Genetics Chapter 9

the study of DNA and RNA structure and function at the molecular level

• information
• transmission
• replication
• variation 

nucleotide linked together in a linear manner to form a strand of DNA and RNA

double helix (DNA)

3D structure of DNA results from folding and bending of the helix

the repeating structural units of nucleic acids

• phosphate group
• pentose sugar
• nitrogenous base 

• hydroxyl group
• 2' 

• adenine
• guanine  

• uracil
• cytosine
• thymine 

• base attached only to a sugar (deoxyribose vs. ribose)
• i.e. deoxyadenosine, deoxyguanine 

a nucleoside with one or more phosphate groups covalently attached to the 3' and/or 5' hydroxyl group

• adenosine triphosphate (ATP)
• adenosine diphosphate (ADP)
• adenosine monphosphate (AMP)

• base is attached to the 1' carbon 
• one or more phosphate groups attach at the 5' carbon 

a linkage between two carbons and a phosphate group through two oxygens

• dehydration synthesis
• DNA
• RNA

negatively

• 5' to 3' direction
• 5'-TAGCGAAT-3' complementary strand would be 5'-ATTGCGTA-3'

shuffling or rearrangement of sequences

• 1950's
• proposed alpha helix as a secondary structure of some proteins

• 1950
• worked with the chrmical compostion of DNA
• discovered the amount of A=T and C=G
• "Chargaff rule"- always an equal amount of A to T and C to G

• 1951
• X-ray diffraction of DNA was consistant with a helical structure
• diameter too wide to only be single stranded helix
• suggested DNA was composed of 2 or more strands with 10 bases per turn
• died of ovarian cancer from the radiation from her work 

• assistant was Rosalind Franklin
• took Franklin's work to Watson and Crick and put the pieces together and were awarded the 1962 Nobel Prize for the discovery of the double helix DNA molecule

• double stranded
• 10 base pairs within a complete twist 360^o around the backbone
• stablilized by hydrogen bonding between base pairs  

• purines (A & G) will always bond with pyrimidines (T & C)
• keeps width of double helix consistant
• DNA strands are complementary to each other
• knowing the sequence on one strand allows us to predict the sequence of its complementary strand 

• three
• two 

• sugar and phosphate group
• outer surface in direct contact with water 

indentation where the atoms of the bases are in contact with surrounding water 

• right handed twist
• predominant in living cells
• wild type
• 10 base pairs per 360^o turn
• bases tend to be centrally located
• hydrogen bonds between base pairs occurs perpendicular to central axis  

• right handed twist
• 11 base pairs per 360^o turn
• more tightly round
• hydrogen bonds between base pairs are tilted
• occurs under low humidity conditions
• not biologically significant in DNA 

• left handed twist
• zigzag appearence to it
• 12 bases per 360^o turn
• more tilted than A-DNA
• occurs at high ionic strength (high salt concentration)
• sequence aternat between purines and pyrimidines
• at lower ionic strenths methylation of cytosine bases favors Z DNA
• recently determined to be biologically important 

• triple helix
• synthetic DNA that binds into the major grooves of natural double-stranded DNA in a sequence specific way
• T in synthetic DNA will bind to an AT pair inthe natural DNA strands
• used as a way to silence genes like cancer to try to turn it off

DNA-binding proteins are necessary to help compact chromosomal DNA in order to fit into a living cell 

• shorter than DNA
• one strand of DNA is used as a template to make one complementary copy of single stranded RNA during transcription
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