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Ap Biology Discussion Notes
Monday 5/2
Goals for the Day
• Be able to tie together multiple
disciplines in biology
• Be prepared for the AP test
Question of the Day
5/2
• Is it possible that things that are
advantageous in one environment are
“maladaptive” or disadvantageous in
others? Give an example to explain
your answer.
Dichromatic Vision
Trichromatic Vision
Day 3
The Cell Biology of
Color Vision in Monkeys
How Does Color Vision Work?
Cell Biology
• The retina has two types of cells: rod cells and
cone cells. There are more rod cells than cone
cells. Cone cells are responsible for color
vision.
How Does Color Vision Work?
Cell Biology
How Does Color Vision Work?
How Does Color Vision Work?
There are three types of cone cells.
More accurately, any given cone cell may be
using only one of three types of transmembrane
opsin proteins.
Three types of Cone Cell
• Different kinds of opsin proteins embedded in
the membrane of cone cells make each kind
able to receive different information from the
others.
• Central Dogma of Molecular Biology:
DNA  RNA  Protein
Genes code for…. Proteins which lead to function!.
Chromatic Vision: Cone Cells
Cone cells in the retina of the eye allow light of different
wavelengths to be interpreted as color in the brain. The
following slides describe how this pathway works.
The Brain
Light Waves
Color
The Cone cell
•
To produce the signal for color vision, retinal must
stimulate the opsin protein but this cannot occur while
the retinal molecule is in its cis- conformation.
•
When 11-cis-retinal absorbs a photon (a basic unit of
light), it changes from 11-cis-retinal to All-trans-retinal.
•
All-trans-retinal stimulates the opsin in the membrane
of the cone cell.
•
The cone cell sends a signal to the brain, resulting in
vision.
Opsin Image modified from Scientific American, April 09
All-trans-retinal
11-cis-retinal
Opsin
•
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When
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light),
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the retinal molecule is in its cis- conformation.
The Cell Biology of
Color Vision in Monkeys
• A retinal chromophore opsin molecule
is activated by a photon of light. This
in turn stimulates the opsin protein
that tells the cone cell to send a signal
to the brain.
The Role of Opsins
There are three types of opsins:
Short Wave Sensitive (SWS)
Medium Wave Sensitive (MWS)
Long Wave Sensitive (LWS)
An individual possessing only
SWS and MWS opsins will have
dichromatic vision.
An individual possessing SWS,
MWS and LWS opsins will have
trichromatic vision.
How Does Color Vision Work?
How Does Color Vision Work?
- When cone cells with the MWS opsin protein are
stimulated, green color is perceived by the brain.
- When cone cells with the LWS opsin protein are
stimulated, red color is perceived by the brain.
- When cone cells with the SWS opsin protein are
stimulated, blue color is perceived by the brain.
- When cone cells with the MWS opsin protein are
stimulated AND cone cells with the LWS opsin are
stimulated, yellow color is perceived by the brain.
How Does Color Vision Work?
- When cone cells with the MWS opsin protein are
stimulated AND cone cells with the SWS opsin are
stimulated, violet color is perceived by the brain.
- When cone cells with the SWS opsin protein are
stimulated AND cone cells with the LWS opsin are
stimulated, cyan color is perceived by the brain.
- When all cone cells are stimulated in equal
proportions, white light is perceived by the brain.
- We perceive different shades of light when our
different types of cone cells are stimulated in
different proportions.
Chromatic Vision: Opsins
What is the
building block
( ________mer) of
an opsin protein?
3D Visualization
Chromatic Vision: Opsins
3D Visualization
2D Visualization
The opsin protein is composed of a string of amino acids.
Each green dot in the 2D visualization represents one amino acid.
Opsin Structure
MWS
opsin
LWS
opsin
The LWS opsin differs from the MWS opsin in three
significant places in the amino acid sequence:
Position 180: alanine to serine
Position 277: phenylalanine to tyrosine
Position 285: alanine to threonine
Opsin Structure
The LWS opsin differs from the MWS opsin in three
significant places in the amino acid sequence:
Position 180: alanine to serine
Position 277: phenylalanine to tyrosine
Position 285: alanine to threonine
MWS
opsin
LWS
opsin
Opsin Response to Light
The responses to light of
each opsin protein (S, M
and L) in trichromats
are shown to the right.
Note how similar the
curves look for M and L.
The L curve is shifted by
about 30 nm response
maximum to the right
(longer wavelength).
