Home / IBDP Biology 2025 SL&HL: A1.2 Nucleic acids Study Notes

IBDP Biology 2025 SL&HL: A1.2 Nucleic acids Study Notes

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A1.2.1—DNA as the genetic material of all living organisms

Genetic material is a store of information. If copied, it can be passed from cell to cell and also from parent to offspring. Because genetic material is inherited it is sometimes called hereditary information. All living organisms use DNA to store hereditary information.
The full name for DNA is deoxyribonucleic acid. The other type of nucleic acid is ribonucleic acid or RNA. Nucleic acids were first discovered in the cell nucleus, hence the name. They are very large molecules, made from subunits called nucleotides which link to form a polymer.
Some viruses use RNA as their genetic material, for example, coronaviruses and HIV. This observation does not seem to fit the theory that genes are made of DNA in all living organisms. However, reproduction is a fundamental property of living organisms and viruses cannot reproduce themselves. Instead, they rely on a host cell for this process so they are not considered to be true living organisms. Therefore, they do not falsify the claim that all living organisms use DNA as their genetic material.
DNA is Blueprint of life. Molecule that contains genetic information

two types of nucleic acids used in cells.

  • DNA: deoxyribonucleic acid
  • RNA: ribonucleic acid

two primary functions of nucleic acids.

  • Pass genetic information between generations.
  • Code for protein production

meaning and implication of DNA being the genetic material of all living organisms.

Meaning:

All living organisms use DNA as the genetic material.

Implication:

The use of the genetic code across all forms of life is evidence of universal common ancestry of life. The sequences of DNA in cells can be analyzed and compared to determine evolutionary relationships between organisms. The more similar the sequence, the more closely related the organisms.

RNA viruses do not falsify the claim that all living things use DNA as the genetic material.

Some viruses use RNA as their genetic material. However, because viruses are not made of cells, they are not considered to be living.

A1.2.2—Components of a nucleotide

three components of a nucleotide.

A nucleotide is the monomer subunit of the nucleic acids. A nucleotide has three component parts:

  • A nitrogenous base
  • A 5-carbon “pentose: sugar (ribose or deoxyribose)
  • A phosphate group

label the carbons of a pentose sugar.

The carbons of the sugar component of the nucleotide are numbers clockwise, starting from the oxygen in the ring at the top and the phosphate group to the left.

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