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Unit 5: Genetics Learning Goal 4: Describe how DNA is used by cells to produce proteins. RNA (Ribonucleic Acid) RNA vs. DNA Both consist of long chains of nucleotides. Three main differences: RNA sugar is ribose. RNA is generally singlestranded. RNA contains uracil in place of thymine. Types of RNA Types of RNA Messenger Carries copies of instructions for assembling amino acids into proteins to ribosomes. Ribosomal RNA (rRNA) A form of RNA that makes up ribosomes. Ribosomes are also made up of several dozen proteins. Transfer RNA (mRNA) RNA (tRNA) Transfer each amino acid to the ribosomes as it is specified by coded messages in mRNA. Transcription The process of forming RNA molecules by copying part of the nucleotide sequence of DNA into a complementary sequence in RNA. Transcription Requires RNA polymerase to bind to the DNA and separate the DNA strands. RNA polymerase then uses one strand of DNA to use as a template. “Promoters” are areas on a DNA molecule that an RNA polymerase enzyme will attach. These “promoters” have specific base pairs. Similar signals in DNA cause transcription to stop. RNA editing • Introns Exons Areas of the DNA molecule that are not involved in coding for proteins. DNA sequences that code for proteins. Before mRNA is complete the introns must be cut out and the remaining exons spliced together. The Genetic Code Four different bases. A= Adenine U= Uracil C= Cytosine G= Guanine Read by Codons Three consecutive nucleotides that specify a single amino acid that is to be added to the polypeptide. 64 possible codons. Start and Stop codons Codons = Amino Acids Translation Translation 1. 2. 3. mRNA is transcribed in the nucleus and released into the cytoplasm where it attaches to a ribosome. tRNA carries each amino acid to the ribosome where they attach to one another according to the genetic code forming a polypeptide (protein chain). The process continues until the ribosome reaches one of the three stop codons. The result is a complete polypeptide. Translations Genes and Proteins Genes contain nothing more than instructions for assembling proteins. Many proteins are enzymes, which catalyze and regulate chemical reactions. Causing certain things to be produced such as pigment. Proteins are specifically designed to build or operate a component of a living cell.