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DNA and Protein Synthesis California Standards 4 and 5 The Components and Structure of DNA DNA is made up of . A nucleotide is a made up of a a a There are four kinds of bases in in DNA: 1 2 3 4 The backbone of a DNA chain is formed by of each nucleotide. The nucleotides can be joined together in any order. X-Ray Evidence used X-ray diffraction to get information about the structure of DNA. She aimed an at concentrated DNA samples and recorded the scattering pattern of the X-rays on film. The Double Helix Using clues from Franklin’s pattern, built a model that explained how DNA carried information and could be copied. Watson and Crick's model of DNA was a , in which were wound around each other, like a . The Components and Structure of DNA Watson and Crick discovered that can form only between certain base pairs— , and This principle is called of the DNA double helix has all the information needed to by the mechanism of base pairing. In most prokaryotes, DNA replication begins at a single point and continues in two directions. In eukaryotic chromosomes, occurs at hundreds of places. Replication until each chromosome is completely copied. The sites where separation and replication occur are called Duplicating DNA Before a cell divides, it in a process called . Replication ensures that each resulting cell will have a complete set of DNA. DNA Replication During DNA replication, the into two strands, then produces two new complementary strands following the rules of base pairing. Each strand of the double helix of for the new strand. This form of replication is called . How Replication Occurs DNA replication is carried out by that “unzip” a molecule of DNA. base pairs are broken and the two strands of DNA unwind. The principal enzyme involved in DNA replication is joins individual nucleotides to produce a DNA molecule and then “ ” each new DNA strand. Replication can begin in the middle of the DNA chain. The two chains unzip to form a The two chains unzip until both chains have be separated and copied. . As the replication bubble expands, one of the new DNA chains is replicated in This is the “ ” strand. The opposite strand, being formed in the opposite direction is the “ ” strand. It is formed in that are ultimately by an enzyme called DNA ligase attaches all DNA fragments together into a . RNA Function are coded that control the . Genetic messages can be decoded by copying part of the nucleotide sequence from DNA into RNA. . The Structure of RNA RNA consists of a . Each nucleotide is made up of 1 2 3 . There are three main differences between RNA and DNA: The sugar in is instead of deoxyribose. RNA is generally . RNA contains in place of thymine. There are three main types of RNA: 1 2 3 carries copies of instructions for assembling amino acids into proteins. Ribosomes are made up of proteins and During protein construction, each amino acid to the ribosome. transfers Transcription What is transcription? molecules are produced by part of a nucleotide into a complementary sequence in RNA. This process is called . Transcription requires the . During transcription, binds to DNA and the strands. then uses one strand of from which nucleotides are assembled into a strand of RNA. RNA polymerase binds only to regions of DNA known as . Promoters are signals in DNA that indicate to the enzyme to make RNA. RNA Editing The DNA of eukaryotic genes contains sequences of nucleotides, called , that are in coding for proteins. The are called . When RNA molecules are formed, introns and exons are copied from DNA. The of RNA molecules. The exons are the to form The Genetic Code The genetic code is the “language” of mRNA instructions. The code is written using four “letters” ( ). A consists of on mRNA that specify a particular amino acid. specifies a particular that is to be placed on the polypeptide chain. . Some amino acids can be specified by more than one codon. There is one codon that can either specify the amino acid methionine or serve as a for protein synthesis. There are that do not code for any amino acid. These “stop” codons signify the . Translation What is translation? Translation is the message into a Translation takes place on . During translation, the cell uses information from is transcribed in the nucleus, and then enters the cytoplasm where it when an mRNA molecule attaches to a ribosome. As each codon of the mRNA molecule moves through the ribosome, the proper is brought into the ribosome . In the ribosome, the amino acid is transferred to the growing polypeptide chain. molecule carries kind of . In addition to an amino acid, each tRNA molecule has . These bases, called the , are complementary to one mRNA codon. The ribosome binds new tRNA molecules and amino acids as it moves along the mRNA. The process continues until the ribosome reaches a stop codon. . The Roles of RNA and DNA The cell to prepare The DNA stays in the nucleus. The RNA molecules go to the protein building sites in the cytoplasm—the ribosomes. Genes and Proteins . Many proteins are , which catalyze and Proteins are each specifically designed to build or operate a component of a living cell. The sequence of bases in DNA is used as a template for mRNA. The of mRNA specify the sequence of in a protein. Mutations are in the genetic material. Kinds of Mutations Mutations that produce changes in a are known as . Mutations that produce changes in whole chromosomes are known as chromosomal mutations. Gene mutations involving a change in are known as because they occur at a single point in the DNA sequence. Point mutations include . usually affect no more than a . The effects of insertions or deletions are more dramatic. The of a nucleotide causes a shift in the grouping of codons. Changes like these are called . Frameshift mutations may that follows the point of the mutation. Frameshift mutations can so much that it is unable to perform its normal functions. In an , an is inserted into a base sequence. In a , the is deleted and the reading frame is shifted. Manipulating DNA The Tools of Molecular Biology How do scientists make changes to DNA? Scientists use their knowledge of the structure of DNA and its chemical properties to study and change DNA molecules. Scientists use different techniques to: from cells into smaller pieces the sequence of in a DNA molecule of DNA In , biologists make changes in the DNA code of a living organism. DNA Extraction DNA can be extracted from most cells by a simple chemical procedure. The cells are opened and the DNA is separated from the other cell parts. Cutting DNA Most DNA molecules are too large to be analyzed, so biologists using . Each cuts DNA at a of nucleotides. A restriction enzyme will cut a DNA sequence only if it matches the sequence precisely. The locations where the enzyme opens the DNA are called . Using the DNA Sequence Cutting and Pasting Short sequences of DNA can be assembled using . “Synthetic” sequences can be joined to “natural” sequences using enzymes that splice DNA together. These enzymes also make it possible to take a and it to the Such DNA molecules are sometimes called . . Separating DNA In , DNA fragments travel through a , a porous material. The than the longer lengths. Gel electrophoresis can be used to of different organisms or different individuals. Making Copies is a technique that allows biologists to . A biologist adds short pieces of DNA that are complementary to portions of the sequence. DNA is heated to separate its two strands starts making copies of the region between the primers two separated strands Transforming Bacteria can be so the bacteria will . Human is common example. Foreign DNA is first joined to a found in bacteria. These rings are known as . Using restriction enzymes, human the bacteria , and in . Transforming Plant Cells To help improve the quality of many crops, plants receive for a variety of genes. Plants receive genes that make them pesticides. and Transcription Translation