Nucleic AcidsNucleic acids are responsible for passing information from one generation to the next. There are two types of nucleic acids - DNA and RNA. Nucleotides are the monomers for nucleic acids, while DNA/RNA are the polymers.
DNADNA is the abbreviation for deoxyribonucleic acid. It is the only biomolecule that contains instructions for its own replication. Within every DNA molecule there are thousands of genes which controls the synthesis of RNA (more specifically, messenger RNA, or mRNA). DNA molecules are in the form of a double helix.
RNARNA is the abbreivation for ribonucleic acid. It has a single strand shape. There are many forms of RNA, but for protein synthesis purposes, we are concerned with mRNA (messenger RNA). mRNA relays the genetic information from the nucleus to ribosomes in the cytoplasm to instruct protein synthesis.
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Structure of Nucleic Acids
![Picture](/uploads/4/0/2/7/40270815/114759.png?250)
Each DNA monomer is made up of three parts: a pentose sugar, a phosphate group, and a nitrogenous base.
The pentose sugars in DNA are deoxyribose, while those in RNA are ribose. As their name implies, deoxyribose has one less oxygen atom than ribose.
The phosphate groups are the same for DNA and RNA.
There are two types of nitrogenous bases: purines and pyrimidines. Purines have 2 rings, while pyrimidines have only 1 ring. There are two purine bases, adenine (A) and guanine (G), both of which can be used in DNA and RNA. There are three pyrimidine bases, cytosine (C), thymine (T), uracil (U). Cytosine is found in both DNA and RNA, but thymine is only found in DNA while uracil is only found in RNA. This means there are always four different bases whether it's in DNA and RNA.
DNA: A, C, G, T
RNA: A, C, G, U
In the DNA double helix, nitrogenous bases form hydrogen bonds to each other. A always bonds to T (in DNA) or U (in RNA). C always bonds to G. Note that Purines always form bonds with pyrimidines. This is called complementary base pairing.
DNA: A-T, C-G
RNA: A-U, C-G
The combination of pentose sugar, nitrogenous base, and phosphate group makes an entire nucleotide monomer. The pentose sugar and nitrogenous base together without the phosphate group is called the nucleoside.
The pentose sugars in DNA are deoxyribose, while those in RNA are ribose. As their name implies, deoxyribose has one less oxygen atom than ribose.
The phosphate groups are the same for DNA and RNA.
There are two types of nitrogenous bases: purines and pyrimidines. Purines have 2 rings, while pyrimidines have only 1 ring. There are two purine bases, adenine (A) and guanine (G), both of which can be used in DNA and RNA. There are three pyrimidine bases, cytosine (C), thymine (T), uracil (U). Cytosine is found in both DNA and RNA, but thymine is only found in DNA while uracil is only found in RNA. This means there are always four different bases whether it's in DNA and RNA.
DNA: A, C, G, T
RNA: A, C, G, U
In the DNA double helix, nitrogenous bases form hydrogen bonds to each other. A always bonds to T (in DNA) or U (in RNA). C always bonds to G. Note that Purines always form bonds with pyrimidines. This is called complementary base pairing.
DNA: A-T, C-G
RNA: A-U, C-G
The combination of pentose sugar, nitrogenous base, and phosphate group makes an entire nucleotide monomer. The pentose sugar and nitrogenous base together without the phosphate group is called the nucleoside.
Antiparallel StrandsThe phosphate part of the nucleotide is called the 5' end, and the part where it is attached to the phosphate group of the previous nucleotide is called the 3' end (see right image).
If the DNA strand to the left is has its 5' end facing up, then its complementary strand must have its 5' end facing down. Because of this, we say that DNA strands run antiparallel to each other. This is an important concept in DNA replication, which will be discussed in the future. |