1. Genetics Unit I DNA and RNA: Structure and Function
-an interactive learning experience!

2. DNA and RNA as the genetic material
Why do you need genetic material?
to keep the species going, must pass on information in some form
for individuals to survive, must have “code” to allow for proteins to be made. “Code” must be carried by a molecule

3. DNA and RNA as the genetic material
What properties must the genetic material have?
it must contain, in stable form, information for an organism’s cell structure, function, development, + reproduction
it must replicate accurately, so progeny receive same information as parents
it must be capable of variation, as organisms must be capable of change. Evolution needs to occur.

4. DNA and RNA as the genetic material
What could the genetic material be?
Must be an organic compound, so it’s either:
carbohydrate
lipid
protein
nucleic acid
Carbohydrates and lipids were eliminated by scientists for various reasons:
can’t replicate
isn’t found in all organisms (viruses)
not capable of variation
This led to a great debate among scientists about whether proteins or nucleic acids were the genetic material

5. DNA and RNA as the genetic material
Many experiments were done, including:
Griffith – late 1920’s
studied P. pneumonia strains of bacteria, specifically looked at 2 strains
1.) s-strain – forms smooth colonies in culture, causes death in infected mice
2.) r-strain – forms rough colonies in culture, no effect is seen on infected mice

6. Transformation Of Bacteria Two Strains Of Streptococcus
Rough Strain
(Harmless)
Capsules
Smooth Strain
(Virulent)

7. Transformation Of Bacteria The Griffith’s 1928 Experiment
OUCH!
+ Control
- Control
- Control
Experimental

8. DNA and RNA as the genetic material
Griffith treated mice in 4 ways and found these results:
injected s-strain- mice died
injected r-strain- mice alive
injected heat-killed s-strain- mice alive
injected heat killed s-strain + regular r-strain- mice death
His conclusion: a component found in only s-strain changed the r-strain, making it lethal, this component is the genetic material, as it passed a trait on to the mice
He termed this genetic transformation.

9. Avery, MacLeod and McCarty
1944 Avery, MacLeod and McCarty repeated Griffith’s 1928 experiment with modifications designed to discover the “transforming factor”
After extraction with organic solvents to eliminate lipids, remaining extract from heat killed cells was digested with hydrolytic enzymes specific for different classes of macro molecules:
Transformation?
Enzyme
Protease
Yes
Saccharase
Yes
Nuclease No
Conclusion – DNA was the genetic material

10. The Hershey-Chase Experiement
The Hershey-Chase experiment showed definitively that DNA is the genetic material
Hershey and Chase took advantage of the fact that T2 phage is made of only two classes of macromolecules: Protein and DNA H OH P O HO
NH2
Nucleotides contain phosphorous, thus DNA contains phosphorous, but not sulfur. H OH O
H2N C
CH2 SH
CH3 S
Some amino acids contain sulfur, thus proteins contain sulfur, but not phosphorous.
Cysteine
Methionine

11. Using S35 Did protein enter the bacteria?
T2 grown in S35 containing media incorporate S35 into their proteins
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The supernatant is radioactive, but the pellet is not.
Blending causes phage protein coat to fall off
Did protein enter the bacteria?
Is protein the genetic material?

12. Using P32 Did DNA enter the bacteria? Yes!
T2 grown in P32 containing media incorporate P32 into their DNA
Bacteria grown in normal non-radioactive media
T2 attach to bacteria and inject genetic material
When centrifuged, phage protein coats remain in the supernatant while bacteria form a pellet
Mix-O-Matic
The pellet is radioactive, but the supernatant is not.
Blending causes phage protein coat to fall off
Did DNA enter the bacteria? Yes!
Is DNA the genetic material? Yes!

13. DNA and RNA structure DNA + RNA are classified as nucleic acids.
They contain the elements C, H, O, N, + P
The fundamental structure of DNA + RNA are repeating units known as nucleotides
Nucleotides have the following components:
1 pentose sugar
1 nitrogenous base
1 phosphate group

14. A Nucleotide Base Sugar P O OH HO NH2 N - OH O CH2 H Nucleotide
Phosphate
NH2 N
Base - OH O
CH2
Sugar H 2’ 3’ 4’ 5’ 1’
Nucleotide
Nucleoside
(just the sugar
And base) OH

15. Comparing the two nucleic acids
DNA
RNA
sugar
deoxyribose
ribose
nitrogen bases
adenine
guanine
cytosine
thymine
uracil
adenine and guanine are purines
cytosine, thymine, and uracil are pyrimidines

16. Purines Pyrimidines Uracil CH3 N O NH Thymine N Adenine NH2 NH2 O N NH
(RNA)
CH3 N O NH
Thymine
(DNA) N
Adenine
NH2
NH2 O N NH
Guanine N O
NH2
Cytosine

17. Base Pairing Guanine And CytosineH O N
Guanine - N O H
Cytosine + + - - +

18. Base Pairing Adenine And Thymine- +
Adenine
CH3 N O H + -
Thymine

19. DNA and RNA structure
DNA + RNA are made up of long chains of repeating nucleotides
The phosphate and sugar are in the “backbone” of the chain, while the nitrogen base sticks out.
DNA is double-stranded, so the nitrogen bases that stick out may hydrogen bond together.

