DNA structure and function Flashcards
What is the Central Dogma of Biology
The two step process of transcription and translation where genetic information flows from DNA to a protein
What is the genome
The complete set of DNA in an organism
What is the DNA replication error rate
1 error per 10 to the power of 10 per division
Are nitrogenous bases hydrophobic or hydrophilic
Hydrophobic
What are the purines
Guanine and Adenine
What are the pyrimidines
Cytosine, thymine and uracil
How many rings do purines and pyrimidines have
Purines have 2, pyrimidines have 1
What is the difference between a ribose and deoxyribose sugar
Ribose has a hydroxyl group (OH) bonded to carbon 2’ while deoxyribose has no oxygen bound to carbon 2’ (H)
What type of bonds are phosphodiester bonds
Covalent
Where do covalent bonds form
Between atoms that share electrons (very strong bonds)
Where do phosphodiester bonds form between nucleotides
Between the 5’ carbon of one nucleotide and the 3’ carbon of the next nucleotide
What is the difference between nucleotides and nucleosides
Nucleosides are only the base and sugar, nucleotides are the base, sugar and phosphate
Where do hydrogen bonds form in DNA
Between nitrogenous bases due to an electrostatic attraction between a proton in one and an electronegative atom in the other
What is Chargaff’s rule
There is always an equal amount of A and T and C and G in DNA and the total of purines and pyrimidines is always equal
How many hydrogen bonds form between A and T
2
How many hydrogen bonds form between C and G
3
Which complementary base pairs require more energy to separate and why
C-G as they have more hydrogen bonds between them
Why are DNA strands antiparallel
Bases can only fit together in a specific orientation so the sugar phosphate backbone must be in opposite directions
What direction does the sense strand (forward) run in
From 5’ to 3’, left to right
What direction does the antisense (reverse) strand run in
5’ to 3’, right to left
What direction are DNA sequences always written in
5’ to 3’
What are the grooves in DNA
The major groove and minor groove are sections of DNA where base pairs are exposed and can be accessed and interact with other molecules
Why are the bases inside the DNA structure
They are hydrophobic
Why is the sugar phosphate backbone outside the DNA structure
As the negativity charged phosphate interacts with cations (positively charged ions) and cationic proteins to reduce electrostatic repulsion of the phosphate groups
What are the advantages of the DNA structure
- extremely stable backbone due to negatively charged phosphates on the outsides
- thermodynamically more stable than separated strands
What is the chromatin structure
The packaging of DNA with proteins
How is DNA packaged
By association with histones and non-histone proteins
What is heterochromatin
Densely packaged chromatin, inactive as less accessible for transcription, darker region when stained
What is euchromatin
Less densely packed region of chromatin, active region for gene expression as more accessible for transcription
What is the order of packaging in chromatin
DNA, nucleosomes, solenoid fibre( chromatin fibre), scaffold loop( section of chromosome ), chromatid, chromosome
What are nucleosomes
Fundamental repeating subunits of eukaryotic chromatin, where DNA is wrapped around a octamer (made of 8 histones)
What are the roles of histone proteins
- Packaging of DNA molecules so DNA is compact (structural)
- regulatory mechanisms as reduce gene expression as DNA becomes more compact, (functional)
- interact with negative charge of phosphate in DNA as histones are positively charged
- dynamic so enable interactions with other proteins
What are the roles of non-histone proteins in chromatin
- functional role of regulating gene expression and stimulating genetic activity in transcription
- negatively charged so interact with positively charged histones to reduce DNA-histone interactions or directly interact with DNA sequences
In a sample of DNA if 30% is thymine, what are the percentages of other bases
A- 30%
G- 20%
C-20%
