Download Unfinished Material - Answer Key

Unfinished Material - Answer
Key
Supplemental Instruction
Iowa State University
Leader:
Course:
Instructor:
Date:
Brandon
Biol 212
Dr. Coffman/Manz
4/30/2017
Unfinished Exam 2 Material
Chapter 47
 How are hair cells triggered?
- Pressure waves bend stereocilia.

How do hair cells convert pressure waves (sound waves) into electrical and chemical
signals?
- Pressure waves bend stereocilia
- Potassium channels open in response to bending.
- Membrane depolarizes due to influx of potassium ions.
- Depolarization triggers inflow of calcium ions
- Synaptic vesicles fuse with plasma membrane
- Neurotransmitter is released and diffuses to afferent neuron

How are sound waves transmitted from the external environment to the hair cells?
- Sound waves enter into canal
- The waves hit the tympanic membrane (ear drum)
- This causes the tympanic membrane to vibrate back and forth at the same frequency
as the sound wave
- The vibrations from the tympanic membrane are passed to the three tiny bones in the
middle ear (ear ossicles)
- The ear ossicles vibrate against one another
- The last ossicle (stapes) vibrates against the oval window
- The oval window oscillates (moves back and forth) in response, generating waves in
the fluid inside the cochlea
- The pressure waves are sensed by hair cells in the cochlea

Why are the eyes of some animals different from each other?
- Animals use their eyes to exhibit different behaviors such as predation and escaping
predation.
- Animals live under different environmental conditions in which the necessity of eyes
varies.

What effect would a stiffened lens have on vision?
- Would have blurry vision because the lens cannot focus light (presbyopia).

What effect would defective red, green, or blue cones have on vision?
- Would not be able to see certain colors or certain shades of colors.

Describe the anatomical pathway for odor detection?
- Airborne molecules called odorants reach the nose and diffuse into a mucus layer in
the roof of the nose.
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Olfactory neurons are activated by the binding of the odorants to membrane-bound
receptor proteins.
Axons from the olfactory neurons project up tot eh olfactory bulb, where the olfactory
signals are processed and interpreted.

How do olfactory receptors detect the large variety of different molecules?
- Each olfactory neuron has only one type of receptor and neurons with the same type
of receptor are linked to distinct regions in the olfactory bulb of the brain.

In which environment is electroreception commonly used in?
- Aquatic environments
- Water is a good conductor of the weak electrical impulses given off by animals.
Chapter 48
 What is the organization of the components that make up muscle tissue?
- Muscle tissue
- Muscle tissue made up of bundle of muscle fibers
- Within bundle is single muscle fiber
- Muscle fiber made up of myofibrils
- Myofibrils contain many sarcomeres

What is the sliding filament model?
- The hypothesis that the thick filaments (myosin) and the thin filaments (actin) slide
past one another during contraction.
o So the sarcomere shortens (contracts); the lengths of the thick filaments
(myosin) and the thin filaments (actin) themselves do not change.

What is the process of actin-myosin interaction during muscle contraction?
- Look at Figure 48.4 in the book.

How do troponin and tropomyosin prevent muscle contraction? What effect do calcium
ions have on troponin and tropomyosin?
- The conformation of troponin and tropomyosin blocks the myosin binding sites.
- Calcium ions bind to troponin and cause a conformational change, exposing the
myosin binding sites, allowing myosin to bind to actin.

What are the functions of smooth muscle?
- Lungs – controls size of airways.
- Blood vessels – can contract or relax to alter blood-flow patterns and blood pressure.
- Digestive system, Urinary bladder – layers of smooth muscle in the gastrointestinal
tract help mix and move food.
- Reproductive system – uterine smooth muscle is responsible for expelling the fetus.

What is the function of cardiac muscle?
- Responsible for pumping blood throughout the body.
- Makes up walls of the heart.

What is the function of skeletal muscle?
- Moving the skeleton.
- Attached to the skeleton.
Unfinished Exam 3 Material
Chapter 17
 How does transcription differ in eukaryotes in comparison to bacteria?
- Eukaryotes have three polymerases – RNA polymerase I, RNA polymerase II, RNA
polymerase III
o Each polymerase transcribes only certain types of RNA in eukaryotes.
o RNA polymerase II is the only polymerase that transcribes protein-coding
genes.
- Promoters in eukaryotic DNA are more diverse than bacterial promoters.
o Eukaryotic promoters include the TATA box and other important diverse
sequences.
- Eukaryotic RNA polymerases recognize promoters using basal transcription factors
instead of a sigma protein.
- Termination of eukaryotic protein-coding genes involve a poly-A signal.

Describe the process of RNA splicing.
- SnRNPs (small nuclear ribonucleoproteins) bind to the start of the intron marked by
bases G and U, and bind towards the end of the intron marked by base A.
- Other snRNPs assemble with the initial SnRNPs bound to bases G and U, and bound
to base A. This assembly forms a spliceosome.
- The intron is cut between the G base and the U base, forming a loop and a single
stranded stem of the intron called a lariat.
- The lariat is released, the exons that were located on each side of the intron join
together via a phosphodiester linkage.
o This produces the continuous coding sequence known as mRNA.

