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Assignment 6
BIO 151 Summer 2016
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CHAPTER 11: CELL COMMUNICATION
1. Define the 3 stages of cell signaling:
1) Reception – During reception, a target cell detects signalling from its
environment. and its membrane receptors bind with the signal molecule, known as a
ligand.
2) Transduction – During transduction the molecular signal is transmitted from
the exterior of the cell to the interior. The signal is changed to it can cause a specific cell
response.
3) Response – Response is the cell's reaction, meaning the cell is changed in some
way to produce a specific response.
2. Explain the two main types of direct contact (the 1st type has different name for
plants/animals; 2nd type is just found in animals – see Fig11.4):
1) Plants: Plasmodesmata are used in plants to connect the cytoplasms of cells
adjacent to each other.
Animals: Gap junctions do the same thing in animals cells; that is, they connect
cytoplasms of adjacent cells.
2) Animals: Animals also use cell-to cell recognition through direct contact between
molecules bound to the cell surfaces.
3. What is local signaling? What is an example of this?
Local signaling occurs when signals only are carried for a short distance. An example of
local signaling is when growth factor signals cells that are nearby to divide.
4. What are hormones? What type of signaling are they involved in?
Hormones are released by animal cells and travel to target cells a distance away through
the bloodstream. It is a type of long distance signaling.
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5. Define: Ligand – A ligand is a type of molecule that has the ability to bind specifically
to a different molecule.
Target cell – A target cell has a specific receptor that allows it to interact
with the ligand.
6. Are signal receptors general (will they bind a variety of different signals) or
are they very specific?
The receptor protein associated with a target cell has a very specific binding site for the
signal molecule.
7. Where are intracellular receptors found?
Intracellular receptors are found in the cytoplasm or in the nucleus.
What types of molecules bind to intracellular receptors? Why must these
signals have those characteristics?
Intracellular receptors bind to hydrophobic ligand molecules. They must use these
signals because the intracellular receptors are in the cytoplasm, and these
hydrohobic ligand molecules are able to pass through the cell membrane.
8. When a cell surface receptor receives a signal, what generally happens to the
receptor? Use the ion-gated receptors as an example.
When a cell surface receptor receives a signal it changes shape to let ions pass through. For
example, gated ion channel receptors are surface receptors that are important in the
nervous system. The gate is closed until the ligand binds with the surface receptors. When
that happens, the gate opens up to let the ions pass through.
9. What is a signal transduction pathway?
A signal transduction pathway is usually a multistep pathway if the receptors are
membrane pathway.
Having multiple steps in the pathway provides what two things?
Having multiple steps provides amplification of the signal and provides more opportunities
for a fine-tune response and regulation of the signal.
What are relay molecules?
Relay molecules pass the message through the cytoplasm.
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Is the actual original signal passed along the pathway?
The actual signal is passed along the pathway when proteins become activated as
phosphate groups are added.
10. What are second messengers? Where do they function?
Second messengers are water soluble, non-protein small molecules or ions.
The two most common second messengers are:
1)
AMP
2) Ca2+
11. Is the calcium ion concentration higher inside or outside the cell? Why? (What
does the cell do to create this gradient?)
Calcium ion concentration is lower inside the cell because the ions ae actively pumped out.
12. If the final activated molecule in a signal transduction pathway is a
__transcription factor________________________________________, then the response is turning
genes on or off.
13. If hormones are spread all around the body in the bloodstream, then why do only
certain cell types respond to certain hormones?
Even though hormones spread all around the body in the bloodstream, only certain cell
types respond to certain hormones because they are target cells that have receptors for the
hormone.
CHAPTER 19: VIRUSES
1. Why are viruses generally not considered to be living organisms?
Viruses are generally not considered to be living organisms because they can't reproduce
or carry out metabolic activities if they are not in a host cell.
2. What is the general structure of a virus? What is a capsid?
Viruses are merely a nucleic acid in a protein coat. A capsid is a protein shell made of
capsomeres that encloses the viral genome.
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3. Viruses are classified by their type of genetic material. (See Table 19.1) What are
the different forms of genetic material that viruses can have?
Viruses can have DNA or RNA. DNA viruses use the host DNA and RNA polymerases. RNA
viruses use their own polymerase but can take advantage of RNA to serve as a template.
They are also group by whether they are single stranded (ss) or double stranded (ds).
4. Phages infect what type of host? Draw/depict a simple phage.
Phages infect bacteria as their hosts.
5. What does it mean that viruses have a host range?
A host range refers to the range of types of cells and species a virus can infect.
6. Some viral infections (such as polio) cause permanent cell damage, while others
(such as colds) do not. What determines this difference?
Some viruses persist in a cell and do not damage it, so the cell becomes carrier. Others,
when mature, allow the daughter virus cells to break out of the cell and spread, which is
called a lytic cycle.
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7. What does it mean that viruses are obligate intracellular parasites? What things
does the host cell provide for the virus to reproduce?
Viruses are obligate intracellular parasites because they can't grow or reproduce by
themselves and can only reproduce by using the host's machinery.
8. Why can’t RNA viruses use the cell’s enzymes to replicate their viral RNA? So
what else do these viruses have to bring into the host cell?
RNA viruses can't use the cell's enzymes to replicate viral DNA because only their own
polmerases are able to use RNA for a template. It is only DNA viruses that use the host's
polymerases.
