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Winter 2023 - Biology > Cycle 1: Chlamydomonas and How it uses Light > Flashcards

Cycle 1: Chlamydomonas and How it uses Light Flashcards

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1
Q

What is the function of a photosystem?

A

Catalyzes the conversion of light energy into chemical energy

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2
Q

What is the structure of a photosystem?

A

two complexes built around proteins that bind pigment molecules involved in light absorption

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3
Q

What occurs to an electron when an atom absorbs energy?

A

e- moves from ground state to an excited state and is farther away from the nucleus

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4
Q

When does the absorption of energy occur in an atom?

A

energy of a PHOTON is transferred to an electron within a molecule

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5
Q

What are the three possible occurrences of an excited electron in a PIGMENT molecule?

A
  1. electrons RETURNS to ground state and releases its energy as heat or emitting a less energetic photon (fluorescence)
  2. electron transfers its energy to an electron in a neighbouring pigment molecule and RETURNS to ground state
  3. the electron itself transfers from the pigment molecule to a nearby electron accepting molecule
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6
Q

What is the result of an electron transferring to a different molecule?

A

the e- can energize the second molecule or pump protons across a membrane to increase membrane potential

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7
Q

Which pigments absorb light in photosynthesis?

A

chlorophylls and carotenoids (yellow-orange pigments)

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8
Q

What is an ABSORPTION spectrum?

A

how much light is intercepted by the pigment (absorbed) as a function of wavelength

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9
Q

What is the requirement for a photon of light to be absorbed?

A

the energy of the photon = amount of energy required to raise a pigment electron from GROUND to EXCITED state

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10
Q

What is Chlamydomonas reinhardtii?

A

eukaryotic green alga that has an eye spot (primitive eye), chloroplasts and a nucleus and is mostly haploid

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11
Q

Why is Chlamy a good model system?

A

it is HAPLOID - haploids have one set of chromosomes so their DNA is easy to detect mutations
- has flagella (identical to cilia) so it can be studied for ciliopathies
- grows fast
- doesn’t needs much space to grow
- nuclear/chloroplast genome sequenced

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12
Q

What are the structures and functions specific to eukaryotes?

A

nucleus - stores DNA
mitochondria - supplies energy
chloroplasts - plants, photosynthesis site
endoplasmic reticulum - production and transport of proteins
Golgi apparatus - processes proteins from ER
lysosomes - gets rid of waste

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13
Q

What are the structures specific to prokaryotes?

A

cell membrane, ribosome, DNA, RNA, plasmid, pili (like cilia), cytoplasm, flagellum

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14
Q

When would Chlamy not be haploid?

A

when conditions are not favourable + and - mating types are produced

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15
Q

What is a haplontic life cycle?

A

Haploid dominant life cycle
haploid form for mitosis and growth
diploid only for fusion then meiosis occurs which returns to haploid

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16
Q

What is a diplontic life cycle?

A

Diploid dominant life cycle
diploid mitosis and growth
meiosis occurs then becomes haploid
fusion then diploid again

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17
Q

How is Chlamy grown in the lab?

A

in one mating type is growth = cell division (mitosis)

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18
Q

What media is Chlamy grown in?

A

liquid called TAP that contains macronutrients and micronutrients that are dissociated in water

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19
Q

Why do we need ammonium?

A

nitrogen – backbone of DNA and needed for proteins and amino acids

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20
Q

Why do we need phosphate?

A

phosphorus in ATP and DNA/RNA backbone

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21
Q

Why does a cell need iron?

A

to make DNA, cofactors of enzymes

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22
Q

Why does a cell need molybdenum?

A

cofactors enzymes need it to catalyze reactions

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23
Q

Why do we need sulfur?

A

acetyl coA has sulfur

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24
Q

why do we need magnesium?

