1. Chapter 11 At a Glance 11.2 What Is the Structure of DNA?
11.3 How Does DNA Encode Genetic Information?
11.4 How Does DNA Replication Ensure Genetic Constancy During Cell Division?
11.5 What Are Mutations, and How Do They Occur?

2. DNA: The Molecule of Heredity Ch. 11

3. 11.2 What Is the Structure of DNA?
Knowing that DNA is made up of _______ does not provide an answer to the critical questions about __________
The secrets of ___________ and, therefore, of _________ itself are found in the three-dimensional structure of the DNA molecule

4. Cell Division Transmits Hereditary Information to Each Daughter Cell
Chromosome: consists of DNA and __________which organize its ______________and regulate its use
________: unit of inheritance; segments of DNA that range in length of #’s of ____________
spell out instructions for making proteins of a cell

5. 11.2 What Is the Structure of DNA?
DNA is composed of four nucleotides
DNA is made of chains of small subunits called ___________
Each nucleotide has three components
A phosphate group
A deoxyribose sugar
One of four nitrogen-containing bases
________(T)
________ (C)
_________(A)
_________(G)

6. Figure 11-3 DNA nucleotides
phosphate
phosphate
base  thymine
base  adenine
sugar
sugar
phosphate
phosphate
base  cytosine
sugar
sugar
base  guanine 6

7. 11.2 What Is the Structure of DNA?
DNA is composed of four nucleotides (continued)
In the ______ Erwin Chargaff, a biochemist at Columbia University, analyzed the amounts of the four bases ___________from diverse organisms
He discovered a consistency in the _____ amounts of adenine and thymine, and ______ amounts of guanine and cytosine for a given species, although there was a difference in proportion of the bases
This finding was called ___________

8. 11.2 What Is the Structure of DNA?
DNA is a double _______ of two ________ strands
In the 1940s, several other scientists investigated the structure of DNA
Rosalind ________ and Maurice _______ studied the structure of DNA crystals using X-ray diffraction
They bombarded crystals of purified DNA with X-rays and recorded how the X-rays bounced off the DNA molecules
The resulting pattern does not provide a direct picture of ______structure, but the researchers were able to extract specific information

9. 11.2 What Is the Structure of DNA?
DNA is a double helix of two nucleotide strands Wilkins and Franklin deduced the following information about DNA from the patterns they found:
1. A molecule of DNA is __________, with a uniform diameter of 2 nanometers
2. DNA is a ____________like a
Corkscrew or a spiral staircase
3. DNA is a _______ helix
4.DNA has __________subunits
5. Phosphates are probably on _________of the helix

10. 11.2 What Is the Structure of DNA?
DNA is a double helix of two nucleotide strands (continued)
____________________________ combined the X-ray data with bonding theory to deduce the structure of DNA
They proposed that a single _______ DNA is a polymer consisting of many nucleotide subunits
Within each DNA strand, the __________ group of one nucleotide bonds to the sugar of the next nucleotide in the same strand
The deoxyribose and phosphate portions make up the _________________________

11. 11.2 What Is the Structure of DNA?
DNA is a double helix of two nucleotide strands (continued)
The __________ bases protrude from the sugar-phosphate backbone
All the nucleotides within a _______________are oriented in the same direction, and thus have an _______sugar at one end and an _________ phosphate at the other end

12. 11.2 What Is the Structure of DNA?
Hydrogen bonds between complementary bases hold two DNA strands together in a double helix
Watson and Crick’s findings provided the following insight about the DNA model:
The ________ model consists of two DNA strands, assembled like a twisted ladder
The _______ protrude inward toward each other from the sugar-phosphate backbone like rungs on a ladder
___________bonds hold the base pairs together, composing the rung

13. 11.2 What Is the Structure of DNA?
Hydrogen bonds between complementary bases hold two DNA strands together in a double helix (continued)
The two strands in a DNA double helix are said to be ____________ that is, they are oriented in opposite directions
From one end of the DNA molecule, if one strand starts with the free _________and ends with the free __________ the other strand starts with the free phosphate and ends with the free sugar

14. Francis Crick & James Watson:
combined X-ray data with other research
and built the first double helix model
of DNA (3/7/53)
single strand of DNA is a polymer
of many nucleotide subunits
sugar-phosphate backbone
strands are antiparallel
(see next slide)
Watson, Crick, & Wilkins received
Nobel Prize in ’62
Franklin died in ’58 so she was not
included in award

15. Complementary base pair & Chargaff’s Rule #A = #T #C = #G
Antiparallel strands
1 end  ‘free’ or unbonded
phosphate (5’)
sugar ) (3’)
Complementary base pair
& Chargaff’s Rule
#A = #T
#C = #G
Size of bases
A & G – 2 fused rings
(large-Purines)
C & T - single rings
(small – Pyrimidines)
rungs are same width – constant diameter

16. 11.2 What Is the Structure of DNA?
Hydrogen bonds between complementary bases hold two DNA strands together in a double helix (continued)
Because of their structures and the way they face each other, ________(A) bonds only with _______ (T) and _________(G) bonds only with cytosine (C)
Bases that bond with each other are called ______________ base pairs
Thus, if one strand has the base sequence CGTTTAGCCC, the other strand must have the sequence _______________

