[AP Bio] Chapter 6 & 8 Flashcards

Metabolism & Photosynthesis

Metabolism

totality of an organism’s chemical reactions, consisting of catabolic and anabolic pathways, which manage the material and energy resources of the organism

Metabolic Pathway

a series of chemical reactions that either builds a complex molecule (anabolic pathway) or breaks down a complex molecule to simpler molecules (catabolic pathway)

Anabolic Pathway

metabolic pathway that consumes energy to synthesize a complex molecule from simpler molecules

Catabolic Pathway

metabolic pathway that releases energy by breaking down complex molecules to simpler molecules

• Energy stored in the organic molecules becomes available to do cellular work

Chemical Equilibrium

a state of maximum stability where the forward and reverse reactions occur at the same rate in a chemical reaction

• Any change from the equilibrium position will have a positive ΔG and will not be spontaneous—processes are spontaneous and can perform work only when it is moving towards equilibrium

Exergonic Reaction

a spontaneous chemical reaction where there is a net release of free energy

• ΔG is negative for an exergonic reaction because the chemical mixture loses free energy (G decreases) as energy goes “outward”

Endergonic Reaction

a nonspontaneous chemical reaction where free energy is absorbed from the surroundings

• ΔG is positive for an endergonic reaction because this kind of reaction essentially stores free energy in molecules (G increases) as energy goes “inward”

What are the 3 types of work a cell does?

• Chemical Work

• Transport Work

• Mechanical Work

Chemical Work

the pushing of endergonic reactions that would not occur spontaneously, such as the synthesis of polymers from monomers

Transport Work

the pumping of substances across membranes against the direction of spontaneous movement

Mechanical Work

such as the beating of cilia, the contraction of muscle cells, and the movement of chromosomes during cellular reproduction

ATP (adenosine triphosphate)

releases free energy when its phosphate bonds are hydrolyzed, where the energy is used to drive endergonic reactions in cells

• Bonds between the phosphate groups of ATP can be broken through hydrolysis, turning it into adenosine diphosphate (ADP), which is an exergonic reaction (releases energy)

Enzyme

a macromolecule serving as a catalyst, a chemical agent that increases the rate of a reaction without being consumed by the reaction (most of these are proteins)

Activation Energy

the amount of energy that reactants must absorb before a chemical reaction will start (also called “free energy of activation”)

Catalysis

a process by which a chemical agent called a catalyst selectively increases the rate of a reaction without being consumed by the reaction

• An enzyme CANNOT change the ΔG for a reaction, as it cannot make an endergonic reaction exergonic. Enzymes can only hasten reactions that would eventually occur.

Substrate

the reactant on which an enzyme acts on

Enzyme-Substrate Complex

a temporary complex formed when an enzyme binds to its substrate molecule(s). The enzyme’s catalytic action converts the substrate into the reaction product(s)

Active Site

the specific region of an enzyme that binds the substrate and that forms the pocket in which catalysis occurs

Cofactors

any nonprotein molecule or ion that is required for the proper functioning of an enzyme (MUST be an inorganic molecule)

• Cofactors can be permanently bound to the active site or may bind loosely and reversibly, along with the substrate, during catalysis

Coenzymes

an organic molecule serving as a cofactor (MUST be an organic molecule)

• Most vitamins function as coenzymes in metabolic reactions

Competitive Inhibitors

a substance that reduces the activity of an enzyme by entering the active site in place of the substrate, whose structure it mimics

Noncompetitive Inhibitors

a substance that reduces the activity of an enzyme by binding to a location remote from the active site, changing the enzyme’s shape so that the active site no longer effectively catalyzes the conversion of substrate to product

• Bonds to allosteric site (a binding site on a protein or enzyme that is separate from the active site)

Chloroplast

an organelle found in plants and photosynthetic protists that absorbs sunlight and uses it to drive the synthesis of organic compounds from carbon dioxide and water

Photosynthesis

the conversion of light energy to chemical energy that is stored in sugars or other organic compounds; occurs in plants, algae, and certain prokaryotes

Autotrophs

(“self-feeders”) organisms that sustain themselves without eating anything derived from other living beings

