In the cell cytoplasm, the ribosome reads the sequence of the mRNA in groups of three bases to assemble the protein. One of these resources focuses on the topics of transcription and translation. This resource is an interactive activity that starts with a general overview of the central dogma of molecular biology, and then goes into more specific details about the processes of transcription and translation. In addition to the interactive activity, the resource also includes a background narrative and discussion questions that could be used for assessment.
Although the material is designated as appropriate content for grades, , it would serve as an excellent introduction to the topic for biology majors, or would be well suited for non-biology majors at the post-secondary level. These animations are useful as a lecture supplement or for students to review on their own.
The DNAi modules," Reading the Code" and "Copying the Code," describe the history of the process, the scientists involved in the discovery, and the basics of the process, and also include an animation and interactive game. The genetic code is almost universal. Except for a few microorganisms, all of life uses the same genetic code - the same triplets of nucleotides code for the same amino-acids. When the ribosome is assembled around a molecule of mRNA, the translation begins with the reading of the first triplet.
Small tRNA molecules bring in the individual amino-acids and attach them to the mRNA, as well as to each other, forming a chain of amino-acids. When a stop signal is reached, the entire complex disassociates. The ribosome, the mRNA, the tRNAs and the enzymes are then either degraded or re-used for another translational event. The exact sequence of amino-acids in a polypeptide chain is the primary structure of the protein.
As different amino-acids are molecules of somewhat different shapes, sizes and electrical polarities, they react with each other. The attractive and repulsive forces between amino-acids cause the chain to fold in various ways. The three-dimensional shape of the polypeptide chain due to the chemical properties of its component amino-acids is called the secondary structure of the protein.
Enzymes called chaperonins further modify the three-dimensional structure of the protein by folding it in particular ways. The 3D structure of a protein is its most important property as the functionality of a protein depends on its shape - it can react with other molecules only if the two molecules fit into each other like a key and a lock.
The 3D structure of the fully folded protein is its tertiary structure. The primary and secondary structure of the prion is almost identical to the normally expressed proteins in our brain cells, but the tertiary structure is different - they are folded into different shapes.
When a prion enters a healthy brain cell, it is capable of denaturing unwinding the native protein and then reshaping it in the same shape as the prion. Thus one prion molecule makes two - those two go on and make four, those four make eight, and so on, until the whole brain is just one liquifiied spongy mass. Another aspect of the tertiary structure of the protein is addition of small molecules to the chain. This means that adenine will always pair up with uracil during the protein synthesis process.
Gene expression begins with the process called transcription, which is the synthesis of a strand of mRNA that is complementary to the gene of interest. Transcription begins in a fashion somewhat like DNA replication, in that a region of DNA unwinds and the two strands separate, however, only that small portion of the DNA will be split apart. The triplets within the gene on this section of the DNA molecule are used as the template to transcribe the complementary strand of RNA Figure 2.
A codon is a three-base sequence of mRNA, so-called because they directly encode amino acids. Like DNA replication, there are three stages to transcription: initiation, elongation, and termination. Figure 2. Stage 1: Initiation. A region at the beginning of the gene called a promoter—a particular sequence of nucleotides—triggers the start of transcription.
Stage 2: Elongation. One strand, referred to as the coding strand, becomes the template with the genes to be coded. This process builds a strand of mRNA. Stage 3: Termination. Before the mRNA molecule leaves the nucleus and proceeds to protein synthesis, it is modified in a number of ways. For this reason, it is often called a pre-mRNA at this stage. For example, your DNA, and thus complementary mRNA, contains long regions called non-coding regions that do not code for amino acids.
Their function is still a mystery, but the process called splicing removes these non-coding regions from the pre-mRNA transcript Figure 3. The removed segment of the transcript is called an intron. The remaining exons are pasted together. An exon is a segment of RNA that remains after splicing. Interestingly, some introns that are removed from mRNA are not always non-coding. When different coding regions of mRNA are spliced out, different variations of the protein will eventually result, with differences in structure and function.
This process results in a much larger variety of possible proteins and protein functions. When the mRNA transcript is ready, it travels out of the nucleus and into the cytoplasm. Figure 3. Splicing DNA. In the nucleus, a structure called a spliceosome cuts out introns noncoding regions within a pre-mRNA transcript and reconnects the exons.
From RNA to Protein: Translation Like translating a book from one language into another, the codons on a strand of mRNA must be translated into the amino acid alphabet of proteins. Translation is the process of synthesizing a chain of amino acids called a polypeptide.
The substrate on which translation takes place is the ribosome.So let me get my pen tool out now, let me deselect this, get the pen tool out. One of the most important classes of proteins is enzymes, which help speed up necessary biochemical reactions that take place inside the cell. As different amino-acids are molecules of somewhat different shapes, sizes and electrical polarities, they react with each other. Interestingly, some introns that are removed from mRNA are not always non-coding.
So for example this could be, this whole thing could be a strand of DNA, but this part right over, let's say in orange I'll do it, this part in orange right over here could be one gene, it might define information for one gene, it could define a protein, this section right over here could be used to define another gene. So actually I think I'm on the wrong, let me go back here. The removed segment of the transcript is called an intron. Transcription Genetics Translation DNA Video transcript - [Voiceover] We've already talked about how DNA's structure as this double helix, this twisted ladder, makes it suitable for being the molecular basis of heredity. So protein is essentially a bunch, a sequence of these amino acids put together.
So that's replication. Well you have one of four bases and you have them in three different places, so you have four times four times four, possible codon words I guess you could say. So translation. So once again it might be part of a molecule that has not seven or eight base pairs, but might have 70 million base pairs. It's a new tool I'm using, so let me make sure I'm doing it right. The second step is translation in which the RNA molecule serves as a code for the formation of an amino-acid chain a polypeptide.
So maybe I'll do the new sugar phosphate backbone in yellow. Transcription Genetics Translation DNA Video transcript - [Voiceover] We've already talked about how DNA's structure as this double helix, this twisted ladder, makes it suitable for being the molecular basis of heredity.
For this reason, it is often called a pre-mRNA at this stage. So let's say you have that right over there, let me copy and paste it. And how many possible codons do you have? It's a new tool I'm using, so let me make sure I'm doing it right.
So for the RNA and in this case the mRNA that's going to leave the nucleus A is going to pair with U, U for uracil, so uracil, that's the base we're talking about, let me write it down, uracil. So you have 64 possible codons that need to code for 20 amino acids. Next, tRNA molecules shuttle the appropriate amino acids to the ribosome, one-by-one, coded by sequential triplet codons on the mRNA, until the protein is fully synthesized.
And just like that I was able to construct a new right hand side using that left hand side.
And then I copy and then I paste, and it's just like that.