DNA

• What elements are in DNA?

  Carbon, hydrogen, oxygen, nitrogen and phosphorus
• What is the monomer of DNA called and what is it made up of?

  DNA nucleotide - made of a pentose sugar called deoxyribose, a phosphate group and a nitrogen-containing organic base.
• Describe DNA as a polymer.

  Many DNA nucleotides are chemically joined in condensations reactions to form phosphodiester bonds between them. This forms a polynucleotide chain. DNA is made up from 2 polynucleotide chains in a double helix structure.
• What different nitrogen-containing bases are found in DNA?

  Adenine, thymine, cytosine and guanine
• What is the sugar-phosphate backbone?

  The phosphate of one nucleotide is attached to the deoxyribose sugar of the adjacent nucleotide by phosphodiester bond. This means there are alternating phosphate then sugar all down the 'backbone' of the polynucleotide strand.
• What are phosphodiester bonds?

  Strong covalent bonds that hold adjacent nucleotides together.
• In which direction do the two polynucleotide strands of DNA run in relation to each other?

  Anti-parallel

  (one runs 5' to 3', the other 3' to 5')
• Which end of the polynucleotide strand is the 3' end in DNA?

  The hydroxyl group attached to the deoxyribose sugar.
• Which end of the polynucleotide strand is the 5' end in DNA?

  The phosphate group.
• How are the two polynucleotide strands in DNA held together?

  Hydrogen bonds between complementary base pairings.
• What are the complementary base pairings in DNA and how many hydrogen bonds form between each?

  thymine + adenine (2 H bonds)

  cytosine + guanine (3 H bonds)
• When in the cell cycle is DNA replicated?

  Interphase
• In DNA replication what happens to the double helix structure?

  It uncoils
• What does helicase do to DNA during replication?

  Helicase breaks the hydrogen bonds between the two polynucleotide strands, exposing the DNA nucleotides, forming two template strands.
• What happens to the exposed DNA nucleotides on the template strand during DNA replication?

  Free-floating DNA nucleotides form hydrogen bonds with their complementary base pairs on the template strand.
• What does DNA polymerase do in DNA replication?

  DNA polymerase catalyses condensation reactions between adjacent DNA nucleotides (bonded to a template strand) forming phosphodiester bonds in the newly synthesised strand.

  It has a specific tertiary structure with an active site complementary to the 3' end. Therefore it reads 3' to 5' and builds 5' to 3'.
• What is produced from one DNA replication?

  Two double helix DNA molecules, each with one parent strand and one daughter strand.
• What type of replication is DNA replication and what does this mean?

  Semi-conservative

  The DNA strands produced contain one parent strand and one daughter strand in their double helix.
• Which experiment provides evidence for DNA replication being semi-conservative?

  Meselson and Stahl
• What are the three stages of the cell cycle?

  Interphase, mitosis and cytokinesis
• What occurs in interphase?

  . cell enlarges

  . organelles replicate

  . new proteins are synthesised

  . DNA replicates to produce chromosomes with two sister chromatids joined at the centrometer
• What are the four stages of mitosis in order?

  Prophase, metaphase, anaphase, telophase
• What occurs in prophase?

  . chromosomes condense and become visible

  . the nuclear membrane begins to break down

  . spindles begin to form
• What occurs in metaphase?

  . chromosomes line up individually at the equator of the cell

  . chromosomes are attached to spindles at the centrometre

  . the nuclear membrane is completely broken down

  . spindles fully form
• What occurs in anaphase?

  . spindles contract

  . sister chromatids are separated and pulled to opposite poles by the centrometer as the spindles contract
• What occurs in telophase?

  . chromosomes decondense

  . spindles break down

  . nuclear membranes reform
• What is mitotic index?

  The proportion of cells which are undergoing mitosis in a tissue (written as a decimal).
• How do you calculate mitotic index?

  number of cells in mitosis ÷ total number of cells
• What factors affect time taken for the cell cycle to occur?

  Cell type and environmental conditions.
• How do we work out the duration of the cell cycle that a cell spends in a particular stage?

  . view the growing tissue under the microscope

  . measure the overall time the cell cycle takes

  . count the number of cells in the particular stage of mitosis

  . count the overall number of cells

  The number of cells at each stage of mitosis is proportional to the time each cell spends undergoing that stage.
• What is another name for cell division?

  Cell proliferation
• How does DNA's long, coiled, compact structure relate to its function?

  Allows storage of lots of genetic material in a small space.
• How does DNA's sugar-phosphate backbone relate to its function?

  Provides strength and protects the nitrogen-containing organic bases.
• How does DNA's double-stranded structure relate to its function?

  Both strands can act as templates in semi-conservative replication.
• How does DNA's complementary base pairings within its structure relate to its function?

  Ensures accurate replication.
• How does DNA's many hydrogen bonds within its structure relate to its function?

  . There are many of them to provide stability to the two strands

  . Individually they are weak so can be easily broken by DNA helicase to produce template strands for semi-conservative replication