Biology Chapter 16 Flashcards

Questions and Answers

What are the two chemical components of chromosomes?

DNA and protein

Why did researchers originally think that protein was the genetic material?

Proteins had been discovered as macromolecules and were known to have great variety and specificity. Little was known about nucleic acids.

Distinguish between virulent and nonvirulent strains of Streptococcus pneumoniae studied by Frederick Griffith.

The virulent strain caused disease, and the nonvirulent was harmless.

What does transformation mean in a genetic context?

A change in genotype and phenotype due to the assimilation of external DNA. Signup and view all the answers

What did Oswald Avery determine to be the transforming factor?

DNA Signup and view all the answers

Explain Oswald Avery's experiment.

He experimented with RNA, DNA, and protein. One was inactivated in each sample and injected into live bacteria. Only those with active DNA were transformed. Signup and view all the answers

How does a bacteriophage destroy a bacterial cell?

It attaches to the outside of the cell and injects its own DNA, which results in transforming the infected cell. Signup and view all the answers

How did Hershey and Chase label viral DNA and viral protein so that they could be distinguished?

They designed their experiment to test if DNA or protein was inherited. Radioactive sulfur was used in proteins and radioactive phosphorus was used in DNA. Signup and view all the answers

What are Chargaff's rules, and how did he arrive at them?

Adenine only pairs with thymine, and guanine only pairs with cytosine. Signup and view all the answers

List the three components of a nucleotide.

A nitrogenous base, deoxyribose, phosphate group. Signup and view all the answers

Who built the first model of DNA and shared the 1962 Nobel Prize for the discovery?

James Watson and Francis Crick. Signup and view all the answers

What was the role of Rosalind Franklin in the discovery of the double helix?

She first x-rayed DNA, discovered the x-shaped form that revealed the double helix. Signup and view all the answers

Structurally, what is the difference between purines and pyrimidines?

Purines have a double sugar, pyrimidines have a single sugar. Signup and view all the answers

What is considered the backbone of DNA and the rungs?

The backbone is the sugar and phosphate, nitrogenous bases are the rungs. Signup and view all the answers

What do we mean when we say the two strands of DNA are antiparallel?

The end of one strand matches with the beginning of the other, seen by the 5' end lining up with the other's 3' end. Signup and view all the answers

What is the semiconservative model of replication?

During DNA replication, the strand splits and each side is translated, creating 2 new strands half old DNA and half new DNA. Signup and view all the answers

Who performed the experiments that elucidated the correct mechanism of DNA replication?

Matthew Meselson and Franklin Stahl in the late 1950s. Signup and view all the answers

How did Meselson and Stahl create heavy DNA for their experiments?

They used isotopes of nitrogen, 15N and 14N. The heavier isotope caused differences when centrifuged. Signup and view all the answers

Define the origins of replication.

The sequence where replication begins in S phase. Signup and view all the answers

Distinguish between the leading strand and lagging strand during DNA replication.

3' end of the original strand is leading, 5' of the original strand is lagging. Signup and view all the answers

What is the direction of synthesis of the new strand?

Nucleotides can only be added to the 3' end of the new strand DNA. Signup and view all the answers

What are Okazaki fragments and how are they welded together?

They are segments added to the lagging strand of DNA synthesis. They are welded together with DNA ligase. Signup and view all the answers

What does helicase do?

It untwists and separates the strand of DNA. Signup and view all the answers

What do single-strand binding proteins do?

They hold the DNA strands apart. Signup and view all the answers

What does primase do?

It synthesizes the RNA primer. Signup and view all the answers

What does DNA polymerase do?

It adds DNA nucleotides to the new strand of DNA. Signup and view all the answers

What is the purpose of topoisomerase?

To relieve strain caused by unwinding of DNA. Signup and view all the answers

What does DNA ligase do?

Joins DNA fragments together. Signup and view all the answers

What does DNA polymerase I do?

