This document summarizes key discoveries and scientists involved in understanding DNA and genetics. It describes Frederick Griffith's experiments in 1928 which showed bacteria could undergo transformation through incorporation of DNA from other bacteria. Later experiments by Avery, MacLeod and McCarty in 1944 confirmed DNA was the transforming agent. The document then outlines discoveries around DNA structure including its double helix shape discovered by Watson and Crick in 1953 based on X-ray crystallography data from Rosalind Franklin. It also summarizes DNA replication and basic concepts in genetics like transcription, translation and genetic code.

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2. Frederick Griffith
• British bacteriologist
• 1928 = designed and performed experiment
on rats and bacteria that causes pneumonia.
• 2 strains of the bacteria
• Type S = causes severe pneumonia
• Type R = relatively harmless

3. Griffith’s Rats
1. First he injected living Type S bacteria into
rats:

4. • Second he injected dead Type S into the
rats.

5. • Next he injected living type R bacteria

6. • Finally he injected a mixture of living Type R
and dead Type S :

7. Results of experiments:
• Because the dead rat tissue showed living
Type S bacteria, something “brought the Type
S back to life”
• Actually one bacterial type incorporated the
DNA, or instructions, from the dead bacteria
into its own DNA
• Known as transformation. Confirmed by
Avery, MacLeod, and McCarty in 1944

8. Oswald Avery
• Canadian
biologist (18771955)
• Discovered
DNA in 1944
with a team of
scientists.

9. Hershey and Chase
• 1952
• Attempted to solve
the debate on
whether DNA or
proteins are
responsible for
providing the
genetic material.

10. • They used a
bacteriophage (a
virus which
attacks bacteria)
to prove that
DNA was
definitely the
genetic material.

12. Phoebus A. Levene
• Russian born; immigrated to America,
moves to Europe.
• 1920’s discovered nucleotides (building
blocks of DNA)
1. Sugar
2. Phosphate group
3. Nitrogenous base

13. Composition of DNA

14. Components and structure of DNA
• A very long molecule. 4 nitrogenous bases:

15. Chargaff’s rules
• The relative amounts of adenine and thymine
are the same in DNA
• The relative amounts of cytosine and guanine
are the same.
• Named after Erwin Chargaff

16. Rosalind Franklin
• Used X-Ray diffraction to
get information about the
structure of DNA:

17. Structure of DNA
• Discovered in 1953
by two scientists:
• James Watson
(USA)
• Francis Crick (GBR)
• Known as the
double-helix
model.

19. The double-helix
• A twisted ladder with two long chains of
alternating phosphates and sugars. The
nitrogenous bases act as the “rungs”
joining the two strands.

20. How long is the DNA molecule?

21. Chromosomes & DNA replication
• The nucleus of one human cell contains
approximately 1 meter of DNA.
• Histones = DNA tightly wrapped around a
protein
• Nucleosome:

22. Chromosome structure:

23. DNA replication
• Must occur
before a cell
divides.
• Each new cell
needs a copy of
the information
in order to grow.

24. DNA replication. Why needed?
• Before DNA strand can
be replicated or
copied it must be
“unzipped”
• DNA polymerase
(enzyme that unzips)
• Starts at many
different points. Why?

25. Completing the replication
• After the DNA
molecule comes
apart, bases of
free nucleotides
in the nucleus
join their
complimentary
bases.

26. RNA
• Very similar to DNA.
• Exceptions:
1) Ribose is the 5-carbon sugar
2) Uracil replaces thymine
3) Single-stranded

27. mRNA (messenger)
• Copies genetic
code of DNA by
matching bases.
• Occurs in the
nucleus.
• DNA changing to
RNA

28. TRANSCRIPTION
• DNA is copied into mRNA with the
aid of RNA polymerase.
• The RNA polymerase will bind to
promoters that act as signals in the
DNA sequence to make RNA.

