Lecture 7: Photosynthesis

autotroph

organism that creates their own food from inorganic substances using light energy and converting that into food

chloroplast

organelle which photosynthesis takes place

mesophyll

structure in the lead where chloroplasts usually remain

• 2 cells thick 

• contain two layers the palisade (upper), and the spongy (lower) 

stomata 

the opening between a pair of guard cells in the epidermis of a plant leaf 

vascular bundles

plant tissue that contains the phloem and xylem which helps transport water, minerals, and food throughout the plant

intermembrane space 

region located between the outer and inner membranes of the chloroplast envelope

• holding area for proteins being transported into/out of the chloroplast 

thylakoid space

internal compartment within each thylakoid

thylakoid

membrane-bound compartment within each chloroplast

• space why light reactions occur 

stroma

a part of the chloroplast which is the fluid within the compartment formed by the inner membrane of the chloroplast

grana

stacks of thylakoid

electromagnetism

the absorption of visible light by pigment molecules to excite electrons 

photon

“particle like” quantum of light energy 

Porphyrin ring

ring structure in chloroplast where there is Mg++ ion in the middle 

light reactions 

the first stage of photosynthesis where radiant energy is absorbed and converted to chemical energy → ATP & NADH 

• occurs in the thylakoid membrane 

NADP+ 

Nicotinamide adenine dinucleotide phosphate acts as an essential electron carrier during the light-dependent reactions

Calvin cycle

light independent reaction where CO2 is being converted to sugars using ATP and NADPH produced from the light-dependent reactions 

• three phases: carbon fixation, reduction and regeneration of CO2 acceptor 

• occurs in the stroma 

• 1 cycle produces triose G3P

carbon fixation

process where autotrophic organisms convert inorganic carbon (CO2) to organic compounds

pigment

light absorbing molecules in photosynthesis

chlorophyll 

type of pigment in plants where there are two different kinds a and b

• green pigment

xanthophylls

red, yellow color produced → chlorophylls are broken which represents a leaf color change 

• protect carotenoid pigments from light damage

carotenoids

yellow-orange pigment by which light is absorbed in photosynthesis

photoexcitation

when a photon is absorbed by an exited electron going from an area of low energy to high energy

• three scenarios can happen 

  • energy gets lost as flourescence or heat

  • energy gets absorbed by a pigment as it returned to its ground state

  • an electron hungry molecule accepts the high energy electron

action spectrum

shows the rate of photosynthesis at different wavelengths of light

photosystem

large complex where light-absorbing pigments for photosynthesis are organized with proteins and other molecules 

antenna complex

sites where light is absorbed and converted to chemical E; contain several hundred chlorophyll a,b and carotenoids

• role → harvest E and take it to the reaction center

reaction center

apart of PS1 and PS2 in the chloroplast which will receive light energy absorbed by antenna complex in the same photosystem 

reaction center chlorophyll

contains 2 chlorophyll a → transfer excited e- to ETC

• a pair of chlorphylls 

primary e- acceptor

receives an excited electron from the reaction center chlorophyll during the light-dependent reactions of photosynthesis, initiating the electron's journey down the electron transport chain

Pc

plastocyanin which passes e- to oxidized chlorophyll molecules in PS 1

Pq

plastoquinone; crucial electron and hydrogen carrier in the light-dependent reactions of photosynthesis, moving electrons from Photosystem II to the cytochrome b6f complex

ferrodoxin

mobile carrier that transfers high E e- from PSI to NADP+ reductase

B6-F complex

protein complex that linked PSII and PSI in ETC during photosynthesis; containing cytochromes

• creates electrochemical gradient for ATP synthase

NADP+ reductase

an enzyme that catalyzes the reduction of NADP+ to NADPH

photophosphorylation

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

• analogous to oxidative phosphorylation in mitochondria

ribulose bisphosphate

a five-carbon organic molecule that acts as the primary CO₂ acceptor in photosynthesis 

• the starting and ending substrate of the Calvin cycle 

rubisco 

An enzyme that catalyzes the key reaction of the Calvin cycle, carbon fixation, in which combines with RuBP (ribulose 1,5-bisphosphate) to form 3-phosphoglycerate

glyceraldehyde-3- phosphate 

the ending produce of phase 2 of the calvin cycle (reduction) 

• a direct product of the Calvin cycle, a three-carbon sugar used to synthesize glucose and other carbohydrates, as well as to regenerate ribulose-1,5-bisphosphate (RuBP) for carbon fixation