AP Biology Unit 6: Gene Expression and Regulation

Comprehensive vocabulary flashcards covering the Central Dogma, DNA replication, transcription, RNA processing, translation, gene regulation, mutations, and molecular biotechnology.

Central Dogma of Biology

The directional flow of genetic information: replication (DNA makes DNA), transcription (DNA is used to make RNA), and translation (RNA instructions are used to make a protein).

Plasmids

Small, extra, usually circular, double-stranded pieces of DNA found in prokaryotes that may contain beneficial genes, such as those for antibiotic resistance.

Purines

Nitrogenous bases containing two rings; specifically adenine (A) and guanine (G).

Pyrimidines

Nitrogenous bases containing one single ring; specifically cytosine (C) and thymine (T).

Topoisomerase

An enzyme that relieves twisting and tension ahead of the replication fork during DNA replication.

Helicase

An enzyme that unzips double-stranded DNA by breaking the hydrogen bonds between complementary base pairs.

Primase

An enzyme that synthesizes short RNA primers to provide DNA polymerase with a starting point for DNA synthesis.

DNA Polymerase

An enzyme that adds complementary DNA nucleotides to synthesize new strands in the $5' \rightarrow 3'$ direction and helps proofread the sequence.

Ligase

An enzyme that seals gaps in the sugar-phosphate backbone and joins DNA fragments, such as Okazaki fragments.

Leading Strand

The DNA strand that is synthesized continuously in one section toward the replication fork in the $5' \rightarrow 3'$ direction.

Lagging Strand

The DNA strand that is synthesized discontinuously in short pieces away from the replication fork.

Okazaki Fragments

Short pieces of DNA synthesized discontinuously on the lagging strand that are later joined together by DNA ligase.

Semiconservative Replication

The process of DNA replication in which each newly formed DNA molecule consists of one original parent strand and one newly synthesized strand.

Template Strand

The DNA strand that is read by RNA polymerase to make a complementary RNA transcript.

Coding Strand

The DNA strand that has nearly the identical sequence as the newly synthesized RNA, except DNA contains thymine (T) where RNA contains uracil (U).

Introns

Non-coding sections of pre-mRNA that are excised and removed during RNA splicing.

Exons

Coding sequences of pre-mRNA that are kept and joined together to produce mature mRNA.

5′ Cap

A post-transcriptional modification added to the $5'$ end of pre-mRNA that protects the molecule and helps the ribosome recognize and attach to it.

Poly-A Tail

A post-transcriptional modification added to the $3'$ end of pre-mRNA that protects mRNA and aids its export from the nucleus.

RNA Splicing

A post-transcriptional modification in eukaryotes that removes non-coding introns and joins coding exons together.

mRNA

Messenger RNA; carries genetic instructions from DNA to the ribosome for protein synthesis.

tRNA

Transfer RNA; brings specific amino acids to the ribosome, using its anticodon to pair with a complementary mRNA codon.

rRNA

Ribosomal RNA; forms structural and catalytic components of the ribosome and helps catalyze peptide bond formation.

Codon

A triplet sequence of $3$ RNA nucleotides that specifies a particular amino acid or signals a stop in translation.

Reverse Transcriptase

An enzyme found in retroviruses that synthesizes DNA using an RNA template ($\text{RNA} \rightarrow \text{DNA}$).

Epigenetics

Changes in gene expression that take place without altering the underlying DNA nucleotide sequence.

DNA Methylation

The addition of methyl groups to DNA, which typically decreases gene expression by making DNA less accessible for transcription.

Histones

Proteins around which DNA winds; chemical modifications to them regulate how tightly DNA is packaged and accessible to transcription machinery.

Operon

A cluster of genes regulated together under a single control system, commonly found in prokaryotes.

MicroRNAs (miRNAs)

Small RNA molecules that regulate gene expression by binding complementary mRNA to cause degradation or inhibit translation, decreasing protein output.

lac Operon

An inducible operon that controls the production of enzymes required by bacteria to digest lactose.

CAP (Catabolite Activator Protein)

An activator protein that becomes active under low glucose concentrations to enhance transcription of the lac operon.

Substitution

A mutation in which a single nucleotide base is swapped or replaced by a different nucleotide.

Insertion

A mutation characterized by the addition of one or more nucleotide bases into a DNA sequence.

Deletion

A mutation characterized by the loss or removal of one or more nucleotide bases from a DNA sequence.

Frameshift Mutation

A mutation resulting from insertions or deletions of nucleotides in numbers not divisible by $3$, altering the translational reading frame.

Silent Mutation

A point mutation that changes the DNA sequence but leaves the encoded amino acid unaltered.

Missense Mutation

A point mutation that results in the replacement of one amino acid with a different amino acid in the polypeptide chain.

Nonsense Mutation

A point mutation that substitutes an amino acid codon with a premature stop codon, terminating translation early.

Thymine Dimers

Abnormal covalent linkages formed between adjacent thymine bases caused by ultraviolet (UV) radiation damage.

Gel Electrophoresis

A technique that separates DNA fragments according to molecular size as negatively charged DNA travels toward a positive electrode.

DNA Fingerprinting

A laboratory method used to compare DNA samples from different individuals or organisms by analyzing specific electrophoretic band patterns.

Transformation

A process where bacteria take up foreign, exogenous DNA directly from their surroundings and express it.

Conjugation

A mechanism of genetic transfer where bacteria pass DNA directly to another bacterium via physical contact.

Crossing Over

The reciprocal exchange of genetic segments between homologous chromosomes during meiosis.

Fertilization

The combination of two haploid gametes to form a diploid zygote, contributing to genetic variation.

PCR (Polymerase Chain Reaction)

A molecular biotechnology technique used to amplify DNA by making numerous copies of a specific target sequence.

Taq Polymerase

A heat-resistant DNA polymerase isolated from thermophilic bacteria that remains functional through repeated thermal cycles during PCR.

Restriction Enzymes

Endonucleases that recognize and cut double-stranded DNA at specific nucleotide sequences.