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What is the significance of the discovery of unusual amino acids in relation to the genetic code?
What is the significance of the discovery of unusual amino acids in relation to the genetic code?
Why is it possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
Why is it possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
In what manner are Selenocysteine and Pyrrolysine incorporated into proteins?
In what manner are Selenocysteine and Pyrrolysine incorporated into proteins?
What is the significance of the discovery of Selenocysteine and Pyrrolysine in relation to the universal genetic code?
What is the significance of the discovery of Selenocysteine and Pyrrolysine in relation to the universal genetic code?
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What can be deduced when obtaining a DNA sequence from new or unknown sources, according to the text?
What can be deduced when obtaining a DNA sequence from new or unknown sources, according to the text?
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How are Selenocysteine and Pyrrolysine incorporated into proteins?
How are Selenocysteine and Pyrrolysine incorporated into proteins?
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What is the reason behind the inability to always assume universal incorporation of Selenocysteine and Pyrrolysine based on the genetic code?
What is the reason behind the inability to always assume universal incorporation of Selenocysteine and Pyrrolysine based on the genetic code?
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What is the significance of the discovery of unusual amino acids specified by an extension of the genetic code?
What is the significance of the discovery of unusual amino acids specified by an extension of the genetic code?
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Why is it possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
Why is it possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
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In what manner are Selenocysteine and Pyrrolysine incorporated into proteins?
In what manner are Selenocysteine and Pyrrolysine incorporated into proteins?
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What does the discovery of unusual amino acids specified by an extension of the genetic code tell us about the assumption of universal incorporation?
What does the discovery of unusual amino acids specified by an extension of the genetic code tell us about the assumption of universal incorporation?
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What is the significance of the discovery of Selenocysteine and Pyrrolysine in relation to the universal genetic code?
What is the significance of the discovery of Selenocysteine and Pyrrolysine in relation to the universal genetic code?
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Why is it not always possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
Why is it not always possible to deduce the possible sequence of the protein encoded from a DNA sequence obtained from new or unknown sources?
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How are Selenocysteine and Pyrrolysine incorporated into proteins?
How are Selenocysteine and Pyrrolysine incorporated into proteins?
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What does the discovery of unusual amino acids specified by an extension of the genetic code tell us?
What does the discovery of unusual amino acids specified by an extension of the genetic code tell us?
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Why is the genetic code not as universal as previously thought?
Why is the genetic code not as universal as previously thought?
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Study Notes
The Central Dogma
- The central dogma is a fundamental principle that describes the flow of information from genes (in the form of DNA) to a transient copy of the gene (in the form of messenger RNA), which then directs the sequence of amino acids in a polypeptide/protein.
- The flow of information is absolute and unchanging, with no reversal.
Components of the Central Dogma
- DNA (Gene): a polymer of deoxyribonucleotides, carrying sequences of 4 bases (A, C, G, and T) with a double helical structure, and exhibiting complementary pairing of bases (A:T and C:G) on the two strands.
- mRNA (Messenger RNA): a transient copy of the gene, carrying the information from DNA to the ribosome, where it is translated into a protein.
- Protein (Polypeptide): a polymer of amino acid residues, formed from the translation of mRNA, which carries out biological activities.
Transcription
- The process of creating a complementary RNA copy from a DNA template.
- Occurs in the nucleus of eukaryotic cells and in the cytoplasm of prokaryotic cells.
- Involves the enzyme RNA polymerase, which binds to DNA, unwinds the duplex, and adds nucleotides to the RNA chain.
- Results in a primary transcript, which undergoes post-transcriptional processing in eukaryotic cells.
Translation
- The process of creating a polypeptide chain from the mRNA sequence.
- Occurs in the cytoplasm of both eukaryotic and prokaryotic cells.
- Involves the ribosome, which reads the mRNA sequence and adds amino acids to the growing polypeptide chain.
- Results in a mature protein, which may undergo further modification.
Codons and Amino Acids
- A codon is a sequence of three nucleotides in mRNA that codes for a specific amino acid.
- There are 64 possible codons, which code for 20 amino acids and three stop codons.
- The genetic code is the set of rules that defines the relationship between codons and amino acids.
- The code is redundant, with multiple codons coding for the same amino acid.
Prokaryotic and Eukaryotic Cells
- Prokaryotic cells: lack a nucleus, and transcription and translation occur in the cytoplasm.
- Eukaryotic cells: have a nucleus, and transcription occurs in the nucleus, with the mRNA transcript migrating to the cytoplasm for translation.
Post-Transcriptional Processing
-
Eukaryotic cells only: the primary transcript undergoes modifications, including:
- Addition of a 5' cap
- Addition of a poly-A tail
- Removal of introns (splicing) to join exons
Post-Translation Modification
- The process of modifying the polypeptide chain after translation.
- Examples include:
- Disulfide bond formation
- Cleavage of signal peptides
- Formation of mature proteins
Exceptions to the Central Dogma
- RNA viruses: carry their genome in the form of RNA, rather than DNA.
- Reverse transcription: the process of creating a DNA copy from an RNA template, used by some viruses.
- Selenocysteine and Pyrrolysine: two uncommon amino acids that do not follow the standard genetic code.### The Central Dogma
- The central dogma is a fundamental principle in all forms of life, describing the flow of information from genes (in the form of DNA) to a transient copy of the gene (in the form of messenger RNA) to a polypeptide/protein.
