Enzymes in Biochemistry

Enzymes

• Biological catalysts that speed up chemical reactions
• Enzymes assist in metabolic pathways
• Help make reactions start, requiring less energy
• Enzymes are proteins that speed up chemical reactions, making them more likely to happen
• They don't make reactions happen that wouldn't have happened otherwise
• Enzymes make reactions cheaper to run
• Enzymes push reactants up the hill until they reach an energy state high enough for the bonds to break - this is referred to as the transition state
• Transition state is the point at which the reaction goes from needing energy to put into the reaction to releasing energy
• Energy of activation is the energy needed to reach the transition state
• Reactants energy is greater than products energy= Exothermic
• Products energy is greater than reactants energy= Endothermic
• Enzymes speed up a reaction by lowering the energy of activation
• Want to get the benefit with minimal effort

Characteristics of Enzymes

• They don't create reactions
• Not altered or used up by the reaction, they are recycled
• Substrate specific (specific to reaction type)
• Function is based on 3-dimensional shape
• Mostly proteins

Photosynthesis

• Life is powered by solar energy
• Photosynthesis converts solar energy into chemical energy
• Autotrophs are the producers of the biosphere
• Photoautotrophs are photosynthetic organisms including plants, multicellular algae, unicellular protists, cyanobacteria, and purple sulfur bacteria
• Heterotrophs are the consumers of the biosphere and typically depend on photoautotrophs for food and oxygen

Plant Leaf Morphology

• Some plant structures have evolved to absorb sunlight
• Leaves are the main area for photosynthesis
• Leaves have about half a million chloroplasts per square millimeter
• Chloroplasts are found mainly in the mesophyll
• Mesophyll cells are densely packed with chloroplasts (about 30-40 per cell)
• Leaves have a high surface area to act as photosynthetic arrays
• They are wide and thin to absorb sunlight to power photosynthesis
• Leaves are organs composed of tissues (layers of cells) like the mesophyll
• CO2 and O2 enter and exit through stomata and the open/close state is controllable by the plant
• H2O enters through the roots, reaches the leaves through a network of veins and veins export sugar to roots and other non-photosynthetic parts of the plant
• Plants have both chloroplasts for photosynthesis and mitochondria for cellular respiration
• Chloroplasts have multiple membranes because they were once free-living organisms (bacteria) that was engulfed by another organism (eating)
• This deposited another membrane, referred to as the endosymbiotic theory

Chloroplast Structure

• Thylakoid is a cookie-shaped sack in a stacked structure called granum (contains a lumen)
• This is where photosynthesis takes place
• Stroma is the space around the thylakoids
• Chemical equation for photosynthesis is 6CO2 + 12H2O + light -> C6H12O6 + 6O2 + 6H2O
• The reaction is the reverse of cellular respiration
• It's an endergonic redox process
• H2O is oxidized to O2 and CO2 is reduced to glucose
• The goal is to make sugar for food or structure
• Water is oxidized to oxygen, and CO2 is reduced to sugar

Photosynthesis Stages

• Two stages of photosynthesis: the light reaction and the Calvin Cycle (light-independent reaction)
• Light reaction converts light energy into ATP and NADPH (reducing power) which is sent to the Calvin Cycle
• Thylakoid membranes transport the energy from light-dependent reactions to the Calvin Cycle
• Calvin Cycle uses ATP and NADPH to fix carbon
• The goal of the Calvin Cycle is to create glucose from CO2
• This takes place in the stroma

Light Energy

• Light is electromagnetic energy or radiation
• Electromagnetic spectrum ranges from 380 to 750 nm (visible light spectrum)
• Light travels in rhythmic waves but consists of discrete particles called photons
• Photons have a fixed quantity of energy
• Pigments absorb visible light

ATP Production During Photosynthesis

• ATP is made through the same process as cellular respiration
• Hydrogen ion gradient
• Dropping ions through ATP Synthase, spins it to produce ATP
• Stoma/Stomata are openings that allow CO2 and O2 in and out

Light Absorption

• Light energy causes electrons to become excited
• The electrons move to a higher energy shell, which makes them unstable
• They fall back to a stable ground state, releasing heat and a photon (fluorescence)
• Pigments are organized into photosystems in the thylakoid membrane
• Light harvesting complexes are proteins with suspended chlorophyll molecules that can absorb photons of light energy
• This energy is handed off until it gets to paired chlorophyll a molecules, which energizes an electron that jumps up to the primary electron acceptor found in the reaction-center complex
• The primary electron acceptor prevents the energized electron from falling back down

Photosystems

• Two photosystems: Photosystem I (P700) and Photosystem II (P680)
• P700 absorbs wavelengths of 700nm (far-red)
• P680 absorbs wavelengths of 680nm (also red part of the spectrum)
• Light drives the synthesis of NADPH and ATP
• The key to energy transformation is the flow of electrons through photosystems
• There are two types of electron flow: non-cyclic and cyclic electron flow
• Non-cyclic electron flow is the primary type
• Water is oxidized, which provides electrons
• This is why oxygen is produced during photosynthesis

Electron Transport Chain

• Electrons move to an electron transport chain between the photosystems
• This provides energy to regenerate ATP
• ATP is regenerated by sticking electrons onto NADP+
• This requires H+
• H+ is needed for RuBP regeneration (ribulose bisphosphate)

Calvin Cycle

• The input for the Calvin Cycle is 6 CO2
• There are 6 RuBP (ribulose bisphosphate) molecules.
• These bind to the CO2 and result in 12 molecules of 1,3-BPG (bisphosphoglycerate)
• 12 NADPH donate electrons to reduce 12 BPG to 12 G3P (glyceraldehyde 3-phosphate)
• 12 NADP are produced during this reaction
• 12 G3P are converted to 10 G3P and 2 G3P
• These 2 G3P molecules are used to create glucose
• The remaining 10 G3P molecules are recycled back into 6 RuBP molecules

Breaking Down Photosynthesis Stages

• 6 CO2 + 12 H2O + light -> sugar + 6 O2 + 6 H2O
• H2O is the source of electrons
• This is extracted from the stripping off of electrons and H
• CO2 is the source of carbon fixed into organic molecules
• Water is oxidized to oxygen
• Light-dependent reactions produce ATP and NADPH
• The Calvin Cycle produces sugar
• Light-dependent reactions require water and produce oxygen
• The Calvin Cycle requires CO2 and produces sugar