Structure of DNA Flashcards
H-bonds between Guanine and Cytosine
3 - three
How many H-bonds between Adenine and thymine
Two - 2
Chargoff’s rule
There is a 1:1 ratio between base pairs in DNA.
Eg. If there are 36 thymines in a DNA molecule there must also be 36 adenines in this molecules.
What are the three forms of DNA?
- A-DNA
- B-DNA - most common
- Z-DNA - very rare
What forces contribute to the structure and stability of DNA?
- Hydrogen bonds
- Covalent bonds
- Ionic interactions
- Van der Waals interactions
Which of the forms of atomic bonding is the weakest? A. Hydrogen bonding B. Covalent bonding C. van der Waals interactions D. Ionic interactions
C
What base binds with adenine?
Thymine
What base binds with cytosine?
Guanine
Which double stranded DNA is more stable?
A. 8A-T, 1C-G
B. 5A-T, 4C-G
B. this is because guanine forms three hydrogen bonds with cytosine while adenine only forms two hydrogen bonds with thymine.
Why does salt stabilize DNA?
Ions the form salt neutralize charges found in DNA.
-> less repulsion -> more compact -> more stability
Heterochromatin
Highly condensed - no gene expression
Euchromatin
Less compact - gene expression
In what phase of the cell cycle would you expect to see all of the DNA as heterochromatin?
A. Interphase
B. Mitosis
C. Meiosis
B and C
Cell division occurs in mitosis and meiosis and DNA must be compact and non-expressive to occur
What is the term for inactive X-chromosome?
Barr body
What overall charges do arginine and lysine have?
Positive
How to does DNA wrap around histones and stay stable?
- Phosphates are negatively charges
- Histones contain positively charged amino acids, arginine and lysine
- these amino acids neutralize negative charges from phosphates
- This allows less repulsion so that DNA wrap around
- Histones also form hydrogen bonds with DNA backbone and DNA bases in the minor groove
- These features allow great stability for DNA.
Why are there minor and major grooves?
Strands are not directly opposite each other and so form unequal grooves
What interacts with major groove?
Proteins
Modifying enzymes
Transcription factors
Restriction enzymes
What interacted with minor groove?
Not sure
What do bacteria do to protect DNA?
Have methylated to add a methyl group to DNA
Type 1 restriction enzymes
Multi-subunit REs that cut at random positions far from their recognition site
Type 2 restriction enzymes
REs that cut at defined positions close to or within their recognition site
Most useful
Type 3 restriction enzymes
REs that cut about 25 base pairs away from their recognition site
Can be useful
Application examples of RE use in lab
- Creating plasmid vectors during gene cloning and protein expression experiments
- Used to distinguish gene alleles by specifically recognizing single base changes in DNA known as single nucleotide polymorphisms (SNPs) - genotyping
- Used to digest genomic DNA for gene analysis by southern blot - allows researchers to identify how many copies of a gene are present in the genome of one individual, or how many gene mutations have occurred within a population