Chapter 14 Flashcards
Frederick Griffith
1920’s
S and R strains of S pneumoniae
s strain kills mice
r strain not lethal
transformation
Avery, Macleod, McCarthy
1944
Confirmed genetic material is DNA
No transformation with DNase (enzyme that breaks down DNA)
RNAse and Proteases no effect
Hershey and Chase
1956
Worked with T2 bacteriophages
viruses infect bacteria and hijack cellular processes and produce more viruses
Found DNA entered cell and incorporated into host cell DNA
proteins did not enter cell
Erwin Chargaff
1950
Chargaff’s rules (base pairs)
A=T C=G
Rosalind Franklin
1952
Discovered structure of DNA
helical structure and stacked bases
Watson and Crick
1962
Combined all knowledge
described double helix and ladder structure of bases
1 page paper
Nobel Prize 1962
Nucleotides
nitrogenous base (single or double)
Pentose sugar
Phosphate group
Purines
Double ring
Guanine
Adenine
Pyrimadines
Single ring
Thymine
Cytosine
Uracil (RNA only)
Phosphodiester bonds
Between nucleotides
sugar-phosphate backbone
“railing” of spiral staircase
Orientation of strands
Hydrogen bonds
Between complementary bases
base pairing rule
“stairs” of spiral staircase
purines -> pyrimidine
A-T (2 H bonds)
G-C (3 H bonds)
holds strands together
Van der Waals force
Temporary weak electrical force = proximity
stairs interact with another
and hold molecule together
DNA diameter
2 nm
Bases apart
0.34 nm
One full turn every
10 base pairs
3.4 nm
Histone protein
wrap DNA and keep packaged normally
High AA’s
Each complex -> 8 histones
tails regulate gene expression
double helix -> 2 nm
Nucleosome
DNA wrapped around histones
forms the “beads”
linker DNA connects beads together
Euchromatin and Heterochromatin
Euchromatin
less dense -> more open
available for transcription
more linker DNA between beads
Heterochromatin
more dense -> compacted
not available for transcription (too tightly packed)
centromeres + telomeres hold them together
Fully unwound DNA
Pro and Euk
Prokaryotes: 4.6 million nucleotides
stretched out 1mm, 1000x wider than cell width
Eukaryotes: 1.5 x 10^8 ( 1 chrome)
stretched out 4 cm
1000x wider than cell nucleus
2 meters per human cell
Interphase DNA
Chromatin w histones
sister chromatids produced after replication
Prophase DNA
Condensin II proteins (condense DNA)
10mm fibers form loops
Prometaphase DNA
Condensin I protein
smaller sub-loops
causes helical twists
Metaphase DNA
fully condensed DNA
chromatids ready to separate
Prokaryotes DNA
circular; less DNA overall
replication in two directions
one replication bubble
two replication forks (similar to mitosis)
shorter replication time <1hr
Eukaryotes DNA
linear; more DNA
Requires longer replication
multiple replication bubbles
multiple replication forks
join together (except ends) telomeres; lose DNA when replicate
full replication in hours
Helicase
breaks hydrogen bonds, unwinds parental double helix at replication forks
Single-strand binding protein
stabilize single strand DNA
until template
binds with unwound strand and prevents re-pairing
Topoisomerase
before helicase, stabilizes DNA
alleviates strain from unwinding on unbound helix in front of fork
DNA polymerase III
Uses primer to start replication
DNA polymerase I
Switches RNA -> DNA; change nucleotides
DNA ligase
ligation; strands sealed and continuous
Leading strand
5’ -> 3’
one primer needed
follows helicase
immediate/continuous
Lagging strand
3’ -> 5’
multiple primers needed
“lag” wait for helicase
jumps primer to primer
Primase
synthesize RNA primer
uses template strand
5-10 nucleotides long
“replication starts here”
DNA polymerase (III and I)
finds primer, reads T strand, and starts
only works in 5’ -> 3’
joins complementary bases
adds to 3’ end of primer
triphosphate nucleotide pulls out of cytoplasm
condensation rxn.
DNA polymerase I
targets the primers
replaces RNA -> DNA
1 per leading strand
1 per okazaki fragments
can NOT connect pieces
DNA ligase
Catalyzes “ligation”
connects okazaki fragment
seals sugar backbone
makes on continuous strand
DNA polymerase III
only works (creates) in 5’ -> 3’
within replication bubble
main replicating enzyme
Telomeres
non-coding nucleotide sequence
TAG (TTAGGG) sequence
every replication decreases DNA length
telomere shortening correlated with aging
Telomerase
found in Euk germ cells
conserves DNA by adding TTAGGGs
ensure zygote has max DNA length
cancer cells have increased telomerase
target telomerase for cancer therapy?
Proofreading
DNA polymerase
check new relative to template
replaces incorrect nucleotides
Mismatch repair
proofreading fails to find mistakes
mut proteins label mistakes
nucleases cleave and remove sequence
polymerase and ligase repair
Mut proteins
MutS/MutL/MutH
label mistakes
Nucleases
cleave and remove DNA sequence
Nucleotide excision repair
DNA is damaged (UV)
UV causes thymine dimer (adjacent thymines bind)
Nucleases cleave and remove
polymerase and ligase repair