A

chlamy does for conjugated chlorophyll system

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25
What is an element NOT needed in TAP? What does this mean?
carbon »» no sugar
26
What is the difference between macro and micronutrients?
macro -- needed in larger amounts (~10x higher concentration)
27
What are the 3 phases of the growth curve common to Chlamy and most microbes?
Lag phase (beginning slow growth) Exponential phase (middle fast growth) Stationary phase (end slow growth) caused by limiting macronutrient
28
How is the reaching of the stationary phase determined?
limiting factor -- run out of macronutrient
29
What is an SDS page?
an electrophoresis method that allows protein separation by mass --> used to compare proteins in flagella
30
What is a common feature in Chlamy and humans?
flagella!
31
Why do plants not have flagella?
mutation in plants for flagella to disappear
32
What is CILIOPATHIES?
diseases liked to mutations in genes involved in motile and non-motile cilia structure/function
33
What are motile and non motile cilia?
motile: some diseases bc cilia can't move sensory/non motile" proteins that migrate up the cilium that are on the plasma membrane that interact with light, sound, chemicals
34
How does the flagella in eukaryotes and prokaryotes compare?
structures and functions are different = convergent evolution (homoplasy)
35
How much of Chlamy's proteins are homologs to humans, plants, and both?
humans - 10% (organelle functions, flagella) plants - 26% (organelles including chloroplast) both - 33% (organelles excluding chloroplasts, mito)
36
Why does Chlamy need light?
1. energy for photosynthesis 2. phototransduction: light is a source of Information about surroundings
37
How does Chlamy use its carotenoid layers?
acts as reflector if channelrhodopsin doesn't absorb light directly from the front side - located in chloroplasts - acts as barrier from rear side -> chlamy knows where light is and how orient itself
38
What is phototaxis?
movement towards (+) or away (-) from light source
39
Where is the eye spot located?
partially in the chloroplast and partially in the plasma membrane
40
What is channelrhodopsin?
protein on plasma membrane that is a light gated channel that opens when light is absorbed and allows + changed molecules in
41
What does it mean for a cell to be polarized?
charge across plasma membrane
42
What happens to the cell when calcium ions are let in by the channelrhodopsin?
depolarizing membrane - loss of charge difference across the plasma membrane This results in an ACTION POTENTIAL
43
How does the action potential move in Chlamy? What does it result in?
action potential moves along the plasma membrane towards the base of the flagella which interprets the action potential causing positive or negative phototaxis
44
What is a photoreceptor?
a structure that responds by light falling into it
45
What are the two parts of channelrhodopsin?
pigment (retinal) that is attached to protein (opsin)
46
What is the role of the pigment - retinal?
absorb light
47
What is opsin?
7 transmembrane helices
48
What is a conjugated double bond? What molecule has this?
double bond, single bond carbon carbon chain --> carotene and retinal
49
What is the implication of electrons for conjugated double bond?
delocalized electrons --> electrons that aren't assigned to one molecule and float around
50
What wavelength goes pure retinal absorb (without opsin)
green (550-600nm)
51
What is the relationship between wavelength and energy?
longer wavelength = less energy
52
What is the process of light absorption in chlorophyll?
1. 1 photon excites 1 electron 2. electron moves from ground state to wavelength of blue light (more energy) 3. heat loss in 10^-12 seconds as the electron decays to lower energy wavelength of red light 4. photosynthesis uses red excited state (or the electron is immediately excited to red)
53
What are the three possibilities of an excited electron in chlorophyll?
1. photosynthetic electron transport 2. loss some heat and eject the energy as a photon of fluorescence that has a slightly longer wavelength and lower energy than red 3. loss as heat
54
Why are red and blue wavelengths absorbed in chlorophyll?
photon of light of red and blue matches the excited state of the electron
55
Why is green the colour seen in chlorophyll?
there is no excited state that matches the green photon wavelength so it is reflected and not absorbed
56
What is photoisomerization?
cis-trans isomerization due to light absorption
57
What is the result of photoisomerization of channelrhodopsin?
before light absorption it is all-trans retinal 1. photon excites one electron in one of the bonds of a double bond 3. bond swivels and isomerize 4. electron decays 5. double bond reforms 6. 13-cis retinal 7. conformational change in OPSIN causing pore to open
58
What is the photoreceptor in the eye? What is the photoreceptor in Chlamy?
eye = RHODOPSIN chlamy: CHANNELRODOPSIN
59
Where is rhodopsin in the eye?
in rod/cone cells inside photoreceptor discs
60
How does rhodopsin work in rod cell?
1. light causes trans to cis for rhodopsin 2. conformational change to g-protein 3. g-protein opens channel, depolarization
61
What kind of cilia is in the rod/cone cell?
sensory non motile
62
Are CHANNELRHODOPSIN and RHODOPSIN evolutionary related?
NO convergent evolution/homoplasy type 1 opsin (channelrhodopsin and bacterio rhodopsin) and g-protein coupled receptors (rhodopsin) both RECRUITED RETINAL AS PIGMENT
63
Why did type 1 opsin and g-protein coupled receptors both recruit retinal?
it is much simpler to make than chlorophyll for light absorption
64
How was it determined that channelrhodopsin and bacterio rhodopsin are related?
homologous protein (common ancestry) had similar protein sequences
65
What was the result of comparing Chlamy and Human sequences of flagella protein ODA16?
share common ancestry shown by protein alignment!
66
What is photochemistry?
a change in chemical structure caused by PHOTON ABSORPTION
67
What are two types of photochemistry?
photoreceptor - change in shape in retinal through photon energy (cis↔trans) photosystem - oxidized molecule: e- lost in photosynthesis electron transport

Winter 2023 - Biology (11 decks)

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