Eukaryotes Bio 114 (Science, Dr. Hyman, Organisms)
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This 12 page Class Notes was uploaded by Morgan Sawyer on Saturday November 7, 2015. The Class Notes belongs to Bio 114 (Science, Dr. Hyman, Organisms) at James Madison University taught by Dr. Oliver Hyman in Fall 2015. Since its upload, it has received 19 views. For similar materials see Biology of Organisms (Bio 114) in Biology at James Madison University.
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Date Created: 11/07/15
Bio114 Eukaryotes Eukaryotes - Can be multicellular and unicellular - Very diverse lineage - Very diverse morphology o Tiny to huge in size o Unicellular and multicellular - Diverse reproduction o Asexually by mitosis (split DNA in two) o Sexually by meiosis (sperm and egg) What do all eukaryotes have in common? - They all have membrane bound DNA (nucleus) and organelles (mitochondria) - Linear chromosomes Surface area to volume ratio relate to cellular processes? - Volume dictates energy needs and waste production - As cells increase in size, energy needs increase by X^3, but SA only by X^2 - So bigger cells need to add SA without adding volume to increase infoldings Advantages of cell membrane infoldings - If cells can infold they can increase volume without decreasing SA: V ratio - They take in food and let out wastes through the cell membrane - In prokaryotic cells, cell membranes is where ATP is generated and is increased when infolding is increased Evolution by natural selection led to formation of the nuclear envelope - Over time/generations you see an increased infolding leading to a nuclear envelope - The current leading hypothesis is that they nuclear envelope of eukaryotes evolved from the infolding of prokaryote cell membranes - Infolding would enable cells to grow larger by increasing SA: V ratios - Prokaryotic species have been found with infoldings in their plasma membranes - The nuclear envelope and endoplasmic reticulum are connected to each other Where did mitochondria come from? - Endosymbiosis theory When did eukaryotes first appear? - 2 billion years ago The Nuclear Envelope - This is what formed the nucleus SA: V ratio - Lower SA: V lose heat less quickly - Higher SA: V lose heat more quickly o How to remember.. Africans are tall and skinny to let off heat while Eskom’s are all short and chubby to keep in heat - As you get more and more infoldings you get a higher SA: V ratio Endosymbiosis “inside-together-living” - Symbiosis: individuals of two different species live in physical contact - Endosymbiosis: when an organism of one species lives inside the cells of another Endosymbiosis Theory - Mitochondria originated when a bacterial cell took up residence inside another cell two billion years ago - This process is that the host cell is doing glycolysis without the bacterium Evidence for Endosymbiosis - Mitochondria all have their own circular genome because mitochondria use to be free living - Mitochondria have two cell membranes - Mitochondria replicate by binary fission and do so independently of the eukaryotic cell o Binary Fission – just like other prokaryotes - CR in prokaryotes and eukaryotes is almost exactly the same - Mitochondria have 2 cell membranes - Mitochondria have their own separate genome - Mitochondria have circular DNA - Mitochondria sexually reproduce by binary fission SIDE: Chloroplasts are organelles - Mitochondria and chloroplasts both came via endosymbiosis Chloroplasts have all of the same bacteria-like characteristics as mitochondria: 1. Circular chromosome 2. Their own genome 3. Double cell-wall 4. Replicate by fission 5. Bacteria ribosomes Recall: - Nuclei and mitochondria are Synapomorphy for the eukaryotes - The most accepted hypothesis is that the nucleus evolved from natural selection for ancestral cells that developed infoldings in their cell membranes - Infolding in cell membranes are hypothesized to have provided a selective advantage by increasing SA: V ratio, which tends to increase rates of ATP production and nutrient absorption in single celled organisms - Mitochondria are hypothesized to have evolved through a process called endosymbiosis, in which a bacterial cell capable of aerobic cellular respiration was engulfed by a host that could do glycolysis - The observation that mitochondria have their own circular genome, replicate by