UTA Plant Science Exam 2

mama a girl behind you

how do plant cells and animal cells differ

plants have:

• chloroplasts with [Circular DNA]

• cell wall with cellulose

• large central vacuole for water

• plasmodesmata

the two parts of a plant cell

• protoplast

• cell wall

protoplast

plasma membrane and everything inside of it

cell wall

limits the enlargement of the protoplast

primary cell wall

• all plant cells have this

• made of cellulose

• deposited during and after cell growth

• allows for growth (flexible)

• unevenly thickened

  • role in immune response

secondary cell wall

• NOT in all cells

• deposited only AFTER cell stops growth

• almost always impregnated with lignin

  • not permeable to water

components of the primary cell wall

• cellulose (all cells)

• hemicellulose (polysaccharides)

• pectins (polysaccharides)

• glycoproteins

  • cutin, suberin, waxes

primary cell wall: Cellulose

• long chains of glucose => microfibril => cellulose

• depositzed by enzymes in the plasma membrane

  • deposited before and during cell growth

primary cell wall: Hemicellulose

• polysaccharides

  • act as tethers holding the microfibrils together (flexy)

primary cell wall: Pectins

• polysaccharides

• cell adhesion and hydration

  • interwoven within the cell wall

primary cell wall: Glycoproteins & Enzymes

• proteins help strengthen wall

• breakdown cell wall components

  • defense against pathogens

primary cell wall: Middle Lamella

• pectin- hydrophillic

• external to primary cell wall

  • “glues” cells together

pause and draw a wall

image here

secondary cell wall characteristics 

• NOT present in all cells

• strength and water conduction

• deposited interior to the Primary cell wall

• appears AFTER cell stops growing

• more [cellulose] than in primary

• lacks [plasticity]

  • no pectin

secondary cell wall: Lignin

• deposits provide compressive strength

• prevents cell division/increase in size 

how many layers does the secondary cell wall have?

3 layers

• S₁ S₂ S₃

Imagine two plant cells capable of secondary growth. Starting from the cytoplasm of one cell, list the layers crossed as you travel to the cytoplasm of the second cell.

image here

pit-fields (Primary wall) and pits (Secondary wall)

openings in the cell wall that allow for exchange of materials between the cell, other cells, and the environment

plasmodesmata

• channels in the primary cell wall for intercellular communnication

• has [desmotubules]

• forms [symplast]

desmotubules

strands of endoplasmic reticulum

• extends through the pits to connect adjacent cells

symplast

vast interconnected network of the protoplasm of ALL living cells in the plant

vacuoles

membrane-bound region filled with liquid (cell sap)

• membrane is called [tonoplast]

• may be 90% of cell volume

function:

• maintain tissue rigidity

• store primary and/or secondary metabolites

• store pigments

• may breakdown and recycle macromolecules

plastids

• function in photosynthesis and storage

• site of the synthesis of Some amino acids

• have their circular DNA and ribosomes

• DOUBLE MEMBRANE

• divide by binary fission

• are classified in part by the type of pigments they contain

plastids: chloroplasts

• site of photosynthesis

• contain [chlorophylls] and [carotenoids]

• temporary starch storage

• synthesis of other compounds

  • amino acids

  • fatty acids

  • metabolites

plastids: chromoplasts

• lack chlorophyll

• synthesize and store carotenoids and other pigments

• highly colored (reds and oranges)

plastids: leucoplasts

• non-pigmented

• synthesize and store sugars as starch

• amyloplast

  • specific type of leucoplast for storing starch in roots and tubers

plastids: proplastids

• undifferentiated plastid

  • any type of plastid can convert from one type of plastid to another depending on the environment! (shapeshifters)

what two events are unique to plant cell cycles?

1. formation of the phragmosome

2. formation of a band of microtubules (preprophase band)

phragmosome

transverse sheet of cytoplasm

Formation of the phragmosome

• move nucleus to the center of the cell 

• starts in the G1 phase of mitosis, just before DNA replication

• nucleus is anchored in cytoplasmic strands

• strands merge to form a phragmosome that bisects the cell where it will ultimately divide

preprophase band

band of microtubules that guide the formation of the [cell plate]

cell plate

initial partition between daughter cells

formation of the preprophase band

• ringlike band of microtubules forms just beneath the plasma membrane

• encircles nucleus in a plane corresponding to equatorial plane of future mitotic spindle

• occurs during G2, just before prophase

• disappears AFTER prophase

plant cells may have all of the following EXCEPT:

1. chloroplasts

2. vacuoles

3. mitochondria

4. centrioles

centrioles

the ______ helps in building the cell plate when a plant cell divides:

1. cleavage furrow

2. preprophase band

3. plasmodesmata

4. phragmosome

preprophase band

the organelle that is responsible for maintaining tissue rigidity and storing many molecules like pigments is the:

1. endoplasmic reticulum

2. vacuole

3. vesicle

4. amyloplast

vacuole 

potential energy

energy of chemical/electrochemical gradients across the plasma membrane

• energy stored in chemical bonds

kinetic energy

energy released

anabolic

requires energy, building large molecules using smaller molecules

catabolic

releases energy, breaking down large molecules into smaller molecules

metabolism

ALL chemical processes that occur (both anabolic and catabolic) in a living organism

is respiration catabolic or anabolic?

catabolic pathway

glucose + O₂ => CO₂ + H₂O + Energy

is photosynthesis catabolic or anabolic?

anabolic pathway

CO₂ + H₂O + Energy => glucose + O₂

what are the 4 major stages of cellular respiration?

