DNA Codon Quiz

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