Nucleic acids

• What is a gene?

  Length of DNA coding for a polypeptide
• What is a mutation?


  A mutation is a change in the DNA sequence of a gene, which can result in a change in the protein produced by that gene.
• What is a codon?

  A codon is a sequence of three nucleotides in DNA or RNA that codes for a specific amino acid during protein synthesis.
• What is an anti-codon?

  A sequence of three nucleotides on a tRNA molecule that is complementary to a codon on mRNA.
• What is transcription?


  Transcription is the process of converting DNA into RNA, coping DNA to form RNA
• What is translation?


  The process of converting the information in mRNA into a sequence of amino acids to form a protein.
• Where does translation occur?


  In the ribosomes.
• What is a polypeptide?


  A polypeptide is a chain of amino acids linked together by peptide bonds.
• What does each gene contain?

  Each gene contains a sequence of DNA base triplets that determines the amino acid sequence (or primary structure) of a protein.
• Why can't the instructions in genes pass out of the nucleus?


  Because the instructions are contained in genes they cannot pass out of the nucleus directly.
• How is the genetic information from a gene transported out of the nucleus?


  A copy of each gene must be transcribed (copied) into a length of mRNA.
• What are base triplets called after they are transcribed into mRNA?


  Base triplets in mRNA are called codons.
• Where does the mRNA travel after transcription, and what happens there?


  The mRNA travels out of the nucleus to the ribosome, where the codons are translated into a polypeptide.
• What is the primary structure of a protein determined by?


  The amino acid sequence determined by the DNA base triplets in a gene.
• What is transcription in the context of protein synthesis?


  Transcription is the process of copying a gene into a length of mRNA.
• What role does mRNA play in protein synthesis?


  mRNA carries the genetic instructions from the nucleus to the ribosome for translation.
• What process occurs at the ribosome involving mRNA?


  Translation, where the sequence of codons in mRNA is used to assemble a polypeptide.
• What is the relationship between codons and amino acids?


  Each codon specifies a particular amino acid to be added to the growing polypeptide chain.
• Why is mRNA necessary for protein synthesis?


  Because the original DNA instructions cannot leave the nucleus, mRNA acts as a messenger.
• What determines the sequence of amino acids in a polypeptide?


  The order of the codons along the mRNA strand determines the sequence of amino acids in the polypeptide.
• How are codons read by ribosomes?


  Codons are read by ribosomes in sequence, separate from the codon before and the codon afterwards.
• What does it mean for codons to be non-overlapping?


  Codons do not share bases; each codon is distinct and does not overlap with another.
• How is the genetic code described in addition to being non-overlapping?


  The genetic code is described as universal.
• Why is the genetic code considered universal?


  The same DNA bases (or mRNA codons) code for the same amino acids in almost all organisms.
• Why are there three nucleotides in a codon?


  There are three nucleotides in a codon because it allows for 64 unique combinations, which is more than enough to code for the 20 amino acids.
• How many bases are there in DNA, and what are they?

  4 bases in DNA: adenine, guanine, thymine, and cytosine.
• Why can't one base or two bases code for all 20 amino acids?


  One base would only allow for 4 amino acids, and two bases would allow for 16 amino acids—both are insufficient for coding 20 amino acids.
• What is the advantage of having 64 unique codon combinations?


  It provides spare coding capacity, allowing several codons to specify the same amino acid.
• What does the term "degenerate" mean in the genetic code?


  Degenerate means that several codons can have the same meaning, or code for the same amino acid.
• Why is the genetic code described as degenerate?


  Because many codons specify the same amino acid, creating redundancy in the code.
• What is the advantage of a degenerate genetic code for organisms?


  A degenerate code reduces the impact of mutations by allowing certain base changes without altering the amino acid produced.
• What is a "stop codon"?


  A stop codon is a sequence of three mRNA bases that signals the end of translation, terminating the synthesis of a polypeptide.
• What are the sequences that act as stop codons?


  The stop codons are UAA, UAG, and UGA.
• What does mRNA stand for?


  Messenger RNA.
• What is mRNA a "copy" of?


  mRNA is a "copy" of the DNA base sequence of a gene
• What is mRNA complementary to?


  mRNA is complementary to one strand of the DNA (template strand).
• What does the coding sequence of mRNA determine?


  The coding sequence of mRNA determines the amino acid sequence in the polypeptide that is produced.
• What is unique about mRNA's structure?


  mRNA is single-stranded and uses uracil (U) in place of thymine (T).
• What does rRNA stand for?


  Ribosomal RNA.
• What are ribosomes made of?


  Ribosomes are made of rRNA and protein (two sub-units).