Non-membrane-bound organelles that synthesize proteins. Composed of rRNA and proteins; consists of a small and large subunit. Free ribosomes synthesize proteins for use within the cell; bound ribosomes (on rough ER) synthesize proteins for secretion or membrane insertion
Rough ER: studded with ribosomes; synthesizes and processes proteins destined for secretion or membrane insertion. Smooth ER: lacks ribosomes; synthesizes lipids (including steroids), detoxifies harmful substances, stores calcium. Both are continuous with the nuclear envelope
Receives proteins from rough ER via vesicles; modifies them (glycosylation, phosphorylation); sorts and packages them for secretion (exocytosis) or delivery to other organelles (lysosomes, plasma membrane). Consists of cis (receiving) and trans (shipping) faces
Double-membrane organelle. Outer membrane: smooth. Inner membrane: highly folded into cristae (increases surface area) to house electron transport chain. Intermembrane space: between membranes. Matrix: interior space containing Krebs cycle enzymes and mitochondrial DNA (circular, prokaryote-like). Site of cellular respiration (aerobic ATP production)
Membrane-bound sacs containing hydrolytic enzymes (optimal pH ~4.5-5). Functions: intracellular digestion (phagocytosis, autophagy), recycling of cellular components, apoptosis (programmed cell death). Formed from Golgi apparatus. Defects cause storage diseases (e.g., Tay-Sachs)
Large membrane-bound storage vesicles. Central vacuole (plants): stores water, nutrients, pigments, waste; maintains turgor pressure. Contractile vacuoles (protists): pump excess water out of cell. Food vacuoles (protists): digest prey. Storage vacuoles (fungi, some protists): store nutrients, toxins
Double-membrane organelle unique to plants and algae. Outer membrane: smooth. Inner membrane: encloses stroma. Thylakoids: membrane sacs where light reactions occur; stacked into grana. Stroma: fluid-filled interior containing Calvin cycle enzymes and chloroplast DNA. Site of photosynthesis
Mitochondria and chloroplasts each have a double membrane (two phospholipid bilayers). The inner membrane is highly specialized: cristae in mitochondria, thylakoids in chloroplasts. Evidence supporting endosymbiotic theory - prokaryotic ancestors had their own membranes
Thylakoids: flat, membrane-bound sacs that contain chlorophyll and the photosystem reaction centers. Light-dependent reactions occur on thylakoid membranes. Grana: stacks of thylakoids. Stroma: the fluid-filled space outside thylakoids; contains Calvin cycle enzymes and ribosomes
The Krebs cycle (also called Citric Acid Cycle) occurs in the mitochondrial matrix. This is the interior compartment of the mitochondrion. Acetyl-CoA enters the matrix and is fully oxidized over one turn of the cycle, producing NADH, FADH2, ATP, and CO2
As a cell grows, its volume increases faster than its surface area. SA/V ratio decreases with size. This limits cell size because the membrane must supply nutrients and remove waste for the entire volume. Cells must stay small or flatten/branch to maintain adequate SA/V
The rate of diffusion across a membrane is proportional to surface area. The metabolic demand (nutrients needed, waste produced) is proportional to volume. When SA/V is too low, diffusion cannot keep up with metabolic needs. This is why cells divide when they grow too large
The fundamental structure of the plasma membrane. Composed of two layers of phospholipids with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward. Creates a selectively permeable barrier - small nonpolar molecules pass easily; polar molecules and ions require transport proteins
The phosphate group head is polar and hydrophilic (water-loving), facing the extracellular fluid and cytoplasm. The fatty acid tails are nonpolar and hydrophobic (water-fearing), facing the interior of the bilayer. This amphipathic property drives spontaneous bilayer formation in water
Two types: Integral proteins span the entire bilayer (transmembrane); Peripheral proteins attach to one face of the membrane. Functions: transport (channels, carriers, pumps), receptors (signal reception), enzymes (catalysis), adhesion (cell junctions), identity (MHC proteins, blood group antigens)
