7.1 The Genetic Code [HY]

Question 1

How do nucleotide become the building block of DNA?

Answer 1

• the genetic code is used to translate this genetic information into proteins
• the proteins they encode that help organisms develop and perform the necessary functions of life

Question 2

Gene

Answer 2

• a unit of DNA that encodes a specific protein or RNA molecule, and through transcription and translation, that gene can be expressed

Question 3

What’re the 3 main types of RNA?

Answer 3

mRNA, tRNA, and rRNA

Question 4

Messenger RNA (mRNA)

Answer 4

• carries the information specifying the amino acid sequence of the protein to the ribosome
• the only type of RNA that contains information that is translated into protein; to do so, it is read in three nucleotide
  segments termed codons
• each mRNA molecule translates into only one protein product
• the cell has a different mRNA molecule for each of the thousands of different protein made by that cell

DNA -> RNA polymerase -> mRNA

Question 5

mRNA in prokaryotes

Answer 5

• may be polycistronic, and starting the process of translation at different locations in the mRNA can result in different proteins.

Question 6

Transfer RNA (tRNA)

Answer 6

• responsible for converting the language of nucleic acids to the language of amino acids and peptides
• Each tRNA molecule contains a folded strand of RNA that includes a three-nucleotide anticodon; the anticodon recognizes and pairs with the
  appropriate codon on an mRNA molecule while in the ribosome
• To become part of a nascent polypeptide in the ribosome,
  amino acids are connected to a specific tRNA molecule; such tRNA molecules are said to be charged or activated with an amino acid

Question 7

Aminoacyl-tRNA synthetase

Answer 7

• Each AA is activated by different aminoacyl-tRNA
  synthetase.
• requires two high-energy bonds from ATP, implying that the attachment of the amino acid is an energy rich bond
• transfers the activated amino acid to the 3′ end of the correct tRNA. Each tRNA has a CCA nucleotide sequence where the amino acid binds

Question 8

Ribosomal RNA (rRNA)

Answer 8

• Synthesized in the nucleolus and functions as an integral part of the ribosomal machinery used during protein assembly in the cytoplasm.
• Many function as ribozymes
• helps catalyze the formation of peptide bonds and is also important in splicing out its own introns within the nucleus

Question 9

Codon

Answer 9

• Each codon represents only one amino acid; however, most amino acids are represented by multiple codons
• the codon of the mRNA is recognized by a complementary anticodon on a (tRNA)

Question 10

Anticodon

Answer 10

• sequence allows the tRNA to pair with the codon in the mRNA

Question 11

The 3 stop codons? (Mneumonic)

Answer 11

Stop codons:
UAA—U Are Annoying
UGA—U Go Away
UAG—U Are Gone

Question 12

Wobble Position

Answer 12

• variable third base in the codon
• for the amino acids with multiple codons, the first two bases are usually the same, and the third base in the codon is variable
• Wobble is an evolutionary development designed to protect against mutations in the coding regions of our DNA

Question 13

Silent or Degenerate mutations

Answer 13

• Mutations in the wobble position
• there is no effect on the expression of the amino acid and therefore no adverse effects on the polypeptide
  sequence.

Question 14

Point mutation

Answer 14

• mutation occurs and it affects one of the nucleotides in a codon

Question 15

Expressed mutations

Answer 15

• point mutations can affect the primary amino acid sequence of the protein
• 2 types of expressed point mutations: Missense and Nonsense

Question 16

Missense mutation

Answer 16

A mutation where one amino acid substitutes for another

Question 17

Nonsense mutation

Answer 17

• a mutation where the codon now encodes for a premature stop codon
• also called truncation mutation

Question 18

Frameshift mutation

Answer 18

• occurs when some number of nucleotides are added to or deleted from the mRNA sequence.
• Insertion or deletion of nucleotides will shift the
  reading frame, usually resulting in changes in the amino acid sequence or premature truncation of the protein