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BIOL 1000 Study Guide - Final Guide: Precursor Mrna, Plasmid, Pyruvic Acid

Course Code
BIOL 1000
Y I Sheng
Study Guide

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Fial Ea LOs
Light and Life
1. Describe the molecular basis of vision. What is the molecular basis and sequence of light
activation, retinal and opsin protein conformational change, and generation of vision? What is
the molecular basis and function of photoreceptors?
Light enters the pupil; and strikes a light sensitive detector called the retina which is located along
the inner surface of the back of the eye. The light is mapped as in image along the surface of the retina
by activating a series of light sensitive cells known as rods and cones. These photoreceptor cells convert
the light into electrical impulses which are transmitted to the brain via nerve fibres. For an image to be
recognized, many photo receptor cells will be activated and the visual information will be transported to
the brain via numerous nerve fibers. The brain then determines, according to which nerve fibers carried
the electrical impulse, which photoreceptors were activated by the light and then creates a picture. Thus
the saying, we see with our brain, and not our eyes. The retina is lined with millions of photoreceptor
cells that consist if two types: Cones (6 million) provide colour information and sharpness of images, and
Rods (120 million) which are extremely sensitive detectors of white light to provide night vision. In short
these photoeeptos otai heials that hage he thee hit  light. This auses a eletial
signal which is then sent to the brain along the optic nerve.
2. How color is detected by eyes?
Cone cells in the retina of the eye allow light of different wavelengths to be interpreted as colour to
the brain. To produce signals for colour vision, the retinal must stimulate the opsin proteins, but this
cannot occur while the retinal is in its cis transformation, and must isomerize into the trans
transformation. There are three types of proteins in cone cells for colour sensing, S, M, and L. S is for
short wavelength of blue light, M is for medium wavelength for green light, and L is for long wavelength
of red light. The L opsin differs from the M opsin n three significant places in the amino acid sequence:
Position 180: alanine to serine, Position 277: phenylalanine to tyrosine Position 285: alanine to
threonine. The lack of L opsin will result in colour blindness, the outcome is either you will have
dichromatic vision, with the lack of the L opsin. The gene coding for the s opsin(SWS) is located on
chromosome 7. The gene coding for the M(MWS) and L(LWS) opsin are located on the X-chromosome.
The L gene arose through gene duplication and gene mutation of the M gene on the X-chromosome.
3. How does light synchronize hormones in the brain to regulate circadian rhythm?
Many physiological and behavioral responses are operated on a 24-hour cycle, synchronized with
our day and night cycles. These daily changes of physiological and behavioral responses are known as
circadian rhythms. They are controlled by an internal, organism based clock which is set by light
(synchronized by light). A key attribute of all biological clocks is that while they are set by the external
light environment, they can run a long time independent of external conditions, a phenomena known as
free running.
Physically the circadian clock is located in the superchiasmatic nucleus (SCN) in the hypothalamus of
the brain, one for each brain hemisphere. The SCN is a tiny pinhead sized are containing just 20,000 or
so very small neurons, but it has the responsibility for sending signals to several other parts of the brain
to regulate the daily sleep wake cycle, body temperature, hormone production, and other functions.
The circadian clock checks its accuracy each day using external Zeitgebers, principally the light dark
cycle. Exposure to natural daylight stimulates a nerve pathway from special photoreceptive ganglion
cells in the retina of the eye cells that are totally separate from rods and cones, our eyes use to generate
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1. Describe and name the different modes of nutrition employed by different organism.
A. Heterotrophic Nutrition Unlike autotrophs who manufacture their own food, heterotrophic
organisms obtain food from other organisms. As heterotrophs depend on other organisms for
their food, they are called consumers, all animals and non green plants fall under this category.
B. Autotrophic Nutrition In autotrophic nutrition, an organism makes its own food from simple
raw materials.
Auto = Self, Chemo = Chemical, Hetero = Both. With this in mind, Photoautotrophs feed themselves
using light to make food. Chemoautotrophs feed themselves by extracting energy from chemicals. This
term refers to organisms like those found at deep sea vents, that extract from H2S instead of utilizing
H2O. Chemoheterotrophs are unable to utilize CO2 to form their own organic compounds, their carbon
source is rather derived from sulfur, carbs, lipids, and proteins. Photoheterotrophs feed themselves in
two ways: they make food using light and they consume food molecules or organisms from their
2. Describe the theory of evolution.
The theory of evolution encompasses the well established scientific view that organic life on our
planet has changed over long periods of time and continues to change by a process known as natural
selection. The change of an organism over a long period of time, able to be passed to this ogaiss
descendants. The two primary mechanisms are genetic mutation and natural selection. Basically a gene
in an organism has mutated or changed and this organism is therefore different from its parents. If this
organism survives long enough to reproduce, its mutation is passed onto its children, and eventually
becomes a part of the species. If it does not reproduce, then the mutation dies with it. Evolution
occurred in species in 4 ways: 1: Variation There is a variation In every population with regard to
heritable traits. 2: Advantage: Organisms compete for limited resources and certain traits offers survival
advantage. 3: Reproduction - Organisms produce more offspring that can survive. 4: Inheritance
Organisms pass genetic traits onto their offspring.
3. Describe Natural Selection, Provide a biological example of this process.
Natural Selection is the evolutionary process by which alleles that increase the likelihood of survival
and the reproductive output of the individuals that carry them become more common in subsequent
generations (Think survival of the fittest).
Examples: In an ecosystem, some giraffes have long necks and others have short ones. If something
caused low-lying shrubs to die out, the giraffes with short necks would not get enough food. After a few
generations, all the giraffes would have long necks.
Insects become resistant to pesticides very quickly, sometime in one generation. If an insect is
resistant to the chemical, most of the offspring will also be resistant. Considering that insect generations
can be a matter of weeks, insects in an area can become immune to a chemical within months.
4. Using a phylogenetic tree to identify closeness or common ancestor in evolution.
Phylogenetic trees represent evolutionary relationships among a set of organisms or groups of
organisms, called taxa. That are believed to have a common ancestor.
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The tips of the phylogenetic tree represent
groups of descendants taxa (often species).
The internal nodes of the tree represent the
common ancestors of those descendants.
The tips are the present and the internal
nodes are the past. The edge lengths in
some trees correspond to time estimates
evolutionary time.
Two descendants that split from the same node
are called sister groups. In the trees above,
Species A and B are sister groups they are
each others closest relatives which means that:
they have a lot of evolutionary history in
common and very little evolutionary history
that is unique to either one of the two sister
species and that they have a common ancestor
unique to them
Many phylogenies also include an outgroup a taxon outside
the group of interest. All the members of the group of interest
are more closely related to each other than they are to the
outgroup. An outgroup can give you a sense of where on the
bigger tree of life the main group of organisms falls.
Phylogenetic trees classify organisms into clades. The
phylogenetic tree depicted here identifies four clades.
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