RNA and Protein Synthesis Chapter 12-3

How are proteins made? In molecular terms, genes are coded DNA instructions that control the production of proteins within the cell. (test question) The first step in decoding these genetic messages is to copy part of the nucleotide sequence from DNA into RNA, or ribonucleic acid. These RNA molecules contain coded information for making proteins.

There are three main differences between RNA and DNA: The sugar in RNA is ribose instead of deoxyribose (test question) RNA is generally single- stranded RNA contains uracil in place of thymine.

Three Types of RNA The assembly of amino acids into proteins is controlled by RNA. messenger RNA ribosomal RNA transfer RNA.

Most genes contain instructions for assembling amino acids into proteins. The RNA molecules that carry copies of these instructions are known as messenger RNA (mRNA) because they serve as “messengers” from DNA to the rest of the cell.

Proteins are assembled on ribosomes. Ribosomes are made up of several dozen proteins, as well as a form of RNA known as ribosomal RNA (rRNA).

a third type of RNA molecule transfers each amino acid to the ribosome as it is specified by coded messages in mRNA. These RNA molecules are known as transfer RNA (tRNA). (test question)

Ribosome

Transcription RNA molecules are produced by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA, a process called transcription. (test question) transcription

Codon A codon is a group of three nucleotides on messenger RNA that specify a particular amino acid. (test question) Because there are four different bases, there are 64 possible three-base codons (4 × 4 × 4 = 64).

Genetic code (test question)

Translation The decoding of an mRNA message into a polypeptide chain (protein) is known as translation. Translation takes place on ribosomes. During translation, the cell uses information from messenger RNA to produce proteins. (test question)

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