AP Biology Unit 6: Molecular Genetics and Cell Division

Comprehensive vocabulary flashcards covering AP Biology Unit 6, including DNA structure, DNA replication, cell cycle control, mitosis stages, transcription, mRNA processing, translation, and genetic mutations.

Nucleotide

The monomer of DNA consisting of a phosphate group, a pentose sugar, and a nitrogenous base ($A=T$ or $G=C$), held together across strands by hydrogen bonds.

Sugar-Phosphate Backbone

The structural outer framework of DNA composed of alternating pentose sugars and phosphate groups.

Antiparallel

The arrangement in DNA where strands run in opposite orientations like upside-down mirror images; one strand features its $5'$ carbon (attached to a phosphate group) at the top, while the complementary strand has its $5'$ carbon at the bottom.

Semiconservative Replication

The mechanism of DNA duplication where the parental double helix separates, and each individual parental strand serves as a template directing the synthesis of a complementary daughter strand.

Topoisomerase

An enzyme that untwists and relieves tension in the DNA double helix ahead of the replication fork.

Helicase

An enzyme that binds to single-strand binding proteins at the origin ($\text{ori}$) and breaks hydrogen bonds between base pairs to unzip the DNA strands.

Primase

An enzyme that synthesizes a short RNA primer (about $5\text{--}10$ nucleotides) to supply a free $3'$ hydroxyl end for DNA polymerase attachment.

DNA Polymerase

The primary enzyme that builds new DNA by reading the template strand in the $3' \rightarrow 5'$ direction and synthesizing antiparallel complementary nucleotides in the $5' \rightarrow 3'$ direction.

Leading Strand

The continuous, unfragmented daughter strand synthesized moving toward the replication fork on the $5'$ side.

Lagging Strand

The discontinuous strand synthesized away from the replication fork in short bursts on the $3'$ side, forming Okazaki fragments.

DNA Ligase

An enzyme that catalyzes the formation of phosphodiester bonds to join fragmented DNA segments (such as Okazaki fragments) into a continuous daughter strand.

Nuclease

An enzyme that excises and removes mismatched or damaged nucleotide segments from replicated DNA during repair processes.

Telomeres

Non-coding, expendable terminal segments of DNA that protect chromosomes from degradation resulting from DNA polymerase's inability to replace the terminal $5'$ RNA primer.

Chromatin

Uncoiled, loose strands of DNA wrapped around histone proteins, characteristic of the cell during interphase.

Chromosome

The condensed, supercoiled form of DNA packaged with proteins, visible during mitosis.

Chromatid

A single linear copy of a chromosome prior to replication in $S$ phase.

Sister Chromatids

Two identical copies of a replicated chromosome joined together at a shared centromere, produced during $S$ phase.

$G_1$ Phase

The first gap phase of interphase where the cell grows and performs normal metabolic functions.

$S$ Phase

The synthesis phase of the cell cycle during which DNA replication occurs.

$G_2$ Phase

The second gap phase of interphase where the cell continues to grow and synthesizes proteins necessary to prepare for division.

Mitosis

The phase of the cell cycle dedicated to the division of the cell nucleus and precise separation of replicated chromosomes.

Cytokinesis

The division of the cytoplasm following mitosis, resulting in two distinct daughter cells.

Prophase

The first stage of mitosis characterized by the condensation of chromatin into visible chromosomes and the disintegration of the nucleus.

Prometaphase

The mitotic stage where the nuclear envelope breaks down and spindle fibers attach to the kinetochores on the centromeres of chromosomes.

Metaphase

The stage of mitosis where chromosomes align along the center of the nucleus/cell (metaphase plate).

Anaphase

The stage of mitosis in which sister chromatids separate at their centromeres and are pulled to opposite poles while spindle fibers disintegrate.

Telophase

The final stage of mitosis during which the nuclear envelope reforms around separated chromosomes, chromosomes decondense back into chromatin, and spindle fibers disassemble.