binary fission, and have two cell membranes support the endosymbiosis hypothesis Recall Continued: - Chloroplasts are organelles therefore only eukarya have chloroplasts Proposed origin of the chloroplast: Endosymbiosis - Chloroplasts have all of the same bacteria-like characteristics as mitochondria: o Circular chromosome o Their own genome o Double cell-wall o Replicate by fission o Bacterial ribosomes Why are cellular processes of photosynthesis and cellular reparation so similar in eukaryotes and prokaryotes? - First we need to understand the key word: HORIZONTAL GENE TRANSFER – transfer of DNA between two different species across branches of the tree; as opposed to normal gene transfer from parent to offspring - Endosymbiosis is a kind of “horizontal” gene transfer across branches of the phylogenetic tree - Normal Gene Transfer aka vertical transfer is from parent to offspring so from one generation to the next generation - Because they are traits that were “horizontally transferred” across branches on the tree of life through endosymbiosis… o Otherwise stating… it first evolved in bacteria then bacteria was engulfed by eukarya hence “horizontally transferred” Overall point - The nucleus enabled the organization of “lots” of DNA which increased its complexity - Mitochondria in chloroplasts enable increased ATP (energy) production in eukaryotic cells o Mitochondria – aerobic respiration over glycolysis o Chloroplasts use autotrophy over heterotrophy The reasoning behind this is because it’s there to provide a selective advantage The Domain Eukarya Objections in this section: How do these organisms reproduce? - Asexual - Sexual What has enabled the diversification of the eukarya? How is genetic diversity created in the eukarya? Reproduction in eukaryotes is complicated 1. Reproduction of a single cell a. To make a new identical copy (asexual) b. For growth/repair of a multicellular organism… ex. A scab (generating more and more cells) 2. Reproduction of a multicellular organisms a. Sexual reproduction (humans) b. Asexual reproduction (ex. Leaves growing on top of other leaves) BIG TAKE HOME: IN EUKARYOES THERE ARE TWO POSSIBLE PROCESSES THAT REGULAT REPRODUCTION 1. Mitosis – produces genetically identical cells similar to binary fission in prokaryotes (more common across the board) 2. Meiosis – produces genetically unique cells (complicated process. Nothing like it in prokaryotes) ***Sexual reproduction is the only one that doesn’t use mitosis. Those who use sexual reproduction use meiosis. Introduction to Mitosis: ***Daughter cells are genetically IDENTICAL to parent cells - This happens in our somatic cells o Muscle, Nerve, Skin, etc. - Key word: Gamete: a haploid reproductive cell that can fuse with another haploid cell to form a zygote. Most multicellular eukaryotes have two distinct forms of gametes: egg cells and sperm cells (Freeman, Biological Science) Eukaryotic Chromosomes and Ploidy (n) - Eukaryotic cells have multiple linear chromosomes (as opposed to circular in prokaryotes) - Humans have 23 different chromosomes - Each has its own unique, essential genes - Must human cells have tow unique copies of each chromosomes o Diploid = two copies of each chromosomes (in all human chromosomes) Diploid represented by: 2n, where 2 = the number of unique copies of each chromosome, and n = the total number of chromosomes o Humans get 23 from each parent so 46 total Eukaryotic Chromosomes and Ploidy (n) - Sex cells (gametes) are usually HAPLOID o Haploid – have one unique copy of each chromosome form their mom or dad (represented by n) - Somatic cells (any other cell type) are usually DIPLOID (2n) o Have two unique copes of each chromosome so two unique copies of each gene, one from Mom’s chromosome and one form Dad’s chromosome EXAMPLES: This cells is haploid (one unique type chromosome) with an n = 6 (because 6 chromosomes) This cell is triploid with a n =4 Triploid because there are three unique copies of each chromosome N = 4 because there are four different types of chromosomes Relationship of Ploidy to variation in traits - Recall: essential to natural selection - Key word: Alleles – different versions of the same gene - Having multiple chromosomes allows for different combinations of alleles - Which could result in different phenotypes (what a genetic trait looks like) Steps of Mitosis: - Create genetically identical