8.1 Identifying DNA as the Genetic Material DNA was identified as the genetic material through a series of experiments.

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1 8 HER From to roteins etting Ready to Learn review Key oncepts 8.1 Identifying as the enetic Material was identified as the genetic material through a series of experiments. 8.2 Structure of structure is the same in all organisms. 8.3 Replication replication copies the genetic information of a cell. 8.4 ranscription ranscription converts a gene into a single-stranded R molecule. 8.5 ranslation ranslation converts an mr message into a polypeptide, or protein. 8.6 ene Expression and Regulation ene expression is carefully regulated in both prokaryotic and eukaryotic cells. 8.7 Mutations Mutations are changes in that may or may not affect phenotype. Review cademic Vocabulary Write the correct word for each definition. enzyme ribosome protein 1. enzyme : biological catalyst 2. ribosome : site of protein synthesis 3. protein : shape determines its function review Biology Vocabulary See how many key terms from this chapter you already know. Rewrite each phrase, using a different word or words for the words in bold. hrase Rewritten with ifferent Words 1. replication allows every new cell to have a complete set of. copying allows every new cell to have a complete set of. 2. Mutagens such as UV light can result in skin cancer. 3. R is found in both the nucleus and the cytoplasm. agents that cause changes to such as UV light can result in skin cancer. is found in both the nucleus and the cytoplasm. a type of single-stranded nucleic acid 122 BI_LEIR687797_08.indd 122 4/13/11 11:20:10 M

2 section 8.1 Identifying as the enetic Material > Virginia standards BIO.1 he student will demonstrate an understanding of scientific reasoning, logic, and the nature of science by planning and conducting investigations. BIO.1.EKS-23; BIO.5.EKS-11 Key oncept was identified as the genetic material through a series of experiments. was identified as the genetic material relatively recently in the 1950s. his section reviews three research projects that all added up to this discovery: 1) riffith s research, 2) very s research, and 3) Hershey and hase s research. ogether, these scientists findings led to the conclusion that is the genetic material. riffith finds a transforming principle. In 1928 a British microbiologist named Frederick riffith investigated two forms of the bacterium that causes pneumonia*. He injected the two different forms into mice. One form of the bacterium killed the mice, but the other form did not. riffith used heat to kill a sample of the ly disease-causing bacteria and then mixed the bacteria with a sample of live, harmless bacteria. He injected this mixture into mice. Even though the disease-causing bacteria that he injected were heatkilled, the mice still died. riffith concluded that some material must have been transferred from the bacteria to the live harmless bacteria. Whatever that material was, itlive con bacteria tained information that changed the harmlessrbacteria into disease-causing bacteria. riffith called this mystery material the transforming principle. riffith s Experiments he S form of the bacterium is ly; the R form is not. + live + live + live live ransform means to change. Why do you think riffith called the mystery material the transforming principle? Because the material changed, or transformed, the harmless bacteria into ly bacteria. live * cademic Vocabulary pneumonia a disease that affects the lungs Interactive Reader BI_LEIR687797_08.indd /13/11 11:20:13 M

3 very identifies as the transforming principle. Oswald very worked with other biologists for over ten years trying to figure out what riffith s transforming principle was. hey thought the transforming principle could be protein or it could be. very s group found a way to separate this mystery material from samples of bacteria. hey ran several tests on the material. heir tests and findings are shown in the chart below. very s Research ES RESUL 1. Standard chemical test for protein and found presence of, but no protein 2. ests to determine the amounts of nitrogen () and phosphorous () 3. ests to see which enzymes could break down the substance the proportions of and matched the makeup of, but not protein enzymes that break down broke down this substance, but enzymes that break down protein did not break down the substance very and his group concluded that must be the transforming principle, or genetic material. Some scientists questioned this conclusion. Scientists also wondered whether was the genetic material for all organisms or just for bacteria. On the chart above, highlight three reasons very concluded that the mystery material was, not protein. Hershey and hase confirm that is the genetic material. In 1952 the work of lfred Hershey and Martha hase provided evidence that is indeed the genetic material. Hershey and hase studied a type of virus that infects bacteria, called a bacteriophage (bak-eer-ee-uh-fayj), or phage for short. phage infects a bacterium by inserting its genetic material into the bacterium. Hershey and hase wanted to find out what material the phage inserted into a bacterium was it protein or was it? hey conducted two experiments. In the first experiment, Hershey and hase marked the phages proteins with radioactive labels. When the phages infected the bacteria, no significant radioactivity was found inside the bacteria. In the second experiment, Hershey and hase marked the phages with radioactive labels. When the phages infected the Bacteriophages are viruses that infect bacteria. protein coat 124 Mcougal Littell Biology

