Biology (Holt)

As the mRNA moves across the ribosome, another ribosome can

find the AUG codon on the same mRNA and begin making a second

copy of the same protein. In this way many copies of the same protein

are made from a single mRNA molecule.

With few exceptions, the genetic code is the same in all organ-

isms. For example, the codon GUC codes for the amino acid valine

in bacteria, in eagles, in plants, and in your own cells. For this rea-

son, the genetic code is often described as being nearly universal. It

appears that all life-forms have a common evolutionary ancestor

with a single genetic code. Some exceptions include the ways cell

organelles that contain DNA (such as mitochondria and chloro-

plasts) and a few microscopic protists read “stop” codons.

214 CHAPTER 10How Proteins Are Made

Analysis

1. Determine the sequence of
   amino acids that will result
   from the translation of the
   segment of mRNA above.


2. Determine the anticodon of
   each tRNA molecule that will
   bind to this mRNA segment.

3.Critical Thinking

Recognizing Patterns

Determine the sequence of

nucleotides in the segment of

DNA from which the mRNA

strand above was transcribed.

4.Critical Thinking

Recognizing Patterns

Determine the sequence of

nucleotides in the segment of

DNA that is complementary to

the DNA segment described

in item 3.

Decoding the Genetic Code

Background

Keratin is one of the proteins in hair. The gene for keratin is

transcribed and translated by certain skin cells. The series of

letters below represents the sequence of nucleotides in a por-

tion of an mRNA molecule transcribed from the gene for ker-

atin. This mRNA strand and the genetic code in Figure 4 can be

used to determine some of the amino acids in keratin.

0100010110
011101010
0010010001001
1100100100010
0000101001001
1101010100100
0101010010010

UUCCGGUAAUUUUCC

Section 1 Review

Distinguishtwo differences between RNA

structure and DNA structure. 6A

Explainhow RNA is made during transcription.

Interpretthe genetic code to determine the

amino acid coded for by the codon CCU. 6A

Comparethe roles of the three different types of

RNA during translation. 6B 9A

Critical ThinkingJustifying Conclusions

Evaluate the following statement: The term

transcriptionis appropriate for describing the

production of RNA, and the term translationis

appropriate for describing the synthesis of proteins.

What is the maximum number

of amino acids that could be coded for by a section

of mRNA with the sequence GUUCAGAACUGU?

A 3 C 6

B 4 D 12

TAKS Test PrepTAKS Test Prep

6B

6A

6B

6B