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PLBI 403 MIDTERM > Ro 1 > Flashcards

Ro 1 Flashcards

1
Q

____ is the process where an extracellular signal activates a receptor, triggering a cascade of intracellular events that lead to a specific cellular response (e.g., altered metabolism, gene expression, or cell division).

A

signal transduction

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2
Q

signal transduction cannot be amplified at any step, true or false

A

false, it can be amplified at any step

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3
Q

Two Major Types of Mutations:

A

Hyposensitive (Insensitive)
Hypersensitive (Constitutive)

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4
Q

What is Hyposensitive (Insensitive) Mutation:

A

Reduced response to signals due to receptor or pathway defects.

signal –> no response (strong signal turns weak and leads to no response)

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5
Q

What is Hypersensitive (Constitutive) mutation:

A

Overactive pathways even in the absence of signals.

No signal –> response

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6
Q

what’s the general pathway for signal transduction:

A

stimuli - receptor - pathway - transmission (transport) - response

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7
Q

Plants use chemical messengers ____ to coordinate growth, development, and environmental responses. What are these messengers?

A

hormones

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8
Q

6 major plant hormones:

A

Auxin (IAA), Cytokinin, Gibberellin (GA), Ethylene, Abscisic Acid (ABA), Brassinosteroids

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9
Q

3 minor plant hormones

A

strigolactone, jasmonic acid, salicyclic acid

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10
Q

____ means “to grow”

A

auxin

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11
Q

The first notion of auxin came from ____ experiments

A

Darwin’s phototropism

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12
Q

how do auxin’s (IAA) function

A

Promotes cell elongation, apical dominance, and root formation.

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13
Q

auxin is considered as “____” in plants

A

Morphogen

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14
Q

IAA regulates ____ (growth toward light) and ____ (growth relative to gravity).

A

phototropism and gravitropism

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15
Q

what are auxins

A

a plant hormone which causes the elongation of cells in shoots and is involved in regulating plant growth.

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16
Q

what is the most active and abundant auxin

A

IAA

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17
Q

A series of experiments for ____light phototropism proved the presence of chemical substance regulating cell growth

A

blue

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18
Q

what is apical dominance

A

when lateral bud growth is inhibited. So the apex bud releases auxins that stop the lower plant stems from growing out laterally. When the apex bud is cut, then the lateral buds grow out and you have bushier plants

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19
Q

____ growths should be responsible for the tropism. (symmetrical or asymmetrical)

A

asymmetrical

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20
Q

how do auxins work, in terms of recpetors or repressors

A

auxin binds to TIR1, a subunit of the SCF complex, IAA proteins are degraded, TFs or ARFs are activated for growth-related genes

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21
Q

cytokinin involves ____ division

A

cell division

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22
Q

New cells are supplied from ____ cells

A

meristem

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23
Q

Once a cell is differentiated for a specific function at a specific position, this
differentiated cell lose ____. However, in certain cases such as
wounding, cells gain a capacity to ____ a couple of more times to heal the
wounding. Then the cells at the wounding site undergo differentiation to
specific cells (____) and stop cell division

A

its capability to divide because they shift their focus to performing specific tasks

divide (dedifferentiation)

protective cork cells (redifferentiation), once wound is sealed, cork cells stop dividing

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24
Q

why are protective cork cells formed?

A

Plants lack a mobile immune system, so they rely on local cellular responses like dedifferentiation and redifferentiation to repair damage.

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25
Q

The Austrian scientist, Gottlieb Haberlandt, proposed a ____ chemical substance, which can promote plant cell division, based on his experiment using ____ tissue experiments

A

water soluble, vascular

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26
Q

Two streams of research resulted in the identification of a chemical substance for cell division:

A

screening natural or synthetic compounds for cell division (purification)

studies of the crown gall forming bacteria (molecular genetics, biochem)

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27
Q

____ discovered that ____ contains an unidentified substance that supports continuous cell division in mature, differentiated cells. Despite its efficacy, this substance could not be purified.

A

Philip White, coconut milk

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28
Q

Skoog found that aged or autoclaved ____ DNA exhibits potent cell-division-promoting activity.
This substance was purified, identified as an adenine derivative, and named ____.
____ is not a natural plant product but a by-product of the ____ of DNA.
This discovery influenced the development of the Murashige and Skoog (MS) medium, widely used in plant tissue culture.