Opsin Response to Light
A third opsin provides
another channel for
sending color signals to
the brain.
Three opsin proteins allow
the eye to detect a richer
variety of light
wavelengths resulting in
the ability to distinguish
more colors.
The Genetics of
Color Vision in Monkeys
The Genetics of Color Vision
• The section of DNA on a chromosome that
codes for an opsin protein is called an opsin
gene.
Location of Opsin Genes
The gene coding for
the SWS opsin
protein is located on
chromosome #7.
The gene coding for
the MWS and LWS
opsins are located on
the X-chromosome.
Evolution of LWS Opsin Gene
The LWS gene arose
through gene
duplication and gene
mutation of the MWS
gene on the Xchromosome.
Origin of the LWS Opsin Gene
The LWS gene arose
through gene
duplication and gene
mutation of the MWS
gene on the Xchromosome.
Gene Duplication
Unequal Crossing Over
(Meiosis, Prophase 1)
Origin of the LWS Opsin Gene
The LWS gene arose
through gene
duplication and gene
mutation of the MWS
gene on the Xchromosome.
Origin of the LWS Opsin Gene
The LWS gene arose
through gene
duplication and gene
mutation of the MWS
gene on the Xchromosome.
The MWS Opsin Gene
The MWS Opsin Gene
1092 Nucleotides
The MWS Opsin Gene
 GTCGTTAGATAG 
1092 Nucleotides
MWS Opsin Gene vs. LWS Opsin Gene
Each opsin gene is exactly the same length
(1092 nucleotides)
MWS Opsin Protein vs. LWS Opsin Protein
These 1092 nucleotides undergo transcription
and translation and result in a protein that is
364 amino acids in length.
MWS Opsin Gene vs. LWS Opsin Gene
(mutations at the nucleotide level that result in protein functional changes)
GT
TA
GA
• Three simple substitution mutations change
the properties of the opsin protein.
• Now, rather than being maximally stimulated
at ~534nm, the resulting opsin protein is
maximally stimulated at ~564nm.
What difference does this make at the
protein level?
Evolution of LWS Opsin Gene
The LWS gene arose
through gene
duplication and gene
mutation of the MWS
gene on the Xchromosome.
Fact or Fiction?
A monkey researcher in South America
discovered that some monkey females are
trichromatic.
1.
2.
3.
4.
Definitely Fact
Possibly Fact
Possibly Fiction
Definitely Fiction
The Case of Trichromatic Females
Genes code for opsin proteins; the opsin
proteins facilitate color vision.
Genes code for opsin proteins; the opsin
proteins facilitate color vision.
• Some new world monkey species have two
different MWS alleles. If a female is
heterozygous for these alleles she can produce
three different types of opsin protein. This
means that SOME females in SOME new world
species are trichromatic. Females that are
homozygous for the MWS gene on the xchromosome are dichromatic.
The Phylogenetics of
Color Vision in Monkeys
Biogeography of Global Monkeys
Photo: Frans de Waal, M Arunprasaad, D Wright, P Gonnet, L DeVoldor, W Endo
Monkeys of the World
Phylogenetics – Exploring Relationships Among Species
Geology: Plate Tectonics and Drift
Wooly Monkey
Spider Monkey
Sakis
Marmoset
Owl Monkey
Squirrel Monkey
Capuchin
Colobus
Langur
Mona
Mangabey
Baboon
Rhesus
Gibbon
Orangutan
Gorilla
Chimpanzee
Human
Continents Split
50 Million Years Ago
Color Vision Evolves!
Gene Duplication and Mutation
Primates In New/Old World
55 Million Years Ago
Rise of Primates
75 Million Years Ago
Ancestral Characteristic
• An Ancestral Characteristic is a characteristic
shared through common ancestry. A
characteristic that is thought to have also been
present in the common ancestor.
• In primates for example DICHROMATIC vision
would be considered an “ancestral characteristic”
while trichromatic vision would be considered a
derived characteristic (one not present in the
common ancestor of 2 groups)
Wooly Monkey
Spider Monkey
Sakis
Marmoset
Owl Monkey
Squirrel Monkey
Capuchin
Colobus
Langur
Mona
Mangabey
Baboon
Rhesus
Gibbon
Orangutan
Gorilla
Chimpanzee
Human
Continents Split
50 Million Years Ago
Color Vision Evolves!
Gene Duplication and Mutation
Primates In New/Old World
55 Million Years Ago
Rise of Primates
75 Million Years Ago
Day 3 Questions