Chap 16 - Molecular basis of Inherita

What did Frederick Griffith do?

Proved that dead infectious bacteria + alive non infectious bacteria = alive infectious bacteria because of "transforming factor".

What did Hershey and Chase do?

They proved that Griffith's "transforming factor" was DNA, and that DNA held hereditary info

Why did scientists think proteins held hereditary info?

DNA has a sugar, phsophate, and 4 bases. Not much going on for all the diversity it causes. BUT proteins have 20 Amino acids in different orders, allowing many more combinations.

What was Hershey and Chase's experiment?

Grew 2 different types of bacteriophages. 1 Had radioactive isotope for sulfur (only in proteins), 1 only radioactivity in phosphates (in DNA). They introduced each type to bacteria, and then centrifuged the bacteria into a pellet. With radioactive sulfur, the radioactivity was in supernatant (liquid), with phosphates it was in the PELLET. This proved DNA was passed into bacteria.

What did Chargaff do?

Proved each species has its own ratio of 4 nitrogenous bases

Chargaff's Rule

equal amounts of A & T
equal amounts of C and G

What did Watson and Crick do?

Figured out DNA structure (did not do any of their own experiments, looked at info from other scientists, like Chargaff and FRanklin)

Who was Maurice Wilkins?

he had a crystalography lab that used X rays, Rosalind Franklin worked for hum.

Who was Rosalind Franklin?

She did X-Ray crystalography fo DNA to figure out the structure of DNA was a double helix with 2 nm width and bases 0.34 nm apart, with a turn at every 10 base pairs in the helix.

What did protein's crystolography xray show?

It was a single helix that did not have the same width throguhout the molecule

Who did Rosalind Franklin prove wrong?

Salt. He thoguht it was a triple helix with bases on the outside.

What were the different models for replication step?

Conservative, semi conservative, dispersive

What was the first step of replication that everyone agreed on?

The two strands seperate and the daughter DNA strands are made with each strand.

What was the conservative model?

The two daughter strands join together and the parent strand joins back.

What was the semi conservative model?

The two new strands stay together

What was the dispersive model?

Parts of the strand switch so new and old copy is on each strand

What did Stahl do?

Proved that semi conservative model was correct

How did Stahl's experiment prove the semi conservative model?

He cultured baceria with 15N isotope, then transferred it to 14 N isotope.

How is DNA replication in Prokaryotes?

DNA = circle with 1 Origin of replication that creates a replication bubble with 2 replication forks

How is DNA replication in Eukaryotes?

DNA = linear with multiple origins of replication with multiple replication forks that join.

DNA replication-to unwind DNA?

Helicase - breaks H+ bonds between Base pairs and unwinds parent DNA
Single Strand Binding Proteins- prevents pairing of parent strands
Topoisomerase - Relieves strain caused by helicase + prevents super coiling of parent strand (GNA gyrase)

DNA replication-start new DNA strand?

New DNA nucleotides dNTs are added by DNA polymerase (ON 3' end after Primase and RNA primer)

DNA replication- addition of dNT?

DNA Nucleotides are created as nucleotipde triphosphates, from which DNA polymerase removes two (pyrophosphates --> 2 inorganic phosphates = energy for ATP) and bonds the third to 3' carbon of sugar in DNA

How does leading strand expand?

3' to 5' continuous

How does the lagging strand expand?

Okazaki fragments: Primase creates RNA primer, DNA polymerase III adds dNTs to 3' end of primer and elongates until it runs into primer from previous okazaki fragment, there it gets off. DNA polymerase I then goes back to bind to primers and replace the RNA with DNA nuclerotides.. DNA ligase then connects the backbone of the fragmnets

DNA proofreading and repair

1 in 100,000 DNA polymerase can often detect errors at the time they are made. If not, there are other enzymes that detect errors after DNA polymerase. If not, then nucleases can detect irregular shapes to DNA and cut out improper bases.

What does DNA polymerase III do?

It adds DNA nucleotides to replicate strands

What does DNA polymerase I do?

It replaces RNA primers with DNA nucleotides after DNA Polymerase passes by.

What are problems with the lagging strand?

DNA Polymerase I is used to replace RNA primers, and it only attaches to 3' end. So no mistakes, other wise no starting pint for replacements.
Linear DNA: Last Okazaki fragments will have primer at the end that can be removed. Chromosomes get smaller every round of replication.

What are telomeres?

Eukaryotic chromosome ends that are made of long-non coding sequences of bases. Serves as sacrificial base sequences that can be lost with each round of replication. Added to cells during gamete formation and certain stem cell lines
Humans: TTAGGC 300,000 times