Cell Cycle, DNA Replication, and Protein Synthesis

Vocabulary flashcards defining key biological terms related to the cell cycle, DNA replication, mitosis, protein synthesis, and mutations as covered in the lecture transcript.

Interphase

The major period of the cell cycle from initial cell formation up until cell division, during which the cell grows, carries out routine activities, and synthesizes proteins.

G1 phase

The gap 1 subphase of interphase when the cell is most metabolically active, growing, making proteins, and performing its specialized functions.

S phase

The synthesis subphase of interphase during which the cell replicates its DNA and produces histone proteins in preparation for cell division.

G2 phase

The gap 2 subphase of interphase occurring after S phase, during which the cell synthesizes protein enzymes necessary for cell division.

G0 phase

A non-dividing state entered by cells such as nerve cells and cardiac muscle cells that opt out of the cell cycle or fail G1 checkpoint requirements.

Helicase

An enzyme that uncoils the DNA double helix and unzips the hydrogen bonds between complementary nitrogenous bases during replication.

Topoisomerase

An enzyme that assists in uncoiling the DNA double helix during replication so nitrogenous bases can be accessed.

Replication Fork

The specific point where DNA strands are unzipped and separated by breaking hydrogen bonds during replication.

Replication Bubble

The entire opened region of DNA where strands have been separated for replication.

DNA Polymerase

An enzyme family that adds complementary nucleotides to exposed DNA strands strictly in a $5'$ to $3'$ direction.

Leading Strand

The newly synthesized DNA strand that is formed continuously in the $5'$ to $3'$ direction toward the replication fork.

Lagging Strand

The newly synthesized DNA strand built discontinuously in short segments away from the replication fork due to directional constraints.

Okazaki Fragments

Short segments of DNA synthesized discontinuously on the lagging strand during DNA replication.

DNA Ligase

An enzyme that joins Okazaki fragments together on the lagging strand after RNA primers are removed.

Semiconservative Replication

The process of DNA replication resulting in two identical double helices, each containing one original parent strand and one newly synthesized strand.

Histones

Packaging proteins produced in the cytoplasm around which DNA is wound to form chromatin inside the nucleus.

Cohesin

The specific protein complex that holds sister chromatids together at the centromere.

Centromere

The constricted region of chromatin and protein complexes where sister chromatids are held together by cohesin.

Prophase

The first phase of mitosis during which chromatin condenses into visible sister chromatids, mitotic spindles form, and the nuclear envelope breaks down.

Metaphase

The mitotic phase in which kinetochore microtubules align chromosomes along the equator or metaphase plate of the cell.

Separase

An enzyme activated at the end of metaphase that cleaves the cohesin proteins holding sister chromatids together.

Anaphase

The shortest phase of mitosis, characterized by motor proteins dragging separated sister chromatids to opposite poles of the cell.

Telophase

The final stage of mitosis where chromosome movement stops, nuclear envelopes reform, nucleoli reappear, and chromosomes uncondense into chromatin.

Cytokinesis

The division of the cytoplasm beginning in late anaphase, where actin microfilaments form an in-pinching cleavage furrow to divide the cell into two daughter cells.

Vincristine

A chemotherapy agent that targets the mitotic spindle to prevent microtubule formation and stop chromosome segregation.

Doxorubicin

A chemotherapy medication that blocks mRNA synthesis, inhibiting transcription and translation.

Central Dogma

The principle of molecular biology stating that genetic information flows from DNA to RNA to produce protein.

Gene

A specific sequence of DNA that encodes the information required to produce a single polypeptide chain.

Exons

Coding regions of a gene transcript that are joined together to specify the amino acid sequence of a polypeptide.

Introns

Noncoding intervening sequences within a gene transcript that are removed by spliceosomes prior to translation.

Transcription

The process occurring in the nucleus where a DNA gene sequence is copied into messenger RNA (mRNA).

Translation

The process occurring in the cytoplasm at ribosomes where mRNA codons are decoded into a sequence of amino acids to build a polypeptide.

Promoter

A specific sequence of DNA that marks the starting point of a gene where RNA polymerase binds to initiate transcription.

Codon

A sequence of three consecutive nucleotides on an mRNA strand that specifies a particular amino acid or translation stop signal.

Anticodon

A three-base loop sequence on a tRNA molecule that complementary base pairs with a specific mRNA codon.

AUG

The specific mRNA start codon that signals the initiation of translation and codes for the amino acid methionine.

Stop Codons

The mRNA sequences UAA, UAG, and UGA, which bind release factors to terminate translation instead of coding for an amino acid.

Ribozyme

An RNA molecule with catalytic activity, such as rRNA in a ribosome, that catalyzes peptide bond formation between amino acids.

Signal Recognition Particle (SRP)

A complex that identifies an ER signal sequence on a growing polypeptide chain and directs the ribosome to dock at the endoplasmic reticulum.

Silent Mutation

A point mutation in which a nucleotide substitution results in a codon that still codes for the same amino acid, leaving the protein unchanged.

Missense Mutation

A single nucleotide substitution that changes a codon to code for a different amino acid, altering the primary structure and function of a protein.

Nonsense Mutation

A point mutation that prematurely converts an amino acid codon into a stop codon, cutting the resulting polypeptide chain short.

Frameshift Mutation

A mutation caused by inserting or deleting nucleotides in numbers not divisible by three, shifting the reading frame of all downstream codons.

MicroRNAs (miRNAs)

Small RNA molecules that regulate gene expression by silencing mRNAs or targeting them for degradation in the cytoplasm.