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SAM Biology M1: DNA

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SAM Biology M1: DNA
M1: DNA
• DNA
- DNA are the chemical unit for genetic information in most organisms.
- DNA are informational macromolecules that are used to store hereditary information that determines functional and structural characteristics of organisms.
- In eukaryotes, the linear DNA is found primarily in the nucleus of cells.
- In prokaryotes (e.g. bacteria), there is one circular loop of double-stranded DNA in cytoplasm.

• General Structure of DNA
- The structure of DNA as a double helix made up of a sequence of complementary bases joined by weak bonds. The bases are attached to a sugar phosphate backbone
- A DNA molecule is made up of subunits / monomers called DNA nucleotides.
- There are 2 types of DNA nucleotides, purines and pyrimidines.
- Purines are double ringed structure: Adenine and Guanine.
- Pyrimidines are single ringed structures: Thymine, Cytosine and Uracil.
- The DNA nucleotides joined to form two DNA polynucleotide strands.
- The 2 strands are anti-parallel.
- Within a single strand, nucleotides are joined together by strong phosphodiester bonds.

- Each strand has alternating sugar-phosphate backbone with nitrogenous bases attached to the sugar molecule.
- Complementary base pairs are formed between bases on the two strands. The complementary bases are joined by weak hydrogen bonds.
- The DNA molecule has a diameter of 2 nm and makes one turn every 10 nucleotides or 3.4nm.
- Genetic information is encoded in the sequence of bases along the strands.

• Complementary Base Pairing Rule
- Cytosine always pairs with Guanine.
- Adenine always pairs with Thymine.

• Chargaff’s Rule
- Each species has identical amounts of Adenine and Thymine bases in their DNA, and also identical amounts of Guanine and Cytosine, A = T; G = C.
- A + G = T + C

• RNA (Ribonucleic Acid)
- It is a single stranded molecule.
- It can be found in nucleus as well as cytoplasm.
- There are three types of RNA: mRNA, tRNA, and rRNA
- The RNA molecule is made up of repeating units or the building blocks called RNA nucleotides.
- Each nucleotide is made up of three components:
 A ribose sugar
 A phosphate group
 A nitrogenous base (either A, U, C, G)
- The RNA molecules are single polynucleotide strands that contain about 80 nucleotides (tRNA) to more than 5000 nucleotides (mRNA).

• Pentose Sugar

• Difference between DNA & RNA

- DNA molecules are double stranded while RNA molecules are single stranded.

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