Ch.9: Molecular Structure of DNA and RNA Flashcards
What criterium does genetic material have to meet?
Information: It must contain the information necessary to make an entire organism
Transmission: It must be passed from parent to offspring
Replication: It must be copied in order to be passed from parent to offspring
Variation: It must be capable of changes to account for the known phenotypic variation in each
Who showed that a heritable material can transform Streptococcus pneumoniae bacteria and describe how
Frederick Griffith;
Type S: Secretes a polysaccharide capsule, protects the bacterium, allows them to successfully infect the host
Type R: Unable to secrete a capsule
What did Griffith’s experiment determine?
S creates li[ids that protect the virus and R protects the immune system; something from the dead type S bacteria was transforming
type R bacteria into type- transformation
Who’s lab suggested that DNA is a heritable factor? How?
(1944) Oswald Avery’s; Treatment of the DNA extract with Rnase degrades RNA) or protease (degrades the proteins) did not eliminate transformation , treatment with Dnase, (degrades DNA) eliminated the transformation
Who’s lab found that DNA is the heritable factor in T2 phage?
(1952) Alfred Hershey’s laboratory; used T2 bacteriophage to
ask whether DNA or protein is the heritable factor; most of the 32P (DNA) had entered the bacterial cells and was found in the cell pellet (only thing inside was DNA)
Who discovered DNA?
Friedrich Miescher (1869) from the nuclei of white blood cells
- Named the substance “nuclein”: material from
the nucleus of a cell
-Later research showed that DNA and RNA release H+ in water
What is a nucleotide and its 3 components?
The nucleotide is the repeating structural unit of DNA and RNA
- A phosphate group
- A pentose sugar; ribose in RNA, deoxyribose in DNA
- A nitrogenous (nitrogen-containing) base
What’s the only difference between DNA and RNA structures?
their pentose sugars
Nucleoside vs. Nucleotide
Nucleoside: DNA or RNA base plus sugar
Nucleotide: Nucleoside plus phosphate
Nucleotides are linked together by….using…., which is….
covalent ester bonds; phosphodiester linkage; 5’ carbon to adjacent 3’ carbon
Describe the Discovery of the Double Helix
(1953) James Watson and Francis Crick- breakthrough a was provided by a number of other scientists: Linus Pauling, Erwin Chargaff, Maurice Wilkins, Rosalind Franklin
Describe Erwin Chargaff’s experiment
found that in DNA, A% = T% and G% = C%; While the content of purines (adenine, guanine) and pyrimidines (cytosine and thymine)
can vary in different organisms, the ratio of adenine and thymine and the ratio of cytosine and guanine remains constant
Describe Rosalind Franklin’s Experiment
created Photo 51 which showed DNA had an a-helical structure
What are 5 key features of the structure of the double helix?
- Right-handed double helix turns in a clockwise direction.
- The bases in opposite strands hydrogen bond according to the AT/GC rule and are in the center
- The sugar and phosphate are on the outside of the double helix.
- The two strands are antiparallel and complementary: one strand in 5’ to 3’ direction and the other strand in 3’ to 5’ direction
- 10 nucleotides in each strand per complete 360° turn of the helix
How is the double-helical structure of DNA is stabilized?
- A bonded to T by two hydrogen bonds
- C bonded to G by three hydrogen bonds
- Base stacking: in DNA, the bases are oriented so that the flattened regions are facing each other
