Download 2 C

Big Idea 2:
Biological systems utilize free energy and molecular building blocks
to grow, to reproduce and to maintain dynamic homeostasis.
Enduring understanding 2.C:
Organisms use feedback mechanisms to regulate growth and
reproduction, and to maintain homeostasis.
Essential knowledge 2.C.1:
Organisms use feedback mechanisms to maintain
their internal environments and respond to external
environmental changes.
Subobjective 2.15: I can justify a claim made
about the effect(s) on a biological system at the
molecular, physiological or organismal level when
given a scenario in which one or more
components within a negative regulatory system
is altered.
Subobjective 2.16: I can connect how organisms
use negative feedback to maintain their internal
environments.
52) How does the trp operon regulate
tryptophan synthesis by negative feedback in
bacteria?
Describe feedback inhibition
It is a fast response to changing
need for an enzyme
The product inhibits the function
of the enzyme
Describe enzyme production
By transcribing or deactivating
genes, the amount of enzyme is
regulated
Lots of tryptophan
stops enzyme
function so
tryptophan is not
synthesized
Low tryptophan levels
activate enzyme so
more tryptophan is
synthesized
Lots of tryptophan
turns gene expression
off so tryptophan
levels drop
Low levels of
tryptophan turns gene
expression on so more
tryptophan is
produced
Define operator
A sequence of nucleotides of bacterial DNA usually within
the promoter region upstream of a series of related genes
that acts like a switch by allowing or prohibiting RNA
polymerase to bind to DNA
Define operon
The entire sequence of nucleotides of DNA that includes a
promoter, operator, and a series of genes (in prokaryotes
only)
Define repressor
A protein turns an operator off by binding to it and
preventing transcription
Define regulatory gene
A gene that codes for a protein or RNA that regulates the
expression of one or more other genes
In prokaryotes, regulatory genes usually refer to genes
that code for repressor proteins
Define corepressor
Small intermediate products
of metabolism
A molecule, often a metabolite, that activates a repressor
protein, which causes it to bind to the operator and turn
off transcription
How do corepressors work?
Usually by allosteric activation of the repressor
protein
This causes the
protein to change
shape. This new
shape allows it to
bind to the
operator
A binding site away from the
active site of the protein
http://www.youtube.com/watch?v=d5fD
EUhjo-M
trp operon repressor and attenuation
There is much more detail in this video than you
need to worry about. The following slides will clarify
what you need to know
http://www.youtube.com/watch?v=8aAYtMa3GFU&feature=related
Describe how the trp operon functions when tryptophan
concentration is low
Describe the function of the trp operon when tryptophan is
present
There is always a low level of transcription of the gene for the
repressor protein
What happens to gene expression under the following
conditions and why?
1) No tryptophan
2) Lots of tryptophan
3) Mutation to
regulatory gene
produces a repressor
that will not bind to
the corepressor
4) Mutation to
promoter prevents
RNA polymerase
from binding
53) How is hunger regulated by negative
feedback in mammals?
Hunger is influenced by many
factors and brain organs. You
should learn the role of the
hypothalamus, stomach, and the
hormones leptin and ghrelin
What is the hypothalamus?
The hypothalamus is a brain
organ that regulates the
endocrine system
A collection of glands that
secrete hormones that
regulate virtually all
physiological functions
Define hormone
A chemical signal produced by endocrine organs that
cause cellular change and therefore regulate physiological
function
Define peptide
This term typically refers to a protein composed of a single
chain of amino acids folded up into a functional shape
Ghrelin is a peptide hormone
Leptin is a peptide hormone
Define adipose tissue
A tissue specialized for fat
storage
A type of lipid called a
triglyceride used for long term
energy storage, insulation, and
organ protection
The vagus nerve communicates with many
organs including the stomach
Response:
Hypothalamus feels full
and we stop eating
Stomach empties
Sensor/control center:
hypothalamus
Stimulus:
Eating causes stomach stretching
which inhibits ghrelin secretion
Set point:
Appropriate fuel to meet short
term metabolic demand
Stomach fills up
Stimulus:
Empty stomach secretes
ghrelin
Response:
Vagus nerve causes stomach to churn,
hypothalamus feels hungry and we eat
Sensor/control center:
hypothalamus
Response:
Hypothalamus feels full and
causes us to seek food less often
Fat in adipose
tissue decreases
Sensor/control center:
hypothalamus
Stimulus:
Adipose tissue secretes leptin
Set point:
Appropriate amount of fat in
adipose tissue (long term total
energy budget)
Fat in adipose tissue
increases
Response:
Hypothalamus feels hungry and we
seek food more often
Stimulus:
Adipose tissue stops leptin
secretion
Sensor/control center:
hypothalamus
Subobjective 2.17: I can evaluate data that show
the effect(s) of changes in concentrations of key
molecules on negative feedback mechanisms.