Photoautotrophs

organisms that use light as a source of energy to synthesize organic substances (plants are photoautotrophs)

Heterotrophs

an organism that obtains organic food molecules by eating other organisms or substances derived from them

Decomposers

heterotrophs that decompose and feed on the remains of other organisms and organic litter such as feces and fallen leaves

Stomata

microscopic pores surrounded by guard cells in the epidermis of leaves & stems that allows gas exchange between the environment and the plant’s interior

Stroma

dense fluid within the chloroplast surrounding the thylakoid membrane, containing ribosomes and DNA

Thylakoids

flattened, membranous sacs inside a chloroplast; stacked in columns called grana

Chlorophyll

green pigment located in the membranes within a chloroplast; participates directly in the light reactions that convert solar energy to chemical energy

What are the 2 stages of photosynthesis?

1. Light Reactions

2. Calvin Cycle (Dark Reactions)

Light Reactions

the steps of photosynthesis that convert solar energy to chemical energy (ATP & NADPH), releasing oxygen in the process

• Occurs on the thylakoid membranes of the chloroplast or on membranes of certain prokaryotes

NADP+/NADPH
(oxidized form/reduced form)

electron acceptor molecule in photosynthesis that temporarily stores energized electrons produced from light reactions

Photophosphorylation

process of generating ATP from ADP and phosphate through the means of chemiosmosis

Calvin Cycle

series of reactions in photosynthesis that uses CO2 along with ATP and NADPH to create glucose and other organic molecules

• Reduces carbon atoms into carbohydrates by adding electrons, making sugars

Carbon Fixation

initial incorporation of carbon from carbon dioxide into an organic compound by an autotrophic organism

Electromagnetic Spectrum

entire spectrum of electromagnetic radiation, ranging in wavelength from less than a nanometer to more than a kilometer

• Shorter Wavelengths = Higher Energy

• Longer Wavelengths = Lower Energy

Visible Light

portion of the electromagnetic spectrum that can be detected as various colors by the human eye, ranging in wavelength from about 380 nm to about 750 nm

• This is the radiation that drives photosynthesis

Photons

a quantum/discrete quantity of light energy that behaves as if it were a particle

• Photons are not tangible objects, but they act like objects in the way that each of them has a fixed quantity of energy

Pigment

substance that absorbs visible light, with the light color not absorbed (and is therefore reflected) is the color of the pigment

Absorption Spectrum

range of a pigment’s ability to absorb various wavelengths of light

What are the 3 types of pigments in chloroplasts?

• Chlorophyll a

• Chlorophyll b

• Cartotenoids

Chlorophyll a

photosynthetic pigment participating directly in the light reactions to convert solar energy into chemical energy (found in PSI & PSII)

Chlorophyll b

accessory photosynthetic pigment that transfers energy to chlorophyll a

Cartotenoids

accessory pigment made of hydrocarbons that are various shades of yellow and orange because they absorb violet and blue-green light

Photosystem

light-capturing unit located in the thylakoid membrane, consisting of a reaction-center complex surrounded by numerous light-harvesting complexes

• There are two types of photosystems, I and II

Reaction-Center Complex

complex of proteins associated with a special pair of chlorophyll a molecules and a primary electron acceptor

• Located centrally in a photosystem and triggers the light reactions of photosynthesis

Light-Harvesting Complex

complex of proteins associated with pigment molecules that captures light energy and transfers it to reaction-center pigments in a photosystem

Primary Electron Acceptor

a specialized molecule that shares the reaction-center complex with a pair of chlorophyll a molecules and that accepts an electron from them

Photosystem I (PSI)

one of two light-capturing units in a chloroplast’s thylakoid membrane, having two molecules of P680 chlorophyll a at its reaction center

• Best absorbs light with a wavelength of 680 nm (red part of visible light spectrum)

Photosystem II (PSII)

one of two light-capturing units in a chloroplast’s thylakoid membrane, having two molecules of P700 chlorophyll a at its reaction center

• Best absorbs light with a wavelength of 700 nm (far red part of visible light spectrum)

What molecule supplies the photosystems with electrons when they move down to electron acceptors?

