2.7 DNA replication, transcription and translation Flashcards
DNA replication according to the semiconservative model
dna replication is SEMI-CONSERVATIVE mmhm yup
after replication, each new DNA strand consists of:
- 1 strand of DNA from og template molecule
- 1 strand of newly synthesized DNA
three hypotheses proposed for method of DNA replication
- conservative model
entirely new molecule syn from DNA template - semi-conservative model
one new strand, one template strand - dispersive model
segments of new and old DNA
what did the Meselson-Stahl experiment confirm?
the theory that DNA replication was semi-conservative
how did the meselson and stahl experiement yield its results 4
- used radioactive isotopes of nitrogen – heavier 15N and lighter 14N
- DNA molc prepared using 15N and replicated in presence of 14N
- after 1 division: mix of 15N and 14N – disproved conservative model
- after 2: some DNA solely 14N – disproved dispersive model
what are the 2 enzymes that coordinate DNA replication
helicase and DNA polymerase
what role does helicase play in DNA replication
- unwinds double helix, seperates the 2 polynucleotide strands
- breaks hydrogen bonds between complementary base pairs
- the 2 sep strands will act as templates
what role does DNA polymerase play in DNA replication
- synthesizes new strands from the 2 parental template strands
free deoxynucleoSIDE triphosphates (nucleotides with 3 phosphate grps) align opposite their complementary base partner
- cleaves the 2 excess phosphates – uses energy released to link the nucleotide to the new strand
what is PCR and what is it used for
Polymerase chain reaction
- artifical method of replicating DNA
- used to amplify large quantities of a specific sequence from a small sample
- each reaction doubles amt of DNA
3 steps to PCR
- denaturation – DNA sample heated to sep strands
- annealing – sample cooled to allow primers to anneal (at start and end)
- elongation – sample heated to optimal temp for heat-tolerant polymerase (Taq) (extends chain)
what is Taq DNA polymerase and what does it do
- an enzyme isolated from bacterium Thermus aquaticus
- optimal temp of 75C – can function at high temps used in PCR w/o denaturing
- it EXTENDS the nucleotide chain from the primers
what is transcription?
- process by which an mRNA sequence is produced from a DNA template copied by RNA polymerase
- RNA polymerase seperates DNA strands, synthesizes a complementary RNA copy
where does transcription occur
the nucleus (where DNA is)
- rna then moves to cytoplasm for translation
what is the strand that is transcribed called
the antisense strand
- complementary to the RNA sequence
what is the strand that is NOT transcribed called
sense strand
- identical to RNA sequence (with T instead of U)
4 steps of transcription
- RNA polymerase seperates the DNA strands
- RIBONUCLEOSIDE TRIPHOSPHATES align oppose their exposed complementary base partner
- RNA polymerase removes additional phosphate grps – uses the energy released to covalently join the nucleotide to the sequence
- once it has been synthesized, RNA polymerase detaches from DNA and double helix reforms
what direction does transcription occur
5’ –> 3’
what is translation?
- process of protein synthesis – genetic info encoded in mRNA is translated into AA sequence on polypeptide chain
where does translation occur
the cytoplasm
6 steps of translation
- ribosomes bind to mRNA, move in a 5’–>3’ direction until start codon AUG
- anticodons on tRNA align opp codons according to complementary base pairing
- each tRNA molecule carries a specific amino acid
- ribosomes catalyse formation of peptide bonds (betw adjacent AAs)
- ribosome moves along mRNA synthesizing a polypeptide chain until stop codon
- translation ceases at stop codon, polypeptide chain released
stop codons
UAA
UGA
UAG
what are codons and what do they do?
- base sequence of mRNA read by ribosome in triplets of bases – codons
- each codon codes for 1 AA with a polypeptide chain
- order of codons in mRNA determines order of AA
coding region of an mRNA sequence
begins with start codon
ends with stop codon
features of genetic code
- universal
- triplet code
- degenerate (more than one codon can code for the same AA)
- punctuated (start and stop codons)
- non overlapping (Each nucleotide is only read once)
what makes production of human insulin in bacteria possible
- genetic code is universal
- same codons code for same AA – genetic info transferrable
production of human insulin in bacteria
- insulin prod gene extracted and cut using restriction enzyme
- same restriction enzyme cuts bacterial plasmid – complementary sticky ends
- stuck tgt with DNA ligase
- recombinant plasmid inserted into transgenic bacteria w heat shock
- transgenic bacteria selected and cultured in fermentation tank