daughter cells - Prior to mitosis: each chromosome needs to be copied (DNA replication) - Ploidy is the number of unique copies of each chromosome 1. Chromosome are copied from parents 2. Chromosomes self-replicate to sister chromatids 3. The sister chromatids a line in a single file line at the center of the cell (essential for ensuring each daughter cells gets each chromosome) 4. They then are able to separate into two cells ***Ploidy never changes during mitosis ***If chromosome isn’t able to a line it isn’t able to generate identical daughter cells and most likely results in a mutation ***Since two cells are being generated it is a diploid cell since there are two copies of the chromosomes Mitosis: Summary TAKE HOME ***DAUGHTER CELLS ARE GENERTICALLY IDENTICAL TO PARENT CELLS Bio114 Lecture November 6, 2015 Mitosis Review: - Crates daughter cells that are genetically identical to each other - Is used for reproduction in uni- and multicellular organisms - In a diploid organism with 20 total (2n = 20) chromosomes will result in daughter cells with 20 total chromosomes - Is useful for producing genetically identical cells from parent cells Mitosis – What is it good for? 1. Some eukaryotes reproduce a whole new organism by mitosis (one type of asexual reproduction) all are genetically identical 2. Eukaryotes undergo mitosis for growth or organism (2 cells to 4 to 8 to 16 to trillions) 3. When new cells are needed to replace old and damaged cells (ex. Bone marrow, skin, and gut lining… continuously regenerating) Reproduction in Eukaryotes (mitosis vs. meiosis): Meiosis - Directly translated: “to lessen” - Cell division resulting in chromosome reduction by half - *Typically produces haploid (n) cells…but only if you start with diploid (2n) cells - Essential for sexual reproduction - Many (not all) eukaryotes use meiosis to make gametes - Like mitosis, all DNA is copied in 2n cell BUT… o The resulting cells are haploid (n) and not identical (to each other or the parents cell) because of how chromosomes line up o Cell divides twice to make 4 haploid (n) cells Key Words: - Sister chromatids: identical copies of the same chromosome (same as before) - Homologous pairs of chromosomes: pairs of sister chromatids one set from mom, and one set form Dad, both the same chromosome number - Maternal – unique version of chromosome inherited from the mother - Paternal – unique version of chromosome inherited from the father Meiosis Overview - Involves two cell division resulting in reduction of chromosome Ploidy by half - As soon as the two chromosomes are pulled apart in the second step it becomes haploid - M1 is the original split of male and female (where it become haploid) - M2 is the final split of chromosomes Key Differences between mitosis and meiosis - Mitosis: sister chromatids separate (not homologous pairs) o When pulled from single file line there is no change in Ploidy - Meiosis: homologous pairs first separate, then sister chromatids separate o Pulling homologous apart results in a change of Ploidy Summary of Differences Between Mitosis and Meiosis: Yes because this results in a ton of genetic variation by meiosis because of sex 3 Main Sources of genetic variation in meiosis: 1. Independent Assortment 2. Crossing Over 3. Mixing gametes between individuals Independent Assortment - Random aligning of homologous chromosomes during Meiosis I o Leads to variation in the genetic make up of the gametes - Genetic makeup of resulting cells depends on how the homologous align - There can be 8.4 million genetically unique gametes that can be produced by ONE human by independent assortment - From mating there can be 7 X 10^12 different variations of the gene Why do we care about genetic variation? - It creates raw material for natural selection Crossing Over: - Crossing over between homologous chromosomes during meiosis results in even more variation - Early in meiosis (before the first alignment) homologous chromosome pairs come together - Non-sister chromatids can swap pieces of chromosomes which creates crossing over Genetic Variation and modes of Reproduction Goes from least genetic variation to the most genetic variation - Asexual reproduction produces the least amount of genetic variation (only through random mutation) - Self-replication is considered to be sexual reproduction
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