The current model of membrane structure. The phospholipid bilayer is a fluid (liquid) environment where lipids and proteins can move laterally. Proteins "float" in the bilayer like icebergs - mosaic pattern. Carbohydrates attach to lipids (glycolipids) or proteins (glycoproteins) on the extracellular surface
The plasma membrane allows some substances to pass while blocking others. Small nonpolar molecules (O2, CO2) pass freely. Polar molecules and ions require specific transport proteins or energy. This selectivity is essential for maintaining homeostasis
Small nonpolar molecules (O2, CO2, N2) and hydrophobic molecules dissolve directly in the phospholipid bilayer and diffuse across without any protein assistance. Rate is proportional to the concentration gradient and membrane surface area
Polar molecules and large particles cannot pass through the hydrophobic interior of the bilayer. They require: passive transport (facilitated diffusion via channel/carrier proteins) or active transport (pumps using ATP or coupled transport). Examples: glucose, amino acids, ions, water
A rigid, permeable structure outside the plasma membrane in plants, fungi, algae, and bacteria. Primary cell wall: cellulose in plants. Secondary cell wall: additional layers in some cells. Functions: structural support, protection, preventing excessive water uptake, maintaining cell shape
The difference in concentration of a substance between two regions. Passive transport moves with (down) the gradient; active transport moves against (up) the gradient. Steeper gradients drive faster diffusion rates
Movement of molecules across a membrane without energy input, driven by concentration gradient. Includes simple diffusion, facilitated diffusion, and osmosis. Net movement is from high to low concentration until equilibrium is reached
Movement of molecules against their concentration gradient, requiring energy (ATP or coupled transport). Enables cells to accumulate nutrients and expel waste against gradients. Example: Na+/K+ ATPase pump maintains Na+ and K+ gradients
A type of active transport. The cell membrane engulfs external material by forming an invagination/pinching off a vesicle. Three types: phagocytosis ("cell eating" - large particles), pinocytosis ("cell drinking" - fluids), receptor-mediated endocytosis (specific molecules via receptors)
A type of active transport. Vesicles from the Golgi fuse with the plasma membrane, releasing their contents outside the cell. Used for secretion of proteins, hormones, neurotransmitters, and membrane components. The membrane surface area is maintained as vesicle membrane becomes part of the plasma membrane
Integral membrane proteins that form pores or channels allowing specific ions or molecules to cross the membrane. Transport is passive (with gradient). Types: ion channels (Na+, K+, Ca2+, Cl-), aquaporins (water). Channels can be gated (open/close in response to signals)
Membrane proteins that bind a specific molecule and undergo a conformational change to transport it across. Transport is passive (facilitated diffusion) unless coupled to an energy source. Examples: glucose transporters (GLUT), amino acid transporters. Slower but more specific than channel proteins
Specialized channel proteins for water transport. Each aquaporin allows ~3 billion water molecules to pass per second. Essential in cells with high water flux: kidney tubules, plant root hairs, red blood cells. Mutated aquaporins are linked to cataracts and diabetes insipidus
The solution with a higher solute concentration relative to the cell. Water moves out of the cell by osmosis -> cell shrinks (crenation in animal cells, plasmolysis in plant cells). The extracellular environment is hypertonic to the cytoplasm
The solution with a lower solute concentration relative to the cell. Water moves into the cell by osmosis -> cell swells (lysis in animal cells, turgor pressure in plant cells). Plant cells resist lysis due to cell wall
The solution with equal solute concentration on both sides of the membrane. No net water movement -> cell maintains its normal shape. Animal cells thrive in isotonic conditions (e.g., blood plasma). Plant cells are not turgid but not lysed either
