DNA
RNA
&
Proteins
James Watson & Francis
Crick and Their DNA Model
Winning the Nobel Prize
Watson & Crick on the 50th
anniversary of their discovery
Rosalind Franklin’s
Famous Photo 51 of DNA
Rosalind Franklin’s Lab
Erwin Chargaff, Jerry Donahue,
Lawrence Bragg
DNA
• Polymer of nucleotides
(phosphate group bonded to
deoxyribose bonded to a
nitrogen base)
DNA Nucleotide
A Nucleotide
4 Nitrogen Bases of DNA
• Adenine (A)
• Thymine (T)
• Guanine (G)
• Cytosine (C)
• Adenine and guanine are
purines
• Cytosine and thymine are
pyrimidines
Purines
Pyrimidines
Nucleotides Bond Together in
Long Chains
The two
chains of
nucleotides
are bonded in
the middle by
the paired
bases
Base Pairing Rule
• Adenine bonds to Thymine
• Guanine bonds to Cytosine
BASES THAT BOND ARE
CALLED COMPLEMENTARY
BASES
Bases Bond by Hydrogen
Bonds
The 2 DNA Chains are AntiParallel
DNA Replication
Before cell
division, cells
copy
(replicate)
their DNA
• An enzyme breaks the
hydrogen bonds holding the
paired bases together (unzips
the DNA)
• Complementary nucleotides
bond to the separated DNA
chains (A to T and G to C)
• DNA polymerase enzymes
bond new DNA nucleotides to
the original DNA strands
• The original strand serves as a
template for the new strand
DNA Replication
• At the end of DNA
replication, there are two
identical DNA molecules
• Each DNA molecule
contains an original strand
and a new strand (semiconservative)
Proofreading enzymes
check for mistakes during
replication (bonding 50 base
pairs per second means
mistakes will be made!)
http://www.youtube.com/watch?v=Bju4C5GxeQs&feature=r
elated
RNA
• Ribonucleic acid
• A polymer of nucleotides
• The sugar in RNA is ribose
(instead of deoxyribose, as
in DNA)
Comparison of Ribose and
Deoxyribose
• RNA nucleotides do not
have thymine, but contain
uracil instead
• RNA is one strand of
nucleotides (DNA is two
chains of nucleotides)
• So RNA is a single helix,
but DNA is a double helix
3 Types of RNA
• tRNA (transfer RNA)
• mRNA (messenger RNA)
• rRNA (ribosomal RNA)
http://www.dnatube.com/video/1017/Co
mpare-DNA-and-RNA-in-structuralbasis
tRNA
TRANSCRIPTION
(RNA Synthesis)
• A gene for a specific protein
is turned on
• DNA “unzips” and unwinds
(as in replication)
• Complementary RNA
nucleotides bond to one
strand of DNA (function of
RNA polymerase)
• Bases must be
complementary
C on DNA bonds to G on RNA
G on DNA bonds to C on RNA
T on DNA bonds to A on RNA
A on DNA bonds to U on RNA
• RNA breaks away from
the DNA template
• DNA strands reform the
hydrogen bonds
• RNA can then exit the
nucleus via pores in the
nuclear membrane
Transcription
Transcription
Transcription
http://www.youtube.com/watch?v=vJSmZ3D
sntU&feature=related
Translation – the making of
a protein
• Begins when mRNA
attaches to a ribosome
• The genetic code of
mRNA is read three bases
at a time (codons)
• Each codon specifies a
particular amino acid that
will be placed in the chain
to build the protein
molecule
• The tRNA with its specific amino
acid pairs to the codon of the
mRNA
• When a second tRNA with its
specific acid pairs to the next
codon, the attached amino acid
breaks from the first tRNA and
attaches to the amino acid of the
2nd tRNA
• The ribosome forms a peptide
bond between the amino acids
• The empty tRNA moves off and
picks up another matching amino
acid from the cytoplasm in the cell
• This sequence is repeated until the
ribosome reaches a stop codon on
the mRNA, which signs the end of
protein synthesis
Beginning of Translation
Translation
Termination of Translation
http://www.youtube.com/watch?v=NJxobgkP
EAo
The Central Dogma of
Biochemistry
The Central Dogma of
Biochemistry
• http://www.dnatube.com/video/1027/CentralDogma