THE NUCLEIC ACIDS DNA & RNA

DNA-DeoxyriboNucleic Acid  DNA is the genetic material present in chromosomes  Made up of monomers called “nucleotides” which consist of  A. sugar – deoxyribose  B. phosphate group  C. a nitrogenous base (Adenine, Guanine, Cytosine, Thymine)

Nucleotides Sugars Phosphate group

 The shape of the DNA molecule, as discovered by Watson and Crick, is described as a “twisted ladder.” The sugar and phosphate groups make up the sides of the ladder, and the bases, paired across the ladder, make up the rungs. The Double Helix

Note the size difference in the bases that compose the rungs.

Patterns in the DNA molecule  Because of the differences in the sizes of each base (A & G are double rings, T & C are single rings), and because the width of the DNA molecule remains constant, the bases pair in a specific pattern: A with T, and C with G.  All 46 of our chromosomes contain approximately 5 billion nucleotides, paired in the exact same way each time! The exact sequence of these nucleotides controls the production of all proteins.

DNA replication  DNA replicates prior to mitosis and the first division of meiosis  The double helix of DNA “unzips” down the center of the molecule, and free floating nucleotides pair with their complement on each exposed strand, forming 2 duplicate strands.  Energy for this process comes from ATP, and it is aided by enzymes.

Replication

RNA- RiboNucleic Acid  RNA is the second nucleic acid, responsible for copying and translating the DNA language into actual protein molecules.  It is made up of monomers called nucleotides which consist of:  A. sugar – ribose  B. phosphate group  C. nitrogenous base (Adenine, Guanine, Cytosine, Uracil)

DNA vs. RNA Nucleic acid/nucleotides DeoxyriboseRibose Contains thymine (pairs with adenine) Contains uracil (pairs with adenine) In nucleusIn/out of nucleus Double helixSingle helix Large, single moleculeSmaller, 3 “varieties”

RNA Structure

3 types of RNA  mRNA (messenger)- transcribes nucleotide sequence of the DNA molecule which codes for a particular protein  tRNA (transfer)-translates the DNA sequence into a particular amino acid  rRNA (ribosomal) –binds mRNA to tRNA during protein synthesis in order to combine the amino acids

Protein synthesis  The making of a protein molecule, which takes place on the ribosome, in the cytoplasm.  DNA cannot leave the nucleus, so RNA plays an essential role in this process, beginning with transcription.

Transcription:Reading the Gene  During this process, the information in a specific gene is transcribed, or copied, into a mRNA strand.  It begins when the enzyme, RNA polymerase, unwinds and separates the strands of DNA to expose both strands.  As it reads the gene, complementary RNA bases are attached to the exposed DNA, following the same base-pairing rules as DNA, except in mRNA uracil pairs with the adenine.

Codons  Each of the “words” in an mRNA is made up of 3 adjacent bases, called a codon.  The genetic code is based on codons that each represent a specific amino acid.

Translation: RNA to Proteins  Translation converts the “language” of RNA into the “language” of proteins, and occurs at the ribosomes.  As each codon of mRNA is “read,” a corresponding anticodon of tRNA, with a corresponding amino acid, arrives at the ribosome, and they are bonded together forming a polypeptide (protein).