1. DNA is composed of nucleotides
DNA’s Structure
DNA is composed of nucleotides
DNA contains four nitrogen bases:
adenine(A) cytosine(C) guanine(G) thymine (T)
A & G are purines C & T are pyrimidines

2. DNA’s Structure DNA is a double helix
-2 strands of DNA nucleotides joined to form a
“twisted ladder”
-the strands are held by hydrogen bonds between the nitrogen bases

3. Chargaff’s Rule A == T C == G T == A G == C
The nitrogen bases form the “steps” on the DNA ladder by complementary pairing
A == T
C == G
T == A
G == C
A == T A always pairs with T
T == A C always pairs with G
Sugar-phosphate backbone

4. DNA Replication – What and Why
Replication = DNA making copies of itself
DNA must be copied before a cell can divide
Each new cell will have
a complete set of DNA

5. 3 Models of Replication

6. 3 Models of Replication: Semi-conservative Replication
Each strand in a DNA molecule
is used as a template to build
a new strand using
complementary base pairing
Results in new molecule
with one original DNA strand
and one new strand

7. DNA Replication: Process
Step 1: Replication begins when the enzyme DNA helicase opens the DNA forming replication bubbles

8. DNA Replication: Process
The nitrogen bases on the
original DNA strands are
exposed in the replication
bubbles.
the new DNA strands are
built on the exposed
nitrogen bases

9. DNA Replication The ends of the replication bubbles known as the
replication fork is where replication begins

10. DNA Replication – DNA Polymerase
Step 2: The enzyme DNA polymerase
brings new nucleotides to the
replication fork
- it pairs them according to base pairing rules A pairs with T
C pairs with G

11. DNA Replication- Orientation5’ 3’
The DNA polymerase reads
the original DNA strands from
3’- 5’
- as a result, the new DNA
strands are built from 5’-3’ 3’ 5’

12. DNA Replication – Leading Strand
Leading strand- is built
toward the replication fork
–the replication of the leading strand is continuous
- as helicase opens the molecule, DNA polymerase
can continue to add new
nucleotides

13. DNA Replication – Lagging Strand
Lagging strand- replication begins at the replication fork.
- As the new DNA strand elongates, it grows away from the replication fork

14. DNA Replication- The Big Picture
Each Bubble has 2 Forks – each fork has a leading and
lagging strand

15. DNA Replication
The process continues until 2 complete copies of the DNA are produced
Each copy of the DNA contains one strand of DNA from the original DNA molecule and one new strand that was produced by replication
Replication Animation

16. DNA Replication
Step 3 : Termination = DNA polymerase reaches the end of the DNA segment and the replication process stops
Step 4 : Repair Process Takes place
Enzymes fix any mistakes in the replication process

17. DNA Replication

18. Reasons For DNA Replication
DNA replication must be done before a cell reproduce.
DNA replication is essential in passing on of genetic material from one generation to the next.
It is essential in cellular reproduction, growth/repair, and adaptation due to genetic mutations.

19. Why Is This Process So Accurate?
There are several reasons : 1- One half the DNA serves as a template for DNA to copied from, therefore the copying process is relatively simple. 2- The way the base pairs pair up chemically and the space in which they have to fit in force the nitrogenous base pairs to always be a purine and pyrimidine. 3- The proofreading process fixes most errors in the process and will delete any problems in the DNA sequence.

20. Protein Synthesis
From DNA to Protein

21. Protein Synthesis
Protein Synthesis is the process that cells use to produce protein.
- it involves 2 distinct phases
Transcription – occurs in the nucleus
involves the creation of mRNA
Translation – occurs in the cytoplasm
at a ribosome – the protein recipe is “read” and the correct protein is made

22. Function of DNA: controls the function of cells
contains recipes for proteins.
-Proteins are
Enzymes to run chemical reactions
Hormones
Numerous tissues and structures

23. Proteins are chains of amino acids.
amino acid + amino acid + amino acid = protein
The order of amino acids determines protein shape
Shape determines function
DNA recipe consists of the order of amino acids for each protein
- the recipes are known as genes

