What Is Protein Synthesis - How Are Proteins Made - Transcription And Translation

In this video we discuss what is protein synthesis, or how are proteins made in the body. We cover how RNA copies DNA code, and how ribosomes are like manufacturing plants for building protein.

Transcript/notes

Protein synthesis. So, how are proteins built? In this video we are going to go through a very basic look at how this happens.

There are two major events that happen during protein synthesis, transcription and translation.

Transcription has three phases, initiation, elongation and termination.

The initiation phase of transcription occurs in the nucleus of a cell, as specific enzymes unwind DNA, which has a double helix formation, in the region of a gene. A gene is a segment of a DNA molecule that contains information or directions on how to build a protein.

Next, an enzyme called RNA polymerase attaches to the DNA strand and moves to the promoter, or start, region of a gene. The hydrogen bonds between the DNA strands are broken and there is a bubbling out in that region. This allows the nitrogenous bases to be exposed.

In the elongation phase, free RNA nucleotides come in a pair up with the exposed bases in the template strand of DNA. There are four different bases in DNA, and each of these pair up with only one type of base in the developing strand of RNA, which are shown here. DNA bases on the left and RNA bases on the right.

Thymine with Adenine, adenine with uracil, cytosine with guanine, and guanine with cytosine. DNA and RNA bases differ in that RNA contains uracil and DNA contains thymine. These base pairings are done through hydrogen bonds. This process continues as the RNA polymerase moves down the DNA until the entire gene has been transcribed. Once this is completed, a new pre messenger or mRNA has been formed.

Termination occurs once the terminal region of the gene is reached. The hydrogen bonds between the DNA and mRNA are broken, the RNA polymerase is released, the DNA returns to its double helix formation and the newly formed pre mRNA strand has got its recipe for synthesizing a new protein.

Next, the pre mRNA is modified. The strand of pre mRNA has sections called introns and exons. The intron sections are non coding regions that are removed by structures called spliceosomes. Enzymes then come in and splice together the exon sections.

Two other modifications are also made to the mRNA. At one end of the strand capping occurs, which increases the stability of the strand, and at the other end a polyA tail is added, which helps in transportation of the strand. Now, a final edited version of mRNA has been created, and it leaves the nucleus through nuclear pores, enters into the cytoplasm and travels to a ribosome for the second major stage of protein synthesis, translation.

Translation occurs as a complex is formed that is comprised of the large and small sub units of a ribosome, the messenger mRNA and tRNA, or transfer RNA. The mRNA is read three bases at a time, these three base sections are called codons, and they determine the amino acid required. tRNA has a binding site, referred to as the anticodon, that contains the three bases that pair with the bases in the mRNA codon.

So, now the ribosome moves along the strand of mRNA until it reaches the start codon. A tRNA picks up the required amino acid from a pool of free floating amino acids in the cytoplasm, and brings it to the ribosome. Here the anticodon and codon attach, putting the amino acid into place.

Next, the ribosome again moves down the mRNA strand, a tRNA brings in the required amino acid, and the two amino acids form a peptide bond. This process keeps happening, forming a long chain of amino acids. A release factor binds to the complex to signal the end of the process, and the two subunits of the ribosome are separated from the mRNA, and the newly synthesized protein, or polypeptide chain is released.

One last note, the mRNA can be read by more than one ribosome at a time. So, many copies of a protein can be produced quickly.

Timestamps
0:00 Intro
0:10 The 2 major parts of protein synthesis, transcription and translation
0:21 The initiation phase of transcription
0:56 The elongation phase
1:50 Termination
2:56 Translation