Bio Chemistry

The rule for the pairing of nitrogen-containing bases of the polynucleotide chains that form the DNA molecule is pyrimidine base binds to purine base, under the condition that thymine (T) binds to adenine (A), and cytosine (C) binds to guanine (G).

In RNA, there is no binding between nitrogen-containing bases. That is because RNA is formed of only one polynucleotide chain; differently, DNA is formed of two chains. It is not correct so to question about base pairing in RNA.

Nucleic Acid Review - Image Diversity: DNA base paring

The DNA molecule is formed by two polynucleotide chains bound in antiparallel mode (5’-3’ to 3’-5’) and forming a helical structure.

Nucleic Acid Review - Image Diversity: DNA double helix

To form the DNA molecule, purine bases bind to pyrimidine bases by intermolecular bonds called hydrogen bonds. Hydrogen bonds occur when there is hydrogen near one of these electronegative elements: fluorine, oxygen, or nitrogen.

In such conditions hydrogen looks like having, lost electron for those elements and a very strong polarization is created. The highly positive hydrogen attracts pairs of electrons of other molecules making a hydrogen bond.

Ideally, a DNA molecule should replicate in a perfect way. Sometimes however failures in the duplication occur, with alteration (deletion, addition, or substitution) of one or more nucleotides in the molecule.

Those mistakes, or mutations, therefore make changes in the protein synthesis process too. For example, the production of an important protein for cells or tissues may be suppressed new utile or inutile proteins can be created, etc. The mistake in the DNA duplication and the resulting production of altered genetic material are some of the main creative forces for the biological evolution and the diversity of species.

DNA is not completely autonomous in its duplication process because the replication does not occur without enzymatic activity. Therefore, it is not entirely correct to assert that DNA self-replicates.

The fact that the DNA molecule is made of two polynucleotide chains whose nitrogen-containing bases form hydrogen bonds facilitates the duplication of the molecule. During the DNA replication, the binding of the two chains is broken and each of them serves as template for the formation of a new nucleotide sequence along it, with the help of the enzyme DNA polymerase and obeying the pairing rule A-T, C-G. At the end of the process two double helix of DNA are produced, each made of an original template chain and of a new synthesized polynucleotide chain.

During the DNA replication, process hydrogen bonds between nitrogen-containing bases of the polynucleotide chains are broken.

The secondary protein structure is generated by the manner its amino acids interact through intermolecular bond. These interactions create a spatial conformation of the polypeptide filament. The two most studied secondary conformations of proteins are the alpha helix and the beta-sheet.

Protein Structure Review - Image Diversity: protein secondary structure

During replication each chain of the DNA molecule act pairing new nucleotides and after the process, two newly formed chains made with the union of these nucleotides appear. Then two DNA molecules are created, each with one chain from the original molecule and one newly chain formed by new nucleotides. Thus, it is not entirely correct to assert that the replication produces two new molecules of DNA. It is better to affirm that two new half-molecules are created.

For this phenomenon DNA, replication is called semi conservative replication.

The process of copying, or duplication, of the DNA molecule is called replication. The enzyme that participates in the formation of a new DNA chain is the DNA polymerase. There are also other important enzymes in the replication process, the helicase, the gyrase and the ligase.

Nucleic Acid Review - Image Diversity: DNA replication

In the eukaryote cell nucleus, RNA can be found dispersed in the nuclear fluid, along with DNA, and as the main constituent of the nucleolus. In cytosol (in eukaryotes or in bacteria) RNA molecules can be found free, as structural constituent of ribosomes (organelles specialized in protein synthesis) or even associated to them in the process of making proteins. Mitochondria and chloroplasts also have their own DNA and RNA.

Only DNA has two polynucleotide chains. RNA is formed just by one polynucleotide chain.

Nucleic Acid Review - Image Diversity: RNA molecule

The primary protein structure is the linear sequence of amino acids that form the molecule.

The primary structure is the basis of the protein identity. Modification of only one amino acid of the primary structure creates a different protein. This different protein can be inactive or even can have other biological function.

Protein Structure Review - Image Diversity: protein primary structure

The tertiary protein structure is a spatial conformation additional to the secondary structure in which the alpha helix or the beta-sheet folds up itself. The forces that keep the tertiary structure generally are interactions between the –R groups of the amino acids and between other parts of the protein and water molecules of the solution.

The main types of tertiary structure of proteins are the globular proteins and the fibrous proteins.

Protein Structure Review - Image Diversity: protein tertiary structure

Alpha helix and beta-sheet conformations are the two main types of secondary structure of a protein molecule. According to the primary protein structure, its secondary structure can be of one type or other.

In the alpha-helix structure, the polypeptide curls longitudinally by the action of hydrogen bonds forming a spiral, or helix. In the beta-sheet conformation, the protein is more distended and the hydrogen bonds form a zig-zag-shaped protein structure called B-strand. Many assembled beta-strands make a beta-sheet.

Protein denaturizing can be a reversible or an irreversible process, i.e., it can be possible or impossible to make the protein regain its original spatial conformation.

Yes. DNA replication occurs in mitosis as well in meiosis.

The making of RNA from information contained in DNA is called transcription. The enzyme that catalyzes the process is the RNA polymerase.