Bio 151 Exam Review: Cell Cycle, DNA Replication, and Gene Expression

Comprehensive vocabulary flashcards covering eukaryotic cell cycle phases, checkpoints, mitosis, meiosis, cancer genetics, DNA structure, semiconservative replication, transcription, RNA processing, and translation mechanisms.

$$G_0\text{ phase}$$

A resting or quiescent cell state where cells are non-dividing and not actively progressing through the cell cycle.

$$G_1\text{ phase}$$

The gap 1 phase of interphase during which the cell increases in size, accumulates proteins, and prepares for S phase.

S phase

The synthesis phase of interphase during which DNA replication occurs.

$$G_2\text{ phase}$$

The gap 2 phase of interphase where the cell undergoes additional growth, assembles microtubules, and prepares for mitosis.

M phase

The division phase of the cell cycle comprising mitosis (nuclear division) and cytokinesis (cytoplasmic division).

Sister chromatids

Two identical copies of a single replicated chromosome that stay physically joined together until anaphase.

Centromere

The specialized DNA region on a chromosome where sister chromatids are held together.

Kinetochore

A multi-protein structure assembled at the centromere that acts as an anchor for spindle microtubules to attach.

Mitotic spindle

A macromolecular machine composed of microtubules and associated proteins responsible for segregating chromosomes during cell division.

Cytokinesis

The physical division of the cytoplasm following nuclear division, producing two separate daughter cells.

Meiosis I

The first meiotic division characterized by homologous chromosome pairing, crossing over, and separation, resulting in two haploid daughter cells.

Meiosis II

The second meiotic division in which sister chromatids separate, resulting in four genetically unique haploid cells.

Chiasma

The cross-shaped point of physical contact where crossing over and genetic exchange occur between non-sister chromatids of homologous chromosomes.

First-division nondisjunction

The failure of homologous chromosomes to separate during meiosis I, resulting in 0 normal gametes: 2 gametes with $n+1$ chromosomes and 2 gametes with $n-1$ chromosomes.

Second-division nondisjunction

The failure of sister chromatids to separate during meiosis II, yielding 2 normal gametes ($n$), 1 gamete with an extra chromosome ($n+1$), and 1 gamete missing a chromosome ($n-1$).

Cyclin-dependent kinases (CDKs)

The primary protein kinases that regulate the cell cycle, which require binding to regulatory cyclin proteins to become enzymatically active.

Cyclins

Regulatory proteins whose concentrations oscillate cyclically throughout the cell cycle, activating CDKs to trigger specific cell cycle transitions.

$$G_1/S\text{ checkpoint}$$

The DNA damage checkpoint operating prior to S phase entry that arrests the cell cycle if DNA damage is detected.

$$G_2/M\text{ checkpoint}$$

The DNA replication checkpoint occurring at the end of $G_2$ that verifies whether all genome DNA is fully and accurately replicated before mitosis begins.

Spindle assembly checkpoint (SAC)

The M-phase checkpoint preceding anaphase that monitors whether all chromosome kinetochores are properly attached to spindle microtubules.

MAD

A checkpoint protein that binds CDC20 in response to signals from unattached kinetochores, establishing a "wait" signal that halts anaphase initiation.

CDC20

An activator protein released by MAD once all kinetochores are attached to the spindle, which then associates with APC to form an active ubiquitin-ligase complex.

Anaphase-promoting complex (APC)

A ubiquitin-ligase complex that, upon activation by CDC20, ubiquitinates Securin to target it for destruction.

Securin

An inhibitory protein that holds Separase in an inactive state until it is ubiquitinated by APC/CDC20 and degraded.

Separase

A protease that is released upon Securin degradation to cleave Cohesin complexes, allowing sister chromatids to separate during anaphase.

Cohesin

A protein ring complex that glues sister chromatids together along their length until it is cleaved by separase.

Proto-oncogene

A normal cellular gene that encodes proteins promoting cell growth, proliferation, and division.

Oncogene

A mutated, hyperactive, or overexpressed proto-oncogene that drives unregulated cell proliferation and tumor development.

Tumor suppressor gene

A gene encoding a protein that functions to slow the cell cycle, mediate DNA repair, or trigger apoptosis to prevent cancer development.

pRb (Retinoblastoma protein)

A tumor suppressor protein that prevents premature entry into S phase by sequestering E2F transcription factors until phosphorylated by CDK/cyclin complexes.

p53

A key tumor suppressor protein activated by DNA damage that induces transcription of p21 to halt CDK activity and pause cell cycle progression.

HPV E6 and E7 proteins

Oncogenic viral proteins produced by Human Papillomavirus; E6 causes the degradation of p53, while E7 binds and inactivates pRb.

Transforming principle

The chemical substance demonstrated by Griffith and identified by Avery, MacLeod, and McCarty as DNA, which permanently transfers genetic traits from one bacterial strain to another.

