mRNA Splicing animation || Steps of mRNA Splicing

#mRNAsplicing #genes #proteins
Molecules are the building blocks of life. They are made of smaller units called atoms, which are arranged in different ways to form different structures. One of the most important molecules in living organisms is the messenger RNA, or mRNA. mRNA is a type of RNA that carries the genetic information from DNA to the ribosomes, where it is translated into proteins. Proteins are the molecules that perform various functions in the cell, such as catalyzing reactions, transporting substances, and regulating processes.
But how does mRNA get from DNA to ribosomes? This is where mRNA splicing comes in. mRNA splicing is a process that removes the introns and joins the exons in the pre-mRNA molecule. Introns are sequences of DNA that interrupt the coding of amino acids in the protein product. Exons are sequences of DNA that specify the amino acids in the protein product. The transcription of these genes produces a pre-mRNA molecule, which is an exact copy of the gene with both exons and introns.
To make a mature mRNA, the pre-mRNA has to remove the introns and join the exons together. This is called RNA splicing. RNA splicing relies on finding the border between exon and intron. Introns usually start with 5’GU and end with 3’AG. But other bases at both the 5’ and 3’ splice sites also help to define the exon/intron boundaries.
RNA splicing involves several steps that use small nuclear ribonucleoprotein particles, or snRNPs. SnRNPs are complexes of small RNA molecules and proteins that play a key role in RNA processing. The first step in splicing is when the U1 snRNP binds to the 5’ splice site between exon 1 and intron 1. U1 attaches to the GU at the 5’ end of the intron. If a mutation changes one of these bases, splicing at this site is blocked and the intron stays in the mRNA.
Besides the 5’ GU and 3’ AG intron sequences, there is also another sequence that is important for RNA splicing: the branch-point sequence. The branch-point sequence consists of 7 bases near
the 3’ AG splice site. In mammals, this sequence is YNCURAY, where Y is a pyrimidine (a nitrogen-containing base), N is any base, and R is a purine (a carbon-containing base). U1 binding at the 5’ GU leads to the attachment of the U2 snRNP. The U2 binds to the last adenine (A) of the branch-point sequence. A trimer forms between the U4, U5, and U6 snRNPs. This trimer associates with both U1 and U2 bringing them closer together; this makes the intron loop. After U1 and U2 are brought together, U4 is released. This release results in the formation of an active spliceosome, which removes the intron from between the 2 adjacent exons. Cleavage first occurs at the 5’ GU, separating intron 1 from exon 1. The 5’ guanine forms a covalent bond with the last adenine in the branch-point sequence. This looped structure is called a lariat. Cleavage then occurs at the junction between 3’ AG and exon 2. Exon 1 and exon 2 are joined together in a 5’3’ phosphodiester bond and
the intron is released. U1, U2, U5, and U6 stay attached to the intron lariat and carry it to de-branching enzymes in the nucleus. The enzymes break down the RNA and recycle the bases.
This process is repeated for each intron. When all introns have been removed, a mature mRNA is made. Now the mRNA can leave the nucleus and be translated by ribosomes in
the cytoplasm.
In this video, we will explain how mRNA splicing works in more detail,
show you some examples of different types of mRNAs, and discuss how mutations can affect mRNA splicing and cause diseases such as muscular dystrophy.
We hope you enjoy this video and learn something new about how your genes are turned into proteins.