Removes RNA primer and replaces it with DNA. Signup and view all the answers

What is the role of DNA polymerase in DNA proofreading and repair?

To proofread each nucleotide before it is added, removes incorrect pairing. Signup and view all the answers

What is the role of nuclease in DNA proofreading and repair?

It is a DNA cutting enzyme that removes damaged or mutated segments of DNA. Signup and view all the answers

What is the role of ligase in DNA proofreading and repair?

It fills the gaps that nuclease leaves when DNA is excised. Signup and view all the answers

What is the role of repair enzymes in DNA proofreading and repair?

To remove and replace incorrectly paired nucleotides from replication errors. Signup and view all the answers

What is a thymine dimer, how might it occur, and how is it repaired?

It is covalent linking between adjacent thymine bases, caused by ultraviolet radiation, repaired by DNA repair enzymes. Signup and view all the answers

Explain telomere erosion and the role of telomerase.

After a certain number of replications, telomeres shorten, causing aging. Telomerase prevents shortening and restores telomeres to original length in germ cells, not somatic cells. Signup and view all the answers

Why are cancer cells immortal but most body cells have a limited lifespan?

Cancer cells often have telomerase, body cells do not. Signup and view all the answers

What is the difference between heterochromatin and euchromatin?

Heterochromatin is interphase chromatin, showing up as irregular clumps under a microscope, while euchromatin is less compact and more dispersed. Signup and view all the answers

In his pneumonia-causing bacteria and mice, what did Griffith find?

Some substance from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic. Signup and view all the answers

What is the basis for the difference in how the leading and lagging strands of DNA molecules are synthesized?

DNA polymerase can join new nucleotides only to the 3' end of the growing strand. Signup and view all the answers

The elongation of the leading strand during DNA synthesis?

Depends on the action of DNA polymerase. Signup and view all the answers

In a nucleosome, the DNA is wrapped around?

Histone proteins. Signup and view all the answers

E. coli cells grown on 15N medium are transferred to 14N medium. What density distribution of DNA would you expect?

One low density and one intermediate density band. Signup and view all the answers

What combination of proteins could repair the damage from the spontaneous loss of amino groups from adenine in DNA?

Nuclease, DNA polymerase, DNA ligase. Signup and view all the answers

Which direction does the lagging strand get added to in terms of the replication fork?

The lagging strand is being elongated in the direction away from the replication fork. Signup and view all the answers

What is mismatch repair?

When enzymes other than DNA polymerases remove and replace incorrectly paired nucleotides. Signup and view all the answers

How do telomeres act as a buffer zone?

They are long regions of DNA that do not code for genes, which shorten with each replication. Signup and view all the answers

Why are RNA primers necessary for replication?

DNA polymerases cannot initiate replication; they can only add nucleotides to the 3' end. Signup and view all the answers

Why does the shortening of DNA not affect prokaryotes?

Most of them have circular DNA and can access the 3' end at all times. Signup and view all the answers

Study Notes

Chemical Components of Chromosomes

Chromosomes are composed of DNA and protein.

Genetic Material Discovery

Initially, proteins were believed to be the genetic material due to their complexity and variety; little was known about nucleic acids.

Griffith's Experiment

Distinction between virulent (disease-causing) and nonvirulent (harmless) strains of Streptococcus pneumoniae.
Killed virulent strain could transform nonvirulent strain into a pathogenic form.

Transformation

Transformation refers to a change in genotype and phenotype from external DNA uptake.

Avery's Experiment

Avery identified DNA as the transforming factor by inactivating RNA, DNA, and protein in bacteria. Only active DNA caused transformation.

Bacteriophage Structure

T2 bacteriophage is a virus specifically targeting bacteria.

Bacteriophage Infection Mechanism

Bacteriophages destroy bacterial cells by injecting their own DNA into the host cell.

