| What is transcription? | the process by which RNA molecules are synthesized on a DNA template. |
| What is the final result of transcription? | single stranded mRNA molecule complementary to template DNA strand. |
| What is the gene expressed strand called? | DNA sense strand (coding strand) |
| Where is the promoter located? | At 5' OH of the sense strand. |
| How does RNA polymerase synthesize RNA? | it reads from 3' to 5' of the template strand and synthesizes antiparallel (5'- 3') , in the same sequence and sense as the sense strand (only replacing T with U) |
| What is a promoter? | a regulatory sequence that regulates initiation of transcription located at 5' upstream (before transcription) region from point of initial transcription of a gene |
| What is the "+1" region? | first nucleotide transcribed (transcription start site) |
| Where is the terminator region? | At 3' OH of gene (non-transcribed strand) |
| What is present between the initiation site and termination site? | exons and introns (starts with an exon and ends with one) |
| What are exons and introns? | exons= coding sequences, introns=non-coding sequences (translated to amino acids via translation) |
| What are regions that are transcribed but not translated called? | UTR (un translated regions) |
| What is the open reading frame? | exons (mRNA molecules) |
| Talk about the initiation phase of transcription. | RNA polymerase recognizes the promoter, binds to it and starts transcribing the template from transcription site. |
| Talk about the elongation phase of transcription. | subsequent nucleotides complements are inserted and linked through phosphodiester bonds, from 5' P to 3' OH direction of moving w.r.t template is 3' 5' |
| Talk about the termination phase of transcription | enzyme transverses the entire gene until it reaches termination signal sequence. At that point, RNA is released from DNA template and polymerase dissociates. |
| What is the difference between eukaryotic and prokaryotic transcription? | Eukaryotes (within the nucleus and towards the cytoplasm ribosomes, processing of RNA transcript to form mRNA by adding cap to 5' end, and removing introns and ligating exons, and addition of poly A tail to 3' end)
Prokaryotes (no need for going from place to place, no processing) |
| Give a major characteristic of nuclear genetic code. | Nearly universal with minor exceptions. |
| What is a genetic code? | Its the encoding of primary polypeptide synthesis, contains a sequence of codons read from 5' to 3', 64 codons (4^3) 61 are sense (specify an amino acid) there is a start codon (AUG) and three stop codons not recognized by tRNA (UAA UAG UGA) |
| List the main characteristics of genetic code. | linear form
each aa corresponds to three ribonucleotides (triplet codon)
unambiguous code (each triplet codes one aa)
degenerate (residancy) aa can be encoded by more than one codon
the code contains start and stop signals
commaless codes
nonoverlapping code (each nucleotide is part of one triplet) |
| What do ribosomes translate? | ORF (open reading frame- starting with 5' P AUG-met and ending with stop codon UAA UAG UGA 3'OH) |
| What is translation? | biological polymerization of polypeptides according to mRNA codes, It occurs in the ribosomes that serve as a workbench for translation, mRNA serves as an intermediate in transfer of DNA genetic information. |
| Describe tRNA used in translation | charged tRNA, having three single stranded loop regions, 4 double stranded (intramolecular interaction) stem regions and a binding site for amino acid on CCA 3'OH end (3'OH is connected to the carboxyl group of the aa) |
| What is an anticodon? | 3 consecutive ribonucleotides that attach tRNA to mRNA via H-bonds |
| Talk about the initiation phase of translation. | initiator tRNA charged with mehionine bas pairs with initial AUG start codon of mRNA at P (peptidyl) site of ribosomal small subunit the large subunit then attaches to the small one forming a complete ribosome having A,P and E (exist subunit). COMMON FOR ALL nRNA |
| Talk about the elongation process of translation. | Lengthening of polypeptide chain by one amino acid per elongation cycle. role of small subunit is to decode the codons while role of large one is peptide-bond synthesis.
Second charged tRNA with specific anticodon will go to A site, once bonded to the codon, large subunit catalyzes peptide bonds between the two amino acids present at A and P site tRNA by hydrolyzing the bond between aa and tRNA 3'OH. The dipeptide is attached to tRNA at A site which moves to the P site and the initial tRNA moves to E site to exit, then ribosome-dipeptide-tRNAs move in a distance of a codon (3 nucleotides)
P site=peptide A site = amino acid |
| Talk about the termination phase of translation. | signaled by presence of stop codon, whom donot code for an amino acid or tRNA at A site (non sense codons) finished polypeptide is still attached to P site tRNA which is then released from ribosome which dissosciates to subunits |
| What is a gene? | RNA coding sequence |
| What is the transcription unit? | region from promoter to 3' UTR after last exon |
| How to know the real open reading frame of a strand? | See first codon if AUG and ends with stop codon- remove one nucleotide from 5' till AUG |