Watch video before
continuing
54) How is blood glucose homeostasis regulated?
What is the function of the pancreas?
It has both endocrine and digestive functions
For now you need to know it’s endocrine function
It regulates blood glucose levels
by sensing blood glucose levels
and secreting the hormones
insulin and glycogen
Define insulin
A hormone secreted by the pancreas that causes cells to
take up glucose
Define glucagon
A hormone secreted by the pancreas that causes the
liver to breakdown glycogen which releases glucose into
the blood stream
Define glycogen
A polysaccharide
composed of glucose
monomers used by
animal cells to store
glucose
Response:
Pancreas secretes insulin causing
cells to take up glucose
Blood glucose
level decreases
Sensor/control center:
Beta cells of pancreas
Stimulus:
Blood glucose level to high
Set point:
Appropriate blood glucose level
Blood glucose levels
increase
Stimulus:
Blood glucose level too low
Response:
Pancreas secretes glucagon causing
liver cells to break down glycogen and
release the glucose molecules
Sensor/control center:
Alpha cells of pancreas
This graph shows blood
glucose levels over time after a
meal. Describe the blood
glucose concentration over
time of the 3 individuals
shown.
The individual represented by
the blue line has the lowest
pre-meal glucose
concentration, and the
individual represented by the
green line has the highest.
The glucose concentration of the individual represented by the red
line increases faster and reaches a higher level then the blue
individual, but their glucose level returns to the pre-meal level,
while the green individual’s glucose level remains high and
achieves the highest concentration
Describe the insulin level and cellular
response to insulin for each
individual
Insulin levels increase in the blue
individual and the cells take up extra
glucose very quickly
Insulin levels increase in the red
individual and the cells take up extra
glucose very slowly
Insulin levels increase a little or not at all in the green individual,
so cells do not take up much or any glucose. Extra glucose is
eliminated slowly in urine
Blood glucose concentration remains
nearly constant in a healthy
individual
Type I diabetes is an autoimmune
disease where the white blood cells
attack and kill the beta cells of the
pancreas
Type II diabetes is a disease where
the cells become resistant to the
hormone insulin
Label each curve type I diabetes, type II diabetes, or healthy and
explain your answer
Type I diabetes
Type II diabetes
healthy
In type II diabetes, the pancreas is healthy, so it senses blood
glucose concentration and secretes the appropriate amount of
insulin. However, the cells are slow to respond to the signal, so
glucose concentration increases to an unsafe level before slowly
returning to baseline concentration
In type I diabetes, the pancreas is not healthy. Insufficient to no
insulin is secreted, so glucose concentration increases to a life
threatening level, and stays high because kidneys are designed to
save glucose in the blood not excrete excess glucose
55) How does the lac operon regulate lactose
metabolism by negative feedback in bacteria?
Define repressible operon
An operon that is usually on and is turned off
when a specific small molecule (metabolite) is
present
Example: trp operon
Define inducible operon
An operon that is usually off and is turned on
when a specific metabolite is present
Example: lac operon
The Lac operon
There is much more detail in this video than you need to worry
about. The following slides will clarify what you need to know
•
http://www.youtube.com/watch?v=oBwtxdI1zvk
Describe the lac operon when lactose is absent
Describe the lac operon when lactose is present
DO NOT memorize the names of the
enzymes involved
What happens to gene expression under the following
conditions and why?
