DNA Replication, Meiosis And Mitosis

Question 1

What is the purpose of DNA replication?

Answer 1

To duplicate the code it carries. The code can then be passed to daughter cells.

Question 2

Step one of DNA replication.

Answer 2

DNA helicase (enzyme) unwinds and separates the double strand by breaking the weak H bonds. Each half of the parent molecule is used as a template.

Question 3

Step two of DNA replication.

Answer 3

The enzyme primase attaches a short sequence of RNA, known as a primer, to show DNA polymerase where to start adding nucleotides.

Question 4

Step three of DNA replication.

Answer 4

Complementary nucleotides are added by the enzyme DNA polymerase. Synthesis of the new daughter strand is in a 5’ to 3’ direction.

Question 5

Step four of DNA replication.

Answer 5

The result is the production of two identical DNA molecules that are each made of one parent strand and one daughter strand. Therefore it is semi-conservative.

Question 6

Step five of DNA replication.

Answer 6

In eukaryotic organisms, two sister chromatids are now ready for cell division. In prokaryotes, two circular chromosomes are now ready for binary fission.

Question 7

Mitosis

Answer 7

nuclear division occurring in the somatic cells that maintains the parental diploid number of chromosomes in the daughter cells; for bodily growth and asexual reproduction.

Question 8

Meiosis

Answer 8

cell division concerned with the production of gametes in sexually reproducing organisms. Involving one cycle of DNA replication and two rounds of cell division, results in the production of four haploid daughter cells from each original diploid cell.

Question 9

What is the cell cycle?

Answer 9

A continuous but ordered sequence of events in the life of a cell from when it was formed from a parent cell until its own division.

Question 10

What is interphase?

Answer 10

prior to any cell division, a doubling of the genetic material needs to take place.

Question 11

Prophase in mitosis

Answer 11

1. Chromatin threads condense to form chromosomes.
2. Nuclear membrane disintegrates and nucleus disappears.
3. Miotic spindle begins to form and is completed by the end of prophase. Spindle fibres attach to each chromosome at its centromere.
4. The two centrosomes (each containing two centrioles) move toward opposite poles of the cell.

Question 12

Metaphase in mitosis

Answer 12

1. Chromosomes move to centre of cell and line up along the equator.
2. Centromeres of the chromosome are aligned on equator.
3. The centrioles are located at opposite poles of the cell.

Question 13

Anaphase in mitosis

Answer 13

1. Spindle micro tubules shorten and pull on the centromere: sister chromatids separate.
2. Spindle microtubules pull sister chromatids to opposite poles of the cell.
3. At end of phase, each pole has a complete identical set of maternal and paternal chromosomes.
4. Sister chromatids now referred to as chromosomes.

Question 14

Telophase in mitosis

Answer 14

1. Chromosomes decondense to form chromatin; can no longer be seen under microscope.
2. Two new nuclear membranes form, one for each new daughter cell.
3. Nucleoli reappear and spindle apparatus disappears.
4. Cell elongates to become ready for cytokinesis.

Question 15

Prophase I

Answer 15

Chromosomes condense, nucleus disappears, spindle forms.

Question 16

Synapse

Answer 16

The process when homologous chromosomes lie side by side. The chromosomes are now called bivalent.
Chiasma/Chiasmata- the point at which the homologous arms contact.

Question 17

Metaphase I

Answer 17

Nuclear envelope degrades, chromosomes line up at the middle.

Question 18

Anaphase I

Answer 18

Maternal and paternal chromosomes moved to opposite pole. Separation is called disjunction.

Question 19

Telophase I

Answer 19

Spindle breaks down, cell starts to divide, nuclear envelope forms around 2 new nuclei.

Question 20

End of meiosis I

Answer 20

Cytokinesis occurs, meiosis I is complete.

Question 21

Prophase II

Answer 21

Spindle forms at right angles to the first one.

Question 22

Metaphase II

Answer 22

Chromosomes move to equator.

Question 23

Anaphase II

Answer 23

Chromatids separate and move to poles.

Question 24

Telophase II

Answer 24

Spindle fibres disappear, chromosomes decondense, nuclear envelope and nucleoli form.

Question 25

End of meiosis II

Answer 25

Cytoplasmic division follows so that four haploid cells are produced.