gene regulation Flashcards
(8 cards)
Operons system in bacteria
operon structure : includes promotor, operator, and structural genes
repressible operon ( trp operon) : Normally “on” but turned off when trytophan is present ( acts as a compressor)
inducible operon ( lac opereon) normally off but can be turned on when lactose is present ( lactose acts as an inducer)
comparison: Trp operon is repressible ( default is “on”) while lac operon is inducible ( default “off”)
Eukaryotic gene regualtion
DNA packaging : Chromatin structure affects gene expression ( tightly packed chromatin inhibits transciption)
transcription factors:
general transcription factors are needed for all genws
specific trqansciption factors activate or inhibit certain genes
enhancers and silencers: DNA sequences enhance or repress transciption
cell type specific expression : different proteins regualte gene expression in specific cells
alterantive splicing
allows a single gene to code for multiple proteins
ex: Dscam gene in drosphilla can generate 38.016 protein variants
Describe the mechanism of the trp operon when tryptophan is absent versus when it is present.
When tryptophan is absent, the trp operon is active, as the repressor protein is inactive and unable to bind to the operator, allowing RNA polymerase to transcribe genes needed for tryptophan synthesis. When tryptophan is present, it acts as a corepressor, binding to the repressor protein, activating it, and enabling it to bind to the operator, blocking transcription and preventing unnecessary tryptophan production. This negative feedback mechanism conserves energy by only producing tryptophan when needed.
How does chromatin structure affect gene expression in eukaryotes?
Chromatin structure regulates gene expression by controlling the accessibility of DNA to transcription machinery. Euchromatin is loosely packed and associated with active gene transcription, while heterochromatin is tightly packed and generally silences genes. Epigenetic modifications, such as histone acetylation (which loosens chromatin to promote transcription) and DNA methylation (which condenses chromatin to repress transcription), play key roles in regulating gene expression.
Promoters play an essential role in transcription. Explain what a promoter is and its
function in transcription, making sure to include the details of any molecular
interactions.
A promoter is a specific DNA sequence located upstream of a gene that serves as the binding site for RNA polymerase, initiating transcription. In eukaryotes, promoters often contain a TATA box, where transcription factors first bind, recruiting RNA polymerase to form the transcription initiation complex. In prokaryotes, the sigma factor helps RNA polymerase recognize the promoter, ensuring transcription begins at the correct site.
Given the DNA sequence
5’GTCGTCGATGGCTTGTGCCGAGGGGCTGTTAGCATTGTAGGTGTTAT3’
3’CAGCAGCTACCGAACACGGCTCCCCGACAATCGTAACATCCACAATA5’
Identify the amino acid sequence and write it below (use three letter abbreviations)
To determine the amino acid sequence, follow these steps:
Find the mRNA sequence by transcribing the given DNA (using the coding strand: 5’ to 3’):
The template strand (3’ to 5’) will be used to synthesize the complementary mRNA (5’ to 3’).
Replace T (thymine) with U (uracil) in mRNA.
Identify the start codon (AUG) and translate the sequence into amino acids using the genetic code table.
Step 1: Transcribe the mRNA
Template strand (3’ to 5’):
3’ CAGCAGCTACCGAACACGGCTCCCCGACAATCGTAACATCCACAATA 5’
mRNA sequence (5’ to 3’):
5’ GUC GUC GAU GGC UUG UGC CGA GGG GCU GUU AGC AUU GUA GGU GUU AU 3’
Step 2: Identify Codons
Dividing the mRNA into codons (triplets):
GUC | GUC | GAU | GGC | UUG | UGC | CGA | GGG | GCU | GUU | AGC | AUU | GUA | GGU | GUU
A → U
T → A
C → G
G → C
Explain the three things that occur during mRNA processing in Eukaryotes, including
what happens and its purpose/reason.
During mRNA processing in eukaryotes, three key modifications occur to ensure mRNA stability and proper translation. (1) A 5’ cap (a modified guanine nucleotide) is added to the mRNA to protect it from degradation and help ribosomes recognize it for translation. (2) A poly-A tail (a string of adenine nucleotides) is attached to the 3’ end, increasing mRNA stability and aiding in its export from the nucleus. (3) Introns (non-coding regions) are removed, and exons (coding regions) are spliced together, ensuring that only the necessary coding sequence is translated into a functional protein.