1) No lactose
2) Lots of lactose
3) Mutation to
regulatory gene
prevents repressor
from binding to the
inducer
4) Mutation to operator
prevents repressor
from binding
56) How is the lac operon under positive and
negative gene regulation
Watch and read about the following
animations before continuing
http://www.phschool.com/science/biology_pl
ace/biocoach/lacoperon/energy.html
Click
Click
Click
RNA polymerase has a low affinity for the promoter unless CAP
(catabolite activator protein) is present
When glucose levels are low cAMP concentration increases in
prokaryotes
So the enzymes for
catabolizing lactose
are only synthesized
at a high rate if
lactose is present
AND glucose is low
Lactose is present but bacteria prefer to burn glucose
With glucose present, cAMP concentration is low in prokaryotes
RNA polymerase has some affinity without CAP so a low rate of
transcription occurs
β-galactosidase is an enzyme
necessary for hydrolyzing the
disaccharide lactose into the
monosaccharides glucose and
galactose
Explain what this graph
illustrates
There are 2 dependent
variables being measured
simultaneously
Population size of
bacterial colony
Enzyme needed for
lactose metabolism
activity
***you need to memorize that
glucose is the preferred and first
fuel utilized for energy
production
The independent
variable is time
The population is growing
exponentially
Growth at a faster
and faster rate
The bacteria are eating glucose
We know this because
the enzyme needed for
lactose metabolism is
not very active
Population growth rate slows
The bacteria have eaten all
of the glucose and are
beginning to eat lactose.
We know this because...
The enzyme needed to metabolize
lactose is being transcribed at a higher
rate. You know this because the activity
of the enzyme is increasing
Bacteria population is
growing exponentially again
The bacteria are able to
grow exponentially because
the enzyme necessary to
metabolize lactose is being
transcribed at a high rate
You know enzyme transcription is high
because enzyme activity is increasing
exponentially
There are 2 pieces of
information from this graph
that tell you bacteria prefer
to metabolize lactose over
glucose
There is much more
lactose available than
glucose, yet they eat
the glucose first
You know they ate the glucose first because the
enzyme needed to metabolize lactose increases
AFTER an initial population growth surge and once
enzyme activity increases, the population grows
again
Subobjective 2.18: I can make predictions about
how organisms use negative feedback
mechanisms to maintain their internal
environments.
57) How would a bacterium respond to changes
in the components of the lac and trp operons?
Predict how a bacterium would maintain homeostasis in an
environment with lots of tryptophan present and explain your logic
It would stop making tryptophan because tryptophan binds
allosterically to the repressor protein causing it to bind to the
operon and stop transcription
Predict how a bacterium would maintain homeostasis in an
environment with lots of lactose present and explain your logic
It would start making the enzymes needed to metabolize
lactose because lactose binds to the repressor protein
causing it to release from the operon and therefore allow
transcription
Predict how a bacterium would maintain homeostasis in an
environment with little tryptophan present and explain your logic
It would start making tryptophan because the repressor doesn’t
have the right shape to bind to the operator unless it binds to
tryptophan. Repressors do not bind permanently to operators
and corepressors. As tryptophan concentration decreases,
trypophan would disengage with the repressor and tryptophan
synthesis would begin
58) How would an organism maintain blood
glucose homeostasis if one of the components
were changed?
Explain what would happen if there was a mutation in the gene
that codes for the liver enzyme glycogen phosphorylase. This
enzyme hydrolyzes glycogen into glucose monomers.
After a meal, excess glucose would be taken up by liver
cells and stored as glycogen in response to the hormone
insulin
Between meals, the pancreas would secrete glucagon to
maintain blood glucose levels
However, the liver would not be able to respond to the
chemical signal so blood glucose levels would remain
low
Low insulin levels cause the
hypothalamus to feel hungry
You would seek out food to
increase blood glucose levels
The liver would enlarge as it
stores more and more glycogen
59) How would an organism maintain energy
homeostasis if one of the components were
changed?
What would happen if the leptin receptors in the hypothalamus did
not respond to leptin?
This is likely one of the causes of obesity. Obese people have
leptin levels that are higher than the quantity of adipose
tissue would predict. It is likely that the hypothalamus is not
responding to the signal from leptin saying, “we have enough
energy stored in our adipose tissue,” resulting in more energy
consumed than energy used (overeating).
The end result is a higher energy level homeostasis set point.
Most people stay at about the same weight year after year.
60) Why do people
pee a lot when
they drink beer?
