BIOL 300 Exam 2 (Modules 5-8)

A. The Cell Cycle

• The cell cycle is a cell's lifespan. It consists of two main parts: interphase and mitosis/cytokinesis.

• Interphase: Divided into G1, S, and G2 phases. This phase constitutes approximately 75% of the cell's lifespan. During interphase, the cell grows, performs its normal functions, and duplicates its DNA in preparation for cell division.

• G1 Phase: Cell growth and preparation for DNA replication.

• S Phase: DNA replication occurs.

• G2 Phase: Continued cell growth and final preparations for cell division.

• Mitosis/Cytokinesis: Cell division occurs, resulting in two new cells.

B. DNA Replication

• DNA replication occurs during the S phase of interphase.

• DNA Structure: The double helix structure was discovered by James Watson and Francis Crick. Rosalind Franklin's work was also crucial to its discovery.

• DNA Molecule Components: Deoxyribose sugar, phosphate group, and nitrogenous base.

• DNA Base Pairing Rules: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G).

• DNA Packaging: DNA is wrapped around proteins called histones to form chromatin.

1. DNA Replication Steps:Start: Helicase attaches to the double helix.

2. Unzipping: Helicase unwinds the DNA by breaking hydrogen bonds.

3. Base Pairing: DNA polymerase adds nucleotides to the exposed nucleotide bases, following base pairing rules.

4. End: Enzymes continue for the entire length of the DNA. Two copies of DNA are produced.

• Semi-Conservative Replication: Each new DNA molecule consists of one original strand and one newly synthesized strand.

C. Mitosis and Cytokinesis Step-by-Step

• Mitosis and Cytokinesis are the process of creating two genetically identical cells.

• Mitosis: Asexual reproduction resulting in two genetically identical cells. Daughter cells have identical cells.

• Exceptions: Red blood cells, nervous cells, gametes (sperm and egg)

• Chromosome: Tightly coiled piece of DNA. Replicated chromosome consists of two sister chromatids.

• Each cell has a complete set of DNA. Humans have 46 chromosomes or 23 pairs. One set comes from the mother, and the other from the father. Homologous chromosomes are chromosomes with the same set and order of genes.

Steps of Mitosis

1. Prophase/Prometaphase: DNA coils to become the visible chromosome and nuclear membrane disappears. Centrioles form fibers from each end of the cell which attach to a centromere of each chromosome.

2. Metaphase: Fibers pull on chromosomes until they line up in the middle of the cell.

3. Anaphase: Fibers pull sister chromatids to each side of cell.

4. Telophase: Nuclei form around DNA at each side. Cytokinesis begins.

• Cytokinesis: Physical separation of one cell into two cells.

• Animals: A band of actin & myosin form a belt around the cell and pinch them off.

• Plants: A row of vesicles form in the middle of the cell, and the vesicles form a new cell wall called the cell plate.

D. Meiosis

• Meiosis is a specialized type of cell production that produces gametes (sex cells).

• Gametes: sex cells (sperm, egg, pollen), which have ½ the normal amount of DNA (1 copy of each gene = 1N).

• Diploid: a cell that has the normal amount of DNA (2 copies of each gene = 2N).

• Sexual Reproduction: when two gametes from 2 organisms combine to form a third genetically unique individual.

• Zygote: new diploid organism formed by sexual reproduction.

• Meiosis Formula: 1 diploid cell ➔ 4 haploid cells (each with 1 set of genes)

Process of Meiosis

• Occurs in the ovaries or testes (gonads).

• Two sets of cell divisions in meiosis: Meiosis I and Meiosis II.

Meiosis I

1. Prophase I: Homologous chromosomes pair up (synapsis). Cross over occurs, where homologous chromosomes trade small sections.

2. Metaphase I: Homologous pairs line up next to each other in center of cell. Orientation of different maternal/paternal material varies (law of independent assortment).

3. Anaphase I: Homologous chromosomes are separated but sister chromatids remain attached.

• Final Products: 4 cells in meiosis, 2 cells in mitosis. All cells genetically unique in meiosis; all cells genetically identical in mitosis.

• Spermatogenesis is the process where sperm forms in the testes. Oogenesis is the process where eggs form in the ovaries.

E. Cancer

1. What is cancer? Uncontrolled cell reproduction or constant mitosis. Cells have lost normal control of cell cycle and only use interphase to replicate DNA.

2. Cancer: The Disease: Cells are not doing their jobs; they take away the critical blood supply.

• What causes cancer?Mutations to genes that control cell cycle proteins (turns protooncogenes into oncogenes)

• Mutations to tumor-suppressor genes

• Multiple-hit model: most cancers develop after two or more mutations.

• Sources of mutations:Genetic (inherited from parents)

• Environmental (exposure to chemicals that cause DNA mutations)

• Viruses (deliver DNA that causes mutations)

• How do we treat cancer?Surgery (physically remove cancerous cells)

• Radiation (causes massive DNA mutations in all cells undergoing DNA replication)

• Chemotherapy (toxic chemicals that act the same basic way as radiation but throughout body)