Nucleic Acids and Protein Synthesis

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I. DNA= deoxyribonucleic acid A. Contains Genes = specific locations on DNA. Genes specify proteins and traits (eye color, disease, etc)

DNA is bundled into structures called chromosomes. If the DNA in a person was stretched out it would reach to the sun and back 600 times. It is an extremely long molecule that coils really tight.

B. The Structure of DNA Rosalind Franklin and Maurice Wilkins Produced X-ray diffraction photograph of DNA. Showed that: DNA is a double helix.

James Watson and Francis Crick (1953) Used Franklin’s info to build DNA model Model= double helix of repeating nucleotide monomers

                     ` 1953 2003

c. Nucleotides have three parts: Deoxyribose Sugar Phosphate Group Nitrogen Base (4 kinds) Purines = Adenine (A) & Guanine (G) Pyrimidines = Thymine (T) & Cytosine (C)

How do the nitrogen bases bind?

d.Sugar-phosphate molecules on outside of ladder; paired bases on inside. e.Purines paired to pyrimidines. A is hydrogen-bonded to T G is hydrogen-bonded to C f. Watson and Crick - Nobel Prize in 1954 for their model of DNA.

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II. DNA Replication = process of duplicating a molecule of DNA Begins at a specific sequence of nucleotides DNA is unzipped by DNA Helicase enzyme. Helicase breaks the hydrogen bonds between nitrogen bases. Free floating nucleotides bind with complementary bases.

II. DNA Replication = process of duplicating a molecule of DNA E. DNA polymerase enzyme catalyzes the bonding of sugar and phosphates F. Results in 2 new strands of DNA G. Each new DNA molecule has one old and one new strand (semi-conservative replication) H. Special Enzymes (DNA polymerase) “proofread” and repair any mistakes I. If repairs are not made, the mutations may cause cancer.

I. Replication Errors Do Occur Ability to mutate is requirement for genetic material. Only one error per billion nucleotides.

J. The newly synthesized strand always forms from 5’ to 3’.

Animation of DNA Replication http://207.207.4.198/pub/flash/24/menu.swf ~ 15 minutes

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III. Ribonucleic Acid (RNA) = makes proteins DNA ultimately determines amino acid sequence of proteins. DNA molecule cannot directly control the sequence of amino acids. DNA is restricted to nucleus. Go-between is ribonucleic acid (RNA).

The Structure of RNA Polymer of nucleotides (ribose sugar, Nitrogen base, PO 4 group 2. Unlike DNA, RNA : a) Single-stranded b) Contains the sugar ribose c) Contains the nitrogen base uracil instead of thymine. No “T” in RNA A-U

There are three major classes of RNA. Messenger RNA (mRNA)- takes a message from DNA in nucleus to ribosomes in cytoplasm. Ribosomal RNA (rRNA)- and proteins make up ribosomes where proteins are synthesized. Transfer RNA (tRNA)- transfers a particular amino acid to a ribosome.

IV. Central Dogma of Molecular Biology DNA undergoes transcription to mRNA mRNA undergoes translation to a protein.

V. Transcription =process in which mRNA is made according to the sequence of bases in DNA Occurs in the nucleus. Begins when RNA polymerase (enzyme) binds to a DNA molecule. (Unzips the DNA) Complementary RNA nucleotides pair with DNA nucleotides. RNA polymerase joins the RNA nucleotides together. Terminator sequence causes RNA polymerase to stop. DNA strands rejoin.

VI. Translation = assembling proteins from “info” encoded in mRNA

Takes place in cytoplasm. One language (nucleic acids) is translated into another language (protein). How Genes Code for Amino Acids DNA serves as a template to build RNA mRNA contains the genetic code in the form of codons.

Codons 3 sequential nucleotide bases of mRNA. (43=64) Each codes for an amino acid. There are 64 triplets to code for 20 amino acids. The Code Is Universal AUG is universal start codon. There are three stop codons.

Ribosome attaches to a start codon(AUG). tRNA transfers Amino Acids to the ribosome. tRNA is a single-stranded ribonucleic acid that doubles back on itself to create a cloverleaf structure. At one end it binds to amino acid; at other end it has an anticodon that binds to mRNA codon. Brings the correct amino acid to the codon.

Ribosome moves to next codon and a new tRNA brings next amino acid. A peptide bond is formed between amino acids. Process continues until ribosomes hits a stop codon. Polypeptide (protein) is formed.