chapter 16+17

What is the main topic of Chapter 16?

The molecular basis of inheritance.

What molecule is the genetic material in most organisms?

DNA.

What are the two chemical components of chromosomes?

DNA and proteins.

Why did scientists originally suspect proteins were the genetic material?

Proteins appeared more chemically diverse and complex than DNA.

What bacterium did Frederick Griffith study?

Streptococcus pneumoniae.

What was the virulent strain in Griffith's experiment called?

The S strain.

What did the S strain look like?

Smooth colonies.

Why was the S strain virulent?

It had a protective polysaccharide capsule.

What was the nonvirulent strain in Griffith's experiment called?

The R strain.

What did the R strain look like?

Rough colonies.

Why was the R strain nonvirulent?

It lacked a protective capsule.

What happened when living S bacteria were injected into mice?

The mice died.

What happened when living R bacteria were injected into mice?

The mice lived.

What happened when heat-killed S bacteria were injected into mice?

The mice lived.

What happened when heat-killed S bacteria were mixed with living R bacteria?

The mice died.

What living bacteria were recovered from mice injected with heat-killed S and living R cells?

Living S bacteria.

What is transformation?

A change in genotype and phenotype caused by uptake of foreign DNA.

What did Griffith call the substance that changed R bacteria into S bacteria?

The transforming principle.

Who determined that DNA was the transforming factor?

Avery, MacLeod, and McCarty.

What did Avery, MacLeod, and McCarty conclude was the transforming factor?

DNA.

Which enzyme prevented bacterial transformation in Avery's experiment?

DNase.

Why did protease not prevent transformation?

Protein was not the transforming material.

Why did RNase not prevent transformation?

RNA was not the transforming material.

What is a bacteriophage?

A virus that infects bacteria.

What is another name for a bacteriophage?

Phage.

What bacteriophage did Hershey and Chase study?

T2 phage.

What are the two major components of T2 phage?

DNA and protein.

Which radioactive isotope labeled protein in the Hershey-Chase experiment?

Sulfur-35.

Why was sulfur-35 used to label protein?

Proteins contain sulfur but DNA does not.

Which radioactive isotope labeled DNA in the Hershey-Chase experiment?

Phosphorus-32.

Why was phosphorus-32 used to label DNA?

DNA contains phosphorus but proteins generally do not.

What machine did Hershey and Chase use to remove phage coats from bacteria?

A blender.

What process separated infected bacteria from phage coats?

Centrifugation.

What was found in the pellet when DNA was labeled with phosphorus-32?

Radioactive DNA.

What was found in the supernatant when protein was labeled with sulfur-35?

Radioactive protein coats.

What did Hershey and Chase conclude from their experiment?

DNA enters bacteria and directs viral reproduction.

What are Chargaff's rules?

A equals T and G equals C in double-stranded DNA.

What did Chargaff discover about DNA composition among species?

Base composition varies among species.

What are the three parts of a nucleotide?

A nitrogenous base, a sugar, and a phosphate group.

What sugar is found in DNA?

Deoxyribose.

What sugar is found in RNA?

Ribose.

What are the four nitrogenous bases in DNA?

Adenine, thymine, guanine, and cytosine.

What nitrogenous base replaces thymine in RNA?

Uracil.

Which bases are purines?

Adenine and guanine.

Which bases are pyrimidines?

Cytosine, thymine, and uracil.

How many rings do purines have?

Two rings.

How many rings do pyrimidines have?

One ring.

Which base pairs with adenine in DNA?

Thymine.

Which base pairs with adenine in RNA?

Uracil.

Which base pairs with guanine?

Cytosine.

How many hydrogen bonds form between adenine and thymine?

Two.

How many hydrogen bonds form between guanine and cytosine?

Three.

Why does a purine pair with a pyrimidine?

This pairing maintains a consistent width in the DNA double helix.

What is the shape of DNA?

A double helix.

Who developed the double-helix model of DNA?

Watson and Crick.

What technique did Rosalind Franklin use to study DNA structure?

X-ray crystallography.

What did Franklin's X-ray diffraction image reveal about DNA?

DNA is helical and made of two strands.

What role did Maurice Wilkins play in studying DNA structure?

He used X-ray crystallography to study DNA.

What is the sugar-phosphate backbone?

The outer part of DNA made of alternating sugar and phosphate groups.

Where are nitrogenous bases located in DNA?

In the interior of the double helix.

What does antiparallel mean in DNA?

The two strands run in opposite directions.

What is the 5′ end of a DNA strand?

The end with a phosphate attached to the 5′ carbon.

What is the 3′ end of a DNA strand?

The end with a hydroxyl group on the 3′ carbon.

In what direction is a new DNA strand synthesized?

5′ to 3′.

In what direction does DNA polymerase read the template strand?

3′ to 5′.

What is semiconservative replication?

Each daughter DNA molecule contains one parental strand and one new strand.

Who tested the semiconservative model of DNA replication?

Meselson and Stahl.

What isotope did Meselson and Stahl use to make heavy DNA?

Nitrogen-15.

What isotope did Meselson and Stahl use to make light DNA?

Nitrogen-14.

What did Meselson and Stahl observe after one generation in nitrogen-14 medium?

One intermediate-density DNA band.

What did Meselson and Stahl observe after two generations in nitrogen-14 medium?

One light band and one intermediate band.

What model of replication did Meselson and Stahl support?

The semiconservative model.

What is an origin of replication?

A site where DNA replication begins.

What is a replication bubble?

A locally opened region of DNA where replication occurs.

What is a replication fork?

A Y-shaped region where new DNA strands are elongating.

How many origins of replication does most bacterial DNA have?

One.

Why do eukaryotic chromosomes have many origins of replication?

They contain much more DNA and must replicate quickly.

What shape is most bacterial DNA?

Circular.

What shape is eukaryotic chromosomal DNA?

Linear.

What enzyme relieves overwinding ahead of a replication fork?

Topoisomerase.

What enzyme separates the two DNA strands at a replication fork?

Helicase.

What does helicase break during DNA replication?

Hydrogen bonds between base pairs.

What proteins keep separated DNA strands from rejoining?

Single-strand binding proteins.

What enzyme makes an RNA primer?

Primase.

What is an RNA primer?

A short RNA segment that provides a starting point for DNA synthesis.

Why is an RNA primer necessary?

DNA polymerase cannot begin a new strand by itself.

What enzyme adds most DNA nucleotides during replication in bacteria?

DNA polymerase III.

What enzyme removes RNA primers and replaces them with DNA in bacteria?

DNA polymerase I.

What enzyme joins DNA fragments together?

DNA ligase.

What is the leading strand?

The new strand synthesized continuously toward the replication fork.

What is the lagging strand?

The new strand synthesized discontinuously away from the replication fork.

What are Okazaki fragments?

Short DNA fragments made on the lagging strand.

Why is the lagging strand made in fragments?

DNA polymerase can synthesize only in the 5′ to 3′ direction.

What joins Okazaki fragments?

DNA ligase.

What process allows DNA polymerase to correct incorrectly paired nucleotides while replicating?

Proofreading.

What is mismatch repair?

Repair enzymes correct base-pairing errors missed during replication.

What is nucleotide excision repair?

A nuclease removes damaged DNA, and DNA polymerase and ligase replace it.

What is a thymine dimer?

A covalent bond between adjacent thymine bases caused by UV damage.

What can cause thymine dimers?

Ultraviolet radiation.

What are telomeres?

Repetitive DNA sequences at the ends of linear chromosomes.