Ch 12 FRQs - The Cell Cycle
Describe how the cell cycle is regulated and discuss ONE consequence of abnormal regulation.
The cell cycle consists of the following phases: Interphase → Prophase → (Prometaphase) → Metaphase → Anaphase → Telophase → Cytokinesis OR G1 → S → G2 → M The cell cycle checkpoints play an important role in the control system by sensing defects that occur during essential processes such as DNA replication or chromosome segregation, and inducing a cell cycle arrest in response until the defects are repaired. The cell cycle is regulated through action of MPF and CDKs in checkpoint regulation, contact inhibition of mitosis, and hormones -growth factor control of cell cycle activity. A growth factor is a substance, such as a vitamin or hormone, which is required for the stimulation of growth in living cells. ONE consequence of abnormal regulation is uncontrolled cell proliferation (cancer), apoptosis (controlled cell death), and non-disjunction/broken chromosomes from abnormal spindle events. Uncontrolled cell proliferation is an increase in the number of cells as a result of uncontrolled cell growth and cell division. This can lead to the development of cancer. Apoptosis is is a form of programmed cell death that occurs in multicellular organisms. Biochemical events lead to characteristic cell changes and death. These changes include blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay. Non-disjunction is the failure of one or more pairs of homologous chromosomes or sister chromatids to separate normally during nuclear division, usually resulting in an abnormal distribution of chromosomes in the daughter nuclei.
For the following examples, explain in detail how the transfer of information is accomplished. -The genetic material in one eukaryotic cell is copied and distributed to two identical daughter cells
-DNA is copied during interphase, S phase of cell cycle -recognition of origin site on DNA -concept of unwinding enzyme -RNA primer -DNA polymerase: an enzyme that synthesizes DNA molecules from deoxyribonucleotides, the building blocks of DNA. These enzymes are essential for DNA replication and usually work in pairs to create two identical DNA strands from a single original DNA molecule. -Concept of complementary relationship among bases - semiconservative; A-C & T-G -Discontinuous/continuous or lagging /leading or Okazaki fragments (due to antiparallel backbones and 5' to 3' generation of new segments) -DNA ligase: a specific type of enzyme, a ligase, that facilitates the joining of DNA strands together by catalyzing the formation of a phosphodiester bond. It plays a role in repairing single-strand breaks in duplex DNA in living organisms, but some forms may specifically repair double-strand breaks. -Other/Elaboration - telomere replication, proofing by DNA polymerase, expanded details MITOSIS -concept of chromatid pairs or 'doubled chromosomes' -prophase - condensation, spindle formation -metaphase - alignment of chromosomes -anaphase - separation of chromatids or equivalent statement -telophase or origin of cytokinesis - nuclear membrane reforms, cell plate or cell furrow 1 - Other or Elaboration - cell cycle control, cell surface area/volume ratio and mitosis, MTOC(microtubule organizing center), centromere or kinetochore attachment
Many biological structures are composed of smaller units assembled into more complex structures having functions based on their structural organization. describe the smaller units, their assembly into the larger structures, and one major function of these larger, organized structures. -A eukaryotic chromosome
-chromosome: a threadlike structure of nucleic acids and protein found in the nucleus of most living cells, carrying genetic information in the form of genes. Nucleotides: Adenine, Guanine, Thymine, and Cytosine - eukaryotic chromosome structure refers to the levels of packaging from the raw DNA molecules to the chromosomal structures seen during metaphase in mitosis or meiosis. Chromosomes contain long strands of DNA containing genetic information. Compared to prokaryotic chromosomes, eukaryotic chromosomes are much larger in size and are linear chromosomes. Eukaryotic chromosomes are also stored in the nucleus of the cell, while chromosomes of prokaryotic cells are not stored in a nucleus. → DNA → nucleosomes* → chromosome *around histones (non-DNA) Levels of folding: → heterochromatin → condensed chromosome - Describe DNA (or later structure in the sequence): → functional sequences (introns/exons/spacers) → genes → regulatory elements → chromosome -Function/Benefit: • Package DNA • Make for efficient cell division • Juxtaposition of coding elements • Gene regulation • Storage/protection of genetic information
Describe the phases of the cell cycle.
Actively dividing eukaryote cells pass through a series of stages known collectively as the cell cycle: two gap phases (G1 and G2); an S (for synthesis) phase, in which the genetic material is duplicated; and an M phase, in which mitosis partitions the genetic material and the cell divides. Interphase is composed of G1 phase (cell growth), followed by S phase (DNA synthesis), followed by G2 phase (cell growth). At the end of interphase comes the mitotic phase, which is made up of mitosis and cytokinesis and leads to the formation of two daughter cells. INTERPHASE G0- There are times when a cell will leave the cycle and quit dividing. This may be a temporary resting period or more permanent. An example of the latter is a cell that has reached an end stage of development and will no longer divide (e.g. neuron). G1- Cells increase in size in Gap 1, produce RNA and synthesize protein. An important cell cycle control mechanism activated during this period (G1 Checkpoint) ensures that everything is ready for DNA synthesis. (Click on the Checkpoints animation, above.) S- To produce two similar daughter cells, the complete DNA instructions in the cell must be duplicated. DNA replication occurs during this S (synthesis) phase. G2- During the gap between DNA synthesis and mitosis, the cell will continue to grow and produce new proteins. At the end of this gap is another control checkpoint (G2 Checkpoint) to determine if the cell can now proceed to enter M (mitosis) and divide. MITOTIC PHASE -Prophase: chromosomes become visible, the nucleolus disappears, the mitotic spindle forms, and the nuclear envelope disappears. Chromosomes become more coiled and can be viewed under a light microscope. -Prometaphase: the physical barrier that encloses the nucleus, called the nuclear envelope, breaks down. -Metaphase: chromosomes are at their second-most condensed and coiled stage. These chromosomes, carrying genetic information, align in the equator of the cell before being separated into each of the two daughter cells. -Anaphase: replicated chromosomes are split and the newly-copied chromosomes (daughter chromatids) are moved to opposite poles of the cell. -Telophase: the process that separates the duplicated genetic material carried in the nucleus of a parent cell into two identical daughter cells. It begins once the replicated, paired chromosomes have been separated and pulled to opposite sides, or poles, of the cell. -Cytokinesis: part of the cell division process during which the cytoplasm of a single eukaryotic cell divides into two daughter cells. Cytoplasmic division begins during or after the late stages of nuclear division in mitosis and meiosis.
Using a specific example, describe how organisms can reproduce asexually. Discuss TWO evolutionary advantages of asexual reproduction.
Asexual reproduction is is a type of reproduction by which offspring arise from a single organism, and inherit the genes of that parent only; it does not involve the fusion of gametes, and almost never changes the number of chromosomes. Some forms of asexual reproduction include parthenogenesis, budding, binary fission, and fragmentation. Bacteria, archaea, and protists reproduce asexually through binary fission. Binary fission ("division in half") is a kind of asexual reproduction that is the most common form of reproduction in prokaryotes such as bacteria. It occurs in some single-celled Eukaryotes like the Amoeba and the Paramoecium. More specifically, bacteria, archaea, and protists use bacterial binary fission to reproduce. Bacterial binary fission is is the process that bacteria use to carry out cell division. Binary fission is similar in concept to the mitosis that happens in eukaryotic organisms (such as plants and animals), but its purpose is different. Two evolutionary advantages of asexual reproduction are: -offspring can be successfully created without the need for a partnership -occurs over a short period of time without the need to develop the genetics to form a gender