Water potential (Psi) = solute potential (Psis) + pressure potential (Psip). Psis = -iCRT (i = ionization constant, C = molar concentration, R = pressure constant, T = temperature in Kelvin). Water moves from higher (less negative) Psi to lower (more negative) Psi
The component of water potential due to dissolved solutes. Adding solutes lowers (makes more negative) the water potential. Pure water has Psis = 0. Solute potential is always negative for solutions (assuming no pressure applied)
An active transport pump that moves 3 Na+ out and 2 K+ in per ATP hydrolyzed (1 ATP -> 1 cycle). Maintains Na+ and K+ gradients essential for nerve impulse transmission, muscle contraction, and secondary active transport. The Na+ gradient drives many other cotransport systems
The combined effect of concentration gradient and electrical potential on ion movement. Ions are affected by both chemical (concentration) and electrical (charge) forces. The Na+/K+ gradient is critical for secondary active transport and nerve signaling. Resting membrane potential in neurons is ~-70 mV
Membrane-enclosed structures within eukaryotic cells that perform specific functions. Compartmentalize cellular processes, creating specialized microenvironments. Examples: nucleus, mitochondria, ER, Golgi, lysosomes, chloroplasts. Prokaryotes lack membrane-bound organelles
Prokaryotes (bacteria, archaea): no nucleus (circular DNA in nucleoid), no membrane-bound organelles, smaller (~1-10 mum), 70S ribosomes. Eukaryotes: membrane-bound nucleus, membrane-bound organelles, larger (~10-100 mum), 80S ribosomes (in cytoplasm; 70S in mitochondria/chloroplasts)
Proposed by Lynn Margulis. Mitochondria and chloroplasts originated as free-living aerobic bacteria and photosynthetic cyanobacteria engulfed by ancestral eukaryotic cells ~2 billion years ago. Both became symbiotic organelles over evolutionary time
Mitochondria contain their own circular DNA (similar to bacterial chromosome), 70S ribosomes (like bacteria), and divide independently by binary fission. This DNA encodes some but not all mitochondrial proteins (most are encoded by nuclear DNA). Inherited maternally in most animals
Non-membrane-bound organelles that synthesize proteins. Composed of rRNA and proteins; consists of a small and large subunit. Free ribosomes synthesize proteins for use within the cell; bound ribosomes (on rough ER) synthesize proteins for secretion or membrane insertion
Rough ER: studded with ribosomes; synthesizes and processes proteins destined for secretion or membrane insertion. Smooth ER: lacks ribosomes; synthesizes lipids (including steroids), detoxifies harmful substances, stores calcium. Both are continuous with the nuclear envelope
Receives proteins from rough ER via vesicles; modifies them (glycosylation, phosphorylation); sorts and packages them for secretion (exocytosis) or delivery to other organelles (lysosomes, plasma membrane). Consists of cis (receiving) and trans (shipping) faces
Double-membrane organelle. Outer membrane: smooth. Inner membrane: highly folded into cristae (increases surface area) to house electron transport chain. Intermembrane space: between membranes. Matrix: interior space containing Krebs cycle enzymes and mitochondrial DNA (circular, prokaryote-like). Site of cellular respiration (aerobic ATP production)
Membrane-bound sacs containing hydrolytic enzymes (optimal pH ~4.5-5). Functions: intracellular digestion (phagocytosis, autophagy), recycling of cellular components, apoptosis (programmed cell death). Formed from Golgi apparatus. Defects cause storage diseases (e.g., Tay-Sachs)
Large membrane-bound storage vesicles. Central vacuole (plants): stores water, nutrients, pigments, waste; maintains turgor pressure. Contractile vacuoles (protists): pump excess water out of cell. Food vacuoles (protists): digest prey. Storage vacuoles (fungi, some protists): store nutrients, toxins
Double-membrane organelle unique to plants and algae. Outer membrane: smooth. Inner membrane: encloses stroma. Thylakoids: membrane sacs where light reactions occur; stacked into grana. Stroma: fluid-filled interior containing Calvin cycle enzymes and chloroplast DNA. Site of photosynthesis
