What You ll Learn You will relate the structure of DNA to its function. You will explain the role of DNA in protein production.

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Candice Bridges
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What You ll Learn You will relate the structure of DN to its function. You will explain the role of DN in protein production. You will distinguish among different types of mutations.

lthough the environment influences how an organism develops, the genetic information that is held in the molecules of DN ultimately determines an organism s traits.

Enzymes are critical for an organism s function because they control the chemical reactions needed for life.

1 What You ll Learn You will relate the structure of DN to its function. You will explain the role of DN in protein production. You will distinguish among different types of mutations. Section Objectives: nalyze the structure of DN Determine how the structure of DN enables it to reproduce itself accurately. What is DN? lthough the environment influences how an organism develops, the genetic information that is held in the molecules of DN ultimately determines an organism s traits. DN achieves its control by determining the structure of proteins. What is DN? ll actions, such as eating, running, and even thinking, depend on proteins called enzymes. Enzymes are critical for an organism s function because they control the chemical reactions needed for life. Within the structure of DN is the information for life the complete instructions for manufacturing all the proteins for an organism. DN as the genetic material In 1952 lfred Hershey and Martha hase performed an experiment using radioactively labeled viruses that infect bacteria. These viruses were made of only protein and DN. DN as the genetic material Hershey and hase labeled the virus DN with a radioactive isotope and the virus protein with a different isotope. By following the infection of bacterial cells by the labeled viruses, they demonstrated that DN, rather than protein, entered the cells and caused the bacteria to produce new viruses. DN is a polymer made of repeating subunits called nucleotides. Phosphate group Sugar (deoxyribose) Nitrogenous base Nucleotides have three parts: a simple sugar, a phosphate group, and a nitrogenous base. The simple sugar in DN, called deoxyribose (dee ahk sih RI bos), gives DN its name deoxyribonucleic acid. The phosphate group is composed of one atom of phosphorus surrounded by four oxygen atoms. 1

nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. In DN, there are four possible nitrogenous bases: adenine (), guanine (), cytosine (), and thymine (T).

Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide.

In DN, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine.

Watson and rick also proposed that DN is shaped like a long zipper that is twisted into a coil like a spring. Because DN is composed of two strands twisted together, its shape is called double helix.

2 nitrogenous base is a carbon ring structure that contains one or more atoms of nitrogen. In DN, there are four possible nitrogenous bases: adenine (), guanine (), cytosine (), and thymine (T). denine () uanine () ytosine () Thymine (T) Thus, in DN there are four possible nucleotides, each containing one of these four bases. Nucleotides join together to form long chains, with the phosphate group of one nucleotide bonding to the deoxyribose sugar of an adjacent nucleotide. The phosphate groups and deoxyribose molecules form the backbone of the chain, and the nitrogenous bases stick out like the teeth of a zipper. In DN, the amount of adenine is always equal to the amount of thymine, and the amount of guanine is always equal to the amount of cytosine. The structure of DN In 1953, Watson and rick proposed that DN is made of two chains of nucleotides held together by nitrogenous bases. Watson and rick also proposed that DN is shaped like a long zipper that is twisted into a coil like a spring. Because DN is composed of two strands twisted together, its shape is called double helix. The importance of nucleotide sequences The sequence of nucleotides forms the hromosome unique genetic information of an organism. The closer the relationship is between two organisms, the more similar their DN nucleotide sequences will be. The importance of nucleotide sequences Replication of DN DN Scientists use nucleotide sequences to determine evolutionary relationships among organisms, to determine whether two people are related, and to identify bodies of crime victims. Before a cell can divide by mitosis or meiosis, it must first make a copy of its chromosomes. The DN in the chromosomes is copied in a process called DN replication. Without DN replication, new cells would have only half the DN of their parents. Replication of DN Replication Replication 2

Replication of DN opying DN DN is copied during interphase prior to mitosis and meiosis. It is important that the new copies are exactly like the original molecules.

gene to the sequence of nucleotides in DN. Sequence the steps involved in protein synthesis. enes and Proteins The sequence of nucleotides in DN contain information.

enes and Proteins Some proteins become important structures, such as the filaments in muscle tissue.

