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Chapter 16
1. Explain why researchers originally thought protein was the genetic material.
Researches originally though that protein was the genetic material because they
are the links between genotype and phenotype.
2. Summarize experiments performed by the following scientists, which provided
evidence that DNA is the genetic material:
a. Frederick Griffith- found the first evidence that genes are specific molecules
and he experimented with mice
b. Alfred Hershey and Martha Chase – demonstrated that it was DNA, not protein
that functioned as the phages’ genetic material by experimenting with bacteria.
c. Erwin Chargaff – analyzed the base composition of DNA from a number of
different organisms.
3. List the three components of a nucleotide.
Sugar component, selection of nitrogenous bases, and order
4. Distinguish between deoxyribose and ribose.
Deoxyribose – the sugar component of DNA
Ribose – the sugar component of RNA
5. List the nitrogen bases found in DNA, and distinguish between pyrimidine and purine.
Adenine, Guanine, Cytosine, and Tymine
Pyrimidine – single ring
Purine – various rings
6. Explain how Watson and Crick deduced the structure of DNA, and describe what
evidence they used.
They deduced that DNA was a double-helix; they built models that confirmed xray data
7. Explain the "base-pairing rule" and describe its significance.
A specific base goes with another specific base in the opposing strand. This gives
uniformity to the DNA molecule.
8. Describe the structure of DNA, and explain what kind of chemical bond connects the
nucleotides of each strand and what type of bond holds the two strands together.
DNA is structured like a double-helix with sugar-phosphate backbones and inner
nitrogenous bases. The nitrogenous bases are connected with hydrogen bonds
and held together with the same bond.
9. Explain, in their own words, semi conservative replication, and describe the MeselsonStahl experiment.
The two strands of the parental molecule separate, and each functions as a
template for synthesis of a new complementary strand. The experiment was using
the culturing of bacteria.
10. Describe the process of DNA replication, and explain the role of helicase, single
strand binding protein, DNA polymerase, ligase, and primase.
DNA replication involves separating the DNA molecule into two strands.
Helicase – unwinds the DNA helix forming a Y-shaped replication fork.
Single stranded DNA binding protein – attach each strand of the uncoiled DNA to
keep them separate
DNA polymerase – moves in the 3’  5’ direction along each template strand.
Ligase – produce a single compliment strand
Primase – initiates each complementary segment with RNA nucleotides.
11. Explain what energy source drives endergonic synthesis of DNA.
The energy source that drives this is two additional phosphates.
12. Define ant parallel, and explain why continuous synthesis of both DNA strands is not
possible.
The sugar phosphates are upside-down to each other.
13. Distinguish between the leading strand and the lagging strand.
Leading strand – assembled continuously as the double-helix uncoils
Lagging strand – is assembled in short fragment and therefore takes longer
14. Explain how the lagging strand is synthesized when DNA polymerase can add
nucleotides only to the 3¢ end.
It is synthesized in compartments and takes much longer
15. Explain the role of DNA polymerase, ligase, and repair enzymes in DNA
proofreading and repair
Leading strand is synthesized by DNA polymerase, and repair enzymes correct
errors in the DNA replication
Chapter 17
1. Explain how RNA differs from DNA.
They have different nitrogenous bases
2. In your own words, briefly explain how information flows from gene to protein.
It interconnects with the information in the gene and sends out to each protein
3. Distinguish between transcription and translation.
Transcription – RNA molecules are created by using the DNA molecule as a
template
Translation – the processed RNA molecules are used to assemble amino acids into
a polypeptide
4. Describe where transcription and translation occur in prokaryotes and in eukaryotes;
explain why it is significant that in eukaryotes, transcription and translation are separated
in space and time.
In prokaryotic cells transcription and translation occurs inside the cell, but since
there is no nucleus they occur in open space. In eukaryotic cells transcription
occurs inside the nucleus while translation occurs outside the nucleus.
5. Define codon, and explain what relationship exists between the linear sequence of
codons on mRNA and the linear sequence of amino acids in a polypeptide.
Codons are a triplet group of three adjacent nucleotides and linear sequences
provide for alignment and matching of each
6. List the three stop codons and the one start codon.
STOP – UAA, UGA, UAG
START – AUG
7. Explain in what way the genetic code is redundant and unmistakable.
It may be different combinations but each codon means a specific thing.
