8.2: DNA and Chromosomes Flashcards
What is the DNA like in Prokaryotic cells
- DNA molecules are shorter and not associated with histones
- No chromosomes
Plasmids
What is the DNA like in Eukaryotic cells
- DNA molecules are longer and associated with histones
2. Form chromosomes
What are the exceptions in Eukaroytic cells
Mitochondria/Choloroplasts
Why are mitochondria/chloroplasts an exception
They contain DNA but it isnt associated with histones and they dont have chromosomes, therefore they have Prokaryotic like DNA
When are chromosomes visible
During cell division
What are chromosomes like when cell division isnt occurring
They are widely dispersed throughout the nucleus
How do chromosomes appear at the beginning of cell division
They appear as two threads (chromatids) joined at a single part (centromere)
Formation of chromosomes
- The DNA helix is wound around histones to fix it into position
- The DNA-histone complex is then coiled
- The coil is looped and further coiled before being packed into a chromosome
- In this way, lots of DNA is condensed into a single molecule of DNA
What are homologous chromosomes
Chromosomes containing a set of chromosomes from the mother (Maternal) and the father (Paternal)
Feature of homologous chromosomes
They carry the same genes but NOT necessarily the same alleles of the genes
What is an allele
A variation of a gene (form of a gene)
How many forms do genes exist in
2 or more different forms
How many alleles does an organism inherit
1 from the mother, 1 from the father
How are alleles produced
When a change in the DNA base sequence of a gene occurs (mutation)
What is the result of new alleles
A different combination of amino acids occurs, causing a different polypeptide (protein) to be formed