Water (H₂O)

Linear Electron Flow

a route of electron flow during the light reactions of photosynthesis that involves both photosystems (I and II) and produces ATP, NADPH, and oxygen gas

• Net electron flow is from water to NADP+

How can you summarize the Light Reactions?

• -Electron flow pushes electrons from water, where they are at a state of low potential energy, ultimately to NADPH, where they are stored at a state of high potential energy.

  • The light-driven electron flow also generates ATP

• Thus, the equipment of the thylakoid membrane converts light energy to chemical energy stored in ATP and NADPH. (O2 is produced as a by-product)

Is the Calvin Cycle a catabolic or anabolic process?

anabolic process, since it builds carbohydrates from smaller molecules, consuming energy in the process

G3P (glyceraldehyde-3-phosphate)

a three-carbon carbohydrate that is the direct product of the Calvin Cycle (must take place 3 times and use 3 CO2 molecules to make G3P)

What are the 3 phases of the Calvin Cycle?

1. Carbon Fixation

2. Reduction

3. Regeneration of RuBP (CO₂ acceptor)

Phase 1: Carbon Fixation

• One CO₂ molecule is attached to a 5-carbon sugar, ribulose biphosphate (RuBP), 

  • Rubisco: also known as ribulose bisphosphate (RuBP) carboxylase-oxygenase, this is the enzyme that normally catalyzes the first step of the Calvin cycle (carbon fixation)

    • Most abundant protein in chloroplasts, also believed to be the most abundant protein on Earth

• The 6-carbon product (CO₂ + RuBP) is extremely unstable and quickly breaks apart to form 2 molecules of 3-phosphoglycerate (for each CO₂ fixed)

What is the name of the enzyme that catalyzes the first step of the Calvin Cycle and what it does?

RuBisCO catalyzes the first step of the Calvin Cycle (Carbon Fixation)

• Takes CO₂ and attaches it to a molecule of RuBP, making a 6-carbon product

Phase 2: Reduction

• Each 3-phosphoglycerate molecule receives an additional phosphate group from ATP and turns into 1,3-bisphosphoglycerate

• 1,3-bisphosphoglycerate is reduced by NADPH, loses a phosphate group, and turns into G3P

  • G3P is a 3-carbon sugar, and is the same compound formed in glycolysis

• Note that for every three molecules of  that enter the cycle, there are six molecules of G3P formed, but all besides 1 G3P are required to complete the cycle (net gain of 1 G3P)

  • The 5 G3Ps are used to regenerate the 3 RuBP molecules

Phase 3: Regeneration of the CO2 Acceptor (RuBP)

• The carbon skeletons of five molecules of G3P are rearranged into 3 RuBP molecules

  • 3 ATPs are spent to do this

• RuBP is now ready to receive CO2 again, which continues the Calvin Cycle

C3 Plants

a plant that uses the Calvin cycle for the initial steps that incorporate carbon dioxide into organic material, forming a three-carbon compound as the first stable intermediate

• They add CO₂ to ribulose biphosphate, making 3-phosphoglycerate

What happens when a C3 plant close their stomata on hot days?

O₂ is used by Rubisco in the Calvin Cycle instead of CO₂, which uses ATP, doesn’t make sugar, and decreases photosynthetic output

C4 Plants

a plant in which the Calvin cycle is preceded by reactions that incorporate CO2 into a four-carbon compound, the end product of which supplies CO2 for the Calvin cycle

• C4 plants only partially close their stomata when the weather is hot & dry, and continues to make sugar through photosynthetic cells (does NOT go through photorespiration)

Crassulacean Acid Metabolism (CAM)

an adaptation where CO2 entering open stomata during the night is converted to organic acids, which release CO2 for the Calvin cycle during the day, when stomata are closed

• This is an adaptation for photosynthesis in arid conditions

Cyclic Electron Flow

a route of electron flow during the light reactions of photosynthesis that involves only Photosystem I (PSI) and produces ATP but does not produce NADPH or oxygen gas

What are the key differences between linear and cyclic electron flow?

Cyclic: involves only Photosystem I and produces ATP without generating NADPH or O₂

Linear: involves both PSII and PSI, producing ATP, NADPH, and O₂