BIOLOGY 1A03 Lecture Notes - Lecture 3: George Gamow, Start Codon, Genetic Code

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BIOLOGY 1A03 Full Course Notes

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Mo d u le 2 th e ge n e tic co d e. Un it 1: ge n e tic co d e: deciphering code in mrna. Proteins are made from 20 different amino acids, but there are only 4 nucleotides in mrna (a,c,u,g) Un it 3: de c ip h e rin g th e co d e: simple mrna: simple repeated sequence of nucleotides is translated into a simple repeated sequence of identical amino acids. This repeated tract of uracils and cytosines produces a strong of alternating amino acid residues: simple mrnas were used to determine specific amino acid encoded in each triplet codon. Un it 4: s ta n d a rd co d e: only nucleotide triplet aug codes for methionine. First triplet in every protein coding sequence. Aug start codon that signals the region where protein synthesis should begin: there are many examples of redundancy.

Related Questions

Fill in the blank. Elongation during translation does NOT involve ____________.

Question 16 options:

	the translation of codons according to the genetic code
	the formation of bonds catalyzed by the ribosome
	complementary base pairing between RNA molecules
	amino acids being linked together in a polypeptide
	reading the DNA template 3' to 5'

For a given gene, what establishes the reading frame for translation?

Question 17 options:

	the location of the enhancer relative to the gene
	the first three nucleotides at the 5' end of the mRNA
	the first three nucleotides at the 3' end of the mRNA
	the start codon in the mRNA
	the location of the promoter relative to the gene

Which of the following is the LEAST likely direct consequence of a substitution mutation?

Question 18 options:

	changing the length of a protein coded for by a gene
	changing one amino acid in a protein
	creating a stop codon
	eliminating a start codon
	changing the length of the DNA molecule containing a gene

Suppose that the pre-mRNA transcript from a eukaryotic gene is 30,000 nucleotides long, and the gene codes for a sequence of 300 amino acids. What is the best explanation for the relationship between these numbers?

Question 19 options:

	only the first 900 nucleotides of the pre-mRNA transcript are translated
	it takes 100 nucleotides to specify a single amino acid
	300 of the nucleotides in the transcript are important, and the rest are "junk"
	only the last 900 nucleotides of the pre-mRNA transcript are translated
	large portions of pre-mRNA transcripts are cut out during RNA processing

Suppose an individual is born into a population with a novel mutation. Is the new mutation an evolutionary change, and why?

Question 20 options:

	no, because it is not a big enough change to count
	yes, because new mutations are always adaptive
	yes, because the appearance of a new genetic variant is a genetic change in a population
	no, because not enough individuals have the mutation for it to matter
	no, because most mutations are not adaptive

1. Two couples in which both partners have albinism each have three children. All three of the first coupleâs children have albinism, while all of the second coupleâs children have normal pigmentation. How can you explain these findings given that the development of pigmentation is a multi-step biochemical pathway?

2. All of the genome is replicated during the DNA synthesis phase of the cell cycle, but only part of the genome is transcribed each time transcription is initiated. How is it determined which base pairs of thegenome are transcribed into RNA?

3. To encode all 20 amino acids using a genetic code that is unambiguous, what would be the minimum codon size if there were ________ different bases (rather than four)?

a) two

b) five

c) Suppose that only the first two nucleotides of a three nucleotide codon are base-specific, and position three is dependent on whether it is occupied by a purine or pyrimidine, how many triplets of different meaning would there be?

4. A segment of a polypeptide chain is Arg-Gly-Ser-Phe-Val-Asp-Arg. If it is encoded by the followingsegment of DNA, which DNA strand acts as the template for transcription? Appropriately label the ends ofeach DNA strand with 5â and 3â.
- G G C T A G C T G C T T C C T T G G G G A â- C C G A T C G A C G A A G G A A C C C C T -

I just came across this abstract:

Aminoacyl-tRNA synthetases (aaRSs) are responsible for creatingthe pool of correctly charged aminoacyl-tRNAs that are necessaryfor the translation of genetic information (mRNA) by the ribosome.Each aaRS belongs to either one of only two classes with twodifferent mechanisms of aminoacylation, making use of either the29OH (Class I) or the 39OH (Class II) of the terminal A76 of thetRNA and approaching the tRNA either from the minor groove (29OH)or the major groove (39OH). Here, an asymmetric pattern typical ofdifferentiation is uncovered in the partition of the codonrepertoire, as defined by the mechanism of aminoacylation of eachcorresponding tRNA. This pattern can be reproduced in a uniquecascade of successive binary decisions that progressively reducescodon ambiguity. The deduced order of differentiation is manifestlydriven by the reduction of translation errors. A simple rule can bedefined, decoding each codon sequence in its binary class, therebyproviding both the code and the key to decode it. Assuming that thepartition into two mechanisms of tRNA aminoacylation is a relicthat dates back to the invention of the genetic code in the RNAWorld, a model for the assignment of amino acids in the codon tablecan be derived. The model implies that the stop codon was alwaysthere, as the codon whose tRNA cannot be charged with any aminoacid, and makes the prediction of an ultimate differentiation step,which is found to correspond to the codon assignment of the 22ndamino acid pyrrolysine in archaebacteria.

Granted, this is a few years old, but I often find myself havingto admit that "I don't know" when at the root of discussions onevolution. That is, once abiogenesis has occurred, we can go on andexplain the rich diversity of life, but sadly we really don't knowmuch before that critical step. Generally, those satisfied with"magic" as an answer posit their myths and fables, whereas I'drather try to actually find out what happened. Sadly, as theabstract shows, you actually need a level of education tounderstand papers such as this that is generally well beyond thosewho would deny the reality of evolution.

Does anyone have a collection of papers on abiogenesis that aremore accessible and understandable to laypeople?

BIOLOGY 1A03 Lecture Notes - Lecture 3: George Gamow, Start Codon, Genetic Code

BIOLOGY 1A03 Full Course Notes

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