Cell Division, Cell Diversity & Cellular Organisation

Question 1

What is the cell cycle ?

Answer 1

The regulated sequence of events that occurs between one cell divsion and the next

Question 2

What are the stages of the cell cycle ?

Answer 2

Interphase 
Nuclear division (mitosis)
Cell division (cytokines)

Question 3

What happens during interphase?

Answer 3

G1 - Cells make RNA, Enzymes and other proteins requires for growth, Cell doubles in size
S - DNA replicates (resulting in each chromosome consisting of two identical sister chromatids)
G2 - Organelles Replicate

Question 4

What is the purpose of mitosis ?

Answer 4

growth and repair

Question 5

What are the stages of mitosis ?

Answer 5

Prophase
Metaphase
Anaphase
Telophase

Question 6

What happens during prophase ?

Answer 6

• Chromosomes condense - Chromosomes consists of two identical chromatids called sister chromatids joined at a centromere
• Centrosomes move towards opposite poles, spindle fibres form
• Nuclear envelopes condense, nucleolus disappears

Question 7

What happens during metaphase ?

Answer 7

Chromosomes line up along the equator, Spindle fibres attach to the centromere of the chromosomes

Question 8

What happens during anaphase ?

Answer 8

Sister chromatids separate at the centromere
Spindle fibres begin to shorten
The chromosomes are pulled to opposite poles

Question 9

What happens during telophase ?

Answer 9

Chromosomes decondense
Nuclear envelopes begin to reform around each set of chromosomes
Spindle fibres break down
Nucleolus reforms

Question 10

What is cytokinesis ?

Answer 10

Division of the cytoplasm and cell and cell into two

Question 11

How is the cell cycle regulated ?

Answer 11

Checkpoints throughout the cell cycle where genetic material is checked for any possible errors
In many cases the cell may destroy itself to prevent harmful mutations

Question 12

How is the cell regulated during G1 ?

Answer 12

Chromosomes are checked for damage. If damage is detected then the cell doesn’t advance into the S phase until repairs have been made

Question 13

How is the cell regulated during S Phase ?

Answer 13

Chromosomes are checked to ensure that they have been replicated. If all hormones haven’t been correctly replicated then the cell cycle stops

Question 14

How is the cell regulated during G2 phase ?

Answer 14

An additional check for DNA damage occurs after the DNA has been replicated. The cell cycle will be delayed until any necessary repairs are made

Question 15

How is the cell regulated during Metaphase ?

Answer 15

The final check determines whether the chromosomes are correctly attached to the spindle fibres prior to anaphase

Question 16

What is meiosis ?

Answer 16

Form of nuclear division that results in 4 genetically different haploid cells
Known as gametes (Contain half of the parents genetic material)

Question 17

What happens during meiosis I ?

Answer 17

Homologous Chromosomes pair up
Crossing over (exchange of sections of genetic material) occurs 
Cell divides into two. Homologous chromosomes separate

Question 18

What happens during meiosis II ?

Answer 18

Independent assortments of sister chromatids

Each cell divides again producing 4 haploid cells

Question 19

How does Meiosis produce genetic variation ?

Answer 19

Crossing Over - During Meoisis 1 the process which non-sister chromatids exchange alleles
Swapping of alleles result in a new combination of alleles
Independent assortment - Different combinations of chromosomes
Random fusion of gametes - During fertilisation any male gamete will form with any female gamate

Question 20

How do cells become specialised ?

Answer 20

Some genes are expressed while others are silenced due to cell differentiation mediated by transcription factors. Cells produce proteins that determine their structure & function.

Question 21

What is a transcription factor ?

Answer 21

A protein that controls the transcription of genes so that only certain parts of the DNA are expressed in order to allow cells to specialise

Question 22

How do transcription factors work ?

Answer 22

Move from the cytoplasm into the nucleus
Bind to promoter region upstream of target gene
Makes it easier or more difficult for RNA polymerase to bond to gene