2.7 dna replication, transcription & translation Flashcards
why is dna replication semi-conservative?
because when a new double-stranded DNA molecule is formed:
One strand will be from the original template molecule
One strand will be newly synthesised
how was the theory that DNA replication was semi-conservative confirmed?
with the Meselson-Stahl experiment in 1958
describe the 3 hypotheses for dna replication
- conservative: An entirely new molecule is synthesised from a DNA template (which remains unaltered)
- semi-conservative: Each new molecule consists of one newly synthesised strand and one template strand
- dispersive model: New molecules are made of segments of new and old DNA
describe the Meselson-Stahl experiment
- Nitrogen is a key component of DNA and can exist as a heavier N-15 or a lighter N-14
- DNA molecules were prepared using the heavier 15N and then induced to replicate in the presence of the lighter 14N
- DNA samples were then separated via centrifugation to determine the composition of DNA in the replicated molecules
results of the Meselson-Stahl experiment
After one division, DNA molecules were found to contain a mix of 15N and 14N, disproving the conservative model
After two divisions, some molecules of DNA were found to consist solely of 14N, disproving the dispersive model
what does helicase do?
Helicase unwinds the double helix and separates the two polynucleotide strands
It does this by breaking the hydrogen bonds that exist between complementary base pairs
The two separated polynucleotide strands will act as templates for the synthesis of new complementary strands
what does dna polymerase do?
DNA polymerase synthesises new strands from the two parental template strands
Free deoxynucleoside triphosphates (nucleotides with 3 phosphate groups) align opposite their complementary base partner
DNA polymerase cleaves the two excess phosphates and uses the energy released to link the nucleotide to the new strand
what does PCR stand for?
polymerase chain reaction
what is PCR?
an artificial method of replicating DNA under laboratory conditions, used to amplify large quantities of a specific sequence of DNA from an initial minute sample
what is Taq polymerase?
an enzyme isolated from the thermophilic bacterium Thermus aquaticus, extends the nucleotide chain from the primers
what is transcription
the process by which an RNA sequence is produced from a DNA template
direction of transcription
5’ to 3’
describe the process of transcription (4)
- RNA polymerase separates the DNA strands and synthesises a complementary RNA copy from one of the DNA strands
- When the DNA strands are separated, ribonucleoside triphosphates align opposite their exposed complementary base partner
- RNA polymerase removes the additional phosphate groups and uses the energy from this cleavage to covalently join the nucleotide to the growing sequence
- Once the RNA sequence has been synthesised, RNA polymerase detaches from the DNA molecule and the double helix reforms
gene
The sequence of DNA that is transcribed into RNA
antisense strand
The DNA strand that is transcribed and is complementary to the RNA sequence
sense strand
The strand that is not transcribed and is identical to the RNA sequence (with T instead of U)
where does transcription of genes occur?
in nucleus
where does translation occur?
in cytoplasm
codon
3 bases which code for one amino acid
translation
the process of protein synthesis in which the genetic information encoded in mRNA is translated into a sequence of amino acids on a polypeptide chain
translation mnemonic
mr cat app
process of translation
Messenger RNA -> goes to
Ribosome -> reads sequence in
Codons -> recognised by
Anticodons -> found on
Transfer RNA -> which carries
Amino acids -> which join via
Peptide bonds -> to form
Polypeptides
how has genetic code universality been utilised to produce human insulin in bacteria (for mass production)?
The gene responsible for insulin production is extracted from a human cell
It is spliced into a plasmid vector (for autonomous replication and expression) before being inserted into a bacterial cell
The transgenic bacteria (typically E. coli) are then selected and cultured in a fermentation tank (to increase bacterial numbers)
The bacteria now produce human insulin, which is harvested, purified and packaged for human use (i.e. by diabetics)
what is the start codon?
AUG
what are the stop codons?
UAA, UAG, UGA
how is replication and transcription similar?
Both DNA replication and transcription unwind and unzip the DNA. Hydrogen bonding is
broken. Strands are read to make complimentary base pairs. The original strand is read from
the 3’ to 5’ direction. The mRNA molecule has a phosphate sugar backbone as well
how are replication and transcription different?
mRNA, the product of transcription, is single stranded. It is created by RNA polymerase, not
DNA polymerase. There are no thymines in the transripted region but has Uracil in its place.
The phosphate sugar backbone is made of ribose, not deoxyribose
function of RNA polymerase
RNA polymerase creates the mRNA complementary strand from the parent DNA gene region.
What organelle does mRNA deliver the genetic code to?
ribosome
the process that results in protein synthesis
transcription
the function of tRNA in protein synthesis?
tRNA will transfer 1 of the 20 amino acids to another amino acid in the ribosome for polypeptide
formation
explain: the genetic code is universal
All living organisms use the same genetic code components: nucleotides, mRNA, amino acids,
transcription and translation processes
how many nucleotides per amino acid
3
what does AUG code for
methionine
To which end of a DNA strand are new nucleotides added?
3’
Name the enzyme used in the polymerase chain reaction.
Taq polymerase
