CHAPTER 10, 11, 12

Photosynthesis

Calvin Cycle

Chloroplast

Light Capturing Reactions

USES: Water and light

PRODUCES: Oxygen

USES: Carbon Dioxide

PRODUCES: Sugar and 3RuBP

Thylakoid: Has ETC and ATP synthase for photo-phosphorylation

Granum: Stack of thylakoid

Stroma: Space inside chloroplast

Pigment: Molecules that absorb certain wavelengths

Chlorophyll b: Absorbs light

Carotenoids/Carotene: Absorb/pass energy to chlorophyll

Light

Blue light excites electrons better than red light

3 possible fates for electrons when absorbed

More Terms

Antenna Complex: Group of chlorophyll molecules and accessory pigments by an array of proteins

Energy is transferred to nearby pigments

Reduction/Oxidation = electrons are transferred to a new compound/acceptor

Emission of heat/light

Resonance Energy Transfer: Pigments in an antenna complex absorb photons from light, the energy (but not the photon itself) is passed to a nearby chlorophyll molecules, where another electron is excited in response to it

Reaction Center: Photons are absorbed by chlorophyll molecules

Photosystem

Photosystem I

Photosystem II

STEPS

End of photosystem I

  1. Electrons are excited in reaction center chlorophyll molecules

  1. The reaction center pigments are oxidized, and the excited electrons are passed through a series of carriers inside the photosystem, then to a molecule called ferredoxin, and then to the enzyme NADP+

  1. Pigments in the antenna complex absorb photons and pass the energy to the photosystem I reaction center

  1. NADP+ reductase transfers 2 electrons and a proton to reduce NADP+ and form NADPH

Final Electron Acceptor: NADP+

Molecule Produced When Electron Accepted: NADPH

Pheophytin

Water donates electrons to photosystem II

accepts excited electron from chlorophyll

Key to transforming light energy to chemical energy

Same as chlorophyll but lacks mg atom in the head region

OCCURS FIRST in photosystems

Z-Scheme: A model for how Photosystems II and I interact

STEPS

1. Carbon Fixation

The process converts CO2 into a more biologically useful form, carbon in the compound is reduced by attaching it to another carbon

Addition of CO2 to an organic compound

2. Reduction

3.Regeneration of RuBP: ATP is reduced to ADP

6 NADPH are reduced to NAD and H

Sugar is also produced here

How is it Regulated?

  1. When sugar supplies are high, the production of proteins required for photosynthesis is inhibited, but the production of proteins required to process and store sugars is stimulated

  1. Rubisco is activated by regulatory molecules that are produced when light is available, but inhibited in conditions of low CO2 availability – when photorespiration is favored 

  1. Presence of light triggers the production of proteins required for photosynthesis

Stomata

Pores away from cuticles that get CO2 in and oxygen out of cells

Open during day time

Cuticles:Prevents water evaporating out of tissues, prevents transport of gases like CO2 and oxygen

Closed when too hot or nightime

Maximizing CO2 Concentration

CAM = Crassulacean Acid Metabolism

C4 Pathway

Acts as additional fixation step

When fixing CO2 produces 4-carbon molecule than a 3-carbon molecule

Beneficial in conditions to space

Beneficial in condition to time

Same as C4 but during the nighttime and the products are then used during the day in the calvin cycle

Sugars

SUCROSE: when photosynthesis is done slowly

STARCH: when photosynthesis is done fast

GLUCOSE: gluconeogenesis

Cell-Cell Interaction

Extracellular material

Cross-linked network of long filaments in a stiff surrounding material

FUNCTION: Defines cell shape and attches it to another cell/acts a first-line defense against the outside world. Withstands compression and straining

Ground substance: concrete gel mixture, withstands pressure

Filaments: longs rods that resist pulling and pushing

Extracellular Matrix: Fiber composite secretion, provides structural support

Animals = more protein than carbohydrate

Plants = more carbohydrate than protein

Made of collagen protein and ground substance Proteoglycan, fibronetin

Cell Wall in Plants

Turgor Pressure

Pectin

Secondary Cell Wall: made when cells matures and stops growing

When incoming water pushes the plasma membrane against the cell wall

In normal conditions: the concentration of solutes is higher inside the cell than outside, causing water to enter the cell via osmosis

Made in the rough ER and Golgi

It’s hydrophilic and attracts/hold large amounts of water

Gaps

Small molecules go through these gaps between cells

  1. Activate/inactivate proteins that already exist in the cell that are involved with metabolism, membrane transport, secretion, and the cytoskeleton

  1. Gene expression, altering which proteins are produced and which are not

PLANTS: Plasmodesmata

ANIMALS: gap junction

Cell-Cell Communication

Lipid Molecules

SOLUBLE: Can diffuse across hydrophobic regions, enter cytosol, INSIDE THE CELL

INSOLUBLE: Cannot cross membrane, INSIDE PLASMA MEMBRANE

Signal Deactivation

Crosstalk

Phosphatases: This enzyme removes phosphate groups from necessary components of these signal-receptor reactions

Second Messenger Concentration: Second messengers are converted into storage molecules through pumps in the ER of the cytosol

GTP Hydrolysis: The hydrolysis of GTP to GDP makes the G protein inactive and therefore production of second messengers are stopped

Second messenger CAN STIMULATE 2nd pathway

Second messenger IS STIMULATED by 2nd pathway

Second messenger CAN INHIBIT 2nd pathway

For Prokaryotic

Quorum Sensing

Use of signal pathways that respond to population density

Cell Cycle

Middle Lamella

Allows plant cells to stick to each other, top layer of cell

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