Nucleic Acid structure - part 1

download report

Transcript Nucleic Acid structure - part 1

Nucleotides & Nucleic Acids
Roles:
Energy currency (ATP, GTP)
Chemical links in response of cells to hormones (cAMP)
Involved in cofactors (NAD, FAD, CoA)
Metabolic intermediates (acetyl CoA)
Constituents of nucleic acids, DNA and RNA
Central Dogma of Biology
Storage and transmission of genetic info
Contains genes
rRNA - structural components of ribosomes
mRNA - carries genetic info from gene to
ribosome to make protein
tRNA - adaptor that translates info in mRNA
into amino acid sequence
Nucleotides & Nucleic Acids
Nucleotides:
1. Nitrogenous base
2. Pentose sugar
3. Phosphate
Nucleosides:
1. Nitrogenous base
2. Pentose sugar
Nitrogenous bases are either pyrimidines or purines
Nucleotides & Nucleic Acids
Nitrogenous bases are either pyrimidines or purines
Nucleotides & Nucleic Acids
Ribose sugars can be either 2’-deoxy (DNA) or have a 2’-OH (RNA)
Nucleotides & Nucleic Acids
Nucleotides & Nucleic Acids
Hydrolysis of RNA
Nucleotides & Nucleic Acids
Properties of RNA and DNA
Forces involved in structure
1.
Nucleotides & Nucleic Acids
Properties of RNA and DNA
Forces involved in structure
1. Hydrophobic
Bases hydrophobic at neutral pH, hydrophobic stacking interactions
Nucleotides & Nucleic Acids
Properties of RNA and DNA
Nitrogenous rings are mostly planar
Resonance in cyclic rings allow nucleotide bases to absorb UV light
Nucleotides & Nucleic Acids
Properties of RNA and DNA
Forces involved in structure
2. Hydrogen bonding patterns in RNA and DNA
Involve ring N, carbonyls, amino groups
Permits complementary association of 2 strands of nucleic acid
(structure of DNA by Watson & Crick)
Uridine (RNA)
Nucleotides & Nucleic Acids
Discovery of DNA structure and its role in housing genetic information
Miescher 1868
Isolate phosphorus-containing substance which he termed “nuclein”
Acidic (DNA) & basic portions (protein)
Hypothesize that nuclein associated with genetic inheritance
Avery-MacLeod-McCarty 1944
Direct evidence that DNA carries genetic info
Nucleotides & Nucleic Acids
Discovery of DNA structure and its role in housing genetic information
Avery-MacLeod-McCarty 1944
Direct evidence that DNA carries genetic info
Nucleotides & Nucleic Acids
Discovery of DNA structure and its role in housing genetic information
Avery-MacLeod-McCarty 1944
Direct evidence that DNA carries genetic info
Griffith
Avery-MacLeod-McCarty
?? Results
Treat DNA with protease
- transform
Treat DNA with
deoxyribonucleasesdestroy transforming
activity
Nucleotides &
Nucleic Acids
Hershey-Chase 1952
More evidence that DNA
carries genetic info
DNA radiolabeled
Protein radiolabeled
Nucleotides & Nucleic Acids
Chargaff’s rules 1940s
1. Base composition of DNA varies from one species to another
2. DNA from different tissues of same species have same base
composition
3. Base composition of DNA in given species does not change with
age, nutritional state, environment
4. In all cellular DNAs, regardless of species, the number of
adenosine residues is equal to the number of thymidine residues
(A=T), and the number of guanosines = cytidines (G=C)
A + G (purines) = C + T (pyrimidines)
Nucleotides & Nucleic Acids
Watson & Crick 1953 (Franklin & Wilkins too)
Franklin & Wilkins
Used x-ray crystallography to analyze fibers of DNA
Heavy bands - indicates recurring bases
X - indicates helical structure
Nucleotides & Nucleic Acids
Watson & Crick 1953 (Franklin & Wilkins too)
Watson & Crick
Used x-ray crystallography data
Used Chargaff’s rules
3D structure of DNA, strands antiparallel
Nucleotides & Nucleic Acids
DNA structure
Complementarity (replicate by separating strands and synthesizing
complementary strand for each)
Strands not identical in base sequence or composition
DNA replication
Nucleotides & Nucleic Acids
DNA structure - different 3D forms