[8.1] genes and the genetic code

Question 1

what is a gene?

Answer 1

a section of DNA that codes for:

• a strand of mRNA that is then coded into a protein
• functional RNA (tRNA strands and rRNA strands, which are used to make ribosomes)

Question 2

what are the special features of the triplet code?

Answer 2

1. the degenerate code
2. the universal code
3. the non-overlapping code

Question 3

what is the degenerate code?

Answer 3

• there are 20 AAs
• each AA must have its own code of bases in the DNA
• three bases produce 64 (4³) which is more than enough
• therefore, amino acids can be coded for by more than one triplet

Question 4

what is the universal code?

Answer 4

each triplet codes for the same amino acid in all organisms

this is indirect evidence for evolution

Question 5

what is the non-overlapping code?

Answer 5

each base in the sequence is read only once

Question 6

what is the difference between introns and exons?

Answer 6

• intron = non-coding
• exon = a sequence of DNA that codes for an amino acid sequence

Question 7

how were introns discovered?

Answer 7

because mRNA was always shorter than DNA

Question 8

what are some theories for introns?

Answer 8

1. role in regulation of gene expression
2. multiple splicing to create several polypeptide chains from one strand of DNA
3. junk DNA

Question 9

in eukaryotes, where are the 2 places where sections of DNA that do not code for an amino acid can be found?

Answer 9

• introns = sequences of non-coding DNA within genes
• non-coding multiple repeats = sequences of non-coding DNA between genes