Glossary
Cis-Acting Elements
DNA sequences that regulate the expression of genes located on the same DNA molecule.
Example:
Enhancers and silencers are examples of cis-acting elements because they must be physically linked to the gene they control to exert their regulatory effects.
Differential Gene Expression
The process by which different genes are expressed at varying levels in different cells or at different times, leading to specialized cell types and functions.
Example:
Differential gene expression is why a muscle cell and a nerve cell, despite having the same DNA, perform vastly different roles in the body.
Enhancers
Cis-acting DNA sequences that can be located far from a gene's promoter but significantly increase the rate of its transcription.
Example:
An enhancer might be thousands of base pairs away from a gene, yet it can loop around to interact with the promoter and dramatically boost gene expression.
MicroRNAs (miRNAs)
Small non-coding RNA molecules that bind to the 3' untranslated regions (3'UTRs) of target messenger RNAs (mRNAs), leading to inhibition of translation or promotion of mRNA degradation.
Example:
An miRNA might bind to the mRNA of a viral protein, preventing its translation and thus helping the cell fight off infection.
Negative Regulatory Molecules
Molecules that inhibit or reduce the expression of genes, often by interfering with transcription or translation.
Example:
Negative regulatory molecules play a crucial role in maintaining cellular homeostasis by preventing the overproduction of certain proteins.
PIWI-interacting RNAs (piRNAs)
Small non-coding RNAs that primarily function to silence transposable elements and other repetitive DNA sequences, thereby maintaining genome integrity.
Example:
piRNAs act as a crucial genomic security system, preventing 'jumping genes' from disrupting essential coding sequences or causing mutations.
Promoters
Specific DNA regions located upstream of a gene's start site, serving as the binding point for RNA polymerase to initiate transcription.
Example:
The promoter region of the insulin gene ensures that it is only transcribed in pancreatic beta cells.
RNA Polymerase
The enzyme responsible for synthesizing an RNA strand from a DNA template during the process of transcription.
Example:
During transcription, RNA polymerase unwinds the DNA double helix and adds complementary RNA nucleotides to build a new RNA molecule.
Repressors
Proteins that bind to specific DNA sequences, typically near the promoter, to block RNA polymerase and prevent the transcription of a gene.
Example:
In bacteria, a repressor protein binds to the operator region of an operon, preventing the transcription of genes until a specific molecule is present.
Silencers
Cis-acting DNA sequences that decrease the rate of gene transcription by binding to repressor proteins, effectively acting as brakes on gene expression.
Example:
A silencer sequence might prevent the expression of a specific gene in tissues where its protein product is not needed, conserving cellular resources.
Small Interfering RNAs (siRNAs)
Double-stranded RNA molecules that are processed by the RISC complex and primarily function to target specific messenger RNAs (mRNAs) for degradation, leading to gene silencing.
Example:
Researchers often use siRNAs in laboratory experiments to 'knock down' the expression of a particular gene to study its function.
Small RNA Molecules
Short, non-coding RNA molecules (typically 20-25 nucleotides long) that play diverse roles in regulating gene expression, often by affecting mRNA stability or translation.
Example:
Small RNA molecules act as versatile cellular editors, fine-tuning the amount of protein produced from specific genes.
TATA Box
A common DNA sequence (TATA) found within eukaryotic promoters that acts as a recognition site for the TATA-binding protein (TBP), crucial for accurate transcription initiation.
Example:
The TATA box helps position the transcription machinery correctly, ensuring the gene starts transcribing at the precise location.
Transcription Factors
Proteins that bind to specific DNA sequences, often near the promoter, to regulate the initiation of transcription by helping or hindering RNA polymerase binding.
Example:
Specific transcription factors are essential for activating the genes required for a stem cell to differentiate into a specialized neuron.
Transcriptional Corepressors
Molecules that do not directly bind DNA but interact with repressor proteins to enhance their inhibitory effect on gene transcription.
Example:
A transcriptional corepressor might bind to a repressor, altering its conformation and increasing its affinity for DNA, thereby strengthening the repression of a gene.