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4.1 The Function of the Nucleus within the Cell Animal Cells Animal cells are equipped with many structures that allow the cell to perform a variety of functions. See page 122 (c) McGraw Hill Ryerson 2007 Cell Parts and Organelles Animal Cell Parts (also found in plant cells) cell membrane - thin covering that controls the flow of materials in and out of the cell. cytoplasm - jelly-like substance contains the organelles (specialized cell parts) mitochondria - provide energy for cells ribosomes - manufacturing plants for proteins endoplasmic reticulum - membrane-covered channels that act as a transport system for materials made in the cell vesicles - membrane-covered sacs formed by the endoplasmic reticulum. Vesicles transport new proteins to the Golgi body. Golgi body - sorts and packages proteins for transport nucleus - controls all cell activities nucleolus - membrane-free organelle that makes ribosomes nuclear membrane - protects the contents of the nucleus Nuclear pores - openings in the nuclear membrane that allow only certain materials to pass vacuoles - membrane-bound storage containers See pages 122 - 124 (c) McGraw Hill Ryerson 2007 Cell Parts and Organelles Plant Cells Plant cells are equipped with some structures that animal cells do not have. chloroplasts - trap energy from Sun to make glucose, food for the plant cell wall - tough, rigid structure that surrounds cell membrane, provides protection and structural support large vacuoles - plant cells are equipped with a large vacuole for storing water See pages 122 - 124 (c) McGraw Hill Ryerson 2007 The Nucleus and DNA • The nucleus contains DNA (deoxyribonucleic acid); DNA is the molecule has the master set of instructions for how cells function, what they will produce, and when they will die Structure of DNA • • • • DNA looks like a twisted ladder - two strands wrap around each other in a spiral shape. The sides of the DNA ladder are made of sugar and phosphate. The steps of the ladder are made of four nitrogen bases: adenine (A), guanine (G), cytosine (C), and thymine (T). The bases join in a specific way • A always joins with T • G always joins with C See page 126 (c) McGraw Hill Ryerson 2007 DNA Structure See page 126 (c) McGraw Hill Ryerson 2007 DNA in the Nucleus • Most of the time DNA is in the form of chromatin • Chromatin coils tightly into X-shaped chromosomes • Every organism has a specific number of chromosomes • Human cells have 46 chromosomes arranged in 23 pairs • The 23rd pair determines sex; XX for females and XY for males See pages 127 - 128 (c) McGraw Hill Ryerson 2007 Genes • Genes are small segments of DNA located on a chromosome • Genes store the information needed to produce proteins • Each chromosome can carry thousands of genes • All your body cells have the same genes, but only specific genes are “read” in each cell to produce specific proteins • Specialized proteins called enzymes and hormones carry out important specific functions in the body See pages 129 - 130 (c) McGraw Hill Ryerson 2007 Production of Proteins • Protein production in the cell involves several important steps: 1. 2. 3. 4. 5. 6. 7. 8. 9. The nucleus receives a chemical signal to make a specific protein. The DNA message for the protein is copied into a small molecule called RNA. RNA leaves the nucleus through a nuclear pore. The RNA message is delivered to a ribosome, the ribosome makes the protein. The manufactured protein enters the endoplasmic reticulum (ER). A vesicle forms at the end of the ER, and carries the protein to the Golgi body. The Golgi body repackages the protein for transport out of the cell. A vesicle forms off the end of the Golgi body to carry the protein to the cell membrane. The vesicle attaches to the cell membrane, and its protein contents are released out of the cell. Take the Section 4.1 Quiz (c) McGraw Hill Ryerson 2007 See page 131 4.2 Mutation • A gene mutation involves a change in the order of bases (A,C,T,G) that make up the gene. There are several types of gene mutation: • Deletion (base missing) • Addition (extra base added) • Substitution (one base substituted for another) • Gene mutations may produce proteins that are beneficial or harmful to the organism, or may have no effect at all. • Example: a particular mutated gene produces white coat Kermode bears - they occur as only a small percentage of the population (they are normally black in colour). GNU