Unit 06 Study Guide - Cell Cycle & Meiosis

Flashcards reviewing the Unit 06 Study Guide on the cell cycle, mitosis, regulation, cell differentiation, meiosis, gametogenesis, and chromosomal mutations.

Why are cells small in size?

The smaller the cell, the larger the ratio of surface area to volume, which increases the rate of diffusion in a cell.

What is the structural organization of a chromosome as illustrated from DNA to the fully condensed form?

DNA wraps around histone proteins to form chromatin, which then becomes supercoiled. Chromosomes are made from this supercoiled DNA.

What occurs during each phase of the cell cycle depicted in this diagram?

G1: cell grows and carries out normal cell functions; S: DNA is replicated; G2: cell continues to grow and prepares for mitosis; M: nucleus and cell divide (mitosis/cell division).

Which phases together comprise interphase?

Gap 1 (G1), Synthesis (S), and Gap 2 (G2).

What is the primary purpose of mitosis in unicellular versus multicellular organisms?

Unicellular organisms use mitosis to reproduce (asexual reproduction). Multicellular organisms use mitosis to grow new cells and repair tissues, though some multicellular organisms can also use it to reproduce.

What major events occur during each phase of mitosis shown in this diagram?

Prophase: chromosomes condense, spindle fibers form, nuclear envelope breaks down. Metaphase: chromosomes line up at the equator, spindle fibers attach to centromeres. Anaphase: sister chromatids are pulled apart to opposite sides. Telophase & Cytokinesis: chromosomes relax, new nuclei form, spindle fibers break down, and the cell divides into two identical daughter cells ($2n$).

How is cancer related to the disruption of the cell cycle?

Cancer cells ignore checkpoints in the cell cycle, leading to unregulated division.

How do benign tumors differ from malignant tumors?

Benign tumors remain clustered together. In malignant tumors, cells can break away and spread to other parts of the body via the bloodstream or lymphatic system (metastasis).

What role do checkpoints, cyclins, and kinases play in regulating the cell cycle?

Checkpoints check the cell for damage and verify DNA errors, forcing abnormal cells into apoptosis. Cyclins and kinases are the proteins that run these cell cycle checkpoints.

How do cell-to-cell contact and growth factors externally regulate cell division?

Cell-to-cell contact causes cells to stop dividing when there is no more room to divide. Growth factors are external proteins that act on the cell to stimulate cell division.

What is the difference between a mutagen and a carcinogen?

Mutagens are substances that cause DNA mutations, whereas carcinogens are substances that cause cancer.

What are examples of mutagens?

Tobacco smoke, radiation (UV, x-ray), and asbestos.

What is fertilization, and what is the developmental progression of structures that follows it?

Fertilization is the union of an egg cell and a sperm cell, producing a zygote. The zygote undergoes mitosis to become an embryo ($2-8$ weeks of development in humans), and after $8$ weeks, the offspring is called a fetus.

What does this stem cell division model illustrate about stem cell renewal and differentiation?

A stem cell can divide either into two new stem cells or into one new stem cell and one specialized cell.

What does it mean that stem cells are pluripotent, and how does differentiation occur?

Pluripotent stem cells can divide into any specialized cell type. In differentiation, only a small part of the cell's DNA is used, even though every cell contains an entire copy of the DNA.

How do haploid ($n$) cells compare to diploid ($2n$) cells?

Haploid cells have one copy of every chromosome (human gametes have $22$ autosomes and $1$ sex chromosome). Diploid cells have two copies of every chromosome (human body cells have half of their chromosomes from each parent).

How do somatic cells differ from gametic cells?

Somatic cells (body cells) make up most body tissues and organs and are diploid ($2n$). Gametic cells (gametes) are sex cells, are haploid ($n$), and carry DNA that can be passed on to children.

What is the purpose of meiosis during gamete formation?

Meiosis reduces the number of chromosomes in a cell by half and creates genetic diversity.

What are the distinguishing chromosome movements between Meiosis I and Meiosis II shown in this diagram?

In Meiosis I, homologous pairs line up and are separated, yielding two haploid ($n$) cells. In Meiosis II, sister chromatids line up and are pulled apart, resulting in four genetically unique haploid ($n$) granddaughter cells.

What are autosomes, sex chromosomes, and homologous chromosomes?

Autosomes contain genes not directly related to sex (pairs $1-22$ in humans). Sex chromosomes directly control sexual characteristics (females are XX, males are XY). Homologous chromosomes have the same length, general appearance, and copies of the same genes.

How do the outcomes of spermatogenesis and oogenesis differ?

Spermatogenesis produces $4$ mature sperm cells in males. Oogenesis produces $1$ mature egg cell and $3$ polar bodies that eventually break down in females.

What are the primary differences between mitosis and meiosis in terms of cell outcome, ploidy, lifetime occurrence, and reproduction?

Mitosis produces genetically identical diploid cells ($2n$), occurs throughout an organism's lifetime, and is involved in asexual reproduction. Meiosis produces genetically unique haploid cells ($n$), occurs only at certain times in the life cycle, and is involved in sexual reproduction.

What is nondisjunction, and what chromosome conditions can result from it?

Nondisjunction occurs when chromosomes do not separate properly during division; it can result in trisomy (having three copies of a chromosome, such as Downs Syndrome / Trisomy 21) or monosomy (missing a particular chromosome).

What is polyploidy?

Polyploidy occurs when an organism has more than two sets of chromosomes.

What chromosomal mutation is shown in this diagram, and what occurs during it?

Duplication; during replication, a section of the chromosome is duplicated.

What chromosomal mutation is shown in this diagram, and what occurs during it?

Deletion; during replication, a section of the chromosome is deleted.

What chromosomal mutation is shown in this diagram, and what occurs during it?

Inversion; a section of the chromosome is inverted (rotated $180^\circ$).

What chromosomal mutation is shown in this diagram, and what occurs during it?

Translocation; a segment of the chromosome is transferred to a completely different chromosome.