Hershey and Chase Experiment

Used radioactive sulfur and phosphorus to distinguish between DNA and protein, concluding that DNA is the hereditary material.

Chargaff's Rules

Adenine pairs with thymine; guanine pairs with cytosine.
Base pair ratios are consistent within species, confirming the complementary base pairing.

Nucleotide Components

Each nucleotide consists of a nitrogenous base, deoxyribose sugar, and a phosphate group.

Watson and Crick Model

First DNA model constructed by James Watson and Francis Crick, contributing to the understanding of the double helix structure.

X-ray Diffraction

Rosalind Franklin utilized X-ray diffraction to reveal DNA's double helix structure.

Purines vs. Pyrimidines

Purines: Adenine and Guanine (double-ring structure).
Pyrimidines: Cytosine and Thymine (single-ring structure).
Adenine pairs with Thymine (2 hydrogen bonds); Guanine pairs with Cytosine (3 hydrogen bonds).

Structure of DNA

DNA's backbone consists of sugar and phosphate groups, while nitrogenous bases form the rungs.

Antiparallel Strands

DNA strands run in opposite directions; one has a 5' end facing the other’s 3' end.

Semiconservative Replication Model

DNA replication results in two strands, each containing one old and one new strand.

Meselson and Stahl Experiment

Used isotopes of nitrogen (15N and 14N) to demonstrate semiconservative replication through density differences in centrifuged samples.

Origins of Replication

The sequence where DNA replication begins during the S phase of the cell cycle.

Leading vs. Lagging Strand

Leading strand synthesized continuously towards the replication fork; lagging strand synthesized in short Okazaki fragments away from the fork.

DNA Synthesis Direction

Nucleotide addition occurs at the 3' end of the new strand, starting at its 5' end.

Okazaki Fragments

Short segments synthesized on the lagging strand, joined together by DNA ligase.

Role of Helicase

Unwinds and separates the DNA strands for replication.

Single-Strand Binding Proteins

Keep separated DNA strands apart during replication.

Primase Function

Synthesizes RNA primers necessary for initiating DNA replication.

DNA Polymerase Role

Adds nucleotides to the growing DNA strand and proofreads for accuracy.

Topoisomerase Function

Relieves tension and strain ahead of the replication fork to prevent supercoiling.

Ligase Function

Joins together DNA fragments, especially Okazaki fragments on the lagging strand.

DNA Polymerase I Role

Replaces RNA primers with DNA nucleotides.

Proofreading and Repair Mechanisms

DNA polymerase checks for accuracy; nuclease removes damaged segments; ligase fills gaps!

Thymine Dimers

Covalent links between adjacent thymine bases caused by UV radiation, repaired by DNA repair enzymes.

Telomeres and Telomerase

Telomeres shorten with each replication; telomerase restores their length in germ cells, preventing aging effects on DNA.

Immortality of Cancer Cells

Cancer cells often retain active telomerase, allowing indefinite division.

Heterochromatin vs. Euchromatin

Heterochromatin: tightly condensed, irregular clumps; Euchromatin: less compact and more accessible for transcription.

Griffith's Transfer of Pathogenicity

Pathogenic substance transferred from dead harmful cells to live harmless cells, resulting in disease.

Lagging Strand Synthesis Direction

Lagging strand elongates away from the replication fork.

Mismatch Repair

Enzymes recognize and correct incorrectly paired nucleotides during DNA replication.

Telomere Functionality

Telomeres act as protective buffers to prevent loss of important genetic information during DNA replication.

RNA Primers Necessity

RNA primers are essential for DNA replication initiation, as DNA polymerases cannot start without them.

Prokaryotic DNA Structure

Circular DNA structure allows prokaryotes to replicate without shortening effects during replication.

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Explore the crucial concepts of the molecular basis of inheritance with these flashcards. Test your understanding of chromosomes, genetic material, and the distinctions between virulent and nonvirulent strains. Ideal for students studying genetics and molecular biology.