Studied by 0 people
Cell
is the basic structural and functional unit of living organisms/life.
three major regions of a generalized cell
Plasma Membrane Cytoplasm Nucleus
Plasma membrane
The outer boundary of the cell which acts as a selectively permeable barrier.
Cytoplasm
The intracellular fluid packed with organelles, small structures that perform specific cell function.
Nucleus
an organelle that controls cellular activities.
Plasma Membrane Composition
Lipid bilayer and proteins in constantly changing fluid mosaic
Plays dynamic role in cellular activity
Separates intracellular fluid (ICF) from extracellular fluid (ECF)
Interstitial fluid (IF) = ECF that surrounds cells
Plasma Membrane Lipids
75% phospholipids (lipid bilayer) Phosphate heads: polar and hydrophilic Fatty acid tails: nonpolar and hydrophobic (Review Fig. 2.16b)
5% glycolipids Lipids with polar sugar groups on outer membrane surface
20% cholesterol Increases membrane stability
Plasma Membrane Protein
Allow communication with environment
½ mass of plasma membrane
Most specialized membrane functions
Some float freely
Some tethered to intracellular structures
Two types of Plasma Membrane Proteins
Integral proteins and peripheral proteins
Integral Proteins
Firmly inserted into membrane (most are transmembrane)
Have hydrophobic and hydrophilic regions
Can interact with lipid tails and water
Function as transport proteins (channels and carriers), enzymes, or receptors
Peripheral proteins
Loosely attached to integral proteins
Include filaments on intracellular surface for membrane support
Function as enzymes
motor proteins for shape change during cell division and muscle contraction
cell-to-cell connections
Six Functions of Membrane Proteins
Transport
Receptors for signal transduction
Attachment to cytoskeleton and extracellular matrix
Enzymatic activity
Intercellular joining
Cell-cell recognition
The Glycocalyx
Sugar covering" at cell surface
Lipids and proteins with attached carbohydrates (sugar groups)
Every cell type has different pattern of sugars
Specific biological markers for cell to cell recognition
Allows immune system to recognize "self" and "non self"
Cancerous cells change it continuously
Cell Junctions
Some cells "free" e.g., blood cells, sperm cells
Some bound into communities
Cell Junction: Three ways cells are bound
Tight junctions Desmosomes Gap junctions
Tight Junctions
Impermeable junctions prevent molecules from passing through the intercellular space
Desmosomes
Anchoring junctions bind adjacent cells together like a molecular "Velcro" and help form an internal tension-reducing network of fibers.
Gap junctions
Communicating junctions allow ions and small molecules to pass for intercellular communication.
Cells surrounded by interstitial fluid (IF) which
Contains thousands of substances, e.g., amino acids, sugars, fatty acids, vitamins, hormones, salts, waste products
Plasma membrane allows cell to
Obtain from IF exactly what it needs, exactly when it is needed
Keep out what it does not need
Membrane transport
Plasma membranes selectively permeable
Some molecules pass through easily; some do not
Two ways substances cross membrane
passive processes and active processes
Passive Processes
No cellular energy (ATP) required
Substance moves down its concentration gradient
Active Processes
Energy (ATP) required
Occurs only in living cell membranes
Two types of Passive Transport
Diffusion and Filtration
Types Of Diffusion
Simple diffusion
Facilitated diffusion [Carrier-mediated or Channel-mediated]
Osmosis
Diffusion
Collisions cause molecules to move down or with their concentration gradient
Difference in concentration between two areas
Speed influenced by molecule size and temperature
Molecule will passively diffuse through membrane if
It is lipid soluble, or
Small enough to pass through membrane channels, or
Assisted by carrier molecule
Filtration
Usually across capillary walls
Simple Diffusion
Nonpolar lipid-soluble (hydrophobic) substances diffuse directly through phospholipid bilayer
E.g., oxygen, carbon dioxide, fat-soluble vitamins
Facilitated Diffusion
Certain lipophobic molecules (e.g., glucose, amino acids, and ions) transported passively by:
Binding to protein carriers
Moving through water-filled channels
Carrier-mediated Facilitated Diffusion
via protein carrier specific for one chemical; binding of substrate causes transport protein to change shape
Channel-mediated Facilitated Diffusion
through a channel protein; mostly ions selected on basis of size and charge
Osmosis
Movement of solvent (e.g., water) across selectively permeable membrane
Osmosis: Water diffuses through plasma membranes through ____________
Through lipid bilayer
Through specific water channels called aquaporins (AQPs)
Osmosis occurs when water concentration is ________ on the two sides of the membrane
Different
Osmosis
Membrane permeable to both solutes and water
Membrane permeable to water, impermeable to solutes
Importance of Osmosis
Osmosis causes cells to swell and shrink
Change in cell volume disrupts cell function, especially in neurons
Two types of Active Processes
Active transport and vesicular transport
Active transport
Requires carrier proteins (solute pumps)
Bind specifically and reversibly with substance
Moves solutes against concentration gradient Requires energy
Two types of active transport
Primary and secondary
Primary active transport
Required energy directly from ATP hydrolysis
Secondary active transport
Required energy indirectly from ionic gradients created by primary active transport
Depends on ion gradient created by primary active transport
Energy stored in ionic gradients used indirectly to drive transport of other solutes
Most investigated example of primary active transport
Sodium-potassium pump
Carrier (pump) called Na+-K+ ATPase
Located in all plasma membranes
Involved in primary and secondary active transport of nutrients and ions
Cotransport
always transports more than one substance at a time
Symport system
Substances transported in same direction
Antiport system
Substances transported in opposite directions
Vesicular transport
Transport of large particles, macromolecules, and fluids across membrane in membranous sacs called vesicles
Requires cellular energy (e.g., ATP)
Exocytosis
transport out of cell
Endocytosis
Transport into cell
Three types of endocytosis
Phagocytosis pinocytosis receptor-mediated
Phagocytosis
Pseudopods engulf solids and bring them into cell's interior
Form vesicle called phagosome
Used by macrophages and some white blood cells
Pinocytosis [fluid-phase]
The cell "gulps" a drop of extracellular fluid containing solutes into tiny vesicles. No receptors are used, so the process is nonspecific. Most vesicles are protein-coated
Receptor-mediated
Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands may simply be released inside the cell, or combined with a lysosome to digest contents. Receptors are recycled to the plasma membrane in vesicles.
