1. DNA and The Language of Life

2. Genes are Made of DNA
Scientist discovered that DNA was a chemical inside the nucleus
Experiments were by Biologist:
Frederick Griffith
Oswald Avery – worked on Griffith’s experiments
Worked on bacteria to prove DNA was the reason for heredity.
Oswald Avery
1944
Frederick Griffith 1928

3. Genes are Made of DNA Further experiments by: Alfred Hershey
Martha Chase
Worked with viruses to support Avery’s work

4. Genes are Made of DNA
Virus – a package of nucleic acid wrapped in protein
Not made of cells
They can only reproduce by infecting a living cell
Bacteriophage – a virus that infects bacteria

5. The Building Blocks of DNA
Nucleic Acids
The Building Blocks of DNA
Deoxiribonucleic Acid – this where genetic
information is stored
DNA is a kind of nucleic acid, a polymer built from monomers called nucleotides
Ribonucleic Acid (RNA) – another group of
nucleotides, plays a role
in protein synthesis.
Nucleotides – are the building blocks (monomer) of
nucleic acid polymer
Only 4 types of nucleotides make – up DNA

6. DNA - Nucleotides
Each DNA molecule has three parts:

7. DNA - Nucleotides Nitrogenous Base – 4 nucleotides found in DNA
differ only in their nitrogenous
bases
Pyrimidines: single ring structure
Thymine (T)
Cytosine (C)
Purines: double ring structure
Adenine (A)
Guanine (G)

8. Nucleotides are joined by covalent bonds
DNA - Strands
Nucleotides are joined by covalent bonds
Connect one nucleotide to the phosphate group of the next
This pattern (Sugar-Phosphate-Sugar-Phosphate)
This is called Sugar – Phosphate Backbone
Nitrogenous bases (AG ; CT) line – up along this backbone
Nucleotides of a nucleic acid polymer can combine in many different sequences
Sequences are essentially unlimited

9. DNA - Structure
During the 1950’s scientist Rosalind Franklin produces using an X-ray (photograph) called :
X-ray Crystallography – Provided clues as to the shape and dimensions of the DNA molecule

10. The Double Helix Double Helix – Model created by Watson and
At more or less the same time scientist:
James Watson
Francis Crick
Using Franklin’s X-ray crystalography to provide clues to their discovery
Double Helix – Model created by Watson and
Crick; in which two strands of
nucleotides wound about each
other
Sugar phosphate backbones on the outside; Nitrogenous base on the inside.

11. The Double Helix

12. Complementary Base Pairs
Base Pairing Rules
A with T
C with G
AT CG (Coral Gables)

13. DNA Replication
When a cell divides; a complete set of genetic instructions are created for each cell
Genetic material uses the template principle to make more DNA
Watson and Crick’s model for DNA allowed for the hypothesis of specific base pairing
A – T
C - G
If you know one strand of DNA you can determine the sequence on the other

14. Called Daughter Strands
DNA Replication
During DNA copying:
Two strands of the double helix separate
Each strand acts like a picture negative
Nucleotides line up one at a time across the existing strand (as per base pairing rule)
Enzymes link the nucleotides together to form two new DNA strands
Called Daughter Strands

15. DNA Replication

16. DNA Replication
More than a dozen enzymes are involved in DNA replication
DNA Polymerases – Name of enzymes involved in
DNA replication
Make covalent bonds between nucleotides of the new DNA strand
This happens really fast and it is really accurate
An error occurs in only one of a billion nucleotides
DNA Polymerases

17. DNA Replication Origins of Replication - Specific sites where
replication begins
The copying occurs outward in both directions creating replication bubbles.
Daughter Strands grow on the inside

18. DNA Replication
In Eukaryotic Cells this can occur at the same time in different location
They eventually join.
This shortens replication time.

19. DNA Replication
DNA replication occurs before cell division This ensures that cells carry the same genetic information This is also the method for inheritance.

20. Information for Making Protein
The molecular basis for phenotype (physical characteristics) lies in proteins
“One Gene-One Enzyme” Hypothesis
One gene dictates the production of a specific enzyme
Hypothesis developed by geneticists George Beadle and Edward Tatum in the 1940’s
Since then the hypothesis has evolved to:
“one gene – one polypeptide”

21. DNA to RNA = Protein
As we know a gene is a sequence of bases along DNA chain
A gene is like a sentence
Specific strings of bases make-up a gene sentence

22. RNA (ribonucleic acids)
Any nucleic acid whose sugar is ribose rather than deoxyribose (DNA)
Another difference is that the Nitrogenous Base Thymine is replaced by Uracil (U)
Similar to thymine
Also Pair with Adenine
RNA forms single strands NOT a double helix (like DNA)
RNA can twist