Phosphodiester bond

The covalent linkage connecting the $3'\text{-OH}$ group of one deoxyribose to the $5'\text{-phosphate}$ group of the next, forming the structural backbone of a nucleic acid chain.

Chargaff's rules

Principles of DNA base composition stating that the amount of adenine equals thymine ($\text{\%}A = \text{\%}T$), guanine equals cytosine ($\text{\%}G = \text{\%}C$), and total purines equal total pyrimidines.

Semiconservative replication

The mechanism of DNA replication, verified by Meselson and Stahl, where each replicated double helix consists of one original parental strand and one newly synthesized strand.

Helicase

An enzyme that unwinds the parental DNA duplex at the replication fork by breaking hydrogen bonds between complementary base pairs.

Topoisomerase II

An enzyme that relieves torsional strain and overwinding in the DNA duplex ahead of the advancing replication fork.

Single-stranded binding proteins (SSBs)

Proteins that coat and stabilize separated single DNA strands at the replication fork, preventing them from re-annealing or clumping.

RNA primase

An RNA polymerase that synthesizes short RNA primers to provide a free $3'\text{-OH}$ group required for DNA polymerase to initiate synthesis.

DNA polymerase

An enzyme that synthesizes a new DNA strand in the $5' \rightarrow 3'$ direction by extending an existing primer and proofreading newly incorporated nucleotides for errors.

DNA ligase

An enzyme that seals single-strand breaks in the phosphodiester backbone by joining adjacent Okazaki fragments on the lagging strand.

Okazaki fragments

Short, discontinuous stretches of newly synthesized DNA formed on the lagging strand away from the replication fork.

Telomeres

Repetitive, non-coding DNA sequences capping the ends of linear eukaryotic chromosomes that prevent chromosome loss and degradation during successive rounds of replication.

Telomerase

A specialized enzyme containing an RNA template that extends the shortened $3'$ ends of linear template chromosomes by adding telomeric repeat sequences.

Synonymous mutation

A point mutation (silent mutation) in which a nucleotide substitution changes a codon into a synonymous codon that specifies the identical amino acid.

Nonsynonymous mutation

A nucleotide substitution (missense mutation) that alters a codon so that it encodes a different amino acid, potentially affecting protein folding and function.

Nonsense mutation

A nucleotide substitution that changes an amino-acid-specifying codon into a premature stop codon, causing early translation termination.

Frameshift mutation

A mutation caused by the insertion or deletion of a number of nucleotides that is not a multiple of three, altering the translational reading frame of all downstream codons.

Central dogma of molecular biology

The universal rule describing genetic information flow: $\text{DNA} \rightarrow \text{mRNA (transcription)} \rightarrow \text{protein (translation)}$.

Euchromatin

Decondensed, open chromatin structure that is transcriptionally active and accessible to RNA polymerases.

Heterochromatin

Highly condensed, compact chromatin structure where access by transcription machinery is impeded, rendering genes transcriptionally silent.

Promoter

A specific DNA sequence situated upstream of the transcription start site where general transcription factors and RNA polymerase assemble to initiate transcription.

Enhancer sequence

A regulatory DNA sequence that binds transcriptional activator proteins to stimulate transcription from a distance.

Mediator complex

A multi-protein coactivator complex that communicates signals from enhancer-bound activator proteins to RNA polymerase II via DNA looping.

$$5'\text{ cap}$$

A modified guanine nucleotide added to the $5'$ end of eukaryotic primary transcripts that protects mRNA from enzymatic degradation and recruits the ribosome.

$$\text{Poly(A) tail}$$

A sequence of adenine nucleotides added to the $3'$ end of eukaryotic primary transcripts during polyadenylation to confer message stability.

Alternative splicing

A regulated post-transcriptional process by which different combinations of exons from a single pre-mRNA are joined, generating distinct protein isoforms from one gene.

Aminoacyl-tRNA synthetase

An enzyme family responsible for covalently coupling each specific amino acid to its cognate tRNA molecule.

Anticodon

A triplet nucleotide sequence located within the anticodon loop of a tRNA that base-pairs antiparallel to a complementary codon in mRNA.

Ribosomal A site

The aminoacyl site of the ribosome that accommodates an incoming charged tRNA whose anticodon matches the codon displayed on mRNA.

Ribosomal P site

The peptidyl site of the ribosome that holds the tRNA carrying the growing polypeptide chain prior to peptide bond formation.

Ribosomal E site

The exit site of the ribosome where uncharged, deacylated tRNAs are shifted before being ejected.

Release factor

A protein that recognizes a stop codon (UGA, UAA, or UAG) positioned in the ribosomal A site, cleaving the ester bond connecting the polypeptide to tRNA to terminate translation.