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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

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
Q

What is an element NOT needed in TAP? What does this mean?

A

carbon »» no sugar

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26
Q

What is the difference between macro and micronutrients?

A

macro – needed in larger amounts (~10x higher concentration)

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27
Q

What are the 3 phases of the growth curve common to Chlamy and most microbes?

A

Lag phase (beginning slow growth)
Exponential phase (middle fast growth)
Stationary phase (end slow growth) caused by limiting macronutrient

28
Q

How is the reaching of the stationary phase determined?

A

limiting factor – run out of macronutrient

29
Q

What is an SDS page?

A

an electrophoresis method that allows protein separation by mass
–> used to compare proteins in flagella

30
Q

What is a common feature in Chlamy and humans?

A

flagella!

31
Q

Why do plants not have flagella?

A

mutation in plants for flagella to disappear

32
Q

What is CILIOPATHIES?

A

diseases liked to mutations in genes involved in motile and non-motile cilia structure/function

33
Q

What are motile and non motile cilia?

A

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
Q

How does the flagella in eukaryotes and prokaryotes compare?

A

structures and functions are different = convergent evolution (homoplasy)

35
Q

How much of Chlamy’s proteins are homologs to humans, plants, and both?

A

humans - 10% (organelle functions, flagella)
plants - 26% (organelles including chloroplast)
both - 33% (organelles excluding chloroplasts, mito)

36
Q

Why does Chlamy need light?

A
  1. energy for photosynthesis
  2. phototransduction: light is a source of Information about surroundings
37
Q

How does Chlamy use its carotenoid layers?

A

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
Q

What is phototaxis?

A

movement towards (+) or away (-) from light source

39
Q

Where is the eye spot located?

A

partially in the chloroplast and partially in the plasma membrane

40
Q

What is channelrhodopsin?

A

protein on plasma membrane that is a light gated channel that opens when light is absorbed and allows + changed molecules in

41
Q

What does it mean for a cell to be polarized?

A

charge across plasma membrane

42
Q

What happens to the cell when calcium ions are let in by the channelrhodopsin?

A

depolarizing membrane - loss of charge difference across the plasma membrane

This results in an ACTION POTENTIAL

43
Q

How does the action potential move in Chlamy? What does it result in?

A

action potential moves along the plasma membrane towards the base of the flagella which interprets the action potential causing positive or negative phototaxis

44
Q

What is a photoreceptor?

A

a structure that responds by light falling into it

45
Q

What are the two parts of channelrhodopsin?

A

pigment (retinal) that is attached to protein (opsin)

46
Q

What is the role of the pigment - retinal?

A

absorb light

47
Q

What is opsin?

A

7 transmembrane helices

48
Q

What is a conjugated double bond? What molecule has this?

A

double bond, single bond carbon carbon chain
–> carotene and retinal

49
Q

What is the implication of electrons for conjugated double bond?

A

delocalized electrons –> electrons that aren’t assigned to one molecule and float around

50
Q

What wavelength goes pure retinal absorb (without opsin)

A

green (550-600nm)

51
Q

What is the relationship between wavelength and energy?

A

longer wavelength = less energy

52
Q

What is the process of light absorption in chlorophyll?

A
  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
Q

What are the three possibilities of an excited electron in chlorophyll?

A
  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
Q

Why are red and blue wavelengths absorbed in chlorophyll?

A

photon of light of red and blue matches the excited state of the electron

55
Q

Why is green the colour seen in chlorophyll?

A

there is no excited state that matches the green photon wavelength so it is reflected and not absorbed

56
Q

What is photoisomerization?

A

cis-trans isomerization due to light absorption

57
Q

What is the result of photoisomerization of channelrhodopsin?

A

before light absorption it is all-trans retinal

  1. photon excites one electron in one of the bonds of a double bond
  2. bond swivels and isomerize
  3. electron decays
  4. double bond reforms
  5. 13-cis retinal
  6. conformational change in OPSIN causing pore to open
58
Q

What is the photoreceptor in the eye? What is the photoreceptor in Chlamy?

A

eye = RHODOPSIN

chlamy: CHANNELRODOPSIN

59
Q

Where is rhodopsin in the eye?

A

in rod/cone cells inside photoreceptor discs

60
Q

How does rhodopsin work in rod cell?

A
  1. light causes trans to cis for rhodopsin
  2. conformational change to g-protein
  3. g-protein opens channel, depolarization
61
Q

What kind of cilia is in the rod/cone cell?

A

sensory non motile

62
Q

Are CHANNELRHODOPSIN and RHODOPSIN evolutionary related?

A

NO convergent evolution/homoplasy

type 1 opsin (channelrhodopsin and bacterio rhodopsin) and g-protein coupled receptors (rhodopsin) both RECRUITED RETINAL AS PIGMENT

63
Q

Why did type 1 opsin and g-protein coupled receptors both recruit retinal?

A

it is much simpler to make than chlorophyll for light absorption

64
Q

How was it determined that channelrhodopsin and bacterio rhodopsin are related?

A

homologous protein (common ancestry) had similar protein sequences

65
Q

What was the result of comparing Chlamy and Human sequences of flagella protein ODA16?

A

share common ancestry shown by protein alignment!

66
Q

What is photochemistry?

A

a change in chemical structure caused by PHOTON ABSORPTION

67
Q

What are two types of photochemistry?

A

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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