Cell Cycle Regulation and Cyclins Quiz

Cell Cycle Overview

• Living things reproduce by producing more of their own kind.
• The continuity of life depends on the reproduction of cells, or cell division.

Cell Division in Unicellular and Multicellular Organisms

• In unicellular organisms, cell division is the process of reproduction.
• Multicellular organisms use cell division for development (from a fertilized cell), growth, and repair.

Cell Division and Reproduction, Growth and Development, Tissue Renewal

• Cell division is a fundamental aspect of the cell cycle, from the cell's formation to its division.
• Each image illustrates a different aspect of cell division’s function: reproduction, growth and development, and tissue renewal.

Concept 12.1: Genetically Identical Daughter Cells

• Cell division typically creates genetically identical daughter cells with the same DNA.
• Meiosis is an exception; it produces gametes (sperm and egg cells) with half the number of chromosomes.

Cellular Organization of the Genetic Material

• A cell's genome comprises all the DNA within it.
• In prokaryotes, the genome is a single DNA molecule.
• Eukaryotic genomes consist of multiple DNA molecules.
• DNA is packaged into chromosomes within cells.

Eukaryotic Chromosomes

• Eukaryotic chromosomes are composed of chromatin—a complex of DNA and protein that condenses during cell division.
• Every eukaryotic species has a specific number of chromosomes per cell nucleus.
• Somatic cells (non-reproductive cells) have two sets of chromosomes.
• Gametes (reproductive cells) have half as many chromosomes as somatic cells.

Distribution of Chromosomes During Eukaryotic Cell Division

• Before cell division, DNA replicates, and chromosomes condense.
• Each duplicated chromosome has two sister chromatids—joined copies of the original chromosome.
• Sister chromatids are separated during cell division.
• The centromere is the narrow "waist" of a duplicated chromosome, where the sister chromatids are most closely attached.

Phases of the Cell Cycle

• The cell cycle consists of the mitotic (M) phase and interphase.
• Mitotic phase includes mitosis and cytokinesis.
• Interphase is where cells grow and copy chromosomes in preparation for cell division.
• Interphase is further broken down into G₁, S, and G₂ phases, where the cell grows during all three, but DNA replicates only during S phase.

Mitosis Phases

• Mitosis is conventionally divided into five phases: prophase, prometaphase, metaphase, anaphase, and telophase.
• Cytokinesis overlaps the later stages of mitosis.

The Mitotic Spindle: A Closer Look

• The mitotic spindle is a structure composed of microtubules that controls chromosome movements during mitosis.
• In animal cells, the spindle microtubule assembly begins in the centrosome, an organizing center.
• The centrosome replicates during interphase, forming two centrosomes that migrate to opposite ends of the cell during prophase and prometaphase.
• An aster, composed of short microtubules, extends from each centrosome.
• The mitotic spindle consists of centrosomes, spindle microtubules, and asters.

Kinetochores and Metaphase

• During prometaphase, some spindle microtubules attach to kinetochores of chromosomes, causing chromosome movement.
• Kinetochores are protein complexes at centromeres.
• At metaphase, chromosomes align at the metaphase plate, an imaginary plane midway between spindle poles.
• Sister chromatids separate and move toward opposite poles during anaphase, powered by depolymerization of kinetochore microtubules.

Nonkinetochore Microtubules and Cytokinesis

• Nonkinetochore microtubules from opposite spindle poles overlap and push against each other, causing cell elongation.
• Cytokinesis begins during anaphase (or telophase) and the spindle disassembles.

Cytokinesis: A Closer Look

• In animal cells, cytokinesis occurs by a process known as cleavage, forming a cleavage furrow.
• In plant cells, a cell plate forms during cytokinesis.

Loss of Cell Cycle Controls in Cancer Cells

• Cancer cells do not respond normally to the body´s control mechanisms.
• Cancer cells may not need growth factors.
• They may make their own growth factors, send signals without the factor, or have abnormal cell cycle control systems.

Transformation and Tumors

• Transformation is the process where a normal cell is converted into a cancerous cell.
• Tumors form from abnormal cells.
• Benign tumors remain localized.
• Malignant tumors invade surrounding tissues and may metastasize (spread to other parts of the body).

Recent Advances in Cancer Treatment

• Advances in understanding cell cycle and cell cycle signaling have led to improvements in cancer treatment.

Binary Fission in Bacteria

• Prokaryotes (bacteria and archaea) reproduce by a type of cell division called binary fission.
• During binary fission, the chromosome replicates, and the two daughter chromosomes move to opposite ends of the cell.
• The plasma membrane pinches inward, dividing the cell into two.