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- ( outside the cell )
- Bathes cells in a fluid medium known as extracellular fluid (ECF)
- which may be:
-Interstitial fluid = the fluid medium surrounding most body cells outside of the bloodstream, composed of about 98% water.
-Plasma = the fluid medium within the bloodstream, about 98% water.
-Other forms of ECF include saliva, tears, urine, cerebrospinal fluid.
- The area within a cell, separated from the extracellular environment by the cell membrane.
- About 96% water, and includes organic compounds and electrolytes to form intracellular fluid (ICF).
- Includes two compartments:
- -Cytoplasm-containing cytosol (fluids and organelles (small functional packets); and
- -Nucleus, a large structure containing the DNA.
selectively permeable membrane, which allows only certain substances to pass.
- Fluid mosaic model describes a dynamic membrane composed
- of roughly equal amounts of protein and phospholipid molecules; much like cooking oil.
Proteins stabilize the flowing structure, and act as “gatekeepers” and receptors.
- Head --> hydrophilic
- Tail --> hydrophobic
phospholipid bilayer = double layered arrangement
-Peripheral proteins: attached to either surface of the membrane, but are not submerged within.
-Integral proteins: submerged within the bilayer, often extending through it.
Include transmembrane proteins, which extend through the bilayer and may form channels. The channels may form pores to allow some molecules to flow through, such as water and O2, or ion channels, which regulate passage.
Membrane Proteins (cont.)
- -Anchoring proteins
- -Channel proteins
- -Carrier proteins
- -Receptor proteins
Movement across the Membrane
- Include passive processes, which do not require energy and
- include diffusion, facilitated diffusion, osmosis, and filtration; and active
- processes that require energy and include active transport and cytosis.
movement of molecules from a region of high concentration to a region of low concentration. Example: the respiratory gases (O2 and CO2).
- diffusion of molecules across a selectively permeable membrane with the assistance of carrier
- proteins. Because movement is along a concentration gradient, no energy is required. Example: glucose molecules
The movement of water molecules across a selectively permeable membrane along a concentration gradient.
Osmosis generates a force, caused by the flow of water in one net direction. The force required to oppose the movement of water molecules is known as _______ ________
- Osmosis and osmotic pressure are important factors in water management within cells.
- Example: kidney functions
water is able to flow through the cell membrane through pores without restraint
3 Types of Osmosis dynamics
Isotonic = cell at equilibrium with ECF
Hypertonic = ECF has more solutes than cell; leads to crenation.
Hypotonic = ECF has fewer solutes than cell; leads to hemolysis.
Water is forced across a selectively permeable membrane.
- Solutes too small to pass through pores are held back as
- smaller solutes and water pass through to form the filtrate.
- Example: kidneys filter water and solutes from the
- bloodstream, leaving cells and large molecules to remain in the blood.
- As an active process, it demands energy in the form of ATP.
- Requires assistance from enzymes and/or carrier proteins to move substances across a membrane against a concentration gradient.
Example: sodium-potassium pump.
An active form of transport of large molecules and bulk volumes across the cell membrane; involves intracellular vesicle formation.
2 types of vesicular transport
Endocytosis: process that brings substances into the cell (import).
- Example: receptor-mediated endocytosis, which includes the formation of intracellular endosomes.
- Example: phagocytosis and pinocytosis.
Exocytosis: process that exports substances from the cell.
Example: excretion (secretion) = how the cell releases its products, such as enzymes, hormones, lipids, etc.