DNA, Genes And Chromosomes Flashcards
What is the structure of DNA?
• double stranded molecule, each strand is a polynucleotide made up of individual nucleotides
• nucleotides consist of: a phosphate, a deoxyribose sugar and a nitrogenous base
• many millions of base pairs long
Where is DNA found?
- Prokaryotic cells
- Chloroplasts and mitochondria
- Nuclei of eukaryotic cells
Describe DNA in prokaryotic cells
•Have a single molecule of circular DNA (nucleoid)
• some cells also have smaller loops called plasmids
• DNA is named and not associated with histone proteins
What is DNA like in chloroplasts and mitochondria?
Short circular molecule not associated with histone proteins
What is the DNA in the nuclei of eukaryotic cells like?
• Very long linear molecule which is associated with histone proteins
• together a DNA molecule and the histone proteins form a chromosome
How is DNA organised into chromosomes?
• DNA molecule is wrapped around histone proteins to fix it into position, the DNA histone complex is then coiled into solenoids and then further coiled, this means that a very long molecule of DNA can be condensed into a single chromosome
• a lot of genetic information can be stored in the nucleus of each cell
Are chromosomes visible in interphase?
Chromosomes are dispersed throughout the nucleus and are not visible as separate structures during interphase
When are chromosomes visible?
When the nucleus is about to divide and the DNA molecule is already replicated by semi conservative replication
What are homologous chromosomes?
Pair of chromosomes that carry the same genes at the same locus but they do not necessarily carry the same alleles of the gene. Homologous pairs are not genetically identical
What is a gene?
A base sequence of DNA that codes for either:
• the amino acid sequence of a polypeptide
• a functional RNA
How much of the DNA codes for amino acid sequences in humans
Only 2% in humans
What is an Intron?
non coding sequences in the genes
What is a proteome?
The full range of all the proteins that a cell is able to produce using its genome
What is an Allele?
Alleles are versions of genes. Some genes have two or more alternative forms, each allele has a different sequence of bases and consequently codes for a different polypeptide
What is a gene pool?
All the different alleles of all the genes found within a population
