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Lesson 7.2: True or False

Name___________________ Class______________ Date________

Write true if the statement is true or false if the statement is false.

_____ 1. The process in which cells make proteins is called protein expression.

_____ 2. Transcription takes place in three steps: initiation, elongation, and termination.

_____ 3. Splicing removes introns from mRNA.

_____ 4. A codon can be described as a three-letter genetic “word.”

_____ 5. UAG, UGA, AGU, and UAA are the four stop codons

_____ 6. The anticodon is part of each tRNA molecule.

_____ 7. Initiation of transcription occurs when the enzyme, DNA polymerase, binds to the promoter of a gene.

_____ 8. All known living organisms, except some species of primitive bacteria, have the same genetic code.

_____ 9. Elongation is the addition of amino acids to the mRNA strand.

_____ 10. Translation always begins at an AUG codon.

_____ 11. Many proteins are modified in the Golgi apparatus after translation.

_____ 12. During translation, rRNA brings the amino acids into the ribosome.

_____ 13. Termination of transcription occurs at a stop codon.

_____ 14. Transcription uses DNA as a template to make an RNA molecule.

_____ 15. Translation takes place in a ribosome.

Lesson 7.2: Critical Reading

Name___________________ Class______________ Date________

Read these passages from the text and answer the questions that follow.

The Genetic Code

How is the information in a gene encoded? The answer is the genetic code. The genetic code consists of the sequence of nitrogen bases — A, C, G, T (or U) — in a polynucleotide chain. The four bases make up the “letters” of the genetic code. The letters are combined in groups of three to form code “words,” called codons. Each codon stands for (encodes) one amino acid, unless it codes for a start or stop signal. There are 20 common amino acids in proteins. There are 64 possible codons, more than enough to code for the 20 amino acids. The genetic code is shown in the FlexBook.

Reading the Genetic Code

As shown in the Genetic Code figure (see Figure 7.8 in the FlexBook), the codon AUG codes for the amino acid methionine. This codon is also the start codon that begins translation. The start codon establishes the reading frame of mRNA. The reading frame is the way the letters are divided into codons. After the AUG start codon, the next three letters are read as the second codon. The next three letters after that are read as the third codon, and so on. The mRNA molecule is read, codon by codon, until a stop codon is reached. UAG, UGA, and UAA are all stop codons. They do not code for any amino acids.

Characteristics of the Genetic Code

The genetic code has a number of important characteristics.

  • The genetic code is universal. All known living things have the same genetic code. This shows that all organisms share a common evolutionary history.
  • The genetic code is unambiguous. Each codon codes for just one amino acid (or start or stop). What might happen if codons encoded more than one amino acid?
  • The genetic code is redundant. Most amino acids are encoded by more than one codon. What might be an advantage of having more than one codon for the same amino acid?

Questions

1. What is the genetic code?

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2. Explain the significance of an AUG codon.

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3. Why is the genetic code read three bases at a time?

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4. “The genetic code is universal.” Explain this statement.

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5. What might happen if codons encoded more than one amino acid?

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Lesson 7.2: Multiple Choice

Name___________________ Class______________ Date________

Circle the letter of the correct choice.

  1. How many possible codons exist in the genetic code?
    1. 3
    2. 20
    3. 46
    4. 64
  2. The two processes of protein synthesis are
    1. gene expression and protein expression.
    2. transcription and translation.
    3. replication and translation.
    4. transcription and the genetic code.
  3. For protein synthesis to initiate,
    1. RNA polymerase must bind to a gene's promoter.
    2. nucleotides must be added to the mRNA strand.
    3. the mRNA must be flow from the nucleus to the cytoplasm.
    4. the tRNA and rRNA molecules must be made.
  4. Which of the following terms is most closely associated with a tRNA molecule?
    1. codon
    2. anticodon
    3. transcription
    4. ribosome
  5. Which of the following statements is correct?
    1. Translation occurs in a ribosome when the codons on the mRNA are “read.”
    2. Translation occurs in a ribosome when the anticodons on the mRNA are “read.”
    3. Translation occurs in a ribosome when the codons on the rRNA are “read.”
    4. Transcription occurs in a ribosome when the codons on the mRNA are “read.”
  6. “The genetic code is universal.” This statement means that
    1. each codon codes for just one amino acid.
    2. all known living things have the same genetic code.
    3. most amino acids are encoded by more than one codon.
    4. all of the above
  7. Which of the following statements is correct? (1) Translation always begins with an UAG start codon. (2) The start codon establishes the reading frame of mRNA. (3) The mRNA molecule is read one codon at a time until a stop codon is reached.
    1. 1 only
    2. 2 only
    3. 2 and 3
    4. 1, 2, and 3
  8. Which of the following statements is correct?
    1. Editing changes some of the nucleotides in DNA.
    2. Polyadenylation adds a string of Cs to the mRNA.
    3. Splicing removes introns from mRNA.
    4. all of the above

Lesson 7.2: Vocabulary I

Name___________________ Class______________ Date________

Match the vocabulary word with the proper definition.

Definitions

_____ 1. the process in which cells make proteins

_____ 2. removes introns from mRNA

_____ 3. the sequence of A, C, G, T (or U) bases in a polynucleotide chain

_____ 4. complementary to a strand of DNA

_____ 5. contains an anticodon that is complementary to the codon for an amino acid

_____ 6. RNA → Protein

_____ 7. DNA → RNA

_____ 8. a group of three nitrogen bases

_____ 9. regions of mRNA that code for proteins

_____ 10. regions of mRNA that do not code for proteins

_____ 11. the way the groups of three bases are divided into codons

_____ 12. a region of a gene where RNA polymerase binds

Terms

a. codon

b. exons

c. genetic code

d. introns

e. mRNA

f. promoter

g. protein synthesis

h. reading frame

i. splicing

j. tRNA

k. transcription

l. translation

Lesson 7.2: Vocabulary II

Name___________________ Class______________ Date________

Fill in the blank with the appropriate term.

1. Transcription takes place in the ____________ of the cell.

2. RNA polymerase binds to the ____________ of a gene.

3. A group of three bases in the mRNA is a ____________.

4. Transcription takes place in three steps: initiation, elongation, and ____________.

5. All known living things have the same ____________ code.

6. ____________ is the second part of the central dogma of molecular biology: RNA → Protein.

7. Polyadenylation adds a “tail” of ____________ to the mRNA.

8. AUG is the start codon and it codes for the amino acid ____________.

9. Splicing removes ____________ from mRNA.

10. The mRNA molecule is read, codon by codon, until a ____________ codon is reached.

11. An ____________ of the tRNA is complementary to the codon.

12. Transcription is the transfer of genetic instructions in DNA to ____________.

Lesson 7.2: Critical Writing

Name___________________ Class______________ Date________

Thoroughly answer the question below. Use appropriate academic vocabulary and clear and complete sentences.

Describe the genetic code and its important characteristics.

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