Cancer Genome Flashcards
Describe DNA replication
Involves separation of the opposing strands in the double helix; beginning at origins of replication
- helicase unwinds the double helix, single-strand binding proteins prevents the two strands from coming back together
- primase lays down 5-10 nucleotide RN primer, creates 3’ end for DNA polymerase to add nucleotides
-DNA polymerase extends the strand, adding complementary nucleotides
- leading strand runs 5’ to 3’ toward replication fork
-lagging strand runs 5’ to 3’ away from replication fork (done in a series of small fragments)
- topoisomerase: prevents supercoiling of double helix downstream of replication fork (nicks DNA strands to allow unwinding to relieve tension then reseals nicks)
- RNA primers are removed and different DNR polymerase fills gaps, DNA ligase seals remaining nicks
DNA transcription
Process by which RNA polymerases create RNA transcripts from DNA
- mRDNA transcripts can go on to be processed and translated to peptides
RNA polymerases
Create transcripts in the 5’ to 3’ direction
-polymerase 1: mainly transcribes genes encoding ribosomal RNAs
-Polymerase 2: transcribes genes encoding mRNAs
-Polymerase 3: transcribes genes encoding small regulatory RNAs (e.g. miRNAs, and tRNAs)
Steps of DNA transcription
- Initiation
- Elongation
- Termination
- Post-transcriptional RNA processing
DNA transcription: initiation
-first step in transcription
-RNA polymerase binds to promoter region at a consensus sequence (TATA box (TATTAA) is most common consensus sequence)
-additional transcription factors bind with RNA polymerase to create a protein complex to carry out transcription
-enhancer regions bind transcription factors and alter the 3D DNA structure
-binding factors to the promoter and enhancer regions determines whether transcription can start and its rate
DNA Transcription: Elongation
-addition of ribonucleotides to 3’ end of RNA strand by polymerase
-transcription can pause during this stage; may/may not restart
-Myc protein plays key role in ensuring transcription continues
DNA transcription: termination
halting of elongation of the rNA transcription
- involves specific termination sequences
Post-transcriptional RNA processing
-undergo further changes following termination: addition of the 5’7-methyguanosine cap and poly(A) tail stabilize mRNAs and facilitate translation
-pre-mRNAs involves cutting out certain segments (introns) and joining together the remaining segments (exons) that will be translated to the final protein products
-other types of RNAs may also undergo processing to their active forms
mRNA translation
-carried out by ribosomes
-mRNA is read 5’ to 3’
-nucleic acids are divided into triplets to form codons that specify amino acids
-aminoacyltRNA with an anticodon sequence complementary to the codon will bind to the mRNA and ribosome and transfer the appropriate AA to the growing peptide
-large ribosomal subunit has 3 sites that bind aminoacyltRNAs
what are the 3 sites on the ribosomal subunit that binds aminoacyltRNAs
-amino acid (A) site: site where tRNA anticodon base-pairs with the codon –> ensures addition of the appropriate AA
-polypeptide (P) site: site where the AA is transferred from the tRNA to the polypeptide chain
-exit (E) site: site that binds empty tRNA before it is released back into the cytoplasm
Translation starts at the start codon which is always ___ which corresponds to ___
- codon is always AUG
-corresponds to methionine, the first AA in every peptide
Steps of mRNA translation
- Initiation
-initiation factors IF1, IF2m IF3 bind to the small ribosomal subunit - elongation: synthesis of the polypeptide chain
-ribosome moves in 5’-3’ direction
-process requires elongation factors (proteins)
3.termination: release of the polypeptide from the ribosome
-reaches one of 3 termination codons (UAA, UAG, UGA)
-release factors bind and cause dissolution of the ribosome complex, releases both mRNA and the polypeptide
base substitution
a point mutation in which a base is substituted for another,
