FBS 31_CARBOHYDRATE METABOLISM

Carbohydrate Metabolism

Involves both synthesis (anabolism) and degradation (catabolism) of carbohydrates in plants.

Carbohydrates

Polyhydroxy aldehydes and polyhydroxy ketones with general ratio C:H:O = 1:2:1.

Reducing Sugars

Sugars that can donate electrons to another chemical, e.g., glucose, fructose, mannose.

Non-Reducing Sugars

Sugars that cannot donate electrons, e.g., sucrose, raffinose, stachyose.

Monosaccharide

Simplest form of carbohydrate; building units for oligo- and polysaccharides.

Oligosaccharide

Carbohydrates made up of 2 or more monosaccharide units joined by glycosidic linkages.

Polysaccharide

Complex carbohydrates composed of many monosaccharides joined through glycosidic bonds.

Starch

Storage product of plants composed of α-D-glucose; yields glucose upon hydrolysis.

Amylose

Straight-chain polymer of glucose linked by α(1-4) bonds; gives blue-black color with iodine.

Amylopectin

Branched polysaccharide linked by α(1-4) and α(1-3) bonds; gives red to purple color with iodine.

Cellulose

Structural polysaccharide made of β(1-4) glucose units; component of cell walls.

Pectin

Pectic substance that forms gels; important in manufacture of jellies.

Protopectin

Insoluble pectic substance that becomes pectin during fruit ripening.

Pentosans

Polymers of five-carbon sugars like xylan and araban found in cell wall matrix.

Phosphorylation

First step in almost all metabolic sugar reactions; addition of phosphate group.

Photosynthesis

Process where CO2 and H2O are converted to glucose and oxygen using light energy.

Chloroplast

Organelle containing chlorophyll; site of photosynthesis with stroma and grana.

Light Reaction

Stage of photosynthesis where light energy is converted to chemical energy (ATP, NADPH2).

Dark Reaction

Stage of photosynthesis that uses ATP and NADPH to fix CO2 into carbohydrates.

Calvin-Benson Cycle

Cycle that fixes carbon from CO2 into three-carbon sugars using ATP and NADPH.

C4 Pathway

Photosynthetic pathway using PEP carboxylase; more efficient than C3.

CAM Pathway

Photosynthetic adaptation for dry conditions; CO2 fixed at night as malate.

Photosystem I

Uses P700 form of chlorophyll a; generates NADPH.

Photosystem II

Uses P680 form of chlorophyll a; splits water to release oxygen.

Electron Transport Chain

Transfers electrons through membrane proteins to generate ATP via chemiosmosis.

ATP Synthase

Enzyme on mitochondrial inner membrane that produces ATP using proton motive force.

Glycolysis

Breaks glucose into two pyruvate molecules in the cytoplasm; yields 2 ATP.

Krebs Cycle

Also called Citric Acid Cycle; completes oxidation of glucose, generating NADH, FADH2, and ATP.

Electron Transport System

Final stage of respiration; converts energy from reduced cofactors to ATP (34 ATP).

Aerobic Respiration

Respiration using oxygen; produces high ATP yield (36–38 ATP).

Anaerobic Respiration

Respiration without oxygen; produces lactic acid, alcohol, and 2 ATP.

Oxidation

Removal of electrons or hydrogen from a compound.

Reduction

Addition of electrons or hydrogen to a compound.

Rubisco

Enzyme that fixes carbon in the Calvin Cycle (Ribulose biphosphate carboxylase).

Transformation of CH2O

Conversion of carbohydrates into other compounds like proteins and lipids.

Photosynthetic Factors

Light intensity, temperature, CO2, water supply, humidity, and soil fertility affect rate.

Respiration

Biochemical process where substrates are oxidized, releasing CO2 and energy (ATP).

Glycolysis ATP Yield

Produces 2 ATP molecules per glucose.

Krebs Cycle ATP Yield

Produces 2 ATP molecules per glucose.

Electron Transport ATP Yield

Produces about 34 ATP molecules per glucose.

Total ATP Yield

Aerobic respiration yields 36 to 38 ATP per glucose molecule.

ATP Synthase Location

Located on inner mitochondrial membrane; catalyzes ATP production.

Chemiosmosis

Process using proton motive force to make ATP via ATP synthase.

Internal Respiration Factors

Age, tissue condition, substrate availability, and hydration level.

External Respiration Factors

Temperature, gases, soil moisture, light, mechanical injury, and pollutants.