Nucleic Acids DNA & RNA

What are they ? The 4th type of macromolecules The chemical link between generations The source of genetic information in chromosomes

What do they do ? Dictate amino-acid sequence in proteins Give information to chromosomes, which is then passed from parent to offspring

What are they made of ? Simple units called nucleotides, connected in long chains Nucleotides have 3 parts: 1- 5-Carbon sugar (pentose) 2- Nitrogen containing base (made of C, H and N) 3- A phosphate group ( P ) The P groups make the links that unite the sugars (hence a “sugar-phosphate backbone”

2.6.U1 The nucleic acids DNA and RNA are polymers of nucleotides. A nucelotide: a single unit of a nucleic acid Nucleic acids are very large molecules that are constructed by linking together nucleotides to form a polymer. There are two types of nucleic acid: DNA and RNA.

2.6.U1 The nucleic acids DNA and RNA are polymers of nucleotides. A nucelotide: a single unit of a nucleic acid acidic negatively charged contains nitrogen has one or two rings in it’s structure covalent bond five carbon atoms = a pentose sugar If the sugar is Deoxyribose the polymer is Deoxyribose Nucleic Acid (DNA) If the sugar Ribose the polymer is Ribose Nucleic Acid (RNA) covalent bond

Two types of Nucleotides (depending on the sugar they contain) 1- Ribonucleic acids (RNA) The pentose sugar is Ribose (has a hydroxyl group in the 2nd carbon---OH) 2- Deoxyribonucleic acids (DNA) The pentose sugar is Deoxyribose (has just an hydrogen in the same place--- H) Deoxy = “minus oxygen”

RNA DNA Bases Adenine (A) Guanine (G) Uracil (U) Cytosine (C) 2.6.U2 DNA differs from RNA in the number of strands present, the base composition and the type of pentose. RNA DNA Bases Adenine (A) Guanine (G) Uracil (U) Cytosine (C) Thymine (T) Sugar Ribose Deoxyribose Number of strands Single stranded, and often, but not always, linear in shape Two anti-parallel, complementary strands form a double helix http://commons.wikimedia.org/wiki/File:RiboseAndDeoxy.gif

DNA Nucleotides Composition (3 parts): 1- Deoxyribose sugar (no O in 2nd carbon) 2- Phosphate group 3- One of 4 types of bases (all containing nitrogen): - Adenine - Thymine (Only in DNA) - Cytosine - Guanine

2.6.U1 The nucleic acids DNA and RNA are polymers of nucleotides. There are four nitrogenous bases in DNA: Adenine (A) Guanine (G) Thymine (T) Cytosine (C) RNA Shares the same bases except that Uracil (U) replaces Thymine n.b. when talking about bases always use the full name on the first instance

2.6.U3 DNA is a double helix made of two antiparallel strands of nucleotides linked by hydrogen bonding between complementary base pairs.

RNA Nucleotides Composition ( 3 parts): 1- Ribose sugar (with O in 2nd carbon) 2- Phosphate group 3- One of 4 types of bases (all containing nitrogen): - Adenine - Uracil (only in RNA) - Cytosine - Guanine

2.6.U1 The nucleic acids DNA and RNA are polymers of nucleotides. Nucleotides a linked into a single strand via a condensation reaction bonds are formed between the phosphate of one nucleotide and the pentose sugar of the next The phosphate group (attached to the 5'-C of the sugar) joins with the hydroxyl (OH) group attached to the 3'-C of the sugar This results in a phosphodiester bond between the two nucleotides and the formation of a water molecule Successive condensation reactions between nucleotides results in the formation of a long single strand

DNA vs RNA DNA 1- Deoxyribose sugar 2- Bases: Adenine, Thymine, Cytosine, Guanine 3- Double-stranded helix arrangement RNA 1- Ribose sugar 2- Bases: Adenine, Uracyl, Cytosine, Guanine 4- Single stranded

The Double Helix (DNA) Structural model: Model proposed by Watson & Crick, 1953 Two sugar-phosphate strands, next to each other, but running in opposite directions. Specific Hydrogen bonds occur among bases from one chain to the other: A---T , C---G Due to this specificity, a certain base on one strand indicates a certain base in the other. The 2 strands intertwine, forming a double-helix that winds around a central axis

How DNA Works 1- DNA stores genetic information in segments called genes 2- The DNA code is in Triplet Codons (short sequences of 3 nucleotides each) 3- Certain codons are translated by the cell into certain Amino acids. 4. Thus, the sequence of nucleotides in DNA indicate a sequence of Amino acids in a protein.