Define pituitary gland
It is called the master
control gland because
its hormones regulate
many other endocrine
glands
Define signal transduction
The
biochemical
process
where a
signaling
molecule
triggers a
cascade of
events that
leads to a
cellular
response
Watch video before continuing
Response:
Pancreas secretes ADH (antidiuretic hormone)
causing the kidneys to conserve water
Osmolarity of
interstitial fluid
decreases
Sensor/control center:
Hypothalamus
Stimulus:
Interstitial fluid is hypertonic
compared to the cytosol of cells
Set point:
Cells in osmotic equilibrium with
interstitial fluid
Osmolarity of interstitial
fluid increases
Stimulus:
Interstitial fluid is hypotonic compared to
the cytosol of cells
Response:
Pancreas stops secreting ADH
(antidiuretic hormone) causing the
kidneys to excrete water
Sensor/control center:
Hypothalamus
Watch video for clarification
https://www.youtube.com/watch?v=qfWx8msgHqM
Consuming alcohol
inhibits the secretion of
ADH by the posterior
pituitary gland
When aquaporins are
present, the water in
the lumen of the
nephron moves down
its osmotic gradient
out of the nephron
and ultimately back to
the interstitial fluid via
the lymphatic system
Why does inhibiting ADH (antidiuretic hormone) make people
pee?
ADH is a
hormone that
causes a signal
transduction via
the secondary
messenger cAMP.
cAMP causes a
signaling cascade
that results in
aquaporins being
embedded in the
nephrons of the
kidneys
Alcohol prevents the signal
to embed aquaporins
Without aquaporins, lots of
water is added to urine
Subobjective 2.19: I can make predictions about
how positive feedback mechanisms amplify
activities and processes in organisms based on
scientific theories and models.
61) Why does all the fruit on a plant ripen at the
same time?
Define positive feedback
A mechanism where a stimulus causes a response and the
response increases the stimulus
Define ethylene
A gas that is also a plant
hormone involved in stem
elongation apoptosis and
fruit ripening
Sensor/control center:
unknown
Stimulus:
Ripening fruit produces even more
ethylene
Response:
Fruit begins to ripen (cell wall is broken down,
starch converted to sugar, attractive colors and
scents produced)
Sensor/control center:
unknown
Stimulus:
Fruit cells secrete ethylene
Set point:
Unripe fruit (seeds mature and ready for
dispersal)
Stimulus is Gone
All fruit on plant ripens at the
same time and seed dispersing
organism eats the fruit
Sensor/control center:
unknown
Stimulus:
Ripening fruit produces even more
ethylene
Response:
Ripening accelerates
A gene necessary for producing ethylene is disabled in the
fruit producing tissues of an apple tree. Explain what would
happen and why.
The fruit would never ripen because no ethylene
would be produced. This hormone is essential for
fruit to ripen. If you exposed the fruit to ethylene gas,
it would begin to ripen.
An unripe apple is placed in a closed paper bag. Explain
what would happen and why.
The ethylene gas would accumulate in the bag which would
accelerate the ripening process
A crate of unripe apples are aerated with carbon dioxide.
Explain what would happen and why.
The apples would ripen at a slower rate because the
aeration would disperse the ethylene gas quickly and
ensure the fruit would get a weak ripening signal
Subobjective 2.20: I can justify that positive
feedback mechanisms amplify responses in
organisms.
62) How do organisms stop bleeding?
Watch the video before
continuing
https://www.youtube.com/watch?
v=R8JMfbYW2p4
Define platelet
A bit of a cell that is a component of blood plasma
and is involved in clotting
Define collagen
A fibrous structural protein with many functions. It
interacts with platelets initiating blood clotting
Define thrombin
An enzyme produced by the coagulation cascade set
in motion by clotting factors released by platelets that
are activated by collagen
Define fibrin
A protein derived from fibrinogen by the enzyme
thrombin that forms long fibers that reinforce and
seal the platelet plug
Sensor/control center:
Platelets
Stimulus:
Sticky platelets recruit more platelets
Clotting factors produce thrombin which activates fibrin
which seals the blood vessel. Thrombin activates further
production of thrombin.
Response:
Platelets change shape becoming “sticky”
and release clotting factors
Sensor/control center:
platelets
Stimulus:
Platelets contact collagen
Set point:
Plasma components not in contact with
interstitial space
Stimulus is Gone
Set point:
Platelets not in contact with
interstitial space
Blood vessel is completely
sealed by fibrin
Even more thrombin is produced from the
actions of clotting factors and thrombin itself
causing more activation of fibrin
Response:
Platelets produce even more clotting
factors
Watch the video if you still need clarification
https://www.youtube.com/watch?v=RQpBj8ebbNY
63) How does child birth illustrate positive
feedback?
Define oxytocin
A hormone produced by the posterior pituitary gland. It
is important for social bonding in mammals and causes
uterine contractions during child birth.
