gene expression Flashcards
gene expression
the process by which the information encoded in a gene is used to direct the assembly of a protein molecule.
highly regulated so that gene products are only produced if and when they are required by the cell
For a gene to be expressed, it needs to be…
- Transcribed
- Processed in the nucleus
- Translated in the cytoplasm with the help of a ribosome
gene structure
Stop and start triplet sequences - regions where encoding DNA begins and
ends for a gene
• 2. Promotor regions – binding regions upstream of the gene where RNA polymerase can bind in order for transcription to occur
• 3. Exons (“Expressed”) – DNA regions within the gene that contain coding instructions
• 4. Introns (“Interruptions”) – DNA regions that are non-coding segments
promoter region
are sections of a gene found before the start triplet ATG at the 5’ end of the site where RNA polymerase attaches ready to begin transcription
• Promotor regions upstream from a gene are often signalled by the base combination TATAAA (also known as the TATA box)
exon
are regions of the gene that code for an amino acid and are usually “expressed” as proteins or RNA.
• When exons are joined together, they make up mature mRNA
intron
are non-coding regions of a gene
transcription
making an RNA copy of the DNA code
Transcription occurs in three steps:
Initiation – Transcription factors combine with the promotor region at the start of a gene
Elongation – RNA polymerase molecule moves along the template strand in a 3’ to 5’ direction
Termination – transcription ends when the RNA polymerase reaches the
termination site of the gene
transcription factors
proteins that control the rate of transcription of DNA to mRNA by binding to a specific DNA sequence. They regulate (turn on and off) genes in order to make sure that they are expressed in the desired cells at the right time and in the right amount throughout the life of the cell and the organism.
RNA polymerase
attaches to the promotor region at the start of the gene and unwinds and unzips the DNA strand by breaking the weak hydrogen bonds holding the two strands together which exposes the nitrogenous bases
methyl cap
added to the 5’ end of the pre-mRNA molecule during transcription
splicing
spliceosome (a complex molecule composed of protein and RNA molecules) removes the introns from the pre-mRNA strand and joins the exons together to make mature mRNA
poly a tail
added to 3’ end when transcription if finished to stop mRNA from degrading
translation
translation isn’t the mRNA into a protein
