Week 5 Flashcards
What is a nicotinic
acetylcholine receptor?
a ligand
gated ion channel.
What is the function of the a ligand
gated ion channel?
An ion channel which is activated that allows sodium ions to enter the cell.
An ion channel which is either activated or deactivated after it binds.
What is Acetylcholine?
is a neurotransmitter at synapses between
motor neurones and muscle cells
What happens when acetylcholine is binded to the nicotinic acetylcholine receptor (Na+ ion channel)?
results in channel opening and Na+ influx. This results in the generation of an action potential causing Ca2+ influx and muscle contraction. conformational change
What is the nicotinic acetylcholine receptor is composed of?
5 subunits (2xα, 1xβ, 1xγ and 1xδ).
What are the properties of the 5 subunits?
Each subunit is a single
polypeptide containing 4 transmembrane helices (M1-M4).
What do the 5 subunits form?
The 5 subunits form a pentameric structure with a pore in the centre. The M2 helix from each subunit faces into and lines the pore. Together they form the channel “gate”.
What lines the pore of the channel?
M2 helices
What is a characteristic of each helix?
Each helix
has a characteristic kink that forms a constriction or
“gate” in the channel.
What happens when acetylcholine binds to the α subunits?
the gate opens and Na+ enters the muscle cell.
What also happens when acetylcholine binds to the α subunits?
causes all the subunits to rotate very slightly
Why is rotating sufficient?
this is sufficient to
swing the kinked M2 helices outwards such that the gate
opens allowing Na+ entry
plant _______ can be engineered to possibly benefit the human race.
metabolism
what is found in the lower epidermis?
stomatal pores
What are stomatal pores bounded by?
by 2 highly specialised cells which are known as guard cells
What is the role of guard cells?
shrink and swell leads to pores opening and closing. therefore stomata on leaves behave as valves.
What is evaporation responsible for?
for maintaining the uptake of water and mineral nutrients from the soil.
What does drought lead to?
Pores closing, so allows the plant to perserve its existing supplies and withstand limited periods of drought.
Why is Stomata control evapotranspiration
and CO2 uptake important?
➢ Water and mineral supply ➢ Leaf cooling ➢ Ability to withstand drought ➢ Photosynthesis and dry matter accumulation
Stomata opens when…
- High Relative Humidity
- High light
- Blue light
- Low [CO2]
Stomata closes when…
- ABA
- Darkness
- High [CO2]
- Low Relative Humidity
what information do guard cells intergrate?
Guard cells integrate information from environmental signals to “set” the most appropriate stomatal aperture to suit the prevailing conditions.
What does a signalling transmission pathway tell you?
This tells us there is an integration rule for these cells as they’re processing multiple signals
What did Francis Darwin find?
Found that stomata close in the dry air of the room.
What does a reduction in atmospheric relative humidity (exposure to dry) air cause?
stomata to close.
How do we discover components involved in the guard cell reduced RH signalling pathway?
Carry out a forward genetic screen. Screen a mutagenized population of Arabidopsis (a large number of individual plants all of which carry
mutations). Identify the plants that DO not show stomatal closure when exposed to reduced RH
Why does the stomata not close when exposed to reduced RH?
The stomata in these plants do not close because they carry a lesion in a gene involved in the response.
Why is Isolating and identifying the mutated gene (and the protein it encodes) important?
results in the addition of a new component to the guard cell RH signalling pathway.
Why is it challenging to carry out a method of non-invasively measuring stomatal aperture in a large number of Arabidopsis plant?
This is a challenge because typically this is carried out
under a microscope and we need to screen thousands of plants.
What else did Francis Darwin establish about plants exposed to RH.
If you took 2 plants and looked at the temp of the leaves. In 1st plant if the stomata were fully open and they are transpiring evapotranspiration, then leaf temp would be with respect to a plant in which system matter were closed. The leaf temp would be cooler. If we measure leaf temp this will act as a proxy measure for stomatal openness and closer. Able to conclude- that in response to a drop in RH the stomata of these plants did not close and therefore we were able to identity the genes involved.
what do we now use to measuring stomatal aperture?
infrared thermal imaging
What was concuded when Isolation of loci (genes) involved in responses to reduced atmospheric RH.
