Lecture 19 Outline of Last Lecture I. ChromosomesII. Sex-Linked InheritanceIII. Genetic Problems with X-Linked GenesIV. How to Solve a Genetics ProblemV. Chromosomal AlterationsVI. Chromosomal Alterations Based on the Number of ChromosomesVII. Chromosomal Alterations Based on Chromosomal Structure ChangesVIII. HW - Genetics Problems with Solutions (due 4/15/14)Outline of Current Lecture I. DNA and Cell ActivitiesII. TranscriptionIII. TranslationCurrent LectureChapter 17 – Molecular GeneticsI. DNA and Cell Activitiesa. Inherited DNA controls the cell’s activities b. It has the code for how to make enzymes and other proteinsc. DNA does NOT make protein directlyd. How to make proteins:i. DNA is copied to an RNA molecule called “messenger RNA” (mRNA)ii. mRNA programs the making of proteinse. Central Dogma of Molecular Biologyi. The process of making proteins is called the “central dogma of molecular biology”ii. DNA  transcription  mRNA  translation  proteiniii. Transcription – synthesis od RNA from a DNA templateiv. Translation – synthesis of protein using information in mRNA moleculeII. Transcription – synthesis of RNA from a DNA templatea. Information in DNA is copied into an RNA moleculeb. mRNA is made by an enzyme called “RNA polymerase” BIOL 1st Editionc. RNA polymerase binds to DNA at the beginning of a gene at a specific place called “the promoter”d. RNA polymerase is guided to the promoter by special proteins called “transcription factors”e. Once at the promoter, RNA polymerase moves along the DNA and separates the two strands f. One of the two strands acts as a template to make RNA (by the base pairing rules)g. RNA nucleotides (C, G, A, U) line up properly on the DNA template strand (remember that RNA nucleotides include U in place of T) by HYDROGEN BONDINGh. RNA polymerase links the lined up RNA nucleotides together to form the RNA moleculei. RNA is made of approximately 60 nucleotides/secondj. As RNA is made, it peels off the DNAk. Then 2 DNA strands come back togetherl. Transcription stops at a place called the “terminator”m. At the terminator, RNA polymerase releases the finished mRNA molecule and then falls off the DNAi. Base Pairing Rules for DNA1. C – G2. A – T ii. Base Pairing Rules for DNA/RNA pairing1. DNA 3’ G – C – A – T 5’2. mRNA 5’ C – G – U – A 3’III. Translation – synthesis of protein using mRNA informationa. mRNA – polymer of 4 different nucleotides (G, C, U, A)b. Proteins – polymers of 20 different amino acidsc. The Genetic Code – how it translates the language of nucleotides to the language of amino acidsi. 1 nucleotide  1 amino acid 1. Could only code for 4 amino acidsii. 2 nucleotides  1 amino acid1. Number of combinations of 4 things taken 2 at a time  42 = 16 could only specify 16 different amino acidsiii. 3 nucleotides  1 amino acid1. 43 = 64 possible combinations of amino acidsiv. Each 3-nucleotide code word is called a “codon”  codes for some particular amino acidv. First codon was deciphered in 1961 by Nirenberg1. He made a synthetic mRNA test tube – poly u2. Then translated it in vitro (in test tube)3. The protein that was made was composed entirely of the amino acid phenylalanine4. Therefore, the codon UUU codes for the amino acid phenylalanine5. Later, 64 possible combinations of nucleotides were deciphereda. 61 – code for amino acidsb. 3 – don’t code for anything, but are signals to stop translation called “stopcodons”6. All living things share the same genetic code7. Indicates that the genetic code was established very early in evolution (example of unity in life)d. Tools for the process of translation:i. mRNA  RNA molecule that carries the coding information, a series of codons that mustbe decoded, one right after the other1. Translation starts at the first “start codon” from the 5’ end of the molecule2. The region from the “CAP” (a stabilizing and regulatory structure) to the “start codon” is not translated into amino acids  it is called the “5’ untranslated region (5’UTR)”3. Translation ends at a “stop codon”, NOT at the very end of the mRNA4. The region between the “stop codon” and the 3’ end is NOT translated, and is called the “3’ untranslated region (3’UTR)5. The 3’ end of the mRNA has a string of A’s called the “poly A tail” which acts to stabilize mRNA and regulate translationii. tRNA  functions as a “decoder” that pairs the right amino acid with its codon  aminoacids DO NOT recognize their own codons1. tRNA is a small RNA (~80 nucleotides) that is shaped like a L, but upside down and backwards2. One end has a sequence of 3 nucleotides called the “anti-codon” which recognizes a particular codon on the mRNA (by the base pairing rules)3. The other end of the tRNA carries the correct amino acid (the amino acid coded for by the codon that is recognized by the anti-codon of the tRNAiii. Ribosomes  organelle that coordinates the pairing of tRNAs with their mRNA codons1. Ribosomes are composed of 2 subunits – large and small2. The 2 ribosomal subunits are separate except when translating mRNA into protein 3. Each ribosome has one binding site for mRNA and 3 binding sites for tRNAsa. E siteb. P sitec. A sitee. The process of translation – i. Synthesis of proteins using information in the mRNAii. Occurs in 3 stages:1. Initiation – requires energy input from cell AND enzymesa. mRNA and special tRNA (indicator RNA) binds to a small subunit of ribosomeb. Requires a set of initiation factorsc. Initiator tRNA “anticodon” is base paired with the “start codon” on mRNAd. Large subunit of ribosome binds with initiator tRNA in the “P site”  functioning ribosome2. Elongation – requires energy input from cell AND enzymesa. A tRNA with correct anticodon for the next codon (one after the start codon) binds in the “A site” with its anticodon base pairing with next codonb. A peptide bond forms between the 2 amino acids on the tRNAs in the P and A sites.c. The connected amino acids stay attached to tRNA in A site, but are released from tRNA in P sited. The ribosome moves over one codon so that the tRNA in the P site (now without an amino acid) is in the E site (and is released)e. The tRNA that in the A site is now in the P site still holding the growing amino acid chain, and the A site is over the next codonf. Cycle is repeated until protein is complete