DNA and RNA Structure

Lin Exam 3

*Genetic material must meet several criteria:

• Information

  • Must contain info necessary to make a whole organism

• Tranmission

  • Must be passed from parent to offspring (inheritance)

• Replication

  • Must be copied to be passed down

• Variation

  • Must be capable of changes → phenotypic variation

*Streptococcus pneumoniae comes in two strains

• Type S = smooth

  • Invades and causes death in host

  • Why? Polysaccharide capsule → protects from host immune system

• Type R = right

  • Mice survive and bacterium gets killed by the immune system

*What happens when live type R + dead type S?

• Mice die

• Type S bacteria recovered, meaning dead type S transformed by live type R

• Transformation

*What did Avery, MacLeod and McCarty do?

• Experimented to figure out what caused transformation

• Treated DNA, RNA, proteins, and carbohydrates

  • DNA is what converted type R → type S

  • Eliminating DNA by DNase (destroys DNA) stopped transformation

*Hershey and Chase - Blender

• Viruses are made of protein and DNA

  • Phosphorus labels DNA

  • Sulfur labels proteins

• P entered cells, S remained outside

Thus, because ³²P entered bacterial cells → we realized DNA is the genetic material and not proteins

DNA and RNA Structure

• Nucleotides make nucleic acids

• Nucleotides link together to make single strand

• Two strands make double helix

• 3-D structure from double helix folding and bending in on itself → interacting with proteins = chromosomes

Nucleotide Structure

• Phosphate group

• Pentose sugar

  • Ribose = RNA

  • Deoxyribose = DNA

• Nitrogenous base

Structure of a DNA Strand

• Nucleotides linked together by ester bonds = covalent = (single strand)

  • 5’ carbon of a nucleotide to 3’ carbon of another nucleotide = phosphodiester linkage

Watson and Crick

• Helical structure, base pairs, ratios of bases figured out beforehand

• Solved structure of DNA

  • sugar-phosphate backbone

  • bases form hydrogen bonds

Structure of Double Helix

• 10 base pairs per turn

• Antiparallel (strands run in diff directions)

• Clockwise turn

Stabilization of Double Helix

Hydrogen bonding between complementary bases

• A/T bonded by two H-bonds

• C/G bonded by three H-bonds

Grooves

Outside of helix has grooves

• Major

  • Proteins bind to these grooves

    • They can interact with specific sequence of bases

• Minor

RNA Structure

• Ribose has OH group in 2’ carbon instead of Deoxyribose

• Uracil as a base instead of Thymine

• Single-stranded

RNA Secondary Structures

Nucleotides will fold in causing diff structures/loops (bulge, internal, multibranched, stem)