From DNA to Proteins Lesson 1

Lesson Objectives State the central dogma of molecular biology. Describe the structure of RNA, and identify the three main types of RNA. Give an overview of transcription. Describe the genetic code. Explain how translation occurs.

Central Dogma of Biology DNA is found in chromosomes. –eukaryotic cells, chromosomes always remain in the nucleus –proteins are made at ribosomes in the cell How do the instructions in DNA get to the site of protein synthesis outside the nucleus? –Another type of nucleic acid is responsible. –RNA, or ribonucleic acid –RNA is a small molecule that can squeeze through pores in the nuclear membrane

RNA carries the information from DNA in the nucleus to a ribosome in the cell and then helps assemble the protein Central dogma of molecular biology –DNA → RNA → Protein –the phase itself was coined by Francis Crick

RNA and Protein Synthesis Genes are coded DNA instructions that control the production of proteins within the cell. RNA molecules then carry out processes of making proteins.

Structure of RNA Backbone => 5-C sugar and phosphate group –DNA  deoxyribose –RNA  ribose Single- stranded –DNA  double-stranded 4 Nitrogenous bases –Adenine –Uracil –Cytosine –Guanine

Types of RNA 3 main types of RNA –messenger RNA (mRNA) Carry copies of instructions for assembling amino acids into proteins

–ribosomal RNA (rRNA) Proteins are assembled on ribosomes

–transfer RNA (tRNA) Transfers each amino acid to the ribosomes as specified by the coded message of mRNA

Recall replication makes a complementary copy of the entire DNA molecules before cells reproduce or divide

RNA molecules are complementary copies of part of a nucleotide sequence in DNA that are made through the process of transcription –RNA polymerase catalyzes transcription Transcription

RNA polymerase binds to DNA at very specific sites known as promoters –promoters have specific base sequences to start and stop transcription

RNA Editing Compiles the final mRNA molecule after many eukaryotic genes are transcribed –Introns  pieces that are removed Removed while RNA molecule still in nucleus –Exons  remaining portions Spliced back together to form final mRNA

The Genetic Code Proteins made by joining amino acids into long chains called polypeptides.

Reading the Genetic Code ‘Language’ of mRNA is the GENETIC CODE –RNA  4 different nitrogenous bases: A, U, C, G Genetic Code is read 3 letters at a time –Each ‘word’ is 3 bases long Each 3 letter ‘word’ in mRNA is known as a  codon

Examples of Genetic code RNA sequence –UCGCACGGU Read 3 bases at a time –UCG- CAG- GGU UCG = Serine GGU = Glycine CAG = Glutamine

Translation Ribosomes read mRNA and put together polypeptides  decoding= translation

Recap of Transcription/ Translation

The Roles of RNA and DNA DNA “ master plan” –Remains in nucleus RNA “blueprints” –Goes to protein-building sites in cytoplasm ribosomes

Genes and Proteins Most genes contain only instructions for assembling proteins –Genes that code for enzymes can produce pigments for eye color, etc. –Other enzyme-coding genes produce your red blood cell surface antigen thus determining your blood type –Genes can also regulate rate of growth Many proteins are enzymes, which catalyze and regulate chemical reactions –Proteins are the key to almost everything living cells can do