Genomes, Genes And Operons Flashcards
What is the genome?
The whole of the DNA of an organism.
(. The set of genes
. Additional, non-coding sequences)
What marks the beginning and end of the transcribed part of the gene?
Specific DNA sequences
What does a promoter do?
. Provides binding site for RNA polymerase
. Specifies start point and direction of transcription
What does a transcription terminator sequence do?
Specifies where transcription ends
In eukaryotes how are genes usually transcribed?
Individually
In bacteria how are genes transcribed?
Many genes are arranged into operons- clusters of genes. All the genes in an operon are transcribed from one promoter to give a polycistronic mRNA
What are the genes like in an operon?
They have related functions, and so their products are all needed under the same conditions
What is the start codon that specifies the beginning of translation?
AUG
What does the start codon code for?
Methionine
What are the 3 stop codons that specify the end of translation?
UAG, UGA, UAA
What are the ‘problems’ with start and stop codons?
. Methionine is found in the middle of proteins as well as at the beginning
. In an operon, translation must start at more than one place in an mRNA molecule.
Therefore, cells must be able to distinguish start codons from other methionine codons
How does the cell know whether AUG is a start codon or coding for methionine?
AUG will have AGGAGG next to it ( or something similar)
What is the one gene-one enzyme hypothesis?
Each gene controls the production, function, and specificity of a particular enzyme
What is the typical number of genes in bacteria and in animals?
Bacteria- about 4,000
Animals- about 25,000
In a. Operon where must translation start?
Must start in more than one place in an mRNA (the 5’ end) and moves to first AUG I’m the mRNA. Once it has started transcribing it will carry on until it gets to a stop codon
In bacteria what is the Shine-Dalgamo sequence that the 3’ end of the rRNA binds to?
It is the ribosome binding site in mRNA near the start codon. Sequence is similar to AGGAGG- lines up ribosome so that it knows that at this tart codon it needs to start translating (doesn’t have to be this exact sequence, is usually 2 or 3 bases away from the start codon)
What two conserved regions identify most promoters in bacteria?
-35 and -10 (numbering is from the position at which transcription starts). These are consensus sequence (consensus meaning they may not match this exactly but will be similar)- that bass shown are the commonest but not invariable
What are the five polypeptides in the RNA polymerase core enzyme?
Alpha (2 copies), beta, beta prime, and the weird w one
Specific binging to promotors by the core enzyme requires what?
Sigma factor
What a core enzyme and a sigma factor are combined what does it form?
Holoenzyme