Download DNA

What we’ve learned so far…
•Cells make proteins
•Genetic information is passed on through chromosomes
•Compacted DNA and proteins= chromosomes
•Genetic information is stored in the nucleus
•Genetic information is essential so that each cell is identical
(mitosis)
To truly understand genetics, biologists
first had to discover the chemical nature
of the gene.
–How do genes control what you look
like?
12-1 DNA
• Vocabulary:
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•
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Transformation
Bacteriophage
Nucleotide
Base pairing
Key Concepts:
•What did scientists discover about the
relationship between genes and DNA?
•What is the overall structure of the
DNA molecule?
DNA’s “Experiment” History
• Griffith: How do certain types of
bacteria cause pneumonia?
– The experiment that tested this question
led to new knowledge.
– Genetic information could be transformed
from one bacterium to another.
Genetic Info.
Transferred
Transformation
• Heat killed bacteria had passed their disease
causing ability to the harmless strain
• Griffith called this transformation
– One strain of bacteria (harmless) had changed into the
other (disease causing)
• Some factor was transferred from the heat killed
cells to the live cells
– This factor might contain a gene with information that
could change harmless bacteria into disease causing
ones!
Avery & DNA
• Avery and a group of scientists decided to repeat
Griffith’s experiment
– determine which molecule in the heat killed bacteria was
needed for transformation
• Made an extract (juice) from heat killed bacteria and
added enzymes that destroy proteins,
carbohydrates, & lipids
– Transformation still occurred!
• Repeated the experiment but added enzymes that
destroy DNA
– Transformation DID NOT occur!!
Avery’s Conclusion
• What was the “transforming factor”?
• DNA
• Conclusion: DNA is the nucleic acid that
stores and transmits genetic info from
generation to generation
Hershey-Chase Experiment
• Studied viruses; specifically
bacteriophages
– Bacterio = bacteria
– Phage = eater
– Bacteria eater
• Viruses—made up of:
– DNA + protein coat
• Research Question: Which
part of the virus enters the
infected bacteria cell?
• Grew viruses in the presence of
radioactive markers 32P and 35S.
– Sulfur is found in protein coat
– Phosphorus is found in DNA
No
Sulfur!
Phosphorus!
Hershey-Chase Conclusion
• Genetic information of the bacteriophage
that they infected with bacteria was DNA
– NOT protein
What DNA does…
• Carries information from one generation to the
next
• Put that information to work by determining
heritable characteristics
• Must be easily copied since almost every new
cell gets a copy
DNA Structure
• Made up of nucleotides (monomer)
• Each composed of 3 parts:
– Deoxyribose: sugar
– Phosphate group
– Nitrogenous (nitrogen containing) base
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Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)
DNA Structure= Double Helix
• Backbone
– Deoxyribose & Phosphate
Group of each nucleotide
• “Steps of Ladder”
– bases
• Any base
sequence is
possible
Chargaff’s Rules
Percentage of Bases in Four Organisms
Source of DNA
A
T
G
C
Streptococcus
29.8
31.6
20.5
18.0
Yeast
31.3
32.9
18.7
17.1
Herring
27.8
27.5
22.2
22.6
Human
30.9
29.4
19.9
19.8
What does this data suggest to you?
Oooooohhhh!! Aaaaaahhhhh!!!!
• A = T (A pairs with T)
• C = G (C pairs with G)
What DNA Looks Like
• Rosalind Franklin: used X-Ray diffraction
patterns to discover that DNA twisted
around each other like a helix
• Watson & Crick: while
trying to build a 3-D
model of DNA, Watson
was shown Franklin’s
photograph and within
weeks, figured out the
structure of DNA
What’s holding the strands together?
• HYDROGEN BONDS!!!
• Hydrogen Bonds form
between A and T base
pairs as well as between
C and G base pairs