MGD S5 - Transcription and Translation Flashcards
(38 cards)
Give a very basic description of the function of transcription and translation
- Transcription: DNA converted to mRNA, nucleotide to nucleotide, “copying the code”, simple, in nucleus
- Translation: mRNA converted to protein, nucleotide to amino acid, “changing the language” - code translated, more complex, 4 letter to 20 letter code, adaptor molecule needed, in cytoplasm
What is a gene?
- A stretch of DNA at a chromosomal locus (specific location) - “Recipe” for a protein code and regulation - There are ~25,000 genes, 2x25,000 in every cell (not expressed all the time)
What is the difference between heterochromatin and euchromatin?
- Heterochromatin: dark, solenoid 30nm fibre, genes not expressed - Euchromatin: light, beads on a string, genes expressed
What are the different types of RNA?
- mRNA (messenger RNA) - rRNA (ribosomal RNA) - tRNA (transfer RNA) - miRNA (micro RNA) - noncoding RNA: regulate their counterpart
What is involved in making DNA?
- Needs an enzyme: DNA polymerase - Needs activated substrates: dNTPs - Needs a template: DNA - 3 stages process: initiation, elongation, termination
What is involved in making mRNA?
- Needs an enzyme: RNA polymerase - Needs activated substrates: NTPs - Needs a template: DNA - 3 stages process: initiation, elongation, termination
What is involved in making a polypeptide / translation?
- Needs an enzyme: ribosome - Needs activated substrates: amino acids - Needs a template: mRNA - 3 stages process: initiation, elongation, termination
Give an overview of DNA replication
- Initiation: recognition of origin of replication, initiation proteins, DNA polymerase - Elongation: 5’ to 3’ chain growth - Termination: when replication forks meet
Give an overview of transcription
- Initiation: promoter recognition, transcription initiation factors, RNA polymerase - Elongation: 5’ to 3’ chain growth - Termination: sequence dependent - Making a polynucleotide (mRNA) - (rNMP)n + rNTP ➡️ (rNMP)n+1 + PPi
What is a transcription unit?
- A gene - Genes go in different directions
What is the significance of the promoter in initiation?
RNA polymerase must recognise the appropriate point on which to start transcription and the strand of DNA to transcribe. The signals in DNA that RNA polymerase recognises are called promoters. Promoters are sequences in DNA that determine the start point and the frequency of transcription
What is the importance of how the transcription factor binds to the DNA in initiation?
Determines the direction of translation, and therefore the direction of the gene
Describe initiation in transcription
Promoters recruit the RNA polymerase to the transcription start site on DNA. Promoters are usually located in front (upstream) of the gene that is to be transcribed - where promote sits on sequence is where transcription starts. Must be 5’ to 3’ for transcription factor to bind
Describe the difference between promoter sequences and regulation in eukaryotes and prokaryotes
- Eukaryotes: TATA box at -30, variety of upstream sequences, complex regulation - Prokaryotes: Pribnow box at -10, upstream sequences at -35, “simple” regulation
Describe the process of elongation in transcription
- The process by which single nucleotides are added to the growing RNA chain - Ribonucleotides bind to an entry site on the RNA polymerase. If the incoming ribonucleotide matches the next base on the DNA a template, the incoming ribonucleotide is transferred into the polymerase active site and a new phosphodiesrer bond is formed. If not: process repeated until correct ribonucleotide is found - mRNA 5’ to 3’, template 3’ to 5’
What is significant about the DNA coding strand in transcription?
Sequence identical to mRNA sequence. Both complementary to template/non-coding strand
Describe termination in transcription
- Catalysed by multiple mechanisms - At the end of a transcriptional unit, the RNA polymerases terminate RNA synthesis at defined sites
Summarise transcription
RNA polymerase binds to the transcription factor complex in the promoter region and to the DNA. The helix unwinds within a region near the start point of transcription. DNA strand separation occurs. Synthesis of RNA transcript is initiated, and the RNA transcript is elongated, copying the DNA template. The DNA strands separate as the polymerase approaches and rejoin as the polymerase passes
What is an open reading frame (ORF)?
A portion of a DNA molecule that, when translated into amino acids, contains no stop codons
Describe in RNA processing how pre-mRNA is transformed to mature mRNA
- Capping: at 5’ end, a 5’ cap. Protection against degradation - Tailing or Polyadenylation: at 3’ end a PolyA tail is added. Protection against degradation - Splicing: in the middle. Removes introns. Sequence dependent
Describe capping
- A 5’-5’ linkage is created (extra nucleotide being added on) - Provides protection against degradation - Plays role in translation
Describe nucleases
Degradation of nucleic acids - Endonuclease: breaks within polynucleotide. Non-specific (random cutting) or specific (recognises specific sequence and makes cut) - Exonuclease: degrades polynucleotide from end. 5’ specific or 3’ specific
Describe polyadenylation/tailing
See image
Describe splicing
Introns cut out - highly sequence-dependent. Leaves mature mRNA. Happens in all cells. Can go wrong
