Download Ch 16 DNA structure and replication powerpoint

Chapter 16
The molecular basis of
inheritance
DNA
T
Get it?
I. Genetic material
A. RNA
1. first genetic material in young RNA world
B. DNA
1. eukaryotes: multiple linear double stranded in
nucleus
2. organelle: mitochondria and chloroplast
similar to prokaryotic
II. DNA is the genetic material
A. Proteins?
1. heterogenous, diverse
2. specific in function
B. Search for genetic material
Fred Griffith- used Streptococcus pneumoniae,
nonpathogenic R-strain, pathogenic S- strain
-pathogenic S strain- kills mice
-nonpathogenic R- no effect
-heated treated S- no effect
-mixing R and heat treated S still kills mice
1. Griffith realized R bacteria became transformed
by S bacteria.
2. The use of heat to inactivate cells suggested
that the agent was not protein.
3. This phenomenon is now called transformation
- a change in phenotype by taking genetic
material from the environment.
C. Alfred Hershey and Martha Chase
-used viruses (bacteriophages) to infect
bacteria
C. Alfred Hershey and Martha Chase -used
viruses (bacteriophages) to infect bacteria
1. labeled viruses with sulfur isotope which
attaches to proteins, viruses infect bacteria,
blend to shake off viruses, put in centrifuge to
separate virus and bacteria, viruses still have
radioactive sulfur
2. labeled viruses with phosphorus isotope
(DNA), viruses infect bacteria, blend to shake
off viruses, put in centrifuge to separate virus
and bacteria, bacteria now have radioactive
phosphorus and descendents with radioactive
phosphorus
Erwin Chargaff1. showed that in different species, DNA
contained different amounts of the four
nitrogen bases, suggesting that its
composition was diverse
2. realized that A = T and C = G,
although he could not explain this
observation
D. Avery, McCarty, and MacLeod
1. isolated various chemicals from bacteria
and used them to try transform bacteria
2. only DNA worked
III. Structure of DNA
A. Nucleotides
1. 5 carbon sugar: deoxyribose
2. phosphate group
3. nitrogenous base (ATCG)
Nitrogenous base
Nitrogenous base
B. Nitrogen bases found in DNA
1. purines- double ring
a. adenine (A)
b. guanine (G)
2. pyrimidine- single ring
a. thymine (T)
b. cytosine (C)
Purines
Pyrimidines
IV. Watson and Crick
A. Used X-ray crystallography evidence from
Williams and Franklin
1. learned helical shape and width → two
strands
2. Franklin knew sugar phosphate backbone
which places hydrophobic bases in the
middle
3. trial and error to see which bases fit the
width → one purine and one pyrimidine
4. hydrogen bonds placed A-T and C-G
Watson and Crick
Probably 2 of the most important guys ever
in science!
(equal with Darwin in revolutionizing how
humans should think of themselves in
relationship to other living things)
Are they still alive?
• TED
Talks
• Team
work
• Alpha
helix
Purines
Pyrimidines
B. Chargaff's rule- A-T and C-G
1. Explained Chargaff's original findings or
equal amounts of AT and CG
2. still a allowed random sequence of bases
→ diversity of function
3. allows for copying
V. Structure of DNA and bonding
Covalent bond
C. Structure of DNA and bonding
1. double helix with a sugar phosphate
backbone and nitrog. bases connecting the
two strands
2. sugars bonded covalently to phosphate
3. bases attracted using hydrogen bonds
(weak- easy to unzip)
V. Semiconservative replication and the
Meselson-Stahl experiment
A. Semiconservative- parent double helix
contains two strands which serve as
templates for new complementary strands
B. Meselson-Stahl experiment
1. grew bacteria growing for several generations
on a heavy isotope of N (15N) were allowed to
grow for one generation on a light isotope of N
(14N).
2. the new cells had DNA of one weight,
indicating that it was constructed from half heavy
(old) and half light (new) N.
3. after a second generation (i.e., another
replication) the cells had DNA of two distinct
weights. Half was all light and half was a mixture of
light and heavy. This showed that replication is
semi-conservative.
