DNA, RNA & Protein Synthesis

A. DNA and the Genetic Code 1. DNA controls the production of proteins by the order of the nucleotides

2. Watson & Crick discovered the double helix model of DNA

a. DNA is shaped like a twisted ladder and referred to as a “double helix” b. Sides-alternating sugars and phosphates bonded together by a strong covalent bond c. the sugar is deoxyribose (thus the name, deoxyribonucleic acid, or DNA)

d. Rungs-pairs of nitrogen bases (nucleotides) that always pair in the same way Adenine ↔ Thymine Cytosine ↔ Guanine the bases are held together by a weak hydrogen bond

3. DNA Replication a. Hydrogen bonds break, strands separate b. nucleus contains a “chemical pool” of free nucleotides

c. free nucleotides match up with exposed bases d. Each strand of original molecule acts as a template for new DNA e. two identical strands are formed

B. RNA is necessary for protein synthesis Differences between DNA & RNA

1. RNA has ribose sugar, not deoxyribose sugar 2. RNA is single stranded not double stranded

3. RNA has the base uracil, not thymine 4. RNA can leave the nucleus, DNA can’t

C. Protein Synthesis 1. Divided into two parts, transcription and translation

2. Transcription a. DNA unzips and serves as a pattern for mRNA b. RNA nucleotides match up with exposed DNA bases of one strand

c. gene is transcribed (read), mRNA is released and travels to ribosomes in cytoplasm d. DNA molecule closes

3. Translation a. ribosome attaches to a mRNA molecule at the beginning of a coding region

b.tRNA matches up with the mRNA and carries an amino acid with it. c. rRNA brings the mRNA and the tRNA together and links the amino acids into their proper sequence.

d. tRNA is released after the amino acids are linked together e. when the ribosome reaches the end of the mRNA strand translation is over and the newly formed protein molecule is released