MCAT Biochemistry Ch. 6 DNA & Biotechnology

1. Deoxyribose
2. H
3. Ribose

Nucleosides are a 5-carbon sugar pentose, covalently bonded to a nitrogenous base at the C-1' of the sugar Nucleotides are formed when one or more phosphate groups are attached to C-5' of a nucleoside; high energy compounds because of the negative repulsion between the phosphate groups

PURe As Gold (as A & G are purines) gold wedding rings, need to rings to make a marriage. Adenine & Guanine are purines, & purines have 2 rings in their structure.

CUT the Pye (as C, U, & T are pyrimidines), pie has one ring of crust. Cytosine, Uracil, & Thymine are pyrimidines, which have one ring.

1. Cyclic
2. Planar
3. Compound is conjugated (alternating & single & multiple bonds or lone pairs, creating at least one unhybridized p-orbital for each atom in the ring
4. The compound has 4n + 2 (where n is any integer) π electrons (Huckel's Rule)

1. The 2 strands are antiparallel, when 1 strand has 5' to 3' polarity down the page, the other has 5' to 3' polarity up the page
2. Sugar phosphate backbone is outside helix w/ nitrogenous bases on inside
3. Complementary Base-Pairing: A always w/ T via 2 hydrogen bonds, C always w/ G via 3 hydrogen bonds
4. Chargaff's Rule: because of specific base-pairing, the amount of A always equals the amount of T, & the amount of C always equals the amount of G

DNA that makes up chromosomes is wound around a group of small basic proteins called histones, which forms chromatin (the material of which chromosomes are made of). There are 5 histone proteins in eukaryotic cells w/ 2 copies each of H2A, H2B, H3, & H4 that form a core for about 200 base pairs of DNA to wrap around, forming a nucleosome. H1 seals off the DNA as it enters & leaves the nucleosome, stabilizing the structure. Nucleosomes make DNA more organized & compact.

Because of specific base-pairing, the amount of A always equals the amount of T, & the amount of C always equals the amount of G. Ex: If a sample of DNA has 10% G, what is the % of T?10% G = 10% C, thus G + C = 20%100% - 20% = 80% (A + T), therefore T = 40%

Proteins that associate w/ DNA, like histones

Heterochromatin:

1. Stays compacted during interphase
2. Is not transcribed, doesn't contain genetically active DNA
3. Appears dark under microscope & is more dense

Euchromatin:

1. Decondenses during interphase
2. Contains genetically active DNA that is transcribed
3. Appears lighter under microscope & is less dense

Repeating unit (TTAGGG) at the end of DNA, which saves DNA from being lost through repeated replication, since DNA polymerase can't go all the way to the end of a chromosome. Very stable because of lots of C to G bonds (3 H bonds each)

Region of DNA found in center of chromosomes. Sites of constriction that form noticeable indentations. Composed of heterochromatin, w/ lots of C to G bonds (very stable). Helps sister chromatids stay connected during mitosis until they are pulled apart by microtubules in anaphase.

DNA replication is semiconservative because half of the original parent strand is in each of the 2 daughter strands

5' to 3':

1. DNA synthesis
2. DNA repair
3. DNA transcription
4. RNA translation (reading of codons)