1. glycolysis

   1. energy investment

   2. energy payoff

2. pyruvate oxidation

3. the citric acid cycle

4. oxidative phosphorylation

what is the primary function of glycolysis?

function is to split sugar

• glucose is split into two 3-carbon sugars called pyruvate (2 pyruvates made)

where does glycolysis occur in the cell?

occurs in the cytosol

is O₂ required for glycolysis to occur?

no it takes place whether or not O₂ is present

is CO₂ released during glycolysis

no, CO₂ is released during this process

what happens in the energy investment phase of glycolysis?

2 ATP is used to create 2 molecules of G3P from 1 glucose 

what happens in the energy payoff phase of glycolysis?

2 NADH are formed as electron carriers for the ETC (electron transport chain) along with 2 ATP.

• the final product of glycolysis is 2 pyruvates from 1 glucose

what is the function of pyruvate oxidation?

function is to oxidize pyruvate into Acetyl CoA

where does pyruvate oxidation occur in the cell?

occurs in the mitochondrial matrix (pyru)

what is the mechanism of pyruvate oxidation?

1. pyruvate moves into the matrix via active transport

   1. oxidation of 1 pyruvate generates CO₂, Acetyl-CoA, and 1 NADH for each pyruvate molecule

what is the function of the citric acid cycle?

function is to harvest high-energy electrons (e^-)

where does the citric acid cycle occur in the cell?

occurs in the mitochondrial matrix (krebs)

what is the mechanism of the citric acid cycle?

the acetyl-CoA (reactant) is completely oxidized to CO₂ (product)

• 1 ATP is generated per turn of the cycle by substrate-level phosphorylation (product)

• most of the energy is transfered to 3 NAD⁺ and 1 FAD per turn of the cycle ===>>> 3 NADH and 1 FADH₂ (products)

citric acid cycle (krebs cycle) mechanism part 2

1 glucose => 2 Acetyl-CoAs

• for each Acetyl-CoA, 3 NADH and 1 FADH₂ is created (electron carriers)

• ATP is made by substrate-level phosphorylation

what is the function of oxidative phosphorylation?

function is to produce a hydrogen concentration gradient which powers ATP synthesis

where does oxidative phosphorylation occur in the cell?

occurs in the inner membrane of the mitochondrion

what are the major inputs of oxidative phosphorylation?

O₂ and electrons from NADH and FADH₂

what is the major output of oxidative phosphorylation?

ATP

Electron Transport Chain mechanism

1. electrons are carried by NADH and FADH into protein electron carriers embedded in the inner membrane

2. as electron moves to lower state of energy, the lost energy is used to pump (H⁺) out of the matrix and into the intermembbrane space

   1. H⁺ supplies energy that drives ATP synthesis

ATP Synthesis (Chemiosmosis) mechanism

• H⁺ ions have a tendency to diffuse back across the membrane down their electrochemical gradient, creating the proton motive force

• as H⁺ ions flow through ATP synthase, ATP is produced

what is the formula for photosynthesis?

6 CO₂ + 6 H₂O + Light energy → C₆H₁₂O₆ + 6 O₂

where does photosynthesis take place?

in the chloroplast

what is chloroplast made of?

• double membrane (inner and outer)

• stroma 

• thylakoids

• granum

stroma 

interstitial liquid in the chloroplast  surrounding the granum

• dark reaction occurs here!

thylakoids

flattened, interconnected sacs in the chloroplast

• light reactions occur in the thylakoid membranes

granum

a stack of thylakoids

why do leaves appear green?

the green color is the wavelength that doesn’t get absorbed

• red and blue often gets absorbed

chlorophyll

the pigment in chloroplast that absorbs light, is what makes chloroplast green

chlorophyll a

the main essential pigment for photosynthesis

• embedded in membrane proteins in the thylakoids of chloroplast

• absorbs violet, blue, and red

• reflects green

• moves electrons (e^-)

what are accessory pigments and name a few?

absorb light energy and work together to pass it to chlorophylls

• chlorophylls b and c

• carotenoids (orange carrot)

• phycobilins

chlorophyll b

• not directly involved in photosynthetic energy transduction

• broadens spectrum of light absorption (DLC)

• transfers energy to chlorophyll a

chlorophyll c

replaces chlorophyll b in some algae

• brown algae

• diatoms

• purple bacteria

carotenoids

accessory pigment (DLC)

• red, orange, and yellow lipid-soluble pigments

• in ALL chloroplasts and cyanobacteria

• embedded in thylakoid membranes

what is the order of the electromagnetic spectrum from shortest, highest energy to longest, lowest energy?

