4.1 DNA, Genes and Chromosomes

Question 1

Similarities between Euk and Pro DNA:

Answer 1

1. Nucleotides structure is identical- deoxyribose attached to phosphate and a base.
2. Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds.
3. DNA in mitochondria and chloroplasts have similar structure to DNA in prokaryotes. (Short, circular, not associated with proteins).

Question 2

Differences:

Answer 2

1. Eukaryotic DNA is longer.
2. Eukaryotic DNA is linear, prokaryotic DNA is circular.
3. Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not.
4. Eukaryotic DNA contains introns, prokaryotic DNA does not.

Question 3

Chromosome:

Answer 3

1. Long, linear DNA and its associated histone proteins.
2. In the nucleus of eukaryotic cells.

Question 4

Gene:

Answer 4

A sequence of DNA (nucleotides) bases on a specific locus that codes for the amino acid sequence of a polypeptide or a functional RNA.

Question 5

Locus:

Answer 5

Fixed position a gene occupies on a particular DNA molecule.

Question 6

Nature of the Genetic Code:

Answer 6

1. Triplet code: A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid.
2. Universal: The same base triplets code for the same amino acids in all organisms.
3. Non- overlapping: Each base is part of only one triplet so each triplet so each triplet is read as a discrete unit.
4. Degenerate: An amino acid can be coded for by more than one base triplet.

Question 7

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

Answer 7

1. DNA that does not code for amino acids/polypeptides.
2. Between genes.
3. Within genes- introns. (Only in eukaryotic cells).
4. Exons do code for amino acids.