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What do all of these have in common? Collagen Melanin Hemoglobin Lactase Immunoglobulins Actin & Myosin They are ALL types of Proteins that do “work” that contribute to our genetic traits Protein Synthesis DNA RNA Proteins Honors Biology Ms. Pagodin Review… Summarize the structure and function of genes Describe the function of ribosomes Differentiate between DNA and genes Describe the structure and function of DNA State the base pairing rules Compare RNA & DNA RNA (Ribonucleic Acid) Single Strand of Nucleotides 5 C sugar is ribose Uses the N base uracil (U) instead of thymine (T) 3 Types: Messenger RNA (mRNA) An RNA copy of the gene Carries and delivers genetic info from nucleus to ribosome Ribosomal RNA (rRNA) Components of a ribosome Site of translation Transfer RNA (tRNA) Acts as an interpreter Translates mRNA into amino acid sequences All 3 types of RNA are essential for processing information from DNA to proteins.. Gene Expression or Protein Synthesis Gene Expression Organisms traits are determined by proteins Proteins are assembled according to genes on DNA DNA can not leave the nucleus, but proteins are made in ribosomes, therefore need an intermediate messenger… RNA 2 stages: Transcription – copying DNA info to mRNA (nucleus) Translation – mRNA used to build protein (cytoplasm) Overview Transcription 1. 2. 3. 4. 5. RNA polymerase binds to promoter region of DNA Promoter region – specific sequence of DNA that serves as a START signal DNA unwinds and 2 strands separate only 1 side is used as a template RNA polymerase reads each nucleotide on the 3’ end and pairs it with a complimentary RNA nucleotide Same base pairing rules except “U” pairs with “A” RNA dangles off the enzyme like a tail Proceeds at 60 nt/sec until RNA polymerase reaches a specific STOP sequence RNA is released as a free transcript mRNA Processing Introns are cut out before mRNA leaves the nucleus mRNA is a copy of exons (coding) and introns (non-coding) regions Alternative splicing Introns allow for evolutionary flexibility, genes to shuffle, and limits effects of mutations Add a 5’ cap Binds to ribosome Add a 3’ Poly-A tail 100-300 adenine ribonucleotides Determines how long mRNA will last in the cytoplasm Compare Transcription to DNA Replication Only part of the DNA strand is unwound and used as a template The enzyme RNA polymerase adds ribonucleotides Results in a single RNA strand The Genetic Code Instructions for building a protein are written as codons on mRNA Codons – 3 nt that code for a specific a.a. Codon chart - a.a. and stop signals that are coded by each of 64 possible sequences of mRNA codons Highly Conserved (Universal) – the genetic code is the same in ALL organisms…significance? Ex. GUC codes for the a.a. valine in bacteria, dogs, lizards, humans, etc Reading the codon chart Translation tRNA – one loop has 3 nt sequence called an anticodon Anticodon – 3nt complimentary to codon on mRNA Enables tRNA to temporarily H-bond to mRNA No tRNA w/anticodons for STOP codons UAG, UAA, UGA tRNA also carries the a.a. that corresponds to CODON Ribosomes 1,00’s in cytoplasm 2 rRNA subunits (large and small) bind together to form ribosome 3 Binding Sites A site – where tRNA anticodon binds to complimentary codon of mRNA P site – holds tRNA w/ growing polypeptide chain E site – tRNA exits, leaving a.a. in the “P” site Translation: Initiation Initiator tRNA w/ anticodon UAC binds to small ribosomal subunit mRNA start codon binds to tRNA anticodon and finally a large ribosomal subunit binds to the initiation complex Translation: Elongation Translation: Termination Translation: Assembling the Protein 1. 2. 3. 4. 5. 6. 7. 8. mRNA binds to small rRNA subunit w/start codon, AUG, in the “P” site tRNA w/ anticodon UAC and carrying a.a. methionine binds to start codon The next codon, in “A” site, binds w/ complimentary tRNA (carrying the corresponding a.a.) Enzyme forms a peptide bond between adjacent a.a. tRNA in “P” site now exits via “E” site and is recycled tRNA in the “A” site moves to the “P” site w/ growing polypeptide chain, mRNA moves w/it, therefore a new codon is in the “A" site Process continues until it reaches a STOP codon at the end of the mRNA, there is no anticodon W/nothing in the “A” site, the ribosome is disassembled and the newly made polypeptide is released Protein Synthesis Mutations Mutation – any change in an organism’s genetic material Causes Mutagens – environmental agents that cause mutations after exposure X-rays, UV rays, chemicals Carcinogens – mutagens that lead to cancer Asbestos, benzene, tobacco Types of Mutations Chromosomal Mutations Alterations in chromosome structure Deletion, duplication, inversion, translocation Point Mutations Just one or a few nt changed in a gene Substitution – one nt is replaced by a different nt Ex. UGU UGC (no effect b/c both code for cysteine) UGU UGA (early STOP codon) Frameshift mutations Mutations that cause a gene to be read in the wrong 3 nt sequence Insertions – one or m ore nt added to gene Ex. AAU CGC UUU AGA UCG CUU U Deletions – one or more nt deleted from gene Ex. AAU CGC UUU AUC GCU UU Note * If mutation occurs in an intron it will have no effect *if reading frame is displaced 3 nt, the mutation may have no effect Prokaryotic Gene Regulation Prokaryotic Cells – genes are unbroken set of nt Operon controls gene expression in prokaryotes Cluster of genes that code for proteins w/related functions Lac Operon Lac Operon – genes for lactose digesting enzyme Only want lactose digesting enzymes when lactose is present…or else energy is being wasted transcribing genes Operator – acts like an on/off switch If no molecule is bound to operator, then the gene is “ON” and RNA polymerase can move across When a repressor protein binds to the operator, it blocks the RNA polymerase from transcribing, genes are “OFF” Repressor can be removed by inducer (ex. allolactose), now gene is turned ‘ON” Trp Operon Trp Operon – genes for making tryptophan E.coli would typically get trp from environment, therefore gene only needs to be turned on when trp is not present Eukaryotic Gene Regulation No operons…b/c genes w/similar functions are scattered among different chromosomes Multicellular organisms have different types of cells, all somatic cells contain the same DNA…but what makes them different is which genes are turned on/off Ex. Every cell has hemoglobin genes, but only turned “ON” in rbc Transcription takes place at uncoiled regions of chromosome RNA polymerase cannot bind w/o transcription factors Transcription factors are signaled by 20 messengers that bind to the enhancer site to turn “ON” the gene