Griffith’s Experiments
Study suggested that DNA was
probably the genetic material
http://nortonbooks.com/college/biology/ani
mations/ch12a01.htm
Hershey and Chase Experiments
Radioactive
bacteria!
32P
was injected into
Hershey & Chase proved that DNA was the
cell’s genetic material!
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapt
er14/animations.html
Protein coat labeled
with 35S
T2 bacteriophages
are labeled with
radioactive isotopes
S vs. P
Hershey
&
Chase
bacteriophages infect
bacterial cells
bacterial cells are agitated
to remove viral protein coats
Which
radioactive
marker is found
inside the cell?
Which molecule
carries viral
genetic info?
DNA labeled with 32P
35S
radioactivity
found in the medium
32P
radioactivity found
in the bacterial cells
Chargaff
Discovered that amts of Adenine = Thymine, and Guanine = Cytosine
James Watson and Francis Crick
Double helix …..held together by hydrogen bonds
http://www.dnalc.org/view/15874-Franklin-s-X-ray.html
http://www.dnalc.org/search?q=Rosalind+Franklin
Rosalind Franklin (1920-1958)
HHMI DNA Scientists
DNA
1. Sugar deoxyribose
2. Phosphate
3. Nitrogen base
-thymine
RNA
1. Sugar ribose
2. Phosphate
3. Nitrogen base
-uracil
Base Pairing
DNA
Thymine (T) – Adenine (A)
PYRIMIDINE
PURINE
Guanine (G) – Cytosine (C)
PURINE
T
A
G
C
PYRIMIDINE
Weak hydrogen bonds
T or C
A or G
DNA
5
O
3
3
P
5
O
O
C
G
1
P
5
3
2
4
4
P
5
P
2
3
1
O
T
A
3
O
3
5
O
5
P
P
10
Base Pairing
RNA
Uracil (U) – Adenine (A)
PYRIMIDINE
PURINE
Guanine (G) – Cytosine (C)
PURINE
PYRIMIDINE
U
A
G
C
1.
DNA unzips (hydrogen bonds between the nitrogen
bases are broken by Helicase).
Wiley DNA Replication Animation (detailed)
2.
Free nucleotides pair with exposed bases on each
template strand of DNA. DNA Polymerase bonds the
nucleotides together.
HHMI DNA Replication
3. Two identical double stranded DNA molecules are
formed. “Semi-conservative” one original and one
replicated DNA strand Class Zone
http://nortonbooks.com/college/biology/
animations/ch12a04.htm
1. RNA is single stranded DNA is double
2. RNA can leave the nucleus and enter the
cytoplasm DNA can not.
3. RNA has the sugar ribose, DNA has the
sugar deoxyribose
4. RNA- uracil, DNA- thymine
http://highered.mcgrawhill.com/sites/0072437316/student_view0/chapter1
4/animations.html
• 1. mRNA: messenger RNA, a copy of
DNA from the nucleus.
• Reads DNA and copies it into RNA
T
A
DNA
A
U
C
G
RNA
• 2. rRNA : ribosomal RNA, found on the
ribosomes and functions in
attaching to mRNA to assemble the
correct order of amino acids.
Binds to mRNA
Binds to tRNA
• 3. tRNA : transfer RNA, located in
cytoplasm
• it picks up amino acids and like a factory
worker it puts the correct amino acid in
place to build a protein.
• Each tRNA has an anticodon on it that
corresponds to the mRNA codon read off
of the DNA.
A
U
Serine (amino acid)
tRNA
G
U
C
A mRNA
Central Dogma
Intro to Protein Synthesis
From gene to protein
transcription
DNA
translation
mRNA
mRNA leaves
nucleus through
nuclear pores
nucleus
a
a
a
a
a
a
a
a
a
a
protein
a
a
ribosome
a
a
a
a
proteins synthesized
by ribosomes using
instructions on mRNA
cytoplasm
http://www.dnatube.com/video/3450/DNATranscription
I. Transcription: in the nucleus
1. Initiation: RNA Polymerase unzips the DNA
2. Elongation: mRNA reads the DNA, RNA
Polymerase bonds the RNA nucleotides
together.
3. Termination: mRNA breaks off and
pre-mRNA.
