The molecular basis of inheritance

Name the 5 nitrogenous bases and if they are purine, pyrimidine and found in DNA or RNA

1. Adenine is a purien found in both DNA and RNA 2. Guanine is a purine found in both DNA and RNA 3. Cytosine is a pyrimidine foudn in both DNA and RNA 4.Thymine is a pyrimidine found in only DNA 5. uracil is a pyrimidine found in only RNA

What are the five levels of DNA packing

1. DNA wraps around histones. 2. Nucleosomes 3. interactions between histone tails and linker DNA and nucleosomes form a siber about 30nm in thickness 4. The fiber loops around a chromosome scaffold creating looped domains and forming a 300nm fiber 5. The looped domains coil and fold forming the metaphase chromosome

Cytosine makes up 38% of the molecules in a sample of DNA from an organism. Approximately, what percentage of the nucelotides in this sample will be thymine?

12

Word Roots: helic-

= a spiral (helicase: an enzyme that untwists the double helix of DNA at the replication forks)

Word Roots: telos-

= an end (telomere: the protective structure at each end of a eukaryotic chromosome)

Word Roots: liga-

= bound or tied (DNA ligase: a linking enzyme for DNA replication)

Word Roots: -phage

= to eat (bacteriophages: viruses that infect bacteria)

Word Roots : semi-

=half (semiconservative moedle: type of DNA replication in which the replicated double hleix consists of one old strand dervied from the parent molecule, one newly made strand)

replication fork

A Y-shaped region on a replicating DNA molecule where new strands are growing

how did Watson and Crick's model explain the basis for Chargaff's rules

A and T pair together, C and G pair together

Transformation

A change in genotype and phenotype due to assimilation

lagging strand

A discontinuously synthesized DNA strand that elongates by means of Okazaki fragments, each synthesized in a 5' 3' direction away from the replication fork.

What is the Dipersive model?

A model of DNA replication in which each strand of bothe daughter molecules contain a mixture of old and newly synthesized DNA.

nonsense mutation

A mutation that changes an amino acid codon to one of three stop codons, resulting in a shorter and usually nonfunctional protein

Which of the following best describes the addition of nucleotides to a growing DNA chain?

A nucleoside triphosphate is added to the 3' end of the DNA, releasing a molecule of pyrophosphate

topisomerase

A protein that functions in DNA replication, helping to relive strain in the double helix ahead of the replication fork.

Heterchromatin

A type of interphase chromatin visible as irregular clumps with a light microscope; more compact than euchroamtin

bacteriophage

A virus that infects bacteria; also called a phage

In an analysis of the nucleotide composition of DNA, which of the following is true?

A=G and C=T with A+C=G+T

Explain telomere erosion and the role of telomerase

After a certain number of replications, telomeres shorten (causes aging). Telomerase prevents shortening and restores telomeres to original length in germ cells, not somatic cells

Phage with labled proteins or DNA was allowed to infect bacteria. It was shown that the DNA, but not the protein, entered the bacterial cells, and was therefore the gentic material

Alfred Hershey and Martha Chase

DNA polymerase

An enzyme that catalyzes the formation of the DNA molecule

telomerase

An enzyme that catalyzes the lengthening of telomeres in eukaryotic germ cells

primase

An enzyme that joins RNA nucleotides to make the primer using the parental DNA strand as a template

Helicase

An enzyme that untwists the double helix at the replication forks, separating the two parental strands and making them available as template strands.

Explain the experiment of Meselson and Stahl

Bacterium with 15N DNA and 14N DNA were separately centrifuged. When allowed to replicated, hyrbid DNA was created that weighed a mass intermediate to the 15N and 14N DNA

nucleosomes

Basic units of DNA packing. DNA wrapped twice around a protein core of eight histones

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

Cancer cells often have telomerase, body cells do not. This protects cancer cells from their telomeres shortening and limiting their number of possible division. they can divide infinitely.

messenger RNA (mRNA)

Carries genetic message from the DNA to the protein-syntheiszing machinery of the cell

Avery and his colleagues purified various chemical from pathogenic bacteria and showed that DNA was (were) the transforming agent

DNA

What did Oswald Avery determine to be the transforming factor?

DNA

Two chemical components of chromosomes

DNA and protien

In trying to determine whether the DNA or protein is the genetic material. Hershey, and Chase made use of which of the following facts?

