DNA & RNA The Nucleic Acids Chapter 4 DNA & RNA The Nucleic Acids Remember: Each chromosome is a very long DNA molecule that contains many genes. The DNA controls the production of proteins within a cell. Gene: A segment of DNA that is part of a chromosome that is responsible for inherited traits such as eye color, hair color, skin color, etc. It directs the protein production that controls the cell. Kendall/Hunt

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DNA: (Deoxyribonucleic Acid): Is an organic molecule composed of nucleotides. Is a molecule that is common to all living things, from bacteria to humans. It is the blueprint of an organism; DNA is made of chains of nucleotides shaped much like that of a spiraling ladder, and they called it a double helix. A DNA molecule can NOT be viewed with a compound light microscope. In 1953, Watson and Crick constructed the first model of DNA, and they called it a double helix. Rosalind Franklin-used x-ray diffraction to determine that a chromosome has DNA in a spiraled shape. Chapter 4 Kendall/Hunt

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Structure of DNA: (DNA is composed of nucleotides.) Chapter 4 Structure of DNA: (DNA is composed of nucleotides.) Nucleotides of DNA have three Parts: 1. Deoxyribose (a five carbon sugar) 2. Phosphate group (these two bond together to make up the sides of the ladder) 3. 1 of 4 Nitrogen Bases Adenine (A) Guanine (G) *These hydrogen, weak, bonds together Cytosine (C) form the rungs of the ladder. Thymine (T) Kendall/Hunt

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Cytosine always bonds with guanine, and Chapter 4 The 2 bases on the same rung of the DNA ladder are referred to as a base pair. In DNA Cytosine always bonds with guanine, and Thymine always bonds with adenine! C=G G=C T=A A=T Kendall/Hunt

1st strand of DNA has T C G A A T T Chapter 4 Base Pairing Rules. The strictness of base-pairing results in 2 strands that are complementary, which means the sequence of bases on one strand determines the sequence of bases on the other strand. Example: 1st strand of DNA has T C G A A T T The other strand must have A G C T T A A All organisms contain chromosomes composed of DNA made up of nucleotides with adenine, thymine, guanine, and cytosine. The reason organisms can be different from each other even though their genetic material is made of the same molecules is because the order of nucleotides in two different organisms are different. It is the sequence of nucleotides that forms the genetic information of an organism. Kendall/Hunt

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Chapter 4 How can organisms be different from each other if their genetic material is made of the same DNA: A, T, C, G? They are the different because the order of nucleotides in the 2 organisms is different. Example: A squirrel differs from a rosebush because the order of nucleotides in its DNA is different. Replication: During mitosis and meiosis the cells divide. Each time a cell divides it must make a copy of its DNA. Replication is the process by which DNA is duplicated, forming two identical copies from one original. Kendall/Hunt

These are the steps of replication: Chapter 4 These are the steps of replication: The enzyme DNA helicase breaks the hydrogen bonds between the nitrogen bases that hold the two strands together, unzipping the DNA molecule. As the DNA continues to unzip, free nucleotides from the surroundings in the nucleus bond to the single strands base pairing. The enzyme DNA polymerase forms the sugar-to-phosphate bonds that connect nucleotides on each strand of DNA. Errors occur once for every billion nucleotides due to DNA Polymerase Replication of DNA doesn’t begin at one end of the molecule and proceed to the other. It occurs simultaneously at many points on the molecule, speeding up to process. Replication is completed when the entire molecule has been unzipped and replicated. Kendall/Hunt

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has one nucleotide strand from the original DNA Chapter 4 Each new DNA molecule has one nucleotide strand from the original DNA molecule (template) and one nucleotide strand that has been newly synthesized (complementary strand) from free nucleotides in the cell. Kendall/Hunt

Gene Expression takes place in 2 stages: Chapter 4 Gene Expression is the use of genetic information in DNA to make proteins. Gene Expression takes place in 2 stages: Transcription is when the RNA copy of a gene is made. Translation is the 2nd stage of gene expression where 3 different kinds of RNA work together to assemble amino acids into a protein molecule. Those 3 different kinds of RNA that work together are mRNA, tRNA, rRNA. Kendall/Hunt

