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Session Length
~18 min
Adaptive Checks
16 questions
Transfer Probes
9
Gene expression is the process by which information encoded in DNA is used to synthesize functional gene products such as proteins and functional RNA. Transcription converts a DNA template into messenger RNA in the nucleus, while translation at the ribosome decodes mRNA codons into a polypeptide chain. The central dogma of molecular biology -- DNA to RNA to protein -- provides the foundational framework, but the reality of gene regulation is far more nuanced.
Gene regulation determines when, where, and how much of a gene product is made. In prokaryotes, operons such as the lac operon and trp operon coordinate expression of functionally related genes through inducible and repressible systems. In eukaryotes, regulation occurs at multiple levels: chromatin remodeling and epigenetic modifications (DNA methylation, histone acetylation), transcriptional control via transcription factors and enhancers, post-transcriptional processing (alternative splicing, mRNA stability), translational regulation, and post-translational modifications.
Understanding gene expression is essential for grasping development, cell differentiation, and disease. Every cell in a multicellular organism contains the same genome, yet cells become specialized through differential gene expression. Disruptions in gene regulation underlie cancer, genetic disorders, and developmental abnormalities. Modern biotechnology tools like CRISPR and RNA interference exploit these regulatory mechanisms for research and therapeutic applications.
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The process of synthesizing mRNA from a DNA template, catalyzed by RNA polymerase, which reads the template strand 3' to 5' and builds mRNA 5' to 3'.
Example: RNA polymerase binds to the promoter of a gene, unwinds DNA, and assembles a complementary mRNA strand using A-U and G-C base pairing.
The process of decoding mRNA into a polypeptide chain at the ribosome, using tRNA molecules that carry amino acids matched to mRNA codons.
Example: The mRNA codon AUG is recognized by a tRNA with anticodon UAC, delivering methionine as the first amino acid in the polypeptide.
A cluster of genes in prokaryotes transcribed together under the control of a single promoter and operator, allowing coordinated regulation.
Example: The lac operon in E. coli contains lacZ, lacY, and lacA genes, which are transcribed together only when lactose is present and glucose is absent.
A protein that binds to specific DNA sequences (promoters or enhancers) to regulate the rate of transcription of a target gene.
Example: The p53 protein acts as a transcription factor that activates genes involved in DNA repair and apoptosis when DNA damage is detected.
Heritable changes in gene expression that do not alter the DNA sequence itself, typically involving chemical modifications to DNA or histone proteins.
Example: DNA methylation of CpG islands in a promoter region silences gene expression without changing the nucleotide sequence.
A post-transcriptional process in which different combinations of exons from the same pre-mRNA are joined together, producing multiple protein variants from a single gene.
Example: The Drosophila Dscam gene can produce over 38,000 different mRNA variants through alternative splicing of its exons.
A three-nucleotide sequence in mRNA that specifies a particular amino acid or a stop signal during translation.
Example: The codon UGG always codes for tryptophan, while UAA, UAG, and UGA are stop codons that signal translation termination.
The dynamic modification of chromatin architecture by enzyme complexes that alter histone-DNA interactions, making DNA more or less accessible for transcription.
Example: Histone acetylation loosens chromatin structure (euchromatin), allowing transcription factors to access DNA and activate gene expression.
More terms are available in the glossary.
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