BIO: Introduction to Chromosomes, DNA and RNA

General Introduction to DNA and RNA

• DNA Location: Found in the nucleus of eukaryotic cells; in the cytoplasm (nucleoid region) of bacterial cells.

• Central Dogma of Molecular Biology: The flow of genetic information is DNA $<br>ightarrow$ RNA $<br>ightarrow$ Protein.

Nucleotide Structure

• The monomer of nucleic acids (DNA and RNA) is a nucleotide.

• Each nucleotide consists of:

  • $1)$-carbon sugar (pentose).

  • $2)$ Phosphate group (hydrophilic, negatively charged).

  • $3)$ Nitrogenous base.

• Polymerization: Nucleotides link via phosphodiester bonds to form a polymer.

• Ends:

  • $5'$ end: Phosphate group attached to the $5'$ carbon of the sugar.

  • $3'$ end: Hydroxyl group attached to the $3'$ carbon of the sugar.

DNA vs. RNA Structure

• DNA (Deoxyribonucleic acid):

  • Sugar: Deoxyribose.

  • Bases: Adenine (A), Guanine (G), Cytosine (C), Thymine (T).

  • Structure: Double-stranded helix.

• RNA (Ribonucleic acid):

  • Sugar: Ribose.

  • Bases: Adenine (A), Guanine (G), Cytosine (C), Uracil (U).

  • Structure: Single-stranded.

Nitrogenous Bases and Base Pairing

• Purines (two rings): Adenine (A), Guanine (G).

• Pyrimidines (one ring): Cytosine (C), Uracil (U) (in RNA), Thymine (T) (in DNA).

• DNA Base Pairing Rules:

  • Adenine (A) forms $2$ hydrogen bonds with Thymine (T) (A-T).

  • Guanine (G) forms $3$ hydrogen bonds with Cytosine (C) (G-C).

• RNA Base Pairing Rules (e.g., in transcription or RNA folding):

  • Adenine (A) forms $2$ hydrogen bonds with Uracil (U) (A-U).

  • Guanine (G) forms $3$ hydrogen bonds with Cytosine (C) (G-C).

DNA Double Helix Features

• Held together by hydrogen bonds between complementary bases of the two strands.

• Antiparallel: The two strands run in opposite directions, with one in $5' <br>ightarrow 3'$ orientation and the other in $3' <br>ightarrow 5'$ orientation.

Predicting Base Proportions in DNA

• Based on base pairing rules, in a double-stranded DNA molecule:

  • The percentage of Adenine ($$) equals the percentage of Thymine ($$).

  • The percentage of Guanine ($$) equals the percentage of Cytosine ($$).

• Example Calculation: If a DNA segment has $20$ Adenine ($$):

  • Then $$.

  • Remaining percentage for G and C is $100$.

  • Since $$, then $$ and $$.