1. Chapter 12
DNA & RNA

2. 12 – 1 DNA
Deoxyribonucleic acid

3. • In the middle of the 1900’s biologists
were wondering how genes work.
What they are made of, and how they
determine the characteristics of
organism
• If the structures that carry genetic
information could be identified, it
might be possible to understand how
genes control the inherited
characteristics of living things

4. How does DNA do the following
things?
1. Carry info from one generation
to the next
2. Put info to work by determining
the inheritable characteristics
3. Copies itself, every time a cell
divides

5. Nucleotides
• Units that make up DNA
molecule
• Made of three parts
1. 5 carbon sugar (deoxyribose)
2. Phosphate group
3. Nitrogen bases

6. 4 kinds of nitrogen bases
1. Adenine (A)
2. Guanine (G)
3. Cytosine (C)
4. Thymine (T)

7. Chargaff’s Rule
• A=T and G=C

8. X-Ray Evidence
• Rosalind Franklin
• British Scientist
• Used a technique
called X-Ray
diffraction
• Provided important
clues about the
structure of DNA

9. X-Ray Evidence
• There were 2
strands
• Strands were
twisted around
each other
(helix)
• The nitrogen
bases are in the
middle

10. Watson & Crick

11. The Double Helix
• Francis Crick & James Watson
• Trying to understand the structure of DNA by
building models
• Unsuccessful until early 1953, Watson was
shown a copy of Franklin’s X-ray pattern
• “The instant I saw the picture my mouth fell open
and my pulse began to race.”
– James Watson
• Within weeks Watson and Crick had figured out
the structure of DNA
• Published their results in a historic one page
paper in April of 1953

13. • Watson and Crick later discovered what
held the two strands together
• Hydrogen bonds could form between
certain nitrogen bases and provide
enough force to hold the two strands
together
• Hydrogen bonds could only form between
certain base pairs adenine and thymine
and guanine and cytosine
• This principal is called Base pairing
• This explains Chargaff’s Rule

15. 12 – 2 Chromosomes
and DNA Replication

16. • To extract DNA for analysis, you
need to know where to find it and
how its organized
• DNA is located in the nucleus
• DNA is organized into
chromosomes

17. Prokaryotic Cells
• Prokaryotic cells have a single
circular DNA molecule that contains
nearly all of its genetic information
• Located in the cytoplasm

18. Eukaryotic Cells
• Much more complex
• 1000 times the amount of DNA as
prokaryotes
• DNA is located in the nucleus in
the form of chromosomes

19. Chromosome Structure
• Q: If eukaryotic DNA can contain
a meter or more of DNA, how
does it get packed in so tight into
chromosomes?
• A: Eukaryotic chromosomes
contain both DNA and protein that
form a substance called
chromatin

20. Histones
• Proteins that coil up DNA
• DNA + histone molecules form a
bead-like structure called a
nucleosome
• Nucleosomes pack together to form
thick fibers that loop and coil together
to form chromosomes

22. DNA Replication
• When Watson and Crick discovered
the double helix structure of DNA they
recognized immediately how DNA
could copy itself
• The strands are complementary
• If you could separate the two strands,
the rules of base pairing would allow
you to reconstruct the base sequence
of the other strand

23. Replication
• When the DNA splits into 2
strands, then produces 2 new
strands following the rules of base
pairing

24. How Replication Occurs
• Replication is carried out by
enzymes
• Before DNA replicates, the double
helix must unwind and unzip
• There are many regulatory
molecules used in replication

25. DNA polymerase
• Joins individual nucleotides to
produce a DNA molecule, which
is a polymer
• Also proof reads each new DNA
strand

26. The Steps of Replication
1. DNA unwinds
2. DNA unzips
3. The bases attach from a supply
in the cytoplasm
4. Sugar and phosphate groups
form the side of each new strand

29. Do Now
Place the following steps of
Replication in order.
DNA unwinds DNA Unzips
Sugar and phosphate groups
form the side of each new
The bases attach from a
strand
supply in the cytoplasm

30. Do Now
Place the following steps of
Replication in order.
DNA replication results in 2 DNA
1. DNA unwinds molecules
2. DNA Unzips
a. Each with two new strands
3. The bases attach from a
supply in the cytoplasm b. One with two new strands and
4. Sugar and phosphate the other with two original
strands
groups form the side of
each new strand c. Each with one new strand and
one original strand
d. Each with two original strands

31. 12 – 3 RNA and Protein
Synthesis

32. Genes
• Coded DNA instructions that
control the production of proteins

33. • DNA never leaves the nucleus,
therefore the code must be copied into
• RNA, or ribonucleic acid
• There are 3 main differences between
RNA and DNA
1. It has the sugar ribose, instead of
deoxyribose
2. RNA is single stranded
3. RNA contains uracil in place of thymine

