Purpose of DNARNA How is DNA information used

Purpose of DNA/RNA

How is DNA information used by the cell? • DNA is information (like a library book) that is used to make proteins. • But DNA cannot leave the nucleus (library). • DNA needs a copy machine to copy the information (RNA).

What is the process that copies DNA to be able to leave the nucleus? Transcription: • RNA transcribes (copies) DNA and leaves the nucleus to make proteins. • Parts of cell involved: m. RNA, DNA, nucleus

What are the steps in the process of Transcription? 1. m. RNA goes into the nucleus and copies (transcribes) a part of the DNA strand. The m. RNA strand is complementary (C-G, A-U) 2. This occurs in the nucleus only, and then m. RNA leaves the nucleus. 3. m. RNA goes to the ribosomes to begin the next step (protein synthesis or translation).

REVIEW • Where does transcription take place in the cell? • In the “book”metaphor, what is RNA? Why ? • What is DNA’s information used to make?

How does m. RNA make proteins? Process called Translation: 1. 3 complex steps 2. m. RNA is the template for the synthesis of proteins 3. Parts of cell involved: m. RNA, t. RNA, ribosome, amino acid 4. Process happens in the cytoplasm, at ribosomes

Translation: Step 1: Initiation • Ribosome binds to m. RNA • Nucleotides are “read” in groups of 3 called a codon • The initiation (start) codon is AUG. • A t. RNA brings in the amino acid Met. (Remember proteins are made of amino acids). • The t. RNA attaches to the m. RNA through the ribosome. • Another t. RNA brings another amino acid (Ala), they are joined through the ribosome. • A peptide bond is made between the two amino acids (Met and Ala). • The t. RNA for Met is released, it goes back to the cytoplasm to get more amino acids.

Translation: Step 2: Elongation • The ribosome moves along the m. RNA. • Elongation of the peptide (amino acid chain) occurs.

Translation: Step 3: Termination • Termination occurs when a stop codon is reached. • There are no t. RNAs for UAA, UAG, or UGA. • Ribosome releases polypeptide into the cytoplasm • Polypeptides are proteins that serve major structural and functional roles for the cell.

Review • What is the name of the process of RNA making proteins? • What are three steps in Protein Synthesis (Translation)? • What four structures (parts of the cell) are involved in translation? • What is the start codon?

Summary of Transcription and Translation