23. RNA Transcription – The process of converting a DNA
sequence to a form a single
stranded RNA molecule.
RNA molecule leaves the nucleus and is involved with the making of protein

24. RNA Genetic Translation – Converts nucleic acid
language into amino acid
language
Codon – A 3 – Base “word” that codes for one
amino acid
This is how the flow of information from gene to protein is based on
Several codons form a sentence – that translates into polypetide

25. Triplet Code There are specific codons to represent amino acid
Some amino acids are coded by more than one codon
But no codon represents more than one amino acid

26. This coding is shared by ALL organisms (almost all)
Triplet Code
There is also a code for stop
These come at the end of a sequence
There are sequence that do not code form an amino acids
This coding is shared by ALL organisms (almost all)
Evidence of Evolution??????

27. From Gene to Protein Transcription: DNA RNA Three Types of RNA
messenger RNA (mRNA)
Transcribed from a DNA template
Only one DNA strand serves as a template for forming mRNA

28. From Gene to Protein - Steps
1st – DNA strand separates – This is where
transcription will start
2nd – RNA bases pair with complementary DNA
bases (same as DNA replication, except Uracil)

29. From Gene to Protein RNA Polymerase – An enzyme; links RNA
nucleotides together.
Still in second step; specific sequences of DNA nucleotides tell polymerase where to begin and end the transcribing process
RNA Polymerase

30. From Gene to Protein Introns – non-coding regions in mRNA
Only found in eukaryotic cells (most plants and animals)
Exons – parts of mRNA translated or expressed.
Before RNA leaves the nucleus the introns are removed and exons are joined together
RNA Splicing – the process of removing introns and
joining exons

31. From Gene to Protein Translation: RNA to Protein
Requires enzymes and ATP
Transfere RNA (tRNA) – translates the 3 – Letter
codons of mRNA to the
amino acids that make up
proteins.

32. From Gene to Protein - Translation
Anticodon
Located at one end of the folded tRNA molecule
It is a specific triplet of bases
Are complementary (or matched up with) a specific codon in m RNA
Recognition follows base pair rules (AU / CG)
At the other end is the site where a particular amino acid recognizes both tRNA and its amino acid partner and links both together.
Requires

33. From Gene to Protein - Translation
Ribosome – coordinates the functioning of mRNA
and tRNA
Made of Two Subunits:
Both made of proteins and rRNA (ribosomal)
rRNA – acts like a “vise”; holds mRNA and tRNA
molecules close together.
P - Site and A – Site
P – Site - a location on the t RNA molecule that
allows for the polypeptide strand to hold
together.
A – Site – a location on the tRNA molecule that
allows for amino acids to hold together.
Ribosomes connect Amino Acid to polypeptide chain

34. Do not code for amino acid
The Process
1st Step in Translation
All parts needed are brought together
mRNA
First tRNA with amino acid attached
Two subunits of a ribosome
The start codon AUG
Next Step
Amino Acids are added one by one to the chain of amino acids.
Each addition occurs in a 3-step process
Continues till you reach a stop codon
UAA
UAG
UGS
Do not code for amino acid

35. The Process - continued
Finally
The complete polypeptide (several 100 amino acids) is set free by hydrolysis from tRNA
A single ribosome can make an average polypeptide in less than a minute.
This is happening all over the cell at the same time.

36. Protein Synthesis

37. Mutations

38. Mutations
Any change in the nucleotide sequence of DNA They can involve large regions of a chromosome or just a single nucleotide pair

39. Two Catagories of Mutations
Base Substitution – the replacement of one base or nucleotide with another
Usually causes no change to the protein
But sometimes change results in a change that affects protein function
Sometime drastically
Because several amino acids have more than one codon it makes it possible that a mutation have no effect on a protein

40. Mutations - Base Substitution
Silent Mutation – a mutation to DNA causes mRNA
codon to change from GAA to
GAG (no change in protein
Some changes for amino acids have similar chemical properties – THUS: No Change

41. Mutations Base Insertions or Deletion Has a more significant effect
Because mRNA is read as a series of triplet grouping, adding or subtracting
Will alter grouping of genetic message

42. Mutations - Base Insertions or Deletions
Causes:
Mutations may occur when errors are made during DNA replication or when errors are made during chromosome cross-over
Mutagens – a physical or chemical agent that cause
mutations
High energy radiation (x-rays and uv rays)
One type of chemical mutagen are chemicals that are similar to normal DNA bases but causes incorrect base-pairing

43. Mutations Can be harmful Can be helpful in certain environments
If mutation is present in gametes it can be passed on to its offspring
Mutations are the ultimate source of genetic diversity.