Biology Chapter 16

Who performed X-Ray Crystallography of DNA in 1950?

Rosalind Franklin.

When did Rosalind Franklin perform X-Ray Crystallography of DNA.

1950.

What kind of pattern did Rosalind Franklin’s work reveal?

One that was regular and repetitive.

What was Edwin Chargaff doing while Rosalind Franklin was performing X-Ray Crystallography?

He was analyzing DNA samples from different species.

What rules hold true for all species?

1. The amount of adenine equals the amount of thymine.
   A=T

2. The amount of cytosine equals the amount of guanine.
   C=G

“Purine” is a smaller word, therefore…

It has a bigger structure.

“Pyrimidines” is a bigger word, therefore…

It has a smaller structure.

What kind of structure do Purines have?

Double ring structure.

What kind of structure do Pyrimidines have?

Single ring structure.

What are Purines made of?

Adenine and Guanine.

What are Pyrimidines made of?

Cytosine, Uracil, and Thymine.

What is Nucleotide Pairing?

It refers to the specific and complementary base pairing between the nitrogenous bases of nucleotides in DNA and RNA.

How many hydrogen bonds do Adenine and Thymine have?

They have two hydrogen bonds.

How many hydrogen bonds do Cytosine and Guanine have?

They have three hydrogen bonds.

How might hydrogen bonds aid in DNA replication?

They will allow for the DNA stands to be easily separated during the replication process.

Who created the first 3D model of a double helix DNA strand?

Watson and Crick.

How did Watson and Crick create the first 3D double helix model of DNA?

They combined the findings of Franklin and Chargaff.

What are the two key features of DNA structure?

1. DNA is a double stranded helix.

2. DNA strands are antiparallel.

What are the two parts of the double stranded helix of DNA?

The backbone and center.

What is the backbone made of?

Sugar-phosphate.

What is the Center made of?

Nucleotides pairing.

How are DNA strands antiparallel?

One strand runs 5’ to 3’, the other strand runs in the opposite, upside-down direction 3’ to 5’.

What is at the end of a 5’ strand?

Free phosphate group.

What is at the end of a 3’ strand?

Free hydroxyl group.

What is DNA the primary source of?

Heritable information.

How is genetic information stored and passed from one generation to the next?

Through DNA.

When is genetic information not passed down through DNA?

With specific viruses, DNA is not used but RNA is.

How is heritable information passed down in viruses?

Through RNA.

Where is the DNA found in a Eukaryotic Cell?

In the nucleus.

Where is the DNA found in Prokaryotic Cells?

In the nucleoid region.

What shape are the chromosomes in Eukaryotic Cells?

Linear chromosomes.

What shape are the chromosomes in Prokaryotic Cells?

Circular chromosomes.

Where are Plasmids found?

They are found primarily in Prokaryotes but also a few Eukaryotes.

What are Plasmids?

They are small, circular DNA molecules that are separate from the chromosomes.

How do Plasmids replicate?

They replicate independently from the chromosomal DNA.

What do Plasmids contain?

They contain genes that may be useful to the prokaryote when it is in a particular environment, but may not be required for survival.

Where can Plasmids be manipulated?

In laboratories.

How is Recombinant Plasmid DNA created?

Plasmids are removed from bacteria, then a gene of interest is inserted into them.

What will happen when the recombinant plasmid is inserted back into the bacteria?

These gene that was inserted is expressed.

What can bacteria do with genes found on plasmids?

It can exchange them with neighboring bacteria.

What happens when DNA is exchanged between bacteria?

The bacteria will be able to express the genes that they acquired.

What helps with the survival of prokaryotes?

When DNA is exchanged between bacteria.

What are the nucleobases for RNA?

Cytosine, Guanine, Adenine, and Uracil.

What are the nucleobases for DNA?

Cytosine, Guanine, Adenine, and Thymine.

What is the full name for RNA?

Ribonucleic Acid.

What is the full name for DNA?

Deoxyribonucleic Acid.

How many strands does RNA have and what values are the same?

It is single stranded, Adenine = Uracil , Cytosine = Guanine.

How many strands does DNA have and what values are the same?

It is double stranded, Adenine = Thymine , Cytosine = Guanine.

What was Chargaff’s rule?

In any species, the amount of Adenine is equal to the Thymine and the amount of Cytosine is equal to the Guanine in the DNA.

Which Nucleotides are purines?

Adenine and Guanine.

What kind of bond holds together nucleotides?