17. 11.2 What Is the Structure of DNA?
Hydrogen bonds between complementary bases hold two DNA strands together in a double helix (continued)
Complementary base pairing explains ________that for a given molecule of DNA, adenine equals thymine and guanine equals cytosine
Since every _________, for example, is paired with a thymine, no matter how many adenines are in the DNA molecule, there will be an equal number of __________

18. 11.2 What Is the Structure of DNA?
Hydrogen bonds between complementary bases hold two DNA strands together in a double helix (continued)
Adenine and guanine are large molecules; thymine and cytosine are relatively smaller
Because base pairing always places a large molecule with a small one, the diameter of the double helix remains constant
In 1953, James Watson and Francis Crick consolidated all the historical data about DNA into an accurate model of its structure

19. Hydrogen bonds between complementary bases hold 2 DNA strands together

20. Figure 11-5 The Watson-Crick model of DNA structure
nucleotide
nucleotide
free
phosphate
free
sugar
phosphate
base
(cytosine)
sugar
hydrogen
bonds
free sugar
free
phosphate
Hydrogen bonds hold complementary
base pairs together in DNA
Two DNA strands
form a double helix
Four turns of
a DNA double
helix 20

21. BUILD DNA

22. Quiz nucleic acid dna structure

23. How Does DNA Replication Ensure Genetic Constancy During Cell Division?
Rudolf Virchow (1850’s):
“All cells come from ______________”
Cells reproduce by dividing _________
Each of the 2 ___________gets an exact
copy of the parent cells genetic
information
DNA replication = duplication of the
parent cell _______

24. Animation: DNA Replication

25. Figure 11-6 Basic features of DNA replication
Parental DNA
double helix
The parental DNA
is unwound
New DNA strands
are synthesized with
bases complementary
to the parental
strands
free nucleotides
Each new double helix is composed
of one parental strand (blue) and one
new strand (red) 25

26. How Does DNA Replication Ensure Genetic Constancy During Cell Division?
DNA replication produces two DNA double helices, each with one original strand and one new strand (continued)
The two resulting DNA molecules have one old parental strand and one new strand (__________________)
If no mistakes have been made, the base sequences of both new DNA __________ are identical to the base sequence of the parental DNA double helix

27. Figure 11-7 Semiconservative replication of DNA
One DNA
double helix
DNA replication
Two identical DNA
double helices, each
with one parental
strand (blue) and
one new strand (red) 27

28. DNA replication produces 2 DNA double helices each with
1 original strand and 1 new strand
Complementary _______pairing provides a model for how DNA replicates
Ingredients for replication:
__________DNA strands
Free __________
Variety of ________ to unwind
parental DNA and synthesize new
DNA strands

29. DNA helicase: enzyme that ____________parental DNA double helix at H-bonds btwn complementary pairs
DNA polymerase: _________that pairs free nucleotides with their complementary nucleotide on each separated strand
Replication fork

30. Since ____________always moves from 3’ (sugar-end) to 5’ (phosphate-end) and DNA strands are antiparallel, DNA polymerase molecules move in opposite directions.
Short lagging strands are synthesized while the ________continues to unwind in the opposite direction
DNA ligase:
enzyme that ties
DNA together
at 9min mark – lagging strand replication

31. How long does DNA replication take?
Human chromosomes range from 50mill nucleotides in the Y chromosome to 250mill nucleotides in Chromosome 1.
Eukaryotic DNA copied at 50 nucleotides/sec; takes days to copy a human chromosome in one continuous piece. MAKE SENSE? EFFICIENT?
Several DNA
helicases & DNA
polymerases
work to split
and copy small
pieces of the
DNA strand at
the same time.

32. Semiconservative replication: 2 resulting DNA molecules have 1 old parental strand and 1 new strand
If no mistakes have been made, the base sequence of both new strands are IDENTICAL to the base sequence of the parental DNA

33. DNA paper lab

34. 11.5 What Are Mutations and How Do They Occur?
mutations: infrequent changes in the nucleotide sequence that result in defective genes
often ________- can cause organism to die quickly
Some _____________ functional effect
Some may be ________ and provide an advantage to an organism in certain environments (basis for evolution?)

35. Accurate replication and proofreading produce almost error-free DNA
________mismatches nucleotides once every 1,000 to 100,000 base pairs
Completed __________contain only about 1 mistake in every 100 mill to 1 bill base pairs
In _______, this amounts
to less than 1 error /
chromosome / replication
Toxic chemicals &
__________ can also
alter/damage DNA

36. Types of mutations
_____________(nucleotide substitutions): changes to individual nucleotides in the DNA sequence
_______________: when 1 or more new nucleotide pairs are inserted into the
DNA double helix
_______________:
when 1 or more
nucleotide pairs are
removed from the
double helix

37. Types of mutations
__________: when a piece of DNA is cut out of a chromosome, turned around, and re-inserted into the gap
__________: when a chunk of DNA (usually large) is removed from 1 chromosome and attached to another

38. Figure 11-8a Nucleotide substitution
original DNA sequence
substitution
nucleotide pair changed
from A–T to T–A 38

39. Figure 11-8b Insertion mutation
original DNA sequence
T–A nucleotide pair
inserted 39

40. Figure 11-8c Deletion mutation
original DNA sequence
C–G nucleotide pair
deleted 40

41. Inversion original DNA sequence breaks DNA segment inverted
Figure 11-9a Inversion
Inversion
original DNA sequence
breaks
DNA segment
inverted 41

42. Figure 11-9b Translocation
original DNA sequences
break
DNA
segments
switched
break 42