A

herring sperm, kinetin, kinetin, heat induced degradation

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29
Q

Letham isolated a **natural **cell-division-promoting substance, ____, from immature maize endosperm.
Zeatin is an adenine derivative with an ____ side chain and is now recognized as the ____ in plants.
It is synthesized in chloroplasts from ____ and ____ (dimethylallyl diphosphate) through the action of the enzyme isopentenyl transferase (____).

A

zeatin, isoprene, dominant cytokinin, ATP, DMAPP, IPT

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30
Q

Cytokinin-like compounds produced by bacteria and fungi can cause abnormal growth patterns, such as ____.

A

fasciation

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31
Q

what does fasciation look like

A

perpendicular growth relative to main stem, 2 flowers smushed together, flattened stems, flower heads that look like compressed stems together

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32
Q

what delays senescence (aging) in leaves.

A

cytokinins

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33
Q

Agrobacterium tumefaciens infects plants through wounded tissues where it can enter and interact with the plant cells.

The bacterium transforms infected plant cells into tumor-like tissue, known as a ____, which is an unorganized, ____ mass of dividing cells.
These cells lose the usual regulatory controls on growth and division, continuing to divide throughout the plant’s lifecycle.

A

gall, undifferentiated

34
Q

Heating the gall tissue to 42°C kills A. tumefaciens without harming the plant cells. The bacteria-free gall tissue retains the capacity to ____, forming undifferentiated callus tissue in a hormone-free culture medium.

Significance:
The ability of plant cells to grow uncontrollably after bacterial removal hints at a permanent transformation of the plant genome, drawing parallels to cancer in animals, where cells grow uncontrollably.

A

divide indefinitely

35
Q

Ti Plasmid (Tumor-Inducing Plasmid):

A key component in A. tumefaciens that carries genes responsible for gall formation.
Contains ____ which integrates into the plant cell genome and hijacks its machinery.

Genes Encoded on T-DNA:
____, a plant hormone, is synthesized from tryptophan, promoting excessive cell growth.

____, produced by bacterial enzymes, promote uncontrolled cell division.

____ is a unique molecule synthesized from arginine and alanine, serving as a nutrient source exclusively for A. tumefaciens.

A

T-DNA, auxin, cytokinins, octopine

36
Q

High cytokinin:low auxin ratio → ____ formation.
Low cytokinin: high auxin ratio → ____ formation.

A

long shoot, long root

37
Q

“____” Disease:

Observed in ____ plants, where infected plants grew abnormally ____, causing ____ seed production.
In the 1930s, Japanese scientists identified the pathogen as the fungus Gibberella fujikuroi

A

Foolish Seedling, rice, tall, reduced

38
Q

Gibberellin Purification

In the 1950s, UK and US scientists purified a compound from Gibberella cultures and named it gibberellic acid.
Simultaneously, Japanese researchers purified three related compounds, naming them GA1, GA2, and GA3.
____ was found to be identical to the UK/US’s gibberellic acid, establishing it as one of the most bioactive forms. (which GA)

A

GA3

39
Q

Researchers confirmed that plants ____ produce gibberellins (naturally or synthetically). These hormones are synthesized in multiple cellular locations: (3 locations)

A

naturally
Chloroplasts.
Endoplasmic Reticulum (ER).
Cytosol.

40
Q

Gibberellins belong to the ____ (or isoprenoid) family.

A

terpenoid

41
Q

Gibberellins played a key role in the ____ (1940-1960):
Scientists used dwarf varieties of crops (which are more resistant to lodging, or falling over).
Gibberellins’ role in manipulating plant growth contributed to higher yields and the development of modern agriculture.

A

Green Revolution

42
Q

Seedlessness in grapes arises from a genetic defect that causes early seed abortion after fertilization. This defect ____ impacts berry size. (size)

A

negatively (smaller)

43
Q

Treating seedless grapes with gibberellins ____ berry size and ____ fruit stalks (pedicels). (length shorter or longer?)
GAs compensate for the absence of seeds, which typically promote fruit growth through hormonal signaling.

A

increases, elongates

44
Q

Mechanisms Behind Seedless Fruit Formation

____ :
Fruit develops without fertilization, e.g., bananas and some citrus fruits.

A

Parthenocarpy

45
Q

Mechanisms Behind Seedless Fruit Formation

____:
Pollination and fertilization occur, but seeds abort early in development, as in seedless grapes.

Gibberellins stimulate cell expansion and division in the fruit, improving size and quality despite aborted seeds.