VI. DNA replication
• http://207.207.4.198/pub/flash/24/menu.sw
f
• http://www.wiley.com/college/pratt/047139
3878/student/animations/dna_replication/i
ndex.html
• http://www.stolaf.edu/people/giannini/flash
animat/molgenetics/dna-rna2.swf
A. Origin of Replication
1. A specific sequence of nucleotides marks
the origin or starting point, replication
bubble.
2. Humans have hundreds of bubblesreplicate in both directions
3. Separated strands are exposed =
replication fork.
4. Enzyme helicase separates the strands.
5. single stranded binding protein stabilizes
single stranded DNA to allow nucleotides to
be added
6. topoisomerase (gyrase)- corrects
overwinding created by helicase
B. DNA strands are antiparallel, continuous synthesis
of both DNA strands is not possible
1. chains have direction - one end (5') has a free
phosphate, the other (3') a free hydroxyl (-OH)
2. double stranded molecule, the two strands are
opposite, one is 3' to 5' and the other is 5' to 3'
antiparallel.
3. New nucleotides can only be added to the 3' end
4. Continuous synthesis of both strands is not
possible
5. DNA synthesis is continuous on one strand but
discontinuous along the other
C. leading strand and the lagging strand
1. leading strand- continuous synthesis of
DNA from 5' → 3' toward replication fork
2. lagging strand- discontinuous synthesis of
DNA away from replication fork
a. forms short Okazaki fragment
eventually joined by ligase
b. made in the 5' to 3' direction using RNA
primer
D. Elongating the new strand
1. RNA primase adds RNA nucleotides to the
parent strand to provide an open 3' end
2. nucleoside triphosphates are added to
separated strands using DNA polymerase
3. elongation occurs in opposite directions on the
leading and lagging strand (Okazaki
fragments)
4. DNA polymerase replaces RNA primers
5. ligase joins Okazaki fragments
E. Energy from ATP drives the endergonic
synthesis of DNA
1. nucleotide triphosphates are added to
separated strands using DNA polymerase
2. triphosphates are reactive (3P)- and lose
a diphosphate when added to parent strand
3. hydrolysis of diphosphate is exergonic
which drives the reaction
• http://www.hhmi.org/biointeractive/media/
DNAi_replication_vo2-lg.mov
• http://highered.mcgraw-hill.com/olcweb/cgi
/pluginpop.cgi?it=swf::535::535::/sites/dl/fr
ee/0072437316/120076/micro04.swf::DNA
%20Replication%20Fork
VII. Mutations in the DNA.
A. Errors in DNA replication or DNA repair
mechanisms, and external factors, including
radiation and reactive chemicals, can cause
random changes
B. The environmental (various selection
pressures) determine whether or not a mutation is
detrimental, beneficial or neutral.
C. Mutations are the primary source of genetic
variation.
VIII. Role of DNA polymerase, ligase, and repair
enzymes in DNA proofreading and repair
A. Mismatch repair
1. DNA polymerases check if correct base
has been added 1 in 10,000
2. DNA polymerase removes incorrect
base and special enzymes replace it with
correct base (1 in 10 billion)
B. Nucleotide excision repair-sometimes
reactive chemicals, radioactive emissions,
X-rays, UV light changes base sequences
1. nucleases cut damaged base sequence
2. DNA polymerase adds new bases
3. ligase reconnects new and old sequence
(EX. removing adjacent thymines which have
covalently bonded and buckled the DNA
inhibiting DNA replication)
IX. Replicating ends of DNA molecules
A. Ends of molecules get shorter as RNA
primer cannot be replaced as no free 3' end is
available
B. Not a problem with circular DNA of
prokaryotes
C. Would be a problem in eukaryotes except that
chromosomes contain repeated sequences of
TTAGGG to prevent gene erosion = telomeres
1. erosion of telomeres is connected to
aging
D. Gametes would ultimately lose genes
however telomerase relengthens DNA by
providing an RNA primer to extend the
telomeres
E. Telomeres may help prevent cancer by
limiting number of cell divisions
F. Cancer cells have shown unusual telomerase
activity (remember, only gametes use
telomerase) extending cell life, allow for more
divisions which lead to more errors in DNA
causing cancer.
The End!