DNA structure Flashcards
What must happen for a molecule to serve as genetic material
It must be able to replicate, store info, express info, and allow variation by mutation
Why did geneticists favor proteins over nucleic acids as genetic material?
Proteins are more diverse and abundant in cells
DNA was thought to be too simple to be the genetic material
What did Griffith do?
found transforming principle for genetic info
used living IIR colony and heat killed IIIs (virulent) and killed mice, finding living IIIs In tissue
What did Avery, Macleod and McCarty do?
used IIIs cells and treated them with compounds that would kill proteins, ribosomes, and deoxyribosomes. Transformation occured in all the assays except for the one treated with deoxyribonuclease,
SHOWED DNA IS TRANSFORMING FACTOR
What did Hershey and chase do?
injected labeled phage genetic material in bacterium
infected bacteria either had 12P label or unlabeled showing that DNA and not protein was transforming factor by showing that DNA enters the bacterial cell during infection and directs viral reproduction
What is indirect evidence for DNA as the genetic info?
Protein is abundant in the cytoplasm and protein is not
Mitochondria and chloroplast perform genetic function, and DNA is also part of these organelles
DNA is found only where the primary genetic function occurs
DNA and RNA absorb UV light at 260 nm, which a wavelength that is most mutagenic, proteins absorb most strongly at 280 nm
This provides indirect evidence for DNA as the genetic material
What is the strongest direct evidence for DNA as genetic material?
Recombinant DNA technology shows presence of eukaryotic gene product in bacteria
What do nucleotides consist of?
What do nucleosides consist of?
A nitrogenous base, a pentose sugar, and a phosphate group
A nitrogenous base and a pentose sugar
What are the two kinds of nitrogenous bases?
Purines - 2 membered ring, A, G
Pyrimidines - one membered ring, C, T (DNA), U (RNA)
What is the difference between ribose and deoxyribose?
ribose- contains two hydroxyl groups at 2’ and 3’
deoxyribose - contains only one hydroxyl group at 3’
Where is the phosphate group located?
The C’5 position on a nucleotide
What are phosphodiester bonds?
Link nucleotides by phosphate at C-5’ position and OH at C-3’ position
What did Chargaff do?
Showed that amount of A is proportional to T and amount of C is proportional to G, but A+T doesn’t equal C+G
What did Rosalind Franklin do?
X ray diffraction to show 3.4 angstrom periodicity, characteristic of a helical structure
What did Watson and Crick propose?
DNA is a right handed double helix with two antiparallel stands, based on Chargaff and Franklin model
