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TCT: Going Viral Biology
Your Task Assume you are a student in Emily and Jared’s class. Carefully analyze and interpret the figures they have provided below, then make a claim about whether the Influenza A virus is living or not and support your claim with evidence and reasoning based on patterns in the data that Emily and Jared provided.
For The Writing… • Think back to the 8 characteristics of life… use those notes if you need to! • Read through the table thoroughly and study the diagram – discuss both with a partner or small group! • Make a claim – is Influenza A living or nonliving? • Provide evidence on why you think that. • Provide reasoning – explain how that evidence supports your claim. Work collaboratively. Think independently. Answer uniquely.
Cell Growth and Division Chapter 10 (pages 240-252)
Limitations • There are 2 limitations that cause cells to divide instead of grow indefinitely Big Question Why do cells divide instead of growing indefinitely?
The larger the cell… 2 Limitations: • Larger the cell, more demands placed on DNA • Example: Library • Larger the cell, harder to move nutrients and wastes across the cell membrane • Volume increases much more rapidly than SA in a growing cell – smaller ratio • Example: Town Road
Chromosomes • In eukaryotic cells, chromosomes pass genetic information from one generation to the next • Made up of DNA and proteins • Not visible to the human eye because the DNA and proteins are spread out through the nucleus, but condense at beginning of cell division • We have 46 chromosomes
Centromerecenter attachment Sister chromatids Identical replications of the chromosome
Homologous Chromosomes vs. Sister Chromatids • Homologous chromosomes are a chromosome pair that are similar but not identical • One chromosome of each homologous pair comes from the mother and one comes from the father • Sister chromatids = identical! • Chromatin: DNA that is spread out in a non-dividing cell
Cell Division • Process by which a cell dividesinto 2 new daughter cells • Prokaryotes: simple process • Prokaryotic division usually takes the form of binary fission – DNA replicated and cytoplasm splits • Eukaryotes: more complex process Prokaryotes do not have organelles or a nucleus to replicate, Eukaryotes do!
The 4 Phases of the Cell Cycle… • G1 phase • Cell growth and normal processes • S phase • DNA replication • Chromosome replication • G2 phase • Growth, preparation for mitosis • Organelle production • M phase • Includes mitosis and cytokinesis • *Go phase • Cell is done dividing; resting phase
Interphase • Interphase: period of growth that prepares the cell for division • Includes G1, G2, and S phase • Cell size increases • DNA replication
Mitosis • Division of the cell nucleus • 4 Phases • Prophase • Metaphase • Anaphase • Telophase
Prophase • 1st and longest phase (takes 50-60% of the total time) • Chromosomes become visible • Spindle starts to form • fanlike microtubule structure that separates the chromosomes • Nucleolus disappears and nuclear envelope breaks down Nucleus
Metaphase • Short phase • Chromosomes line up across middle of cell • Microtubules connect the centromere to the 2 poles of spindle
Anaphase • Centromeres split, allowing sister chromatidsto separate and become individual chromosomes • Chromosomes move until they are at opposite ends of the cell • Ends when chromosomes stop moving Sister Chromatids
Telophase • Final phase of mitosis • Chromosomes begin to lose their distinct shape • A new nuclear envelope forms around each cluster of chromosomes Nucleus Reforming
Cytokinesis • Cytoplasm pinches in half • Each daughter cell has an identical set of duplicate chromosomes
Cytokinesis in plants… • A structure known as the cell plate forms midway between the divided nuclei • The cell plate gradually develops into a separating membrane • A cell wall then begins to appear in the cell plate Cell Plate
Cell Cycle Regulation Day 2 – Mitosis
Regulation of the Cell Cycle • Cellular division in a multicellular organism is a carefully controlled process • Not all cells move through the cell cycle at the same rate and some do notcontinue to divide after development • Don’t keep dividing: • Nerve cells • Muscle cells (hypertrophy) • Do keep dividing: • Skin cells • Digestive tract cells • Bone marrow cells • Blood cells (but wait, they don’t have a nucleus?!)
Cell Cycle Regulators • Scientists found a particular protein they associated with cell cycle regulation – they help control the cycle • This protein is called cyclin • Cyclin is found in large quantities during cell division • However, cyclin is not the only regulator that plays a role in cell division • There are both internal and external regulators that affect the cell cycle
Internal vs. External • Internal regulators – regulate internal factors of cell growth • Example: proteins that regulate mitosis so that it does not occur until all chromosomes have been replicated • External regulators – regulate external factors of cell growth • Example: growth factors present on the surface of cells so they know when to stop/start dividing
Controlled Cell Growth • Scientists have observed controlled cell growth in a lab by using a petri dish with nutrient broth • What is a common reason why our cells are stimulated to grow?
Uncontrolled Cell Growth • Uncontrolled cell growth is extremely severe! • Cancer: disorder in the body in which cells lose their ability to control their growth • Result of cancer: cells divide uncontrollably and form masses of cells called tumors • Cells break loose from the tumors and spread to other parts of the body
Skin Cancer Lung Cancer Brain Cancer Pancreatic Cancer Bone Cancer
Causes of Cancer • Some cancers have a cause • Tobacco Use • Radiation Exposure • All cancer has 1 thing in common – the cell has lost its ability to control cell division • A large number of cancers have been tied to a defect in the p53 gene • p53: regulator that halts the process of mitosis until all chromosomes have been replicated • If the cell starts dividing too early, it loses valuable info it needs to regulate cell division from there on out