What is the function of the 5’ cap and the poly(A) tail in mRNA?
- Protect mRNAs from degradation by ribonucleases and enhance the efficiency of
translation.
o Ribonucleases = enzymes that degrade RNA.

Compare and contrast where and when the process of translation occurs in bacteria and
eukaryotes.
- In bacteria, translation occurs at the same time that transcription occurs
o This happens because there is no nuclear envelope to separate the processes.
- In eukaryotes, translation and transcription occur at separate times and in separate
locations.
o Transcription is conducted in the nucleus to produce a mature mRNA; the
mRNA is then exported to the cytoplasm of the cell where translation occurs.

What is the function of tRNAs?
- Transfer amino acids from the RNA to a growing polypeptide.
- tRNAs act as an interpreter during translation
o This allows amino acids to interact with an mRNA template.

Describe the three step protein synthesis sequence by ribosomes?
1. An aminoacyl tRNA diffuses into the A site; if its anticodon matches a codon in
mRNA, it stays in the ribosome.
2. A peptide bond forms between the amino acid held by the aminoacyl tRNA in the A
site and the growing polypeptide, which was held by a tRNA in the P site.
3. The ribosome moves down the mRNA by one codon, and all three tRNAs move one
position within the ribosome. The tRNA in the E site exits; the tRNA in the P site
moves to the E site; and the tRNA in the A site switches to the P site.
Bacterial Control of Gene Expression (Chapter 18)
 What are two ways that transcription can be regulated? Describe what happens during
each method.
- Negative control: occurs when a regulatory protein called a repressor binds to DNA
and shuts down transcription.
- Positive control: occurs when a regulatory protein called an activator binds to DNA
and triggers transcription.

If lactose is present and glucose is absent, will transcription occur if there is a mutation in
the promoter of the lac operon? Why?
- No, the promoter is responsible for allowing RNA polymerase to bind, and RNA
polymerase is responsible for synthesizing mRNA. So if there is a mutation in the
promoter, that means that RNA polymerase will not be able to bind, therefore, mRNA
will not be able to be synthesized.

If lactose is present and glucose is absent, will transcription occur if there is a mutation in
the operator of the lac operon? Why?
- Yes, the operator is responsible for allowing the repressor to bind; so if the repressor
cannot bind, then transcription will occur.

Will transcription occur if there is a mutation in the lacI gene? Why?
- Yes, the lacI gene is responsible for synthesizing the repressor; therefore, a mutation
would mean that the repressor is not synthesized, so transcription will occur.

If a mutation occurs that prevents the binding of the inducer, will transcription be able to
occur?
- No, an inducer is a small molecule that triggers transcription of a specific gene; so if
the inducer is unable to bind, then transcription cannot be initiated.

If there is a mutation of the lacY gene encoding galactoside permease that causes
galactoside permease to be unrecognized and inactivated in the presence of glucose, will
transcription occur if:
a. Lactose is absent and glucose is absent? Why?
- No, there is nothing present to remove the repressor.
-
-
b. Lactose is present and glucose is absent? Why?
Yes, lactose can come into the cell and remove the repressor.
c. Lactose is present and glucose is present? Why?
Yes, even though glucose is present, the mutation allows for lactose to pass into
the cell unnoticed and remove the repressor.
Eukaryotic Gene Regulation (Chapter 19)
 How does alternative splicing allow different proteins to be produced from the same
gene?
- When splicing occurs, selected exons are removed from the primary transcript along
with the introns; however, the same primary RNA transcript can yield more than one
kind of mature, processed mRNA, consisting of different combinations of exons.
- If you have a different combination of exons, therefore different combinations of
mRNA, then the polypeptides translated will be different.
- So splicing the same primary RNA transcript in different ways will produce different
mature mRNAs, and therefore produce different proteins; and this is what is known as
alternative splicing.

What is RNA interference and what happens during this process?
- RNA interference is a form of gene regulation that directly prevents mRNA from
undergoing translation.
- RNA polymerase is going to transcribe genes that code for RNAs that double back on
themselves to form a hairpin structure.
- The double stranded hairpin is going to be moved outside of the nucleus and into the
cytoplasm.
- In the cytoplasm, an enzyme is going to cut the hairpin loop, forming a doublestranded RNA molecule.
- The double-stranded RNA is going to bind to a group of proteins called the RISC
protein complex (RNA induced silencing complex) and one strand of the RNA is
going to be degraded.
o This is called a microRNA (miRNA)
- The miRNA is going to bind to the complementary sequences of the target mRNA.
- If the match between the miRNA and the target mRNA is perfect, then the target
mRNA will be destroyed by being cut in half by an enzyme from the RISC protein
complex.
- If the match between the miRNA and the target mRNA is not perfect, then the mRNA
will not be destroyed, but translation will be inhibited.