Chapter 14 Flashcards by Allison Garrett

Frederick Griffith

1920’s
S and R strains of S pneumoniae
s strain kills mice
r strain not lethal
transformation

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Avery, Macleod, McCarthy

1944
Confirmed genetic material is DNA
No transformation with DNase (enzyme that breaks down DNA)
RNAse and Proteases no effect

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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

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Erwin Chargaff

1950
Chargaff’s rules (base pairs)
A=T C=G

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Rosalind Franklin

1952
Discovered structure of DNA
helical structure and stacked bases

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Watson and Crick

1962
Combined all knowledge
described double helix and ladder structure of bases
1 page paper
Nobel Prize 1962

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Nucleotides

nitrogenous base (single or double)
Pentose sugar
Phosphate group

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Purines

Double ring
Guanine
Adenine

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Pyrimadines

Single ring
Thymine
Cytosine
Uracil (RNA only)

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Phosphodiester bonds

Between nucleotides
sugar-phosphate backbone
“railing” of spiral staircase
Orientation of strands

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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

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Van der Waals force

Temporary weak electrical force = proximity
stairs interact with another
and hold molecule together

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DNA diameter

2 nm

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Bases apart

0.34 nm

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One full turn every

10 base pairs
3.4 nm

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Histone protein

wrap DNA and keep packaged normally
High AA’s
Each complex -> 8 histones
tails regulate gene expression
double helix -> 2 nm

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Nucleosome

DNA wrapped around histones
forms the “beads”
linker DNA connects beads together
Euchromatin and Heterochromatin

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Euchromatin

less dense -> more open
available for transcription
more linker DNA between beads

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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