Eukaryotic Test 3 Lecture 6

• Long linear polymers of nucleotides
• Function primarily in storage & transmission of genetic info (may also have structural or catalytic roles)

DNA: Deoxyribonucleic Acid, genetic materials

RNA : Ribonucleic Acid (mRNA, rRNA, tRNA)

RNA functions in transmission of genetic info from DNA to protein, but may also contain genetic info such as in viruses.

NucleoSide is a sugar and a base (without the phosphate)

1. Base composition of DNA in the cells of all tissues of an organism is identical

2. [A]=[T], [G]=[C]

3. [A]+[T] DOES NOT EQUAL [G]+[C]

1. DNA molecule composed of 2 chains of nucleotides

2. 2 chains spiral around each other to form a pair of right-handed helices

3. 2 chains comprising 1 double helix run in opposide directions (antiparallel)

4. Sugar-phosphate backbone located on the outside of each strand, while the 2 sets of bases project toward the center

5. Bases occupy planes that are approx. perpendicular to long axis of molecule & are stacked on top of another. Hydrophobic interactions & van der waals forces between stacked planar bases provide stability for entire molecule

6. The 2 strands are held together by hydrogen bonds

7. Distance from phosphorous atom to the center of the axis is 1nm

8. A pyrimidine is always paired w/a purine

9. N atoms linked to C4 of cytosine & C6 od adenine are predominantly in NH2 configuration rather than NH (imino) form. O atoms linked to C6 of guanine and C4 of thymine are primarily in keto form

10. Spaces betwen adjacent turns from 2 grooves of different width (major & minor groove) that spiral around the outer surface of double helix

11. Double helix makes one complete turn every 10 residues (3.4 nm)

12. Nucleotide sequences of the 2 strands are always fixed relative to one another (complementary

1. Storage of genetic information

2. Replication and inheritance

3. Expression of the genetic message

1. Relaxed: Supercoiled

2. Underwound: Negatively supercoiled

3. Overwound: Positively supercoiled

Circular DNAs found in nature are invariably negatively supercoiled

Changes the topology of DNA

Type I Topoisomerases: Changes the supercoiled state of a DNA molecule by creating a transient break in ONE strand of the duplex

Type I essential for processes such as DNA replication and transcription

Creates a transient break in BOTH strands of the duplex

Topoisomerase II required to unlink DNA before duplicated chromosomes can be separated during mitosis