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• Human chromosomes: 50->250 million base pairs. • Average gene: 3000 base pairs. • <5% of DNA codes for protein. 1 What is a Gene? Short stretch of DNA on chromosome. • Two parts: • Regulatory region Coding region DNA Information in genes used to make proteins. • Two Stages: • • Transcription • Translation 2 12-3 Protein Synthesis 3 DNA vs. Double stranded Sugar = deoxyribose Thymine (no Uracil) Stays in nucleus One type Same copy in the cell all the time RNA Single stranded Sugar = ribose Uracil (instead of Thymine) Nucleus & cytoplasm 3 types (mRNA, tRNA, rRNA) Disposable copies 4 5 Ribose vs. Deoxyribose 6 RNA many functions but mostly just protein synthesis three main types of RNA: messenger RNA, ribosomal RNA, and transfer RNA 7 Types of RNA 8 mRNA RNA molecules that carry copies of the DNA instructions = mRNA messenger RNA (mRNA) = serve as “messengers” from DNA to the rest of the cell 9 Transcription & Translation 10 Transcription (DNA mRNA) RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA required enzyme = RNA polymerase 1. RNA polymerase binds to DNA (in nucleus) 2. separates the DNA strands 3. RNA polymerase then uses one strand of DNA as a template 4. nucleotides are assembled into a strand of mRNA Transcription Animation 11 TRANSCRIPTION Similar to DNA replication, but different. 1. Copies only one of the two strands. 2. Makes a copy as RNA, not DNA. 12 csadaksjdfllasdailsdflRaiseyourhandifyoucan readthis.aksdjfjasdkjaskklasdjfkkjajdfiodlskj 13 Where does RNA start? csadaksjdfllasdailsdflRaiseyourhandifyoucanreadthis.aksdjfjasd kjaskklasdjfkkjajdfiodlskj Need punctuation to identify where coding region begins and ends: promoters - signals in DNA that indicate where the enzyme should bind (“start sequence”). Similar signals in DNA cause transcription to stop when the new RNA molecule is completed. 14 RNA Editing Intron = intervening sequence of DNA; does not code for a protein Exon = expressed sequence of DNA; codes for a protein When RNA molecules are formed, both the introns and the exons are copied from the DNA – introns are cut out of RNA molecules while they are still in the nucleus – exons are then spliced back together to form the final mRNA 15 16 The Genetic Code Proteins = long chains of amino acids (polypeptides) polypeptide = combination of any or all of the 20 different amino acids properties of proteins are determined by the order in which different amino acids are joined together to produce polypeptides 17 The “language” of mRNA instructions is called the genetic code RNA contains four different bases: A, U, C, and G Letters read “3” at a time = codon Codon = a group of three nucleotides on messenger RNA that specify a particular amino acid. 18 Translation (mRNA tRNA amino acid chain) Occurs at the Ribosome mRNA = instructions for the order of the amino acid sequence Ribosome = reads the instructions of the mRNA 19 Translation DNA/RNA Adenine Cytosine Guanine Thymine/Uracil Amino Acid Alanine Arginine Asparagine Aspartate Cysteine Glutamine Glutamate Glycine Histidine Isoleucine Leucine Lysine Methionine Phenylalanine Proline Serine Threonine Tyrosine Tryptophan Valine 20 rRNA Ribosomes are made up of several dozen proteins, as well as a form of RNA known as ribosomal RNA (rRNA). 21 tRNA During the construction of a protein, a third type of RNA molecule transfers each amino acid to the ribosome – as specified by coded messages in mRNA. These RNA molecules are known as transfer RNA (tRNA). 22 Identify the players at work 3 1 2 4 23 Steps of Translation mRNA is released from the nucleus enters cytoplasm 2. mRNA attaches to the ribosome 3. mRNA codons move through the ribosome proper amino acid brought by tRNA 4. Amino acids are bound together polypeptide chain 1. 24 Each tRNA carries only one type of amino acid The three bases on tRNA = anticodon (complementary to mRNA) 25 26 The ribosome forms peptide bonds between the neighboring amino acids It also breaks the bonds between tRNA and the amino acids Translation ends when a “stop” codon is reached 27 28 Translation Animation 29 30 Bases in DNA/RNA form triplet code Codon Table: U U First base A G GUU GUC GUA GUG Phe (F) Leu (L) Leu (L) Ile (I) Met (M) Start Val (V) UCU UCC UCA UCG CCU CCC CCA CCG ACU ACC ACA ACG UAU Tyr (Y) UAC UAA Stop UAG Stop CAU His (H) CAC Pro (P) CAA Gln (Q) CAG AAU Asn (N) AAC Thr (T) AAA AAG Lys (K) Ser (S) GCU GCC Ala (A) GCA GCG GAU GAC GAA GAG Asp (D) Glu (E) G UGU Cys (C) UGC UGA Stop UGG Trp (W) CGU CGC Arg (R) CGA CGG AGU Ser (S) AGC AGA AGG Arg (R) U C A G U C A G U C A G GGU GGC GGA GGG U C A G Gly (G) Third base C UUU UUC UUA UUG CUU CUC CUA CUG AUU AUC AUA AUG Second Base C A 31 What amino acids are made? Use the mRNA strand on the Genetic Code Chart DNA: TAC AAA CAC GGA CCA ACT (coding strand) mRNA: AUG UUU GUG CCU GGU UGA tRNA: UAC AAA CAC GGA CCA ACU Amino acids: Methionine – Phenylalanine – Valine - Proline - Glycine - STOP 32 33