ap biology: ch. 16 the molecular basis of inheritance
TRANSCRIPT
![Page 1: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/1.jpg)
AP Biology: Ch. 16The MOLECULAR BASIS OF
INHERITANCE
![Page 2: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/2.jpg)
DNA can transform bacteria Frederick Griffith performed experiments
showing evidence that genetic material was a specific molecule (1928).
Showed that bacteria had been transformed; their phenotype changed due to the assimilation of external genetic material
![Page 3: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/3.jpg)
![Page 4: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/4.jpg)
Viral DNA can program cells Alfred Hershey and Martha Chase
conducted studies showing that DNA was the genetic material of a bacteriophage called T2. (1952)
They concluded that viral proteins stay outside the host cell, and that viral DNA is injected into the host cell.
![Page 5: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/5.jpg)
![Page 6: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/6.jpg)
![Page 7: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/7.jpg)
![Page 8: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/8.jpg)
Chargaff’s Rules In 1947, Erwin Chargaff analyzed the DNA
composition of different organisms using paper chromatography to separate nitrogenous bases.
He discovered that DNA composition is species-specific; amounts and ratios of nitrogenous bases vary among species
![Page 9: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/9.jpg)
Chargaff, cont. In a DNA sample, the amount of adenine
(A) = the amount of thymine (T). Guanine (G) = Cytosine (C)
Watson and Cricks’ structural model for DNA explained these rules.
![Page 10: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/10.jpg)
Base-pairing rules:
A—T
G—C
![Page 11: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/11.jpg)
Rosalind Franklin at King’s College in London produced an X-ray photo of DNA (1950s)
![Page 12: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/12.jpg)
![Page 13: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/13.jpg)
Discovering the Double Helix Watson and Crick studied Franklin’s work
and suggested that: DNA is a double helix with uniform width (2
nm) Purine and pyrimidine bases are
stacked .34 nm apart. There are 10 layers of nitrogenous base
pairs in each turn of the helix.
![Page 14: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/14.jpg)
To be consistent with a 2 nm width, a purine on one strand must pair by hydrogen bonding with a pyrimidine on the other
![Page 15: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/15.jpg)
![Page 16: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/16.jpg)
DNA Replication and Repair Watson and Crick proposed that genes on
the original DNA strand are copied by a specific pairing of complementary bases.
The complementary strand can then be used as a template to produce a copy of the original strand.
This is a semiconservative model of DNA replication.
![Page 17: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/17.jpg)
![Page 18: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/18.jpg)
![Page 19: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/19.jpg)
DNA replication, cont. Enzymes and other proteins carry out DNA
replication. The process is complex, extremely rapid,
and accurate. DNA replication is similar in prokaryotes
and eukaryotes.
![Page 20: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/20.jpg)
Origins of Replication DNA replication begins at special sites called
origins of replication that have a specific sequence of nucleotides.
Specific proteins required to initiate replication bind to each origin, causing the double helix to open.
Replication forks spread in both directions away from the origin creating a replication bubble.
![Page 21: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/21.jpg)
*Bacterial or viral DNA may have only one replication
origin.
![Page 22: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/22.jpg)
Elongating a new strand Enzymes called DNA polymerases catalyze
synthesis of a new DNA strand. According to base-pairing rules, new nucleotides
align along the template of the old DNA strand. DNA polymerase links the nucleotides to the
growing strand in the 5’3’ direction. Hydrolysis of nucleoside phosphates provides the
energy necessary to synthesize the new DNA strands.
![Page 23: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/23.jpg)
![Page 24: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/24.jpg)
Antiparallel DNA strands The sugar-phosphate backbones of the two
complementary DNA strands run in opposite directions.
DNA polymerase can only elongate strands in the 5’ 3’ direction.
The problem of antiparallel DNA strands is solved by the continuous synthesis of one strand (leading strand) and discontinuous synthesis of the complementary strand (lagging strand).
![Page 25: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/25.jpg)
![Page 26: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/26.jpg)
Leading vs. Lagging strands The leading DNA strand is synthesized as a
single polymer in the 5’ to 3’ direction towards the replication fork.
The lagging strand is synthesized against the overall direction of replication. It is produced as a series of short segments called Okazaki fragments.
The many fragments are connected by DNA ligase, which catalzes the formation of a covalent bond between the 3’ end of each new fragment to the 5’end of the growing chain.
![Page 27: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/27.jpg)
![Page 28: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/28.jpg)
Priming DNA synthesis Before new DNA strands can form, there must be
small preexisting primers to start the addition of new nucleotides.
Primers are short RNA segments (linked by primase enzymes) that are complementary to DNA segments. Needed to begin DNA replication.
Only one primer is needed for replication of the leading strand, but many are required to replicate the lagging strand. An RNA primer must initiate the synthesis of each Okazaki fragment.
![Page 29: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/29.jpg)
![Page 30: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/30.jpg)
Other proteins assisting in DNA replication
Helicases are enzymes which catalyze unwinding of the parental double helix to provide the template.
Single-strand binding proteins are proteins which keep the separated strands apart and stabilize the unwound DNA until a complementary strand can be synthesized.
![Page 31: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/31.jpg)
![Page 32: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/32.jpg)
![Page 33: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/33.jpg)
DNA Proofreading and Repair DNA replication is highly accurate due to
base-pairing specificity and proofreading/repair mechanisms.
DNA can be repaired as it is being synthesized (mismatch repair) or after the accidental changes in existing DNA (excision repair)
![Page 34: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/34.jpg)
DNA repair, cont. Mismatch repair- DNA polymerase proofreads
each newly added nucleotide against the template. Incorrectly paired nucleotides are removed and replaced before synthesis continues.
Excision repair- Segments damaged by physical or chemical agents are removed by a repair enzyme, then the gap is filled in by base-pairing nucleotides with the undamaged strand. DNA polymerase and DNA ligase catalyze the filling in process.
![Page 35: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/35.jpg)
![Page 36: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/36.jpg)
Telomeres DNA polymerase can only add nucleotides to the
3’ end of a preexisting DNA chain. Repeated replication produces shortened DNA
molecules, potentially deleting some gene sequences.
Telomeres are special nucleotide sequences (not containing genes) at the end of eukaryotic chromosome molecules that prevent this.
Telomerase is an enzyme that catalyzes the lengthening of telomeres
![Page 37: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/37.jpg)
![Page 38: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/38.jpg)
Telomeres (The yellow dots!)
![Page 39: AP Biology: Ch. 16 The MOLECULAR BASIS OF INHERITANCE](https://reader035.vdocuments.site/reader035/viewer/2022081501/56649e7d5503460f94b80332/html5/thumbnails/39.jpg)