Unit 4, Lesson 15
Lesson 15 - Taking a Deeper Look at Cellular Nucleic Acids and their Functions
Student Performance Objectives
1. Explain DNA replication.
2. Compare DNA replication with DNA's transcription of a message to m-RNA.
3. Describe translation utilizing the following terms: ribosome, m-RNA, t-RNA's, amino acids,
codons and anticodons.
4. Define mutation and describe the effect of a deletion or substitution mutation on the m-RNA
A. DNA is a most remarkable molecule with the ability to make exact copies of itself, a process called
replication and clearly important for the continuation of life from generation to generation. Read about
this at the following website:
1. DNA replication is semiconservative. To see what this means go to
http://www.brooklyn.cuny.edu/bc/ahp/BioInfo/REP/DR.Semi.html Also see
2. DNA codes for the synthesis of proteins. To get an overview of this process, go to
http://www.johnkyrk.com/DNAtranscription.html for a more detailed view.
B. The DNA molecule, in the cell's nucleus, sends a messenger molecule to the ribosomes,
located in the cell's cytoplasm, to begin the process of protein synthesis. The messenger
molecule formed is called messenger RNA. Its formation is called transcription. S ee an
animation of the process at
C. The messenger RNA molecule, interacting with the ribosomes can take part in the synthesis
of proteins, a process called translation.
D. Animations of the process of translation may be found at
http://www.johnkyrk.com/DNAtranslation.html which is very detailed but revealing.
F. The occurrence of a mutation changes the sequence of bases in a DNA molecule. This
changes the sequences of bases on a messenger RNA molecule transcribed from the mutated
DNA molecule. The resultant protein synthesized from the translation of this m-RNA
molecule will have an altered sequence of amino acids. This protein might function normally,
might function suboptimally, or might not function at all. Read more about mutations at:
1. Deletion mutations - a base is removed from the sequence which alters the reading
2. Substitution mutation- one base is substituted for another. The reading frame is not
altered but the codon containing the substituted base is not different and may code for
a different amino acid than the original.