License Photo See pages 136 - 138 (c) McGraw Hill Ryerson 2007 Effects of Mutations • Positive Mutations • When a gene mutation benefits the individual. • Example: Some plants have developed resistance to bacterial and fungal infections. • Negative Mutations • When a gene mutation harms the individual • Example: Sickle cell genes in affected humans cause blood cells that are abnormally shaped. • Neutral Mutation • When a gene mutation has no effect on the individual • Example: The white Kermode bear See pages 139 - 140 (c) McGraw Hill Ryerson 2007 Mutagens & Mutation Repair • Mutagens are substances or factors that cause mutations • Environmental mutagens such as mercury, cigarette smoke, X-ray and UV radiation, and certain viruses can cause mutations • Correcting mutations is difficult, but new techniques such as gene therapy offer hope. • Gene therapy is complicated and experimental: • • • • A virus in engineered to carry a normal gene The virus must somehow be targeted to the cells with the defective gene The normal gene must then replace the defective gene The normal gene must then be “switched on” so that the replacement normal gene produces the proper healthy proteins. It is also important that the normal gene make the correct amount of healthy protein. Take the Section 4.2 Quiz (c) McGraw Hill Ryerson 2007 See pages 141 - 143 5.1 The Cell Cycle and Mitosis • Due to the loss and death of cells, the body must replace them. A good example of this is human skin cells - each day millions are shed. • • • • The life of a cell is divided into three stages known as the cell cycle: Interphase: cell carries out normal functions. Mitosis: nucleus contents duplicated and divide into two equal parts. Cytokinesis: separation of two nuclei and cell contents into two daughter cells. See pages 150 - 153 (c) McGraw Hill Ryerson 2007 Parts of the Cell Cycle • • Interphase, the longest cell cycle stage, is when a cell performs normal functions and grows. For example, an intestinal lining cell absorbing nutrients. In late interphase, DNA copies itself in the process of replication. Replication involves several steps: 1. 2. 3. The DNA molecule unwinds with the help of an enzyme. New bases pair with the bases on the original DNA. Two new identical DNA molecules are produced. See pages 153 - 154 (c) McGraw Hill Ryerson 2007 Mitosis • At the end of interphase, the cell continues to grow and make proteins in preparation for mitosis and cytokinesis. Mitosis • • Mitosis is the shortest stage of the cell cycle where the nuclear contents divide, and two daughter nuclei are formed. It occurs in 4 stages: Prophase, Metaphase, Anaphase and Telophase. As the nucleus prepares to divide, replicated DNA in interphase joins to form sister chromatids, joined by a centromere. See pages 155 - 156 (c) McGraw Hill Ryerson 2007 Stages of Mitosis Early Prophase - nucleolus disappears and spindle fibres form Late Prophase - spindle fibres attach to centromeres of chromosomes Metaphase - chromosomes align on equator of cell Anaphase - spindle fibres pull sister chromatids to opposite poles of cell Telophase - in this final stage, spindle fibres disappear and a nuclear membrane forms around each separated set of chromosomes. Cytokinesis is the separation of the nuclei into two daughter cells See pages 156 - 157 (c) McGraw Hill Ryerson 2007 Cell Cycle Problems Checkpoints in the cell cycle will prevent division if: • • • If the cell is short of nutrients If the DNA within the nucleus has not been replicated If the DNA is damaged Mutations in genes involving checkpoints can result in an out-of-control cell cycle. The result can be uncontrolled cell division: cancer. • • • • Cancer cells have large, abnormal nuclei Cancer cells are not specialized, so they serve no function Cancer cells attract blood vessels and grow into tumours. Cells from tumours can break away to other areas of the body Take the Section 5.1 Quiz (c) McGraw Hill Ryerson 2007 See pages 159 - 161 5.2 Asexual Reproduction • A clone is an identical genetic copy of its parent • Many organisms naturally form clones via asexual reproduction • Cloning is also used in agriculture and research to copy desired organisms, tissues and genes Type of Asexual Reproduction • • • • • Binary fission - single cell organisms splitting into identical copies Budding - areas of multicellular organisms undergo repeated mitosis to form an identical organism. Buds sometimes detach to