Unit 3.2.5 - DNA Replication and Cell Cycle Flashcards
What type of replication does DNA replicate through?
Semi-conservative replication
What are the four steps in DNA replication?
- ) DNA helicase breaks down the hydrogen bonds between the bases
- ) The two straps of DNA are unzipped into two single strands
- ) Free nucleotides from the nucleus attach to the complementary bases
- ) DNA polymerase makes the hydrogen bonds reform
Why is it called semi conservative DNA replication?
Each DNA molecule contains one strand from the original DNA and then one new strand
What were the original three ides for how DNA was replicated?
Conservative, dispersive and semi conservative
Which experiment proved DNA replication was semi conservative?
Melson’s and Stahl’s experiment
Describe how the heavy DNA was formed?
A sample of bacteria was grown in a broth containing heavy nitrogen, as the bacteria grew they took up the heavy nitrogen to make the nucleotides for the new DNA creating the heavy DNA
What is heavy nitrogen?
N - 15
What is light nitrogen?
N - 14
How did Melson’s and Stahl’s experiment prove that DNA replication was semi conservative?
The bacteria grown in heavy nitrogen was transferred to a broth containing light nitrogen and allowed to replicate. A new sample of DNA was taken and spun in a centrifuge and the DNA settles in the middle showing that the sample contained the old heavy nitrogen and the light nitrogen and so it must have replicated semi conservatively
What is the difference between DNA containing only heavy nitrogen and the DNA containing only light nitrogen when spun in a centrifuge?
The heavy DNA settled a lot lower than the light nitrogen in the test tube
What two sections is the cell cycle split into?
Interphase and mitosis
What are the three sections within interphase?
G1 phase, S phase and G2 phase
What happens during the G1 phase within interphase?
New proteins and organelles formed whilst the cell grows
What happens during the S phase within interphase?
DNA replicated and amount of chromatins doubled
What happens during the G2 phase within interphase?
Spindle proteins synthesised ready for mitosis
What is mitosis?
A type of cell division that produces two genetically identical daughter cells
Give two reasons why mitosis is important?
For cell growth and repair
What is cytokinesis?
When the cytoplasm divides after mitosis or meiosis forming two daughter cells
What is cell mass continually increasing during the cell cycle?
Because the cell is growing
When does the DNA mass double during the cell cycle?
During the S phase
Why does the DNA and cell mass all of a sudden half?
When the cell divides during cytokinesis
What four stages can mitosis be split into?
Prophase, metaphase, anaphase and telophase
What three things happen during prophase?
- ) Chromosomes condense becoming more visible
- ) Nuclear membrane breaks down
- ) Spindle fibres form
What two things happens during metaphase?
- ) Chromosomes line up along the equator
2. ) Spindle fibres attach to the chromosomes
What two things happen during anaphase?
- ) Chromosomes are pulled apart by the spindle fibres
2. ) Sister chromatids move to opposite poles
What two three things happen during telophase?
- ) Chromatids are at opposite ends of the cell
- ) Nuclear membrane reforms
- ) Cell divides
Describe the structure of a chromosome during mitosis?
Two sister chromatids joined together by a centromere
Label the stages within the cell cycle?
See flash card
Label the stages within mitosis?
See flash card
What is a mutagen?
Anything that causes a mutations
What is meant by mutagens are often carcinogenic?
They are cancer causing
Give three examples of mutagens?
Ionising radiation, UV radiation and certain chemicals like thalidomide
How can a mutation cause a tumour?
If a mutation occurs in a cell that controls cell division it can cause a cell to grow and divide out of control forming a tumour
How does chemotherapy kill cancer?
Prevents the synthesis of enzymes needed for DNA replication and so the cell is unable to replicate disrupting the cell cycle causing it to kill itself
How does radiation kill cancer?
It damages the DNA so that when it gets to the S phase and checks for damaged DNA it finds damaged DNA and kills itself preventing further growth of the cancerous cells
