DNA function, structure and replication Flashcards
What are the functions of DNA? (3)
- Storing and transferring genetic information
- Template and regulator for transcription and protein synthesis.
- DNA is the genetic material thus the structural basic of hereditary and genetic diseases.
Where is DNA found?
In the nucleus and mitochondria
How is DNA arranged?
- Arranged in a double helix with complimentary base pairing
- DNA coils around proteins (histones) and form nucleosomes > supercoils > chromosomes
How many chromosomes are there?
46, 22 pairs and a pair of sex chromosomes (X,Y)
What is a Karyotype?
number and appearance of chromosomes in a cell. Spreads are arranged in size order
Prokaryotes and DNA?
No nuclear membrane, DNA arranged in a single chromsome
Eukaryote and DNA?
- DNA is in a nucleus, bound to proteins (chromatin complex)
- Each chromosome is made of 2 identical strands of chromatids joined in the centre (centromere).
- Some DNA is found in mitochondria (purely maternal DNA.)
What is the structure of a nucleotide base?
- Phosphate group (energy for reactions)
- Sugar group
- Nitrogenous base
What is a duplication mutation?
sections repeating leading to an incorrect protein generated
What is a deletion mutation?
Out of frame – sequence shifts meaning the reading frame of the gene is changed.
In frame – whereby one codon is removed thus only one amino acid is lost. Reading frame is not changed.
What does a mutation of regulatory sequence mean?
coding sequence still intact, but gene itself is switched on or off etc
How can DNA be damaged?
From chemicals, UV and radiation
How can DNA have issues with repairing?
base or nucleotide excision, mismatch repair or transcription-couples repair
What is a Non-Sense mutation?
Point mutation that produces a stop codon - results in an incomplete, usually non-functional protein. E.g. Duchenne’s muscular dystrophy
What is a Mis-Sense mutation?
A point mutation in which a single nucleotide change results in a codon that codes for a different amino acid (substitution). This can have a varied affect and can result in a silent mutation and a non functional protein E.g Sickle cell disease where CAG was replaced with CTG.
What is a spice site mutation?
Affects the accurate removal of an intron
what is an expansion of tri-nucleotide repeat?
Huntington’s disease : CAG. Triple repeat is repeated several times in the first part of the coding sequence If > 36, the patient will develop Huntington’s-
What is meant by the process anticipation?
In diseases such as Huntington’s, repeats get bigger when they are transmitted to the next generation resulting in earlier symptoms of greater severity t his process is called anticipation.
What is meant by heterogeneity?
One gene one variant one disease e.g. Huntingtons
ALLELIC HETEROGENEITY - Lots of different variants in one gene e.g. cystic fibrosis
LOCUS HETEROGENEITY - Variants in different genes give the same clinical condition e.g. hypertrophic cardiomyopathy
Different variants in the same gene can give rise to different clinical conditions – genotype/phenotype correlations
