A1.2 Nucleic acids

DNA

Deoxyribonucleic acid that carries all the genetic material for living organisms

What is the macromolecule, polymer and monomer of DNA?

Macromolecule → deoxyribonucleic acid

Polymer → polynucleic acid

Monomer → nucleotides

Where is DNA found?

• Mainly found in the nucleus (chromosomes)

• Also in chloroplast and mitochondria of eukaryotes

RNA

Ribonucleic acid (type of DNA) is used in protein synthesis and can be found in cytoplasm and nucleus

• Used as genetic material for some viruses (Covid or HIV)

Components of a nucleotide

1. Pentose sugar (five carbon atoms)

2. Phosphate group (acidic and negatively charged)

3. Nitrogenous base (has 1 or 2 rings in structure)

The nitrogenous base and the phosphate bond to the sugar by covalent bonds

How is the sugar-phosphate backbone linked to form a polymer?

The phosphate of one nucleotide links to the pentose of another through covalent bonds

What are the four nitrogenous bases?

1. Adenine

2. Thymine (Uracil)

3. Cytosine

4. Guanine

The sequence of these bases is how information is stored

RNA form

1. RNA is a polymer

2. The nucleotides are always linked by a condensation reaction

3. The hydroxyl group (OH) of one phosphate is combined with the OH of a pentose

4. OH + H → H2O (water as waste product)

5. The remaining oxygen atom forms covalent bond between the two nucleotides

DNA structure

• Composed of strands/polymers of nucleotides

• Double helix shape

• Has bases A,T,C,G

• Two antiparallel strands

• The pentose sugar is deoxyribose

• Has constant diameter of 2 nanometers

Complementary base pairs

• Adenine and thymine pair together (form 2 hydrogen bonds)

• Cytosine and guanine pair together (form 3 hydrogen bonds)

Differences between DNA and RNA

DNA replication

• Semi-conservative (produces two identical new molecules, containing 1 original and 1 new strand)

• Replicated by complementary base pairing

Gene

Specific section of DNA that genetic information consists of

Gene expression

When a gene has an effect on a cell

How is the information stored in DNA limitless?

• Genetic information is stored in base sequence of one of two strands

• 4 possibilities for each base

• 4² possibilities for a sequence of two bases

• 4^n possibilities for a sequence with n bases

• DNA molecules can be any length

• Stored in very small size, thus making it efficient storage

Codon

• Made of 3 bases

• there are 64 codons

• Most codons specify one amino acid

• One codon signals start of protein synthesis

• 3 codons signal stop

Universal genetic code

All living organisms and viruses use the same genetic code, all codons code for the same amino acids (few minor exceptions)