A

Stenospermocarpy

46
Q

Defoliation Observed (1901):

Street lamps fueled by ____ caused trees nearby to lose leaves. A Russian graduate student identified ____ as the active compound in coal gas responsible for this effect.

A

coal gas, ethylene

47
Q

It was noted that ____ emit a gaseous substance that accelerates the ripening of nearby immature fruits.

A

ripened fruits

48
Q

____ was identified as a natural product synthesized by plants. Synthetic ethylene and its analogs were found to induce dramatic physiological changes in plants, particularly ____ and leaf abscission.

A

ethylene, fruit ripening

49
Q

Climacteric Fruits:
Show a rise in ____ and a spike in ____ production before ripening.
Ethylene has an autocatalytic effect, meaning it ____, creating a positive feedback loop that accelerates ripening.
Examples: ____, ____, mangoes, peaches, and ____. (think of fruits you have at home and see ripening)

A

respiration, ethylene, promotes its own production, apples, bananas, tomatoes

50
Q

Non-Climacteric Fruits:
____ respiratory or ethylene production changes during ripening. (how do they compare to climacteric fruits)
____ sensitive to externally applied ethylene, making ripening control ____.
Examples: Citrus, ____, cherries.

A

do not exhibit the same, less, more difficult, grapes

51
Q

Applications for ethylene, how is ethylene used in real life?

A

used to regulate the ripening process, reducing losses from spoilage

trigger uniform ripeneing

inhibitors prevent or delay ripening for storage

52
Q

The biosynthesis of ethylene involves the Yang Cycle, where ____ is converted into ____ and then to ____. This process is tightly regulated and highly active in climacteric fruits during ripening.

A

methionine -> ACC -> ethylene

53
Q

Non-climacteric fruits, like grapes and citrus, do not rely on ethylene for ripening.
Their ripening mechanisms are less understood, and controlling their post-harvest ripening remains a challenge.
For example, the trigger for ____ (the onset of ripening in grapes) is still unknown, complicating their management.

A

veraison

54
Q

Enzymes that add phosphate groups to target molecules (phosphorylation) are ____

A

kinases

55
Q

Enzymes that remove phosphate groups (dephosphorylation), reversing the effect of kinases are ____

A

phosphatases

56
Q

Sequential phosphorylation events are known as ____, such as the MAP kinase cascade:

____ activates ____, which in turn activates MAPK.
These cascades amplify the signal, allowing small stimuli to trigger a significant cellular response.

A

kinase cascades, MAPKKK, MAPKK

57
Q

4 main differences between plant and animal signal transduction

A

GCPRs aren’t important in plant transduction
plant transduction evolved from prokaryotic and eukaryotic ancestors
signals are sensed at multiple subcellular sites in plants
depresiion is common in plant transduction

58
Q

No functional GPCRs have been identified in ____, except for one heterotrimeric G-protein encoded in the ____ genome.
Plant signaling evolved differently, incorporating mechanisms inherited from both eukaryotic and prokaryotic ancestors.

A

plants, arabidopsis

59
Q

Plants have ____ Systems:

Inherited from prokaryotes, these systems involve a ____ protein and a ____ protein.
Examples in plants include pathways involving: (2 examples)

A

two-component, sensor and response

cytokinin signalling, ethylene signalling

60
Q

____, derived from prokaryotic ancestors, contribute signaling mechanisms like those involving ____ (blue-light photoreceptor).

A

chloroplasts, cyrptochrome (blue-light recpetors)

61
Q

Unlike animals, plants can sense signals at multiple subcellular locations:

Brassinosteroids: Plasma membrane.
Cytokinin: Plasma membrane.
Red light: ____
Blue light:
Plasma membrane (involving ____).
Nucleus (involving ____).
Chloroplast thylakoid membrane (Zeaxanthin).
____: Endoplasmic reticulum.
____: Nucleus (via SCFTIR1 complex).

A

cytosol, ethylene, photoropin, cryptochrome, auxins

62
Q

Plants often regulate signals through de-repression, which involves: 2 things

A

repressor protein inactivation, ubiquination

63
Q

Ubiquitination tags proteins for degradation by the ____ proteasome.

