(DNA)Deoxyribonucleic acid (DNA) –Stores info., copies itself –Directs cell activities –hereditary material passed from cell → cell nucleotideNucleic Acid – polymer; monomer = nucleotide.. –two kinds: DNA and RNA.
Sections in a DNA mol. called genes. Genes code for proteins; the hereditary info. in DNA tells cell how to make proteins
Nucleotide: three components (CP: 230) (Hon: 197) – 5 C sugar – phosphate group –nitrogenous base (4 kinds in DNA)
Nucleotide: three components (CP: 230) (Hon: 197) – a 5-carbon sugar – a phosphate group –a nitrogenous base (4 kinds in DNA)
Four Kinds of Nitrogenous Bases Pyrimidines - single ring bases.Pyrimidines - single ring bases. –Thymine and Cytosine Purines - double ring bases.Purines - double ring bases. –Adenine and Guanine Base pairsBase pairs (also called nucleotide pairs) are formed when a purine bonds with a pyrimidine A-T and C-G (always)A-T and C-G (always) C C C C N N O O Thymine C C C C C N N O N Cytosine C C C C N N N Adenine N N C C C C C N N O N Guanine N N C
DNA STRUCTURE Shape is like twisted ladder. Called a double helix -two strands bonded together & twisteddouble helix –The bases form the rungs of the ladder hydrogen bonds hold pairs together; A-T, C-G –Sugars and phosphates form sides of ladder.
Nucleosomes Lowest DNA packaging level Can be thought of as a length of thread wound around a spool, the thread representing DNA and the spool being histone proteins.
DNA - By The Numbers! Each cell has about 2 meters (6 ft) of DNA. The average human has 60-75 trillion cells. Avg human has enough DNA to go from the Earth to the sun more than 400 times. DNA has a diameter of only 0.0000000002 meters (20Ǻ) [1Ǻ =10 -10 m] The earth is 150 billion meters or 93 million miles from the sun.
Karyotypes Normal human male karyotype (the total set of chrom. of an organism)
The History of DNA Gregor Mendel-1866 –Determined “Unit characters” were the method of passing on traits for inheritance Friedrich Meischer - 1868 –Studied nuclei of pus cells obtained from discarded surgical bandages –Detected a phosphorus-containing substance that he named nuclein.
Frederick Griffith 1928 : Work with Bacteria –Found that DNA taken from a virulent (disease-causing) strain of bacteria (Streptococcus pneumoniae) –Transformed a non-virulent form of the bacterium into a virulent form.
Oswald Avery, Colin MacLeod, and Maclyn McCarty 1943 Continued the study of “Transformation” principle
Transformation Of Bacteria Two Strains Of Streptococcus Smooth Strain w/Capsule (Virulent) Rough Strain (Harmless) Capsule
Experimental Transformation Of Bacteria -Griffith’s Experiment Control OUCH! Rough Smooth (virulent)
The History of DNA Alfred Hershey and Martha Chase - 1952 –radioactive isotope tracer experiment –bacterial virus (bacteriophage T2) infects a host cell ( bacterium Escherichia coli) –found that T2 virus DNA, not its protein coat, enters the host cell –genetic information for replication of the virus
Using S 35 Bacteria grown in normal non- radioactive media T 2 grown in media containing S 35 incorporate S 35 into their proteins Blending causes phage protein coat to fall off T2 attach to bacteria and inject genetic material Is protein the genetic material? When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet. The supernatant is radioactive, but the pellet is not. Did protein enter the bacteria?
Using P 32 Bacteria grown in normal non- radioactive media T2 grown in P 32 containing media incorporate P 32 into their DNA Blending causes phage protein coat to fall off T2 attach to bacteria and inject genetic material Is DNA the genetic material? When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet The pellet is radioactive, but the supernatant is not. Did DNA enter the bacteria?
The History of DNA Structure Erwin Chargaff- 1940 - “Chargaff’s rule” – four bases may occur in varying proportions in DNA of different organisms –# of A = # of T, w/ two hydrogen bonds – = # of G and C are present w/ 3 hydrogen bonds Rosalind Franklin and Maurice Wilkins –X-ray diffraction study concluded DNA fibers have two strands.
The History of DNA Structure James Watson and Francis Crick - University of Cambridge -1953 Worked on problem of making a DNA molecule model that was double stranded but also had the specific A - T and G - C base equivalencies Solution-double helical structure for DNA.