A&P Chapter 3: Cells, The Living Units

Interstitial fluid
Cells are submersed (bathed) in this fluid
Blood Plasma
Fluid component of blood
Cerebrospinal Fluid
Fluid surrounding nervous system organs
(5) Functions of the Plasma Membrane
1. Mechanical Barrier
2. Selective Permeability
3. Production of electrochemical gradient across membrane (positive outside compared to negative)
4. Communication
5. Cell Signalling (allows response to chemical messengers)
Fluid Mosaic Model
Membrane lipids form a flexible lipid bilayer in which specialized membrane proteins are dispersed
(3) Membrane Lipids
-Phospholipids (75%): polar phosphate heads and non-polar fatty acid tails
-Glycolipids (5%): Lipids with sugar groups on the outer membrane surface
-Cholesterol (20%): Interspersed among phospholipids, providing stability to the membrane
Integral Proteins
Extend deeply into membrane, often extending from one surface to the other -- can form channels through the membrane
Peripheral Proteins
Loosely attached to integral proteins at either the inner or outer surfaces of the lipid bilayer
(6) Functions of Membrane Proteins
1. Transport
2. Receptors for signal transduction
3. Attachment to the cytoskeleton and ECM (provides support and shape)
4. Enzymatic activity
5. Intercellular joining
6. Cell-cell recognition
(3) Types of Cell Connections
1. Tight Junctions
2. Desmosomes
3. Gap Junctions
Tight Junctions
-Integral proteins on adjacent cells fuse to form an impermeable junction that encircles the whole cell
-Prevents fluid and most other molecules from passing through the ECM between adjacent cells
-Disk-shaped regions of cell membrane; often found in areas that are subjected to stress
-Rivet-like cell junction formed when linker proteins (cadherins) of neighboring cells interlock like the teeth of a zipper
-Linker protein is anchored to its cell through areas on inside of plasma membrane called plaques
-Keratin filaments extend from cytoplasmic side of plaque to plaque on cell's opposite side for added strength
-reduce the possibility of two cells tearing apart under tension
Gap Junctions
-Protein channels that aid in intercellular communication
-Transmembrane proteins (connexons) form tunnels that allow small molecules to pass from cell to cell
-Allows electrical signals to be passed quickly from one cell to the next cell
-ex: In heart, gap junctions are associated with intercalated discs in the heart --> allows for coordinated contraction
Passive Transport
-no energy
-diffusion or filtration
Collisions between molecules in areas of high concentration cause them to be scattered into areas with lower concentration
Water moves by osmosis from areas of low solute (high water) concentration to areas of high solute (low water) concentration
Isotonic Solution
Has same osmolarity as inside the cell, so volume remains unchanged
Hypertonic Solution
Has higher osmolarity than inside the cell, so water flows out of the cell, resulting in cell shrinking
Hypotonic Solution
Has lower osmolarity than inside the cell, so water flow into the cell, resulting in cell swelling
Transport one substance into the cell while transporting a different substance out of the cell
Transport two different substances in the same direction
Primary Active Transport
Required energy comes directly from ATP hydrolysis
Secondary Active Transport
Required energy is obtained indirectly from ionic gradients created by primary active transport
(6) Steps of Na/K Pump
1. Three cytoplasmic Na+ bind to pump protein
2. Na+ binding promotes hydrolysis of ATP. The energy released during the reaction phosphorylates the pump
3. Phosphorylation causes the pump to change shape, expelling Na+ to the outside
4. Two extracellular K+ bind to the pump
5. K+ binding triggers release of the phosphate. The dephosphorylated pump returns to the original conformation
6. Pump protein bind ATP, releases K+ to the inside, and Na+ sites are ready for bind Na+ again.
Vesicular Transport
-Involves transport of large particles, macromolecules, and fluids across membrane in membranous sacs (vesicles)
-Includes endocytosis, exocytosis, transcytosis, and vesicular trafficking
Transport into cell -- Phagocytosis, pinocytosis, or receptor-mediated endocytosis
-Transport out of the cell
-Substance being ejected is enclosed in secretory vesicle
-Protein on vesicle is call v-SNARE and finds and hooks up to target t-SNARE proteins on membrane
Transport into, across, and then out of cell
Vesicular Trafficking
Transport from one area or organelle in cell to another
(6) Steps of Endocytosis
1. Coated pit ingests substance
2. Protein-coated vesicle detaches into the cell
3. Coat proteins are recycled to plasma membrane
4. Uncoated vesicle fuses with an endosome
5. Transport vesicle containing membrane components moves to the plasma membrane for recycling
6. Fused vesicle may either a) fuse with lysosome for digestion of its contents, or b) deliver its contents to the plasma membrane on the opposite side of the cell (transcytosis)
The cell engulfs a large particle by forming projecting pseudopods ("false feet") around it and enclosing in within a membrane sac called a phagosome. The phagosome is combined with a lysosome. Undigested contents remain in the vesicle (now called a residual body) or are ejected by exocytosis. Vesicle may or may not be protein-coated but has receptors capable of binding to microorganisms or solid particles.
