Cell division

Question 1

What is the cell cycle?

Answer 1

Results in division of cell and formation of two genetically identical daughter cell.

Question 1

What occurs during interphase?

Answer 1

DNA replicated

Portein synthesis occurs in cytoplasm

mitochondria/chloroplast grow and divide

Normal metabolic processes of cells occur

Question 2

Describe G0

Answer 2

When cell leave cycle either temporarily or permanently

Differentiation: cell becomes specialised to carry out specific function.

DNA may be damaged so cell enters permanent cell arrest.

Cell can become senescent —>. reached maximum number of divisions

Question 3

Describe G1

Answer 3

Transcription/translation/protein synthesis occur

Organelles duplicate

Cell grows in size.

Question 4

Describe synthesis

Answer 4

DNA replicated

During DNA replication, DNA polymerase makes many random and spontaneous errors resulting in mutations to DNA.

—-> Can be harmful, beneficial or neutral

Question 5

Describe G2

Answer 5

Second growth phase

Cell continues to increase in size

ATP increases

Duplicated DNA checked for errors

Question 6

What are the roles of the checkpoints?

Answer 6

Control mechanism of cell cycle.

Monitor and verify whether stages of cell cycle have been accurately completed.

G1 ——> if checked, triggers to being DNA replication. If not —> enters G0.

G2 ——> Determines if DNA has been replicated without error. If checked then cell initiates mitosis.

Metaphase checkpoint —-> spindle assembly checkpoint where all chromosomes should be attached to spindles.

Question 7

What is mitosis?

Answer 7

Nuclear division.

Both daughter cells genetically identical.

Each new cell has exact copy of DNA present int eh parent cell and same number of chromosomes.

Necessary for asexual reproduction.

Question 8

What is a chromosome?

Answer 8

All DNA in nucleus replicated in interphase.

A chromosome is a DNA molecule.

Two identical DNA molecules after synthesis is called a chromatid.

Two chromatids joined together at the region called the centromere.

Question 9

Why is it necessary to keep the chromatids together during mitosis?

Answer 9

So they can be precisely manoeuvred and segregated equally, one into each daughter cell.

Question 10

What are the stages of mitosis?

Answer 10

Prophase

Metaphase

Anaphase

Telophase

Question 11

Outline what happens in Prophase!

Answer 11

Chromatin fibres coil and condense to form chromosomes ——> visible with stain under light microscope.

Nucleolus disappears.

Nuclear membrane starts to break down.

Spindle shaped structures are formed from microtubules.

Two centrioles migrate to opposite poles of the cell.

Spindle fibres attach to specific areas on the centromere and move chromosomes to centre of cell.

Nuclear envelope = disappeared

Question 12

Outline what happens in metaphase!

Answer 12

Chromosomes moved by spindle fibres to form a plane in centre of the cell ——-> metaphase plate.

Question 13

Outline what happens in anaphase!!

Answer 13

Centromeres holding the chromatids in each chromosome divide.

Chromatids separated —> pulled to opposite poles of the cell by shortening of spindle fibres.

Question 14

Outline what occurs in telophase!!!

Answer 14

Chromatids now reached the poles —> now called chromosomes.

Two new sets of chromosomes assemble at each pole

Nuclear envelope reforms around them.

Chromosomes start to uncoil and nucleolus is formed

Cytokinesis begins.

Question 15

What is cytokinesis?

Answer 15

Actual division of the cell into two separate cells

Begins during telophase.

Question 16

How is cytokinesis performed in animal cells?

Answer 16

Cleavage furrow formed in middle of cell.

Cell-surface membrane pulled inwards by cytoskeleton until its close enough to fuse around the middle —> formation of 2 cells.

Question 17

How is cytokinesis performed in plant cells?

Answer 17

Vesicles from Golgi apparatus begin to assemble where the metaphase plate was formed.

Vesicles fuse with each other and cell surface membrane, diving the cell into 2.

New sections of cell wall form along the new sections of the membrane.

Question 18

What does meiosis mean?

Answer 18

Cell division that halves the original genetic material i cells to make haploid cells/gametes for sexual reproduction.

Sexual reproduction

Nucleus divides twice to produce 4 daughter cells.

Question 19

What are homologous chromosomes?

Question 20

What happens in Prophase 1?

Answer 20

Same initial steps of mitosis prophase.

Homologous chromosomes pair up

Crossing over occurs.
~~ Swapping of alleles
Happens at the chiasmata (point of breakage)

Question 20

What does bivalent mean?

Answer 20

Homologous chromosome pair.

Question 21

What happens in metaphase 1?

Answer 21

Homologous pairs of chromosomes assemble on the metaphase plate.

Independent assortment occurs —-> orientation of each homologous pair is random and can face either pole.

~~~Leads to genetic variation.

Question 22

What happens in anaphase 1?

Answer 22

Separates homologous chromosomes

No separation of the centromere.

Question 23

What happens in telophase 1?

Answer 23

Diplod —> Haploid

same as mitosis

Chromosomes uncoils and nuclear envelope reforms.

Question 24

What happens in meiosis II?

Answer 24

The second division is similar to mitosis, and the pairs of chromatids present in each daughter cell are separated, forming two more cells.

Question 25

What happens in prophase II?

Answer 25

Chromosomes condense and become visible.

Nuclear envelope breaks down

Spindle fibres form

Question 26

What happens in metaphase II?

Answer 26

Independent assortment occurs as due to crossing over the sister chromatids are no longer identical.

Question 27

What happens in anaphase II?

Answer 27

Separation of sister chromatids

Splitting of the centromere.

Question 28

What happens in telophase II?

Answer 28

Nuclear envelope reforms

Cytokinesis occurs

1 somatic diploid cell undergoing meiosis = 4 haploid cells in the end (gametes)