form a separate organism Fragmentation - part of an organism breaks off due to injury, and the part grows into a clone of the parent Vegetative reproduction - special cells in plants that develop into structures that form new plants identical to the parent Spore formation - some bacteria, micro-organisms and fungi can form spores - single cells that can grow into a whole new organism See pages 168 - 175 (c) McGraw Hill Ryerson 2007 Asexual Reproduction Grafting Binary fission Bud -----> Budding in Hydra Vegetative reproduction (c) McGraw Hill Ryerson 2007 Asexual Reproduction Advantages and Disadvantages See page 175 (c) McGraw Hill Ryerson 2007 Human Assisted Cloning • Humans use all the asexual cloning methods in order to produce desired results with organisms. This is done in several ways: • Reproductive cloning - purpose is to produce a genetic duplicate of an existing or dead organism. Steps involved: 1. Remove nucleus from an egg cell 2. A mammary gland cell is removed from an adult female 3. Electricity fuses mammary and egg cell 4. Fused cell begins dividing 5. Dividing embryo is inserted into surrogate mother See pages 176 - 177 (c) McGraw Hill Ryerson 2007 Cloning Dolly (c) McGraw Hill Ryerson 2007 Therapeutic cloning (c) McGraw Hill Ryerson 2007 Human Assisted Cloning • Therapeutic cloning - purpose is to correct health problems • • • • Very important to therapeutic cloning are stem cells - cells that can become different types of cells Stem cells can be used to replace cells damaged from injuries or disease Diabetes, spinal injuries, Parkinson’s disease are only a few that can benefit from stem cell therapy Controversial because the best stem cells are from embryos which are destroyed when harvesting cells Mouse Stem Cells Take the Section 5.2 Quiz (c) McGraw Hill Ryerson 2007 See pages 177 - 178 6.1 Meiosis • Meiosis is an important aspect of sexual reproduction • Sexual reproduction, through the shuffling of DNA, produces genetic diversity. • This variation offspring produces individuals that may have advantages over one another. See pages 188 - 189 (c) McGraw Hill Ryerson 2007 Role of Gametes • Normal body cells have a diploid chromosome number, meaning chromosomes occur in pairs. In humans, the male and female each contribute 23 chromosomes - when fertilization takes place, 23 (egg) + 23 (sperm) = 46 (zygote) • The zygote goes on to develop into an embryo, and on into a complete individual. When the time comes, the cycle repeats humans produce gametes (either egg or sperm) that have half (haploid) the normal number of chromosomes. See page 190 (c) McGraw Hill Ryerson 2007 Meiosis • Meiosis produces gametes with half the chromosomes compared to body cells: See pages 191 - 192 (c) McGraw Hill Ryerson 2007 Meiosis Events Meiosis I • Matching chromosome pairs (homologous chromosomes) move to opposite poles of the cell - two daughter cells result. Meiosis II • Chromatids of each chromosome are pulled apart - the end result is four haploid cells, each with half the number of chromosomes. These develop into gametes. Crossing Over • In meiosis I, chromatids of chromosome pairs can cross over each other and exchange DNA segments - this increases genetic possibilities and produces more variation Independent Assortment • The pairs of chromosomes in meiosis I separate independently, creating many different combinations of chromosomes in the daughter cells See pages 191 - 193 (c) McGraw Hill Ryerson 2007 Meiosis Details Gametes do not form equally in males and females • • In males, all 4 cells resulting from meiosis develop into sperm. In females, 1 cell gets most of the cytoplasm and becomes the egg. Chromosome mutations sometimes occur spontaneously • Chromosome changes during meiosis can cause changes in the genetic information. Parts of chromosomes can be inverted, deleted, duplicated or moved to another spot. Cromosome mutations can occur because of mutagens • Chromosome changes, sometimes leading to genetic disease or death, can be cause by mutagens such as radiation or chemicals. Failed separation of chromosomes in meiosis has serious consequences • Failed separation means that a gamete may end up with no chromosome or too many of a chromosome. Zygotes that result from these gametes rarely survive, and if they do, they will have serious genetic disorders. See pages 194 - 195 (c) McGraw Hill Ryerson 2007 Genetic Disorders The chromosomes of an individual can be studied • • • By