Gene Expression & Regulation: every key term you need (+ practice quiz)
63 flashcard terms for AP Biology Unit 6, written to match the course framework. Study them here, then drill them as interactive flashcards, or test yourself with the 20-question quiz — free, no account needed.
The flow of genetic information: DNA → RNA (transcription) → Protein (translation). DNA is the blueprint, RNA the messenger, protein the functional product.
Gene Expression
The process by which the information in a gene is used to synthesize a functional product, usually a protein, via transcription and translation.
Transcription
The synthesis of an RNA molecule from a DNA template, occurring in the nucleus (eukaryotes); copies one gene's information into mRNA.
RNA Polymerase
The enzyme that synthesizes RNA from a DNA template during transcription, reading the template strand 3'→5' and building RNA 5'→3'.
Promoter
A DNA sequence upstream of a gene where RNA polymerase (and transcription factors) bind to initiate transcription.
Template Strand
The DNA strand read by RNA polymerase and used to synthesize a complementary RNA strand during transcription.
mRNA (Messenger RNA)
The RNA transcript that carries genetic information from DNA in the nucleus to ribosomes in the cytoplasm for protein synthesis.
Pre-mRNA Processing
Modifications made to the initial RNA transcript in eukaryotes before it leaves the nucleus: adding a 5' cap, a poly-A tail, and splicing out introns.
Introns and Exons
Introns are non-coding RNA sequences removed during splicing; exons are the coding sequences that remain and are joined together to form mature mRNA.
RNA Splicing
The removal of introns and joining of exons from pre-mRNA, carried out by the spliceosome, producing mature mRNA ready for translation.
Alternative Splicing
Different combinations of exons can be joined from the same pre-mRNA, allowing a single gene to code for multiple different protein products.
5' Cap and Poly-A Tail
Protective modifications added to mRNA ends: a modified nucleotide cap at the 5' end and a chain of adenine nucleotides at the 3' end, aiding stability and export from the nucleus.
Translation
The synthesis of a polypeptide from an mRNA template at the ribosome, using tRNA to match codons to amino acids.
Ribosome
The molecular machine (rRNA + protein) where translation occurs, reading mRNA codons and catalyzing peptide bond formation between amino acids.
tRNA (Transfer RNA)
An RNA molecule that carries a specific amino acid and has an anticodon that base-pairs with a complementary mRNA codon during translation.
Codon
A sequence of three mRNA nucleotides that specifies a particular amino acid (or a start/stop signal) during translation.
Anticodon
The three-nucleotide sequence on tRNA that is complementary to and base-pairs with an mRNA codon.
Genetic Code
The set of rules mapping each of the 64 possible codons to a specific amino acid (or stop signal); nearly universal across all living organisms.
Redundancy of the Genetic Code
Most amino acids are specified by more than one codon (the code is 'degenerate'), which can buffer some mutations from changing the resulting protein.
Start Codon
AUG, which signals the beginning of translation and codes for the amino acid methionine.
Stop Codon
UAA, UAG, or UGA — codons that signal the ribosome to terminate translation and release the completed polypeptide.
Universal Genetic Code
The near-universality of the genetic code across all domains of life is strong evidence for a shared common ancestor of all living things.
Mutation
A change in an organism's DNA sequence, which may alter the protein product and, in turn, the phenotype — the ultimate source of new genetic variation.
Point Mutation
A change involving a single nucleotide base in DNA — includes substitutions, insertions, or deletions of one base pair.
Substitution Mutation
One nucleotide base is replaced by another; effects range from silent to significant, depending on the resulting codon change.
Silent Mutation
A substitution mutation that, due to the genetic code's redundancy, still codes for the same amino acid — no change in the protein.
Missense Mutation
A substitution mutation that changes the codon to specify a different amino acid, potentially altering protein structure and function.
Nonsense Mutation
A substitution mutation that changes a codon into a premature stop codon, truncating the protein and usually destroying its function.
Frameshift Mutation
An insertion or deletion of nucleotides (not in multiples of three) that shifts the reading frame, altering every codon downstream of the mutation — usually severely disruptive.
Effects of Mutations on Phenotype
Mutations can be harmful (disrupting function), beneficial (improving function or creating new function), or neutral (no functional change), depending on where and how they alter the protein.
Gene Regulation
The control of when, where, and how much a gene is expressed — essential for cell specialization, development, and response to environmental signals.
Operon
A cluster of genes in prokaryotes transcribed together as a single mRNA unit, controlled by one shared promoter and regulatory region.
