1. Understanding
DNA
Presented by:
Mrs. Nelson

2. OVERVIEW
 Name the four organic compounds
found in all living things.
 The focus of this chapter will be:
 What are the elements found in nucleic
acids?
 What is the subunit?
 What are the two types of nucleic acids?
 What is the function of DNA?

3. Discovering DNA
 Frederick Griffith
studied bacteria
cause pneumonia.
 Smooth strain
-disease
 Rough strain -
harmless
 What caused the
difference?

4. Griffith’s Experiment

5. Griffith’s Conclusion
 The harmless bacteria could “acquire”
the ability to cause disease. How?
 Transformation
 Bacteria can take “something” from
each other
 By doing so, they can take on different
traits.

6. Transformation

7. Discovery of DNA
 Griffith didn’t know what it was that
bacteria were taking from each other.
 He did know that this “something”
gave organisms their traits.
 Later, it was discovered that this was
DNA.

8.  DNA (Deoxyribonucleic acid).
 All living things contain DNA.
 Source of genetic traits because it is the
the directions cells use to build
proteins.

9. Where is DNA?
Cell Nucleus Chromosome Gene DNA

10. Chromosomes a closer look …

11. What does DNA look like?
 DNA made subunits: nucleotides
 Nucleotide: sugar (deoxyribose),
phosphate group, nitrogen base
 DNA 4 nitrogen bases: adenine,
guanine, thymine and cytosine
 ***Scientists knew DNA was made of
these parts- they did NOT know how
all the pieces fit together!

12. “The race to build the 1st DNA
model”
 Rosalind Franklin
1) 2 strands like a
twisted rope
2) Molecules were
evenly spaced out…

13. 2 Categories of Bases:
 Purines-
“larger bases”
adenine (A)
guanine (G)
 Pyrimidines-
“smaller bases”
cytosine (C)
thymine (T)

14. Chargaff’s Rule
 Measured amounts of each base in
various organisms and found:
amount of adenine (A) = thymine (T)
amount of cytosine (C) = guanine (G)
 This meant A only bonds T and C
only bonds G

15. Structure of DNA
 Double helix- “spiral staircase”, 2 strands of
nucleotides
 “siderails” sugar and phosphate
 “rungs” bases (base pairs connected by hydrogen
bonds)
 bases attach sugar molecules, phosphate molecules
between sugars
 complementary- sequence of bases on one strand
determines the sequence of bases on other strand
 antiparrallel- strands are oriented opposite to each
other with respect to the carbon atoms in the sugar
molecules

16. Watson and Crick
“Double Helix”

17. Antiparallel- 5’ and 3’ ends

18. What is the job of all cells???
 Process called Protein Synthesis:
 DNARNA Protein
 2 stages: Transcription and Translation

19. RNA (Ribonucleic acid)
 Nucleic acid… helps DNA make
proteins
 _____RNA____vs._____DNA___
single strand double strand
sugar= ribose sugar= deoxyribose
A, C, G, U (uracil) A, T, C, G
mRNA, rRNA, tRNA “DNA is DNA”
all over nucleus only

20. Structure RNA

21. Transcription: Part 1 :
Protein Synthesis
 Problem:
DNA (directions build protein) can
not leave nucleus go to ribsome
 Information DNA copied RNA
(messenger)
 DNA complementary mRNA
 occurs nucleus

22. Steps in Transcription
 1st
- DNA untwists
 2nd-
enzyme
RNA polymerase
moves along DNA
strand creating
“complementary
mRNA”

23. Genetic Code
 Goal make protein
 protein - bunch amino acids
 every 3 bases (nucleotides) mRNA
code amino acid - called codon
 DNA: ATA CGG AAT (3 triplets)
 mRNA: UAU GCC UUA (3 codons)

24. What amino acids are needed to build the
protein?
mRNA - UAU GCC UUA

25. Translation: Part 2:
Protein Synthesis
Protein built
Happens ribosome
requires tRNA (transfer RNA)
tRNA carries amino acids ribosome
mRNA complementary tRNA

26. tRNA
 One end amino
acid
 Other end 3
bases called
anticodon
 anticodon
complementary
codon
(mRNA/tRNA)
“safety check”

27. Steps Translation
 mRNA leaves nucleus goes ribosome (made
of rRNA)
 1st- “start” codon
 2nd- tRNA brings amino acids ribosome
(codons-anticodons pair)
 3rd- bonds join amino acids
 4th- stop codon
 ribosome releases protein cytoplasm

28. What is DNA Replication?
 Process of “copying” DNA exactly
 Process must be completed before
cells can divide (reproduce)
 Multicellular organisms- cell division =
growth and repair/replacement
 Unicellular organisms- cell division =
reproduction

29. DNA Replication

30. DNA Replication (process)
 1st
- enzyme helicase
attaches to DNA and causes it to unzip at the
replication fork (must break hydrogen bonds-bases)
 2nd
- enzyme DNA polymerase
moves along leading strand adding complementary
bases (continuously in 5’3’ direction toward replication
fork)
 3rd
- lagging strand completed next but Okazaki
fragments result (discontinuous away from replication
fork)
 4th
- enzyme ligase joins the fragments on lagging strand
 Summary: 1 DNA molecule 2 DNA molecules

31. Mutations
 If DNA does not get copied correctly, a
mutation can arise.
 Mutation- change in DNA sequence
 “Mutagens” are things found in the
environment that can get into your cells
and “scramble” your DNA.
 Three known mutagens:
1.) chemicals 2.) viruses 3.) UV radiation

32. Mutations – change in DNA

Substitution

33. Effects of Mutations…
 DNA carries instructions to build proteins.
 If the DNA is changed, proteins will be built
incorrectly.
 Two general types of mutations:
1. Gene mutation (effects one gene on
chromosome)
2. Chromosome mutation
 Three different types of gene mutations
1. subsitution
2. Insertion
3. Deletion

34. Substitution
THE FAT CAT SAT
THE FAT RAT SAT
Changing one letter, changes one
word, which changes the meaning of
the sentence.

35. Substitution
DNA: TAC GCA TGG AAT
MRNA: AUG CGU ACC UUA
A.ACID: Met - Arg - Thr - Leu
DNA: TAC GTA TGG AAT
MRNA: AUG CAU ACC UUA
A. ACID: Met - His - Thr - Leu
Results in one amino acid being altered

36. Insertion
THE FAT CAT SAT
THE SFA TCA TSA
T
Inserting one letter, shifts all other
letters over, creating several words to
be incorrect. This is also known as a
“frame-shift” mutation.

37. Insertions
DNA: TAC GCA TGG AAT
MRNA: AUG CGU ACC UUA
A.ACID: Met - Arg - Thr - Leu
DNA: TAT CGC ATG GAA T
MRNA: AUA GCG UAC CUU A
A.ACID: Iso - Ala - Tyr - Leu
Results in several amino acids being altered

38. Deletion
THE FAT CAT SAT
THE ATC ATS AT
Similar to Insertion (frame-shift).
REMOVE

39. Deletion
DNA: TAC GCA TGG AAT
MRNA: AUC CGU ACC UUA
A.ACID: Met - Arg - Thr - Leu
DNA: TAG CAT GGA AT
MRNA: AUC GUA CCU UA
A. ACID: Iso - Val - Pro - None
Results in several amino acids being altered

40. Significance of Mutations
 Some mutations may be “neutral,” they
won’t have an effect on the protein
being built.
 Some mutations can be very harmful
and cause genetic disorders.
 Some mutations lead to genetic
variation in a species.
(Ex. Tongue rolling)