6. Did you know?
Each cell has about 2 m 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.
7. The Structure of DNA
• DNA = deoxyribonucleic acid
• DNA is a polymer built up from monomers
• Monomers are called nucleotides
14. • In DNA G hydrogen bonds with C
• T hydrogen bonds with A
Pairing of Bases
C G G T A C A T G C A T
A
G C C A T G T A C G T A T
15. The rules of base pairing are:
A with T: the purine adenine (A) always pairs
with the pyrimidine thymine (T)
C with G: the pyrimidine cytosine (C) always
pairs with the purine guanine (G)
Base Pairing
16. (Chargaff's rule)
The amount of adenine (A) in the DNA
of an organism, the amount of
thymine (T) is the same.
(A = T)
The amount of guanine (G), the amount
of cytosine (C) is the same.
(G = C)
20. H-bonding
• Hydrogen bonding (H-bond) is a
non-covalent type of bonding between
molecules or within them. This type of
bonding is much weaker and much
longer than the covalent bond and
ionic bonds, but it is stronger than a
van der waals interaction.
21. The H-bond donor is the molecule that has a hydrogen
atom bonded to a highly electronegative, small atom
with available valence (N, F, and O follow the above
description the best because they are very
electronegative, making H, which is covalently
attached to them, very positive)
The H-O, H-N, and H-F bonds are extremely polar;.
The partially positive hydrogen in one molecule
attracts to partially negative lone pair of the
electronegative atom on the other molecule and H-
bond forms as a result of such an interaction.
23. This is consistent with there not being
enough space (20 Å) for two purines
to fit within the helix and too much
space for two pyrimidines to get close
enough to each other to form
hydrogen bonds between them.
25. But why not A with C and G with T?
only with A & T and with C & G are
there opportunities to establish
Hydrogen bonds (shown as dotted
lines) between them (two between A &
T; three between C & G). These
relationships are often called the rules
of Watson-Crick base pairing, named
after the two scientists who discovered
their structural basis.
26.
27. PCR
Regions of a genome that need to
separate frequently for example, the
promoter regions for often-transcribed
genes are comparatively GC-poor. GC
content and melting temperature must
also be taken into account when
designing for PCR reactions
28. Why DNA Contains Thymine
Instead of Uracil
The presence of thymine instead of
uracil in DNA prevents potentially
lethal mutations. Cytosine can
tautomerize to form an imine, which
can be hydrolyzed to uracil. The
overall reaction is called a
deamination since it removes an
29.
30. Fortunately, a U in DNA is recognized as a
“mistake” by cell enzymes before an incorrect
base can be inserted into the daughter strand.
These enzymes cut out the U and replace it with
a C. If U’s were normally
found in DNA, the enzymes could not distinguish
between a normal U and a U formed by
deamination of cytosine. Having T’s in place of
U’s in DNA allows the U’s that are found in DNA
to be recognized as mistakes.
31. ATP : The Carrier of Chemical
Energy
All cells require energy to
ensure their survival and
reproduction. They get the
energy they need by converting
nutrients into a chemically
useful form of energy.
32. Classes of Nucleic Acids
DNA - one type, one purpose
RNA - 3 types
ribosomal RNA - the basis of
structure and function of ribosomes
rRNA
messenger RNA - message mRNA
transfer RNA - carries tRNA
33. Transfer RNAs (tRNAs)
tRNAs are RNA molecules that
provide the means of translating
the genetic code. One end of the
tRNA contains a three
nucleotide sequence called the
anticodon loop that is
complementary to the codon of
themRNA.
34. Cancer
• The division of normal cells is precisely
controlled. New cells are only formed for growth
or to replace dead ones.
• Cancerous cells divide repeatedly out of control
even though they are not needed, they crowd
out other normal cells and function abnormally.
They can also destroy the correct functioning of
major organs.
35. What causes cancer?
• Cancer arises from the mutation of a normal
gene.
• Mutated genes that cause cancer are called
oncogenes.
• It is thought that several mutations need to
occur to give rise to cancer
• Cells that are old or not functioning properly
normally self destruct and are replaced by
new cells.
• However, cancerous cells do not self destruct
and continue to divide rapidly producing
millions of new cancerous cells.
36. • A factor which brings about a mutation is
called a mutagen.
• A mutagen is mutagenic.
• Any agent that causes cancer is called a
carcinogen and is described as
carcinogenic.
• So some mutagens are carcinogenic.
37. Gout
• Elevated uric acid levels in
the blood
• Can be caused by a defect
in an enzyme of purine
metabolism or by reduced
secretion of uric acid into
the urinary tract.
tophus
