I

Answer 19

• the chromosomes synapse (align) and they cross-over

Question 20

Metaphase I

Answer 20

• microtubules attach to the homologous chromosomes

- homologous chromosomes align on the metaphase plate

Question 21

Anaphase I

Answer 21

• Homologous pair of chromosomes separate into opposite poles of the cell and separate into cells
• daughter cells contain one chromosome from each homologous pair
• cell is diploid

Question 22

Centromere

Answer 22

region of a chromosome where 2 chromatids are attached.

Question 23

Centrosome

Answer 23

Area surrounding the centrioles which serves as a microtubule organising centre.

Question 24

Centriole

Answer 24

An organelle that is involved in the development of spindle fibres during cell division. present in eukaryotic (but not plant cells).

Question 25

Diploid

Answer 25

Having 2 sets of chromosomes (2n); each chromosome exists in pairs.

Question 26

Aster

Answer 26

star like arrangement of microtubules radiating from centrioles.

Question 27

Chromatin

Answer 27

Material which eukaryotic chromosomes are composed.