DNA strucutre and replicationDNA strucutre and replicationDNA strucutre and replicationDNA strucutre and replicationDNA strucutre and replication

1. DNA&RNA
HEREDITY: INHERITANCE AND VARIATION

2. Discovering the structure of DNA
• DNA = Deoxyribose nucleic acid
• Made out of sugars (deoxyribose),
phosphates and nitrogen bases

3. •DNA is a
double helix
structure
that
contains the
instructions
for making
proteins
within the
cell.

4. Discovering the structure of DNA
• Structure
was
discovered
in 1953 by
James
Watson and
Francis
Crick

5. `It has not escaped our
notice that the specific
pairing we have
postulated immediately
suggests a possible
copying mechanism for
the genetic material’
Watson & Crick
Nature (1953)
Original drawing by Francis Crick

6. Discovering the structure of DNA
Rosalind Franklin’s DNA image

7. Discovering the structure of DNA
“Chargoff’s rule”
A = T & C = G

8. Cell division and DNA replication
• Cells divide
Growth, Repair, Replacement
• Before cells divide they have
to double cell structures,
organelles and their genetic
information

9. ONE STRAND OF DNA
•The backbone of
the molecule is
alternating
phosphate and
deoxyribose, a
sugar, parts.
•The teeth are
nitrogenous bases.
phosphate
deoxyribose
bases

10. • Each side of the
ladder is made up of
nucleic acids.
• The backbone is a
phosphate and a
sugar
• The rung of the
ladder is the nitrogen
base.

11. FOUR NITROGENOUS BASES
• Cytosine C
• Thymine T
• Adenine A
• Guanine G
DNA has four different bases:

12. TYPES OF NITROGEN BASES
•A= adenine
•G= guanine
•C= cytosine
•T= thymine

13. TWO STRANDED DNA
• Remember, DNA has two
strands that fit together
something like a zipper.
• The teeth are the
nitrogenous bases but why
do they stick together?

14. IMPORTANT
• Adenine and Thymine
always join together
A -- T
• Cytosine and Guanine
always join together
C -- G

15. HYDROGEN BONDS
• When making
hydrogen bonds,
cytosine always
pairs up with
guanine,
• And adenine
always pairs up
with thymine.
• (Adenine and
thymine are
shown here.)
C
C
C
C
N
N
O
O
C

16. RNA
•Ribonucleic Acid
•Single stranded
•Types:
a. mRNA
b. rRNA
c. tRNA

17. RNA
•In RNA Thymine
is replaced by
Uracil
•A-U (RNA)
Instead of
A-T (DNA)

18. DO NOW!
• Where is
DNA located?
• What does it
look like?
• What are its
bases?
• Why do you
think DNA is
located
there?
• Check your understanding!

19. WHAT’S THE MAIN
DIFFERENCE BETWEEN DNA
AND RNA

20. DID YOU KNOW?
• Each cell has about 2M
of DNA.
• The average human has
75 trillion cells.
• The average human has
enough DNA to go from
the earth to the sun more
than 400 times.
• DNA has a diameter of
only 0.000000002 m.
The earth is 150 billion m
or 93 million miles from
the sun.

21. DNA
REPLICATION

22. BASIC RULES OF REPLICATION
A. Semi-conservative
B. Starts at the ‘origin’
C. Synthesis always in the 5’-3’ direction
D. Can be uni or bidirectional
E. Semi-discontinuous
F. RNA primers required

23. Semi-conservative
replication:
One strand of
duplex passed on
unchanged to each
of the daughter
cells. This
'conserved' strand
acts as a template
for the synthesis
of a new,
complementary
strand by the
enzyme DNA
polymerase

24. B) STARTS AT ORIGIN
Initiator proteins identify specific base sequences on
DNA called sites of origin
Prokaryotes – single origin site E.g E.coli - oriC
Eukaryotes – multiple sites of origin (replicator)
Eukaryotes

25. In what direction does DNA replication occur?
C) Synthesis is ALWAYS in the 5’-3’ direction

26. Why does DNA replication only occur in the 5’ to 3’ direction?
Should be PPP here

27. E) SEMI-DISCONTINUOUS REPLICATION
Anti parallel strands replicated simultaneously
Leading strand synthesis continuously in 5’– 3’
Lagging strand synthesis in fragments in 5’-3’

28. SEMI-DISCONTINUOUS REPLICATION
New strand synthesis always in the 5’-3’ direction

29. F) RNA PRIMERS REQUIRED

30. CORE PROTEINS AT THE REPLICATION
FORK
Nature (2003) vol 421,pp431-435 Figure in ‘Big’ Alberts too

31. THE MECHANISM OF DNA
REPLICATION
•Initiation
• Proteins bind to DNA and open up
double helix
• Prepare DNA for complementary base
pairing
•Elongation
• Proteins connect the correct sequences
of nucleotides into a continuous new
strand of DNA
•Termination
• Proteins release the replication complex

32. COPYING DNA
• Step 1- DNA unwinds
and unzips
• Step 2- Once the
molecule is separated
it copies itself.
• The new strand of
DNA has bases
identical to the
original

33. • IF the DNA strand is GTACCAGATTAGC
• What would the RNA strand be?

34. PROTEIN
SYNTHESIS
TRANSCRIPTION AND TRANSLATION

35. INFORMATION FLOW: DNA
TO RNA TO PROTEIN

37. TRANSCRIPTION
•When a secretary
transcribes a
speech, the
language remains
the same.
However, the form
of the message
changes from
spoken to written

38. TRANSCRIPTION
•Transcription- RNA
is made from a
DNA template in
the nucleus.
•This type of RNA is
called messenger
RNA or mRNA

39. TRANSCRIPTION
•DNA is
protected inside
the nucleus.
•mRNA carries
the message of
DNA into the
cytoplasm to the
ribosome's

41. TRANSLATION
• To translate English
into Chinese requires
an interpreter.
• Some person must
recognize the worlds
of one language and
covert them into the
other.

42. tRNA : TRANSFER RNA
•The cells
interpreter
•tRNA translated
the three-letter
codons of
mRNA to the
amino acids that
make up
protein.

43. TRANSLATION
•Genetic
translation
converts nucleic
acid language
into amino acid
language.

44. CODON
•The flow of
information from
gene to protein
is based on
codons.
•A codon is a
three-base word
that codes for
one amino acid

45. •The flow of information from gene
to protein is based on codons.

47. INFORMATION FLOW: DNA
TO RNA TO PROTEIN