24. DNA contains recipes for all of the proteins in living things -these recipes are called genes

25. Recipe has to get from DNA to the ribosome which builds the protein

26. Transcription: makes a copy of the protein recipe
This is necessary because:
DNA cannot leave the nucleus!!!
Proteins are made on ribosomes in the cytoplasm.
mRNA provides the solution
Messenger ribonucleic acid
mRNA is a copy of the protein recipe that can leave the nucleus

27. mRNA – messenger RNA
mRNA is a copy of the recipe for a protein. It is a copy of a gene
- it can leave the nucleus
- takes the recipe to the ribosome where it is converted to a protein

28. mRNA carries the recipe from DNA to the ribosomes

29. Meet mRNA: RNA has three structural differences from DNA
Structure of RNA
1. Sugar is ribose
2. Single strand
3. Uracil replaces
thymine as a
base pair

30. Transcription: Initiation The Process Begins
The enzyme RNA polymerase finds the beginning of a protein recipe called the promotor
- promotor = a series of nucleotides that indicate the start of a protein recipe
The RNA polymerase opens the DNA molecule at the promotor
Promotor analogy- title of recipe in cookbook.
If thousands of recipes were in a cookbook together, and they weren’t separated by titles then it would be hard to find them

31. Transcription: Initiation
The RNA polymerase uses one DNA strand as a template to build the mRNA
- only one of the DNA strands contains the protein recipe
- the strand with the recipe is the
template strand
- the strand without the recipe is
the non-template strand
- it is not copied
Both strands contain recipes. Different genes are on different strands. DNA also contains recipes for tRNA and rRNA which are produced by transcription as well

32. Transcription: Elongation Building the mRNA Molecule
RNA polymerase brings RNA nucleotides to the template strand
-pairs them with their complements on the original DNA molecule
-this follows the base pairing rules except that uracil replaces thymine
- Adenine on DNA is paired with Uracil (U) on the new mRNA

33. Transcription: Elongation
The RNA polymerase reads the template strand in the 3’ to 5’ direction
RNA polymerase builds the mRNA in the 5’ to 3’ direction

34. Transcription: Termination The Process Ends
the RNA polymerase continues to add new nucleotides until it reaches the terminator
- the terminator is a sequence of nucleotides that indicates the end of the recipe
the mRNA drops off the DNA
-this is pre-mRNA it needs further
processing before it can be translated

35. Processing pre-mRNA
Pre-mRNA contains sections of nucleotides called introns
-introns are sections of mRNA that don’t
contain information needed to build the
protein
-they are extras and must be removed
before the protein can be built
Pre-mRNA also contains sections called exons
-these contain the protein recipe and are
joined to form the finished or mature
mRNA

37. Summary DNA contains recipe for protein – can’t leave nucleus
2. RNA polymerase opens DNA molecule at recipe
3. RNA polymerase builds a complementary mRNA copy of the protein recipe
4. pre-mRNA is processed
and the introns are
removed
5. mRNA takes recipe to ribosome outside nucleus

38. Vocabulary Transcription Gene mRNA Ribose Uracil RNA polymerase
Promotor
Template Strand
Non-Template Strand
Terminator
intron
exon

39. Translation
From mRNA to Protein

41. There are twenty different amino acids that build proteins
There are 64 different triplets/codons
Each amino acid is coded for by more than one triplet/codon

42. The Players mRNA:messenger RNA
- carries protein recipe from the nucleus
tRNA: transfer RNA
-brings amino acids to the ribosome
Ribosome: the site of protein synthesis
- made of rRNA (ribosomal RNA )and Protein

43. The Process of Translation
mRNA takes recipe to the ribosome in cytoplasm
ribosome attaches to the mRNA

44. Translation
The ribosome moves along the mRNA until it reaches the “Start” codon
Start codon = AUG signals the start of the recipe
AUG also codes for the amino acid methionine

45. The process of Translation cont.
A molecule of transfer RNA brings the amino acid called for by the mRNA to the ribosome
transfer RNA = tRNA

46. The process of Translation cont.
A second tRNA bringsthe second amino acid to the ribosome
The amino acids are joined together to begin the protein

47. The process of Translation concluded
The ribosome moves over 1 codon and another tRNA molecule brings another amino acid
The process continues until the stop codon on the mRNA is reached
-the stop codon = the end of the protein recipe

