Name Class Date. Read the passage below. Then answer the questions that follow.

Transcription

1 Active Reading Section: The Structure of DNA Read the passage below. Then answer the questions that follow. In 1928, bacteriologist Frederick Griffith worked with two strains of Streptococcus pneumoniae. The first strain was enclosed in a capsule made of polysaccharides. The capsule helped make the microorganism able to cause disease. The second strain of S. pneumoniae lacked the polysaccharide capsule and did not cause disease. Griffith knew that mice infected with S bacteria grew sick and died, while mice infected with R bacteria were not harmed. To determine if the capsule on the S bacteria was causing the mice to die, Griffith injected the mice with dead S bacteria. The mice remained healthy. Griffith then prepared weakened S bacteria by raising their temperature until the bacteria were heat-killed, meaning they were dead but maintained the capsule. When Griffith injected the mice with the heat-killed S bacteria, the mice still lived. He then mixed the harmless live R bacteria with the harmless heat-killed S bacteria. Mice injected with this mixture died. Somehow, the harmless R bacteria underwent a change and became live, pneumonia-causing S bacteria. This phenomenon is now called transformation, a change in genotype caused when bacterial cells take up foreign genetic material. SKILL: READING EFFECTIVELY 1. What does the term strain refer to in the first sentence? 2. What effect might the polysaccharide capsule have on a bacterium contained within the capsule? 3. What does the term transformation mean? Holt Biology 7 DNA, RNA, and Proteins

2 Active Reading continued 4. What effect did an injection of R bacteria have on the mice Griffith studied? 5. What effect did an injection of heat-killed S bacteria have on the mice Griffith studied? 6. What effect did an injection of live R bacteria mixed with heat-killed S bacteria have on the mice? Inthespaceprovided,writetheletterofthephrasethatbestcompletesthe statement. 7. In order to determine whether the disease-causing properties of the S bacteria could be passed to the harmless R bacteria, Griffith injected mice with a. heat-killed S bacteria. b. live R bacteria. c. heat-killed R bacteria. d. Both (a) and (b) Holt Biology 8 DNA, RNA, and Proteins

3 Active Reading Section: Replication of DNA Read the passage below. Then answer the questions that follow. The process of making a copy of DNA is called DNA replication. The process can be broken down into three steps. Step 1: Before replication can begin, the double helix must unwind. This is accomplished by enzymes called DNA helicases, which open up the double helix by breaking the hydrogen bonds that link the complementary nitrogenous bases. Once the two strands of DNA are separated, additional proteins attach to each strand, holding them apart and preventing them from twisting back into their double-helical shape. The two areas on either end of the DNA where the double helix separates are called replication forks because of their Y shape. Step 2: At the replication fork, enzymes known as DNA polymerases move along each of the DNA strands, adding nucleotides to the exposed nitrogenous bases according to the base-pairing rules. Step 3: The process of DNA replication produces two DNA molecules, each composed of a new and an original strand. The nucleotide sequences in both of these DNA molecules are identical to each other and to the original DNA molecule. SKILL: READING EFFECTIVELY 1. What is replication? 2. When does replication occur? 3. What must occur before replication can begin? Holt Biology 9 DNA, RNA, and Proteins

4 Active Reading continued SKILL: INTERPRETING GRAPHICS 4. The figure below shows DNA replicating. In the space provided, describe what is occurring at each lettered section of the figure. Part a. Part b. Part c. Part a. Part b. Part c. Inthespaceprovided,writetheletterofthetermorphrasethatbestcompletesthe statement. 5. DNA helicases and DNA polymerases are alike in that both are a. nucleotides. b. nitrogenous bases. c. enzymes. d. Both (a) and (b) Holt Biology 10 DNA, RNA, and Proteins

5 Active Reading Section: RNA and Gene Expression Read the passage below. Then answer the questions that follow. Like DNA, ribonucleic acid (RNA) is a nucleic acid a molecule made of nucleotides linked together. RNA differs from DNA in three ways. First, RNA consists of a single strand of nucleotides instead of the two strands found in DNA. Second, RNA nucleotides contain the five-carbon sugar ribose rather than the sugar deoxyribose found in DNA nucleotides. And third, RNA has a nitrogenous base called uracil abbreviated as U instead of the base thymine (T) found in DNA. No thymine (T) bases are found in RNA. Like thymine, uracil is complementary to adenine whenever RNA base-pairs with another nucleic acid. SKILL: RECOGNIZING SIMILARITIES AND DIFFERENCES 1. In the spaces provided, write D if the statement is true of DNA. Write R if the statement is true of RNA. Write B if the statement is true of both DNA and RNA. a. consists of a single strand of nucleotides b. is made of nucleotides linked together c. contains deoxyribose d. has the nitrogenous base uracil e. contains ribose f. is a nucleic acid g. consists of a double strand of nucleotides h. contains a base that pairs with adenine Ananalogyisacomparison.Inthespaceprovided,writetheletterofthetermor phrase that best completes the analogy. 2. RNA is tou as DNA is to a.c b.g c.t d.a Holt Biology 11 DNA, RNA, and Proteins

6 Vocabulary Review Matchthewordsontheleftwiththestatementsontheright. 1. DNA replication 2. DNA helicase 3. DNA polymerase a. enzyme that unwinds the DNA helix b. catalyzes the formation of DNA c. the process of making a copy of DNA Matchthewordsontheleftwiththestatementsontheright. 4. gene 5. nucleotide 6. DNA a. subunit of DNA containing a phosphate, sugar, and a base b. has a double helix c. segment of DNA that codes for a trait Matchthewordsontheleftwiththestatementsontheright. 7. RNA 8. codon 9. gene expression a. a three-nucleotide sequence in DNA b. nucleic acid that plays an important role in building proteins c. the process of gene activation to produce specific traits Using the word bank below, fill in each blank provided. transcription translation purine pyrimidine 10. making RNA from DNA 11. thymine and cytosine 12. making a protein from RNA 13. adenine and guanine Holt Biology 12 Mendel and Heredity

7 Science Skills Interpreting Information Use the figure below to answer questions In the space provided, identify the structures labeled A E. A. B. C. D. E. 2. What do the lines connecting the two strands represent? Why are there three lines connecting the strands in some instances and only two lines in others? 3. Suppose that a strand of DNA has the base sequence ATT CCG. What is the base sequence of the complementary strand? Holt Biology 14 DNA, RNA, and Proteins