Transcript DNA Basics - Haiku Learning : Login

Molecular Basis
of Inheritance
Chapter 14
•DNA Studies
• Frederick
Griffith – 1928
• Streptococcus
•2
pneumoniae
strains – pathogenic & harmless
• Killed pathogenic  mixed with
living harmless  living cells
converted to pathogenic 
offspring inherited pathogenic
•DNA Studies
• Called
•
process transformation
Substance transforming was DNA
•DNA Studies
• Hershey
& Chase – 1952
• Studied
bacteriophages (viruses that
infect bacteria)
• Virus
– mostly DNA &
protein
• Through
radioactive isotopes,
studied T2 (virus that infects
E. coli in mammalian intestine)
•DNA Studies
• Each
separately added to E. coli:
• Radioactive
sulfur for proteins
• Radioactive
phosphorus for DNA
• Culture
allowed to grow
• Bacteria
broken from virus & studied –
radioactivity in bacteria with
phosphorus
• Result
– DNA entered bacteria, not
protein
•DNA Studies
• Erwin
Chargaff –
determined
A-T and G-C
•DNA Structure
• James
Watson
&
Francis
Crick
•DNA Structure
• Through
use of Rosalind Franklin’s
X-ray diffraction photograph, W&C
determined double helix structure
•DNA Structure
• Sugar-phosphate
• Nitrogenous
backbone
bases on inside (10 per
turn of helix)
• Bond
purine to
pyrimidine
•A
has 2 H bonds with T only
•G
has 3 H bonds with C only
•DNA Replication
• DNA
untwists & unzips
• Complementary
base pairs free in
cytosol bond appropriately
• New
strands re-zip and re-twist
•DNA Replication
• Result
– Two daughter DNA molecules
• One parent strand
• One new strand
• Called the semi-conservative model
•Origins of Replication
• Where
DNA replication begins
• Has specific nucleotide sequence
• Proteins recognize this at these sites 
help separate DNA (open replication
“bubble”)
•Origins of Replication
• Can
be hundreds of bubbles
• Extending from bubble – replication
fork (where new strands are
elongating)
• Replication
in both
directions
until bubbles
fuse
•DNA Elongation
• DNA
Polymerases – enzymes aiding
elongation at a replication fork
•Strand Arrangement
• Opposite
sides of backbone run
antiparallel (upside down) to each other
•
5’ end – phosphate
• 3’
end – hydroxyl group
• Phosphates
connect
from 5’ C of one sugar
to 3’ C on next sugar
•Strand Arrangement
•
FYI…find nitrogenous
base…that is 1’C…
count clockwise
to find others
•
New nucleotides are
added ALWAYS from
5’ end of the new
DNA to 3’ end
(3’-5’ of old strand)
•Strand Arrangement
• When
DNA unzips,
the 3’-5’ strand
can fill in easily
– leading strand
• Copies
toward
replication fork
• Helped
by
DNA polymerase
•Strand Arrangement
• The
5’-3’ strand fills
in with pieces –
lagging strand
• Pieces
called
Okazaki fragments
• DNA
ligase helps
to join sugars &
phosphates together
•How Does It Start?
• When
replication starts, new chain
begins with a primer
• Section
of RNA
• Primase
joins approx 10 RNA
nucleotides together to start
replication
• Later
replaced by DNA with DNA
polymerase help
•How Does It Start?
• One
primer for
leading strand
• Each
fragment of
lagging strand
is primed &
then replaced
by DNA
•Other help
• Helicase
– enzyme untwists DNA
• Single-strand
binding proteins – keep
DNA apart during process
• Overview
of
DNA Replication
•Proofreading
•
Mismatch repair
•
Polymerase matches new nucleotide to
parent strand  will remove if incorrect
•
Each cell monitors DNA for new changes due
to cell error or envi.
•
Nucleotide Excision Repair
•
New error found  a nuclease cuts it out
 polymerase & ligase fill in proper
pieces
•Last fix
• Once
the
last RNA
primer
comes off,
there
is a gap that
needs to be
fixed
•Last Fix
• Nucleotides
can only add to the 3’ end
of a preexisting polynucleotide
• No
way to complete 5’ end
• Over
time, DNA would progressively
shorten – problem
• Solution
– telomerase
•Last Fix
• End
of DNA – telomeres
• Repetitive
expendable (non-coding)
nucleotide sequence
• Protect
• Will
major shortening of DNA
shorten somewhat over time
• Telomerase
will help lengthen
•Last Fix
• Has
RNA on it
• Serves as
template to
extend telomere
at 3’ end of the
telomere
• Telomeres
• Telomeres and
Cancer