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The Genetic Code
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.
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.
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The Genetic Code
What Forms the Genetic Code?
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?
I get it! Now I know that the genetic code of nitrogen bases specifies
I need extra help with _____________________________________________________________
How Does DNA Copy Itself?
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.
What do you think would happen if the DNA code in a
daughter cell did not match the code in the parent cell?
I get it! Now I know that DNA replication is the process in which
I need extra help with ______________________________________________________________
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Chapter 12: Lesson 1: The Genetic Code
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?
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The Genetic Code
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.
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?
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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
4. Chromosomes carry genes, which are made of
DNA.
1. Morse code has 2 characters: dot (•) and
dash (–).
5. Every cell needs a complete set of instructions,
so DNA must make an accurate copy of itself.
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.
6. a molecule that is made of nitrogen and other
elements and that makes up part of DNA
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.
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.
1. deoxyribonucleic acid
2. a sugar molecule and a phosphate molecule
3. Adenine pairs with thymine, and cytosine pairs
with guanine.
7. the process by which DNA makes a copy of
itself
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.
1. phosphate
2. DNA
3. thymine
4. gene
5. amino acid
6. chromosome
7. replication
8. true
9. order
10. true