3 Replication of DN opying DN DN is copied during interphase prior to mitosis and meiosis. It is important that the new copies are exactly like the original molecules. opying DN Original DN Strand New DN Strand New DN molecule Free Nucleotides Original DN Strand New DN molecule lick this image to view movie Original DN Section Objectives Relate the concept of the gene to the sequence of nucleotides in DN. Sequence the steps involved in protein synthesis. enes and Proteins The sequence of nucleotides in DN contain information. This information is put to work through the production of proteins. Proteins fold into complex, threedimensional shapes to become key cell structures and regulators of cell functions. enes and Proteins Some proteins become important structures, such as the filaments in muscle tissue. Other proteins, such as enzymes, control chemical reactions that perform key life functions breaking down glucose molecules in cellular respiration, digesting food, or making spindle fibers during mitosis. enes and Proteins In fact, enzymes control all the chemical reactions of an organism. Thus, by encoding the instructions for making proteins, DN controls cells. enes and Proteins You learned earlier that proteins are polymers of amino acids. The sequence of nucleotides in each gene contains information for assembling the string of amino acids that make up a single protein. RN RN like DN, is a nucleic acid. RN structure differs from DN structure in three ways. First, RN is single stranded it looks like one-half of a zipper whereas DN is double stranded. 3

RN The sugar in RN is ribose; DN s sugar is deoxyribose.

racil Hydrogen bonds denine racil forms a base pair with adenine in RN, just as thymine does in DN.

They take from DN the instructions on how the protein should be assembled, then amino acid by amino acid they assemble the protein.

On the factory floor, mrn moves to the assembly line, a ribosome.

4 RN The sugar in RN is ribose; DN s sugar is deoxyribose. Ribose RN Both DN and RN contain four nitrogenous bases, but rather than thymine, RN contains a similar base called uracil (). racil Hydrogen bonds denine racil forms a base pair with adenine in RN, just as thymine does in DN. RN DN provides workers with the instructions for making the proteins, and workers build the proteins. The workers for protein synthesis are RN molecules. RN DN provides workers with the instructions for making the proteins, and workers build the proteins. The workers for protein synthesis are RN molecules. They take from DN the instructions on how the protein should be assembled, then amino acid by amino acid they assemble the protein. RN There are three types of RN that help build proteins. Messenger RN (mrn), brings instructions from DN in the nucleus to the cell s factory floor, the cytoplasm. On the factory floor, mrn moves to the assembly line, a ribosome. RN The ribosome, made of ribosomal RN (rrn), binds to the mrn and uses the instructions to assemble the amino acids in the correct order. RN Transfer RN (trn) is the supplier. Transfer RN delivers amino acids to the ribosome to be assembled into a protein. Transcription In the nucleus, enzymes make an RN copy of a portion of a DN strand in a process called transcription. DN strand Transcription RN strand lick image to view movie lick image to view movie B RN strand DN strand 4

5 Transcription The main difference between transcription and DN replication is that transcription results in the formation of one singlestranded RN molecule rather than a doublestranded DN molecule. RN Processing Not all the nucleotides in the DN of eukaryotic cells carry instructions or code for making proteins. enes usually contain many long noncoding nucleotide sequences, called introns, that are scattered among the coding sequences. RN Processing Regions that contain information are called exons because they are expressed. When mrn is transcribed from DN, both introns and exons are copied. The introns must be removed from the mrn before it can function to make a protein. RN Processing Enzymes in the nucleus cut out the intron segments and paste the mrn back together. The mrn then leaves the nucleus and travels to the ribosome. The enetic ode The nucleotide sequence transcribed from DN to a strand of messenger RN acts as a genetic message, the complete information for the building of a protein. s you know, proteins contain chains of amino acids. You could say that the language of proteins uses an alphabet of amino acids. The enetic ode code is needed to convert the language of mrn into the language of proteins. Biochemists began to crack the genetic code when they discovered that a group of three nitrogenous bases in mrn code for one amino acid. Each group is known as a codon. The enetic ode Sixty-four combinations are possible when a sequence of three bases is used; thus, 64 different mrn codons are in the genetic code. The enetic ode The Messenger RN enetic ode First Letter Second Letter Phenylalanine () Serine () Tyrosine () ysteine () Phenylalanine () Serine () Tyrosine () ysteine () Leucine () Serine () Stop () Stop () Leucine () Serine () Stop () Tryptophan () Leucine () Proline () Histadine () rginine () Leucine () Proline () Histadine () rginine () Leucine () Proline () lutamine () rginine () Leucine () Proline () lutamine () rginine () Isoleucine () Threonine () sparagine () Serine () Isoleucine () Threonine () sparagine () Serine () Isoleucine () Threonine () Lysine () rginine () Methionine; Threonine () Lysine () rginine () Start () Valine () lanine () spartate () lycine () Valine () lanine () spartate () lycine () Valine () lanine () lutamate () lycine () Valine () lanine () lutamate () lycine () Third Letter The enetic ode Some codons do not code for amino acids; they provide instructions for making the protein. More than one codon can code for the same amino acid. However, for any one codon, there can be only one amino acid. 5

