DNA, genes & chromosomes

Question 1

What are the similarities & differences of DNA in eukaryotic & prokaryotic cells?

Answer 1

Similarities:
- nucleotide structure is identical
- adjacent nucleotides joined by phosphodiester bonds & complementary base pairs joined by hydrogen bonds
- DNA in mitochondria/ chloroplasts have similar structure to DNA in prokaryotes (short, circular & not associated with proteins)
Differences:
- eukaryotic DNA is longer
- eukaryotic DNA is linear, prokaryotic is circular
- eukaryotic DNA is associated with histone proteins, prokaryotic isn’t
- eukaryotic DNA contains introns, prokaryotic DNA doesn’t

Question 2

What is a chromosome?

Answer 2

• long linear DNA that is associated with histone proteins
• in the nucleus of eukaryotic cells

Question 3

What is a gene?

Answer 3

• a sequence of DNA bases that codes for amino acid sequence of polypeptides or functional RNA

Question 4

What is a locus?

Answer 4

fixed position a gene occupies on a particular DNA molecule

Question 5

What is the nature of the genetic code?

Answer 5

• triplet code - sequence of 3 DNA bases that code for a specific amino acid
• universal - same base triplets code for the same amino acids in all organisms
• non-overlapping - each base is part of only one triplet so each triplet is read as a discrete unit
• degenerate - an amino acid can be coded for by more than one triplet

Question 6

What are non-coding base sequences & where are they found?

Answer 6

• non-coding base sequence is DNA that doesn’t code for polypeptides
• found between genes & within genes (introns)
• most nuclear DNA in eukaryotes doesn’t code for polypeptides

Question 7

What are introns & exons?

Answer 7

• introns - base sequence of a gene that doesn’t code for amino acids in eukaryotes
• exons - base sequence of a gene coding for amino acid sequence