Mitochondria and chloroplasts each have a double membrane (two phospholipid bilayers). The inner membrane is highly specialized: cristae in mitochondria, thylakoids in chloroplasts. Evidence supporting endosymbiotic theory - prokaryotic ancestors had their own membranes
Thylakoids: flat, membrane-bound sacs that contain chlorophyll and the photosystem reaction centers. Light-dependent reactions occur on thylakoid membranes. Grana: stacks of thylakoids. Stroma: the fluid-filled space outside thylakoids; contains Calvin cycle enzymes and ribosomes
The Krebs cycle (also called Citric Acid Cycle) occurs in the mitochondrial matrix. This is the interior compartment of the mitochondrion. Acetyl-CoA enters the matrix and is fully oxidized over one turn of the cycle, producing NADH, FADH2, ATP, and CO2
As a cell grows, its volume increases faster than its surface area. SA/V ratio decreases with size. This limits cell size because the membrane must supply nutrients and remove waste for the entire volume. Cells must stay small or flatten/branch to maintain adequate SA/V
The rate of diffusion across a membrane is proportional to surface area. The metabolic demand (nutrients needed, waste produced) is proportional to volume. When SA/V is too low, diffusion cannot keep up with metabolic needs. This is why cells divide when they grow too large
The fundamental structure of the plasma membrane. Composed of two layers of phospholipids with hydrophilic (water-attracting) heads facing outward and hydrophobic (water-repelling) tails facing inward. Creates a selectively permeable barrier - small nonpolar molecules pass easily; polar molecules and ions require transport proteins
The phosphate group head is polar and hydrophilic (water-loving), facing the extracellular fluid and cytoplasm. The fatty acid tails are nonpolar and hydrophobic (water-fearing), facing the interior of the bilayer. This amphipathic property drives spontaneous bilayer formation in water
Two types: Integral proteins span the entire bilayer (transmembrane); Peripheral proteins attach to one face of the membrane. Functions: transport (channels, carriers, pumps), receptors (signal reception), enzymes (catalysis), adhesion (cell junctions), identity (MHC proteins, blood group antigens)
The current model of membrane structure. The phospholipid bilayer is a fluid (liquid) environment where lipids and proteins can move laterally. Proteins "float" in the bilayer like icebergs - mosaic pattern. Carbohydrates attach to lipids (glycolipids) or proteins (glycoproteins) on the extracellular surface
The plasma membrane allows some substances to pass while blocking others. Small nonpolar molecules (O2, CO2) pass freely. Polar molecules and ions require specific transport proteins or energy. This selectivity is essential for maintaining homeostasis
Small nonpolar molecules (O2, CO2, N2) and hydrophobic molecules dissolve directly in the phospholipid bilayer and diffuse across without any protein assistance. Rate is proportional to the concentration gradient and membrane surface area
Polar molecules and large particles cannot pass through the hydrophobic interior of the bilayer. They require: passive transport (facilitated diffusion via channel/carrier proteins) or active transport (pumps using ATP or coupled transport). Examples: glucose, amino acids, ions, water
A rigid, permeable structure outside the plasma membrane in plants, fungi, algae, and bacteria. Primary cell wall: cellulose in plants. Secondary cell wall: additional layers in some cells. Functions: structural support, protection, preventing excessive water uptake, maintaining cell shape
The difference in concentration of a substance between two regions. Passive transport moves with (down) the gradient; active transport moves against (up) the gradient. Steeper gradients drive faster diffusion rates
Movement of molecules across a membrane without energy input, driven by concentration gradient. Includes simple diffusion, facilitated diffusion, and osmosis. Net movement is from high to low concentration until equilibrium is reached
Movement of molecules against their concentration gradient, requiring energy (ATP or coupled transport). Enables cells to accumulate nutrients and expel waste against gradients. Example: Na+/K+ ATPase pump maintains Na+ and K+ gradients