8. Explain the evolutionary significance of a nearly universal genetic code.
Everyone knows what everything means therefore there is not confusion.
9. Explain the process of transcription including the three major steps of initiation,
elongation, and termination.
In initiation, the RNA polymerase attaches to promoter regions on the DNA and
begins to unzip. Then elongation occurs as the RNA polymerase unzips the DNA
and assembles the RNA nucleotides. Finally there is termination which occurs
when the RNA polymerase reaches a special sequence of nucleotides that serve as
a termination point.
10. Distinguish among mRNA, tRNA, and rRNA.
mRNA – (messenger RNA) a single strand of RNA that provides the template used
for sequencing amino acids into a polypeptide.
tRNA – (transfer RNA) a short RNA molecule that is used for transporting amino
acids.
rRNA – (ribosomal RNA) molecules that are the building blocks of ribosomes
11. Describe the structure of tRNA and explain how the structure is related to function.
tRNA resembles the three leaflets of a clover leaf and creates a “wobble” which
allows some tRNA’s to base-pair with more than one kind of codon.
12. Describe the difference between prokaryotic and eukaryotic mRNA.
Eukaryotic – carries info specifying amino acid sequences of proteins from DNA to
ribosomes.
Prokaryotic – the translation can begin almost instantaneously
13. Describe some biological functions of introns and gene splicing.
Introns are intervening sequences that are non-coding. Gene splicing is when they
are put together.
14. Explain why base-pair insertions or deletions usually have a greater effect than base-pair
substitutions.
Insertions or deletions completely change a base-pair wile substitution can
sometimes have no effect.
15. Describe how mutagenesis can occur.
A number of physical and chemical agents called mutagens interact with DNA to
cause the mutations.
Chapter 18
1. List and describe structural components of viruses.
Capsid – nucleic acid surrounded by a protein coat.
Envelope – assists in penetrating their hosts
2. Explain why viruses are obligate parasites.
They are obligate parasites because they can only survive off of another living thing,
as soon as they are brought into the air they die.
3. Explain the role of reverse transcriptase in retroviruses.
Reverse transcriptase in retroviruses is an enzyme that is used to make a DNA
complement of the retroviruses’ RNA.
4. Describe how viruses recognize host cells.
By a “lock and key” fit between proteins on the outside of the virus and specific
receptor molecules on the surface of the cell.
5. Distinguish between lytic and lysogenic reproductive cycles using phage T4 and phage l as
examples.
Lytic – the host cell is killed
Lysogenic – the host cell stays alive
6. Explain how viruses may cause disease symptoms, and describe some medical weapons
used to fight viral infections.
Some viruses cause the infected cells to produce toxins that lead to disease
symptoms and a medical weapon used to fight them are vaccines.
7. List some viruses that have been implicated in human cancers, and explain how tumor
viruses transform cells.
The retrovirus, papovirus, adenovirus, and herpesvirus have been implicated on
human cancers. When certain tumor viruses infect animal cells growing in cultures,
the cells undergo transformation in a cancerous state.
8. List some characteristics that viruses share with living organisms, and explain why viruses
do not fit our usual definition of life.
Viruses share characteristics such as DNA, RNA and replication with living
organisms, except they do not fit our usual definition of life because viruses need a
living organism in order to live off of.
9. Describe the structure of a bacterial chromosome.
One double-stranded DNA molecule arranged in a circle
10. List and describe the three natural processes of genetic recombination in bacteria.
Conjunction – a process of DNA exchange between bacteria.
Transduction – occurs when a new DNA is introduced into bacteria by a virus.
Transformation – occurs when bacteria absorb DNA from their surroundings.
11. Explain how the F plasmid controls conjugation in bacteria.
The F plasmid contains the genes that enable a bacterium to produce pili.
12. Briefly describe two main strategies cells use to control metabolism.
Lac operon and trp operon - lac controls the breakdown of lactose and trp produces
enzymes for the synthesis of amino acids.
13. Distinguish between structural and regulatory genes.
Regulatory – produces a repressor protein a substance that can prevent gene
expression by blocking the action of RNA polymerase.
Structural – contain DNA sequences that code for several related enzymes that
direct the production of some particular end product.