PPT 11: Cell Reproduction and the Cell Cycle

Vocabulary flashcards covering cell division, eukaryotic and prokaryotic cell cycles, mitosis, cytokinesis, and the regulatory mechanisms and failure points (cancer) discussed in Lecture 11.

Zygote

An embryo formed from the fusion of a sperm and an egg, marking the beginning of human life.

Genome

A cell's total DNA packaged as a double-stranded DNA molecule.

Plasmids

Smaller loops of DNA in prokaryotes that are not essential for normal growth but can be exchanged, often spreading beneficial genes like antibiotic resistance.

Nucleoid

The region in a prokaryotic cell where the single double-stranded circular DNA molecule is contained.

Ploidy

The number of complete sets of chromosomes in a cell, denoted by the letter $n$.

Diploid ($2n$)

Cells containing two matching sets of chromosomes, with one set inherited from each parent.

Haploid ($1n$)

Cells containing only one set of chromosomes, such as human gametes which have 23 chromosomes.

Homologous

Matched pairs of chromosomes that are the same length and have genes in the exact same location (locus).

Locus

The specific location of a gene on a chromosome.

Genes

Specific nucleotide segments that serve as functional units of chromosomes and determine specific characteristics by encoding for proteins.

Traits

Variations in characteristics determined by genes.

Allele

Alternative forms of a gene that code for the same trait, such as the different sequences for blood types A, B, and O.

Histone

Proteins that DNA wraps around to form chromatin, facilitating the condensing of DNA into chromosomes.

Chromatin

The structure formed by DNA wrapped around histone proteins; it is seven times shorter and five times wider than the DNA double helix.

Sister chromatids

Two identical copies of the same chromosome produced during DNA replication and linked by cohesion proteins.

Centromere

The area of greatest connection between sister chromatids, typically located near the center of the replicated chromosome.

Cell cycle

An ordered series of events involving cell growth and division that produces new daughter cells.

Interphase

The major phase of the cell cycle where the cell undergoes normal growth and DNA is replicated, consisting of $G_1$, $S$, and $G_2$ stages.

Mitotic phase

The phase of the cell cycle where replicated DNA and cytoplasmic contents are physically separated.

Cytokinesis

The physical separation of the cytoplasmic components into two separate daughter cells following nuclear division.

$G_1$ Phase (First Gap)

The first stage of interphase where the cell accumulates nucleotides for DNA replication, amino acids for proteins, and energy reserves.

$S$ Phase (Synthesis of DNA)

The stage of interphase where DNA replication occurs, producing sister chromatids, and the centrosome is duplicated.

Mitotic spindle

An apparatus composed of spindle fibers that orchestrates the movement of chromosomes during cell division.

$G_2$ Phase (Second Gap)

The final stage of interphase where the cell replenishes energy stores, synthesizes proteins for chromosome movement, and dismantles the cytoskeleton.

Karyokinesis

The process of nuclear division, which is the first step of the mitotic phase.

Prophase

The first phase of mitosis where the nuclear envelope disintegrates, the nucleolus disappears, and chromosomes coil more tightly to become visible.

Prometaphase

The phase where the kinetochore develops in the centromeric region to attract and orient sister chromatids toward opposite poles.

Kinetochore

A protein formed in the centromeric region that attracts the mitotic spindle to orient sister chromatids.

Metaphase

The phase where chromosomes are aligned in a plane called the metaphase plate, reaching maximum condensation.

Metaphase plate

The equatorial plane located halfway between the poles where chromosomes align during metaphase.

Anaphase

The phase where cohesion proteins dissolve, and sister chromatids (now called chromosomes) move rapidly toward opposite poles.

Telophase

The phase where chromosomes reach opposing poles, start to decondense back into chromatin, and the nuclear envelope redevelops.

Cleavage furrow

A fissure created by a contractile ring that pulls the equator of an animal cell inward during cytokinesis.

Cell plate

A structure formed by Golgi vesicles in plant cells during cytokinesis that becomes the new cell wall dividing the two daughter cells.

$G_0$ Phase

An inactive or quiescent stage where cells exit the cell cycle and are not actively preparing to divide, often due to unfavorable conditions or cell maturity.

Cell-cycle checkpoints

Specific points in the eukaryotic cell cycle (near the end of $G_1$, at the $G_2/M$ transition, and during metaphase) where progression can be halted.

Cyclins and cyclin-dependent kinases

Molecules that provide positive regulation to promote the progress of the cell cycle.

Negative regulation

The halting of the cell cycle by molecules such as Retinoblastoma protein (Rb), $P53$, and $P21$, especially under cell stress.

Proto-oncogenes

Normal genes that code for positive cell-cycle regulators; they can become oncogenes when mutated.

Oncogenes

Mutated proto-oncogenes that have the potential to drive the cell cycle forward even when the cell is not ready, leading to uncontrolled growth.

Tumor suppressor genes

Genes that code for negative regulator proteins which can halt the cell cycle, such as $P53$; their failure is compared to "brakes failing on a car."

Binary fission

The process by which prokaryotes reproduce, involving the replication of a single circular chromosome and its allocation into two identical daughter cells.

Origin

The starting point of DNA replication in prokaryotic cells, located where the chromosome attaches to the plasma membrane.

Septum

A barrier formed by the $FtsZ$ ring at the cell midpoint that directs the division of a prokaryotic cell during binary fission.