Genetics Lecture Notes PDF

# Nucleic Acids (DNA and RNA) ## 1. Nucleic Acids (DNA and RNA) * DNA saves genetic information and is found in the nucleus of the cell. * RNA is transient in the cytoplasm of the cell and is needed for the creation of proteins. mRNA is an informative molecule and other types of RNA are functiona...

# Nucleic Acids (DNA and RNA) ## 1. Nucleic Acids (DNA and RNA) * DNA saves genetic information and is found in the nucleus of the cell. * RNA is transient in the cytoplasm of the cell and is needed for the creation of proteins. mRNA is an informative molecule and other types of RNA are functional. * Nucleic Acids are polymers of monomers called nucleotides (nt.). * Nucleotide polymer creates DNA, which creates a chromosome. ## 2. Nucleotides Occurrence in the Cell: * **Monomers** * Energetic compounds: ATP, ADP, AMP, GTP, GDP, GMP, CTP, CDP, CMP, TTP, TDP, TMP. * **Polymers:** * DNA and RNA ## 3. Nucleic Acids: Nucleotide & Nucleoside * **Nucleotide** * Consists of three parts: Sugar + Nitrogen base + Phosphate group * **Nucleoside** * Consists of three parts: Sugar + Nitrogen base * **Sugar is oxyribose pentose in RNA** * **Sugar is deoxyribose pentose in DNA ** ## 4. Nucleoside composition * Pentose Sugar + N.B. without phosphate * Ribonucleoside (R = OH; cytidine) * 2'-Deoxyribonucleoside (R = H; deoxycytidine) ## 5. Nucleotide composition * Pentose Sugar + N.B. + phosphate * Nitrogenous base (A, T, C, G) ## 6. Pentose sugars in RNA and DNA: * There are two related pentose sugars: * RNA contains ribose. * DNA contains deoxyribose. * The sugars have their carbon atoms numbered with primes to distinguish them from the nitrogen bases. * **Ribose in RNA** has an oxygen atom at the 2' position of the pentose ring. * **Deoxyribose in DNA** does not have an oxygen atom in the 2' position of the pentose ring. ## 7. Nucleic Acids * There are two types of nucleic acids: * RNA (Ribonucleic acid) = (Ribonucleotide)_n- A U C G. * DNA (Deoxyribonucleic acid) = (Deoxyribonucleotide)_n- A T C G. * These are polymers consisting of long chains of monomers called *nucleotides* linked in a chain through a **phosphodiester bond**. * A nucleotide consists of a nitrogenous base, a pentose sugar, and a phosphate group. ## 8. Chemical structure of nucleic acids: Monomers * **2'-Deoxyribonucleotide** - deoxyadenosine 5'-triphosphate (dATP) * **Ribonucleotide** - cytidine 5'-monophosphate (CMP) * **Pyrimidines** are linked to the *pentose sugar* through C1 to C'1. * **Purines** are linked to the *pentose sugar* through N9 to C'1. ## 9. Nitrogen Bases * **Purines** are composed of two C,N rings (C'1-N9) * Adenine (A) * Guanine (G) * **Pyrimidines** are composed of one C,N ring (C'1-N1) * Cytosine (C) * Uracil (U; R = H) * Thymine (T; R =CH₂) ## 10. RBONUCLEOTIDES * **Polymer:** RNA * **Monomer:** energetic compounds * **PURINES** * (AMP) adenosine monophosphate * (GMP) guanosine monophosphate * **PYRIMIDINES** * (CMP) cytidine monophosphate * (UMP) uridine monophosphate ## 11. Nomenclature of Nucleotide * **Adenine** = Adenylic acid = dATP = dA or 2'-deoxyadenosine 5'-triphosphate * **Guanine** = Guanylic acid = dGTP or dG or 2'-deoxyguanosine 5'-triphosphate * **Cytosine** = Cytidilic acid = dCTP or dC or 2'-deoxycytosine 5'-triphosphate * **Thymine** = Thymidilic acid = dTTP or dT or 2'-deoxythymidine 5'-triphosphate ## 12. TYPES OF BONDS IN DNA * **Glucosidic bond** between C'1 of sugar and: * N1 of the pyrimidine * N9 of the purines * **Phosphodiester bond:** between C' 3- of one nucleotide and the phosphate group of C'5 of the next nucleotide * **Hydrogen bond:** between each complementary nucleotides * C with G with 3 bonds (strong) * A with T with 2 bonds (weak) ## 13. Formation of the 3' -> 5' phosphodiester bond * **Strong covalent bonds** between a phosphate group and two 5-carbon ring carbohydrates (pentoses) over two ester bonds. * The phosphodiester bond is the *linkage* between the 3' **carbon atom** of one sugar molecule and the 5' carbon of another. ## 14. DNA Helix * DNA is a very large molecule made up of a long chain of sub-units that called *nucleotides*. * **Nucleotides:** Deoxyribose sugar + phosphate + N.B. ## 15. The most common organic bases are: * Adenine (A) * Thymine (T) * Cytosine (C) * Guanine (G) ## 16. Bonding 2 * Adenine bonds with Thymine. * Cytosine bonds with Guanine. ## 17. DNA Properties: Model of Watson and Crick (1953) * It is a 3-D structure. * Two antiparallel polynucleotide chain: one directed from 5' to 3'; the other is in the 3' to 5' direction. * Has the polarity of 3'-OH at one end and 5'phosphate group at the other end of each chain. ## 18. DNA Properties Model of Watson and Crick (1953) * DNA usually consists of a double strand of nucleotides. * The sugar-phosphate backbone is directed outside. * Both strands are held together by chemical bonds between the nitrogen bases that act as stairs of a ladder (hydrogen bonds). ## 19. Bonding 1 * The bases always pair up in the same way. * Adenine bonds with Thymine through two hydrogen bonds. * Cytosine bonds with Guanine through three bonds. ## 20. DNA Properties * According to the Model of Watson and Crick (1953), each round has 10 bases occupying about 34 A. * The diameter of the molecule is 20 A = 2 n.m in the case of the B-form. * It has minor and major grooves.