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Unit IV
CHAPTER 16
THE MOLECULAR BASIS
OF INHERITANCE
List the three components of a nucleotide.
Five-carbon sugar, a phosphate, and a nitrogenous base.
Distinguish between deoxyribose and ribose.
A deoxyribose is the sugar component of DNA, having one less hydroxyl
group than ribose, the sugar component of RNA, which ribose is the sugar
component of RNA.
List the nitrogen bases found in DNA, and distinguish between pyrimidine
and purine.
The nitrogen bases are adenine, guanine, cytosine, and thymine. A pyrimidine
, in which cytosine and thymine belong to, have a single ring, while purines, in
which adenine and guanine belong to, are nitrogenous bases with two organic
rings.
Explain the "base-pairing rule" and describe its significance.
Only A-T and C-G can form th mRNA
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.
Each nucleotide unit of the polunucleotide chain consists of a nitrogenous base
(T, A, C, or G), the sugar deoxyribose, and phosphate group. The phosphate
of one nucleotide is attached to the sugar of the next nucleotide in line. The
result is a “backbone” of alternating phosphates and sugars, from which the
bases project.
Explain, in their own words, semiconservative replication.
Semiconservatives replication is when the two strands of the parental
molecule sepeprate, and each functions as a template for synthesis of a new
complementary strand
Describe the process of DNA replication, and explain the role of helicase,
single strand binding protein, DNA polymerase, ligase, and primase.
In this simplification, a short segment of DNA has been untwisted to convert
the double helix to a two-dimensional version of the molecule that resembles a
ladder. The first step in replication is separation of the two DNA strands.
Each “old” strand now serves as a template that directs synthesis of “new”
complememntary strands. Nucleotides plug into specific sites along the
templates surface according to the base-pairing rules. The nucleotides are
connected to form the sugar-phosphate backbones of the new strands. Each
DNA molecule now consists of one “old” strand and one “new” strand,
resulting in two copies identical to the one DNA molecule with which we
started. Helicase is an enzyme that works at the crotch of the replication fork,
untwisting the double helix and separating the two “old” strands. Singlestrand binding proteins then attach in chains along the unpaired DNA
strands, holding these templates straight until new complementary can be
synthesized. DNA ligase, an enzyme, joins RNA nucleotides to make the
primer. Only one primer is required to polumerase to begin synthesizing the
leading strand of new DNA.
Define antiparallel.
Antiparalle is when the 5’to3’ direction of one strand runs counter to the
other strand.
Distinguish between the leading strand and the lagging strand.
Leading strand is the new continous complementary DNA strand synthesized
along the template strand in the mandatory 5’to3’ direction, while the lagging
strand is a discountinously synthesized DNA strand that elongates in a
direction away from the replication fork.
Explain how the lagging strand is synthesized when DNA polymerase can add
nucleotides only to the 3’ end.
To elongate the new strand of DNA, polymerase must work along the template
away from the replication fork. The DNA synthesized in this direction is
called the lagging strand. As a replication bubble opens, polymerase can
work its way away from a replication fork and synthesize a short segment of
DNA. As the bubble widens, another short segment of the lagging strand can
be made by a polymerase working away rrom the fork. In contrast to the
leading strand, which can be elongated continuously, the lagging strand is first
synthesized as a series of segments. DNA polymerase cannot initiate a
polynucleotide strand; it can only add to the 3’ end of an already-started
strand.
Explain the role of DNA polymerase, ligase, and repair enzymes in DNA
proofreading and repair.
One DNA repair mechanism, called mismatch repair, fixes mistakes, when
DNA is copied. The polumerase proofreads each nucleotide against its
template as soon as it is added to the strand. One function of the DNA repair
enzymes in our skin cells is to repair genetic damage caused by the ultraviolet
rays of sunlight.
CHAPTER 17
FROM GENE TO PROTEIN
Explain how RNA differs from DNA.
The two types of nucleic acid are named for their pentose sugars: deoxyribose
in the case of DNA; ribose in the case of RNA. A second difference is that
RNA has the nitreogenous base uracil in place of thymine.
