genetic code

Question 1

what did george gamow suggest

Answer 1

suggested the number of nucleotides necessary to code for one amino acid (3-base code)

• multiple triplets would code for the same amino acid = a redundancy in the code

Question 2

what is the reading frame of a protein?

Answer 2

three codons are read, deduced, and transformed into the amino acids of the protein

Question 3

what is the open reading frame

Answer 3

the entire continuous sequence of a gene that begins at a triplet start codon code and ends with a triplet stop codon code; The coding region of a gene

Question 4

what are the three ways to read a nucleotide sequence

Answer 4

1) first reading frame: codons read from first nucleotide
2) second reading frame: codons read from second nucleotide
3) third reading frame: codons read from third nucleotides

Question 5

what happens if a single nucleotide was added within the nucleotide sequence?

Answer 5

• the code is misread
• the series of codons after the added nucleotide are different from the original series; they code for different amino acids in polypeptides

Question 6

what are frameshift mutations?

Answer 6

when one or two nucleotides are added or removed, changing the reading series and coding for new amino acids

Question 7

what happens if three nucleotides are removed?

Answer 7

• nothing; there is no frameshift (stays the same, no change in reading frame)
• a triplet codon is removed, meaning a single amino acid in the polypeptide is removed and all the other amino acids are conserved

Question 8

what happens if a codon is added in the nucleotide sequence?

Answer 8

• one amino acid will get added to the protein
• the reading frame of the mRNA and remainder of polypeptide sequence is conserved

Question 9

what direction are codons written in?

Answer 9

5’ to 3’ direction

Question 10

what is the start codon?

Answer 10

AUG –> methionine

• signals the region where protein synthesis should begin
• first triplet in every protein coding sequence

Question 11

what are the 3 features of the genetic code

Answer 11

1) the genetic code has redundancy

• this occurs because there are more unique triplets than unique amino acids

2) the genetic code is unambiguous

• a unique codon triplet will ALWAYS code for a specific amino acid and will never code for more than one amino acid

3) the genetic code is mostly universal

Question 12

what are the stop codons?

Answer 12

• UAA, UAG, UGA
• codons found at the end of the protein coding sequence and signal that the translation of mRNA into a polypeptide sequence is complete

Question 13

what makes the non-template strand the coding strand?

Answer 13

• RNA transcript has the same sequence as the non-template strand of DNA
• this strand contains the same codons as the mRNA, while the non-coding/template strand contains complementary anticodons

Question 14

what did Marshall Nirenberg & Johann Matthaei discover

Answer 14

• used a cell-free system to decipher the first level of the code in 1961
• they were able to determine what specific amino acids a particular RNA nucleotide template could give rise to
• started by making a simple nucleic acid from a string of uracil; noticed that the nucleic acid produced a repeated polypeptide sequence that contained identical amino acids (phenylalanine)
• follow up research used a string with alternating uracil and cytosines; produced a polypeptide string of altering serine and leucine
• these results confirmed that three nucleotides make up a codon that codes for an amino acid

Question 15

what are some examples that show that the genetic code is not 100% universal

Answer 15

• in some ciliate, ex. paramecium, UAA and UAG are not stop codons; they code for glutamine
• in mitochondria yeast, CUA codes for threonine but in mammalian mitochondria, CUA codes for leucine

Question 16

what is retinoblastoma

Answer 16

disruption of the Rb protein, which then fails to serve as a cell cycle break and leads to the development of cancer on the retinas

• treated by the delivery of chemotherapy drugs via liposomes to target areas

Question 17

what are some health conditions leaded to transcription errors

Answer 17

diabetes, alzheimer’s disease, parkinson’s disease, aging and cancer, down syndrome (some may be genetic)

Question 18

how do chemotherapy drugs work

Answer 18

they inhibit the proper functioning of enzymes (topoisomerases) needed to unwind DNA for replication and transcription

• this stops cancer cells from dividing and growing

Question 19

what did Dr. Juliet Daniel discover

Answer 19

• discovered and named Kaiso, which regulates the expression of genes which control cell proliferation and cell-cell adhesion (is a transcription factor)
• Kaiso’s malfunction in tumors (breast, colon, prostrate) contributes to tumor progression and spread of cancer in humans

Question 20

what is triple negative breast cancer

Answer 20

• most aggressive (spreads quickly)
• no treatment/cure
• lacks the expression of all 3 biomarkers (estrogen receptor, progesterone receptor, HER 2 receptor)
• only possible treatment is chemo and radiation
• African Black women are more targeted