Gamma rays, X-rays, UV light, Visible light, Near-infrared, Infrared light, Microwaves, Radio waves

what happens when a pigment absorbs light?

it goes from ground state to an excited state, making it unstable

light-dependent reactions

• occurs in thylakoid membrane

• energy transduction reactions

• energy of sunlight absorbed, converted into chemical energy (ATP & NADPH)

• NADPH carries e^- that are pushed to high energy levels by absorbed light

light independent reactions (dark reactions)

• occurs in stroma

• carbon fixation reactions

• electrons in NADPH and ATP are used as a source of energy to convert inorganic CO₂ to an organic form (CO₂ fixation)

study this overview of photosynthesis

photosynthesis light reaction and dark reactions

what two main processes are involved in the light reactions?

1. light absorption

2. synthesis of NADPH and ATP

what are photosystems?

pigment molecules embedded in the thylakoid membrane organized into discrete units 

what two components do each photosystem have?

1. Antenna complex 

2. Reaction center

antenna complex

pigment that funnel light energy through resonance to the reaction center 

reaction center 

chlorophyll molecules that enable light energy to be converted to chemical energy 

photosystem II

P 680 pigment, contains very little chlorophyll b

1. light excites pigment, pigment use resonance to give energy to other pigment until it reaches chlorophyll a in the reaction center

2. P 680 in chlorophyll a excites, expels e^- from reaction center

3. passes excited e^- to ETC (plastoquinones) which pick up H⁺

4. “lost” e-  are replaced by oxidation of water (oxygen-evolving complex unique to PS II)

5. e^- deposited into mobile carrier, Plastoquinone 

6. carrier deposits e^- and H⁺ into the Cytochrome b₆/f Complex

photosystem I 

P 700 pigment, contains nearly as much chlorophyll b as a

1. light energy causes resonance in pigments in antenna complex

2. P 700 pigment in reaction center excites, ejects e^- into a second ETC (Ferrodoxins, etc) and deposits NADP+

3. NADP+ is reduced to NADPH

4. lost e^- is replaced by electrons carried from Cytochrome b₆/f Complex

Cytochrome b₆/f Complex

• receives H⁺ from plastoquinone and deposits them into thylakoid lumen

• receives e^- from from plastoquinone

• transfers electrons to another mobile electron carrier protein, Plastocyanin, which carriers electrons, one at a time to PS I

why does the Cytochrome b₆/f Complex transfer H⁺ into the lumen?

the H⁺ is used for Photophosphorylation

linear (non-cyclic) electron flow

electrons flow continuously from water through photosystems II and I to NADP+, resulting in the oxidation of water to oxygen and reduction of NADP+ to NADPH

photophosphorylation

• synthesis of ATP coupled to the transfer of electrons energized by photons of light

• proton-motive force contributes energy for ATP synthesis by ATP synthase (chemiosmosis)

cyclic electron flow

makes ATP ONLY!

• electrons cycle back into PS I reaction center via Cytochrome b₆/f Complex

• contributes to increasing proton concentration gradient (H⁺)

• generates ATP, does not reduce NADP+

• must occur to produce ATP necessary to drive Calvin cycle and other processes

  • more ATP than NADPH is needed in Calvin cycle

• occurs only in PS I

cyclic electron flow part 2 (extra facts)

• some organisms like purple sulfur bacteria have PS I ONLY

• cyclic electron flow is thought to have evolved before linear electron flow

• cyclic electron flow may protect cells from light-induced damage

light independent reactions: Carbon-Fixation

process in which inorganic carbon in the form of CO₂ is converted into an organic molecule

• ATP and NADPH, generated by light reactions, is used to fix and reduce carbon to synthesize simple sugars 

1. C₃ (three molecule fixing)

2. C₄ (four molecule fixing)

3. CAM

how does CO₂ get into plants?

CO₂ is taken in through the stomata

• diffuses into all open-air spaces in the mesophyll

• dissolved into moist surface of spongy parenchyma cells

C₃ Pathway

• utilizes ONLY the Calvin cycle 

• fixes CO₂ into 3-carbon molecule by feeding into a molecular cycle (Calvin cycle)

• cycle starts AND ends with RuBP, 5 carbon sugar w/ 2 phosphate groups

• catalyzed by RUBISCO (enzyme)

• uses ATP and NADPH that was produced during light-dependent reactions

• produces G3P molecule (3 carbons)

C₃ inputs

• 3x RuBP 

• 3x CO₂

• Rubisco enzyme

C₃ outputs

1x G3P molecule

• 3-carbon precursor to glucose

• AKA GA3P or PGAL (same thing!)

• *5x GA3P remain in the cycle