WEEK 9 (DNA organisation) Flashcards
What are the four levels of complexity of DNA?
- nucleotides form the repeating structural unit of nucleic acids
- nucleotides are linked together in a linear manner to form a strand of DNA or RNA
- two strands of DNA interact with each other to form a double helix
- the three-dimensional structure of DNA results from the folding and bending of the double helix
What is the name of the linkage in DNA/RNA strands?
Phosphodiester linkage
What does the phosphodiester backbone consist of?
The phosphates and sugar molecules
How many nucleotides in each strand are included in one full turn of the DNA double helix?
10 nucleotides
Two strands of DNA form a right-handed ______________________
double helix
The bases in opposite strands hydrogen bond according to which rule?
AT/GC rule
The two strands are ____________ with regard to their 5’ to 3’ directionality
antiparallel
What is the genetic term to say that the two sequences are complementary to each other?
the two sequences exhibit complementarity
What does a Nucleosome “bead” consist of?
8 histone molecules + 146 base pairs of DNA
Describe chromatin structure
- DNA exists in the condensed, chromatin form to fit into the nucleus
- DNA loops twice around a histone octamer to form a NUCLEOSOME
- H1 binds to the nucleosome and to “linker DNA” stabilising the chromatin fibre
How many hydrogen bonds are between Adenine and Thymine
2 hydrogen bonds
How many hydrogen bonds are between Cytosine and Guanine?
3 hydrogen bonds
What charge do Phosphate groups give DNA?
a negative charge
What charge does Lysine and Arginine give histones?
a positive charge
What happens to DNA during mitosis?
DNA condenses to form chromosomes. DNA and histone synthesis occurs during S phase.
Describe mitochondrial DNA
Mitochondria have their own DNA, which is circular and does not utilise histones
What is the difference between Heterochromatin and Euchromatin?
Heterochromatin is condensed, appears darker on the electron microscope, transcriptionally inactive and has increased methylation and decreased acetylation.
(e.g Barr bodies)
[Heterochromatin = highly condensed]
Euchromatin is less condensed, appears lighter on the electron microscope, transcriptionally active and sterically accessible.
[Euchromatin is expressed]
What are Polytene chromosomes?
Large chromosomes consisting of thousands of DNA strands derived from larval salivary gland cells of Drosophila
What are lamp brush chromosomes?
a special form of chromosomes found in the growing oocytes (immature eggs) of most animals
How do you calculate the map distance between two genes?
(New recombinants / Total offspring) X 100
What is the smallest structure of a chromosome?
A nucleosome
How many types of histones proteins are involved in the nucleosome?
4
What are the types of histones proteins are involved in nucleosomes?
H2A
H2B
H3
H4
How many codons code for amino acids?
64
What are the start and stop codons?
Start codon is AUG (Methionine) and stop codon is UAG, UAA & UGA (no amino acid is coded)
What is the Wobble position?
The wobble position of a codon refers to the 3rd nucleotide in a codon. This nucleotide has two major characteristics: Binding of a codon in an mRNA the cognate tRNA is much “looser” in the third position of the codon