A

26s

64
Q

Ubiquitin:

A small ____ protein (8.5 kDa) found in all eukaryotic cells.
It tags specific proteins for ____ or other cellular processes, acting as a molecular “marker.”
Ubiquitin is encoded by ____ genes in humans.

Ubiquitination Process:

A sequence of enzymatic steps that ____, leading to their degradation by the 26S proteasome or modulation of their activity.

A

regulatory, degradation, 4

tags proteins with ubiquitin for degradation, acts as molecular marker

65
Q

Ubiquitin-____ Enzyme (E1):
Activates ubiquitin by loading it onto itself.
This step requires ____.

Ubiquitin-____ Enzyme (E2):
Accepts ubiquitin from the E1 enzyme and transfers it to a ____ protein.
Works in conjunction with ____.

Ubiquitin-Protein Ligase (E3):

The most diverse group, with 500-1000 genes in humans. This step determines the ____.

A

Activation (E1), activates ubiquitin by loading it onto itself, requires ATP
Conjugation (E2)
substrate, E3 ligases

specificity of the ubiquitination process.

66
Q

what is the most diverse ubiquitin enzyme group

A

ligase group (E3)

67
Q

The ____ is a major type of E3 enzyme that regulates plant hormone signaling.

A

SCF complex

68
Q

____ were first extracted from the pollens of Brassica napus (rapeseed or canola).
These hormones stimulate stem elongation and cell division but are present in ____ quantities

A

Brassinosteroids, extremely low

69
Q

The ____ mutant was identified as part of studies on etiolation, a process in ____.

Normal Etiolation:
In the dark, plants ____ their stems (hypocotyl) to reach light, and cotyledons remain ____ and unexpanded.

DET2 Mutant Phenotype:
____ hypocotyl elongation.
Exhibited ____ cotyledons and even began synthesizing photosynthetic proteins in the dark, mimicking a ____ environment.

A

DET 2 mutant, plants grow in the absence of light

normal: elongate, folded

mutant: lacked hypocotyl elongation, expanded, light environment

70
Q

____, the most active brassinosteroid, resembles human steroid hormones like ____, progesterone, and estrogen.
Like human steroids, brassinolide is an ____ molecule.

A

brassinolide, testosterone, isoprenoid

71
Q

____: Regulates growth and development in darkness (etiolation).

A

skotomorphogenesis

72
Q

Brassinosteroids, including brassinolide, are synthesized in the ____.

A

cytosol

73
Q

The DET2 mutant lacks____, explaining its abnormal phenotype in the dark.

A

brassinolide

74
Q

Scientists hypothesized the existence of a hormone that actively inhibits seed germination and bud sprouting during dormancy in plants.
Dormancy in seeds (annual plants) and buds (trees) was observed to be negatively regulated by such an inhibitory hormone: ____

Purification of Dormin:

The hypothetical hormone, initially called dormin, was isolated from ____ tissues entering dormancy in early autumn.
Dormin was found to be chemically identical to a compound that promotes abscission (shedding of leaves, fruits, or seeds), and was subsequently named ____ .

A

dormin, tree, ABA

75
Q

Mutants like ____ in maize, which exhibit precocious germination, helped identify genes involved in ABA biosynthesis and signaling.
Vivipary in plants is analogous to animal viviparity, where embryos develop ____ instead of being laid as eggs (oviparity).

A

vivipary, inside the mother

76
Q

High ABA leads to:
High GA leads to :

A

dormancy, germination

77
Q

Under drought conditions, ABA levels ____ dramatically, triggering stomatal ____.

A

increase, closure to minimize water loss

78
Q

how does ABA regulate stomatal closure:

ABA ____ cytosolic Ca²⁺ levels in ____ cells.
Elevated Ca²⁺ leads to ____, causing guard cells to shrink and close the stomatal pores.

A

increase, guard, ion loss

79
Q

____ promotes abscission, the shedding of leaves, fruits, flowers, or seeds, allowing plants to conserve resources under stress.

A

ABA

80
Q

ABA is synthesized in the ____

A

chloroplast

81
Q

ABA is a breakdown product of a C40 ____ molecule, part of the terpenoid biosynthesis pathway.

A

isoprenoid

82
Q

four major isoprenoid-based plant hormones:

A

cytokinin, brassinolide, ABA, gibberellin

PLBI 403 MIDTERM (9 decks)

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