9. Why can HIV not be cured? What type of human cells does HIV infect?
HIV can't be cured because new viruses ae actually made inside the host cell and then bud
off from the cell. HIV infects white blood cells.
What is a retrovirus?
A retrovirus is an RNA animal virus that uses reverse transcriptase to transcribe an RNA
template into DNA.
What is reverse transcriptase?
Reverse transcriptase is an enzyme that can generate DNA from an RNA template.
10. What are restriction enzymes and what type of organism has these as defense
against viruses?
Restriction enzymes cut DNA into smaller fragments at a specific site called a restriction
site. Bacteria use them for defense against viruses.
11. Do antibiotics kill viruses?
Antibiotics do not kill viruses; they only kill bacteria.
12. What is an emerging virus?
Emerging viruses are new viruses that appear suddenly.
Where do emerging viruses come from? (3 main ways viruses “emerge”)
Emerging viruses can come from mutations, which happens when existing viruses evolve to
from new strains. They also come from contact between species by jumping form one to
another. Emerging viruses can spread from isolated populations, which increases their
geographic range.
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CHAPTER 20: BIOTECHNOLOGY
1. What is recombinant DNA?
Recombinant DNA is DNA that is formed by uniting segments of DNA from two sources.
2. Describe restriction enzymes that are used in molecular techniques.
Restriction enzymes can be used to map DNA fragments or genomes and can also be used
to identify a specific DNA fragment due to the restriction enzymes it is known to contain.
What are sticky ends?
Sticky ends are formed when restriction enzymes cut DNA, producing a few nucleotides
that are not paired and extend to form an overhang.
If two different DNA molecules are cut with the same restriction enzyme, can they
connected together?
Yes, two different molecules that are cut wit the same restriction enzyme will have
segments of DNA that contain sticky ends able to base pair with each other.
What enzyme can join two DNA molecules together by forming the phosphodiester
bond in the DNA backbone?
DNA ligase can join segments of DNA together by forming the phosphodiester bond in the
DNA strand backbone.
3. What is a plasmid? Where do they come from?
A plasmid is a circular piece of DNA. They come from the cytoplasm of bacteria.
4. What is the purpose of gene cloning? Why might we want to do this?
Gene cloning is performed to express and produce a large amount of a protein
product. Gene cloning can help solve splicing problems and also can produce useful cells
without introns.
Using Figure 20.5, what are the steps in cloning a gene in a plasmid?
1)The DNA is isolated from the organism that contains the desired gene
2) The isolated gene is purified and fragmented with a restriction enzyme.
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3) The DNA fragments are incorporated into plasmids
4)The plasmids are incorporated into bacterial host cells by transformation.
5. Explain how gel electrophoresis separates DNA or proteins by size.
Gel electrophoresis separates DNA or proteins because shorted molecules move faster
through the gel than longer ones as they are attracted to the positive electrode.
6. What is the purpose of PCR?
PCR is used to amplify a gene of interest by making billions of copies of certain DNA
fragments.
Why is Taq polymerase used in PCR? Where does it come from?
Taq polymerase is used because it can function at high temperatures since it comes from
bacteria that live in hot springs.
What happens during the three steps in PCR?
1) Denaturation - hydrogen bonds holding the complementary strands of DNA
together are broken.
2) Annealing – the primers anneal, or attach, to the DNA template.
3) Extension – amplifies the DNA product
Do we need much starting DNA to get PCR going? How is this useful in forensics?
No, only a minute amount of DNA is needed to get PCR going. This is useful in forensics
because DNA can be amplified with only a small amount of cellular material, which is often
all that is available as evidence.
7. Plasmids used as cloning vectors often are made with an antibiotic resistance
gene. WHY?
The antibiotic resistance gene is often incorporated into the plasmid as a marker.
8. What is the purpose of cloning an organism? Why might we want to do this?
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One reason organisms are cloned is to produce embryonic cells that can be used in
research to develop treatments for diseases. It is also used for selective breeding of plant
and animals.
9. Where are totipotent cells and where are they found?
Totipotent cells are singel stem cells that can give rise to any and all types of cells. They
come from cells like zygotes or spores.
10. What type of cells are pluripotent and what does this mean?
Pluripotent cells are self-replicating, coming from human embryo tissue and capable of
giving rise to all three germ layers
11. What is the difference between embryonic and adult stem cells?
Embryonic stem cells are pluripotent and can produce any cell type indefinitely in culture.
Adult stem cells can only led to certain cell types, such as blood cells arising from bone
marrow.
CHAPTER 21: GENOMES & THEIR EVOLUTION
1. When comparing eukaryotic and prokaryotic genomes, in what three ways are
these two major groups different?
1) Genome size: Eukaryotic genomes are far larger than prokaryotic genomes.
2) Number of genes: Eukaryote genomes have more genes due to larger sizes of
genomes, but not significantly more.
3) Gene density: Prokaryotes generally have a higher gene density than eukaryotes.
2. How do eukaryotes get more “bang for their buck” with their coding sequences?
(See p. 443)
Eukaryotes get more bank for their buck with their coding sequences due to extensive
alternative splicing of RNA.
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3. What are two ways in which non-coding DNA is useful in eukaryotes?
It can function as a genetic switch to turn on and off other genes. It can also determine
where transcription factors can attach , which controls transcription of the genetic code
from DNA to RNA.
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