Hydrogen Bonds.

In what phase of the cell cycle does DNA replicate?

The S phase.

How does DNA replicate?

During DNA replication, the double helix unwinds, its strands separate, and new complementary nucleotides are added, creating two identical DNA molecules.

What are the 3 alternative models for DNA replication?

Conservative, Semi Conservative, and Dispersive.

What is the Conservative Model of DNA replication?

When the parental strands direct synthesis of an entirely new double stranded molecule.

What happens to the Parental Strands in the Conservative Model of DNA replication?

They are fully conserved and they are not used up to make the new ones.

What is the Semi Conservative Model of DNA replication?

This is where the two parental strands each make a copy of itself.

What happens to the Parental Strands in the Semi Conservative Model of DNA replication?

After one round of replication, the two daughter molecules each have one of the parental strands and 1 new strand.

What is the Dispersive Model of DNA replication?

This is where the material in the two parental strands is dispersed randomly between the two daughter molecules.

What happens to the Parental Strands in the Dispersive Model of DNA replication?

After one round of replication, the daughter molecules contain a random mix of parental and new DNA.

Who performed an experiment using bacteria in 1954?

Meselson and Stahl.

What was the first step of the process that Meselson and Stahl used in their experiment?

Bacteria was cultured with a heavy isotope ¹⁵N.

What was the second step of the process that Meselson and Stahl used in their experiment?

Bacteria was transferred to a medium with ¹⁴N, a light isotope

What was the third step of the process that Meselson and Stahl used in their experiment?

DNA was centrifuged and analyzed after each replication.

Which model was correct in Meselson and Stahl’s experiment?

After analyzing samples of DNA after each generation, they found that it was the Semi Conservative model.

Where does DNA replication begin?

At sites called origins of replication.

How is a Replication Fork formed?

Various proteins attach to the origin of replication and open the DNA.

What unwinds the DNA strands at each replication fork?

Helicase.

How is DNA kept from re-bonding with itself?

Proteins called single strand binding proteins (SSBPs) bind to the DNA to keep it open.

What is Topoisomerase?

It helps prevent strain ahead of the replication fork by relaxing supercoiling.

How does the enzyme “Primase” initiate replication?

By adding short segments of RNA called “primers” to the parental DNA strand.

Where can the enzymes that synthesize DNA attach new DNA nucleotides to?

They can only attach them to an existing strand of nucleotides.

What do primers serve as?

They serve as the foundation for DNA synthesis.

What does DNA polymerase III do in Antiparallel Elongation?

It attaches to each primer on the parental strand and moves in the 3’ to 5’ direction.

What happens as the DNA Polymerase III moves?

It adds nucleotides to the new strand in the 5’ to 3’ direction.

What is the DNAP III that follows helicase known as and how many primers does it require?

It is known as the Leading Strand and it only requires ONE primer.

What is the DNAP III that moves away from helicase known as and how many primers does it require?

It is known as the Lagging Strand and it requires many primers.

How does DNAP III move in the Leading Strand?

3’ to 5’ following helicase.

How does DNAP III move in the Lagging Strand?

3’ to 5’ away from helicase.

How is the Leading Strand synthesized?

In one continuous segment.

How is the Lagging Strand synthesized?

It is synthesized in chunks.

What are Okazaki Fragments?

Segments of the lagging strand.

What happens after DNAP III forms an okazaki fragment?

DNAP I replaces RNA nucleotides with DNA nucleotides.

What does DNA ligase do?

Joins the okazaki fragments forming a continuous DNA strand.

Why is there no way to finish replication on the 5’ end of a lagging strand?

Because DNAP III can only add nucleotides to a 3’ end.

Since DNAP III can only add nucleotides to a 3’ end, what happens over many replications?

The DNA would become shorter and shorter.

How are the genes on DNA protected from becoming shorter and shorter?

Telomeres form a cap at the end of DNA to help postpone erosion.

What is Telomeres?

Repeating units of short nucleotide sequences that do not code for genes.

What does the enzyme telomerase do?

It adds telomeres to DNA.

What proofreads the bases that are added to the new DNA strand?

DNA Polymerase while it is adding nucleotides.

When will Mismatch Repair take place?

When errors still occur.

What do enzymes do in Mismatch Repair?

They remove and replace the incorrectly paired nucleotide.

What can Nuclease do if segments of DNA are damaged?

It can remove segments of nucleotides and DNA polymerase and ligase can replace the segments.