48. Meet tRNA each molecule of tRNA carries a specific type of amino acid
- each tRNA molecule can
only carry one type of
amino acid
The tRNA has a group of 3 nucleotides at the base called the anticodon

49. How does tRNA know which amino acid goes where?
The anticodon on tRNA is complementary
to a mRNA codon
the amino acid that a tRNA molecule
carries is the amino acid that the complementary mRNA codon codes for
Example:
mRNA codon = GAC = aspartic acid
tRNA anticodon = CUG carries only aspartic acid

50. Vocabulary
tRNA
Triplet
Codon
Anticodon
Start codon
Stop codon

51. The Key to Protein Synthesis
The Dna code
The Key to Protein Synthesis

52. The Question of DNA
DNA stores information to build proteins in sequences of nucleotides
- DNA nucleotides contain one of 4 nitrogen
bases A T C G
- there are 20 different amino acids used to
build protein
Problem: How to code for 20 amino acids with only 4 nitrogen bases?
Solution: Use groups of 3 nucleotides to code
for each amino acid

53. Why are 3 nucleotides required?
Using one nucleotide can only code for 4 amino acids
Using pairs of nucleotides produces 16 combinations – can code for 16 amino acids
Using groups of three nucleotides produces
64 different combinations – can code for all
20 amino acids
- several different groups can each code
for the same amino acid

54. The DNA Code The DNA code is: - universal to all living things
-the groups of nucleotides code for the
same amino acid in all living things
3 DNA nucleotides = Triplet
- one triplet = one amino acid
Examples – TCA = Serine
CTG = Aspartic Acid

55. The Code continued 3 mRNA nucleotides = Codon
- codon is the complement of a triplet
- codon codes for the same amino acid
as the triplet it is complementary to
Example:
DNA triplet = CTG = Aspartic Acid
mRNA codon = GAC = Aspartic Acid

56. Triplet Codon Amino Acid
Transcription Translation
DNA mRNA Amino
Triplet Codon Acid
CTG GAC Aspartic Acid
CGC GCG Alanine

57. The Codon Chart – From Codon to Amino Acid
Codon = UGC Cysteine Codon = CAC Histidine Codon = AAA Lysine Codon = GCG Alanine

58. Mutations
Hollywood’s images of
mutation

59. Mutations
Actual Mutations
in fruit flies

60. What is a mutation? A mutation is any change in a cell’s DNA
A mutation can occur in an individual gene
- results in a single changed protein
- cystic fibrosis a mutation in the protein that makes a type of ion channels in cell membrane
- bacterial resistance to antibiotics is an example of a beneficial gene mutation

61. What is a mutation continued
A mutation can occur in a chromosome
- a chromosome contains many genes
- chromosomal mutations affect many
proteins
Examples: Down Syndrome
Edward’s Syndrome
Cri-du-Chat

62. What Causes Mutations?
Can be caused by mutagens- a physical or chemical cause of mutation. Examples: UV light, radiation, drugs, and benzene.
Mutagens are often also carcinogens – anything that causes cancer
Can be natural, random events.
- mutations occur in 1/100,000 DNA replications
Mutations do not have to be bad (evolution)

63. Gene Mutations

64. Point Mutations
A single nucleotide is altered. Can change one amino acid in a protein
Milk – Mile
GGACAATCA GGACCATCA
proline -valine-serine proline-glycine-serine

65. Frameshift Mutations
A nucleotide is either inserted or deleted from a gene.
-all of the triplets from the point of mutation onward will be changed

66. Frameshift Mutations Insertion
An insertion occurs when a nucleotide is added to a gene
Example: A nucleotide is inserted
The fat cat ate the rat
The faa tca tat eth era t
-the extra nucleotide shifts all of the triplets that follow

67. Frameshift Mutations Deletions
A deletion occurs when a nucleotide is removed from a gene.
Example: A nucleotide is removed
The fat cat ate the rat
Thf atc ata tet her at

68. proline -valine-serine arginine-cysteine-stop Deletion
Insertion
GGACAATCA GCGACAATCA
proline -valine-serine arginine-cysteine-stop
Deletion
GGACAATCA GGAAATCA
proline -valine-serine proline-leucine

69. Vocabulary Mutation Mutagen Carcinogen Point mutation
Frameshift mutation
- insertion
- deletion