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· A sugar --has five carbon( C ) atoms（pentose sugar）

· A phosphate group --acidic and negatively charged

· A base (1 ring or 2 rings )--contains nitrogen ( N )

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5 possible nitrogenous bases within nucleic acids

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5 possible nitrogenous bases within nucleic acids

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bases in DNA ：

Adenine（A）

Thymine（T）

Cytosine（C）

Guanine（G）

bases in RNA：

Adenine（A）

Uracil（U）

Cytosine（C）

Guanine（G）

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RNA is a single, unbranched polymer of nucleotides with ribose as the pentose sugar in each nucleotide, and linked by covalent sugar-phosphate bonds.

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Unlike DNA, RNA molecules are relatively short with lengths of between a hundred to a few thousand nucleotides.

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Different types of RNA in living organisms:

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Different types of RNA in living organisms:

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· messenger RNA(mRNA)--Codon--formed in the nucleus and transported to the ribosomes in the cytoplasm

· transfer RNA(tRNA)--Anticodon--responsible for transporting amino acids to ribosomes during protein synthesis

· ribosomal （rRNA）-- forms part of ribosomes

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DNA consists of two chains or strands of nucleotides linked to each other by their bases(hydrogen bonds)

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2 strands of nucleotides are parallel to each other, but run in opposite directions

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A helix is a coiled structure that has a constant diameter of 2 nanometres (nm). Because of the two strands, DNA is a double helix.

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· structural framework： sugars and phosphate groups

· Genetic messages（codes for amino acids）： sequences of nitrogenous bases

· A key feature in the unity of life: genetic material in all living organisms is DNA.(deoxyribonucleic acid )

· DNA- mainly found in the nucleus where it forms chromosomes. It is also found in chloroplasts and mitochondria of eukaryotic cells.

· RNA- main component of ribosomes which play an important role in protein synthesis. Some could also be found in the nucleus and cytoplasm.

Viruses--Certain viruses (such as SARS-CoV-2) contain · · · · RNA as their genetic material instead of DNA. These viruses cause a variety of different diseases, such as COVID-19, Ebola, mumps and influenza.Viruses are not considered to be living organisms, since they are unable to replicate by themselves. They are dependent on other living cells for replication and survival. Viruses also lack a cellular structure, which is another reason they are not considered to be living