The enetic ode ll organisms use the same genetic code. This provides evidence that all life on Earth evolved from a common origin.

sequence of amino acids in protein is known as translation. Translation takes place at the ribosomes in the cytoplasm.

Translation: From mrn to Protein In eukaryotic cells, mrn is made in the nucleus and travels to the cytoplasm.

The role of transfer RN For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the

mino acid hain of RN nucleotides Transfer RN molecule The role of transfer RN s translation begins, a ribosome attaches to the

When a trn anticodon pairs with the first mrn codon, the two molecules temporarily join together.

6 The enetic ode ll organisms use the same genetic code. This provides evidence that all life on Earth evolved from a common origin. Translation: From mrn to Protein The process of converting the information in a sequence of nitrogenous bases in mrn into a sequence of amino acids in protein is known as translation. Translation takes place at the ribosomes in the cytoplasm. In prokaryotic cells, which have no nucleus, the mrn is made in the cytoplasm. Translation: From mrn to Protein In eukaryotic cells, mrn is made in the nucleus and travels to the cytoplasm. In cytoplasm, a ribosome attaches to the strand of mrn like a clothespin clamped onto a clothesline. The role of transfer RN For proteins to be built, the 20 different amino acids dissolved in the cytoplasm must be brought to the ribosomes. This is the role of transfer RN. The role of transfer RN Each trn molecule attaches to only one type of amino acid. mino acid hain of RN nucleotides Transfer RN molecule The role of transfer RN s translation begins, a ribosome attaches to the starting end of the mrn strand. Then, trn molecules, each carrying a specific amino acid, approach the ribosome. When a trn anticodon pairs with the first mrn codon, the two molecules temporarily join together. nticondon The role of transfer RN Ribosome The role of transfer RN sually, the first codon on mrn is, which codes for the amino acid methionine. signals the start of protein synthesis. When this signal is given, the ribosome slides along the mrn to the next codon. The role of transfer RN trn anticodon Methionine mrn codon 6

The role of transfer RN new trn molecule carrying an amino acid pairs with the second mrn codon. The role of transfer RN The amino acids are joined when a peptide bond is formed between them.

7 The role of transfer RN new trn molecule carrying an amino acid pairs with the second mrn codon. The role of transfer RN The amino acids are joined when a peptide bond is formed between them. The role of transfer RN chain of amino acids is formed until the stop codon is reached on the mrn strand. lanine Methionine lanine Peptide bond Stop codon Section Objectives: ategorize the different kinds of mutations that can occur in DN. ompare the effects of different kinds of mutations on cells and organisms. Mutations Organisms have evolved many ways to protect their DN from changes. In spite of these mechanisms, however, changes in the DN occasionally do occur. ny change in DN sequence is called a mutation. Mutations can be caused by errors in replication, transcription, cell division, or by external agents. Mutations in reproductive cells Mutations can affect the reproductive cells of an organism by changing the sequence of nucleotides within a gene in a sperm or an egg cell. If this cell takes part in fertilization, the altered gene would become part of the genetic makeup of the offspring. Mutations in reproductive cells The mutation may produce a new trait or it may result in a protein that does not work correctly. Sometimes, the mutation results in a protein that is nonfunctional, and the embryo may not survive. In some rare cases a gene mutation may have positive effects. Mutations in body cells What happens if powerful radiation, such as gamma radiation, hits the DN of a nonreproductive cell, a cell of the body such as in skin, muscle, or bone? If the cell s DN is changed, this mutation would not be passed on to offspring. However, the mutation may cause problems for the individual. Mutations in body cells Damage to a gene may impair the function of the cell. When that cell divides, the new cells also will have the same mutation. Some mutations of DN in body cells affect genes that control cell division. This can result in the cells growing and dividing rapidly, producing cancer. 7

