Lectures 15 & 16: DNA, RNA, Cell Cycle, and Mitosis

Vocabulary flashcards covering nucleic acid structures (DNA vs RNA), nitrogenous bases, cell cycle phases and checkpoints, and the stages and apparatus of mitosis.

Deoxyribonucleic Acid (DNA)

A nucleic acid biomolecule composed of nucleotide monomers, featuring an anti-parallel, complementary double helix structure oriented in $5'$ to $3'$ directions.

Nucleotide

The monomer subunit of nucleic acids, consisting of a 5-carbon sugar, a nitrogenous base, and a phosphate group.

Deoxyribose

The five-carbon sugar found in DNA nucleotides, distinguished by having a hydrogen atom ($-\text{H}$) at the $2'$ carbon position rather than an extra oxygen.

Ribose

The five-carbon sugar found in RNA nucleotides, which has an extra oxygen as a hydroxyl group ($-\text{OH}$) at the $2'$ carbon position.

Pyrimidine

A class of nitrogenous bases characterized by a small, single six-ringed structure; includes Cytosine, Thymine (found only in DNA), and Uracil (which replaces Thymine in RNA).

Purine

A class of nitrogenous bases characterized by a larger, double-ringed structure (double $\text{N-C}$ ring); includes Adenine and Guanine.

DNA Nucleotides

The four nitrogenous bases of DNA—Adenine, Cytosine, Thymine, and Guanine (A, C, T, G)—which share the same sugar and phosphate group structure.

$G_1$ Phase

The cell cycle phase where non-dividing cells leave the cycle and dividing cells commit to continuing through the cycle.

$G_1$ Checkpoint

A checkpoint occurring at the end of $G_1$ that evaluates cell size, volume, and nutrients. Passing leads to commitment to $S$ phase; failure directs the cell into $G_0$ (non-dividing state) or apoptosis.

$S$ Phase

The phase of interphase during which DNA replicates, doubling the amount of DNA in the cell.

$G_2$ Phase

The subphase following DNA synthesis where two centrosomes have formed and the mitotic spindle begins to form.

$G_2$ Checkpoint

A checkpoint occurring during the transition from $G_2$ to $M$ phase that verifies whether all chromosomes were fully and accurately copied during $S$ phase and checks for DNA damage or mutations. If unfixable, kinases halt the cycle to repair damage or trigger apoptosis.

$M$ Phase

The division phase of the cell cycle where the cell divides to produce two daughter cells.

$M$ Checkpoint

A checkpoint occurring during metaphase that checks if all sister chromatids are attached to spindle microtubules via kinetochores and aligned at the center of the cell; failure causes mitotic arrest to allow attachment, or apoptosis/aneuploidy if unfixable.

Binary Fission

Prokaryote cell division in which the chromosome and cell divide together in one single process.

Mitosis

The process of eukaryotic cell division that segregates replicated chromosomes into two nuclei.

Cytokinesis

The division process beginning in late anaphase or telophase where the active cell divides to form two cells that each start their own cycle.

Mitotic Spindle

A cell structure composed of microtubules that forms during early mitosis to coordinate chromosome separation.

Centrosome

An organelle that organizes microtubules and functions to separate chromosomes during mitosis.

Chromatin

The complex of DNA and histone proteins that condenses to form visible chromosomes during cell division.

Centromere

The region where identical DNA molecules are most attached after chromosomes condense; holds two sister chromatids together.

Kinetochore

A protein complex positioned directly on top of the centromere where spindle microtubules attach.

Sister Chromatids

Identical replication products of a DNA molecule produced during $S$ phase and held together at the centromere.

Daughter Cells

The resulting cells of cell division that possess the exact same genome as the parental cells.

Prophase

The first phase of mitosis, during which chromatin condenses into chromosomes, the nuclear envelope breaks, and the mitotic spindle forms from the centrosomes.

Prometaphase

The stage of mitosis where the nuclear envelope completely disintegrates, microtubules from the centrosomes invade the nucleus, and sister chromatids attach to microtubules from opposite centrosomes.

Metaphase

The stage of mitosis where chromosomes align along the metaphase plate (equatorial plane) due to spindle fiber tension, facilitating equal distribution of chromosomes.

Anaphase

The stage of mitosis where spindle fibers pull chromosomes apart and sister chromatids move to opposite poles, ensuring each new cell receives an identical set of chromosomes.

Telophase

The final stage of mitosis where chromatids reach the poles, a nuclear envelope re-forms around each set of chromosomes, and chromosomes de-condense back into chromatin.

In a typical animal, mitosis produces ____________  while meiosis produces _____________.

two diploid daughter cells ... four haploid daughter cells

What must happen to a chromosome before a cell starts mitosis?

The single DNA molecule in the chromosome must be replicated.