8.2 - DNA and Chromosomes Flashcards
Describe the DNA in a prokaryotic cell?
DNA molecules are shorter, forming a circle (plasmid)
They are not associated with protein molecules.
Describe the DNA in a eukaryotic cell
DNA molecules are longer, form a line (linear), occur in association with proteins called histones to form chromosomes.
Describe the DNA found in mitochondria and chloroplasts.
Contain DNA, short, circular, not associated with proteins.
What two parts make up a chromosome?
2 chromatid strands/threads
Centromere
What is the DNA and chromosomes held together by?
The DNA and chromosomes is held together by histones, DNA is wound around his stones to hold it in position.
When are the chromosomes of a cell visible under a microscope?
The chrome zones are only visible when cells dividing by mitosis
What is an allele?
An allele is one of a number of alternative forms of a gene
What is meant by homologous chromosomes?
Homologous chromosomes always carry the same jeans but do not necessarily carry the same alleles they contain the same number of chromosomes.
How many chromosomes are in a diploid cell?
The number of chromosomes in a diploid cell is 46.
Therefore the number of chromosomes in a haploid cell is 23.
What is a mutation?
A mutation is a change in base sequence of a gene producing a new alleles which results in new amino acid and therefore polypeptide and hence a protein.
What is the danger of a mutation in the gene?
The new protein formed may not function properly for example a mutation in an enzyme might change active site and therefore it cannot function causing serious consequences
Explain how the considerable length of the DNA molecule is compacted into a chromosome.
It is looped and coiled a number of times.