Exocytosis
Usually activated by cell-surface signal or change in membrane voltage
Substance enclosed in secretory vesicle
v-SNAREs ("v" = vesicle) on vesicle find t-SNAREs ("t" = target) on membrane and bind
Functions of exocytosis
Hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes
Exocytosis
Resting membrane potential - how it is established
Diffusion causes ionic imbalances that polarize the membrane, and active transport processes maintain that membrane potential
Cell-Environment Interactions always involve
glycocalyx
Cell adhesion molecules (CAMs)
Plasma membrane receptors
Voltage-gated channel proteins
Roles of Cell Adhesion Molecules
Attract WBCs to injured or infected areas
Stimulate synthesis or degradation of adhesive membrane junctions
Transmit intracellular signals to direct cell migration, proliferation, and specialization
Contact signaling
touching and recognition of cells; e.g., in normal development and immunity
Chemical signaling
interaction between receptors and ligands (neurotransmitters, hormones, and paracrines) to alter activity of cell proteins (e.g., enzymes or chemically gated ion channels)
Chemical signaling diagram
Composition of cytosol
Located between plasma membrane and nucleus
Composed of: Cytosol Organelles Inclusions
Cytosol
Water with solutes (protein, salts, sugars, etc.)
Organelles
Metabolic machinery of cell; each with specialized function; either membranous or nonmembranous
Inclusions
Vary with cell type; e.g., glycogen granules, pigments, lipid droplets, vacuoles, crystals
Mitochondria
Double-membrane structure with inner shelflike cristae
Contain their own DNA, RNA, ribosomes
Mitochondria provide most
of cell's ATP via aerobic cellular respiration
Requires oxygen
Mitochondria is similar to bacteria because it is capable of cell division called
fission
Mitochondrion
Ribosome
Granules containing protein and rRNA
Site of protein synthesis
Free ribosomes
synthesize soluble proteins that function in cytosol or other organelles
Membrane-bound ribosomes
(forming rough ER) synthesize proteins to be incorporated into membranes, lysosomes, or exported from cell
Endoplasmic Reticulum (ER)
Interconnected tubes and parallel membranes enclosing cisterns
Continuous with outer nuclear membrane
Two varieties of ER
Rough ER and Smooth ER
Rough ER
External surface studded with ribosomes
Manufactures all secreted proteins
Rough ER synthesizes membrane integral _____ and ______
proteins and phospholipids
Smooth ER
Network of tubules continuous with rough ER
The enzymes of Smooth ER function in
Lipid metabolism; cholesterol and steroid-based hormone synthesis; making lipids of lipoproteins
Absorption, synthesis, and transport of fats
Detoxification of drugs, some pesticides, carcinogenic chemicals
Converting glycogen to free glucose
Storage and release of calcium
Golgi apparatus
Stacked and flattened membranous sacs
The golgi apparatus modifie, concentrates, and packages proteins and lipids from the _______ __
Rough ER
Golgi apparatus diagram
Peroxisomes
Membranous sacs containing powerful oxidases and catalases
Peroxisomes detoxify harmful or toxic substances and
Catalysis and synthesis of fatty acids
Peroxisomes neutralize dangerous
free radicals (highly reactive chemicals with unpaired electrons)
Lysosomes are
Spherical membranous bags containing digestive enzymes (acid hydrolases)
"Safe" sites for intracellular digestion
Lysosomes digest ingested bacteria, viruses, and toxins as well as
Degrade nonfunctional organelles
Lysosomes
Destroy cells in injured or nonuseful tissue (autolysis)
Break down bone to release Ca2+
Cytoskeleton
Elaborate series of rods throughout cytosol; proteins link rods to other cell structures
Three types fibers that make up the cytoskeleton
Microfilaments
Intermediate filaments
Microtubules
Microfilaments
Thinnest of cytoskeletal elements
Dynamic strands of protein actin
Each cell has a unique arrangement of strands
Microfilaments are involved in cell motility, change in shape, endocytosis and ____________
exocytosis
Microfilaments diagram
Intermediate filaments
Tough, insoluble, ropelike protein fibers
Composed of tetramer fibrils
Resist pulling forces on cell; attach to desmosomes
Intermediate Filaments diagram
Microtubules
Largest of cytoskeletal elements; dynamic hollow tubes; most radiate from centrosome
Microtubules determine overall shape of the cell and distribution of _______
organelles
Note 
Flashcard (151)