Chapter 6 Biology

• a protective cap at the end of the DNA
• every time a cell divides the telomere gets a bit shorter
• when the telomere becomes too short, the cell dies

• cells that rebuild the telomere with each division can become cancerious
• cells that have forgotten how to die
• unrestrained cell growth and division
• can lead to tumors
• second leading cause of death in US

• genetic info is carried in a single circular chromosome
• this strand of DNA is attached at one site to the cell membrane

• genetic info is organized into linear chromosomes
• eukaryotic chromosomes float freely in the nucleus

• prokaryotes divide by binary fission
• bacteria divide by binary fission
• circular chromosome duplicates itself and the cell splits into two indentical new cells
• asexual reproduction (daughter cells inherit their DNA from single parental cell)

• occurs in the mitotic phase
• the rest of the cycle is called interphase (two gap phases for growth, synthesis phase for replication of DNA)

• Gap 1: cell's primary growth phase. Normal cellular functions (making proteins, getting rid of waste, etc) take place
• DNA Synthesis: cell begins preparations for division. Every chromosome creates an exact duplicate of itself in a process called replication
• Gap 2: Second period of growth and preparation for cell division.
• ALL ABOVE ARE INTERPHASE
• Mitosis: cell's nucleus duplicates, then divides
• Cytokinesis: cell then duplicates, forming two separate cells

• the process of DNA duplication
• cell division is preceded by replication
• unwinding then rebuilding (enzyme connects appropriate complementray base to the exposed base)

characteristic that in the double-stranded DNA molecule the base on one strand always has the same pairing-partner (called complementary base) on the other strand

• Adenine to Thymine
• Guanine to Cytosine

• errors in replication can lead to changes in the DNA sequence called mutations
• several DNA repair processes occur after replication
• if error remains, the sequences in a replicated DNA molecule can be different from those in the parent molecule

• most cells are not immortal: mitosis generates replacements
• two reasons for mitosis: growth and replacement

A form of cell death in which a programmed sequence of events leads to the elimination of cells without releasing harmful substances into the surrounding area. Apoptosis plays a crucial role in developing and maintaining health by eliminating old cells, unnecessary cells, and unhealthy cells. PROGRAMMED DEATH

• cells duplicate themselves, occurs in four steps then followed by the replication of chromosomes
• 1. chromosomes condense
• 2. all of the duplicated and condensed pairs of chromosomes move to the center of the cell
• 3. each chromosome is pulled apart from its duplicate
• 4. new cell membranes form around each complete set of chromosomes and the cytoplasm duplicates as well
• one parent cell becomes two daughter cells

• first step in mitosis (preparation)
• chromosomes replicate in preparation for mitosis
• long, linear chromosomes that have replicated condense

joint between two sister chromatids

• FIRST STEP IN MITOSIS
• nuclear membrane breaks down
• sister chromatids (replicated chromosomes) condense
• spindle forms

• SECOND STEP IN MITOSIS
• sister chromatids line up at the center of the cell

• THIRD STEP IN MITOSIS
• sister chromatid pairs are pulled apart by the spindle fibers
• One full set of chromosomes goes to one side of the cell and another identical set goes to the other

• FOURTH STEP IN MITOSIS
• chromosomes begin to uncoil as the nuclear membrane is reassembled around them

• cytoplasm and organelles duplicate and are divided into approximately equal parts
• cell splits into two

cancer cells can separate from a tumor and spread throughout the body via the circulatory system

• requires special cells made by meiosis (generates sperms and eggs)
• diploid cells: two copies of each chromosome
• haploid cells: one copy of each chromosome

• starts with a diploid cell (from gonads)
• gametes: special reproductive cells (gametes are produced through meiosis)/ have only half as many chromosomes as the rest of the cells in the body
• you have two copies of every gene
• reduces amount of genetic material in gametes (gametes have half as much genetic material as the parent cell)
• produces gametes that all differ from each other with respect to the combinations of alleles they carry (gametes carry different combinations of alleles)

• Homologues are the maternal and paternal copies of a chromosome
• A sister chromatid is a chromosome and its identical duplicated version held together at a centromere

• cells undergoing meiosis divide twice (4 total)
• interphase: each chromosome in a homologous pair replicates to form a sister chromatid
• meiosis I: homologous pairs seperate
• meiosis II: sister chromatids seperate. results in four haploid cells, two contain a single copy on one of the original chromosomes and the other two contain a single copy of the other chromosome

• most complex of all phases of meiosis
• replicated chromosomes condense
• spindle is formed
• nuclear membrane disintegrates

each pair of homologous chromosomes moves to the equator of the cell

• beginning of the first cell division that occurs during meiosis
• homologues are pulled apart toward opposite sides of the cell
• maternal and paternal sister chromatids are pulled to the ends of the cell in a random fashion

• marked by the chromosomes arriving at the two poles of the cell
• the cytoplasm divides and the cell membrane pinches the cell into two daughter cells

separating the sister chromatids

• genetic material once again coils tightly making the chromatids visible under the microscope
• in the brief interphase prior to prophase II there is no replication of any of the chromosomes

sister chromatids (each appearing as an X) move to the center of the cell

the fibers attached to the centromere begin pulling each chromatid in the sister chromatid pair toward opposite ends of each daughter cell

the cytoplasm then divides, the cell membrane pinches the cell into two new daughter cells, and the process ends

crossing over during meiosis produces a mixture of maternal and paternal genetic material on each chromatid

the homologues and sister chromatids distributed to each daughter cell during meiosis are a random mix of maternal and paternal genetic material

each parent donates his or her own set of genetic material

• crossing over in the production of gametes
• shuffling and reassortment of homologues during meiosis
• combining alleles from two parents at fertilization

• in humans, male if the Y chromosome is present
• in birds, female if W chromosome is present
• presence or absence of sex chromosomes
• number of chromosome sets
• environmental factors

• a display of an individuals complete set of chromosomes
• can be used to identify abnormalities in a fetus's chromosomes early in development
• Down Syndrome: Trisomy 21 (caused by having an extra copy of chromosome 21)

• amniotic fluid: contains many cells from the fets (four months into pregnancy)
• tissue is removed from the placenta
• because the fetus and placenta both develop from the same fertilized egg, their cells contain the same genetic composition
• can be done several weeks earlier in the pregnancy, usually between 10 and 12

• unequal distribution of chromosomes during meiosis
• error of cell division that creates a gamete with zero or two copies of a chromosome rather than a single copy

• Turner Syndrome: X_, short height, web of skin between neck and shoulders, underdeveloped ovaries (sterile), learning difficulties
• Klinefelter Syndrome: XXY, underdeveloped, testes, lower testosterone, some female features, long limbs, slightly taller
• XYY Males: taller than average, acne, lower intelligence
• XXX Females: may be sterile, no obvious physical or mental problems