A type of active transport. The cell membrane engulfs external material by forming an invagination/pinching off a vesicle. Three types: phagocytosis ("cell eating" - large particles), pinocytosis ("cell drinking" - fluids), receptor-mediated endocytosis (specific molecules via receptors)
A type of active transport. Vesicles from the Golgi fuse with the plasma membrane, releasing their contents outside the cell. Used for secretion of proteins, hormones, neurotransmitters, and membrane components. The membrane surface area is maintained as vesicle membrane becomes part of the plasma membrane
Integral membrane proteins that form pores or channels allowing specific ions or molecules to cross the membrane. Transport is passive (with gradient). Types: ion channels (Na+, K+, Ca2+, Cl-), aquaporins (water). Channels can be gated (open/close in response to signals)
Membrane proteins that bind a specific molecule and undergo a conformational change to transport it across. Transport is passive (facilitated diffusion) unless coupled to an energy source. Examples: glucose transporters (GLUT), amino acid transporters. Slower but more specific than channel proteins
Specialized channel proteins for water transport. Each aquaporin allows ~3 billion water molecules to pass per second. Essential in cells with high water flux: kidney tubules, plant root hairs, red blood cells. Mutated aquaporins are linked to cataracts and diabetes insipidus
The solution with a higher solute concentration relative to the cell. Water moves out of the cell by osmosis -> cell shrinks (crenation in animal cells, plasmolysis in plant cells). The extracellular environment is hypertonic to the cytoplasm
The solution with a lower solute concentration relative to the cell. Water moves into the cell by osmosis -> cell swells (lysis in animal cells, turgor pressure in plant cells). Plant cells resist lysis due to cell wall
The solution with equal solute concentration on both sides of the membrane. No net water movement -> cell maintains its normal shape. Animal cells thrive in isotonic conditions (e.g., blood plasma). Plant cells are not turgid but not lysed either
Water potential (Psi) = solute potential (Psis) + pressure potential (Psip). Psis = -iCRT (i = ionization constant, C = molar concentration, R = pressure constant, T = temperature in Kelvin). Water moves from higher (less negative) Psi to lower (more negative) Psi
The component of water potential due to dissolved solutes. Adding solutes lowers (makes more negative) the water potential. Pure water has Psis = 0. Solute potential is always negative for solutions (assuming no pressure applied)
An active transport pump that moves 3 Na+ out and 2 K+ in per ATP hydrolyzed (1 ATP -> 1 cycle). Maintains Na+ and K+ gradients essential for nerve impulse transmission, muscle contraction, and secondary active transport. The Na+ gradient drives many other cotransport systems
The combined effect of concentration gradient and electrical potential on ion movement. Ions are affected by both chemical (concentration) and electrical (charge) forces. The Na+/K+ gradient is critical for secondary active transport and nerve signaling. Resting membrane potential in neurons is ~-70 mV
Membrane-enclosed structures within eukaryotic cells that perform specific functions. Compartmentalize cellular processes, creating specialized microenvironments. Examples: nucleus, mitochondria, ER, Golgi, lysosomes, chloroplasts. Prokaryotes lack membrane-bound organelles
Prokaryotes (bacteria, archaea): no nucleus (circular DNA in nucleoid), no membrane-bound organelles, smaller (~1-10 mum), 70S ribosomes. Eukaryotes: membrane-bound nucleus, membrane-bound organelles, larger (~10-100 mum), 80S ribosomes (in cytoplasm; 70S in mitochondria/chloroplasts)
Proposed by Lynn Margulis. Mitochondria and chloroplasts originated as free-living aerobic bacteria and photosynthetic cyanobacteria engulfed by ancestral eukaryotic cells ~2 billion years ago. Both became symbiotic organelles over evolutionary time
Mitochondria contain their own circular DNA (similar to bacterial chromosome), 70S ribosomes (like bacteria), and divide independently by binary fission. This DNA encodes some but not all mitochondrial proteins (most are encoded by nuclear DNA). Inherited maternally in most animals