AP Biology Life’S Beginning on Earth According to Scientific Findings (Associated Learning Objectives: 1.9, 1.10, 1.11, 1.12, 1.27, 1.28, 1.29, 1.30, 1.31, and 1.32)
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AP Auburn University AP Summer Institute BIOLOGYJuly 11-14, 2016 AP Biology Life’s beginning on Earth according to scientific findings (Associated Learning Objectives: 1.9, 1.10, 1.11, 1.12, 1.27, 1.28, 1.29, 1.30, 1.31, and 1.32) I. The four steps necessary for life to emerge on Earth. (This is according to accepted scientific evidence.) A. First: An abiotic (non-living) synthesis of Amino Acids and Nucleic Acids must occur. 1. The RNA molecule is believed to have evolved first. It is not as molecularly stable as DNA though. 2. The Nucleic Acids (DNA or RNA) are essential for storing, retrieving, or conveying by inheritance molecular information on constructing the components of living cells.. 3. The Amino Acids, the building blocks of proteins, are needed to construct the “work horse” molecules of a cell. a. The majority of a cell or organism, in biomass (dry weight of an organism), is mostly protein. B. Second: Monomers must be able to join together to form more complex polymers using energy that is obtained from the surrounding environment. 1. Seen in monosaccharides (simple sugars) making polysaccharides (For energy storage or cell walls of plants.) 2. Seen in the making of phospholipids for cell membranes. 3. Seen in the making of messenger RNA used in making proteins using Amino Acids. 4. Seen in making chromosomes out of strings of DNA molecules. (For information storage.) C. Third: The RNA/DNA molecules form and gain the ability to reproduce and stabilize by using chemical bonds and complimentary bonding. 1. Adenine with Thymine OR Uracil. 2. Guanine with Cytosine. 3. The single strands of DNA/RNA molecules are held together by covalent bonds. 4. The two sides of the DNA double helix are held together by Hydrogen bonds. (To be discussed later in this unit.) D. Fourth: The evolution of a protobiont (means “first life form”) membrane of phospholipids and proteins to keep the “cell” intact. II. The scientific supporting evidence for the above steps. (These are laboratory testable experiments; not “hunches” or guesses without proof.) A. Step 1 - Abiotic synthesis – The Stanley Miller and Harold Urey Experiment (1953) supports this claim. 1. The experiment took the inorganic gases hypothesized to have been in early Earth’s atmosphere, H2, CH4, NH3, and water vapor and formed a variety of organic molecules, such as amino acids and oils. These organic molecules are the building blocks of all life forms. The energy source for the formation was an electrical spark that was to represent lightning in the early atmosphere. The gases hypothesized to be present in the early Earth’s atmosphere came from data associated with analyzing active volcanoes eruptions. Volcanoes would have been very active and present in the early Earth time period, as well as still today. These organic molecules would have accumulated in the Earth’s early oceans over millions of years and thus making possible the formation of more complex structures, as seen in step 2. B. Step 2 –Complex polymer formation – Researchers have shown that by exposing Pyrite (fool’s gold), sand, or clay to the intense heat of sunlight, and in the presence of the tidal actions of the oceans, that complex polymers can form from the simple building blocks of amino acids and oils, from step 1, which are dissolved in water. These complex polymers would then also have accumulated in the Earth’s oceans over millions of years and then making possible the formation of more complex structures in Step 3. C. Step 3 – RNA formation and reproduction – The experiments of Thomas Cech and Sidney Altman have shown that small strands of RNA molecules can act as enzymes (biological catalyst for chemical reactions). The enzymatic RNA molecules are called Ribozymes. These small strands of RNA would have been the product of step 2. RNA is great for being enzymatic; as well as temporarily, storing and transmitting molecular information (as seen in protein synthesis using messenger RNA). Over millions of years, a more stable and longer lasting molecule would have evolved. This molecule, DNA, would become, over millions of years, the more stable and longer lasting means for storing molecular information and transferring this important information from a cellular generation to the next in the process of binary fission/mitosis. This would “create” the ability to reproduce cells or organisms, which would come into existence with step 4. D. Step 4 - Protobiont membrane formation – Experiments have shown that lipids and other organic molecules, from steps 1-3, can form membrane bound structures, similar to cell membranes. This formation allows for complex molecular interactions to