Transcript DNA

What are you looking at?
What are you looking at now?
DNA
What are genes made of?
Where are genes located?
How do they determine characteristics?
After reading this, try to answer
the questions with your partner…
• Deoxyribonucleic acid (DNA) is a nucleic acid that
contains the genetic instructions used in the
development and functioning of all known living
organisms and some viruses. The main role of DNA
molecules is the long-term storage of information. DNA is
often compared to a set of blueprints or a recipe, or a
code, since it contains the instructions needed to
construct other components of cells, such as proteins
and RNA molecules. The DNA segments that carry this
genetic information are called genes, but other DNA
sequences have structural purposes, or are involved in
regulating the use of this genetic information.
Try to figure out what happened?
Harmless
bacteria
Disease-causing
bacteria
Heat-killed
disease causing
Harmless & Heatkilled disease causing
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Go to
Section:
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Figure 12–2 Griffith’s Experiment
Section 12-1
Heat-killed,
disease-causing
bacteria (smooth
colonies)
Disease-causing
bacteria (smooth
colonies)
Harmless bacteria Heat-killed, disease(rough colonies) causing bacteria
(smooth colonies)
Dies of pneumonia
Go to
Section:
Lives
Lives
Control
(no growth)
Harmless bacteria
(rough colonies)
Dies of pneumonia
Live, disease-causing
bacteria (smooth colonies)
Some History
• While Frederick Griffith was experimenting with
pneumonia, he discovered that mice injected
with dead bacteria still died of pneumonia… so it
was something inside the bacteria that was still
passed on to the next generation.
• Oswald Avery and other scientists discovered that
DNA is the nucleic acid that stores and transmits
the genetic information from one generation of
an organism to the next.
Some More History
• Alfred Hershey and Martha Chase concluded that
the genetic material of the bacteriophage (a virus
that “eats” bacteria) is DNA, not protein.
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Go to
Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Go to
Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
Figure 12–4 Hershey-Chase
Experiment
Section 12-1
Go to
Section:
Bacteriophage with
phosphorus-32 in
DNA
Phage infects
bacterium
Radioactivity inside
bacterium
Bacteriophage with
sulfur-35 in protein
coat
Phage infects
bacterium
No radioactivity inside
bacterium
DNA
• Genes are made of DNA = deoxyribonucleic acid
• How could DNA code for everything genes do?
– Genes had to carry information from one generation
to the next
– Genes had to put that information to work by
determining the inheritable characteristics of
organisms
– Genes had to be easily copied, because it is
replicated every time the cell divides
DNA’s Structure
• A long molecule made of units called
nucleotides
• Each nucleotide is made of 3 basic parts:
– A 5-carbon sugar called deoxyribose
– A phosphate group
– A nitrogenous base (There are 4 kinds…)
A (Adenine)
G (Guanine)
T (Thymine)
C (Cytosine)
Purines
Pyrimidines
Figure 12–5 DNA Nucleotides
Section 12-1
Purines
Adenine
Guanine
Phosphate
group
Go to
Section:
Pyrimidines
Cytosine
Thymine
Deoxyribose
A Single
DNA Nucleotide
Phosphate
Group
Deoxyribose
Sugar
Nitrogenous
Base
DNA Structure
Nitrogenous Base
Weak Hydrogen Bonds
Deoxyribose
Sugar
Figure 12–7 Structure of DNA
Section 12-1
Nucleotide
Hydrogen
bonds
Sugar-phosphate
backbone
Key
Adenine (A)
Thymine (T)
Cytosine (C)
Guanine (G)
Go to
Section:
The Chargaff “rule”
• It was discovered that the percentages of
guanines (G) and cytosines (C) are almost
equal and the percentages of adenines (A) and
thymines (T) are almost equal
• Erwin Chargaff came up with a “rule” that
guanine (G) pairs with cytosine (C) and
adenine (A) pairs with thymine (T).
DNA Base Pairing
• Nitrogenous base
pairs:
– Adenine (A)
with Thymine (T)
– Guanine (G)
with Cytosine (C)
Let’s pair up DNA!
• What would pair up with ATCG?
TAGC
• What would pair up with ATTAGC?
TAATCG
• What would pair up with ATACGGTC?
TATGCCAG
The Double Helix
• Rosaline Franklin’s x-ray showed that two DNA
strands are twisted around each other.
• James Watson and Francis Crick used Franklin’s xray to make a model of DNA.
• Watson and Crick’s model of DNA was a double
helix, in which two strands were wound around
each other.
• Watson and Crick also discovered that hydrogen
bonding held the nitrogenous bases together.
Let’s wrap it up with a few questions together…
1. How many strands does DNA have?
a. one
b. two
c. three
d. four
2. Which scientists came up with the double helix
model of DNA?
a. Hershey & Chase
b. Watson and Crick
c. Galileo & Aristotle
d. Darwin & Malthus
3. What holds the strands of DNA together?
a. Phosphate Group
b. Deoxyribose Sugar
c. Hydrogen Bonds
d. Nitrogen bonds
4. What DNA bases would pair up with CATTAT?
a. CATTAT
b. TATTAC
c. GTAATA
d. GUAAUA
5. What DNA bases would pair up with GAATCC?
a. CTTAGG
c. CGGAGG
b. GAATCC
d. GCCTCC
Is your
answer
the same
as earlier…
• What are
genes
made of?