From Gene to Protein. Lesson 3

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1 From Gene to Protein Lesson 3

2 Gregor Mendel Mendel hypothesized that certain factors were responsible for the traits that were inherited by pea plants Today, these factors are known as genes A sequence of nucleotides in DNA that contain instructions for building proteins Genes à Proteins à Physical characteristics, anti-bodies, hormones, proteins that drive cellular metabolism, and those that manifest genetic disorders by their absence or alteration

3 Archibald Garrod (early 1900s) Certain illnesses occurred in some families more often than others Alkaptonuria à genetic disorder where urine appears black because it contains alkapton (chemical) Inherited trait à Mutation of a gene that normally codes for an enzyme that breaks down the amino acid tyrosine If not broken down, chemical called alkapton accumulates (turns black in air) First see that enzymes are under the control of hereditary material

4 One gene-one enzyme hypothesis Beadle and Tatum (1941) used bread mold (Neurospora crassa) Normal Neurospora grows on a minimal medium (MM): salts, sucrose and a vitamin Able to use simple chemicals to synthesize complex molecules needed for growth and reproduction Mutant strains did not grow unless additional nutrients (i.e. amino acids and vitamins) were added

5 Placed mutant strains in vials containing MM plus one main nutrient Different mutants could grow in different conditions

6 Hypothesized that each mutated strain had a defect in a gene that coded for one of the enzymes needed to make a particular nutrient that was not in the MM Concluded that one gene controls the production of one enzyme Showed direct relationship between genes and enzymes = one geneone enzyme hypothesis

7 One gene-one polypeptide hypothesis One gene-one enzyme hypothesis needed to expand to include other proteins Many proteins are not enzymes, and may consist of more than one subunit Subunit = polypeptide Restated as one gene-one polypeptide hypothesis

8 The Central Dogma Francis Crick (1956) gave the name Central Dogma to the flow of information from DNA à RNA à Protein

9 The Central Dogma Two major steps: 1. Transcription = information coded in DNA is copied into RNA (in the nucleus) RNA is able to exit the nucleus and enter the cytosol 2. Translation = information in RNA is copied into amino acids (on ribosomes)

10 Ribonucleic Acid (RNA) Like DNA, RNA is a carrier of genetic information Deoxyribonucleic acid Deoxyribose sugar Double stranded Adenine-thymine Guanine-cytosine Resides in nucleus Ribonucleic Acid Ribose sugar Single stranded Adenine-uracil Guanine-cytosine Resides in nucleus and cytoplasm

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12 Types of RNA Messenger RNA (mrna) = end product of transcription of a gene Varies in length depending on the size of the gene Translated by ribosomes into protein Transfer RNA (trna) = delivers amino acids to the ribosomes for translation Short in length (70-90 bp long) Ribosomal RNA (rrna) = binds with ribosomal protein to form ribosomes

13 Messenger RNA (mrna) = end product of transcription Transfer RNA (trna) = delivers amino acids for translation Ribosomal RNA (rrna) = binds with ribosomal protein to form ribosomes

14 Transcription and Translation: Overview Transcription (3 sequential processes): 1. Initiation enzyme RNA polymerase binds to DNA at a specific site 2. Elongation - RNA polymerase reads the template strand of DNA and creates a complementary strand of RNA 3. Termination recognizes code to stop à mrna transcript released from nucleus

15 Transcription and Translation: Overview Translation (3 sequential processes): 1. Initiation ribosome recognizes a specific sequence on the mrna and binds to the site 2. Elongation ribosome moves along the mrna 3 nucleotides at a time (each 3 nucleotides = an amino acid) 3. Termination a 3-base sequence is reached that codes for a stop signal à ribosome falls off mrna and polypeptide chain is released

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17 The Genetic Code Universal viruses to bacteria to mammals (exceptions) 4 bases in RNA à 20 amino acids (AA) found in proteins Sequence of 3 nucleotides (codon) used for each AA Start codon - signaling initiation for translation AUG (Met) Stop codon - signaling termination at the end of translation UAA, UAG, UGA

18 Homework Investigation Work in groups to create a role play for DNA replication (role-play and questions due Friday Nov 17) Textbook Questions