29. Transcription continued:

30. Exons and Introns
• EXONS
• A segment of DNA in
eukaryotic organisms
that codes for a specific
amino acid
• INTRONS
• A segment of DNA that
does NOT code for an
amino acid.

31. Confusing genetic terms:
• Polypeptide = a chain of amino acids.
• Protein = a complex structure composed of
polypeptides
• Amino acids = smallest structural unit of a
polypeptide.
• Gene = a distinct unit of material found on a
chromosome

32. Reading the genetic code
• The genetic code is responsible for
building all the proteins in the body using
20 different amino acids.
• How many 3 letter words can you make
from the letters A,T,G and C?
• Answer: 64

33. Codons
• A three letter “word” that specifies
an amino acid.

34. Genetic code:

35. tRNA (transfer)
• approx. 80 nucleotides in
length.
• Cross-like shape
• At one end an amino acid
is attached
• At the other end there is
an anticodon
• Acts like a truck

36. Polypeptide assembly
• Translation = reading
or “translating” the
RNA code to form a
chain of amino acids.
• Known as protein
synthesis
• Occurs in the
cytoplasm. (p.304)

37. Mutations
• The source of variation in a genetic
sequence.
• Can be either gene or chromosomal
mutations.
• Point mutations = a change in a single
nucleotide in a sequence of DNA.

38. Frameshift Mutation
• Inserting an extra nucleotide which, in turn,
shifts the entire sequence one way or the
other.

39. Chromosomal mutations
• Involves a change in the number or structure
of the chromosomes.
• Deletion : when a piece of a chromosome
breaks off and is lost.
• Duplication : when a segment of a
chromosome is repeated
• Inversion : when a segment of a chromosome
is reversed.

40. More chromosomal mutations
• Translocation :
when part of a
chromosome
breaks off and is
attached to a
non-homologous
chromosome.

41. Control of gene expression
• Genes are often like light switches
that can be turned off and on.
• Operon = occur in prokaryotes.
(bacteria) different genes that work
together to activate gene functions

42. Eukaryotic gene expression
• Controlled by
complex
sequences of
DNA.
• Example:
“TATA box”

43. Protein Structure
• Serve various function including structural roles,
catalysts, transporter and hormones
• Polymers of amino acids covalently linked
through peptide bonds into a chain
• Each of amino acid has a fundamental design
composed of a central carbon bonded to ;
i. a hydrogen
ii. a carboxyl group
iii. An amino group
iv. A unique side chain of R-group

45. • the characteristic that distinguishes one amino
acid from another is its unique side chain, and
it is the side chain that dictates an amino acids
chemical properties
• The unique side chains confer unique chemical
properties on amino acids, and dictate how
each amino acid interacts with the others in a
protein.

46. Peptide bonds are formed between the carboxyl
group of one amino acid and the amino acid of the
next amino acid
 Peptide bond formation occurs in a condensation reaction
involving loss of a molecule of water
 The head-to-tail arrangment of amino acids in a protein means
that there is a amino group on one end (called the aminoterminus or N-terminus) and a carboxyl group on the other end
(carboxyl-terminus or C-terminus).
 The carboxy-terminal amino acid corresponds to the last one
added to the chain during translation of the messenger RNA.

47. Levels of Protein Structure
• Structural features of proteins are usually described at
four levels of complexity
a. Primary structure
b. Secondary Structure
c. Tertiary Structure
d. Quaternary Structure

48. Primary Structure
• - the linear arrangement of amino acids in a
protein and the location of covalent linkages
such as disulfide bonds between amino acids

49. Secondary Structure
• areas of folding or coiling within a protein;
examples include alpha helices and pleated
sheets, which are stabilized by hydrogen
bonding

50. Tertiary Structure
• the final three-dimensional structure of a
protein, which results from a large number of
non-covalent interactions between amino
acids.

51. Quaternary Structure
• Two or more tertiary proteins joined
• non-covalent interactions that bind
multiple polypeptides into a single, larger
protein. Hemoglobin has quaternary
structure due to association of two alpha
globin and two beta globin polyproteins.