The final group of macromolecules to examine consist of nucleic acids, DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). Each nucleic acid contains carbon (C), hydrogen (H), oxygen (O), nitrogen (N), and phosphorus (P). Nucleic acids are macromolecules that store and transfer genetic information in cells. They are large, complex polymers formed by linking nucleotides into long chains, similar to the long amino acid chains of proteins.
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Nucleotides play an important role in many processes of the cell, including storage and the transmission of genetic information and energy. A single nucleotide is a three-part molecule made of (1) pentose sugar, (2) one or more phosphate groups, and (3) a carbon-nitrogen ring structure called a nitrogenous base.
Other important Nucleotides
The smallest nucleotides include the energy-transferring compounds ATP (adenosine triphosphate) and ADP (adenosine diphosphate). A closely related nucleotide is cyclic AMP (cyclic adenosine monophophate, or cAMP), is an important molecule in the transfer of signals between the extracellular environment and the cell. Other energy transferring nucleotide-containing molcules, include NAD (nicotinamide adenine dinucleotide) and FAD (flavin adenine dinucleotide). Both molecules participate in the production of ATP that occurs in cellular mitochondria.
Pentose (5-carbon) sugar
Every nucleotide has 1 of two possible sugars: either ribose or deoxyribose (de-, without; oxy-, oxygen). Nucleic acids are named for the sugar they contain. The five carbon sugar for Deoxyribonucleic (DNA) acid is deoxyribose and it is ribose for Ribonucleic acid (RNA).
Nitrogenous Bases: Purines and Pyrimidines
A phosphate functional group and a nitrogenous base are attached to the pentose sugar. There are 2 types of nitrogenous bases: the purines and the pyrimidines. Double-ring nitrogenous bases are called purines and include adenine (A) and guanine (G). Single ring nitrogenous bases are called pyrimidines and include cytosine (C), uracil (U), and thymine (T)…use the acronym C-U-T to remember these single ring bases.
Creating a Nucleotide Polymer...also known as a Nucleic Acid
Both polymers of DNA and RNA are formed by linking nucleotides together through covalent bonds. The 5 carbon sugar of one nucleotide links to the phosphate of the next nucleotide, creating a chain, or backbone of alternating sugar-phosphate-sugar-phosphate groups. The nitrogenous bases extend toward the inside of the chain or backbone.
Deoxyribonucleic acid (DNA) is a double stranded nucleic acid and it is organized into chromosomes found within the nucleus of the cell. A small circular strand of DNA is also found within the mitochondria of a cell. The nucleotides that construct DNA contain deoxyribose sugar, a phosphate, and one of 4 nitrogenous bases: adenine, guanine, cytosine, or thymine. DNA does not contain uracil.
To get an idea of how DNA is constructed, imagine a ladder…The upright (hand rails) represent alternating sugars and phosphates, with steps attached to sugars. These steps are paired nitrogenous bases (held together by hydrogen bonds) that match up specifically according to complementary base pairing rules- adenine (A) and thymine (T) are always together, and guanine (G) and cytosine are always on a step together. Now imagine twisting the ladder into a spiral staircase. This image represents the classical shape of DNA.
Ribonucleic acid (RNA) is a single stranded nucleic acid located both within the cell nucleus and within the cytoplasm of the cell. The nucleotides that comprise RNA molecules are composed of ribose sugar, a phosphate, and one of 4 nitrogenous bases: adenine (A), guanine (G), cytosine (C), or uracil (U). RNA does not contain thymine (T).
Differences between DNA and RNA
The table below offers a comparison of the components of DNA and RNA:
Click on the link below to play a DNA game: The Double Helix educational game and related reading are based on the 1962 Nobel Prize in Physiology or Medicine, which was awarded for the discovery of the molecular structure of DNA – the double helix.
Brief Overview of the Function of DNA and RNA working together…
DNA contains the instructions needed for an organism to develop, survive and reproduce. To carry out these functions, DNA sequences must be converted into messages that can be used to produce proteins. The organic nitrogenous bases of DNA store information in the form of a molecular code that provides instructions for building your proteins. A length of DNA with instructions for a single polypeptide is a gene. These instructions are what you inherit from your parents- half from your mother and half from your father.
RNA's job is to carry out the DNA's instructions. Imagine DNA as the blueprint for building a protein, and RNA is analogous to the workers that do the building. RNA accomplishes this building by existing in three major types: messenger RNA (mRNA), ribosomal RNA (rRNA), and transfer RNA (tRNA).
Click on the following link for a brief overview of How a Collagen Protein is made: