Chapter 12 - Transcription and RNA Modification Flashcards
What is the first step in gene expression?
Transcription
What is transcription?
Copying DNA into RNA
Protein encoding genes
Encode the amino acid sequence
Transcription produces…
mRNA
Making DNA copies transmitted from cell to cell is…
DNA replication
Stores information in genes
Chromosomal DNA
Temporary copy of a gene that contains information for making a polypeptide
Messenger RNA
Production of a polypeptide using mRNA
Translation
Process by which information in a gene is used to produce a functional product
Gene expression
Site for regulatory protein binding to influence rate of transcription
Regulatory sequences
Site for RNA polymerase binding to begin transcription
Promoter
Signals end of transcription
Terminator
Site for ribosome binding in bacteria nearing the start of translation
Ribosome-binding site
3 nucleotide sequence within mRNA that codes for a certain amino acid
Codon
Specifies first amino acid in a polypeptide sequence
Start codon
Specifies the end of polypeptide synthesis
Stop codon
DNA strand that is actually transcribed
Template strand
The opposite, non transcribed DNA strand
Coding strand / sense strand
Recognize the promoter and regulatory sequences to control transcription
Transcription factors
Three stages of transcription
Initiation, elongation, and termination
Promoter is recognition site for TFs, which enable binding of RNA polymerase
Initiation
RNA polymerase slides along DNA in open complex to synthesize RNA
Elongation
Reaches a terminator that causes RNA polymerase and RNA transcript to dissociate from the DNA
Termination
Sequences at which promoters vary
-35 and -10
Most common promoter sequence likely to result in a high level of transcription
Consensus sequence
Enzyme that catalyzes RNA synthesis
RNA polymerase
Binds loosely to DNA and scans until promoter recognition
RNA polymerase holoenzyme
Binding of RNA polymerase to promoter forms…
Closed complex
Formed when the TATAAT box in the -10 sequence is unwound
Open complex
Rate of RNA synthesis
43 nucleotides per second
Direction of RNA polymerase movement
3’ to 5’
Direction of RNA synthesis
5’ to 3’
Requires the presence of a rho protein
rho-dependent termination
Does not require the presence of a rho protein
rho-independent termination
Transcribes al rRNA genes except for 5S rRNA
RNA pol I
Transcribes all mRNAs and some snRNA
RNA pol II
Transcribes all tRNA, 5S rRNA, and microRNA genes
RNA pol III
Consists of the TATA box and transcriptional start site
Core promoter
Low levels of transcription produced by the core promoter
Basal transcription
Stimulate transcription
Enhancers
Inhibit transcription
Silencers
DNA sequences that exert their effect only over a particular gene
cis-actin elements
Regulatory proteins that bind to such DNA sequences
Trans-acting factors
Basal transcription apparatus
RNA pol II, five GTFs, and a mediator
Composed of TATA binding protein and alther TBP associated factors
TFIID
Binds to TFIID and enables RNA pol II to bind to the core promoter
TFIIB
Binds to RNA pol II and helps its ability to bind to TFIIB and the core promoter
TFIIF
Plays a role in the formation or maintenance of the open complex
TFIIE
A multi-subunit protein that has multiple roles - acts as helicase to form open complex, phosphorylate the carboxyl terminal domain
TFIIH
Multi-subunit complex that mediates the effects of regulator transcription factors on the function of RNA pol II
Mediator
Sequence of DNA in the coding strand corresponds to the sequence of mRNA which provides instructions for the sequence of amino acids in the polypeptide
Colinearity of gene expression
Coding sequence
Exon
Intervening sequence
Intron
When introns are removed and exons are connected together
RNA splicing
Larger RNA transcripts are cleaved into smaller functional pieces:
rRNAs and tRNAs
Cleave a covalent bond between two nucleotides at one end of a strand
Exonucleases
Cleave bonds within a strand
Endonucleases
Found in rRNA genes within the nuclei of simple eukaryotes
Group I intron splicing
Found in a few protein-encoding, tRNA and rRNA genes within mitochondrial DNA
Group II intron splicing
Very commonly found in protein-encoding genes within nuclei of eukaryotic cells
Spliceosome
Splicing that does not require the aid of enzymes as the RNA functions as its own ribozyme
Self-splicing
Proteins that enhance the rate of splicing
Maturases
The long transcript produced by the transcription of protein-encoding genes in eukaryotes
pre-mRNA
Multicomponent structure composed of several snRNPs
Spliceosome
Catalyze chemical reactions to remove introns and covalently link exons
Spliceosome
When a pre-mRNA with multiple introns can be spliced in different ways so two or more polypeptides can be derived from a single gene
Alternative splicing
Always found in the mature mRNA from all cell types
Constitutive exons
Prevent splicing
Splicing repressor
Facilitate splicing
Splicing enhancer
Covalent attachment of a 7-methyl-guanosine at the 5’ end
Capping
Role of the 5’ cap:
movement of RNAs out of nucleus, early translation, intron splicing
String of adenine nucleotides at the 3’ end
polyA tail
Change in the sequence of an RNA molecule after it is synthesized
RNA editing