34. • RNA is like a disposable copy of a
segment of DNA
• RNA is like a working copy of a
single gene

35. Types of RNA
1. Messanger RNA (mRNA)
• Serve as messangers from DNA to
the rest of the cell
2. Ribosomal RNA (rRNA)
• Type of RNA that makes up parts of
ribosomes
3. Transfer RNA (tRNA)
• Transfers each amino acid to the
ribosome as it is specified by the
mRNA

36. Types of RNA

37. Transcription
• RNA molecules are produced by copying
part of the DNA sequence into RNA
• Transcription requires an enzyme known
as RNA polymerase
• During transcription, RNA polymerase
binds to DNA and separates the DNA
strands. RNA polymerase then uses one
strand of DNA as a template from which
nucleotides are assembled into a strand of
RNA.

38. • Q: How does RNA polymerase
“know” where to start and stop
making a RNA copy of DNA?
• A: promoters
• Signals in DNA that indicate to the
enzyme where to bind to make
RNA
• Similar signals in DNA cause
transcription to stop

41. RNA Editing
• Remember, a lot of DNA doesn’t
code for proteins
• Introns – not involved in coding
for proteins
• Exons – code for proteins

42. • The introns get cut out of the RNA
molecules before the final mRNA is made

43. The Genetic Code
• Proteins are made by joining amino acids
into long chains called polypeptides
• Each polypeptide contains a combination
of any or all of the 20 different amino acids
• The properties of proteins are determined
by the order in which different amino acids
are joined together
• The language of mRNA instructions is
called the genetic code

44. • The code is read three letters at a
time
• Each 3 letter “word” is called a codon
• Each codon corresponds to an amino
acid that can be added to the
polypeptide

46. UCGCACGGU
This sequence would be
read three bases at a time
as:
UCG-CAC-GGU
The codons represent the
different amino acids:
UCG-CAC-GGU
Serine-Histidine-Glycine

47. Translation
• The sequence of nucleotide
bases in an mRNA molecule
serves as instructions for the
order in which amino acids are
joined to make a protein
• Proteins are put together on
ribosomes

48. Translation
• Decoding mRNA into a protein

49. Steps of Translation
1. mRNA is transcribed from DNA in the
nucleus and released into the cytoplasm
2. mRNA attaches to a ribosome
3. as each codon of the mRNA molecule
moves through the ribosome, the proper
amino acid is transferred to the growing
amino acid chain by tRNA
• tRNA carries only one kind of amino acid
and three unpaired bases called the
anticodon

50. 4. The amino acid chain continues
to grow until the ribosome
reaches a stop codon on the
mRNA molecule

52. The Roles of RNA and DNA
• You can compare the different roles played by DNA and
RNA molecules in directing protein synthesis to the two
types of plans used by builders. A master plan has all
the information needed to construct a building. But
builders never bring the valuable master plan to the
building site, where it might be damaged or lost. Instead,
they prepare inexpensive, disposable copies of the
master plan called blueprints. The master plan is safely
stored in an office, and the blueprints are taken to the job
site. Similarly, the cell uses the vital DNA “master plan”
to prepare RNA “blueprints.” The DNA molecule remains
in the safety of the nucleus, while RNA molecules go to
the protein-building sites in the cytoplasm—the
ribosomes

53. Genes and Proteins
• Q: If most genes contain nothing
more than instructions for
assembling proteins, what do
proteins have to do with traits?
• A: Everything, proteins are
microscopic tools designed to
build or operate a component of a
living cell

54. 12 – 4 Mutations

55. Mutations
• Changes in the genetic material

56. Point mutations
• Changes in one or a few
nucleotides
Ex.) substitutions, insertions,
deletions

60. Frameshift mutations
• Mutation that shifts the “reading”
frame of the genetic message by
inserting or deleting a nucleotide

61. Chromosomal Mutations

65. Significance of Mutations
• Most mutations don’t do anything
• Mutations that cause drastic
changes in proteins produce
defective proteins that disrupt
normal biological activities
• Mutations are also a source of
genetic variability which can be
beneficial

66. Polyploidy
• When plants produce triploid (3N)
or tetraploid (4N) organisms
• These plants are often larger and
stronger

68. Do Now
• Look at the bottom strand of DNA on the
window blinds
• Suppose the second T was changed to a
C
• How would this specifically alter the
resulting amino acid chain?
• What kind of mutation is this?

69. Do Now #2
• What if we got rid of the first G in the
bottom strand of DNA
• How would this specifically alter the amino
acid chain produced?
• What kind of mutation is this?

70. Do Now #3
• How are substitution/point mutations and
frameshift mutations similar?
• How are they different?