3.4.1 - DNA, genes and chromosomes Flashcards
Topic 4
Similarities between DNA in eukaryotic cells and DNA in prokaryotic cells
● 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
Differences between DNA in eukaryotic cells and DNA in prokaryotic cells
● Eukaryotic DNA is longer, prokaryotic DNA is shorter
● 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 found:
1. Between genes - eg. non-coding multiple repeats
2. Within genes - introns
In (1), much of the nuclear DNA does not code for polypeptides
(1) eukaryotes
Intron
Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells
Exon
Base sequence of a gene coding for amino acid sequences (in a polypeptide)
