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Name Date Class

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The Genetic Code

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1. observe  There are 26 different letters, or characters, in the English

alphabet. How many different characters does Morse code have?

List them.

2. analyze sources of error  In the lab, the letters of the Morse code

message were separated by slash marks. Could you decode and read

the message if there were no slash marks? Explain.

3. predict   Suppose you were missing a small part of the code, just one

or two letters in the Morse code table. Do you think you would still be

able to decode and read the message? Explain.

4. predict  Suppose you were missing a larger part of the code, 10 or

more letters in the Morse code table. Do you think you would still be

able to decode and read the message? Explain.

Name Date Class

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The Genetic Code

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1a. identify  These letters represent the nitrogen bases on one strand of

DNA: GGCTATCCA. What letters would form the other strand of the

helix?

b. explain  How do parents pass traits such as eye color to their offspring?

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[pic] I get it! Now I know that the genetic code of nitrogen bases specifies

[pic] I need extra help with

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2a. review  The (nitrogen base pattern/number of genes/size of DNA)

determines how DNA is replicated.

b. describe  Where in the cell does DNA replication take place?

c. [pic]  What do you think would happen if the DNA code in a

daughter cell did not match the code in the parent cell?

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[pic] I get it! Now I know that DNA replication is the process in which

[pic] I need extra help with

Name Date Class

Chapter 12: Lesson 1: The Genetic Code

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1. Describe the structure of DNA and how it functions in genes.

2. What is the full name of DNA?______________________________________________________________________

3. What molecules make up the sides of a DNA molecule?_____________________ and _____________________

4. What are the pairs of nitrogen bases in DNA?________________________, ___________________, ______________________, and __________________________

5. How are DNA, genes, and chromosomes related?

6. Why is DNA replication important?

Name Date Class

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The Genetic Code

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Paving the Way for Watson and Crick

Many people mistakenly think that James Watson and Francis Crick discovered DNA. In fact, the pair

identified the structure of DNA. A great deal work by earlier scientists helped paved the way for their

groundbreaking discovery.

In the 1920s, Frederick Griffith was credited with discovering a process that he termed the “transforming

principle.” Griffith, who was working on a vaccine to prevent infection in the Spanish flu outbreak

following World War I, showed that genetic information from dead bacteria could be transferred to living

bacteria with the living bacteria expressing the new genetic information.

But scientists still had yet to identify the source of this genetic information. Most thought that genetic

material was contained in cell protein, an idea that persisted for many years. It was not until 1944 when

Oswald Theodore Avery and his colleagues Colin MacLeod and Maclyn McCarty, continuing the work

done by Griffith, identified the DNA molecule as the source of genetic information. Eight years later,

experiments conducted by Alfred Hershey and Martha Chase clearly confirmed that DNA was indeed the

source of genetic material.

In the early 1950s, Maurice Wilkins, working with Raymond gosling, began to explore using X-rays to

photograph DNA. Not long after, Rosalind Franklin refined Wilkins’ pioneering techniques and produced

startling new images of DNA. Franklin’s X-ray photographs came to play an important role in the

formation of Watson and Crick’s hypothesis about the helical structure of DNA. Early in 1953, the two

scientists completed their model and revealed that DNA is a double-helix of two strands, each with a

carbon-phosphate backbone and pairs of nucleotides arranged like rungs on a ladder. Their findings

were published in Nature on April 25, 1953, and ushered in the field of modern genetics.

In 1962, Watson, Crick, and Wilkins were awarded the Nobel Prize in Medicine for their pioneering work

on the structure of DNA. Franklin, who died in 1958, was not eligible to be nominated for the award

because rules state that it cannot be given posthumously.

  1. What did Avery and his colleagues discover? What was the significance of this discovery?

  2. How does this passage demonstrate the idea that a single scientific discovery is often the result of research and contributions by earlier scientists?

  3. Why do you think other scientists who made important discoveries in the field of genetics are not as familiar as Watson and Crick?

Name Date Class

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The Genetic Code

Fill in the blank to complete each statement.

  1. The sides of a DNA molecule are made up of sugar molecules alternating

with _____________ molecules.

  2. Chromosomes are made up mostly of _____________.

  3. In DNA, adenine always pairs with _____________.

  4. Each _____________ on a chromosome contains the information to

code for one specific protein.

  5. Each group of three DNA bases on a gene codes for a single

__________________________.

If the statement is true, write true. If the statement is false, change the underlined word

or words to make the statement true.

  6. _____________ Each gene is located at a specific place on a(n) protein.

  7 _____________ DNA synthesis is the process by which DNA copies itself.

  8. _____________ The process of DNA copying itself begins when the two sides of

the DNA molecule unwind and separate.

  9. _____________ The genetic code is determined by the sizes of the

nitrogen bases.

10. _____________Nitrogen bases are molecules that contain nitrogen and

other elements.

The Genetic Code

Answer Key

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1. Morse code has 2 characters: dot (•) and

dash (–).

2. No, you could not decode and read the

message without the slash marks because you

would not know which pieces of the list of

dots and dashes stood for individual letters of

the alphabet.

3. Yes, I probably could still decode and read the

message even if I were missing one or two

letters of the code. With all the known letters

in the message decoded, I would probably be

able to guess the missing letters.

4. No, I probably could not decode and read the

message if I were missing 10 or more letters

of the code. Depending on which letters were

unknown, there might not be enough of the

message decoded for me to guess the missing

letters.

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DNA is shaped like a twisted ladder, or “double

helix.” the rungs of DNA are made of four kinds

of nitrogen bases: adenine (A), thymine (T),

guanine (G), and cytosine (C). A gene is a section

of a DNA molecule that contains the code—a

series of nitrogen bases in a specific order, such

as ATGACGTAC—for one specific protein. Each

group of three DNA bases codes for one specific

amino acid. The order of these three-base units

determines the order in which amino acids are put

together to form a protein.

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1. deoxyribonucleic acid

2. a sugar molecule and a phosphate molecule

3. Adenine pairs with thymine, and cytosine pairs

with guanine.

4. Chromosomes carry genes, which are made of

DNA.

5. Every cell needs a complete set of instructions,

so DNA must make an accurate copy of itself.

6. a molecule that is made of nitrogen and other

elements and that makes up part of DNA

7. the process by which DNA makes a copy of

itself

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1. Sample: Avery and his colleagues were able to

identify DNA as the source of genetic material.

Prior to this discovery, scientists thought genetic

material came from cell protein.

2. Sample: Without the research done by other

scientists, Watson and Crick may not have been

able to identify the structure of DNA. Avery

continued on work that had been started by

Griffith. Franklin’s work, might not have been

possible if not for Wilkins and gosling. Without

the contributions of Franklin, Watson and Crick

may not have been able to formulate their

hypothesis about DNA’s structure.

3. Sample: Watson and Crick’s discovery ushered

in modern genetics and won them a Nobel

Prize. Therefore, they are more well-known

than the other scientists who came before them

and who helped paved the way for their work.

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|  1. phosphate |  2. DNA |

|  3. thymine |  4. gene |

|  5. amino acid |  6. chromosome |

|  7. replication |  8. true |

|  9. order |10. true |

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Inquiry Warm-Up, Can You Crack the Code?

In the Inquiry Warm-Up, you investigated what a code is, as well as what codes can be

used for. Using what you learned from that activity, answer the questions below.

What Forms the Genetic Code?

How Does DNA Copy Itself?

James Watson and Francis Crick are credited with discovering the structure of DNA.

Read the passage below. Then use a separate sheet of paper to answer the questions

that follow.

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