DNA contains phosphorus, but protein does not

Suppose one were provided with an actively diving culture of E. coli bacteria to which radioactive thymine had been added. What would happen if a cell replicated once in the presence of this radi

DNA in both daughter cells would be radioactive

covalently connects segments of DNA

DNA ligase

Replicating the lagging strand of DNA that is, adding bases in the 3' 5' direction utilizes which of the following

DNA ligase RNA primers Okazaki fragments

DNA pol III is completing synthesis of fragment 4. When it reaches the RNA primer on fragment 3, it will detach and begin adding DNA nucleotides to the 3 end of the fragment 5 primer in the replication fork

DNA pol I removes the primer from the 5 end of fragment 2, replacing it with DNA nucelotides added one by one to the 3 end of fragment 3. After the last addtion, the backbone is left with a free 3' end

Which enzyme catalyzes the elongation of a DNA strand in the 5' 3' direction?

DNA polymerase

DNA- cutting enzymes used in the repair of DNA damage

DNA polymerase I

removes the RNA nucleotides from the primer and adds equivalent dna nucleotides to the 3' end of okazaki fragments

DNA polymerase I

adds nucleotides in the 5' 3' direction in DNA replication

DNA polymerase III

A new DNA strand elongates only in the 5' --> 3' direction because

DNA polymerase begins adding nucleotides at the 5' end of the template

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.

Why are RNA primers necessary for replication?

DNA polymerases cannot initiate replication, they can only add nucelotides to the 3' end

After mixing a heat-killed phosphorescent strain of bacteria with a living non-phosphorescent strain, you discover that some of the living cells are now phosphorescent. The best evidence that the ability to fluoresce is a heritable trait that would be an observation that

Descendants of the living cells are also phosphorescent

Meselson and Stahl

Determined that DNA replication is semiconservative

hersy-chase experimement

Devised an experiment that showed that only the DNA of T2 phages enters a bacterial cell during infection

Erwin Chargaff

Discovered that DNA composition varies, but the amount of adenine is always the same as thymine and the amount of cytosine is always the same as guanine

Frederick Griffith

Discovered transformation during an experiment that involved injecting mice with smooth S cells, rough R cells, heat-killed S cells, an heat-killed S cells with living R cells

What is the semiconservative model of replication

During DNA replication, the strand split and each side is translated. This creates 2 new strands half of DNA and half of the new DNA

In DNA from any species, the amount of adenine equals the amount of thmine, and the amount of guanine equals the amount of cytosine

Erwin Chargaff

The following scientists made significant contribution to our understanding of structure and function of DNA. Place the scientists' names in the correct chronological order, starting the first scientist(s) to make a contribution.

Fredrick Griffith, Oswald Avery, Maclyn McCarty, and Colin MacLeod, Alfred hershey and Martha Chase, james Watson and Francis Crick, Matthewy Meselson and Franklin Stahl

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

Make a detailed list of the steps that occur in the synthesis of a new strand

Helicase splits the strands apart. single strand binding proteins attach to prevent the DNA from rebinding. Topoisomerase helps relieve strain by binding the parental strands ahead of the replication fork. Primes synthesizes RNA primers that attach to the DNA. DNA bind complimentary, instead of thymine, uracil is used. DNA polymerase III then begin to add complimentary base pairs after the primer. Each nucleotide added is a nucleoside triphosphate, composed of a sugar base pair and three phosphate groups. When the two base pairs bind, two phosphates are released. This serves as an energy source for polymerization. This addition of base pairs can only occur on the 3' end of the new strand. A leading strand a lagging strand form since they run antiparallel. The leading strand is continually added to. The lagging strand must be unwound a certain amount before new base pairs can be attached. Because of this, there are multiple segments of RNA primers. The replication is added to in okazaki fragments, not base pair by base pair like in the leading strand. DNA ligase adds these fragments, acting as glue. After replication has occurred, DNA polymerase I comes in and replaces the RNA primers with DNA base pairs.

What are Chargaff's rules? How did he arrive at them

His rule states that Adeninine only pairs with Thymine and that Guanine only pairs with Cytosine. He discovered that bases may vary between species but somehow the number of adenines was always equal to the number of thymines, same with cytosine an guanine

All of the following are functions of DNA polymerase in DNA replication except

I dont know

terminator

In prokaryotes, a special sequence of nucleotides in DNA that marks the end of a gene

What does DNA polymersase do?

It adds DNA nucleotides ot the new strand of DNA

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

Whwat is the role of ligase in DNA proofreading and repair

It fills the gaps that nuclease leaves when DNA is excised

What is a tymine dimer? How might it occur? How is it repaired?