occur in a safe, inner “environment” away from the outside “environment”. In simple terms, you have an “inside” area separated from an “outside” area by a lipid (oil) based structure referred to as a membrane. Over millions of years of evolution these enclosed environments would become the first Prokaryotic cells. These Prokaryotic cells would posses DNA and RNA molecules inside them. The RNA would be used to construct Ribosomes, which are needed to link Amino Acids together in the making of proteins. The DNA would be for storing that protein “making” information as well as passing it on to the next generation. Thus life could come into existence, according to science by these means over billions of years. AP Biology Basic Cell Structure (Associated Learning Objectives: 1.9, 1.10, 1.11, 1.12, 1.14, 1.15, 1.16, 1.27, 1.28, 1.29, 1.30, 1.31, 2.4, 2.7, 4.5) I. Cells A. These are considered to be the basic unit of life. B. The cell is an example of Emergent Properties. If you only have organelles, nothing can happen; but if you have all the organelles together and inside a membrane “life” could emerge. C. All cells are considered Open Systems in their natural settings because there are materials coming into the cell from the surrounding environment; as well as, materials leaving the cell and going into the surrounding environment. The cell is open to interaction with the environment. II. Cytology is the study of cells; Cytologist – a person who works with cells. III. Cell Types that exist A. Prokaryotic cells (“pro” means “before” , “kary” means “nucleus”, “ote” means “organism” ) 1. These organisms (bacteria) would have evolved before a nucleus had evolved into existence. 2. It is believed that the first prokaryotic cells came into existence about 3. 5 Billion Years Ago (BYA). 3. The oldest prokaryotic fossils are found on stromatalites (bacterial mounds) in Shark Bay, Australia. B. Eukaryotic cells (“Eu” means “true”) 1. These cells would have “truly” evolved after a nucleus had evolved, as all they possess a nucleus. 2. The Endosymbiotic Hypothesis proposed by Lynn Margulis in the 1960s. a. It basically hypothesized that Prokaryotes came to live together in a symbiotic relationship, the smaller living inside the larger, to gain a survival advantage over other prokaryotes and eventually they evolved into Eukaryotic cells over many generations that spanned hundreds of thousands of years. i. Smaller organism gained protection. ii. Larger organism gained energy production or faster motility. iii. Over time DNA segments were “swapped” to create a more permanent existence. This “swapping” is referred to as genetic annealing. b. Supporting pieces of evidence will be in seen in the structures of the Mitochondria, Chloroplasts, and Flagella. IV. Surface- to- Volume Ratio is of GREAT Importance for all cells. A. Cells can only be so small. (There has to be enough room (volume) to hold things and to perform work inside a cell using the cell membrane.) B. Cells can only be so large. (Larger means more traffic going in both directions across the cell membrane.) C. A cell must be large enough to contain DNA and Ribosomes for making proteins, and some cytoplasm to act as working “space”. They can only be so big because we have to be able to move enough “food” into and “waste” out of a cell efficiently. If it is too large the cell becomes inefficient at moving these things so it divides to get back to a smaller state. D. Think of cells as cubes. We can find the surface area of a cubodial cell by using the formula: Length X Width X 6 OR 6 X S2. S represents “a side” and the measurement is Squared. (i.e. cm2, mm2, or m3) E. We can also find the interior volume of a cell by the formula: Length X Width X Height OR S3. This measurement is cubed. (cm3, mm3, or m3) F. The comparison is made as such: SA:V, in lowest common denominator form. For all cells, they desire a much higher surface area than volume so as to be most efficient in transport by diffusion across the membrane. V. Basic Prokaryotic Cell (Bacteria) Structure A. All prokaryotes are unicellular. The cell possess inside DNA (in the nucleoid), ribosomes, and cytoplasm. B. Three basic shapes of prokaryotes exists: 1. Cocci (Means “round”) 2. Bacilli (Means “rod”) 3. Helical (Means “spiral”) C. Most prokaryotes will have a cell wall. (This is NOT the same as a plant’s cell wall.) 1. This structure is primarily for protection of the underlying cell membrane. 2. It also helps prevent the prokaryotes from bursting in an aquatic environment. (The cell is hypertonic to the surrounding hypotonic water. Remember, water travels Hypo to Hyper.) 3. The cell wall is mainly composed of proteins and sugars. (What are called peptidoglycans.) (“peptide” refers to the proteins; “glycan” refers to the sugars.) 4. Scientists perform a Gram staining for easy, fast identification of most bacteria.