F. Cell cycle and cancer

Question 1

Cell division can take place in two ways

Answer 1

• mitosis

- meiosis

Question 2

What is produced in mitosis

Answer 2

Two daughter cells that have the same number of chromosomes as the parent cell and each other

Question 3

What is mitosis

Answer 3

Division of a cell that results in each of the genetically identical daughter cells having an exact copy of the DNA of the parent cell

Question 4

Mitosis is always preceded by a period during which the cell is not dividing called

Answer 4

Interphase

Question 5

What is interphase

Answer 5

Period in the cell cycle before mitosis where DNA replication takes

Question 6

What are the 4 stages of mitosis

Answer 6

• prophase
• anaphase
• metaphase
• telophase

Question 7

What happens during prophase

Answer 7

• chromosomes first become visible
• centrioles move to the poles
• spindle fibres develop
• nucleolus disappears and nuclear envelope disappears

Question 8

What are centrioles

Answer 8

Animal cells contain little organelles that produce spindle fibres
Plant cells don’t contain centrioles so centrioles aren’t necessary for spindle fibre production

Question 9

What happens during metaphase

Answer 9

-spindle fibres attach to centromeres of chromosomes and line them up along the equator

Question 10

What are chromosomes made up of

Answer 10

Two chromatids, each chromatid is an identical copy of DNA from the parent cell

Question 11

What are two chromatids joined by

Answer 11

Centromere

Question 12

What happens in anaphase

Answer 12

• centromeres divide into two and the spindle fibres pull the individual chromatid pairs to opposite poles (we now call them chromosomes)
• energy for this is provided by mitochondria

Question 13

What happens if the cell is treated with chemicals that destroy spindle fibres in anaphase

Answer 13

They remain at the equator

Question 14

What happens during telophase

Answer 14

• chromosomes reach poles and become thinner until they disappear leaving widely spread chromatin
• spindle fibres disintegrate
• nuclear envelopes and nucleoli reform
• cytokinesis (cytoplasm divides)

Question 15

What type of cell division occurs in prokaryotic cells

Answer 15

Binary fission

Question 16

Describe the steps in binary fission

Answer 16

• circular DNA and plasmids replicate
• cell membrane begins to grows and divides the cytoplasm
• cell walls form between the two molecules of DNA dividing the original cell into two identical daughter cells, each with a single copy of DNA and a variable number of plasmids

Question 17

How do virus’ replicate

Answer 17

• virus’ are non-living and therefore cannot undergo cell division
• they inject their genetic material into a host cell
• cells machinery assembles this which is a new virus

Question 18

Why is mitosis important (why is it essential to make exact copies of existing cells)

Answer 18

• growth. the growth of an organism requires the dividing of single diploid zygote. Mitosis ensures all genetic material is carried between each divide
• repair. If a cell is damaged or dies it is important new cells have identical structure and function
• reproduction. Single cell cell organisms divide by mitosis to give new organisms

Question 19

Only some cells in multicellular organisms…

Answer 19

Retain the ability to divide

Question 20

What are the three stages of the cell cycle

Answer 20

• interphase
• nuclear division (mitosis / meiosis)
• division of the cytoplasm (cytokinesis)

Question 21

What is the longest stage of the cell cycle

Answer 21

Interphase

Question 22

What is cancer

Answer 22

Uncontrolled growth and cell division causing tumours.

Question 23

What is the difference between benign and malignant tumours

Answer 23

• benign tumours grow more slowly and are more compact so are less life threatening
• malignant tumours grow more rapidly and are less compact so are more life threatening

Question 24

Drugs used to treat cancer usually disrupt the cell cycle, how does it do this

Answer 24

• preventing DNA from replicating

- inhibiting the metaphase stage of mitosis by interfering with spindle formation

Question 25

What is the problem with cancer treatment

Answer 25

They also disrupt the cell cycle of normal cells.

Question 26

What are the 4 requirements of semi-conservative replication

Answer 26

• 4 types of nucleotides
• both strands of the DNA molecule act as a template for the attachment of these nucleotides
• the enzyme DNA polymerase
• a source of chemical energy is required to drive the process

Question 27

Describe semi-conservative replication

Answer 27

• enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA
• double helix separates into its two strands and unwinds
• each exposed nucleotide strand then acts as a template which complementary free nucleotides bind by specific base pairing
• nucleotides are joined together in a condensation reaction by DNA polymerase forming phosphodiester bonds
• each new strand of DNA has one old one new therefore semi conservative

Question 28

Describe and explain the evidence for semi-conservative replication

Answer 28

• Two sample of bacteria grown in growth mediums, one containing N14 and one N15
• Sample of DNA from each batch was put into centrifuge and spun, heavier DNA is denser and settled lower in the centrifuge tube
• When bacteria from the N15 medium was removed and added to a N14 medium it was left for one round of DNA replication.
• If conservative replication old N15 DNA would settle at the bottom and N14 DNA would settle at the top
• If semi-conservative replication the DNA would have a old N15 strand and a new N14 strand meaning it would settle in the middle of the test tube