- The direction of flow is absolute and unchanging, with no reversal.
DNA
- DNA is a polymer of deoxyribonucleotides.
- It carries sequences of 4 bases - A, C, G, and T.
- It has a double helical structure.
- It exhibits complementary pairing of bases (A:T and C:G) on the two strands.
Protein
- Proteins are made up of one or more chains of polypeptides.
- Proteins are polymers of amino acid residues.
- There are 20 types of amino acids used in general, but a rare sub-population of them contains 2 other uncommon amino acids.
- The class of macromolecules that carry out most of the biological activities within an organism are proteins.
Transcription
- Transcription is the process of generating a transient copy of the gene (in the form of messenger RNA) from the DNA.
- The RNA polymerase plays a crucial role in transcription.
- Transcription occurs in the nucleus in eukaryotic cells.
- The RNA transcript then migrates out to the cytoplasm where it gets bound by a ribosome to start the process of translation.
Translation
- Translation is the process of directing the sequence of amino acids in a polypeptide/protein according to the RNA transcript.
- The ribosome plays a crucial role in translation.
- Translation occurs in the cytoplasm.
- There are two stages in the flow of information: transcription and translation.
Codons
- Codons are sets of three bases (nucleotides) in the RNA transcript that code for a specific amino acid.
- There are 64 possible codons, but only 20 amino acids.
- The genetic code translates the information of RNA presented as a set of three bases (codon) into the information of a specific amino acid.
Gene Expression
- The complete coding region of a gene will have to begin with a start codon and end with any one of the stop codons.
- Beyond the coding regions, there are DNA sequences in the non-coding regions that are important for the control of gene expression.
- A gene refers to the complete coding region for that polypeptide and some associated non-coding regions.
Prokaryotes and Eukaryotes
- In prokaryotic cells, the chromosome (genetic material) is not separated from the cytoplasm by a nuclear envelope.
- In prokaryotic cells, transcription and translation occur in the same compartment, and the two processes are coupled.
- In eukaryotic cells, the RNA transcripts are produced within the nucleus, which is separated by a nuclear envelope.
- In eukaryotic cells, the RNA transcript needs to migrate out from the nucleus to the cytoplasm to bind to ribosome to start translation.
Post-Translational Modification
- In eukaryotic cells, the RNA transcript undergoes a series of modifications prior to translation, known as post-transcriptional processing.
- The modifications include the addition of a 5' cap, the addition of a poly-A tail, and the removal of introns (splicing) to join the exons together.
- Insulin is an example of a protein that undergoes post-translational modification.
Exceptions to the Central Dogma
- RNA viruses carry their genome in the form of RNA instead of DNA.
- Selenocysteine and Pyrrolysine are the two uncommon amino acids that do not follow the genetic code system.
- Reverse transcription is the process where viral RNA is converted to DNA.### The Central Dogma
- The central dogma describes the flow of information from DNA to proteins
- The direction of flow is absolute and unchanging (no reversal)
- The flow of information involves two stages: transcription and translation
Transcription
- Transcription is the process of copying a part of the DNA document into a transient mobile form using RNA dialect
- The genetic code translates the information of RNA presented as a set of three bases (codon) into a specific amino acid
- The codons run in a continuous sequence, without extra bases acting as "space" or "punctuation" between one codon and the next
Genetic Code
- The genetic code is a "dictionary" that translates the information of RNA into a specific amino acid
- The code is universal, meaning that a particular codon always codes for the same amino acid
- There are 61 codons that code for 20 amino acids, with some codons being redundant (i.e., coding for the same amino acid)
Protein Synthesis
- Protein synthesis is the process of translating mRNA into a polypeptide
- The process involves the interaction of mRNA, ribosomes, and tRNAs
- The sequence of amino acids in a protein is determined by the sequence of codons in the mRNA
Gene Expression
- Gene expression is the process of transcribing and translating a gene into a protein
- The process involves the copying of a gene's DNA sequence into a complementary RNA sequence, which is then translated into a protein
- Gene expression is regulated by various mechanisms, including transcriptional and translational control
Prokaryotic and Eukaryotic Cells
- In prokaryotic cells, transcription and translation occur in the same compartment (cytoplasm)
- In eukaryotic cells, transcription occurs in the nucleus, and the mRNA is then transported to the cytoplasm for translation
- Eukaryotic cells have a more complex gene structure, with introns and exons, compared to prokaryotic cells
Post-Transcriptional and Post-Translational Modification
- Post-transcriptional modification refers to the processing of mRNA after transcription, including the addition of a 5' cap and a poly-A tail, and the removal of introns
- Post-translational modification refers to the processing of a protein after translation, including the formation of disulfide bonds and the cleavage of signal peptides
Exceptions to the Central Dogma
- RNA viruses, which carry their genome in the form of RNA instead of DNA
- Selenocysteine and Pyrrolysine, two uncommon amino acids that do not follow the genetic code system
- Reverse transcription, which is the process of transcribing RNA into DNA, occurs in some viruses
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Test your knowledge of DNA codons with this quiz. Identify the amino acids represented by the given codons and decode the genetic information.
