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Transcript
Copy into Note Packet and Return to Teacher Chapter 6-1: Chromosomes and Cell Reproduction An adult human body produces about 2 trillion cells every day. This is about 25 million new cells per second! Formation of New Cells by Cell Division What are some of the reasons cells undergo cell division? 1. growth 2. development 3. repair 4. asexual reproduction 5. formation of gametes Regardless of the type of cell division that occurs, all of the information stored in the molecule DNA (deoxyribonucleic acid) must be present in each of the resulting cells. Remember back to Chapter 3, what is the function of DNA? 1. DNA stores the information that tells cells which proteins to make and when to make them. 2. This information directs a cell’s activities and determines its characteristics. Prokaryotic Cell Reproduction DNA: Circular Attached to the inner cell membrane Reproduce by binary fission Asexual reproduction = identical offspring 2 stages 1. DNA is copied. 2. Cell divides Binary fission in Paramecium o A new cell membrane is added to a point on the membrane between the two DNA copies. The growing cell membrane pushes inward and the cell is constricted in the middle. o A new cell wall forms around the new membrane. Eukaryotic Cell Reproduction DNA is organized into units called genes. o A gene is a segment of DNA that codes for a protein or RNA molecule. o A single molecule of DNA has thousands of genes. o Genes determine how a body develops and functions. o When genes are being used, the DNA is stretched out in the form of chromatin so that the information it contains can be used to direct the synthesis of proteins. Cell division o DNA replicates (it makes a copy of itself) o DNA condenses into chromosomes by coiling around proteins, which makes them visible. o The two exact copies of DNA that make up each chromosome are called sister chromatids. o The sister chromatids are attached at a point called the centromere. o The chromatids become separated during cell division and placed into each new cell. *** Demonstration of DNA as 6 ft. strands; replicate strands and coil them into chromosomes around play-doh / clay (protein) w/ 2 sister chromatids connected @ the centromere. Fact: As many as 500 chromosomes lined up end to end would fit in a 0.2 cm space—about the thickness of a nickel. How Chromosome Number and Structure Affect Development Somatic (body) cells o 23 pairs of chromosomes (46 chromosomes) o Differ in size, shape, and set of genes. o Complete set of all chromosomes is essential to survival. Sets of Chromosomes Each of the 23 pairs of chromosomes consists of two homologous chromosomes, or homologues, which are similar in size, shape, and genetic content. Each homologue in a pair of homologous chromosomes comes from one of the two parents. 46 chromosomes = 2 sets of 23 chromosomes; one set from Mom and one set from Dad. Comparison of Somatic Cells and Gametes Somatic Cells in Humans Gametes in Humans Body cells Sex cells = sperm and eggs Diploid = 23 pairs of chromosomes = 46 Haploid = 23 individual chromosomes Diploid number is represented by ―2n‖ Haploid number is represented by ―n‖ When haploid (n) gametes fuse in a process called fertilization, they form a diploid (2n) zygote, which is the first cell of a new individual. Chromosome Numbers The number of chromosomes in cells is constant within a species. Although most species have different numbers of chromosomes, some species have the same number. Many plants have far more chromosomes (Ex: ferns w/ 500). A few have only 1 pair of chromosomes. Autosomes and Sex Chromosomes 23 pairs of chromosomes in humans o 22 pairs of Autosomes Chromosomes that are not directly involved in determining sex or gender o 1 pair of sex chromosomes Determine the sex of an individual XY = male: the genes that cause a fertilized egg to develop into a male are located on the Y XX = female: any individual without a Y chromosome is female Sex of an individual is determined by the male. Structure and number of sex chromosomes vary in different organisms. o Some insects (grasshopper) have no Y chromosome. XX = female XO = male; the O indicates the absence of a chromosome o In birds, moths & butterflies XX = male XO = female Change in Chromosome Number Karyotype – photo of the chromosomes in a dividing cell that shows the chromosomes arranged by size with the sex chromosomes as number 23. Normal karyotype of male (sex) Karyotype of Down syndrome female (sex) Humans with more than 2 copies of a chromosome (trisomy) will not develop normally. o Down syndrome = chromosome 21 trisomy o Incidence of Down syndrome births increases with the age of the mother Mothers under 30 = 1 in 1,500 Mothers 37 years old = 1 in 290 Mothers over 45 = 1 in 46 o All the eggs a female will ever produce are present in her ovaries at birth As female ages, eggs can accumulate an increasing amount of damage. o Males produce new sperm throughout life. Disjunction is the separation of homologous chromosomes. Nondisjunction is the failure of 1 or more chromosomes to separate. o One gamete ends up with both copies of a chromosome o The other gamete receives none. Change in Chromosome Structure Changes in chromosome structure are called