4 bacteria, high levels of radioactivity were found inside the bacteria. hese results finally convinced scientists that the genetic material is and not protein. What is the material that phages insert into bacteria? 8.1 Vocabulary heck bacteriophage Mark It Up o back and highlight each sentence that has a vocabulary word in bold. 1. How did Hershey and hase s research with bacteriophages help confirm that is the genetic material? 8.1 he Big icture Because they are made of protein and, and Hershey and hase found that the was the part of the phage that was injected to spread the virus-and therefore contained genetic material. 2. omplete the following chart about the three main research projects that led to the identification of as the genetic material. Researchers names Summary of research Summary of onclusions riffith used harmless and ly pneumonia bacteria found a transforming principle very did a variety of tests on samples of genetic material that they isolated from bacteria found that the material was, not protein Hershey and hase identified the substance that phages inject into bacteria confirmed that, not protein is the genetic material 3. Which of the three experiments gave evidence that protein was not the genetic material? very s and Hershey and hase s experiments Interactive Reader 125

5 section 8.2 Structure of Key oncept structure is the same in all organisms. is composed of four types of nucleotides. Since the 1920s scientists have known the chemical parts of the molecule. is a very long polymer, or chain of repeating units. he units, or monomers, that make up are called nucleotides (OO-klee-oh-tydz). Each nucleotide has three parts: a phosphate group, a base, and a sugar. here are four different types of nucleotides: cytosine (), thymine (), adenine (), and guanine (). ll of the nucleotides contain a phosphate group and a deoxyribose sugar. hey differ in their nitrogen-containing bases, as shown in the table below. otice that thymine () and cytosine () have nitrogencontaining bases with a single-ring structure. denine () and guanine () are bases with a double-ring structure. single molecule of human is made of billions of nucleotides. VISUL VOB he small units, or monomers, that make up a strand of are called nucleotides. ucleotides have three parts. phosphate group deoxyribose (sugar) > Virginia standards BIO.5.e he student will investigate and understand common mechanisms of inheritance and protein synthesis. Key concepts include historical development of the structural model of. BIO.1.EKS-23; BIO.5.EKS-11; BIO.5.EKS-12 nitrogen-containing base phosphate group: one phosphorus with four oxygens deoxyribose: ring-shaped sugar nitrogen-containing base: a single or double ring built around nitrogen atoms and carbon atoms he Four itrogen-ontaining Bases of YRIMIIES = SILE RI URIES = OUBLE RI ame of Base Structural Formula Model ame of Base Structural Formula Model thymine H 3 O H H H O adenine H H H 2 H cytosine H H 2 H H O guanine H H O H H 2 ircle the names of the four nucleotides shown in the table above. 126 Mcougal Littell Biology

6 Watson and rick developed an accurate* model of s three-dimensional structure. For a long time, scientists hypothesized that in all organisms was made up of equal amounts of the four nucleotides. hen Erwin hargaff found that the proportion of the bases differs from organism to organism. In the of each organism, the amount of equals the amount of, and the amount of equals the amount of. hen in the early 1950s, the scientists Rosalind Franklin and Maurice Wilkins used x-rays to make a kind of photograph of molecules. hese photographs did not show what looks like, but they showed patterns that gave clues about s structure. round the same time, the scientists James Watson and Francis rick were working together to figure out structure, too. Based on the work of other scientists, they hypothesized that might have a spiral, or helix (HEE-lihks), shape. Watson and rick saw Franklin s photos and used the information to complete their model of structure. In pril 1953 Watson and rick published their model in a paper in the journal ature. hey found that nucleotides fit together in a double helix. wo strands of wrap around each other like a twisted ladder. * cademic Vocabulary accurate correct What new information did Watson and rick contribute to science? the three-dimensional shape of a double helix ucleotides always pair in the same way. Each side of the double helix is a long strand of phosphates and sugars, connected by covalent bonds. he two sides of the double helix are held to each other by hydrogen bonds that form between the bases in the middle. Each individual hydrogen bond is weak, but together they are strong enough to hold the shape of. he bases of the two strands always bond according to the base pairing rules: pairs with, and pairs with. he bases pair in this way because of hydrogen bonds. otice that and form two hydrogen bonds, whereas and form three. o help remember the rules of base pairing, notice that the letters and have a similar shape. Once you know that and pair together, you know that and also pair together. If the sequence of bases on one strand is, the other strand will be. Watson and rick s model showed in the shape of a double helix. Interactive Reader 127

7 Base airing Rules he base pairing rules describe how nucleotides form pairs in. always pairs with, and always pairs with. his ribbonlike part represents the phosphate groups and deoxyribose sugar molecules that make up s backbone. hydrogen bond covalent bond he nitrogen-containing bases bond in the middle to form the rungs of the ladder. nucleotide double helix What sequence of bases would pair with? 8.2 Vocabulary heck base pairing rules 1. Label the drawing at the right with the terms nucleotide, base pairing rules, and double helix. Write each term and draw a line that connects the term to the appropriate part of the drawing. 8.2 he Big icture 2. What are the three different parts of a nucleotide? deoxyribose (sugar), and a nitrogen-containing base 3. What are the names of the four nucleotides? thymine Mark It Up o back and highlight each sentence that has a vocabulary word in bold. phosphate group, adenine, cytosine, guanine, and 4. Use the base pairing rules to write the sequence that would pair with the following sequence: nucleotide ouble Helix base pairing rules 128 Mcougal Littell Biology