Watch video
before
continuing
http://www.johnwiley.net.au/highered/interactions/media/Foun
dations/content/Foundations/homeo4a/bot.htm
Sensor/control center:
Hypothalamus
Stimulus:
Increased stretching of cervix
Oxytocin causes uterine
contractions
Response:
Hypothalamus causes the posterior
pituitary to secrete oxytocin
Sensor/control center:
Hypothalamus
Stimulus:
Stretching of cervix
Set point:
Normal sized uterus
Stimulus is Gone
Set point:
Normal sized uterus
Baby is
delivered
Stimulus:
Even more stretching of cervix
More oxytocin causes stronger uterine
contractions
Response:
Hypothalamus causes the posterior
pituitary to secrete more oxytocin
Big Idea 2:
Biological systems utilize free energy and molecular building blocks
to grow, to reproduce and to maintain dynamic homeostasis.
Enduring understanding 2.C:
Organisms use feedback mechanisms to regulate growth and
reproduction, and to maintain homeostasis.
Essential knowledge 2.C.2:
Organisms respond to changes in their external
environments.
Subobjective 2.21: I can justify the selection of
the kind of data needed to answer scientific
questions about the relevant mechanism that
organisms use to respond to changes in their
external environment.
64) How do plants move?
Define phototropism
The movement towards or away from light
Define auxin
A plant hormone that stimulates stem elongation in low
concentration only
Charles Darwin and his son Francis Darwin conducted some of
the first experiments on phototropism (unnecessary
information, but I couldn’t help myself)
This video is sped up 1,800 times
We know plants
grow towards the
direction of light
Cut the tip and no
growth towards the
light
Opaque (not clear)
covering and no
growth towards
light
Transparent
covering
Opaque covering
around the curved
area
A barrier that
allows diffusion
A barrier that
DOES NOT allow
diffusion
The tip of the
plant is placed on
some agar which
absorbs chemicals
Agar not exposed to
tip (control) added to
de-tipped plant
Agar added to detipped plants
directly above
and to either side
The cells on this side of the
plant are relatively long
The cells
on this
side of the
plant are
relatively
short
Stem elongation on the side of the plant AWAY from the
light source causes the plant to grow TOWARDS the light
How do the experiments above prove how cell elongation is
regulated and therefore how phototropism is regulated
We know the tip of the plant regulates phototropism
because plants don’t grow towards the light if it is
removed or if light is prevented from reaching it, while
the amount of light reaching other parts of the plant has
no effect on phototropism
We know some chemical is produced by the tip of the
plant and transported to the part of the plant that bends
because if you insert a barrier that prevents diffusion of
substances from the tip, no phototropism occurs
We know a substance (specifically auxin) produced by the
tip of the plant causes phototropism because
phototropism occurs in plants where the tip is removed
and chemicals from the tip of the plant are added
Subobjective 2.42: I can pose a scientific question
concerning the behavioral or physiological
response of an organism to a change in its
environment.
65) How is the flagellum involved in chemotaxis
and phototaxis?
Define chemotaxis
The movement of an
organism in response
to a chemical signal
Define flagellum
A whip-like structure
used for movement.
This structure evolved
independently in the 3
domains of life
Define phototaxis
An organism moving towards or away from light
Use the video to explain how bacteria use chemical signals
to guide their movement
https://www.youtube.com/watch?v=h4lv7cBYVug
Bacteria move randomly in a solution without a
chemical gradient
When the flagella are rotating counter clockwise, they
move the bacterium in one direction
When their flagella rotate clockwise, they tumble,
change direction randomly, and start moving again
Their flagella stay rotating counter clockwise longer
when going against a chemical gradient than when
going down a chemical gradient
This results in the tendency to move towards a
chemical signal
In the presence of a chemical such
as glucose that attracts bacteria, a
signal transduction that
phosphorylates the flagellum
causing clockwise rotation is
inhibited. This prevents the cell
from tumbling so it continues in the
direction of the chemical.
In the absence of a chemical such
as glucose that attracts bacteria,
a signal transduction that
phosphorylates the flagellum
causing clockwise rotation which
causes the cell to tumble and
randomly change direction.
How do protists such as dinoflagellates “know” where light
is?
“eye spot” pigments
absorb and direct
the flagellum to
propel the protist to
sunlight
flagellum
https://www.youtube.com/watch?v=NepvSAJhlkw
Start at 6:05
Chemotaxis of white blood cells in the inflammatory
response
https://www.youtube.com/watch?v=hE37G6zVkFY