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12

I think given that you're just getting started with genetics, you can say that the codons are interchangeable. This is generally true, though not technically correct. Here are a few reasons for why this is the case, though there's probably more: Specific organisms use specific codons with different frequencies. This is usually related to the tRNA abundance ...


8

Take a look at this schematic of a mature mRNA. [source] The coding region (ie the part that is translated) is between the start and stop codons, but the 5' and 3' untranslated regions (UTRs) are also transcribed by RNA polymerase; these are part of the first and last exons, respectively. The transcription start site is labelled right in front of the 5' ...


7

Yes. Mutations can affect STOP codons and they do relatively commonly. These are important because they can lead to significant changes in the resulting peptide and are likely to affect protein functions or phenotype. For a point mutation (a single base substitution), there are several possible effects: silent mutation is a synonymous base substitution ...


7

Yes, 32 is correct. Technically, I have nothing to add what Gerardo Furtado and a tiger haven't already mentioned but a graphical representation of all permutations might help to understand this a bit better. For the first 2 positions in the codon we have 4 bases to choose from (adenine, guanine, uracil and cytosine). So this can mathematically be ...


7

Yes, it is. Gerardo Furtado has already provided a short answer in the comments, but allow me to explain why. The 4^3 = 64 if all bases can be chosen freely comes down to 4*4*4=64, because you can choose from 4 options for each of the 3 bases. If you restrict the possibilities of one of the bases, e.g. there are only 2 options for the third base (as in ...


7

Let's use an example, a case in point: the best known and plentiful one would be hemoglobin. It is a protein formed through the association of alpha- and beta-globin peptides into dimers or tetramers. The shape is largely a result of the sequence (peptide folding is reproducible, especially with the help of chaperones which may aid the correct folding ...


6

This is what we classify as a homework question, but as it satisfies the criterion of the poster demonstrating an attempt to answer it, I provide the following suggestion of an answer. I assume that as it appeared in an introductory bioinformatics module the exam question is just testing reading frames (obviously) and the punctuation of the genetic code. ...


6

The coding strand refers to the DNA strand with the same base order as the RNA transcript for a particular gene. As one gene is always entirely present on a single DNA strand there are indeed 3 reading frames possible in this strand, with only 1 actually containing the correct codon sequence for this gene. However when we view an entire genome it is ...


5

The textbook is asserting that translation could function without redundant codons, not that it does. In reality, all possible codons are used. See this answer on the interchangeability of codons.


5

You mix up translation and transcription. Transcription creates mRNA from DNA template. Transcription also includes splicing, that is excision of introns so that mature mRNA contains only exons. In your example it goes like that: DNA (chromosome): ---A----B--...--Dstop---E--- premature mRNA: A----B---...---Dstop--E---polyA mature mRNA: AB..DstopE-polyA ...


5

A good answer is already provided by @canadianer, but as with many things in biology it is important to keep in mind what organism and/or cell type we are talking about. Because the nuances of the answer to a question about a seemingly universal process sometimes actually depend on whether we want to know about bacteria, or fungi, or mammalian stem cells, ...


5

It is very difficult to answer this one for certain but I think the codon wheel representation is sometimes attributed to Rosemarie Swanson who represented the amino acid code using Gray code (or reflected binary code). Swanson's work actually went quite a bit deeper than the simplified codon wheels you find in ordinary textbooks (ordering by size of the ...


4

The term ‘redundant’ is not ideal in this respect, as that implies a redundancy in reality rather than theory, as @canadianer points out. Redundancy and Degeneracy However I would mention that there is another term more usually applied to the fact that certain amino acids are encoded by more than one codon — degeneracy. There is a Wikipedia entry on ...


4

An exon can have multiple stop codons but the first codon will terminate the ORF. The remainder of the exon will be a part of the 3'UTR. However, there are some cases in which stop codon readthrough happens [1]. In these cases an internal stop codon does not terminate the translation and the ribosome reads through it. During this process an aminoacyl-tRNA ...


4

In my opinion this question reflects two things: The difficulty students have in appreciating the historical experimental concerns of research workers in an area that is now well understood, and, hence, how it influenced the coining of new technical terms. The way that the use of terms has changed with time as old concerns disappear and new ones arise. Thus,...


3

Let's start with your example: Wild-type gene looks like: GUU CCA CAU AUC UAG* After G insertion, you end up with GUU GCC ACA UAU CUA G There are 3 stop codons: UAG*, UAA*, UGA* You don't see those in your mutated gene, because you truncated sequence. Let's imagine that gene actually goes like this: WT: GUU CCA CAU AUC UAG* GCG UCU AAA ACG CUA ...


3

Assuming that all 1200 bases in the gene code for mRNA, then 1200/3 = 400 is the correct calculation. It's important to understand that a gene will only ever be transcribed from one strand of double-stranded DNA. Think about it mechanistically - first, DNA is transcribed to RNA by a polymerase that can only move in one direction. Second, the strand ...


3

Although the answer to this question may be found in Mitochondrial Genetic code, because that answer is primarily about mitochondrial genetic codes, I shall give a more directed answer here. Because the same genetic code that was elucidated in bacteria was found to apply to higher eukaryotes, it was initially assumed that the genetic code was universal, and ...


3

Tl Dr: In the rosalind example they are showing the 3 reading frames that stem from the definition of a reading frame(non-overlapping triplets), not an example of open reading frames. Open reading frames are non-overlapping triplets between a start codon and a stop codon. Its important to step back and understand what is meant by reading frame first. It has ...


2

Summary Reassignment of an UGA codon as a selenocysteine codon is thought to involve the interaction of obligatory secondary structure elements called selenocysteine insertion sequences (SECIS) with the dedicated translation elongation factor that presents a unique tRNA aminoacylated with selenocysteine to the ribosome. However the location of these elements ...


2

Think about it this way, the G-C content is averaged over the entire genome, and varies between different species. Whether you are dealing with prokaryotes, with relatively compact genomes, or with eukaryotes, with lots of non-coding regions, the open reading frames will, in general, be influenced by the average G-C content across the genome. Therefore we ...


1

I think the question is fairly confusingly worded, so good job on your attempt based on that. If a C is inserted within the start codon, I presume that is referring to making a sequence that was originally ATGXXX and making it either ACTGXXX or ATCGXXX. Either insertion means the start codon will be missing completely. This is going to either cause no ...


1

In the English literature, a sequence like your 3' TAC 5' (when considered as the complement to a 5' ATG 3' or 5' AUG 3' codon) is typically called an anticodon. Most often this is in the context of a tRNA having an anticodon to a codon on an mRNA. See, for example, this page from Molecular Biology of the Cell or, similarly, this page from Berg's ...


1

The non-coding strand is indeed not the coding strand as the name suggests. It is the template strand. The template strand serves as the strand from where the mRNA is constructed upon. The mRNA contains the complement of the template strand, and is ,in fact, the actual codon. This is also the reason why the other strand is called the coding strand, it's the ...


1

Before it was established that there was a triplet, non-overlapping, comma-less genetic code* for what at that time were thought to be only 20† amino acids, there was uncetainty about: The codon size (must be more than 2, but...) Whether the codons overlapped (e.g. in a stretch ABCDEFG with triplet codons, whether ABC, BCD, CDE etc were the codons) Whether ...


1

This is a good question as, although in higher eukaroyotes codon usage does not necessarily correlate with translational efficiency, it does to a large extent in Escherichia coli (see e.g. Boël et al., 2016). The answer is not simple, but the following may contribute. To optimize the strength of base pairing Although in particular circumstances ‘wobble’ ...


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