mutations. Breakage of a chromosome can lead to 4 types of mutations o Deletion – a piece of chromosome breaks off completely – often fatal o Duplication – a chromosome fragment attaches to its homologous chromosome, which will then carry 2 copies of a certain set of genes. o Inversion – chromosome piece reattaches to the original chromosome but in a reverse orientation. o Translocation – a piece of chromosomes reattaches to a nonhomologous chromosome. Chapter 3 Intro: History of Cytology Objectives: Identify the scientists who discovered the cell theory. Explain the cell theory. History of Cytology Many people fell that Anton van Leeuwenhoek invented the first microscope. However, this has been disputed in recent years - Zacharias Jansen is now thought to be the original inventor in 1595. During the 1600’s Leeuwenhoek used his microscopes to look at drops of pond water and other liquids. He discovered that the water contained tiny living things, which he called “animalcules.” At about the same time, Robert Hooke, an English physicist, used a microscope to observe plants. He pointed out that the woody parts (cork) of plants contained tiny rectangular chambers, which he called cells. In 1839, German biologist Theodor Schwann found that some animal tissues closely resembled the circular tissues of plants. As he observed the tissues with better and better microscopes, he concluded that animals are composed of cells as well. Also during this time, Robert Brown discovered an object near the center of many cells – the nucleus. German biologist Matthias Schleiden expanded on Brown’s work, suggesting that the cell’s nucleus plays a role in cell reproduction. In 1855, German physician Rudolf Virchow proposed that animal and plant cells are produced only by cell division. The discoveries and observations of these scientists make up what is now known as the cell theory. 1. All living things are composed of cells. 2. Cells are the smallest working units of living things. 3. All cells come from preexisting cells by cell division. Things all cells have in common: 1. Cell membrane 2. Cytoplasm 4. Ribosomes 5. Cytoplasm 3. DNA Cell Types Prokaryotes – Bacteria Eukaryotes – Unicellular (Protozoa) = Protists – Fungi – Plants – Animals Prokaryotes Eukaryotes Unicellular organisms (bacteria) Can be single-celled or multicullular No nucleus Nucleus No membrane-bound organelles Many membrane-bound organelles Circular DNA Linear DNA Reproduces quickly (20 minutes) Cells reproduce slowly – 24+ hours Relatively small in size Relatively larger in size Peptidoglycan cell wall Cell Wall (Fungi, Plants) or Not (Animals) – Not made of peptidoglycans Plasma/Cell Membrane = “Gatekeeper” Lipid bilayer Filters what goes in and out – Active Transport (Sodium) – Facilitated Transport (Glucose) – Passive Diffusion (Water) Communication with environment Cell Wall = “Retaining wall” Peptidoglycans in prokaryotes – Targeted by antibiotics like penicillin Also in fungi and plants – Different chemistry (cellulose in plants) – Provides rigid support Nucleus = “Brain of the cell” Consists of: – Nuclear membrane – Chromatin (DNA + proteins) – Nucleolus (rRNA ribosomes) DNA replication and transcription occurs in the nucleus Controls all cell activities. Centrioles = “Construction Foremen” Found only in animal cells (US!) Directs construction of the spindle during cell division Composed of 9 triplets of microtubules arranged in a circle. Come in pairs Mitochondria = “Powerhouse of the Cell” ATP (energy) production occurs here All mitochondria come from mother Contain own enzymes and DNA Inner and Outer membrane space with cristae in between May have originally been a ―captured‖ bacterium put to use by cell Ribosomes = “Factories of the Cell” Found free in cytoplasm or attached to ER Translates mRNA (from DNA) into protein Two subunits – 50S and 30S 70S in prokaryotes – 60S and 40S 80S in eukaryotes – Made up of proteins and rRNA Not a true organelle (found in prokaryotes) Endoplasmic Reticulum (ER) = “Highways of the Cell” Rough (with ribosomes) – Membrane protein synthesis – Transport and vesicle formation Smooth (no ribosomes) – Synthesis and metabolism of lipids – Detoxification (lots in liver cells) Golgi Apparatus = “UPS for the Cell” Processes, Packages, and Distributes – Processing of proteins to final form – Packaging into vesicles – Distribution of vesicles to final destinations (secretion, membranes, etc.) Lysosomes and Peroxisomes = “Garbage Disposal of the Cell” Lysosomes – Highly acidic – Have pH sensitive enzymes that break down proteins and lipids Peroxisomes – Produce and metabolize H2O2 – May impact aging? (get/leak more as you age) Vesicles = “Transport Bins of Cell” Bud off of and merge with membranes Endocytosis – forms vesicle carrying substance into the cell Exocytosis – vesicle carries (secretes) substance out of the cell Cytoskeleton = “Skeleton and motion of cell” Three basic types: – Microtubules – Actin filaments – Intermediate filaments Centrosomes serve as microtubule organizing center – In animals, the centrosome has two centrioles, which play role in cell division forming the mitotic spindle Cytosol (cytoplasm) =“Soup of the Cell” Made up of water, ions, and macromolecules of the cell Organelles float within