In your own words, briefly explain how information flows from gene to
protein.
Information flows from gene to protein by transcription to RNA processing to
translation, in Eukaryotic cells and it flows from transcription to translation
in prokaryotic cells.
Distinguish between transcription and translation.
Transcription is the transfer of information from a DNA molecule to a RNA
molecule, while translation is the transfer of information of a RNA molecule
into a polypeptide, involving a change of language from nucleic acids to amino
acids.
Describe where transcription and translation occur in prokaryotes and in
eukaryotes.
In a eukaryotic cell, the two main steps of protein synthesis occur in separate
compartments; transcription in the nucleus and translation in the cytoplasm.
Thus, mRNA must be translocated from the nucleus to cytoplasm via pores in
the nuclear envelope. In a prokaryotic cell, which lacks a nucleus, mRNA
produced by transcription is immediately translated without additional
processing.
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.
A codon is a mRNA base triplet. The relationship that exists between the
linear sequence of codons on mRNA and the linear sequence of amino acids in
a polypeptide are
Explain the process of transcription including the three major steps of
initiation, elongation, and termination.
As an RNA polymerase molecule moves along a gene from the initiation site to
the termination site., it synthesizes an RNA molecule that consists of the
nucleotide sequence determined by the template strand of the gene. The
entire stretch of DNA that is transcribed is called a transcription unit.
Transcription begins at the initiation site when the polymerase separates the
two strands for base pairing with nucleotides. The RNA polymerase works its
way “downstream” from the initiation site, prying apart the two strands and
elongating the mRNA in the 5’to3’ direction. In the wake of transcription, the
two DNA strands re-form the double helix. The RNA polymerase continues to
elongate the RNA molecule until it reaches the termination site, a specific
sequence of nucleotides along the DNA that signals the end of the
transcription unit. The mRNA, a transcripts of the gene, is released, and the
polymerase subsequently dissociates from the DNA.
Describe the general role of RNA polymerase in transcription.
RNA polymerase pry the two strands of DNA apart and hook together the
RNA nucleotides as they base pair along the DNA template. Like the DNA
polumerases that function in DNA replication, RNA polymerases can add
nucleotides only to the 3’ end of the growing polymer. Thus, an RNA
molecule elongates in its 5’to3’ direction.
Distinguish among mRNA, tRNA, and rRNA.
mRNa is messenger RNA, Rna which is a type orf RNA synthesized from
DNA in the genetic material that attaches to ribosomes in the cytoplasm and
specifies the primary structure of a protein. TRNA is tranfer RNA which is
an RNA molecule that functions as an interpreter between nucleic acids and
protein language by picking up specific amino acids and rcognizing the
appropriate codons in the mRNA. Ribosomal RNA or rRNA is the most
abundant type of RNA. Together with protein, it forms the structure or
ribosomes that coordinate the sequential coupling of tRNA molecules to the
series of mRNA codons.
Describe the structure of tRNA and explain how the structure is related to
function.
The structure of tRNA contains the four base paired regions and three loops
characteristics of all tRNAs. At one ens of the molecule is the amino acids
attachment site, which has the same base sequence for all tRNA, within the
middle loop is the anticodon triplet, which is unique to each tRNA type. The
structure of a tRNA molecule fits its function as a shuttle for a specific amini
acid.
Given a sequence of bases in DNA, predict the corresponding codons
transcribed on mRNA and the corresponding anticodons of tRNA.
Describe the structure of a ribosome, and explain how this structure relates to
function.
A functional ribosome consists of two subunits, each an aggregate of
ribnosomal RNA and many proteins. A ribosome has an mRNA binding sites
and two tRNA-binding sites, known as the P and A sites. The structure of a
ribosome reflects its function of bringing mRNA together with amino acidbearing tRNAs.
Describe the process of translation including initiation, elongation, and
termination.
Describe the structure of a ribosome, and explain how this structure relates to
function.
