Protein Synthesis
DNA carries the instructions for the production of proteins. A protein is composed of smaller molecules called amino acids, and the structure and function of the protein is determined by the sequence of its amino acids. The sequence of amino acids, in turn, is determined by the sequence of nucleotide bases in the DNA. A sequence of three nucleotide bases, called a triplet, is the genetic code word, or codon, that specifies a particular amino acid. For instance, the triplet GAC (guanine, adenine, and cytosine) is the codon for the amino acid leucine, and the triplet CAG (cytosine, adenine, and guanine) is the codon for the amino acid valine. A protein consisting of 100 amino acids is thus encoded by a DNA segment consisting of 300 nucleotides. Of the two polynucleotide chains that form a DNA molecule, only one strand, called the sense strand, contains the information needed for the production of a given amino acid sequence. The other strand aids in replication.
Protein synthesis begins with the separation of a DNA molecule into two strands. In a process called transcription, a section of the sense strand acts as a template, or pattern, to produce a new strand called messenger RNA (RNA). The RNA leaves the cell nucleus and attaches to the ribosomes, specialized cellular structures that are the sites of protein synthesis. Amino acids are carried to the ribosomes by another type of RNA, called transfer (RNA). In a process called translation, the amino acids are linked together in a particular sequence, dictated by the RNA, to form a protein.
A gene is a sequence of DNA nucleotides that specify the order of amino acids in a protein via an intermediary mRNA molecule. Substituting one DNA nucleotide with another containing a different base causes all descendant cells or viruses to have the altered nucleotide base sequence. As a result of the substitution, the sequence of amino acids in the resulting protein may also be changed. Such a change in a DNA molecule is called a mutation. Most mutations are the result of errors in the replication process. Exposure of a cell or virus to radiation or to certain chemicals increases the likelihood of mutations.
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Sunday, June 6, 2010
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- How Do We Inherit Our Biological Characteristics
- How are GM foods labeled?
- How are GM foods regulated and what is the govern...
- What are some of the criticisms against GM foods?
- How prevalent are GM crops? What plants are invol...
- What are some of the advantages of GM foods?
- What are genetically-modified foods?
- Reading Chapters In The Genome
- DNA Is Like A Library Of Instructions
- Reading the Sequences
- Unzipping DNA
- The DNA Sequence
- Inheritance
- Tracing Similarities And Differences In Our DNA
- Where Is DNA Found?
- Understanding Gene Testing
- Ethical, Legal, and Social Concerns about DNA Data...
- What are some of the DNA technologies used in fore...
- How is DNA typing done?
- Is DNA effective in identifying persons?
- How does forensic identification work?
- Exceptions to Mendel's Laws
- How Does Inheritance Work?
- Mutations and the Next Generation
- Mechanisms of Genetic Variation and Heredity
- The Influence of DNA Structure and Binding Domains
- Controlling Transcription
- Gene Switching: Turning Genes On and Off
- How Many Genes Do Humans Have?
- Structural Genes, Junk DNA, and Regulatory Sequences
- From Genes to Proteins: Start to Finish
- Gene Prediction Using Computers
- The Core Gene Sequence: Introns and Exons
- Proteins
- Ribonucleic Acids
- Why Study Mitochondria?
- Why Is There a Separate Mitochondrial Genome?
- The Physical Structure of the Human Genome
- WHAT IS A GENOME?
- What is DNA?
- Research and Applications
- Replication
- Protein Synthesis
- Structure
- DNA
- Food Security
- Agriculture and Allied Areas
- Basic Research
- Historical Events in Biotechnology
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- Introduction to "Biotechnology"
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