BIO2: Central Dogma: Transcription and Translation Flashcards
Describe the Central Dogma
Process which proteins are synthesized from genetic code (DNA -> RNA -> protein)
Describe transcription
DNA -> RNA: mRNA is synthesized using DNA as a template
What synthesizes mRNA from the DNA template?
RNA polymerase
Where does DNA transcription occur?
In the nucleus for eukaryotes
What is the difference between DNA Pol and RNA Pol?
RNA polymerase does not require a primer, RNA Pol cannot proofread the synthesized RNA (transcription errors are more common than replication errors)
What are the steps of transcription?
- Initiation: RNA Pol and factor sigma form haloenzyme to bind promoter region of DNA
- Elongation: RNA Pol add free floating nucleotide
- Termination
- Regulation of Transcription: through enhancers and repressors
Define factor sigma
A helper molecule that binds to the promoter region of the DNA along with RNA polymerase
What is the difference between prokaryotic and eukaryotic promoters
Prokaryotic promoters have specific sequences at -10 and -35 (upstream) which bind to RNA Pol. Eukaryotic promoters have “TATA” boxes with many T and A bases
Define promoter
A region of the DNA just upstream from the setart site that binds to RNA polymerase and factor sigma to initatie transcription
What direction is RNA elongated?
5’ to 3’
Describe translation
RNA -> protein: mRNA instructions incode polypeptide formation by ribosomes and tRNA
Where does DNA translation occur?
In the cytoplasm
Describe codon
3 nucleotides of mRNA that are complementary to the DNA template; each codon codes for a single amino acid
Define anticodon
3 nucleotides of tRNA that are complementary to the mRNA codon
Describe wobble pairing
Wobble pairing occurs when baes pairing doesn’t follow watson-crick rules (A/T/U, C/G) between codons and anticodons
Start codon
AUG (methionine)
Stop codon
UAA, UGA, UAG (u are annoying, u go away, u are gone)
How many total codons are there?
There are 64 codons total, 3 stop and remaining 61 codons for 20 AAs
Define the open reading fram
The continuous stretch of nucleotides that has the possibility of being translated as defined by start/stop codons
Describe repressors
Proteins that bind to the promoter region or the silencer regions of DNA to decrease the rate of transcription
What is the relationship between RNA Pol and the promoter?
The stronger the affinity between RNA pol and the promoter, the higher the transcription rate
Describe enhancers
Enhancers are a region of DNA (usually distant from target gene) that activator proteins bind to to increase the rate of transcription
Describe RNA process in eukaryotes
Transcription in eukaryotes produces hnRNA, a precursor to mRNA that is process in the nucleus and mature mRNA is shipped out to be translated
Define splicing
Splicing occurs when a splieosome complex removes introns and joins exons
Define introns
Introns are regions of a gene that are transcribed but not translated and do not encode proteins but are important to break the gene into distinct exons that contain splice sites that are recognized by the spliceosome
Define exons
Exons are regions of a gene that encode the protein sequence (Exons are expressed)
What are the components of a spliceosome?
snRNA (small nuclear RNA) + proteins; aka snRNPs (small nuclear ribonucleoproteins)
Describe alternative splicing
Alternative splicing skips/splices some exons so that different combinations of exons can make more than 1 different mRNA from the same hnRNA
Describe the cap and tail
A 5’cap (methylated guanine) and 3’ poly-A tail (multiple adenine nucelotides) is added to the 5’ and 3’ UTR of the pre-mRNA to increase the mRNA’s stability and protect it from degredation in the cytoplasm
Define ribozymes
RNA enzymes found in ribosomes which catalyze translation and required for splicing
Describe rRNA
rRNA makes up ribosomes which catalyze the synthesis of poly peptides
Describe tRNA
tRNA contains anti-codon complementary to mRNA codons and brings the correct amino acid to the growing polypeptide chain due to this codon-anticodon-interaction
How is the stem/loop structure in tRNA formed?
Intramolecular H-bonds
What is the modified A base in tRNA?
Inosine - often at the wobble position of the anticodon; can pair with A, U, C
Describe the composition of ribosome
Ribosomes are composed of rRNA and contain and large and small subunit
What is the function of the large ribosomal subunit?
Catalyze the peptidyl transfer
What is the function of the small ribosomal subunit?
Recognize and binds to the correct region of the mRNA for translation
What are the names eukaryotic and prokaryotic sequences where the small ribosomal subunit binds for translation?
Eukaryotes: Kozak sequence; Prokaryotes: Shine-Dalgarno sequence
What are the sedimentation coefficients in prokaryotic and eukaryotic ribosomes?
Prokaryotic (70S) = small (30S) + large (50S)
Eukaryotic (80S) = small (40S) + large (60S)
What are the ribosome sites?
Regions of the large ribosomal subunit that the tRNA moves through during protein synthesis (A -> P -> E)
Where is the growing polypeptide primarily synthesized?
On the P site of the large ribosomal subunit
What direction is the polypeptide formed?
mRNA reads 5’ -> 3’; therefore polypeptide is made from the N-terminus to c-terminus
What is the difference between prokaryotic and eukaryotic translation?
Prokaryotes have polycistronic mRNA and lack of RNA processing allows transcription and translation to occur at the same time
How is energy provided to each step in translation?
- Initiation: initiator proteins (eIF) + small subunit associate with Kozak sequence on mRNA –> scan for start codon –> large ribosomal subunit joins
- Elongation: Elongation factor and GTP
- Termination: Release factor and GTP
What are the energy requirements for termination of translation?
AA*4 = #ATP needed
How is tRNA loading initiated?
tRNA and AA attachment is a non-spontaneous process which requires 2 ATP/AA (ATP–> AMP)
What is the function of aminoacyl tRNA synthetase?
Aminoacyl tRNA synthetase attaches the correct AA to the correct tRNA with high specificity
