4.1 DNA, genes and chromosomes

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Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells (similarities)
Similarities:
● Nucleotide structure is identical - deoxyribose attached to phosphate and a base
● Adjacent nucleotides joined by phosphodiester bonds, complementary bases joined by hydrogen bonds
● DNA in mitochondria / chloroplasts have similar structure to DNA in prokaryotes
○ Short, circular, not associated with proteins
Compare and contrast DNA in eukaryotic cells with DNA in prokaryotic cells (differences)
Differences:
● Eukaryotic DNA is longer
● Eukaryotic DNA is linear, prokaryotic DNA is circular
● Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not
● Eukaryotic DNA contain introns, prokaryotic DNA does not
What is a chromosome?
● Long, linear DNA + its associated histone proteins
● In the nucleus of eukaryotic cells
What is a gene?
A sequence of DNA (nucleotide) bases that codes for:
● The amino acid sequence of a polypeptide
● Or a functional RNA (eg. ribosomal RNA or tRNA)
What is a locus? 
Fixed position a gene occupies on a particular DNA molecule.
Describe the nature of the genetic code
Triplet code = A sequence of 3 DNA bases, called a triplet, codes for a specific amino acid
Universal = The 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 base triplet
What are ‘non-coding base sequences’ and where are they found?
Non-coding base sequence - DNA that does not code for amino acid sequences / polypeptides:
Between genes - eg. non-coding multiple repeats
Within genes - introns
In eukaryotes, much of the nuclear DNA does not code for polypeptides.
What are introns? 
Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
What are exons? 
Base sequence of a gene coding for amino acid sequences (in a polypeptide)