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Nucleic Acids and Lipids

nucleic acids - information storage devices of cells; 2 varieties  

  • can serve as templates to create exact copies of themselves
  • deoxyribonucleic acid (DNA) - the hereditary material
  • ribonucleic acid (RNA) - used to read DNA in order to create proteins; used as a blueprint to create amino acid sequences
  • finally able to be seen w/ scanning-tunneling microscope

nucleotides - subunits of nucleic acids  

  • contains 5-carbon sugar, phosphate group, organic base
  • purine - large, double-ring molecules; adenine, guanine (both in RNA/DNA)
  • pyrimidine - smaller, single-ring molecules; cytosine (in RNA/DNA), thymine (in DNA only), uracil (in RNA only)

DNA  

  • made of difference combinations of 4 types of nucleotides (adenine, guanine, cytosine, thymine)
  • 2 chains wrap around each other like a staircase (double helix shape)
  • hydrogen bonds hold 2 chains together
  • adenine only complementary to thymine (in DNA), uracil (in RNA)
  • cytosine only complementary to guanine

RNA  

  • uses ribose sugar instead of deoxyribose (in DNA)
  • has hydroxyl group where a hydrogen is in DNA >> stops double helix from forming
  • uses uracil in place of thymine (has 1 more methyl group than uracil)
  • usually single-stranded (differentiates itself from double-stranded DNA); serves as a transcript of the DNA
  • evolved into DNA to protect the hereditary material from single-strand cleavage
  • "central dogma" of molecular biology - flow of info from DNA to RNA to protein

ATP - adenosine triphosphate (contains adenine, a nucleotide)  

  • energy currency of the cell
  • tinamide adenine dinucleotide (NAD+), flavin adenine dinucleotide (FAD) both carry electrons to make ATP

lipids - insoluble in water  

  • most familiar forms are fats/oils
  • very high proportion of nonpolar carbon-hydrogen bonds
  • can't fold up like proteins
  • spontaneously exposes polar parts and moves nonpolar parts within when placed in aqueous environment

phospholipids - form the core of all biological membranes  

  • glycerol - 3 carbon alcohol; forms the phospholipid's backbone
  • fatty acid - long chains of CH2 groups, ending in a carboxyl; 2 chains
  • phosphate group - attached to an end of the glycerol; usually has an organic molecule attached to it
  • phosphate group serves as the polar "head"; fatty acids serve as the nonpolar "tails"
  • micelle - spherical forms w/ the tails pointed inward
  • phospholipid bilayer - 2 phospholipid layers w/ the tails pointed towards each other; basic framework of biological membranes

fats - do not have a polar end like phospholipids  

  • contains 3 fatty acids
  • aka triglyceride, triacylglycerol
  • fatty acids don't need to be identical
  • energy stored in the C-H bonds of fats
  • clump together in water to form globules since they lack polar ends
  • saturated fats - carbon atoms in fatty acids each bonded to at least 2 hydrogen
  • unsaturated fats - has double bonds between 1+ carbon atoms
  • polyunsaturated fats - has more than 1 double bond; have lot melting points (usually liquid at room temperature)
  • terpene - long-chain lipids usually found in chlorophyll and visual pigment retinal
  • steroid - has 4 carbon rings; can function as hormones
  • prostaglandins - about 20 lipids acting as chemical messengers, with 2 nonpolar tails attached to a five-carbon ring

fats as energy-storing molecules  

  • fats contain about 40 carbon atoms
  • ratio of C-H bonds to carbon atoms in fats is 2x the ratio of carbohydrates
  • animals produce mostly saturated fats
  • plants produce mostly unsaturated fats
  • adding hydrogen can convert an oil into solid fat
  • hydrogenating oils into solids turns unsaturated fats into saturated
  • excess carbohydrates get converted into fats, starch, glycogen
  • plaque - deposits of fatty tissue found on blood vessel lining; broken pieces can cause strokes, block blood flow
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