Chapter 11: DNA
Biology: Exploring Life
Campbell, Williamson, Heyden
Prentice Hall
Genes are made of DNA.
11.1

Griffith’s “Transforming Factor” Is the
Genetic Material
1928 Fredrick Griffith
– Two forms of bacteria

Fatal pneumonia and harmless
Avery Shows DNA Is the
Transforming Factor

What is the “transforming” factor?
– Protein or DNA

1944 Oswald Avery
– Took Griffith work further

DNA is the “transformer”
Virus Experiments Provide More
Evidence

Virus
– Nucleic acid (DNA) wrapped in protein

Bacteriophage
– Virus that infects bacteria

1952 Alfred Hershey and Martha Chase
– DNA is heredity material
Nucleic acids store
information in their
s e q u e n c e s o f c h e m ic a l
u n i ts .
11.2
The Building Blocks of
DNA
The Building Blocks of
DNA cont’

DNA
– Genetic material
– Deoxyribonucleic acid
– “Deoxyribose” is the sugar

Nucleotides
– Building blocks DNA
– Chemical Structure:




Phosphate
Nitrogenous base (only 4)
Sugar
RNA
– Ribonucleic acid
– “Ribose” is the sugar
Nitrogen Bases
The 4 nucleotides differ ONLY in nitrogenous
bases

Pyrimidines (single ring)
– Thymine (T)
– Cytosine (C)
– Uracil (U) , in RNA

Purines (double ring)
– Adenine (A)
– Guanine (G)
DNA Strands
 Sugar-phosphate backbone
– Repeating pattern of …sugar-phosphate-
sugar-…
 Nucleotides form sequences
– Ex:
CTGCTATCGCCGGTATACTAGTGT…
– Unlimited possibilities
DNA Structure

DNA helix
– 1950 Rosalind Franklin and Maurice Wilkins
– X-ray crystallography
“The Double Helix” of DNA
James Watson and Francis Crick

– Showed twisting shape
Complementary Base Pairing
in DNA

Complement Pairs
T–A
G–C
DNA replication is the
m ole c u la r m e c h a n is m o f
i n h e ri ta n c e .
11.3
The Template Mechanism
 Cell division includes copies of DNA
 DNA replication
– Copying DNA molecules
– Nucleotides line up following base-pairing
rules
Replication of the Double
He l i x

DNA polymerases
– Enzymes to break and pair nucleotides
– Covalent bonds hold nucleotides
– Errors: 1/1,000,000,000
A gene provides the
information for making a
specific protein.
11.4
One Gene, One
Polypeptide
Genotype vs. Phenotype
Genotype
 Genetic make-up; nucleotide sequence
Phenotype
 Physical characteristics; Proteins and
functions
“One gene - one polypeptide”
– Gene dictates one chain of amino acids
Information Flow: DNA  RNA 
Protein
 In nucleus
– Transcription
DNA unwinds
matching single strand mRNA is made
*Uracil (U) instead of Thymine (T)!


 In
cytoplasm
– Translation


RNA gives code
– “blue print” for protein
Codon: three bases that code for amino acid
The Triplet Code
 64 combinations
– 61 code for amino acids
– 20 different amino acids
 “Universal”
Using the table (for RNA)
There are two main steps
from gene to protein:
Transcription and
Translation
11.5
Transcription: DNA to
RNA

mRNA
– messenger RNA
– Transcribes from DNA template

RNA polymerase
– Links RNA nucleotides together
– Uracil (U) instead of thymine (T)!

A – U pairing
Editing the RNA Message

Prokaryotic Cells
DNA  mRNA  protein

Eukaryotic Cells
DNA  RNA  mRNA  protein
Editing the RNA Message
cont’

Introns
– Non-coding sections
– Most DNA is introns

Exon
– Coding sections expressed

RNA splicing
– Before leaving the nucleus
– Produces mRNA
Translation: RNA to
Protein

tRNA
– transfer RNA
– Translates 3-letter codons
– Carries protein

Anti-codon
– Complementary to codon in mRNA
Translation: RNA to Protein
cont’

Ribosome
– Cluster of proteins and nucleic acids that
constructs proteins in a cell
– Coordinates mRNA and tRNA
– 2 sections

Small subunit

Large subunit
– mRNA binds here
– tRNA binds here

rRNA
– RNA in ribosome
Translation: RNA to Protein cont’
The Process

Need start codon (AUG)


Amino acids added one by one


mRNA, tRNA (with amino acid), two subunits
Continues until “stop” codon is reached
New polypeptide set free by tRNA

Average sized protein < 1 min.
Review of Protein Synthesis


Genes responsible for polypeptides (proteins) that
make structures and perform functions
Genotype controls phenotype
DNA  mRNA  A.A.  polypeptide  appearance and
function
Mutations can change
th e m e a n i n g o f g e n e s .
11.6
What causes mutations?

Mutation
– Any change in nucleotide sequence of DNA
Ex: ACG to ATG


Errors
Meiosis, Mitosis
– Large or small regions of chromosomes

Mutagen
– Physical or chemical agents causing mutations

Helpful vs. Harmful

Ultimate source of genetic diversity!!
How Mutations Affect
Genes

Base insertions

Base deletion

Base substitutions
– New base(s) inserted
– Base(s) deleted
– Replacement of one (or more) base

“Silent Mutation”
– A change in a base pair (codon) does not change
the amino acid
Permission Statement
Restricted to the use of New Berlin Eisenhower High School
(New Berlin, WI) Students, Faculty and Staff.
Contact S. Schweickhardt for usage permissions.
©2006, 2009
Citations of Links
No Author. (2003). Translation. Cold Spring Harbor Laboratory. Retrieved on Feb 26th, 2006 from
http://www.dnai.org/media/a/translation_big.swf.
No Author. (2003). Transcription. Cold Spring Harbor Laboratory. Retrieved on Feb 17th, 2006 from
http://www.dnai.org/media/a/transcription_big.swf.
No Author. (2003). Replication. Cold Spring Harbor Laboratory. Retrieved on Feb 17th, 2006 from
http://www.dnai.org/media/a/replication_small.swf.
No Author. (2009). Gene Expression.. Retrieved on Jan 29th, 2009 from
http://www.youtube.com/watch?v=OEWOZS_JTgk
No Author. (2004). Zoom Into DNA. The Tech Museum of Innovation . Retrieved on Jan 20th, 2009 from
http://www.thetech.org/genetics/zoomIn/index.html