DNA and chromosomes Flashcards
What are the differences in terms of DNA and chromosomes which prokaryotic and eukaryotic cells have?
Prokaryotic:
- DNA molecules are shorter
- Form a circle
- Not associated with protein molecules, therefore, does not have chromosomes.
Eukaryotic:
- DNA molecules are longer
- Linear
- Associate with proteins called histones to form chromosomes.
- Mitochondria and chloroplast in eukaryotic cells also contain DNA but it’s short, circular and not associated with proteins like prokaryotic cells.
When can the chromosomes be seen?
Only visible during cell division so rest of the time they are widely dispersed throughout the nucleus.
What is the structure of a chromosome?
When it becomes visible during cell division, they appear as 2 strands called chromatid and the middle region where the chromatids are connected is called centromere.
What is the DNA in the chromosomes been held by?
Histones.
How are chromosomes made?
DNA molecule combines with histones and the DNA-histone complex coil up. The coils are then folded into loops and the loops coil and pack together to form chromosomes.
This way a lot of DNA can be condensed into a single chromosome.
How are organisms e.g. human, produced sexually?
Due to the fusion of a sperm and egg, each contributes one complete set of chromosomes to the offspring.
One of each pair is originated from the mother (maternal chromosomes) and other is from the father (paternal chromosomes).
What is a homologous pair of chromosomes?
2 chromosomes that carry the same gene but maybe different alleles of the same gene. e.g. A homologous pair of chromosomes may have genes for tongue rolling and blood group.
1 - Non-roller, group A
2 - Roller, group B
During meiosis, the daughter cell will receive one chromosome from each homologous pair, so one gene for each characteristic of the organism.
When the haploid cells combine, the diploid number is restored.
What is the diploid number?
The full set of chromosomes - in human it’s 46.
What is an allele?
An allele is an alternative form of a gene.
What happens when 2 alleles are different?
Each individual inherits one allele from each of its parent. When the alleles are different, each will have a different base sequence so different amino acid sequence and it will produce a different polypeptide.
What happens to the allele when there’s a change in the base sequence?
It produces a new allele of the gene (mutation) and causes a different sequence of amino acids being coded for and it would produce a different polypeptide, therefore, a different protein.
What happens to the protein which undergoes mutation?
They might not function properly or not function at all. If the protein is an enzyme, it may have a different shape and it might not fit into the substrate so the enzyme will not function properly.