Lac Operon
A classic bacterial operon controlling lactose metabolism genes; expressed only when lactose is present and glucose is scarce.
Repressor Protein
A regulatory protein that binds to DNA (often at an operator) to block RNA polymerase and prevent transcription of a gene or operon.
Operator
A DNA sequence where a repressor protein binds, controlling access of RNA polymerase to the promoter and blocking transcription when occupied.
Inducible Operon
An operon (like lac) that is normally OFF but can be turned ON by the presence of a specific molecule (an inducer) that inactivates the repressor.
Repressible Operon
An operon that is normally ON but can be turned OFF when a specific molecule (a corepressor) binds and activates the repressor.
Negative Regulation
Gene expression control through repressor proteins that block transcription — removing/inactivating the repressor allows expression.
Positive Regulation
Gene expression control through activator proteins that must bind DNA to help RNA polymerase initiate transcription more effectively.
Transcription Factors (Eukaryotes)
Regulatory proteins that bind DNA (at promoters or other regulatory regions) to help or hinder RNA polymerase's ability to transcribe a gene.
Enhancers and Silencers
DNA regulatory sequences, often far from the promoter, that increase (enhancer) or decrease (silencer) a gene's transcription when bound by specific transcription factors.
Epigenetics
Heritable changes in gene expression that do NOT involve changes to the underlying DNA sequence itself, often via chemical modifications.
DNA Methylation
The addition of methyl groups to DNA (often at gene promoters), which typically silences (turns off) gene expression without altering the DNA sequence.
Histone Modification
Chemical changes (like acetylation) to histone proteins around which DNA is wound, affecting how tightly DNA is packed and thus how accessible genes are for transcription.
Chromatin Structure & Gene Access
Tightly packed (heterochromatin) DNA is generally inaccessible and not transcribed; loosely packed (euchromatin) DNA is accessible and can be actively transcribed.
Cell Differentiation
The process by which cells become specialized in structure and function, driven almost entirely by differential gene expression — not different genes, but different genes turned on/off.
Differential Gene Expression
The concept that all cells in a multicellular organism have the same genome, but different cell types express different subsets of genes, producing their distinct identities.
Signal Transduction and Gene Expression
External signals (hormones, growth factors) often trigger pathways that activate transcription factors, ultimately switching specific genes on or off in the target cell.
Viruses
Non-cellular infectious particles consisting of genetic material (DNA or RNA) enclosed in a protein coat, requiring a host cell's machinery to reproduce.
Viral Structure
A capsid (protein coat) surrounding genetic material (DNA or RNA); some viruses have an additional outer envelope derived from host membrane.
Lytic Cycle
A viral reproductive cycle in which the virus immediately hijacks the host cell to replicate, then bursts (lyses) the cell to release new viruses.
Lysogenic Cycle
A viral reproductive cycle in which viral DNA integrates into the host genome and is replicated passively along with host DNA, remaining dormant until triggered to enter the lytic cycle.
Retrovirus
An RNA virus (e.g., HIV) that uses the enzyme reverse transcriptase to convert its RNA genome into DNA, which then integrates into the host cell's genome.
Reverse Transcriptase
An enzyme used by retroviruses to synthesize DNA from an RNA template — the reverse of normal transcription (DNA to RNA).
Biotechnology
The application of biological systems and organisms to develop useful products and technologies, including genetic engineering techniques.
Recombinant DNA
DNA formed by combining genetic material from different sources, typically by inserting a gene of interest into a plasmid or other vector.
Restriction Enzymes
Bacterial enzymes that cut DNA at specific recognition sequences, widely used as molecular scissors in genetic engineering.
Gel Electrophoresis
A technique separating DNA (or protein) fragments by size using an electric current through a gel matrix — smaller fragments migrate farther.
Polymerase Chain Reaction (PCR)
A technique that rapidly amplifies (copies) a specific DNA sequence exponentially in vitro, using primers and a heat-stable DNA polymerase.
DNA Sequencing
Techniques for determining the exact order of nucleotides in a DNA molecule, foundational to genomics and the Human Genome Project.
CRISPR-Cas9
A gene-editing technology derived from a bacterial immune system, using a guide RNA to direct the Cas9 enzyme to cut DNA at a specific target sequence for editing.
Genetically Modified Organism (GMO)
An organism whose genome has been altered using biotechnology, often to introduce a beneficial trait not naturally present.
Applications of Biotechnology
Includes medical diagnostics and gene therapy, agricultural crop improvement, forensic DNA analysis, and industrial production of proteins like insulin.