It is covalent linking between adjacent thymine bases. It can be caused by ultraviolet radation. it is repaired by DNA repair enzymes, possibly in an nucleotide excision repair

What is the role of DNA ligase in the elongation of the lagging strand during DNA replication?

It joins Okazaki fragments together

What does primase do?

It synthesizes the RNA primer

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

James Watson and Francis Crick

Euchromatin

Less compact, more dispersed interphase chromatin

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

Matthew Meselson and Franklin Stahl in the late 1950s

Which scentists contributed to building a structural model of DNA

Maurice Wikins Rosalind Franklin James Watson Francis Crick

In his transformation experiments, Griffith observed that

Mixing of a heat-killed pathogenic strain of bacteria with a living nonpathogenic strain can convert some of the living cells into the pathogenic form

poly-A tail

Modified 3' end of an mRNA molecule consisting of the addition of some 50 to 250 adenine nucleotides

missense mutation

Most common type of mutation, a base pair mutation in which the new codon makes sense in that it still codes for an amino acid

why does the shortening of DNA not affect prokaryotes

Most of them have circular DNA and can access the 3' end of it at all times

frameshift mutation

Mutation occurring when the number of nucleotides inserted or deleted is not a multiple of three, resulting in improper grouping of nucleotides into codons

Compare DNA replication on the leading and lagging strands, including both similarities and differences

On both the leading and lagging strands, DNA polymerase adds onto the 3' end of an RNA primer synthesized by primase, synthesizing DNA in the 5' S 3' direction. Because the parental strands are antiparallel, however, only on the leading strand does synthesis proceed continuously into the replication fork. The lagging strand is synthesized bit by bit in the direction away from the fork as a series of shorter Okazaki fragments, which are later joined together by DNA ligase. Each fragment is initiated by synthesis of an RNA primer by primase as soon as a give stretch of single-stranded template is opened up. Although both strands are synthesized at the same rate, synthesis of the lagging strand is delayed because initiation of each fragment be gins only when sufficient template strand is available.

Chemicals from heat-killed S cells were purified. The chemicals were tested for the ability to transform live R cells. The transforming agent was found to be DNA

Oswald Avery, colin MacLeod, and Maclyn McCarty

the leading strand is synthesized continuously in the 5 to 3 direction by DNA pol III.

Primase begins synthesis of the RNA primer for the fifth Okazaki fragment

Which of the following statements is false when comparing prokaryotes with eukaroytes?

Prokaryotes produce Okazaki fragments during DNA replication, but eukaroytic chromosomes have many

Which of these mechanisms ensures that the DNA sequence in the genome remains accurate?

Proofreading during DNA replication

Why did researchers originally think that protein was the genetic material

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

Distinguish between the structure of pyrimidines and purines. Explain why adenine only bonds with thymine

Purines and adenine and guanine. Pyrimidines are cytosine and thymine. Purines and pyramidines always bond to each other. G-C = 3 h bonds. A-T = 2 bonds

Structurally what is the difference between purines and pyrimidines

Purines have a double sugar, pyrimidines have a single sugar

What kind of molecule or substance is the primer that issued to initiate the synthesis of a

RNA

What kind of molecule or substance is the primer that is used to initiate the synthesis of a new DNA strand?

RNA primers

origins of replication

Site where the replication of a DNA molecule begins, consisting of a specific sequence o nucleotides

In his pneumonia causing bacteria and mice, Griffith found that?

Some substances from pathogenic cells was transferred to nonpathogenic cells, making them pathogenic

anticodon

Specialized base triplet at one end of a tRNA molecule that recognizes a particular complementary codon on an mRNA molecule

5'cap

The 5' end of a pre-mRNA molecule modified by the addition of a cap of guanine nucleotide

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.

RNA processing

The modification of mRNA before it leaves the nucleus that is unique to eukaryotes

leading strand

The new continuous complementary DNA strand syntehzied along the template strand in the mandatory 5' 3' direction.

What is semiconservative

The parental moelcule unwinds, and each strand the nserves as a template for the synthesis of a new strand according to abse-pairing rules

one gene-one polypeptide hypothesis

The premise that a gene is a segment of DNA that codes for one polypeptide

translation

The synthesis of a polypeptide, which occurs under the direction of mRNA

Which of the following is analogous to telomeres?

The two ends of a shoelace

Which of the following statements does not apply to the Watson and Crick model of DNA?

The two strands of the DNA form a double helix

When T2 bacteriophages infect bacteria and make more viruses in the presence of radioactive sulfur, what is the result?

