Replication, Transcription and Translation Flashcards
DNA Replication
- The double helix is unwound by a helicase and topoisomerase
- One DNA polymerase produces the leading strand copy
- Another binds to the lagging strand. This enzyme makes discontinuous segments (called Okazaki fragments)
- DNA ligase joins them together
what is trascription ?
the process of synthesising an RNA transcript with the transfer of sequenece information from a DNA template
what is the DNA molecule trabsribed into ?
a complementary sequence of bases called mRNA which are used for protein synthesis
what is the DNA molecule trabsribed into ?
a complementary sequence of bases called mRNA which are used for protein synthesis
how is mRNA synthesised ?
- from DNA during transcription and forns a single nucleic acid chain
what pattern doe mRNA carry ?
- 3 nucleotide sequences which form codons that specify to the amino acid sequenece for protein sythesis
what is tRNA?
- key molecule that deciphers the 3 nucleotides codons of mRNA in protein synthesis
- tRNA has an antoi codon which which recorgnises the codon on mRNA to bring about protein synthesis
what does rRNA do in protein systhesis ?
- associates with a range of protein to form the small and large sub-units of ribososmes
- provide spatial and complementary structure to move along mRNA to bind to tRNA
what are the main 2 steps in protein systhesis ?
- transcription
- translation
what are the 3 stages of transcription ?
- Initiation
- Elongation
- Termination
what happens in the stage of initiation ?
- RNA polymerase (RNAP) + general trancription factors bind to promoter DNA
- RNAP creates a transcription bubble: separation of 2 strands of DNA by breaking hydrogen bonds between nucleotides
what are the 6 general transcription factors ?
- TFIIA
- TFIIB
- TFIID
- TFIIE
- TFIIF
- TFIIH
What is the RNA polymerase-promoter closed complex referred to as ?
preinitiation complex
what happens in the stage of elengating ?
- RNAP adds RNA nucleotides given that athey are complimentary
- RNA sugar-phosphate backbone forms with assistance from RNAP to form an RNA strand
- Proofreading mechanism for any errors
what happens in the stage of elengating ?
- RNAP adds RNA nucleotides given that athey are complimentary
- RNA sugar-phosphate backbone forms with assistance from RNAP to form an RNA strand
- Proofreading mechanism for any errors
What happens in the stage of termination ?
- hydrogen bonds in RNA-DNA helix break = newly synthesized RNA strand
- RNA is further processed
- RNA may exit cytoplasm through nuclear pore complex
what happen is Translation ?
mRAN is translated into protein
what happen is Translation ?
mRAN is translated into protein
what does each ribosome have ?
- Binding site for mRNA
- Three binding sites for tRNA ( A +P : charged tRNA bind during peptide synthesis, E : discharged tRNA)
what are the 3 stages of translation ?
- Initiation
- Elongation
- Termination
what happens in the initiation stage of translation ?
- initisted by Met-tRNAi coded by AUG near a 5’start codon
- 40S subunit with Met-tRNAi : 5’cap and scans mRNA start codon
what are Eukaryotic Initiation Factors (eIF) ?
interact with the 40S ribosomal subunit to stimulate assembly of the translation initiation complex
what are Eukaryotic Initiation Factors (eIF) ?
interact with the 40S ribosomal subunit to stimulate assembly of the translation initiation complex
what happens in the termination stage of translation ?
- Stop codons triggering release of the completed polypeptide chain UAG,UAA,UGA
- No tRNA exists for the stop codon
- Requires specific protein: releasing factor (eRF)
