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A-Level AS AQA BIOLOGY Flashcards on THE CELL CYCLE, MITOSIS AND CANCER BIOL2, created by ashiana121 on 05/25/2015.

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Question Answer
What are the two main stages of cell division? Nuclear division followed by cell division
What are the two types of nuclear division? Mitosis and meiosis
What is the name given to the method of DNA replication that is universally accepted? Semi-conservative replication
What are the 4 requirements for semi-conservative replication to take place? 1. The four types of nucleotide (and bases) must be present 2. Both strands of the DNA must act as a template for the attachment of the nucleotides 3. The enzyme DNA polymerase is needed to catalyse the reaction 4. A source of chemical energy is required
In the semi-conservative method, which enzyme acts first and what does it do? DNA helicase breaks the h-bonds linking the base pairs of DNA
What does this result in? The double helix separates into two individual strands and unwinds
What do these polynucleotide strands than act as? A template to which free nucleotides are attracted to (attracted to their complementary base)
What is required to activate these free nucleotides? Energy
How are the activated nucleotides jointed to their complementary base pair? DNA polymerase
What does this form? The 'missing' polynucleotide strand on each of the two original strands of DNA
So, what do each of the new DNA molecules contain? One original strand and one new strand - this is why its called semi-conservative
Which two scientists conducted an experiment to test the hypothesis of the semi-conservative method? Meselsohn and Stahl
Which three facts did they base their work on? 1. All the bases contain nitrogen 2. Nitrogen has two isotopes (14 and 15 - 15 is heavier) 3. Bacteria will incorporate nitrogen from their growing medium into any new DNA that they make
They reasoned that bacteria growing on a medium containing 14N would be _______than bacteria grown on a medium containing 15N Lighter
They labelled the 'old' DNA by _______ __ __ _ _______ __ ____ Growing it on a medium of 15N
Where did they then transfer the bacteria and what did they allow it to do? Transferred it to a medium of 14N and allowed it to replicate once (for one generation)
What would the mass of each new DNA molecule depend on? Which method of DNA replication had taken place (conservative or semi-conservative)
How did they separate the different DNA types? They extracted the DNA and centrifuged it
Where did the ligher DNA collect and where did the heavier DNA collect? Lighter DNA - nearer the top Heavier DNA - nearer the bottom
What is the definition of mitosis? Nuclear division producing two daughter nuclei that have the same number of chromosomes as the parent cell and as each other
In which rare event may the daughter cells NOT have identical DNA to the parent cell? Mutation
What is name given to the period of time before mitosis in which the cell is not dividing? Interphase
What important process occurs during interphase? DNA replication
Mitosis is continuous process but it can be divided into 4 stages. What are these four stages? Prophase Metaphase Anaphase Telophase
What happens during prophase? The chromosomes become visible and the nuclear envelope disappears
What happens during metaphase? The spindle forms and chromosomes line up on the center of the cell
What happens during anaphase? Spindle fibres attach to the chromatids and contract Chromatids are pulled appart to opposite poles
What reforms during telophase? The nuclear envelope
And then what follows? Division
What are the three main reasons mitosis is important? - Growth - Differentiation - Repair
What are the three stages of the cell cycle? Interphase Nuclear division Cell division
Interphase occupies most of the cell cycle. What are the three parts of interphase? G1 S G2
What is G1? First growth phase - when the proteins from which cell organelles are made are produced
What happens during S phase? When DNA is replicated
What happens during G2 phase? Organelles grow and divide and energy stores are increased
What happens during nuclear division? The nucleus divides
By what process does the nucleus divide into 2? Mitosis
How many does the nucleus divide into during meiosis? 4
What is cancer? A group of diseases caused by a growth disorder of cells
Cancer is result of damage to what? Genes that regulate mitosis and the cell cycle
What does this lead to? Uncontrolled growth of cells - an abnormal group of cells (tumor) develops and expands in size
How do drugs used to treat cancer (chemotherapy) disrupt the cell cycle? - Preventing DNA from replicating - Inhibiting the metaphase stage of mitosis by interfering with spindle formation
What drugs can be used to prevent DNA from replicating? Cisplatin
What drug can be used to inhibit metaphase by interfering with spindle formation? Vinca alkaloids
What is the problem with such drugs? They also disrupt the cell cycle of normal cells
However why are cancer cells damaged to a greater degree than normal cells? Because they have a fast rate of division
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