The viral proteins will be radioactive

Distinguish between virulent and nonvirulent strains of streptococcnus pnumoniae studied by Frederick Griffith

The virulent strain caused disease and the nonvirulent was harmless. somehow though, the killed sample of the virulent strain infected the nonvirulent strand when the killed pathogenic strain was mixed with the harmless cells

Which of the following statements about telomeres is correct?

They are present at the ends of eukaroytic chromosomes They can be extended by an enzyme called tleoemrase

What are okazaki fragments? How are they welded together?

They are segments added to the lagging strand of DNA synthesis . They are welded together with DNA ligase

Individuals with the disorder xerodermia pigmentosum are hypersyensitive to sunlight because their cells have an imparied ability

They cannot repair thymine dimers

How are nucleic acids unique

They have the ability to direct their own replication from monomers

What do single strand proteins do?

They hold the DNA strands apart

How did Meselson and Stahl create heavy DNA for their experiments

They used isotopes of nitrogens, 15N and 14N. The heavier isotope caused differences when centriguged

semiconservative model

Type of DNA replication in which the replicated double helix consists of one old strand, derived from the old molecule, and one newly made strand.

What determines the nucleotide sequence of the newly synthesized strand during DNA replication

What determines the nucleotide sequence of the newly synthesized strand during DNA replication?

How do telomeres act as a buffer zone?

When the end is reached in replication, there is a small fragment that cannot be replicated since there is no 3' end to be added to. The telomeres are long regions of DNA that do not code for genes, they are repetitions of a short sequence. These areas are where DNA replication must stop each time, each replication resulting in shorter and shorter tleomeres

Define transformation

a change in genotype and phenotype due to the assimilation of external DNA

nuclease

a dna cutting enzyme that excises damanged DNA

List the three components of a nuceotide

a nitrogenous base, deoxiribose, phosphate gorup

nucleotide excision repair is what

a process by which nucleases cut out and other enzymes replace damaged stretches of DNA

Word Roots: trans-

across (transformation: a phenomenon in which external DNA is assimilated by a cell)

For a science fair project two students decided to repeat the hershey and Chase experiment, with modifications. They decided to label the nitrogen of the DNA, rather than the phosphate. They reasoned that each nucleotide has only one phosphate and two to five nitrogen. Thus labeling the nitrogen would provide a stronger signal than labeling the phosphate. Why won't this experiment work?

amino acids ( and thus proteins) also have nitrogen atoms; thus, the radioactive would not distinguish between DNA and protein

What does transformation involve in bacteria

assimilation of external DNA into a cell

What is considered the backbone of DNA? the rungs?

backbone is the sugar and phsophate, nitrogenos bases are the runs

single-strand binding protein

binds to and stablized single-stranded dna until it can be used as a template

exons

coding segments of eukaryotic DNA

chromatin

complex of DNA and protein

ribosomes

complex particles that facilitate the orderly linking of amino acids into polypeptide chains

McCarty, Avery, and MacLeod

confirmed that the transforming agent in Griffith's experiment was DNA

The elongation of the leading strand during DNA synthesis ____?

depends on the action of DNA polymerase

Watson and crick

developed the double helix model of dna

Watson and Crick deduced that DNA is

double helix

The ends of eukaroytic chromosomal DNA get shorter with what?

each round of replication

In mismatch repair, enzymes correct what?

errors that persist

The spontaneous loss of amino groups from adenine results in hypotanthine,an unnatural base, opposite thymine. What combination of molecules could the cell use to repair such damage

exonuclease, DNA polymerase, DNA ligase

separates the DNA strands during replication

helicase

What is the difference between heterochromatin and euchromatin?

heterochromatin is interphase chromatin, it shows up as irregular clumps under a microscope. the chromosomes are very tightly wounded. euchromatin is a true chromatin, it is less compact and more disperesed

To function as the heritable genetic code, DNA molecules must have all of the following structural features except

histone proteins associated with the double helix

in a nucleosome, the DA is wrapped around _____?

histone protiens

What does helices do?

it untwists and separates the stand of DNA

What does a T2 bacteriophase look like

its a virus that infects bacteria

What does DNA ligase do

joins DNA fragments together1

Who works together in DNA replication and repair

many proteins

helicase unwinds the parental double helix

molecules of singlestrand binding protien stabilize the unwound template strands

DNA polymerases proofread what

new DNA replacing incorrect nucleotides

What is the direction of synthesis of the new stand

nucelotides can only be added to the 3' end of the new strand of DNA. Meaning it starts at its 5' and adds until it reaches the 3'