DNA strand
mRNA strand
TAC
AUG
GCT TAG TTA
CGA AUC AAU
http://w
ww.dnat
ube.com
/video/3
446/Bio
Rapreleases
DNAReplicati
on-andProteinSynthesi
ACT
s-with-aUGA Beat
3 Steps
1. Addition of the cap
2. Addition of the tail
3. Removal of introns with the splicing together of exons
Exons - code for parts of the protein
Introns – nucleotides that occur between exons
mRNA processing
II. Translation: on the ribosome
1. Initiation: mRNA attaches to ribosome. The ribosome reads 1 codon
at a time. The process begins with a start codon (AUG).
2. Elongation: tRNA’s carrying the amino acids find their
anticodon complement on mRNA’s codon and leave
the amino acids at the ribosome. This continues along
the length of the mRNA and adjacent amino acids form
peptide bonds.
mRNA : AUG UUU CCC CGA - codons
tRNA : UAC AAA GGG GCU - anticodons
3. Termination: When a stop codon is reached the mRNA
detaches and the ribosome dissociates.
RNA polymerase
DNA
Can you tell
the story?
amino
acids
exon
intron
tRNA
pre-mRNA
5' cap
mature mRNA
polyA tail
large ribosomal subunit
aminoacyl tRNA
synthetase
3'
polypeptide
5'
small ribosomal subunit
tRNA
E P A
ribosome
Protein Synthesis Animation
Protein Synthesis Animation 2
McGraw Hill Animation
http://www.pbs.org/wgbh/nova/body/rnai.ht
ml NOVA video (RNAi)
Prokaryotic Transcription:
Operon – a region of DNA that contains a promoter,
operator, and structural genes.
1. Promoter – DNA segment that allows a gene to be
transcribed, RNA Polymerase binding site.
2. Operator – DNA segment that turns a gene “on” or “off”
*The lac operon was one of the earliest exps of gene
regulation in bacteria
Lac operon
Lactose absent
http://pages.cs
am.montclair.e
du/~smalley/L
acOperon.mo
v
Lactose present
http://wwwclass.unl.edu/biochem/gp2/m_biol
ogy/animation/gene/gene_a2.html
http://www.biologycorner.com/bio4/notes/gene-expression.php
– The lac operon is “off” when lactose is not
present.
– The lac operon is “on” when lactose is present.
Eukaryotic Transcription:
*Transcription is controlled by regulatory DNA sequences and
protein transcription factors.
– Most eukaryotes have a TATA box promoter.
– Enhancers and silencers speed up or slow down the rate
of transcription.
http://nortonbooks.com/college/biology/ani
mations/ch12a05.htm
Gene mutations: a change in the sequence of nucleotides within
a gene.
When do mutations occur?
- most often during DNA replication.
Different Types (pg 253 Fig 8.20)
1. Point Mutations- 1 nucleotide is changed to another, thus
coding for a different amino acid. Single base
pair substitution.
2. Frameshift mutations- add or delete a nucleotide to cause
the other bases to move up or down the
DNA molecule.
http://nortonbooks.com/college/biology/ani
mations/ch13a08.htm
(Change in chromosome structure)
Different Kinds
1. Deletion: when part of a chromosome is left out.
2. Insertion: part of a chromosome breaks off and inserts into
another causing a duplication in the other
chromosome.
3. Inversion: genes break off and are reinserted backwards
4. Translocation: genes break off and add to a different
chromosome.(pg 253)
Causes: mutations are random events. Most often though
environmental factors play a huge role in gene mutations
http://www.teachersdomain.org/asset/lsps0
7_vid_rnai/
*Many chromosome mutations result when chromosomes fail to
separate properly during meiosis.
Nondisjunction - occurs when homologous chromosomes or
sister chromatids fail to separate.
Causes:
Down syndrome, Turners syndrome, Klinefelters
syndrome, cancer, etc.
http://www.biology.iupui.edu/biocourses/N100/2k2human
csomaldisorders.html
copyright cmassengale
• DNA is made up of a long chain of
nucleotides.
• Each nucleotide has three parts.
– a phosphate group
– a deoxyribose sugar
– a nitrogen-containing base
phosphate group
nitrogen-containing
base
http://www.sumanasinc.com/webcontent/
animations/molecularbiology.html
deoxyribose (sugar)