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| Frage | Antworten |
| 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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