Cells

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Plasma Membrane
Structure: fragile barrier; lipid bilayer

Function: controls what goes in and out of the cell; cells are continuously bathed by interstitial fluid that is derived from the blood and is rich in nutrients, the plasma membrane decides what does and does not get in)
Phospholipid
Structure: have polar (phosphate) head and non-polar (fatty acid) tails
Two Protein Populations
1. Integral- firmly inserted in lipid bilayer; transport functions; spans entire membrane

2. Peripheral- appended to the membrane surface; enzymes, mechanical functions
Microvilli (specialization of plasma membrane)
small, fingerlike extensions of the plasma membrane that project from a free, or exposed cell surface; increase surface area; appear on absorptive cells; binds cells together (adhesive glycoproteins)
Tight Junction (specialization of plasma membrane)
protein molecules fuse together tightly forming an impermeable junction; prevents the free passage of molecules through the intercellular space
Desmosomes (specialization of plasma membrane)
act as mechanical coupling or adhesion junctions that prevent separation of tissue layers (plasma membrane do not touch, but held together by glycoprotein filaments)
Gap Junctions (specialization of plasma membrane)
provide direct passage of chemical substances between adjacent cells (embryonic cels, heart, smooth muscle, nerve cells)
Passive Transport
uses kinetic energy; based on concentration gradient; rate affected by size of molecules and temperature
Simple Diffusion (passive process)
net movement of particles from and area of high concentration to low concentration (fats, O2, CO2, ions)
Osmosis (passive process)
diffusion of water through membrane pores
1. hydrostatic pressure
2. osmotic pressure
3. tonicity
a) hypotonic
b) isotonic
c) hypertonic
Facilitated Diffusion (passive process)
diffusion substance is attached to a lipid-soluble membrane carrier protein
Filtration (passive process)
uses hydrostatic (water) pressure to move water and solutes through a semi-permeable membrane
Active Processes
ATP for energy source; used to pass molecules that are too big, unable to dissolve, or require movement against concentration gradient
Active Transport (active process)
(solute pumping) require carrier proteins to move a substance through membrane against a concentration gradient (amino acids and ions)
Bulk Transport (active process)
large particles and macromolecules are transported through plasma membranes
Exocytosis (bulk transport)
substances are moved from the cell interior into the extracellular space (hormone secretion, neurotransmitter release, mucus secretion, ejection of wastes) through a membranous vesicle which fuses to plasma membrane and ruptures
Endocytosis (bulk transport)
large particles enter the cell by being enclosed by a portion of the plasma membrane
Phagocytosis (endocytosis)
cell eating; parts of the plasma membrane expand and flow around some large material (phagosome) contents are digested by enzymes
Pinocytosis (endocytosis)
cell drinking; plasma membrane sinks beneath an external fluid droplet containing small solutes; membrane edges fuse, forming a fluid filled vesicle
Receptor- Mediated Endocytosis
selective; external substance binds to membrane receptor, coated pits are formed
Functions of the Glycocalyx
1. externally facing glycoproteins of the cell membrane
2. determining the ABO and other blood groups
3. providing binding sites for certain toxins
4. recognition of the egg by sperm
5. determining cellular life span
6. serving the immune response
7. helping to guide and direct embryonic development
Cytoplasm
cellular material inside the plasma membrane and outside the nucleus (most cellular activities are accomplished here)

Made of:
1. cytosol- semitransparent fluid where organelles are
2. organelles- metabolic machinery
3. inclusions- number of chemical substances present
Mitochondria (organelle)
site of ATP/ powerhouse of the cell
-two lipid bilayer membranes
-inner membrane has projections called cristae
-cristae protrude into the geo life substance called the matrix
-the matrix breaks down glucose to H2O and CO2
Ribosomes (organelle)
site of protein synthesis
-composed of proteins and one variety of RNA
Rough Endoplasmic Reticulum (organelle)
membrane system enclosing a cavity and coiling through the cytoplasm with external ribosomes; sugar groups are attached to proteins that are bound in vesicles and transported to the Golgi apparatus
Smooth Endoplasmic Reticulum (organelle)
-membranous system of sacs without ribosomes
-site of phospholipids, cholesterol, protein, fat, lipoprotein synthesis
-synthesis and transport of fats
-synthesis and storage of glycogen
-detoxification of drugs
-modify, concentrate, and package proteins
Golgi Apparatus
a stack of smooth membrane sacs near the nucleus, principal traffic director for cellular proteins; modifes, concentrates, and packages proteins
Lysosomes (organelle)
-site of intracellular digestion
-digestion of particles by endocytosis
-digestion of worn out organelles
-uses bacterial enzymes to break down old parts
-metabolic functions
Peroxisomes (organelle)
-also called micro-bodies
- abundant in liver and kidney cells
-change O2-free radicals by converting them to H2O2
-the enzyme catalase reduces H202 to break down materials
Cytoskeletal Elements
helps support the soft cell substance and provide cellular movement
Microfilaments (cytoskeletal elements)
thin strands of actin (protein) involved in cell motilitly
Intermediate Filaments (cytoskeletal elements)
tough, insoluble protein fibers that resist mechanical stress
Microtubules (cytoskeletal elements)
long, hollow tubes formed by tubulins (protein) that help to maintain cell shape and rigidity and help anchor organelles at specific locations
Centrosome
region near the nucleus where microtubules appear to be anchored
Centrioles
-contained in the centrosome
-play a role in cell division
-form cilia and flagella
Cilia
-hairlike motile cellular extensions that occur in large numbers
-move in unison to create a current that propels substances in one direction across the cell surface
Flagella
-longer projections formed by centrioles
-centrioles forming the basis of cilia and flagella are commonly referred to as basal bodies
Nucleus
-control center of the cell
-most cell have only one nucleus
-average size; 5 nanometers (largest organelle)
-conforms to shape of the cell
-nucleoplasm is the fluid within the nuclear membrane
Nuclear membrane
-transport system
-double membrane
-large pores for easy passage of proteins
Nucleoli
-site of ribosome production
-made up of ribosomal RNA and proteins
-one or two per cell
Chromatin
-physical site for the attachment of the chromosomal DNA
-believed to mediate may aspects of DNA function
cell concepts
1. A cell is the basic structural and functional unit of living organisms 2. The activity of an organism is dependent on both the individual and collective activity of its cells 3. According to the principle of complementarity, the biochemical activities of cells are determined and made possible by the specific sub-cellular structures of cells 4. The continuity of life has a cellular basis.
cell shape
spherical (fat cells)- disk shaped (red blood cells)
branching (nerve cells)- cubelike (kidney tuble cells)
main parts of a cell
cytoplasm, nucleus, plasma membrane
Hooke
first to observe plant cells
Schleiden and Schwann
first to assert that all living things are composed of cells
Virchow
cells arise only from other cells (disputing theory of spontaneous generations)