Binary Fission

A form of asexual reproduction occurring in prokaryotic cells where inward growth of the plasma membrane divides the cell into two genetically identical cells.

MPF (Maturation-Promoting Factor)

A protein complex formed when cyclin accumulates and binds to a cyclin-dependent kinase (Cdk), phosphorylating target proteins to drive the cell past the $G_2$ checkpoint into mitosis.

Cell Cycle Checkpoints

Regulatory control points where the cell monitors and verifies whether specific physiological criteria are satisfied before progressing to the subsequent phase, safeguarding against cancer and mutations.

Density-Dependent Inhibition

A regulatory phenomenon exhibited by healthy cells where crowded cells cease dividing once they form a single uniform monolayer.

Anchorage Dependence

The requirement that a healthy cell must be anchored or attached to a solid substratum to initiate cell division.

Central Dogma

The principle that genetic information flows directionally from $\text{DNA} \rightarrow \text{RNA} \rightarrow \text{Protein}$, stating that for every gene there is a protein produced via transcription and translation.

Codon

A three-nucleotide base sequence in mRNA that codes for a specific amino acid during translation.

Promoter Region (TATA Box)

A specific DNA sequence that signals where RNA polymerase and associated transcription factors bind to initiate transcription.

RNA Polymerase

The enzyme responsible for unwinding DNA and synthesizing a complementary pre-mRNA transcript using RNA nucleotides ($U$ replacing $T$).

Transcription Factors

Proteins that facilitate the binding of RNA polymerase to the promoter region to initiate gene transcription.

Terminator Sequence

A specific DNA base sequence that signals RNA polymerase to stop transcription and release the completed pre-mRNA molecule.

Spliceosome

A molecular assembly of snRNPs and proteins that excises non-coding introns and splices coding exons together in pre-mRNA.

snRNP

Small nuclear ribonucleoproteins composed of RNA and proteins that assemble with others to form functional spliceosomes.

snRNA

Small nuclear RNA molecules that associate with proteins to construct snRNPs.

Introns

Non-coding nucleotide sequences in pre-mRNA transcripts that are removed during RNA splicing prior to export from the nucleus.

Exons

Coding sequences in pre-mRNA transcripts that are retained, spliced together, and expressed as mature mRNA.

$5'$ Cap and Poly-A Tail

Post-transcriptional modifications added to the ends of pre-mRNA ($5'$ cap at the beginning, Poly-A tail at the $3'$ end) to protect the transcript and facilitate nuclear export.

mRNA (Messenger RNA)

The RNA transcript that carries genetic information coded in triplets (codons) from nuclear DNA to the ribosome for polypeptide synthesis.

tRNA (Transfer RNA)

An adaptor RNA molecule carrying a specific amino acid to the ribosome; its anticodon pairs complementarily with mRNA codons to position amino acids in order.

rRNA (Ribosomal RNA)

The structural and catalytic RNA component of ribosomes that catalyzes the formation of peptide bonds between incoming amino acids.

A Site (Ribosome)

The aminoacyl-tRNA binding site on the ribosome where incoming charged tRNAs matching the mRNA codon initially bind.

P Site (Ribosome)

The peptidyl-tRNA binding site on the ribosome that holds the tRNA attached to the growing polypeptide chain before translocation.

E Site (Ribosome)

The ribosomal exit site where discharged, uncharged tRNAs are released following peptide bond formation and ribosome translocation.

Silent Mutation

A point mutation where a single base substitution alters the codon sequence but still specifies the identical amino acid, resulting in no functional change.

Missense Mutation

A point mutation in which a single base substitution leads to the incorporation of an incorrect amino acid into the polypeptide chain.

Nonsense Mutation

A point mutation where a nucleotide substitution converts an amino-acid-specifying codon into a premature stop codon, terminating translation early.

Frameshift Mutation

A mutation resulting from nucleotide insertions or deletions not divisible by three, which shifts the triplet reading frame and produces a domino effect on downstream translation.

Insertion

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

Deletion

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