Unit 13: DNA Structure and Replication Flashcards
What are the four main classes of macromolecules in a cell?
- Carbohydrates (sugars)
- Lipids (fats)
- Proteins
- Nucleic acids- DNA and RNA
By the 1920s, we knew that _____ controlled
heritable traits, that genes were on
__________, and ________ divided equally at cell division.
By the 1920s, we knew that genes controlled
heritable traits, that genes were on chromosomes, and chromosomes divided equally at cell division
In the 1920s, it was also known that _________ contain
_______ and ___.
In the 1920s, it was also known that chromosomes contain
protein and DNA.
What was Frederick Griffith working on in 1928?
1928 Frederick Griffith is working with the bacteria that caused pneumonia.
What are the two strains of pneumococcus (bacteria that causes pneumonia)?
- S or smooth strain
- R or rough strain
What is the S or smooth strain?
Causes pneumonia in mice (virulent).
What is the R or rough strain?
Does not cause pneumonia in mice (nonvirulent).
Which of these strains is a mutant strain?
R is a mutant strain of
Pneumococcus that does not cause disease because it lacks the ‘capsule’ that protects it from the mouse immune system.
What was the conclusion of Griffith’s experiement?
The R strain became deadly after mixing with heat-killed S strain, proving that genetic instructions from the S strain were passed to the R strain.
Continuing Griffith’s work, what did Avery, Macleod, and McCarty use to transform the genetic instructions for the S strain to the R strain?
In Avery’s experiment, they used protease and DNase to figure out what caused the R strain bacteria to transform into the S strain (the harmful one).
What was did protease do in the S and R strains in Avery’s experiment?
Protease broke down proteins, but the bacteria still transformed into the harmful strain because DNA was the real “transforming principle.” (Mouse still died).
What did DNase do in Avery’s experiment?
DNase broke down DNA, and without DNA, the transformation didn’t happen — meaning DNA was the key to making the bacteria harmful. (Mouse lived).
What bacterium were used in the Hershey-Chase experiment of 1952?
Many early experiments in molecular biology were done with phage and the bacterium Escherichia coli or E. coli
What did Hershey and Chase know before beginning their experiment?
- Nucleic acids (DNA, RNA) contains phosphorus, but not sulfur.
- Most proteins contain sulfur, but bacterial proteins don’t have phosphorus.
In the Hershey and Chase experiment, they used ___________ ____ to track whether ____ or ________ was the genetic material.
In the Hershey and Chase experiment, they used radioactive labels to track whether DNA or protein was the genetic material.
What did Hershey and Chase discover was the difference between DNA and protein when these macromolecules entered bacteria cell walls?
They found that only the radioactive DNA (labeled with ^32P, a radioactive form of phosphorus) entered the bacterial cell and was passed on to new viruses. The protein (labeled with ^35S, a radioactive form of sulfur) stayed outside in the empty protein coat and wasn’t passed on.
What was the conclusion between DNA versus protein in the Hershey and Chase experiement?
This proved that DNA, not protein, is the genetic material that carries genetic information.
What did the X-ray of Rosalind Franklin show?
Her X ray crystallography studies indicated that DNA was a repeating structure.
What did Watson and Crick publish in 1953?
They published a model for the structure of DNA (they used Franklin’s X-ray without her permission).
Watson and Crick’s model for the structure of DNA (1953) showed that two __________ strands of DNA wrap
around each other in a ______-handed ________
helix that resembles a twisted ladder.
Watson and Crick’s model for the structure of DNA (1953) showed that two polynucleotide strands of DNA wrap
around each other in a right-handed double
helix that resembles a twisted ladder
Watson and Crick’s model for the structure of DNA (1953) showed that the two strands of DNA are in an ________ polarity - ________.
Watson and Crick’s model for the structure of DNA (1953) showed that the two strands of DNA are in an opposite polarity - antiparallel.
Watson and Crick’s model for the structure of DNA (1953) showed that the the ‘______’ (or rails of the ladder) consists of a _____-_________ ‘______’ which carries no information.
Watson and Crick’s model for the structure of DNA (1953) showed that the the ‘outside’ (or rails of the ladder) consists of a sugar-phosphate ‘backbone’ which carries no information.
Watson and Crick’s model for the structure of DNA (1953) showed that the the ‘_____’ (or rungs of the ladder) consists of _______ ____ organized as flat ‘_____’.
_ pairs only with _, _ pairs only with _.
Watson and Crick’s model for the structure of DNA (1953) showed that the the ‘inside’ (or rungs of the ladder) consists of paired bases organized as flat ‘steps’.
A pairs only with T, G pairs only with C
The ___ strands are held together by weak
_________ ____ between the bases.
The two strands are held together by weak
hydrogen bonds between the bases.
What are nucleic acids?
The nucleic acids DNA and RNA are polymers of (long chains) of nucleotides.
What are the parts of a nucleotide?
- A sugar
- A phosphate group (PO4)
- A base
DNA runs from the _ to the _ carbon.
DNA runs from the 5’ to the 3’ carbon
What does each strand of DNA have that gives it a directionality (polarity)?
- The 3’ end has an exposed hydroxyl group on 3’ carbon of the deoxyribose sugar.
- The 5’ end has an exposed phosphate group on 5’ carbon.
DNA is a chain of _________ connected at the ______ and _____ backbone.
DNA is a chain of nucleotides connected at the phosphate and sugar backbone.
What is purine?
Purine is the parent compound of adenine and guanine.
What is pyrimidine?
It’s the parent compounds of Cytosine, Uracil (found in RNA), and Thymine (found in DNA).
Which nitrogenous bases have two hydrogen bonds?
Thymine and Adenine
Which nitrogenous bases have three hydrogen bonds?
Cytosine and Guanine
DNA helix has a _______ _____ (____)
and a ______ ______ (_____)
DNA helix has a major groove - wider
and a minor groove – narrower
When is genetic material replicated?
The genetic material in eukaryotes is replicated during the S phase of the mitotic cell cycle.
What are the three models for the mechanism of DNA replication?
- Semiconservative replication
- Conservative replication
- Dispersive replication
What is semiconservative replication?
Each new DNA molecule has one old (parent) strand and one new strand.
What is conservative replication?
The original DNA stays completely intact, and a whole new double-stranded copy is made from scratch.
What is dispersive replication?
The original DNA is cut up and mixed, so both new molecules are a patchwork of old and new DNA.
What model type of replication does DNA follow?
Semi-conservative replication
In what direction is DNA synthesized?
DNA is copied in one direction only — from 5’ to 3’ — because new building blocks (nucleotides) can only be added to the 3’ end
During DNA replication, the __ __ group of the growing strand attacks the incoming _____, kicks off two _______ (_________), and forms a ________ bond to add the new _______.
During DNA replication, the 3’ OH group of the growing strand attacks the incoming nucleotide, kicks off two phosphates (pyrophosphate), and forms a phosphodiester bond to add the new nucleotide.
What is the first step of DNA replication.
DNA replication starts with parent DNA molecule.
What is the second step to DNA replication?
Parental strand unwinds and separates at several points.
What is the third step to DNA replication?
Each parental strand provides a template for DNA polymerase to bind complementary bases, A with T and G with C.
What is the fourth step to DNA replication?
Sugar-phosphate backbones of daughter strands close.
