Lecture 2 - DNA Continued (Deoxyribonucleic Acid)

• Building a molecule of DNA

  • Each nucleotide piece is attached to the next nucleotide in order by a phosphodiester bond… creating the “backbone” of the DNA mole or the “ladder sides”.
  • The two sides of the DNA molecule are bonded together in the middle by hydrogen bonds holding the nitrogenous bases… creating the “steps” of the ladder
  • Two strands twist together to form a helix shape.. cork screw shape 
• • DNA consists of 2 antiparallel (parallel but running in opposite directions) strands of nucleotides

  ex.

  -ATGCCGTTA -

  -TACGGCAAT - 
• These 2 strands of nucleotides are twisted into a right-handed helix that makes one complete turn every 10 nucleotides ( a distance of 3.4nm )
• If DNA in one cell were laid end to end - 3m (6 billion base pairs long)
• To fit this massive amount of information into each cell, DNA is coiled upon itself to form chromosomes
• Histones (protein molecules) act as “spools” on which DNA molecule coils. They are positively charged. 8 Histones wrapped = nucleosome 
• Nucleosomes (coils) coiled upon themselves to form chromatin fiber
• A group of 6 nucleosomes will wrap into a solenoid
• During interphase DNA is loosely packed in nucleosomes or solenoids.
• Chromatin condenses during mitosis - seen as chromosome
• • RNA stands for Ribonucleic Acid. 
• • RNA is also a carrier of Genetic information in our cells like DNA.
• • The primary function of RNA is to create proteins. RNA carries genetic information that is used by ribosomes to create various proteins necessary for cellular processes. 
• • An RNA molecule is almost, but not quite, like a single strand of DNA.
• RNA like DNA is made of 3 components:

  • Ribose Sugar (5-carbon ring)
  • Phosphate Group (negative)
  • Nitrogenous base
• • The Ribose sugar in RNA is similar to the Deoxyribose Sugar in DNA. A Ribose sugar has a OH Functional group on the 2nd carbon where deoxyribose sugar has a Hydrogen
• • RNA also differs from DNA in the nitrogenous bases.
• RNA nitrogenous bases

  • The bases are adenine, cytosine, guanine and uracil.
• • Uracil is like the thymine in DNA, if it pairs with adenine
• • Thus, there are 3 main structural differences between DNA and RNA