D 1.1 - DNA REPLICATION

• what is a replica


  an exact copy of something
• What is DNA replication?

  the production of new stands of DNA with base sequences identical to existing stands
• why can DNA be replicated

  the structure (double helix) makes it easier/ suited to be replicated repeatedly without limit
• what 2 processes is DNA replication needed for?

  reproduction and growth & tissue replacement in multicellular organisms
• Reproduction

  offspring need copies of the base sequence of their parents, so parents must replicate their DNA to reproduce
• growth and tissue replacement in multicellular organisms

  before cells divide into 2 daughter cells, DNA must be replicated to make new, identical cells
• what is cell division needed for

  growth and to replicate tissues where they have been lost
• what happens when DNA is replicated

  2 strands of the double helix must separate
• what are the original strands used as

  templates to guide the polymerization of a new strand
• what is polymerisation

  add nucleotides one by one to the growing DNA chain, incorporating only those that are complementary to the template
• how are new strands made

  formed by adding nucleotides one by one and linking them together
• What is a replication fork?

  a Y-shaped region where new DNA strands are elongating
• what is produced when replication is completed

  2 identical strands of DNA (composed of both an original strand and a newly synthesised strand)
• What is DNA referred to as?

  semi-conservative
• What does semi-conservative mean?

  Half old strand; half new strand
• what bases can be added to the new strand

  the complementary base that complements the original strands bases (e.g. A pairs with T)
• what do complementary bases form between each other

  hydrogen bonds with each other, stabilising the structure of DNA
• what are the base pairs

  Adenine pairs with ThymineGuanine pairs with Cytosine
• What is complementary base pairing?


  bases pair up with each other in a consistent way
• Why are complementary base pairs important?


  ensures a high degree of accuracy when new strands are assembled on a template strand and
• what accuracy does CBP make

  can check assembled base sequences, recognise any mispairings then cut out and replace the incorrect nucleotides
• what is a diploid human cell

  A cell containing two copies of each chromosome
• what is the accuracy of DNA replication

  1 in 10 billion bases are incorrect
• DNA replication - process overview

  multi-stage process carried out by an assemblage of functional subunits called a replisome (helicase and DNA polymerase are 2 types of proteins in replisomes)
• What is a replisome?

  group of proteins needed for DNA synthesis
• What is helicase?

  ring-shaped protein that separates the 2 strands of DNA molecule so that they can each act as a template for the formation of a new strand
• how does helicase unzip the DNA

  breaks hydrogen bonds between bases (allowing one strand to be pulled through the hole in helicases ring and the other to pass alongside)
• role of helicase

  unwinding and unzipping of DNA
• what does unwinding and unzipping cause

  tensions in the molecule which could cause supercoiling
• what is done to prevent supercoiling

  tensions are relieved by parts of the replisome
• What is the role of DNA polymerase?

  assembles new strands of DNA, using the two original strands as templates
• what does the replisome contain

  separate DNA polymerase for each strand
• How does DNA polymerase work?

  DNA polymerase catalyzes the POLYMERIZATION of deoxynucleotides into DNA. Only work in 5'--->3' direction. It adds deoxynucleotides onto the 3'-OH group.
• what happens when DNA polymerase moves across the template strands

  nucleotides are added, each time only one of the 4 bases are used (to make complementary base pairings) so hydrogen bonds can form
• what happens if hydrogen bonds do not form

  complementary base pairs are not formed, thus nucleotide breaks away again
• how are nucleotides linked to the end of the nucleotide

  makes covalent bonds between the phosphate group of the free nucleotide and the sugar of the nucleotide at the
• What is PCR?

  Polymerase Chain Reaction; used to amplify DNA (automated method)
• function of PCR

  doubles quantity of DNA with each cycle; only small quantity of DNA is required at the beginning
• What is the PCR machine called?

  PCR thermocycler
• what is DNA amplification


  the process of producing more DNA with a specific base sequence