module 2 - 3.9 DNA replication and the genetic code Flashcards
what are the 4 requirements for DNA to be a genetic molecule?
- must carry information (this is the genetic code)
- must replicate (this is DNA replication)
- must allow for the information to change (this is mutation)
- must control the phenotype (this is gene expression using protein synthesis)
where is DNA information stored?
in the sequence of nitrogenous bases
the sequence of A, C, T, and G encodes information in the form of what to make what?
encodes information in the form of genes to make proteins
when are most genes only accessible?
when DNA is unwound (chromatin)
why is extreme accuracy of DNA replication necessary?
in order to preserve the integrity of the genome in successive generations
in eukaryotes, when does DNA replication occur?
during the S phase of the cell cycle (stationary phase)
what is the S phase?
when the cell is doing its job
what is the replication rate like in prokaryotes/ eukaryotes?
prokaryotes - faster rate, lower fidelity (accuracy)
eukaryotes - slower rate, higher fidelity (accuracy)
what is semi-conservative DNA replication?
- one strand of a double helix is passed on unchanged to each daughter cell
- ‘conserved’ strand acts as a template for synthesis of a new, complementary strand by DNA POLYMERASE
what is N14?
non-radioactive isotope of nitrogen
what is N15?
radioactive isotope of nitrogen
where does DNA replication begin?
at the origin (methionine)
what is the origin within prokaryotic cells?
single circular DNA molecule or chromosome and so single origin of DNA replication
where is the origin within eukaryotic cells?
eukaryotic cells have multiple, linear DNA molecules/ chromosomes & each DNA molecule has multiple origins of DNA replication
where does DNA replication always go from and to?
5’ to 3’ direction
what does DNA polymerase require before synthesis can be initiated?
a free 3’ hydroxyl group
what is the difference between the old and new DNA strand to do with the way they are read?
the new DNA template strand is read in a 3’ to 5’ direction, whereas the old strand is read from 5’ to 3’ direction
why is DNA replication discontinuous?
the DNA forms complementary fragments of the DNA molecule from 5’ to 3’ on the new strand
(synthesises in sections)
why is DNA replication continuous?
the DNA forms its complementary strand from 3’ to 5’ continuously on the new strand
how are complimentary base pairs paired together?
collision theory
what is the enzyme that untwists the DNA?
helicase
what is DNA polymerase in a DNA molecule?
the active site
where does DNA replication happen?
a replication fork
what is a replication fork?
the structure that forms within the long helical DNA during DNA replication
what is a replication fork created by?
helicases, which break the hydrogen bonds holding the 2 DNA strands together in the helix
what happens once the hydrogen bonds are broken?
causes 2 strands of DNA and has 2 branching ‘prongs’
what happens when the 2 strands then serve as a template for the leading and lagging strands?
strands will be created as DNA polymerase which matches complementary nucleotides to the templates
what happens when the helicase unwinds the DNA at the replication fork? what does this result in?
the DNA ahead is forced to rotate
results in a build up of twists and tension in the DNA ahead
what are topoisomerases?
- enzymes that temporarily break the strands of DNA, relieving tension caused by unwinding 2 strands of DNA helix
- they add negative supercoils to DNA helix
what does primase do?
- creates short strands of RNA complementary to DNA strand
- allows DNA polymerase to bind to DNA and begin replicating it
what happens if you have a purine + purine?
base pair too thin
what happens if you have pyrimidine + pyrimidine?
base pair too wide
how many mistakes does DNA polymerase make?
1 in every billion base pairs copied
what does DNA polymerase do?
proof-reads the base pairs, corrects mistakes in the newly synthesised DNA
what happens when an incorrect base pair is recognised?
the DNA polymerase moves backwards by one base pair of a DNA
what does the 3’-5’ exonuclease activity of the DNA polymerase allow?
allows the incorrect base pairs to be exercised
what is a mutation within DNA?
mistakes lead to random and spontaneous changes in the base sequence of the newly synthesised strand
what are the differences between polypeptides and proteins?
polypeptides: chain of amino acids
proteins: chain of amino acids, virtually all enzymes are proteins, functional molecules
what is the genetic code?
set of rules used by all living cells to translate the information encoded in genetic material, into proteins
how is translation accomplished?
- by the ribosome which links to amino acids in an order specified by mRNA
- uses tRNA molecules to carry amino acids
what are 4 features of the genetic code?
- it is a triplet code (codon)
- it is universal among all living organisms
- it is a degenerate code (more codes than needed)
- it establishes the reading frame
where does is reading frame always set within polypeptides?
methionine (ATG)
what is the degenerate code?
- the redundancy of the genetic code (more codes than needed)
- the genetic code has redundancy but no variation
how is the reading frame defined/started?
- defined/started by the initial triplet of nucleotides where translation starts
- frame is a run of SUCCESSIVE, NON-OVERLAPPING CODONS