1. RNA is single stranded (DNA is double stranded) Chapter 4 Transcription Transcription is the process of producing RNA (Ribonucleic Acid) from DNA. RNA is the form in which information moves from DNA in the nucleus to the ribosomes in the cytoplasm. The process of transcription is similar to the process of replication, but RNA differs from DNA in 3 ways. 1. RNA is single stranded (DNA is double stranded) 2. RNA has ribose as the sugar (DNA has deoxyribose as the sugar 3. RNA has four nitrogen bases, but Thymine is replaced with Uracil Kendall/Hunt

It makes up the ribosomes, which is the site of protein synthesis Chapter 4 There are 3 Types of RNA: mRNA-messenger RNA: It carries the information from DNA (in the nucleus) out into the cytoplasm tRNA-transfer RNA: It brings amino acids to the ribosomes so they can be assembled into proteins. rRNA-ribosomal RNA: It makes up the ribosomes, which is the site of protein synthesis Kendall/Hunt

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Chapter 4 The Genetic Code Remember that DNA’s purpose is to provide a blueprint for making proteins. Proteins are built from chains of smaller molecules called amino acids, and there are 20 of them. Also recall that there are only four nitrogen bases. So how can four bases code for 20 amino acids? If one base coded for an amino acid there could only be four amino acids. If two bases coded for an amino acid there could be up to 16 amino acids. The answer is that each strand of DNA is read in sets of three nitrogen bases, called a codon. By reading in groups of three bases there are 64 combinations possible. Of these 61 codes for amino acids, and the remaining three are signals to stop the synthesis of amino acids. More than one codon can code for an amino acid, but for only one codon, there can only be one amino acid. This is called the DNA Code. Kendall/Hunt

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Protein Synthesis Equation: Chapter 4 Protein Synthesis Equation: DNA mRNA Protein transcription translation Translation Translation (or protein synthesis, gene expression) is the process of converting the information in a sequence of nitrogen bases in mRNA into a sequence of amino acids that make up a protein. Kendall/Hunt

The steps of translation are: The first codon of the mRNA strand attaches to a ribosome (rRNA). Then a tRNA molecule carrying a specific amino acid approaches the ribosome. The tRNA molecule has a special section called an anti-codon that is complementary to the codon on the mRNA molecule. The first codon on the mRNA is often AUG, which codes for the amino acid methionine. AUG signals the start of protein synthesis. Next the ribosome slides down the mRNA strand to the next codon, and a new tRNA molecule (carrying another amino acid) with a complimentary anti-codon will pair with the codon from the mRNA strand. Chapter 4 Kendall/Hunt

The steps of translation are: Chapter 4 The steps of translation are: When the first and second amino acids are in place, an enzyme joins them by forming a peptide bond between them. This process continues forming a chain of amino acids until the ribosome reaches a stop codon on the mRNA strand. The chain of amino acids are now considered a protein. The type of protein synthesized by a cell is determined by the sequence of amino acids. The order of events that leads to genetic expression: Protein synthesis DNA RNA amino acids protein Kendall/Hunt

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SUBSTITUTION: INSERTION: DELETION: Chapter 4 Mutations: Gene Mutation – mutation where just one gene is changed. May happen when one nucleotide is substituted for another nucleotide or when a nucleotide is added or taken away from a gene. This might cause a protein to change so much that it can’t function properly. *Frame Shift Mutations* (Point Mutations) Ex: THE RAT HID AND THE CAT SAT AND GOT FAT. SUBSTITUTION: Ex: THE PAT HID AND THE CAT SAT AND GOT FAT. INSERTION: Ex: THE RAT HIX DAN DTH ECA TSA TAN DGO TFA T DELETION: Ex: THE RAH IDA NDT HEC ATS ATA NDG OTF AT Kendall/Hunt

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Mutagens increase the incidence of mutation. Chapter 4 Causes of mutations: Mutagens increase the incidence of mutation. Mutagens that cause cancer are called carcinogens. Examples of these: radiation from the sun and tanning booths, radiation from x-rays, tobacco, asbestos, and benzene. Kendall/Hunt

Chromosome mutation –involves a change in the Chromosome mutation –involves a change in the structure or number of chromosomes Examples of chromosomal mutations: duplication, deletion, inversion, and translocation. If this occurs during meiosis, the mutations can be passed on to the offspring since the mutation is in the sex chromosomes. Chapter 4 Kendall/Hunt