Transcription and Translation Flashcards
Transcription Def.
Copying DNA to make mRNA
Translation Def.
Converts mRNA into protein
RNA Outline
Long unbranched sigle strand chain of ribonucleotides joined by 3’ to 5’ phosphodiester bonds. 3 Types: messenger, ribosomal, transfer
Transcription Outline
Catalyzed by RNA polymerase (no primer) Transcribes a DNA strand reading 3’ to 5’ and creating RNA 5’ to 3’. Gene contains distinct promoter (start) and terminator (end) sequences
Untranslated Regions (UTR)
Part of mRNA that doesn’t code for protein but provides information for translation process
Coding Strand (sense) (Def.)
DNA strand that mRNA is identical to (barring Uracil)
Template (antisense) Strand (def.)
DNA strand that RNA polymerase uses to form mRNA
Gene Orientations on DNA strands
Are opposite to each other
Translation Bubble Outline
How RNA Polymerase moves along DNA
Polydenation Signal
Sequences of bases that act as terminator sequence for transcription
Components of Complex (Eukaryotic) Transcription
Activators, repressors, basal transcription factors, Coactivatord
Activators Def.
Proteins that bind to enhancer genes. Speeding up transcription rate
Repressor Def.
Proteins bind to silencer genes . Slow transcription
Coactivators Def.
Adapter molecules. Integrate signals from activators and repressors
Basal Transcription Factors Def.
When stimulated by activators they begin transcription by placing RNA at start sequence
Why Eukaryotic Transcription is more complex
More genes, more non-coding DNA and differentiated/ selective expression
Heterogenous Nuclear RNA (hnRNA)
RNA molecules synthesised RNA polymerase 2 calles primary transcripts
Post-Transcriptional mRNA Processing Modification
hnRNA modified 5’ Capping, splicing and 3’ poly(A) tailing
mRNA precursors 5’ Capping Outline
7-methyl-guanosine residue addition, 5’-5’ triphosphate link to 5’ mRNA, guanyltransferase (capping enzyme) catalyses. Cap binds sets of proteins
5’ Capping Functions
Protect 5’ end from nuclease, guides mRNA through nuclear pore and permits translation initiation
3’ poly(A) tailing mRNA precursors
After polyadenylation signal, endonuclease recruitment and mRNA cleaved poly(A) polymerase adds 40-250 A residues to cleaved (3’) end. Tail shortens after entering cytosol.
Poly(A) Polymerase Functions
Stabilises mRNA molecules, slows 3’ -exonucleases (enzymes cleave nucleotides) and facilitates mRNA nucleus exit
mRNA precursor splicing outline
Necessary for eukaryotes because of genes in different regions in mature mRNA. Non-coding sequences (introns) are cut out. Small nuclear ribonucleoproteins (snRNPs) form spliceossome which atacks 5’ intron end. 5’ becomes attached to A nucleotide forming DNA loop. Free 3’ end attacks 5’ end of other. 3’ and 5’ ends bond covalently
Relationship between protein mRNA codes for and splicing
mRNA that code for different proteins have different genes kept/cut
Open Reading Frame (Def.)
Set of codons that run continuously bound by initiation and termination codons
Codon Def.
3 nucleotides which code for amino acid
Codon Notation
5’ base - Middle Base - 3’ base
Synonymous (silent) Genetic Mutation
Produces same amino acid
Nonsynonymous (missense) Gene Mutation
Produces different amino acid
Nonsense (stop) Gene Mutation
Stop codon added
Genetic Code Characteristics
Specific, universal (across species), redundancy (several codons code same amino acid), non-overlapping (strict sequence)
tRNA Structure
Cloverleaf shape. Amino acid binds to acceptor arm if tRNA molecule is complementary (Aminoacyl-tRNA-synthetases). Anticodon arm binds with mRNA
Wobble Base Pairing
Pairings between tRNA and matching codons are flexible (not perfectly aligned). Some tRNAs match more then 1 codon, single tRNA can recognise 2 codons. Increases tRNA efficency
Translation Initiation Outline
2 Parts. Components of chain formation assembly and recoginition of tRNA(met) molecule
Chain Formation Components assembly
2 ribosomal sub units (40S and 60S), mRNA, complementary tRNA (1st mRNA codon) Guanosine Triphosphate (GTP), initiation factors
Key Ribosome Sites
Aminoacyl Site (tRNA acceptor), peptidyl site (amino acid chain), exit site (deacylated tRNA)
Elongation Outline
Ribosome translates mRNA in 5’ to 3’ direction. Aminoacyl-tRNA delivered to Aminoacyl site via elongation factors. Peptide bonds form between aa by peptidetransferase. Growing aa chain moves to A site. Ribosome bond is translocated 3 nucleotides in 3’ direction (next codon)
Termination Outline
Occurs when 1 of 3 termination codons in A site (release factor signalled). Release binds to A site. New protein released. Disassembly of tRNA-ribososme-mRNA complex