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 Endocytosis
Extracellular substances bind to specific receptor proteins, enabling the cell to ingest and concentrate specific substances (ligands) in protein-coated vesicles. Ligands can either be released inside the cell or combined with a lysosome to digest contents. Receptors are recycled to surface.
Resting Membrane Potential
-difference in electrical charge between the inside and outside of membrane is called a voltage
-membrane voltages range from -50 to -100 mV
-inside of cell is more negative than outside the cell
Sugars projecting from cell surface
-Some are attached to lipids (glycolipids)
-Some are attached to proteins (glycoproteins)
-Two types include Cell Adhesion Molecules (CAMs) and Plasma Membrane Receptors
(5) Functions of CAMs
-Anchor cell to ECM or to each other
-Assist in movement of cells past one another
-Attract WBCs to injured or infected areas
-Stimulate synthesis or degradation of adhesive membrane junctions (ex: tight junctions)
-Transmit intracellular signals to direct cell migration, proliferation, and specialization
Contact Signaling
Cells that touch recognize each other by each cell's unique surface membrane receptors
-Used in normal development and immunity
Chemical Signaling
Interaction between receptors and ligands (chemical messengers) that cause changes in cellular activities
-In some cells, binding triggers enzyme activation; in others, it opens chemically gated ion channels
-Examples of ligands: neurotransmitters, hormones
Receptor Proteins
-Can attach to specific chemical signal molecules and act as an intercellular communication system
-Ligand can attach only to cells with that specific receptor
Cellular material between plasma membrane and nucleus
-Composed of cytosol, cytoskeleton, cytoplasmic inclusions, organelles
Gel-like solution made up of water and soluble molecules such as proteins, salts, sugars, etc.
Support cellular structures and provide machinery to generate cell movement
Insoluble molecules; vary with cell type (glycogen granules, pigments, lipid droplets, vacuoles, crystals)
Metabolic machinery structures of the cell; each with a specialized function
(5) Membranous Organelles
-Golgi apparatus
(3) Non-membranous organelles
Review all parts of the cell from slides 64-67
-Consists of 30% threadlike strands of DNA, 60% histone proteins, 10% RNA
-Arranged in fundamental units called nucleosomes, which consist of DNA wrapped around histones
Condensed chromatin
-Condensed state helps protect fragile chromatin threads during cell division
Cell Cycle
Series of changes a cell undergoes from the time it is formed until it reproduces
Cell grows and carries on its usual activities
Cell Division (mitotic phase)
Cell divides in two
-Period from cell formation to cell division, when cell carries out its routine activities and prepares for cell division
(3) Subphases of Interphase
1. G1 (Gap 1): Vigorous growth and metabolism
2. S (Synthetic): DNA replication occurs
3. G2 (Gap 2): Preparation for division
(4 Stages of the Mitotic Phase
"Go" Signals for Cell Division
-Critical surface-to-volume of cell, when area of membrane becomes inadequate for exchange
-Chemicals (growth factors, hormones
"Stop" Signals for Cell Division
Availability of space -- normal cells stop dividing when they come into contact with other cells
-Referred to as contact inhibition
G1 Checkpoint
-Checks for DNA damage
-Checks for appropriate conditions for division (growth factors, adequate cell size, adequate energy supply)
-If cell does not pass this checkpoint, will go to G0
mRNA made from the DNA template
mRNA decoded to assemble polypeptides
-Involves mRNA, tRNA, Ribosomes, Rough ER (sometimes)
Role of ER in Protein Synthesis
-Short amino acids sequence called the ER signal sequence, present on a growing polypeptide chain, signals associated ribosome to dock on rough ER surface
-Once docked, the newly formed polypeptide enters the ER, sugar groups are added, and shape may be altered
-Protein in RER lumen is enclosed in vesicle for transport to Golgi
Process of disposing of nonfunctional organelles and cytoplasmic bits by forming autophagosomes, which can then be degraded by lysosomes
Used to mark unneeded proteins for destruction
-Proteasomes disassemble ubiquitin-tagged proteins, recycling the amino acids and ubiquitin
Causes certain cell to neatly self-destruct
-Cell shrinks and DNA and cytoskeleton fragment
-Membrane blebs form cell fragments that are phagocytosed by cells of the immune system