How Proteins are Made

I. Decoding the Information in DNA A. Gene – sequence of DNA nucleotides within section of a chromosome that contain instructions or a code to make proteins. B. RNA – ribonucleic acid 1. Contains the sugar ribose (instead of deoxyribose) 2. Is single stranded 3. Has the base uracil (instead of thymine) 4. There are 3 types of RNA a. mRNA – messenger RNA – a portable complement of DNA that travels from the nucleus to the ribosome b. rRNA – ribosomal RNA – part of the structure of a ribosome c. tRNA – transfer RNA – carries or transfers a specific amino acid and contains the anticodon

II. Transcription - Transfer of Information from DNA to RNA A. Transcription – DNA is rewritten into a complementary RNA molecule. B. RNA nucleotides are put together with the help of RNA polymerase. C. DNA RNA C  G A  U T  A G  C

III. The Genetic Code: Three-Nucleotide “Words” A. Codon – group of 3 nucleotides in mRNA which code for a specific amino acid. B. Anticodon – group of three nucleotides on tRNA molecule – is complementary to the codon in mRNA. anticodon

IV. RNA’s Role in Translation A. Translation – mRNA is decoded to form a chain of amino acids. B. During Translation 1. mRNA molecule binds to a ribosome 2. tRNA molecules carry amino acids to the ribosomes according to the codons (3 letters) of the mRNA. 3. The amino acids are joined to form a polypeptide chain which will become a protein

The Genetic Code

V. Gene Regulation and Structure A. Gene Regulation Prokaryotic and eukaryotic cells are able to control which genes are decoded and which are not. B. Protein Synthesis in Prokaryotes 1. In prokaryotes, gene expression is regulated by operons. 2. Gene expression is switched off when repressor proteins block RNA polymerase from transcribing a gene. 3. When an inducer (presence of lactose) is present it binds to the repressor and transcription can continue

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C. Protein Synthesis in Eukaryotes Regulation of genes is more complex in eukaryotes than prokaryotes. In eukaryotes, an enhancer must be activated for a eukaryotic gene to be transcribed. Transcription factors regulate transcripiton by binding to promoters and to RNA polymerase.

D. Intervening DNA in Eukaryotic Genes 1. Introns – segments of DNA that do not code for proteins 2. Exons - segments of DNA that will be decoded and expressed 3. After transcription, the introns are cut out and the exons are spliced together and then translated. 4. Introns add evolutionary flexibility because introns can cause shuffling of exons which can make new genes

VI. Mutations - Changes in DNA A. Mutations in body cells will only affect the individual but mutations in gametes are passed on to offspring. B. Mutations can involve a change in a single nucleotide (point mutation) or an entire gene. 1. Point mutation - a change in a single nucleotide 2. Gene rearrangement – movement of an entire gene 3. Insertion – a sizable length of DNA is inserted into a gene 4. Deletion – segments of a gene are cut 5. Frame shift mutation – mutation that causes a gene to be read in the wrong three nucleotide sequence

The End