Lecture Exam IV

• Step One: The cell copies its DNA
• Step 2: The cell splits in half by binary fission. Forms 2 "daughter cells"
• ONLY applicable to Prokaryotes

• DNA replication begins with the unzipping of the double-stranded DNA at a point called the origin of replication
• a new double helix is formed by adding complementary nucleotides to the exposed DNA strands that have been unzipped
• the end result of replication is that the cell possess two complete copies of the hereditary information

The growing of a cell after replication has taken place

• eventually the cell constricts in two to form
• two daughter cells

each daughter cell is a complete, living cell with its own DNA identical to that of the parent cell

The eukaryotic cell cycle is divided into distinct phases:

• Interphase (G1,S, and G2
• phases)

Mitosis (M phase)

Cytokinesis (C phase)

Eukaryotic cells divide by separating copies of their chromasomes into daughter cells

• A cell division mechanism that occurs in non-reproductive cells
• These cells are called somatic cells
• A microtubular
• apparatus binds to the chromosomes and moves them apart

• A cell division mechanism that occurs in cells that participate in sexual reproduction
• •these cells are called germ cells
• Halves the number of chromosomes found in somatic cells

• The first phase of the cycle
• It is comprised of three phases:

•G1 phase

–the primary growth phase of the cell following division

–most cells spend the majority of their lifespan in this phase

•S phase

–DNA replication occurs in preparation for cell division

•G2 phase

• –further preparation for cell division, including replication of mitochondria and
• synthesis of microtubules

• (In M Phase) (Step 1)
• The chromosomes condense, the nuclear envelope breaks down, and the spindle forms

• (In M Phase) (Step 2)
• The chromosomes line up on the central plane of the cell

• (In M Phase) (Step 3)
• The centromeres divide, and the chromatids moves toward opposite poles

• (In M Phase) (Step 4)
• The chromosomes uncoil, and a new nuclear envelope forms. The spindle fibres dissapear.

The cytoplasm divides, creating two daughter cells

• Most eukaryotes have between 10 and 50 chromosomes in their somatic cells
• Where all eukaryotic cells store their hereditary information
• Coiling of the DNA allows it to fit in the nucleus

• Carry information about the same traits at the same locations on each chromosome
• The actual information can vary between homologues

The site where two sister chromatids are linked before cell division

• Comprises chromosomes
• A complex of DNA & protein

DNA is coiled around protiens called histones

• •The DNA coils around a core of eight histone proteins to form a complex called a nucleosome
• The nucleosomes in turn can be coiled together further to ultimately form a compact chromosome

Ensure that the previous phase is fully completed before advancing to the next phase

• Three principal checkpoints control the cycle in eukaryotes
• •G1, G2, and M checkpoints

Reproductive cells (Eggs & Sperm)

• Formed by gametes fusing together.
• Contains two complete copies of each chromosome
• the fusion of gametes is called fertilization

Have two sets of chromosomes

Have one set of chromosomes

• Meiosis I separates the homologues in a homologous pair
• Includes Prophase I, Metaphase I, Anaphase I, & Telophase I

• Separates the replicate sister chromatids
• Involves Prophase II, Metaphase II, Anaphase II, & Telophase II
• When Meiosis is complete, the result is that one diploid cell becomes four haploid cells

• The two alleles of a trait
• separate from each other during the formation of gametes, so that half of the
• gametes will carry one copy and half will carry the other copy

• Genes located on different
• chromosomes are inherited independently of one another