The spontaneous loss of amino gorups from adenine in DNA results in hypoxanthine, and uncommon base, opposite thymine. What combination of proteins could repair such damage

nuclease, DNA polymerase, DNA ligase

E coli cells grown on 15N medium are transferred to 14N medium and allowed to grow for two more generations. DNA extracted from these cells is centrifuged, what density distribution of DNA would you expect?

one low density and one intermediate density band

synthesizes short segments of RNA

primase

For a couple of decades, as biologists knew the nucleus contained DNA and proteins. The prevailing opinion was that the genetic material was proteins, and not DNA. The reason for this belief was that proteins are more complex than DNA. This is be cause

proteins have a greater variety of three-dimensional forms than does DNA

Histones

proteins responsible for the 1st level DNA packing in chromatin

The DNA double helix has a uniform diameter because purines , which have two rings, always pair with pyrimidines which have one ring

purines; pyrimidines

What is the role of nuclease in DNA proofreading and repair

referred to as nucleotide excision repair, it is a DNA cutting enzymes that removes damaged or mutated segments of DNA

What is the function of topioisomerase?

relieving strain in the DNA ahead of the replication fork

What does DNA polymerase I do?

removes RNA primer and replaces with DNA

telomeres

repeated dna sequences at the ends of eukaroytic chromosomes

The Y-shaped structure where the DNA double helix is actively unwound during DNA replication is called the

replication fork

The meselson-Stahl expriment showed that DNA replication is what

semiconservative

It became apparent to Watson and Crick after completion of their model that the DNA molecule could carry a vast amount of hereditary information in its

sequence of bases

All of the following can be determined directly form X-ray diffraction photographs of crystallized DNA except the

sequence of nucleotides

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

Which of the following help to hold the DNA strands apart while they are being replicated?

single-strand binding proteins

Okazaki fragments

small fragments of dna produced on the lagging strand during dna replication, joined later by DNA ligase to form a complete strand

transcription

synthesis of an mRNA molecule from a DNA template

Which of the following is least related to the other on the list?

telomeres

The strands that make up DNA are antiparallel. This means that

the 5' to 3' direction of one strand runs count ot the 5' to 3' direction of te other strand

What is it meant that two strands of DNA are antiparallel?

the end of one strand matches with the beginning of the other, and is seen by the 5' end lining up with the other 3' end

the nitrogenous bases project into where?

the interior

The leading and the lagging strands differ in that

the leading strand is synthesized in the same direction as the movement of the replication fork, and the lagging strand is synthesized in the opposite direction

The difference between ATP and the nucleoside triphosphates used during DNA synthesis is that

the nucleoside triphosphates have the sugar deoxyribose; ATP has the sugar ribose

Two antiparallel sugar-phosphate chains wind around where?

the outside of the molecule

Define the origins of replication

the sequence where replication begins in S phase

How did Hershey and chase "label" viral DNA and viral protein so that they could be desintinguished

they designed their experiment to test if DNA or protein was inherited Radioactive sulfur was used in protein and radioacive phosphorous was used in DNA

Describe the means by which Hershey and Chase established that only the DNA of a phage enters an E. coli cell. What conclusions did these scientists draw based on these observations

they had two separate bacteriophages, one had radioactive protein in it, the other radioactive DNA. in the infected cells, only the radioactive DNA showed up. They concluded that DNA was what was used to transform cells.

Given that the DNA of a certain fly species consists consists of 27.3% adeninie and 25.5% guanine, use Chargaff's rule to determine the percentages of thymien and cytosine

thymine=27.3% cytosine=25.5%

What is the function of DNA polymersase?

to add nucleotide to the end of a growing DNA st rand

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

to proofread each nucleotide before it is added, removes incorrect pariring

What is the purpose of topisomerase?

to relieve strain caused by unwinding of DNA

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

to remove and replace incorrectly paired nucelotides from replication errors

Tobacco mosaic virus has RNA rather than DNA as its gentic material. In a hypothetical situation where RNA from a tobacco mosaic virus is mixed with proteins from a related DNA virus, the result could be a hybrid virus. If that virus were to infect a cell and reproduce, what would the resulting "offspring" viruses be like?

tobacco mosaic virus

A eukaroytic cell lacking telomerase would

undergo a reduction in chromosome length

What is mismatch repair?

when enzymes other than DNA polymerases remove and replace incorectly paired nucleotides