Mutants exhibit lower thermal profiles than WT consistent with stomata
that are impaired in reduced RH-induced closure. We identified the mutated gene responsible for the 30A phenotype and it encoded an enzyme called ABA2 that is involved in the synthesis of the plant hormone abscisic acid (ABA). This hormone builds up in drought and brings about stomatal closure.
The 34A phenotype was caused by a mutation in a gene called OST1. This encodes a protein kinase involved in the signalling pathway by which ABA brings about stomatal closure.
What do the experiments tell us about the effect of reduced RH-induced reductions in stomatal aperture?
These experiments told us that reduced RH-induced reductions in stomatal aperture involved ABA and at least one component of signalling pathway by which ABA induces stomatal closure.
Manipulating ______
______ to benefit humankind.
biochemical pathways
Why is vitamin A deficiency found in developing countries?
rice grain major source of food in
developing world is deficient in beta carotene
(yellow pigment) which is also known as provitamin A
Why does the lack of beta carotene provide a problem?
As provitamin A is converted to vitamin A in the human body the lack of beta
carotene in the diet is a major factor contributing to vitamin A deficiency
How can we solve the problem with rice that lack the yellow pigment?
Engineer rice grains to synthesise beta carotene and then cultivate the engineered rice in the affected regions. This avoids all the issues with transporting and distributing vitamin A.
What happens if Β Carotene synthesis is
BLOCKED in rice grain?
In rice grains the biosynthesis pathway is blocked thus lucopene and beta-carotene never produced because the pathway is blocked.
How can we complete the pathway in rice?
Complete the pathway by
genetically engineering rice
plants such that they express 3 transgenes in the grain. This is“Golden Rice”
Why is golden rice yellow?
because it contains vitamin A precursor beta carotene
provitamin A
What is the equation for Photosynthesis?
CO2 + 2H2O——— [CH2O] + O2 + H2O
6CO2 + 6H2O → C6H12O6 + 6O2.
What are Photosynthetic organisms?
autotrophs
What are autotrophs?
they sustain themselves without eating anything
derived from other living beings.
Other organisms such as animals are what?
heterotrophs
What are heterotrophs?
they are unable to make their own food, they live on compounds produced by other organisms.
Why is Photosynthesis is essential to life?
it provides all our food (directly or indirectly)
• without photosynthesis we would have no fossil fuels
(laid down by the decay of plant and marine organisms
in the Carboniferous era) – the reality is that until new
technology becomes widely available, and there is the
political will to move away from fossil fuels, they still
play an important role in the world’s economy.
• it provides biomass – 14% of the world’s total final
energy consumption (eg firewood in the third world)
• it was the advent of oxygenic photosynthesis that
changed the atmosphere of the earth from its primitive
reducing state containing virtually no free oxygen to
today’s breathable air
• it is the sole replenisher of oxygen in the atmosphere
What would happen if photosynthesis was stopped?
If photosynthesis stopped the atmosphere would return to its primordial reducing state on this timescale.
What is NADP+?
nicotine adenine dinulcleotide
phosphate (oxidised NADPH) – an
electron acceptor
What is NADPH?
reduced form of NADP+ - an electron
donor (a source of reducing power)
Chloroplasts are ……
Chloroplasts are the site of photosynthesis
• 0.5 million chloroplasts / mm 2 leaf surface
• 30-40 chloroplasts/ mesophyll cell
• chloroplasts are about 5 x 10-6 m in length (5 µm)
What do chloroplasts contain?
chlorophylls
Where are the photosynthetic pigments located?
in the thylakoid membranes.
How are the thylakoid membranes organised?
These are organised into grana.
The remainder of the space inside a chloroplast is the _____
Stroma
What drives the synthesis of organic molecules
during photosynthesis?
It is the solar energy absorbed by the chlorophylls
What are the two processes of photosynthesis?
the light
reactions and the light independent
reactions.
Outline the Light reaction
1) Pigments (chlorophyll) absorb light and this results in energy being passed
from chlorophyll to chlorophyll.
2) the electrons from chlorophyll are passed along an electron transport chain resulting in the generation of NADPH while the H+ are used to produce ATP