using a karyotype, geneticists can view an individual’s chromosomes. Certain genetic disorders or syndromes occur when there are specific chromosomes extra or missing Down syndrome usually occurs when there is an extra 21st chromsome Down syndrome karyotype Take the Section 6.1 Quiz (c) McGraw Hill Ryerson 2007 See pages 196 - 197 6.2 Sexual Reproduction Sexual reproduction brings non-identical gametes together to form a new organism - it occurs in 3 stages: • Mating - the process by which gametes are bought together at same place and same time • Fertilization - process by which egg and sperm join to form a new organism • Development - the process by which an organism develops as an embryo See pages 204 - 206 (c) McGraw Hill Ryerson 2007 Methods of Fertilization External or Internal Fertilization • In order for either of these methods to produce a successfully developing embryo, certain conditions must be met: 1. Embryo must have enough nutrients. 2. Temperature must not be too cold or too hot. 3. There must be enough moisture so that embryo does not dry out. 4. Embryo must be protected from predators and items in environment that can potentially harm it. See page 207 (c) McGraw Hill Ryerson 2007 External Fertilization • In external fertilization, sperm and egg join outside parents Advantages • • • Very little energy required to mate Large numbers of offspring produced Offspring can be spread widely in the environment - less competition between each other and parents Disadvantages • • • Many gametes will not survive Many eggs will not be fertilized Offspring are often not protected by parents, so many of them die Frog Eggs - GNU Free Doc Photo See pages 208 - 209 (c) McGraw Hill Ryerson 2007 Internal Fertilization • In internal fertilization, sperm and egg join inside parents, embryo is nourished inside mother Advantages • • Embryo protected from predators Offspring more likely to survive, as many species will protect their them while they mature Disadvantages • • • Much more energy required to find mate Fewer zygotes produced, resulting in less offspring More energy required to raise and care for offspring See pages 210 - 211 (c) McGraw Hill Ryerson 2007 Pollination • Most plants transfer male gametes as pollen. Pollen can be carried by wind or other organisms. See pages 212 - 214 (c) McGraw Hill Ryerson 2007 Embryonic Development • Embryonic development is the early development of an organism - in humans, it is the first two months after fertilization Stages • End of the first week - ball of cells called morula • By end of second week it is a hollow ball called a blastula • Cells at this stage are stem cells, and have the ability to develop into any kind of cell • In the next stage the embryo is known as a gastrula and develops 3 layers: ectoderm (skin, nerves), mesoderm (muscles, bones), and endoderm (lungs, liver, digestive system lining) See pages 216 - 217 (c) McGraw Hill Ryerson 2007 Fetal Development • The cell layers now differentiate into the organs and tissues of a baby - this is divided into 3 trimesters. First Trimester (0-12 weeks) • Organ systems begin to develop and form. Bone cells form. Second Trimester (12-24 weeks) • Rapid growth from 12-16 weeks. Third Trimester (24+ weeks) • Continued growth, especially of brain. Fat begins to deposit at 32 weeks to keep baby warm at birth. See pages 218 - 219 (c) McGraw Hill Ryerson 2007 Sexual Reproduction Advantages and Disadvantages Take the Section 6.2 Quiz (c) McGraw Hill Ryerson 2007 See page 220 6.3 Assisted Reproductive Technologies • • Infertility is the inability of a couple to have a baby Assisted reproductive technologies involve removing eggs from the woman, fertilizing them, and returning them to the uterus. Types of Assisted Reproductive Technologies 1. 2. 3. 4. • Artificial Insemination - donor sperm is placed in the female. In vitro fertilization (IVF) - egg and sperm are collected and fertilization takes place in a dish. Embryo(s) then placed in female’s uterus. Gamete intrafallopian transfer (GIFT) - eggs and sperm are collected, mixed, then injected into the woman’s fallopian tubes. Intracytoplasmic Sperm Injection (ICSI) - a single sperm is injected directly into an egg. Reproductive technologies help childless couples, but carry a higher risk of birth defects. Also creates the problem of “unwanted” embryos. What should be done with them? Take the Section 6.3 Quiz (c) McGraw Hill Ryerson 2007 See pages 224 - 229