cytosol Many reactions and signaling cascades take place within the cytosol Chloroplasts =“Solar Cells of Plants” Synthesize Sugar from Sunlight (Photosynthesis) Stacked grana and thylakoid membranes filled with chlorophyll (green pigment) Energy stored via the Calvin (Dark) Cycle using carbon dioxide to form sugar Vacuoles = “Water Tower in Plants” Small in animals; used for storage One large central vacuole in plants Membrane surrounds water or other storage materials Also supplies ―turgor pressure‖ against cell wall of plants to allow them to stand up provide structural strength If depleted, plants wilt Plant Cells vs. Animal Cells Plant Cells Animal Cells Have a cell wall Do not have a cell wall Have chloroplasts Do not have chloroplasts Large central vacuole Many small vacuoles No centrioles Pair of centrioles Chapter 6-2: The Cell Cycle Objectives: Identify the major events that characterize each of the five phases of the cell cycle. Describe how the cell cycle is controlled in eukaryotic cells. Relate the role of the cell cycle to the onset of cancer. The Life of a Eukaryotic Cell Eukaryotic cell division is more complex than prokaryotic cell division because o It involves dividing both the cytoplasm and the chromosomes inside the nucleus o Many internal organelles must reproduce or be manufactured and properly rearranged before the cell can divide. The Cell Cycle The cell cycle is a repeating sequence of cellular growth and division during the life of an organism. A cell spends 90 percent of its time in the first three phases of the cycle, which are collectively called interphase. A cell will enter the last 2 phases only if it’s ready to divide. The Cell Cycle The five phases of the cell cycle are: 1. First growth (G1) phase: During the G1 phase, a cell grows rapidly and carries out its routine functions. 2. Synthesis (S) phase: A cell’s DNA is copied during this phase. 3. Second growth (G2) phase: In the G2 phase, preparations are made for the nucleus to divide. Microtubules are rearranged. 4. Mitosis: Mitosis is the process during cell division in which the nucleus of a cell is divided into two nuclei, each with the same number and kinds of chromosomes as the original cell. 5. Cytokinesis: The process during cell division in which the cytoplasm divides is called cytokinesis. Control of the Cell Cycle The cell cycle has key checkpoints (inspection points) at which feedback signals from the cell can trigger the next phase of the cell cycle (green light). Other feedback signals can delay the next phase to allow for completion of the current phase (yellow or red light). Control occurs at three principal checkpoints: 1. Cell growth (G1) checkpoint: This checkpoint makes the decision of whether the cell will divide. 2. DNA synthesis (G2) checkpoint: DNA replication is checked at this point by DNA repair enzymes. 3. Mitosis checkpoint: This checkpoint triggers the exit from mitosis. When Control Is Lost: Cancer Certain genes contain the information necessary to make the proteins that regulate cell growth and division. If one of these genes is mutated, the protein may not function, and regulation of cell growth and division can be disrupted. Cancer, the uncontrolled growth of cells, may result. Chapter 6-3: Mitosis and Cytokinesis Objectives: Describe the structure and function of the spindle during mitosis. Summarize the events of the four stages of mitosis. Differentiate cytokinesis in animal and plant cells. Chromatid Separation in Mitosis During mitosis, the chromatids on each chromosome are physically moved to opposite sides of the dividing cell with the help of the spindle. Spindles are cell structures made up of both centrioles and individual microtubule fibers that are involved in moving chromosomes during cell division. Forming the Spindle When a cell enters the mitotic phase, the centriole pairs start to separate, moving toward opposite poles of the cell. As the centrioles move apart, the spindle begins to form. Separation of Chromatids by Attaching Spindle Fibers The chromatids are moved to each pole of the cell in a manner similar to bringing in a fish with a fishing rod and reel. When the microtubule “fishing line” is “reeled in,” the chromatids are dragged to opposite poles. As soon as the chromatids separate from each other they are called chromosomes. Mitosis and Cytokinesis Mitosis Step 1 Prophase: The nuclear envelope dissolves and a spindle forms. Step 2 Metaphase: During metaphase the chromosomes move to the center of the cell and line up along the equator. Step 3 Anaphase: Centromeres divide during anaphase. Step 4 Telophase: A nuclear envelope forms around the chromosomes at each pole. Mitosis is complete. Mitosis: Label the following picture. Polar fibers - spindle microtubules that extend from the two poles of a dividing cell. Kinetochore fibers - pull chromosomes to opposite poles Cytokinesis As mitosis ends, cytokinesis begins. During cytokinesis, the cytoplasm of the cell is divided in half, and the cell membrane grows to enclose each cell, forming two separate cells as a result. The end result of mitosis and cytokinesis is two genetically identical cells where only one cell existed before. Label the following pictures: Cytokinesis in animal cell Cytokinesis in plant cell