2.7 DNA-> Proteins Flashcards
what kind of process is DNA replication? (3)
semi-conservative process (when a new double-stranded DNA molecule is formed)
- one strand will be from the original template molecule
- one strand will be newly synthesised
why is DNA replication a semi-conservative process?
because each nitrogenous base can only pair with its complementary partner
- A T
- C G
what enzymes are involved when DNA is replicated?
helicase and DNA polymerase
what characteristic does the formed DNA strand have? (2)
- each new strand formed will be identical to the original strand separated from the template
- 2 semi-conservative molecules formed will have an identical base sequence to the original molecule
who confirmed that DNA replication was semi-conservative?
Meselson-Stahl
before the Meselson-Stahl experiment what three hypotheses had been proposed?
- conservative model- an entirely new molecule is synthesised from a DNA template
- semi-conservative - each new molecule consists of one newly synthesised strand and one template strand
- dispersive model - new molecules are made of segments pf new and old DNA
how did Meselson and Stahl experiment the validity of the three models? (3)
using radioactive isotopes of nitrogen (N is a key component of DNA)
- DNA molecules were prepared using heavier 15H and includes to replicate in presence of lighter 14N
- the samples were then separated to determine the composition of DNA in the replicated molecules
what were the results of the experiment? (3)
- 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 is the role of helicase? (3)
- unwinds the double helix and separates the 2 polynucleotide strands
- by breaking the H bonds that exist between complementary base pairs
- 2 separated polynucleotide strands will act as templates for the synthesis of new complementary strands
what is the role of DNA polymerase? (3)
- synthesises new strands from 2 parental template strands
- free deoxynucleoside triphosphates (nucleotide w/ 3 phosphate groups) align opposite their complementary base partner
- DNA polymerase cleaves the 2 excess phosphates and uses the energy released to link the nucleotide to the new strand
what is PCR (polymerase chain reaction)?
artificial method of replicating DNA under laboratory conditions
- PCR is used to amplify large quantities of a specific sequence of DNA from an initial minute sample
- each reaction doubles the amount of DNA (30 cycles creates over 1 billion copies)
what is the process of PCR?
reaction occurs in a thermal cycler and uses variation in temperature to control the replication process:
1. denaturation - DNA sample is heated (-90) to separate the 2 strands
2. annealing - sample is cooled (-55) to allow primer to anneal (primers designate sequence to be copied)
3. elongation - sample is heated to the optimal temp for a heat-tolerant polymers (Taq) to function (-75)
what is Taq polymerase and its function?(3)
- an enzyme isolated from a thermophilic bacterium
- as this enzyme’s optimal temp is -75 it is able to function at the high temps used in PCR without denaturing
- Taq polymerase extends the nucleotide chain from the primers therefore, primers are used to select the sequence to be copied
what is transcription?
the process by which an RNA sequence is produced from a DNA template
what is the process of transcription? (4)
- RNA polymerase separated the DNA strands and synthesised a complementary RNA copy from one of the DNA strands
- when the DNA strands are separated, ribonucleoside triphosphate align opposite their exposed complementary base partner
- RNA polymerase removed the additional phosphate groups and uses the energy from the cleavage to covalently join the nucleotide to the growing sequence
- once the RNA sequence has been synthesised, RNA polymerase detached from the DNA molecules and the double helix reforms
