Glossary
ATP
Adenosine triphosphate; the main energy currency of the cell, used to power most cellular processes.
Example:
Active transport pumps use ATP to move ions against their concentration gradient, like the sodium-potassium pump.
Calvin cycle
The light-independent reactions of photosynthesis that occur in the chloroplast stroma, using ATP and NADPH from the light reactions to convert carbon dioxide into glucose.
Example:
The sugar produced by the Calvin cycle provides the building blocks and energy storage for the plant.
Cellular respiration
A metabolic pathway that breaks down glucose and other organic molecules to produce ATP, the primary energy currency of the cell.
Example:
During intense exercise, your body increases the rate of cellular respiration to meet the higher demand for energy in muscle cells.
Chlorophyll
The primary green pigment found in chloroplasts that absorbs light energy for photosynthesis.
Example:
The reason leaves change color in the fall is due to the breakdown of chlorophyll, revealing other pigments.
Chloroplast
An organelle found in plant cells and other eukaryotic photosynthetic organisms that conducts photosynthesis, converting light energy into chemical energy.
Example:
The vibrant green color of leaves comes from the numerous chloroplasts within their cells, packed with chlorophyll.
Cristae
The folds of the inner mitochondrial membrane that dramatically increase the surface area available for the electron transport chain, maximizing ATP production.
Example:
Without the extensive folding of the cristae, the mitochondria would be far less efficient at generating energy for the cell.
Electron Transport Chain (ETC)
A series of protein complexes embedded in the inner mitochondrial membrane (cristae) that transfer electrons, creating a proton gradient used to synthesize ATP.
Example:
Cyanide poisoning inhibits the Electron Transport Chain, preventing cells from producing ATP and leading to rapid cell death.
Endoplasmic Reticulum (ER)
A vast network of membranes within the cytoplasm of eukaryotic cells, involved in protein and lipid synthesis, folding, modification, and transport.
Example:
The rough Endoplasmic Reticulum is abundant in cells that secrete large amounts of proteins, such as pancreatic cells producing insulin.
Fluid mosaic model
A model describing the structure of cell membranes as a mosaic of protein molecules drifting in a fluid bilayer of phospholipids.
Example:
According to the fluid mosaic model, the cell membrane is not rigid but rather dynamic, allowing for flexibility and movement of its components.
Golgi apparatus
An organelle in eukaryotic cells consisting of flattened membrane-bound sacs (cisternae) that modifies, sorts, and packages proteins and lipids for secretion or delivery to other organelles.
Example:
Proteins synthesized in the ER are transported to the Golgi apparatus for further modification and sorting into vesicles.
Grana
Stacks of thylakoids within the chloroplast, which increase the efficiency of light energy capture during photosynthesis.
Example:
The more grana a chloroplast contains, the more effectively it can capture sunlight for energy conversion.
Homeostasis
The ability of an organism or cell to maintain a stable internal environment despite changes in external conditions.
Example:
The kidneys play a vital role in maintaining homeostasis by regulating water and salt balance in the body.
Hydrolytic enzymes
Enzymes that catalyze hydrolysis reactions, breaking down complex molecules into simpler ones by adding water.
Example:
The hydrolytic enzymes within lysosomes are crucial for digesting macromolecules like proteins, lipids, and carbohydrates.
Interdependence
The concept that different organelles and cellular processes rely on each other's products or functions to maintain overall cell activity.
Example:
The interdependence between the chloroplasts producing glucose and the mitochondria using it for ATP highlights the coordinated nature of energy flow in a plant cell.
Krebs cycle
Also known as the citric acid cycle, it is a series of chemical reactions in the mitochondrial matrix that completes the breakdown of glucose derivatives, producing ATP, NADH, and FADH2.
Example:
The products of the Krebs cycle, NADH and FADH2, are crucial for fueling the subsequent electron transport chain.
Lysosome
A membrane-bound organelle containing hydrolytic enzymes that break down waste materials, cellular debris, and foreign invaders, acting as the cell's recycling center.
Example:
When a cell needs to remove old or damaged organelles, the lysosome fuses with them to digest and recycle their components.
Matrix
The fluid-filled space within the inner mitochondrial membrane where the Krebs cycle takes place.
Example:
The enzymes for the Krebs cycle are located in the mitochondrial matrix, allowing for efficient processing of molecules before the ETC.
Mitochondria
An organelle found in most eukaryotic cells, often referred to as the 'powerhouse' of the cell, where cellular respiration occurs to generate ATP.
Example:
Muscle cells, which require a lot of energy for contraction, are packed with mitochondria to produce the necessary ATP.
Phospholipid bilayer
The fundamental structure of the plasma membrane, consisting of two layers of phospholipid molecules with their hydrophilic heads facing outwards and hydrophobic tails facing inwards.
Example:
The fluidity of the phospholipid bilayer allows membrane proteins to move laterally within the membrane.
Photosynthesis
The process used by plants, algae, and some bacteria to convert light energy into chemical energy (glucose) from carbon dioxide and water.
Example:
Trees perform photosynthesis to produce the sugars they need for growth, releasing oxygen as a byproduct.
Photosystems
Protein complexes embedded in the thylakoid membranes that capture light energy and convert it into chemical energy during the light-dependent reactions of photosynthesis.
Example:
When light strikes the photosystems, electrons are excited and begin their journey through the electron transport chain in the chloroplast.
Plasma membrane
A selectively permeable barrier that surrounds the cytoplasm of a cell, regulating the passage of substances into and out of the cell and maintaining cellular homeostasis.
Example:
The plasma membrane of a neuron has specific protein channels that open and close to allow nerve impulses to travel.
Protein Processing
The series of modifications that a newly synthesized protein undergoes, including folding, glycosylation, and cleavage, to become a functional molecule.
Example:
After synthesis, proteins undergo protein processing in the ER and Golgi apparatus to ensure they achieve their correct three-dimensional shape and function.
Ribosomes
Molecular machines responsible for protein synthesis (translation), found free in the cytoplasm or attached to the rough endoplasmic reticulum.
Example:
The ribosomes on the rough ER synthesize proteins that are destined for secretion or insertion into membranes.
Selectively permeable
A property of biological membranes that allows some substances to pass through more easily than others, while blocking the passage of large or charged molecules.
Example:
The selectively permeable nature of the cell membrane ensures that essential nutrients enter the cell while waste products are expelled.
Stroma
The fluid-filled space surrounding the thylakoids within the chloroplast, where the Calvin cycle (light-independent reactions) of photosynthesis takes place.
Example:
The enzymes necessary for carbon fixation in the stroma convert carbon dioxide into sugar molecules.
Structure dictates function
A fundamental biological principle stating that the specific arrangement of parts (structure) determines the specific role or activity (function) of an organism, organ, tissue, or cell component.
Example:
The highly folded inner membrane of the mitochondria, known as the cristae, is a perfect example of how increased surface area (structure) allows for more ATP production (function).
Surface Area
The extent of a surface, which in biological systems, often relates to the efficiency of processes like absorption, exchange, or chemical reactions.
Example:
The highly folded inner membrane of the mitochondria increases its surface area, allowing for more sites for the electron transport chain and thus more ATP production.
Thylakoids
Membrane-bound compartments within the chloroplast that contain chlorophyll and photosystems, where the light-dependent reactions of photosynthesis occur.
Example:
The stacked arrangement of thylakoids into grana maximizes the surface area for light absorption.