(See figure 16.12)
Describe the difference between prokaryotic and eukaryotic mRNA.
Explain how eukaryotic mRNA is processed before it leaves the nucleus.
First, it helps protect themRNA from hydrolytic enzymes. Second, after the
mRNA reaches the cytoplasm, the 5' capfunctions as an "attach here" sign for
small ribosomal subnits. The other end of an mRNA molecule, the 3'end, is
also modified before the message exits the nucleus.
Explain why base-pair insertions or deletions usually have a greater effect
than base-pair substitutions.
CHAPTER 18
MICROBIAL MODELS: THE GENETICS OF
VIRUSES AND BACTERIA
List and describe structural components of viruses.
Nucleic Acid (DNA or RNA) And Protein Coat; both make the Capsid
Explain why viruses are obligate parasites.
Parasites destroy the host cell and so do viruses.
Explain the role of reverse transcriptase in retroviruses.
Transcribing DNA from an RNA template.
Describe how viruses recognize host cells.
A lock and key fit between proteins on the outside of
the virus and specific receptor molecules on the
surface of the cell.
Distinguish between lytic and lysogenicreproductive cycles
usingphageT4 and phage l as examples.
Figure 17.4 and 17.5
Explain how viruses may cause disease symptoms,and describe
some medical weapons used to fight viralinfections.
They cause cells to be destroyed having the body
compensate for destroyed cells lowers the bodies’
potential to operate. The best way to combat a virus
is by getting a bacterial injection and having it is
lysogenic.
List some viruses that have been implicated in human cancers, and
explain how tumor viruses transform cells.
Cancer for Hepatitis, the Epstein-Barr virus and
Burkit’s lymphoma. When a tumor virus lacks oncogenes
and transforms the cell simply by turning on or
increasing the expression of one or more of the cells
own oncogenes.
List some characteristics that viruses share withliving organisms, and
explain why viruses do not fit our usual definition of life.
They can replicate and use also host cell’s nutrients
to stay alive. It doesn’t meet because it cannot
replicate its own genes and produce ATP.
Describe the structure of a bacterial chromosome.
Double stranded and is in a circular shape containing
3000 genes.
List and describe the three natural processes of
genetic recombination in bacteria.
Transformation-alteration of a bacterial cell’s
genotype by the uptake of naked, foreign DNA from the
surrounding environment, Transduction-Figure 17.10,
Conjugation and Plasmids-direct transfer of genetic
material between two bacterial cells that are
temporarily joined
Explain how the F plasmid controls conjugation in
bacteria.
Briefly describe two main strategies cells use to
control metabolism.
Distinguish between structural and regulatory
genes.
CHAPTER 1 9
THE ORGANIZATION AND CONTROL OF
EUKARYOTIC GENOMES
Compare the organization of prokaryotic and eukaryotic genomes.
Prokaryotic DNA circular, and the nucleoid is so small that it can be
seen only with electron microscope. Eukaryotic chromosomes contain
an enormous amount of DNA relative to their strength.
Describe the current model for progressive levels of DNA packing.
(See Figure 18.1)
Distinguish between heterochromatin and euchromatin.
Heterochromatin is denser than euchromatin (true chromatin)
CHAPTER 20
DNA TECHNOLOGY
Explain how advances in recombinant DNA technology have helped
scientists study the eukaryotic genome.
Scientists can now make gene copies of the gene they want to study.
They can also be good in that they produce new protein product, and
also a plasminogen activator and giving powers to cells that do not have
a certain power.
Describe the natural function of restriction enzymes.
Enzymes protect bacteria against intruding DNA from other organisms,
such as viruses or other organisms.
Describe how restriction enzymes and gel electrophoresis are used to
isolate DNA fragments.
Restriction enzymes can cut out a specific segment of the DNA to
Isolate. Gel electrophoresis separates them from big to small
List and describe the two major sources of genes for cloning.
Describe how "genes of interest" can be identified with the use of a
probe.
DNA isolated directly from an organism and complementary DNA
made in the laboratory from mRNA templates.