4.1 DNA, genes and chromosomes

What are the similarities between DNA in eukaryotes and prokaryotes

• 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 ave similar structure to prokaryotes DNA (short, circular and not associated with proteins)

What are the differences between DNA in eukaryotes and prokaryotes

• eukaryotic is longer

• Eukaryotic is linear, prokaryotic is circular

• Eukaryotic is associated with histone proteins, prokaryotic isnt

• Eukaryotic contains introns, prokaryotic doesn’t

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 (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 (4 things)

• triplet code

• Universal

• Non-overlapping

• Degenerate

The nature of the genetic code: what is a triplet code

• a sequence of 3 DNA bases, called a triplet, codes for a specific amino acid

The nature of the genetic code: Universal

• the same base triplets code for the same amino acids in all organisms

The nature of the genetic code: Non- overlapping

• each base is part of only one triplet so each triplet is read as a discrete unit

The nature of the genetic code: Degenerate

• an amino acid can be coded for by more than one base triplet

What are non coding base sequences

DNA that does not code for amino acid sequences/ polypeptides

Where are non coding base sequences found

• between genes (e.g non-coding multiple repeats)

• Within genes (introns)

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 acids sequences (in a polypeptide)