Intro To Molecular Biology 3 Flashcards
Differences in structure between DNA and RNA:
DNA = double helix
RNA = single strand + may have secondary or tertiary structure (more complex)
Function of DNA:
Information storage
Functions of RNA:
Genetic message - mRNA
Adaptor - tRNA
Structural RNAs - Xist
Catalyst - rRNAs , spliceosome snRNAs
Guide RNAs - for RNA editing
What’s involved in transcription?
DNA used as template
Complementary to one strand
RNA polymerase (5’ to 3’)
Not as accurate as DNA replication
Difference between RNA polymerase and DNA polymerase:
RNA = polymerises 40 bases/second
DNA = 100 bases/second
RNA polymerase doesn’t require primer
What’s the coding strand in transcription?
Non-template strand
Characteristics of coding strand:
Sequence equal to RNA
Not all genes on chromosome are in same orientation
What’s important to know about copies of RNA?
Many copies are made simultaneously
What are promoters?
Region of DNA
Found before transcription site, signals its beginning
What are terminators?
Region of DNA
Marks end of transcription
What are the 3 different types of RNA polymerase?
RNA pol I
RNA pol II
RNA pol III
What RNA does RNA pol I generate?
rRNA
What RNA does RNA pol II generate?
Protein coding RNA
What RNA does RNA pol III generate?
tRNA
What’s the promoter for RNA pol II?
TATA box
What does the TATA box do?
Facilitates binding of RNA polymerase and transcription factors (e.g. TBP)
Located 25 bases upstream of starter code
What does TBP mean?
TATA binding factor
What doers TBP do?
Distorts shape of DNA once bound - allows binding of RNA pol II
What does TBP do to the shape of DNA?
Creates ink in DNA and binds minor groove
Facilitates strand opening to allow transcription to start
What’s the core promoter?
Basal transcription
What does the regulating gene do?
Transcription is tightly controlled - e.g. insulin
What does the housekeeping gene do?
Transcription always on - e.g. actin
How does RNA polymerase bind to DNA?
RNA polymerase binds to factor-promoter complex
Trans-acting factors bind to cis-acting promoter
RNA cannot bind directly to promoter
What are enhancers?
Short DNA sequences
50-1500 base pairs
Where are enhancers located?
Not always located close to transcription start site as they can work from a distance
What do enhancers do?
Bind to transcription factors to increase likelihood of specific section of DNA being transcripted
Stabilise transcription machinery assembly by protein-protein interactions
What are enhancers opposed by?
Silencers
What are the two domains of transcription factors?
DNA binding domain
Activation domain
What ways can transcription be controlled?
Protein only synthesised when transcription happens
Protein inactivated by phosphorylation, dephosphorylation and ligand binding
Protein inhibited and rendered inactive by inhibitor
Protein has inactive binding partner switched with active binding partner
Why must mRNA be processed?
Protection from exonucleases
Aid export from nucleus
Identified as mRNA
What are exonucleases?
Enzymes which cleave nucleotides
What are introns?
Non-coding segment of DNA/RNA
What are exons?
Coding segment of DNA/RNA after introns are spliced
What was the sequence of information in genes and proteins known to be?
Co-linear
What was the sequence of information in genes discovered to be?
Interrupted - not contiguous
What does splicing take place through?
2 esterification reactions
Importance of post-transcriptional modifications:
Many different proteins made from same DNA
