CK-12-Chemistry Intermediate

http://www.ck12.org Chapter 26. Biochemistry

TABLE26.2:(continued)

1st Base: A 1st Base: G 1st Base: T 1st Base: C

ATC End GTC Gln TTC Lys CTC Glu

ACA Cys GCA Arg TCA Ser CCA Gly

ACG Cys GCG Arg TCG Ser CCG Gly

ACT End GCT Arg TCT Arg CCT Gly

ACC Trp GCC Arg TCC Arg CCC Gly

For example, the table above (Table26.2) indicates that the DNA code word GCA corresponds to the amino acid
arginine, while the DNA code word TCG corresponds to the amino acid serine. Most amino acids are represented
by more than one possible triplet code, but each triplet code yields only one amino acid. Three of the DNA code
words (ATT, ATC, and ACT) are end or termination code words. When one of those codons is reached, the chain of
amino acids is released, and no more are added. Recall that proteins consist of up to a hundred or more amino acids.
A protein that contains 120 amino acids would be encoded by a gene that contains 363 DNA base pairs (3 for each
amino acid, plus a stop codon).

Even with only four different bases, the number of possible nucleotide sequences in a DNA chain is virtually
limitless. The DNA sequence of a particular organism constitutes the genetic blueprint for that organism. This
genetic blueprint is found in the nucleus of each cell of the organism and is passed on from parents to offspring. The
incredible diversity of life on Earth stems from the differences in the genetic code of every living thing.

Lesson Summary

• DNA and RNA are biopolymers found in the nuclei of cells. DNA is the carrier of genetic material, while
  RNA takes part in the translation of that genetic code into specific proteins.


• Nucleotides consist of a phosphate, a 5-membered sugar, and a nitrogen-containing base.


• All DNA nucleotides contain one of four bases: adenine, thymine, guanine, or cytosine. In RNA, uracil is
  substituted for thymine.


• DNA adopts the structure of a double helix, with hydrogen bonds between base pairs of each of the two
  strands. The base pairs are A-T (or A-U in RNA) and G-C.


• The genetic code of DNA provides the information needed to generate all of the proteins produced by a
  particular organism. Each three-member sequence of nucleotides codes for the addition of a specific amino
  acid to a peptide chain.

Lesson Review Questions

Reviewing Concepts

1. What two types of nucleic acids are present in all living cells?


2. What are the three components of a nucleotide?


3. How does ribose differ from deoxyribose?


4. What are the base pairs of DNA? What are the base pairs of RNA?


5. What connects the base of one nucleotide to its complementary base on the other strand?


6. How many bases specify an amino acid in the genetic code?