Lecture Three: Genes and Inheritance

Transcription

1 Lecture Three: Genes and Inheritance As we already know, the smallest, most basic unit of life is the CELL. Define: Prokaryotic a cell with no membrane-bounded organelles or nucleus Eukaryotic - a cell with membrane-bounded organelles and nucleus Cells are constructed of non-living components called MOLECULES. Four important types of molecules which are the main building blocks of living cells are the From smallest to largest, what is the organization of living things? Subatomic particles (protons, electrons & neutrons) Atoms Molecules (elements & compounds; inorganic and organic) (an ORGANIC molecule has a carbon/hydrogen backbone, an INORGANIC molecule does not.) Macromolecules (proteins, nucleic acids (DNA & RNA), lipids & carbohydrates) Cell organelles Cells (the smallest truly living thing) Tissues Organs Organ systems Organism Population Community Ecosystem (what are some southern Florida ecosystems?) Biosphere BIOLOGICAL MACROMOLECULES: Carbohydrates - short term energy storage; structure of the organism (plants) Lipids - (also known as fats) - long term energy storage Nucleic Acids (DNA and RNA) - the instructions the cell uses to build proteins Proteins: The highly variable macromolecules that make each organism unique Structural - these make up the physical body of many organisms Functional (enzymes) - these are the "machinery" the cell uses to build other things, from carbohydrates, to lipids, to nucleic acids to other proteins, as well as larger products that may be combinations of the four macromolecules and other molecules and elements. Each of the biological macromolecules has the most basic shape: repeating, similar subunits, somewhat like a string of pearls. Carbohydrates are chains of smaller subunits called sugars Lipids are chains of smaller subunits called fatty acids Nucleic Acids are chains of smaller subunits called nucleotides Proteins are chains of smaller subunits called amino acids Any such "chainlike" molecule is called a POLYMER. it's a string of

2 The activity and function of a protein depends on the exact order of its amino (this is called the primary structure of the protein). Even ONE different amino acid can completely change a protein's shape and function! Ribosomes are biological machines inside the cell that make protein. A ribosome manufacture protein by linking amino acids in the right order to make a specific protein. How does it know the order? The order of amino acids is encoded in the molecule known as Deoxyribonucleic Acid DNA. Like protein, DNA is a chain of repeating subunits (i.e., a polymer). In DNA the subunits are four different nucleotides, that can be represented by four different letters: A (adenine) G (Guanine) C (cytosine) T (Thymine) The DNA Code: Every three letters on the DNA represents one amino acid. In the DNA double helix, A always binds to T and G always binds to C. PROBLEM: DNA is permanently stuck inside the nucleus. The ribosomes are outside the nucleus in the cytoplasm. How does the ribosome get the code? We need a messenger to bring the code to the ribosome. That messenger is Ribonucleic Acid RNA. This type of RNA is called messenger RNA, or mrna. TRANSCRIPTION: Re-writing the DNA code into RNA When a cell needs to make protein, it unzips the DNA double helix, and reads the letters. As it reads, special proteins called enzymes manufacture a brand new strand of RNA that matches the code on the DNA. This process is called transcription. ( Transcription literally means writing again, That makes sense, since the cell is rewriting the DNA code into RNA code.) The enzymes don t read the DNA at random. There are specific three-letter codes that tell them where to start reading. And what they are reading is a GENE: the DNA instructions for making a protein. At the end of the gene, there are three-letter stop codes that tell the enzymes to stop making the mrna. Like DNA, RNA is made of nucleotides that can be represented by letters. RNA has Adenine (A), Cytosine (C), and Guanine (G). But instead of Thymine (T), RNA uses a very similar nucleotide containing Uracil (U). Once the mrna is complete, it is transported out of the nucleus and taken to the ribosome. The ribosome can now read the three-letter codons to make protein.

3 VOCABULARY: chromosome - strand of DNA & protein inside the cell nucleus (. locus - the physical location of a gene on the chromosome (plural - loci) gene - a unit of inheritance; a section of DNA that codes for a protein alleles - different "flavors" of a particular gene. (e.g. there's a human gene for "eye color", and it has alleles that code for "brown" or "blue." A normal (diploid) organism has two copies of every gene, one from mom and one from dad. homozygous - the two copies an organism has for a particular gene are of THE SAME allele. (e.g., if you inherited one brown eye allele from mom, and a brown eye allele from dad, then you are HOMOZYGOUS for the eye color gene: both alleles are the same.) heterozygous - the two copies an organism has for a particular gene are of TWO DIFFERENT alleles. (e.g., if you inherited one brown eye allele from mom, and a blue eye allele from dad, then you are HETEROZYGOUS for the eye color gene: like a person who is homozygous, you have two copies, but unlike that person, each of your alleles is DIFFERENT!) genotype - The genetic makeup of an organism: all of its genes phenotype - They physical characteristics of an organism as determined by both the genotype and environmental influences on the developing body. Is DNA the ONLY thing that controls phenotype? NO! Not all genes are being made into protein all the time. And the environment of the organism can have profound effects on what part of the DNA is actually read, and when. Nature vs. Nurture Environmental factors can have a profound effect on the way genes are activated while an organism is still growing and developing. This, of course, can strongly affect the "finished product," the organism itself. The effect of an organism s genes on its phenotype is sometimes referred to as nature. Environmental factors can affect growth rate, survival, and various phenotypic characters. The effect of environmental influence on an individual s phenotype is sometimes referred to as nurture. Scientists often study how environment and genes interact to produce a wide array of different phenotypes in similar organisms. How much variation is due to genes? How much variation is due to environmental influence? How much of what we are is due to Nature, and how much is due to Nurture? TODAY YOU WILL EXPLORE THE INTERACTION OF GENES AND ENVIRONMENT BY DESIGNING AN EXPERIMENT TO TEST THE EFFECT OF AN ENVIRONMENTAL VARIABLE ON CATERPILLAR DEVELOPMENT. THE MORPHOGENESIS OF A BUTTERFLY... Egg Larva Pupa Adult = METAMORPHOSIS

4 What environmental factors might affect caterpillar development & metamorphosis? 1. light 3. temperature 5. Crowding 7.??? 2. food 4. humidity 6. different nutrients What parameters (physical characteristics you can measure) might these factors affect in the larvae? (And which can you easily measure, given the resources we have?) HINT: #4 and #5 are the only parameters you will be able to measure with the tools we have at hand. Larvae are too fragile to measure and too light to weigh. 1. mass/weight 2. length (of what part of the body?) 3. color (how might you accurately measure this?) 4. duration of larval stage (from experimental set-up to chrysalid formation) 5. duration of pupal stage (between chrysalid formation and emergence as adult) 6. size of various adult features (wings, head, body parts, etc.) Given what you know about caterpillars and what you know about the environmental factors where they live and grow, what is the critical question you are asking about an environmental factor affective caterpillar metamorphosis? (example: Will pesticide in the environment affect caterpillar metamorphosis?) What is your overall experimental hypothesis? (example: Pesticide in the environment will inhibit caterpillar metamorphosis.) What is your null hypothesis? (example: There will be no difference in metamorphosis between caterpillars treated with pesticide and those treated with a placebo.) What is your alternative hypothesis? (example: There will be a difference in metamorphosis between caterpillars treated with pesticide and those treated with a placebo.) What is your prediction? (You can figure this one out.) What will you measure to test your hypotheses? (example: Days to pupation)

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