IMG_0025.jpeg

# Introduction to Genetics ## Chapter 17 ### Figure 17.5 **The relationship between DNA, RNA, and protein synthesis.** - **Nucleus** - DNA strands - Transcription → mRNA - Nuclear pore - Nuclear membrane - **Cytoplasm** - Ribosome - mRNA - Free amino acids - New protein cha...

# Introduction to Genetics ## Chapter 17 ### Figure 17.5 **The relationship between DNA, RNA, and protein synthesis.** - **Nucleus** - DNA strands - Transcription → mRNA - Nuclear pore - Nuclear membrane - **Cytoplasm** - Ribosome - mRNA - Free amino acids - New protein chain - Protein synthesis ### Using the DNA Template Using the DNA as a template, a piece of mRNA is made from the gene to be used. This process is called transcription. The mRNA then leaves the nucleus through the nuclear pores and carries its information to the ribosomes in the cytoplasm. --- ### Transcription #### 17.1 The code is buried within the DNA molecule, and the first step is to open up the helix to expose the bases. Only the gene to be transcribed is opened; the remainder of the chromosome remains coiled. Opening up the helix exposes both DNA strands, but the enzyme that makes the mRNA uses only one of them, so the mRNA molecule is single-stranded and not double-stranded. As the enzyme moves along the opened DNA strand, reading its code, it adds the complementary base to the mRNA. - **Base Pairing:** - If the DNA base is cytosine, guanine is added to the mRNA molecule (and vice versa). - If it is thymine, adenine is added; if it is adenine, uracil is added (remember there is no thymine in RNA, but uracil instead). When the enzyme reaches a "stop" signal, it terminates the synthesis of the mRNA molecule, and the mRNA is released. The DNA is zipped up again by other enzymes, and the mRNA then leaves the nucleus. --- ### Translation #### 17.2 Translation is the synthesis of the final protein using the information carried on mRNA. It takes place on free ribosomes in the cytoplasm and those attached to rough endoplasmic reticulum. First, the mRNA attaches to the ribosome. The ribosome then "reads" the base sequence of the mRNA. - **Protein Synthesis:** - Proteins are built from up to 20 different amino acids. - The base code in RNA is read in triplets, giving a possible 64 base combinations. - Each amino acid has corresponding codons (e.g., starting with a start codon). The ribosome slides along the mRNA, reading the codons, and adds the appropriate amino acids to the growing protein chain until it reaches a stop codon, terminating synthesis and releasing the new protein. ### Figures - **Figure 17.6** - (A) Transcription - (B) Translation --- *Page 479*