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- During gene expression, the information iin DNA is first transcribed (rewritten) as a molecule of mRNA and then translated into amino acids to build a protein.
- The instructions for building a protein aare written as a series of three-nucleotide sequences called codons. Each codon along the mRNA strand either corresponds to an amino acid or signifies a stop signal.
- Because any of four different nucleotidess may be used at each of the three positions, there are 64 different possible codons in the genetic code. All but two amino acids are represented by two or more codons.
- Unlike a DNA molecule, which is a double chain, a molecule of RNA is a single chain. The sugar in RNA is ribose, which has one more oxygen atom per molecule than deoxyribose. Also in RNA, the base thymine is replaced by the base uracil.
- During transcription, the enzyme RNA polyymerase rewrites the genetic information in DNA as a molecule of messenger RNA. Messenger RNA carries the genetic information from the DNA to the site of translation.
-When translation begins, mRNA is bound to a complete ribosome ready for the first amino acid of the protein chain. Transfer RNA molecules pick up designated amino acids and transfer them to the ribosome for protein synthesis. A triplet nucleotide sequence of tRNA that complements a codon on mRNA is called an anticodon. The amino acids are joined by peptide bonds to form a protein chain.
- Phenotypes result from a combination of pproteins produced by a given set of alleles.
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