1. The Molecular Basis of Inheritance

2.  Your DNA – contained in 46 chromosomes you inherited from your parents in mitochondria you inherited from your mother.

3.  Nucleic acids are unique in their ability to direct their own replication.

4.  DNA directs the development of your biochemical, anatomical, physiological, and (to some extent) behavioral traits.

5.  16_05DNAandRNAStructure_A.mpg 16_05DNAandRNAStructure_A.mpg  16_09DNAReplicatOverview_A.mpg 16_09DNAReplicatOverview_A.mpg

6.  At one time, we didn’t know stuff.  But then people discover stuff that provides evidence for a certain hypothesis.  Evidence for DNA as the genetic material came from studies of viruses that infect bacteria  Such viruses, called bacteriophages (or phages), are widely used in molecular genetics research © 2011 Pearson Education, Inc. Phage head Tail sheath Tail fiber DNA Bacterial cell 100 nm

7. © 2011 Pearson Education, Inc. Animation: Phage T2 Reproductive Cycle Right-click slide / select “Play”

8. © 2011 Pearson Education, Inc. Animation: DNA and RNA Structure Right-click slide / select “Play”

9.  Nitrogenous base (A-T) (C-G)  Deoxyribose (a pentose-sugar)  Phosphate group

10.  In any one species, the four bases are found in characteristic, but not necessarily equal, ratios  The #As = # Ts, #Cs = #Gs  Human DNA is 30.3% adenine, 30.3% thymine, 19.5% guanine, 19.5% cytosine  PRACTICE:  In another organisms DNA there is 21 % thymine. What percentage is there of guanine? 29%

11. The Double Helix  The sugar-phosphate strands are like the sides of a rope ladder.  The ladder forms a full turn of the helix every 10 bases.  A-T and C-G form hydrogen bonds, uniting the two strands  The two sugar-phosphate backbones are antiparallel with subunits running in opposite directions.

14.  Pyrimidines- Thymine and Cytosine (made of only one organic ring)  Purines- Adenine and Guanine (made of two organic rings)  How to remember which is which?  Y in both pyrimidine bases

15.  During DNA replication, base pairing enables existing DNA strands to serve as templates for new complimentary strands Initially, there were two ideas:  Conservative: the two parental strands come back together  Dispersive: each new strand is a mix of old and new BUT NOW WE KNOW THE TRUTH  Semi-conservative model of replication predicts that when a double helix replicates, each of the daughter molecules has one old strand and one newly made strand.

18.  More than a dozen enzymes and other proteins participate in DNA replication.  The replication of a DNA molecule begins at special sites called origins of replication.  a short stretch of DNA having a specific sequence of nucleotides – where DNA replication begins

19.  Prokaryotes: origin site is a specific sequence of nucleotides recognized by the replication enzymes.  These enzymes separate the strands, forming a replication bubble  Replication proceeds in both directions until entire molecule is copied.

21.  Eukaryotes: may be 100s and 1000s of origin sites per chromosome  At origin sites – DNA strands separate, forming a replication bubble with replication forks at each end, where the parental DNA is being unwound.  Replication bubbles elongate as the DNA is replicated, and eventually fuse.

22.  Leading: DNA made from 5’ to 3’ direction (continuous)  Lagging: DNA works away from forking strand (discontinuous) made in a series of segments

23.  16_12OriginsOfReplication_A.mpg 16_12OriginsOfReplication_A.mpg

24.  Helicases: untwist the double helix and separate the template DNA strands at the replication fork.  Single-strand Binding Proteins: bind to unpaired DNA strands, stabilizing them  Topoisomerase: helps relieve strain of twisting  Ligase- binds Okasaki fragments together  DNA Polymerase- assembles nucelotides to form new strand  DNA Primase- forms an RNA primer

25.  3’-5’ parental strand only requires a single primer  Elongates continuously

26.  At the replication fork, the leading strand is copied continuously into the fork from a single primer. The lagging strand is copied away from the fork in short segments, each requiring a new primer.

27.  The enzymes that synthesize DNA cannot initiate synthesis of a polypeptide  They can only add nucleotides to the end of an existing chain that is base-paired with the template strand. DNA REPLICATION DOES NOT MAKE PROTEINS

28.  DNA polymerase proofreads each new nucleotide against the template nucleotide as soon as it is added.  Incorrect pairing = the enzyme removes the wrong nucleotide and then resumes synthesis

29.  A nuclease cuts out a segment of a damaged strand, and the resulting gap is filled with nucleotides, using the undamaged strand as a template.

30.  Mutations are the source of the variation on which natural selection operates during evolution and are ultimately responsible for the appearance of new species.

31.  Repeated rounds of replication produce shorter and shorter DNA molecules  Telomeres: ends of eukaryotic chromosomal DNA ends. Special nucleotide sequences. (usually TTAGGG repeated 100=1000 time)  Telomeres do not contain genes. Act as a buffer zone that protects the organism’s genes.

33.  Telomerase: an enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells, restoring their length.

34.  Bacteria: single, circular, double-stranded DNA molecule associated with a small amount of protein.  A bacterium has a dense region of DNA called the nucleoid.

35.  Telomeres become shorter and shorter during every round of replication  Is the shortening of telomeres connected with the aging process?

36.  Eukaryotic DNA is packaged with protein to form chromatin.  Chromatin is found in interphase nucleus.  Heterochromatin: condensed chromatin  Euchromatin: more dispersed chromatin  (genes in this chromatin can be expressed)