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Chapter 13 Section 3: RNA and Gene Expression Key Vocabulary Terms Adapted from Holt Biology 2008 RNA Ribonucleic acid, plays a role in protein synthesis Gene Expression The manifestation of the genetic material of an organism in the form of specific traits. Gene expression produces proteins by transcription and translation. Transcription The process of forming a nucleic acid (RNA) by using another molecule as a template. DNA is used to make RNA Codon In mRNA, the three-nucleotide sequence that codes for an amino acid, or signifies a start or a stop signal Chapter 13 Section 3: RNA and Gene Expression Supplementary Words Adapted from Holt Biology 2008 Uracil (U) An organic compound of the pyrimidine family that occurs as a component of ribonucleic acid (RNA), bonds with adenine Transfer RNA (tRNA) An RNA molecule that transfers amino acids to the growing end of a polypeptide chain during translation Ribosomal RNA (rRNA) The RNA component of the ribosome (P site & A site). Ribosomal RNA provides a mechanism for decoding mRNA into amino acids and interacts with tRNAs during translation. Messenger RNA (mRNA) A molecule of RNA encoding a chemical "blueprint" for a protein product. mRNA is transcribed from a DNA template, and carries coding information to the sites of protein synthesis: the ribosome's. RNA polymerase An enzyme that starts (catalyzes) the formation of RNA by using a strand of a DNA molecule as a template Promoter A nucleotide sequence on a DNA molecule to which an RNA polymerase molecule binds, which initiates the transcription of a specific gene Amino acids Any one of 20 different organic molecules that contain a carboxyl and an amino group and that combine to form proteins Genetic code The rule that describes how a sequence of nucleotides specifies the amino acid sequence of a protein It is read in groups of three consecutive nucleotides (triplets) that correspond to specific amino acids. Polypeptide A long chain of several amino acids Anticodon A region of tRNA that consists of three bases complementary to the codon of mRNA Stop codon In an mRNA molecule, a sequence of three nucleotides (UUA, UAG, and UGA) that does not encode an amino acid and therefore stops protein synthesis Chapter 13 Section 3: RNA and Gene Expression Notes Adapted from Holt Biology 2008 Central Dogma –DNA makes more DNA by ____________ Replication Transcription –DNA makes RNA by ___________ –RNA helps make protein by ___________. Translation An Overview of Gene Expression DNA provides the original information from which proteins are made in a cell, but DNA does not directly make proteins. Ribonucleic acid, or RNA, is a second type of nucleic acid which takes the information from DNA and makes proteins. Gene expression produces proteins by transcription and translation. Both stages involve RNA. Your Turn Activity RNA: A Major Player • All of the steps in gene expression involve RNA. • In cells, three types of RNA complement DNA and translate the genetic code into proteins. • Like DNA, RNA is made of nucleotide subunits linked together. RNA differs from DNA in 3 ways: 1st, RNA is composed of one strand of nucleotides DNA= two strands RNA differs from DNA in 3 ways: 2nd, RNA nucleotides contain the fivecarbon sugar ribose. DNA = deoxyribose RNA differs from DNA in 3 ways: 3rd, RNA nucleotides have a nitrogenous base called uracil (U) DNA = base thymine (T) Uracil (U) is complementary to adenine (A) whenever RNA pairs with another nucleic acid. There are 3 main types of RNA: Messenger RNA (mRNA), Transfer RNA (tRNA), & Ribosomal RNA (rRNA). Messenger RNA (mRNA) is produced when DNA is transcribed into RNA. Carries instructions for making a protein, and delivers instructions. Transfer RNA (tRNA) at the site of translation “reads” the instructions carried by the mRNA, then translates the mRNA sequence into protein subunits called amino acids. Ribosomal RNA (rRNA) is an RNA molecule that is part of the structure of ribosomes. Ribosomes are the cellular structure where protein production occurs. 6 Transcription: Reading the Gene During transcription, the information in a specific region of DNA (a gene) is transcribed, or copied, into mRNA. Transcription: Reading the Gene Transcription is carried out by a enzyme called RNA polymerase. 2 Transcription: Reading the Gene Transcription begins when RNA polymerase binds to the specific DNA sequence in the gene that is called the promoter. Transcription: Reading the Gene RNA polymerase then unwinds and separates the two strands of the double helix to expose the DNA bases on each strand. Transcription: Reading the Gene RNA polymerase moves along the bases on the DNA strand and adds complementary RNA bases as it “reads” the DNA of the gene. Transcription: Reading the Gene As RNA polymerase moves down the DNA strand, a single strand of mRNA grows. Transcription: Reading the Gene Behind the moving RNA polymerase, the two strands of DNA close up and re-form the double helix. Transcription is not the same process as replication. Transcription = a new molecule of RNA is made from the DNA. In DNA replication= a new molecule of DNA is made from the DNA. Transcription http://www.idigitalmotion.com/portfolio.htm The Genetic Code: Three-Letter “Words” • codon = three-nucleotide sequence in mRNA Each codon corresponds to 1 of 20 amino acids. • Codons may act as a start or stop signal for translation. 6th The Genetic Code: Three-Letter “Words” • There are 64 mRNA codons. Each codon specifies only one amino acid, but several amino acids have more than one codon. • This system of matching codons and amino acids is called the genetic code. The genetic code is based on codons that each represent a specific amino acid. 4th, 7th The Genetic Code: Three-Letter “Words” There are 64 mRNA codons. Each codon specifies only one amino acid, but several amino acids have more than one codon. 5th Codons in mRNA Translation: RNA to Proteins • Translation – occurs in a sequence of steps, – involves three kinds of RNA – results in a complete polypeptide (protein). • Translation takes place in the cytoplasm • A specific amino acid is added to one end of each tRNA. The other end of the tRNA has an anticodon. • An anticodon is a three-nucleotide sequence on tRNA that is complementary to an mRNA codon. 4&5 Translation: RNA to Proteins, continued • The mRNA joins with a ribosome and tRNA. • A tRNA molecule that has the correct anticodon and amino acid binds to the second codon on the mRNA. • A peptide bond forms between the two amino acids, and the first tRNA is released from the ribosome. • The ribosome then moves one codon down the mRNA. Translation: RNA to Proteins, continued • The amino acid chain continues to grow as each new amino acid binds to the chain and the previous tRNA is released. • This process is repeated until one of three stop codons is reached. – A stop codon does not have an anticodon, so protein production stops. • Many copies of the same protein can be made rapidly from a single mRNA molecule because several ribosomes can translate the same mRNA at the same time. Translation: RNA to Proteins Complexities of Gene Expression • The relationship between genes and their effects is complex. • Some genes are expressed only at certain times or under specific conditions. • Variations and mistakes can occur at each of the steps in replication, transcription, and translation. • The final outcome of gene expression is affected by – the environment of the cells – the presence of other cells – the timing of gene expression A bundle of DNA is supported by two silicon pillars. DNA's double-helix structure is on display for the first time in this electron microscope photograph of a small bundle of DNA strands.