Cell Biology: Membrane Structure

Passive movement of molecules across a cell membrane from an area of high concentration to an area of low concentration, driven by the inherent kinetic energy of molecules, known as thermal motion.

A solution with a higher concentration of solutes compared to another solution.

A solution with a lower concentration of solutes compared to another solution.

The movement of water across a selectively permeable membrane from a region of higher water concentration to a region of lower water concentration.

The process by which cells transport large molecules across their membranes using vesicles.

A type of vesicular transport where cells take in large particles, such as bacteria.

The first stage of cellular respiration, where glucose is broken down into pyruvate, producing ATP and NADH.

The second stage of cellular respiration, where pyruvate is oxidized in the mitochondria, producing ATP, NADH, and FADH2.

A derivative of a B vitamin that contains sulfur and is involved in various metabolic reactions, especially the breakdown of carbohydrates.

NADH and FADH2 carry high-energy electrons from glycolysis and the Krebs cycle to the electron transport chain.

The process where plants capture sunlight and convert it into chemical energy in the form of glucose, releasing oxygen as a byproduct.

The inner mitochondrial membrane is the site of the electron transport chain.

A cluster of light-absorbing pigments, proteins, and other organic molecules within the thylakoid membrane of chloroplasts.

Reactions where electrons are transferred from one molecule to another. In the electron transport chain, electrons are passed from molecule to molecule, releasing energy.

A group of chlorophyll and carotenoid pigment molecules that capture light energy and transfer it to a reaction center chlorophyll molecule.

The movement of protons across the inner mitochondrial membrane, driven by the electron transport chain, creating a concentration gradient that is used by ATP synthase to produce ATP.

The initial stage of photosynthesis, where light energy is converted to chemical energy.

A complex of proteins in the inner mitochondrial membrane that uses the proton gradient created by the electron transport chain to synthesize ATP.

The second stage of photosynthesis, where carbon dioxide is used to synthesize sugars.

Oxygen accepts the final electron in the Electron transport chain and combines with hydrogen ions to form water.

Proteins, carbohydrates, and fats can all be broken down and used in cellular respiration to generate ATP.

The central chlorophyll molecule in a photosystem that transfers an excited electron to a primary electron acceptor.

A substance that accepts an excited electron from the reaction center chlorophyll, initiating the electron transport chain.

The process where pigment molecules absorb wavelengths of light and reflect others, resulting in the colors we perceive.

The main product of the Calvin cycle, a three-carbon sugar used to make glucose and other organic molecules.

The energy currency of the cell, used to power various cellular processes.

The breakdown of complex molecules into simpler ones, releasing energy. Think of digestion.

The synthesis of complex molecules from simpler ones, requiring energy input. Think of building a protein.

The capacity to do work. It can exist in different forms, like kinetic and potential energy.

The energy of motion. Think of a moving car.

Energy that matter has due to its location or structure. Think of a ball held high up, ready to fall.

The portion of a system's energy that can be used to do work when temperature is uniform. Think of how much energy is actually usable.

The phospholipid bilayer, with its hydrophilic heads facing outward and hydrophobic tails facing inward, creates a selective barrier.

The arrangement of phospholipids and proteins allows for movement and flexibility, contributing to the membrane's fluid nature.

Integral proteins extend through the membrane and act as channels or carriers, allowing hydrophilic molecules to cross. Peripheral proteins are attached to the membrane surface, often aiding in cell signaling.

Membranes allow small, hydrophobic molecules to pass through easily, but larger, hydrophilic molecules like ions and polar molecules require protein channels or carriers to cross.

Active transport moves substances against their concentration gradient, requiring energy from ATP. Passive transport moves substances down their concentration gradient, without requiring energy.

Membrane proteins play a vital role in cellular function by facilitating transport, catalyzing chemical reactions, relaying signals, connecting cells, providing identification markers, and anchoring the cytoskeleton and extracellular matrix.

Phospholipids with double bonds in their fatty acid tails increase membrane fluidity, making it easier for molecules to move around. Cholesterol molecules help to maintain membrane fluidity by preventing it from becoming too rigid or too fluid.

Oligosaccharides are short chains of sugar molecules attached to lipids (glycolipids) or proteins (glycoproteins) on the cell surface, playing a critical role in cell-cell recognition and interactions.

Photosystem II creates a high-energy electron by using light energy, losing its own electron in the process. To replace this electron, water is split, producing molecular oxygen (O₂) as a byproduct.

The energized electron from Photosystem II is passed down an electron transport chain to Photosystem I. This chain involves various components, including plastoquinone, cytochrome proteins, and plastocyanin. The energy released during this transfer helps generate a hydrogen ion gradient across the thylakoid membrane, which is later used by ATP synthase to produce ATP.

The electron that traveled through the electron transport chain from Photosystem II to Photosystem I arrives as low-energy. It is then utilized to replace the activated electron generated by Photosystem I.

Photosystem I absorbs light energy, creating a high-energy electron. This electron is passed to the reaction center chlorophyll a molecule, then to the primary electron acceptor. It then continues down a different electron transport chain to ferredoxin. Ferredoxin then transfers it to the enzyme NADP+ reductase, which converts NADP+ to NADPH.

Sometimes, instead of passing the high-energy electron to NADP+ reductase, Photosystem I passes it to ferredoxin, sending it back to the cytochrome complex of the electron transport chain between Photosystem II and Photosystem I. This occurs because the Calvin cycle needs more ATP than NADPH.

The Calvin cycle utilizes ATP and NADPH produced during the light reactions. It uses carbon dioxide from the air to produce a three-carbon sugar molecule called glyceraldehyde 3-phosphate (G3P).

The Calvin cycle has three phases: Carbon fixation: CO₂ is attached to a 5-carbon molecule called RuBP, which is catalyzed by the enzyme rubisco. Reduction: ATP is used to add phosphate groups, and NADPH is used to reduce the molecules, leading to G3P production. Regeneration: Some G3P is used to make sugars, and the rest regenerate RuBP.