BIOL 3301: Ch 9 Molecular Structure of DNA and RNA

molecular genetics

• study of DNA structure and function at the molecular level

• our knowledge of genetic mechanisms comes from our knowledge of the molecular structure of DNA and RNA

genetic material

• must meet the following criteria

  • information

    • contain necessary info to make entire organism

  • transmission

    • be passed from parent→offspring

  • replication

    • copied to be passed from parent→offspring

  • variation

    • can change to account for the known phenotypic variation in each species

Frederick Griffith

• ? studied a bacterium (pneumococci) now known as streptococcus pneumoniae

  • 2 strains

    • type S→ Smooth

      • polysaccharide capsule

      • protect bacterium from immune system of animals

      • smooth colonies on solid media

    • type R→ Rough

      • no capsule

      • colonies with rough appearance

type S pneumoniae

• secrete a polysaccharide capsule

• protects a bacterium from the immune system of animals

• produce smooth colonies on solid media

type R pneumoniae

• unable to secrete a capsule

• produce colonies with a rough appearance

live type S

• mouse died and type S bacteria recovered from the mouse’s blood

live type R

• mouse survived and no living bacteria isolated from the mouse’s blood (2)

heat killed type S

• mouse survived and no living bacteria isolated from the mouse’s blood (3)

live type R + heat killed type S clls

• mouse died and type S bacteria recovered from the mouse’s blood

transforming principle

• Griffith concluded that something from the dead type S bacteria was transforming type R bacteria → type S

  • transformation

• the substance that allowed this to happen was the ?

  • griffith didn’t know what type of substance it was

capsule

• the formation of a ? by these bacteria fulfilled the 4 required properties of “genetic material”

  • transformed bacteria acquired information to make the

  • variation exists in the ability to make a ?

  • info required to create a ? is replicated and transmitted from mother→ daughter cells

avery, macleod, mccarty experiments

• prepared cell extracts from type S cells and purified each type of macromolecule

• only the extract that contained purified DNA was able to convert type R bacteria→ type S

• treatment of the DNA extract with RNase or protease did not eliminate transformation

  • treatment with DNase did

nucleic acids

• DNA and molecular cousin RNA are known as nucleic acids

• first ID’ed by Friedrich Miescher in 1869 in waste surgical bandages

  • named substance “nuclein”

    • material from cell nucleus

• later research shoed DNA and RNA release H+ in water and therefore are acids

  • became named ?

levels of nucleic acid structure

• nucleotides→ single strand→ double helix→ 3D structure

• DNA and RNA are large macromolecules with several levels of complexity

• nucleotides

  • form repeating unit of nucleic acids

• linear strand of DNA or RNA

  • nucleotides linked

• double helix

  • in DNA, 2 strands can interact to form

• 3D DNA structure

  • folding and bending of the double helix

  • interaction f DNA with proteins produces chromosomes within living cells

nucleotides

• repeating structural unit of DNA and RNA

• 3 components

  • phosphate group

  • pentose sugar

    • ribose in RNA

    • deoxyribose in DNA

  • a nitrogenous (nitrogen containing) base

linear strand

• nucleotides are linked to form ? of RNA or DNA

double helix

• in DNA, 2 strands can interact to form a ?

3D DNA structure

• results from folding and bending of the double helix

• interaction of DNA with proteins produces chromosomes within living cells

2’ carbon of sugar

• main difference btw DNA vs RNA nucleotides

• DNA

  • sugar deoxyribose has H @ ?

• RNA

  • sugar ribose has OH @ ?

nucleoside

• base + sugar

• ex.,

  • adenine + ribose = adenosine

  • adenine + deoxyribose = deoxyadenosine

nucleotide

• base + sugar + phosphate(s)

• ex.,

  • adenosine monophosphate (AMP)

  • adenosine diphosphate (ADP)

  • adenosine triphosphate (ATP)

covalent/ester bonds

• in DNA, nucleotides are linked together by ?

phosphodiester linkage

• a phosphate connects the 5’ carbon of one nucleotide to the 3’ carbon of an adjacent nucleotide

5’ to 3’

• a DNA strand has ? directionality

• in a strand, all sugar molecules are oriented in the same direction

backbone

• the phosphates and sugar molecules form the ? of the nucleic acid strand

  • the bases project from the backbone

double helix

• in 1953, James Watson and Francis Crick elucidated the ? structure of DNA

• the scientific framework for their breakthrough was provided by other scientists

  • Linus Pauling

  • Rosalind Franklin and Maurice Wilkins

  • Erwin Chargaff

erwin chargaff

• pioneered biochemical techniques for isolation, purification, and measurement of nucleic acids from living cells

• it was known that DNA contained 4 bases: A,G,C,T

• He analyzed the base composition of DNA isolated from many different species

  • % adenine = % thymine

  • % cytosine = % guanine

    • ? ‘s rule was crucial for Watson and Crick to elucidate DNA structure

chargaff’s rule

• analyzed base composition of DNA isolated from many species

  • % adenine = % thymine

  • % cytosine = % guanine

• was crucial for Watson and Crick to elucidate DNA structure

double helix stabilization

• ? is stabilized by hydrogen bonding btw complementary bases

  • A bonded to T by 2 hydrogen bonds

  • C bonded to G by 3 hydrogen bonds

• base stacking

  • within the DNA, the bases are oriented so that the flattened regions face each other

base stacking

• within the DNA, the bases are oriented so that the flattened regions face each other

• minimizes the exposure of the hydrophobic (water-repelling) parts of the nitrogenous bases to water.

  • excludes water molecules from the interior of the helix

grooves

• there are 2 asymmetrical ? on the outside of DNA double helix

  • major ?

  • minor ?

• certain proteins can bind within these ?

  • they can thus interact with a particular sequence of bases

DNA

• A=T

• C=G

• double stranded, antiparallel, complementary

RNA

• uracil as a base (instead of thymine)

• ribose sugar with 2’ OH (instead of deoxyribose with 2’ H)

• strands are typically 100s-1000s nucleotides in length

• in ? synthesis, only 1 of the 2 DNA strands is used as a template

RNA structure

• although usually, single stranded ? molecules can form short, double stranded regions

  • this secondary structure is due to complementary base pairing

  • A to U

  • C to G

  • allows short regions to form double helix

• different types of ? secondary structures are possible