A nucleotide is a fundamental building block of nucleic acids (DNA and RNA). It consists of a sugar, a phosphate group, and a nitrogenous base. There are five different nitrogenous bases: adenine (A), guanine (G), cytosine (C), thymine (T) (in DNA), and uracil (U) (in RNA). A gene is a specific sequence of nucleotides within a DNA molecule. It is a functional unit of heredity.

Relationship: A gene is composed of a sequence of nucleotides. The specific order of nucleotides within a gene determines the sequence of amino acids in the polypeptide that the gene codes for. Therefore, the nucleotides within a gene carry the information required to build a protein. The sequence of nucleotides is essentially the 'recipe' for the protein.

Following transcription, the primary RNA transcript (pre-mRNA) undergoes significant processing to become mature mRNA. This processing is crucial for ensuring the production of functional proteins. The primary transcript contains both coding sequences (exons) and non-coding sequences (introns). Introns are segments of RNA that do not code for protein and are interspersed with exons, which contain the protein-coding information.

The key process in RNA processing is splicing. This involves the removal of introns and the joining together of exons. Splicing is carried out by a complex molecular machinery called the spliceosome, which is composed of small nuclear RNAs (snRNAs) and proteins. The spliceosome recognizes specific sequences at the boundaries of introns and exons. These sequences include 5' splice sites, 3' splice sites, and a branch point sequence. The spliceosome then excises the introns and ligates (joins) the exons together.

There are different types of splicing, including constitutive splicing, where all introns are removed, and alternative splicing, where different combinations of exons can be included in the mature mRNA. This allows a single gene to code for multiple different protein isoforms, increasing protein diversity.

The significance of RNA processing is that it produces a mature mRNA molecule that contains only the protein-coding information. This ensures that the ribosome can accurately translate the mRNA into a functional protein. Furthermore, alternative splicing allows for greater protein complexity and regulation.

The strand of a DNA molecule used as a template for transcription is termed the template strand or non-coding strand. The other strand, which is complementary to the mRNA being synthesized, is called the non-template strand or coding strand.

Significance: The template strand provides the sequence of nucleotides that the RNA polymerase uses to synthesize the mRNA molecule. The mRNA sequence is essentially a copy of the coding strand, with uracil (U) replacing thymine (T). The template strand's sequence dictates the order of bases in the newly synthesized mRNA. This ensures accurate genetic information is copied from DNA to RNA. The coding strand has the same sequence as the mRNA (except for U/T), so it can be used to determine the mRNA sequence.