Prokaryotic Gene Organisation & Transcription Flashcards
How many copies of a gene would a prokaryotic organism contain
1 copy of each gene (haploid)
Where are genes found in prokaryotic organisms
On the circular chromosome found within the nucleoid region of the cytoplasm
The coding DNA sequence (CDS) is . . .
The section of the gene which codes to string amino acids together in a particular sequence. (Basically it’s the DNA sequence that contains information to make the protein).
In prokaryotes the coding DNA sequence is contained on . . .
On one continuous uninterrupted piece of DNA
Describe the promoter region and its function.
The promoter region is a sequence within the gene which RNA polymerase binds to during the initiation phase of transcription. It is found upstream of the coding DNA sequence
What are Codons?
Found at the start and the end of the coding DNA sequence. Codons are sequences of 3 DNA nucleotides that correspond to start or stop instructions during transcription. A stop codon signals the termination of the translation process for a particular protein. A start codon signals the beginning of the translation process.
Describe the terminator region
The terminator region signals the RNA polymerase to dettach from the DNA strand, meaning the end of transcription. It is found downstream of the CDS
State the role of the regulatory sequences
Regulatory sequences help to regulate when genes are expressed or transcribed.
Describe an operon
When several genes are required for a common pathway, they may be found next to each other on the chromosome. Prokaryotes can therefore produce a single strand of mRNA which comprises several genes. Such a cluster of related DNA is called an operon. (The region known as an operon includes the promoter and operator region as well)
Name the regulatory regions which regulate the Lac Operon and state where these regions can be found
The Lac repressor gene and the Lac operator. Both of these regions of DNA can be found upstream of the structural Lac genes.
Describe the function of a repressor gene
A repressor gene continously expresses a repressor protein which bind to the operator, preventing RNA polymerase from binding to the promoter region.
State the function of an inducer molecule
An inducer molecule binds to the repressor protein, altering the repressor protein so that it is no longer bound to the operator region. This allows RNA polymerase to attach to the promoter region and begin transcription.
Give 3 advantages of gene expression via operons
- Transcription is more efficient because functionally related proteins are all synthesized from a single mRNA strand.
- The prokaryotic cell conserves energy, amino acid, and mRNA resourcesbecause ATP is not wasted carrying out transcription and translation when the proteins aren’t required.
- Regulation of gene transcription is coordinated because there are several genes under one single control
Describe translation in prokaryotes
In prokaryotes there are no introns and no processing is required.
As there is no nucleus, ribosomes can attach to one end of the mRNA and begin translation even before transcription of the mRNA molecule is complete.
