Structure of genes Flashcards
The central dogma describes…
a flow of information in an
organism
(DNA -> RNA -> protein)
In eukaryotes genes are transcribed as …
…signle units
In eukaryotes genes are transcribed as single units however in bacteria genes involved in the same pathways are often arranged linearly as an…
…operon
When the operon is transcribed all of the genes are transcribed in …
…one continuous mRNA known as a
polycistronic mRNA
In eukaryotes genes are transcribed as single units however in bacteria genes involved in the same
pathways are often arranged linearly as an operon
When the operon is transcribed all of the genes are transcribed in one continuous mRNA known as a polycistronic mRNA.
What does this increase the efficiency of?
This increases the efficiency of gene regulation.
– for instance if the bacterial cell needs to make biotin it makes sense to transcribe all of the genes involved in this process together
–means there can be a simple genetic switch to turn the process on.
Eukaryotic genes are more complex than those of…
…prokaryotes.
Typically the open reading frame (ORF) which is composed from the exons within the gene is split by…
…intervening non-coding DNA in the form of introns
In order to be expressed a transcript from a eukaryotic gene has to be…
…processed to remove the introns.
what is the flow of information in an organism?
DNA -> RNA -> protein
where is prokaryote dna?
prokaryotes have their genomic DNA naked in the cytoplasm (no nucleus)
prokaryote dna does not require…
… polyadenylation or intron removal.
Because prokaryotes have their genomic DNA naked in the cytoplasm (no nucleus) and doesn’t require polyadenylation or intron removal, transcription and translation are…
… coupled
When does translation begin in prokaryotes?
Translation begins as the mRNA molecule is being transcribed, note that a
number of genes in the same operon are being transcribed together from the same mRNA (polycistronic).
Because the eukaryotic cell has a nucleus – mRNA needs to be…
…transported into the cytoplasm to be translated into protein by the ribosome.
What are mRNAs marked for export by?
by the interaction of specific proteins:
- cap-bindings protein
- Poly-A-binding protein
- Exon junction complex (EJC).
Slide 11=
=the differences between gene expression in eukaryotes and prokaryotes.
eukaryotic transcripts need to be transported from…
… the nucleus, where they are transcribed to the cytoplasm where they are translated - uncoupled.
Many eukaryotic genes contain…
…untranslated sequences - introns - these need to be removed before translation.
eukaryotic transcripts are polyadenylated at which end?
at the 3’ end.
mRNA transcripts are capped at…
…the 3’ end
eukaryotic transcripts are monocistronic. What does this mean?
they do not contain the transcripts of several genes.
eukaryotic transcripts do not contain the transcripts of several genes. What is the word thats used to describe this?
monocistronic
What is the core promoter?
TATA box
How many bases in the TATA Box?
25 bases
What is consensus 5’ TATAWAAR -3’ (W = A or T, R = A or G)?
TATA Box
What is known as the mammalian consensus?
Inr (initiator)-0987
Whats DPE?
downstream promoter element.
How many bases in the initiator?
1 bases
How many bases in the DPE?
28 to 32 bases
What does DPE bind to?
TFIID
where is 7bp GC Box?
immediately upstream of TATA Box
What does 7bp GC box bind to?
TFIIB
PSE is only in…
snRNA genes.
Function of RNA polymerase I ?
Transcription of ribosomal genes
What is the function of RNA polymerase II ?
Transcribes all eukaryotic protein-coding genes
Whats the function of RNA polymerase III type 1, type 2, and type 3?
transcribes DNA to synthesize
ribosomal 5S rRNA, tRNA and
other small RNAs
What do elements located upstream of the core promoter do?
allow interaction with RNA polymerase
The complexity of promoter elements varies hugely in …
… eukaryotes
Simple single-celled eukaryotes commonly have promoters that are…
… simple and proximal to the gene itself.
Simple single-celled eukaryotes commonly have promoters that are simple and proximal to the gene
itself whilst multicellular organisms may have…
… regulatory elements that are many kilobases away from the gene itself.
A mixture of small nuclear RNA molecules (snRNA) and proteins are
responsible for…
… excising of introns and joining together the 3’ and
5’ ends of exons to form the mature transcript
Sometimes the exons of genes with multiple introns can be spliced together in different ways. What is this called?
alternative splicing
define alternative splicing
Sometimes the exons of genes with multiple introns can be spliced together in different ways, meaning that the coding sequence of the transcripts can differ and results in different proteins which may be involved in different processes.