8 The effects of point mutations point mutation is a change in a single base pair in DN. change in a single nitrogenous base can change the entire structure of a protein because a change in a single amino acid can affect the shape of the protein. The effects of point mutations mrn Normal Protein Replace with Point mrn mutation Protein Stop Stop The enetic ode The Messenger RN enetic ode First Letter Second Letter Phenylalanine () Serine () Tyrosine () ysteine () Phenylalanine () Serine () Tyrosine () ysteine () Leucine () Serine () Stop () Stop () Leucine () Serine () Stop () Tryptophan () Leucine () Proline () Histadine () rginine () Leucine () Proline () Histadine () rginine () Leucine () Proline () lutamine () rginine () Leucine () Proline () lutamine () rginine () Isoleucine () Threonine () sparagine () Serine () Isoleucine () Threonine () sparagine () Serine () Isoleucine () Threonine () Lysine () rginine () Methionine; Threonine () Lysine () rginine () Start () Valine () lanine () spartate () lycine () Valine () lanine () spartate () lycine () Valine () lanine () lutamate () lycine () Valine () lanine () lutamate () lycine () Third Letter Frameshift mutations What would happen if a single base were lost from a DN strand? This new sequence with the deleted base would be transcribed into mrn. But then, the mrn would be out of position by one base. s a result, every codon after the deleted base would be different. Frameshift mutations Frameshift mrn mutation Protein Deletion of Frameshift mutations This mutation would cause nearly every amino acid in the protein after the deletion to be changed. mutation in which a single base is added or deleted from DN is called a frameshift mutation because it shifts the reading of codons by one base. hromosomal lterations hanges may occur in chromosomes as well as in genes. lterations to chromosomes may occur in a variety of ways. Structural changes in chromosomes are called chromosomal mutations. hromosomal lterations hromosomal mutations occur in all living organisms, but they are especially common in plants. Few chromosomal mutations are passed on to the next generation because the zygote usually dies. hromosomal lterations In cases where the zygote lives and develops, the mature organism is often sterile and thus incapable of producing offspring. When a part of a chromosome is left out, a deletion occurs. B D E F H B E F H Deletion 8

9 hromosomal lterations When part of a chromatid breaks off and attaches to its sister chromatid, an insertion occurs. The result is a duplication of genes on the same chromosome. B D E F H B B D E F H Insertion hromosomal lterations When part of a chromosome breaks off and reattaches backwards, an inversion occurs. B D E F H Inversion D B E F H hromosomal lterations When part of one chromosome breaks off and is added to a different chromosome, a translocation occurs. B D E F H W X B D E F W XY Z Y Z Translocation H auses of Mutations Some mutations seem to just happen, perhaps as a mistake in base pairing during DN replication. These mutations are said to be spontaneous. However, many mutations are caused by factors in the environment. auses of Mutations ny agent that can cause a change in DN is called a mutagen. Mutagens include radiation, chemicals, and even high temperatures. Forms of radiation, such as X rays, cosmic rays, ultraviolet light, and nuclear radiation, are dangerous mutagens because the energy they contain can damage or break apart DN. auses of Mutations The breaking and reforming of a doublestranded DN molecule can result in deletions. hemical mutagens include dioxins, asbestos, benzene, and formaldehyde, substances that are commonly found in buildings and in the environment. hemical mutagens usually cause substitution mutations. Repairing DN Repair mechanisms that fix mutations in cells have evolved. Enzymes proofread the DN and replace incorrect nucleotides with correct nucleotides. These repair mechanisms work extremely well, but they are not perfect. The greater the exposure to a mutagen such as V light, the more likely is the chance that a mistake will not be corrected. 9

UNIT 3. Chapter 12 From DNA to Proteins

UNIT 3. Chapter 12 From DNA to Proteins UNI 3 hapter 12 From DN to Proteins hapter 12: From DN to Proteins I. Identifying DN as the enetic Material (8.1). riffith finds a transforming principle 1. riffith experimented with the bacteria that