20. DNA and RNA structure
The ratio of A:T + C:G was discovered by Erwin Chargraff – known as Chargraff’s rules.
This study, along with work by Wilkins, Franklin, Watson, and Crick, led to structure of DNA being discovered.
Termed the “Double Helix”

21. D N A B A S E S SUGAR-PHOSPHATE BACKBONE 5’Phosphate group
3’Hydroxyl group
SUGAR-PHOSPHATE BACKBONE H P O HO
CH2 OH
NH2 N NH
B A S E S O H P HO
CH2
H2N N HN H OH P O HO
CH2
CH3 HN N
H2O
D N A H P HO O
CH2 N
H2N
H2O
3’Hydroxyl group
5’Phosphate
group

22. The Watson - Crick Model Of DNA
T A
G C
C G
G C
T A
3.4 nm
1 nm
Minor
groove
Major
groove
0.34 nm

23. Forms of the Double Helix
1 nm
Major
groove
Minor
A T
T A
G C
C G
G C
T A
0.34 nm
3.9 nm
B DNA
C G
G C
G C
G C
G C
C G
0.57 nm
6.8 nm
0.9 nm
Z DNA
0.26 nm
2.8 nm
Minor
groove
Major
C G
A T
T A
G C
C G
T A
A T
G C
T A
G C
1.2 nm
A DNA
+34.6o Rotation/Bp
10.4 Bp/turn
+34.7o Rotation/Bp
11 Bp/turn
-30.0o Rotation/Bp
12 Bp/turn

24. Even More Forms Of DNA C-DNA: D-DNA: E-DNA:
Exists only under high dehydration conditions
9.3 bp/turn, 0.19 nm diameter and tilted bases
D-DNA:
Occurs in helices lacking guanine
8 bp/turn
E-DNA:
Like D-DNA lack guanine
7.5 bp/turn
P-DNA:
Artificially stretched DNA with phosphate groups found inside the long thin molecule and bases closer to the outside surface of the helix
2.62 bp/turn
B-DNA appears to be the most common form in vivo. However, under some circumstances, alternative forms of DNA may play a biologically significant role.

25. Denaturation and Renaturation
Heating double stranded DNA can overcome the hydrogen bonds holding it together and cause the strands to separate resulting in denaturation of the DNA
When cooled relatively weak hydrogen bonds between bases can reform and the DNA renatures
TACTCGACATGCTAGCAC
ATGAGCTGTACGATCGTG
HEAT
Denatured DNA
Denaturation
Single stranded DNA
TACTCGACATGCTAGCAC
ATGAGCTGTACGATCGTG
Double stranded DNA
Renaturation
TACTCGACATGCTAGCAC
ATGAGCTGTACGATCGTG
Double stranded DNA

26. Hybridization
The bases in DNA will only pair in very specific ways, G with C and A with T
In short DNA sequences, imprecise base pairing will not be tolerated
Because the source of any single strand of DNA is irrelevant, merely the sequence is important, DNA from different sources can form a double helix as long as their sequences are compatible
Thus, this phenomenon of base pairing of single stranded DNA strands to form a double helix is called hybridization, as it may be used to make hybrid DNA composed of strands which came from different sources

27. Hybridization CTGATGGTCATGAGCTGTCCGATCGATCAT TACTCGACAGGCTAG
DNA from source “X”
TACTCGACAGGCTAG
Hybridization
DNA from source “Y”
TACTCGACAGGCTAG

28. Hybridization
Because DNA sequences will seek out and hybridize with other sequences with which they base pair in a specific way much information can be gained about unknown DNA using single stranded DNA of known sequence
Short sequences of single stranded DNA can be used as “probes” to detect the presence of their complimentary sequence in any number of applications including:
Southern blots
Northern blots (in which RNA is probed)
In situ hybridization
Dot blots . . .
In addition, the renaturation or hybridization of DNA in solution can tell much about the nature of organism’s genomes

29. How Does the Genetic Material Influence Cell Life?
DNA is known as the principle genetic component, found only in the nucleus
RNA is the secondary component, although in some organisms, it is the primary component. It is found in the nucleus and cytoplasm
Their roles are explained by the Central Dogma, the most influential of all theories in Molecular Biology

30. The Central Dogma of Molecular Biology
Cell
DNA
mRNA
Transcription
Polypeptide
(protein)
Translation
Ribosome
©1998 Timothy G. Standish

31. How Does the Genetic Material Influence Cell Life?
1.) Replication – DNA makes copies of itself
2.) Transcription – DNA serves as a template for an RNA copy
3.) RNA replication- RNA can also copy itself
4.) Translation – RNA serves as a template for protein production
These are the central concepts in genetics, learn them well!