Nucleic Acids, DNA replication and protein synthesis.

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How does DNA direct a cell’s activities? How does a cell in your liver “know” it’s a liver cell and not a brain cell or kidney cell. How can all this information needed to regulate the cell’s activities be stuffed into a tiny nucleus?

To begin to find the answer to all these questions, an in-depth in the biological molecules nucleic acids needs to be established.

An organism has some form of nucleic acid that is the chemical carrier of its genetic information. There are two types of nucleic acids, deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) that code for all the information that determines the nature of the organism’s cells. In fact DNA codes for all the instructions needed for the cell to perform different functions.

Nucleic acids are one of the several macromolecules in the body in addition to facts, proteins and carbohydrates.  Nucleic acids are polymers made up of individual molecules linked together in long chains. These molecules are known as nucleotides and the long chain is known as polynucleotides.

Nucleotides itself can be further broken down to three components:

  • A pentose sugar
  • A nitrogen base
  • A phosphate group


Diagram 1 shows a nucleotide

As mentioned above there are two types of nucleic acids: DNA & RNA. DNA stores genetic information, and RNA allows that information to be made use of in the cell.


Both DNA and RNA contain nucleotides with similar components. In RNA the sugar components is ribose and deoxyribose in DNA. The prefix ‘deoxy’ means that an oxygen atom is missing from one of the ribose carbon atom.

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When a sugar bonds together with a nitrogen base, it creates a structure known as a nucleoside. There are five nitrogen bases found in RNA and DNA. These bases are divided into two categories based on their molecular structure

  1. Purines (adenine & guanine)
  2. Pyrimidines (thymine, cytosine & uracil)

Diagram 2 shows the nitrogen bases found in RNA and DNA




In 1953, James Watson and Francis Crick proposed a structure for ...

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This is overall quite well written. There is a little confusion in some places about what happens in eukaryotes vs prokaryotes, and a few notable absences (e.g. mention of the code for a start codon, which is arguably more important than the promoter sequence. There are a few silly mistakes in here, which makes the whole piece seem a bit rushed, but in general the material is well understood. There are a couple of small biological misunderstandings e.g. about what the nucleus actually protects genomic DNA from. At my (Russell group) university, this would score 4/5.