AP Biology Chapter 16 Notes
Molecular Basis of Inheritance
What you need to know…
 The structure of _________.
 The major steps of ____________________.
 The difference between __________________, ____________________, and
________________________.
 How DNA is packaged into a ____________________.
Concept 16.1: DNA is the genetic material
• Important Scientists –
– Alfred Hershey and Martha Chase – Next Slides - ___________ is the genetic material
– James Watson and Francis Crick – structure of DNA
– Rosalind Franklin – next slides - produced a picture of the DNA molecule using ____________
crystallography; discovered DNA is a ____________ ____________
3 Deductions by Watson and Crick
• DNA = ___________________________ (twisted ladder). Sides are made up of sugar and phosphate
backbones and rungs are made up of nitrogenous base pairs.
• Nitrogenous bases are _________________ (A), _________________ (T), _______________ (G), and
____________________ (C).
• Strands are _______________________ – left side runs 5’-3’ while opposite strand runs 3’-5’.
Concept 16.2: Many proteins work together in DNA replication and repair
 Since the two strands of DNA are ______________________, each strand acts as a template for building a
new strand in replication
 In DNA ____________________, the parent molecule unwinds, and two new daughter strands are built
based on base-pairing rules
 It is considered ______________________ replication
 _______________________ – making of DNA from existing DNA strands
o begins at special sites called ________________________________, where the two DNA strands
are separated, opening up a replication “bubble”
o Replication Bubble formed by ________________ that unwinds the DNA. Replication continues
in both directions along strand until copied.
o DNA ______________________ add nucleotides to strand at replication fork.
o DNA Polymerase works in a 5’-3’ direction (_________________ strand) matching bases.
o _____________________ strand (3’-5’) is copied in series of segments.
o Lagging strand segment pieces are called __________________ fragments – tied together with
DNA ______________.
o The initial nucleotide strand is a short RNA ______________
 An enzyme called _________________ can start an RNA chain from scratch and adds
RNA nucleotides one at a time using the parental DNA as a template
 The primer is short (5–10 nucleotides long), and the 3 end serves as the starting point for
the new DNA strand
o Label the Picture: Replication of Leading Strand



o
Replication of the Lagging Strand
o DNA polymerase must work in the direction _________ from the replication fork
o The lagging strand is synthesized as a series of segments called __________________ fragments,
which are joined together by DNA _____________
o See the Handout Replication of the Lagging Strand
Proofreading and Repairing DNA
o DNA ________________ proofread newly made DNA, replacing any incorrect nucleotides
o In ________________ repair of DNA, repair enzymes correct errors in base pairing
o DNA can be damaged by _____________, ______________ emissions, ____________,
_______________, and certain molecules (in cigarette smoke for example)
o In nucleotide excision repair, a ______________ cuts out and replaces damaged stretches of DNA
Replicating the Ends of DNA Molecules
o Limitations of DNA polymerase create problems for the linear DNA of eukaryotic chromosomes
o The usual replication machinery provides no way to complete the 5 ends, so repeated rounds of
replication produce ___________________ DNA molecules
o Eukaryotic chromosomal DNA molecules have at their ends nucleotide sequences called
___________________ - do not prevent the shortening of DNA molecules, but they do postpone
the erosion of genes near the ends of DNA molecules
o An enzyme called ______________________ catalyzes the lengthening of telomeres in germ cells
Concept 16.3 A chromosome consists of a DNA molecule packed together with proteins
o The bacterial chromosome is a double-stranded, _____________________ DNA molecule associated with
a small amount of protein
o Eukaryotic chromosomes have _____________ DNA molecules associated with a large amount of protein
o In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the ________________
o ________________________ is a complex of DNA and protein, and is found in the nucleus of eukaryotic
cells
o _____________________ are proteins that are responsible for the first level of DNA packing in chromatin
You should be able to:
1. Describe the contributions of the following people: Griffith; Avery, McCary, and MacLeod; Hershey and
Chase; Chargaff; Watson and Crick; Franklin; Meselson and Stahl
2. Describe the structure of DNA
3. Describe the process of DNA replication; include the following terms: antiparallel structure, DNA
polymerase, leading strand, lagging strand, Okazaki fragments, DNA ligase, primer, primase, helicase,
topoisomerase, single-strand binding proteins
4. Describe the function of telomeres
5. Compare a bacterial chromosome and a eukaryotic chromosome