DNA Flashcards
What is the structure of DNA
DNA is arranged in a double helix structure with complementary base pairing
The DNA is coiled around his tone proteins
Where is DNA located
In the nucleus and mitochondria
How many chromosomes do each cell have
46 chromosomes - 22 pairs and a pair of sex chromosomes
What is a karyotype
Karyotype is an individuals complete set of chromosomes
How does DNA become chromosomes
DNA wraps around his tone proteins and form a nucleosome which supercoils to become chromosomes
How is DNA stored in a prokaryote
In a prokaryotes there is no nuclear envelope/membrane and the DNA is organised in a single chromosome/loop known as a nucleoid
How is DNA stored in a eukaryotes
DNA is stored in the nucleus, with chromatid wrapped round his tone proteins
What is maternal DNA
The DNA found in the mitochondria is maternal DNA (only from the mother)
Explain how DNA folds into a chromosome
DNA starts as a double helix which winds around core particles (histone proteins) to form nucleosomes. These fold into a zig-zag fibre which folds into irregular to form a thick fibre.
In dividing cells the looped chromatin coils further to from each chromatid. 4 chromatid make up a chromosome which is joined by a centromere in the centre which forms a chromosome
What are the overall functions of DNA
- stores genetic information
- transfers genetic information
- acts as a template and regulator for transcription and protein synthesis
- DNA is the structural basis for hereditary and genetic disease
What are the different types of mutations in DNA
Duplications
Deletions
Mutations of regulatory sequence
DNA damage
DNA repair issue
Non-sense
Mis-sense
Splice site mutation
Expansion of tri-nucleotide
Anticipation
What is a duplication
Sections within DNA that are repeating so the incorrect protein is generated
What are the types of deletions and what do each cause
There are 2 types of deletions
Our of frame deletions which means the sequence shifts meaning the reading frame of the gene is changed
In frame deletions is where one codon is removed meaning one amino acid is lost but the reading frame remains the same
What occurs in a mutation of regulatory sequence
The coding sequence is still in tack but the gene itself is either switched on or switched off
How can DNA become damaged
Chemicals
UV rays
Radiation
What are non-sense mutations
Non-sense mutations are point mutations that produce a stop codon resulting in an incomplete, usually a non-functional protein
What can a non-sense mutation cause
Duchenne’s muscular dystrophy
What is a mis-sense mutation
A mis-sense mutation is a point mutation where a single results in a codon that codes for a different amino acid which can result in silent mutation and a non-functional protein been made
What can be an example disease caused by mis-sense mutation
Sickle cell disease where CAG is replaced with CTG
What is a splice site mutation
A splice site mutation affects the accurate removal of an intron
What disease can be caused by an expansion of tri-nucleotide repeat
Huntingtons disease
CAG triplet code is repeated several times in the first part of the coding sequence- if CAG repeats more than 36 times huntingtons will develop
What does anticipation mean
In terms of Huntington’s disease repeats of the CAG in the coding sequence gets bigger when they are transmitted to the next generation which means the symptoms will occur earlier and of greater severity
