Tags & Description
Qualities of Cells
cells are the basic units of life
activity of the organism depends on the activities of cells
activity of cells depend on their shape, form and internal structure
new cells arise from previously existing cells
the stage of cancer depends of the health of new cells
Cell Types
around 200 kinds in the body
classified on the basis of structure and function
not all cells have the same components
most cells have a plasma membrane, cytoplasm and nucleus
Plasma Membrane
different in different cell types which allows cells to interact differently with the same ECF
Plasma Membrane Structure
Double phospholipid layer that is impervious to water
Protein molecules that permit the movement of specific chemicals and have cell signaling functions
Phospholipid Bilayer Structure
hydrophilic head and hydrophobic tail arranged with the tails always pointing towards each other
cholesterol is arranged within the bilayer
fluid structure with looser bonds allowing the phospholipids to move within the layer
Cholesterol in Phospholipid Bilayer
arranged in between phospholipid molecules
prevent crystallization and provide stability
Function of the Phospholipid Bilayer
Form the structure of the plasma membrane
Forms a barrier to passage of water soluble substances between ECF and ICF
Responsible for fluidity of the membrane as some cells constantly change shape
Proteins
attached to or inserted within bilipid layer
plasma membrane contains approximately 50 times as many lipid molecules
the molecules make up almost half the membranes mass
two types either integral or peripheral
Integral Proteins
embedded in the membrane
Peripheral Proteins
attached to one surface
Protein Function
structural support
transport of molecules across the membrane
enzymatic control of chemical at cell surface (indirect protein control)
receptors for certain molecules (hormones)
markers (such as antigens) identify cells (and an individual)
Carbohydrates
primarily attached to the outer surface of the membrane
negatively charged
affects activity of regulatory molecules and interactions between cells such as keeping red blood cells apart
Cilia
propel fluids across the surface of cells that are firmly attached in place
example includes the cells of the respiratory tract
Flagella
similar structure as cilia but generally move the entire cell
much longer than cilia
such as sperm cells
Cell to Cell Adhesion
three kinds of cell junctions assist in binding cells together including tight junctions, desmosomes and gap junctions
Tight Junctions
integral proteins in adjacent cells fuse together making it difficult for anything to pass between adjacent cells
found primarily in sheets of epithelial tissue
highly selective barriers
seperate compartments having different chemical compositions
passage across epithelial barrier must place through cells
Desmosomes
act like a zipper to hold cells together (adhering to junctions)
important in cells where there is mechanical stress (such as muscle, skin and the uterus)
keratin filaments insides of cell may extend to desmosome on the opposite side
provides increased tensile strength
Gap Junctions
used to communicate between adjacent cells
permit passage of small signaling molecules
provides one mechanism of cooperative cell activity
have connexins made up of six proteins arranged in hollow tube-like structure
two connexins join end to end
especially abundant in cardiac and smooth muscle
Membrane Transport
tissues consist of cells embedded in an extracellular matrix (ECM)
ECM components differ for each type of tissue
provide different local environments
anything that passes between the cell and the surrounding ECM must be able to penetrate the plasma membrane
the plasma membrane is selectively permeable
Properties of Permeability
must be highly lipid-soluble particles that can dissolve in the bilipid membrane including uncharged/nonpolar molecules such as oxygen, carbon dioxides and fatty acids
water soluble particles must be small enough to fit through specific channels
Unassisted Membrane Transport/Passive Transport
molecules that can penetrate the plasma membrane on their own can be driven by diffusion and follow the concentration gradient
Diffusion
movement from a high concentration to a low concentration as molecules have a tendency to be evenly spaced out
Factors Affecting Molecule Movement
temperature is directly proportional to movement speed, substances diffuse faster at higher temperatures
size is inversely proportional to movement speed, larger molecules diffuse slower
Concentration Gradient
difference in concentration between adjacent area
Example of Diffusion
oxygen diffuses out of the lungs, into the bloodstream which then diffuses out of the bloodstream, into tissues
Electrical Gradient
oppositely charged ions attract each other
Electrochemical Gradient
if both electrical and concentration gradients act on an ion
Osmosis
water can readily permeate the plasma membrane because it is small enough to slip between the bilipid
some cells have aquaporins meaning there is no limit to amount of molecules to facilitate the movement
about a billion molecules of H2O can pass through the aquaporin every second
moves by diffusion with the concentration gradient and water flows to areas of higher solute concentration
Concentration of a Solution
the density of solute in a given volume of water
in general one molecule of solute will replace one molecule
as the solute increases the water decreases
What happens if the solute can move through the membrane?
both water and solute move through the membrane until both are evenly distributed
What happens if the solute cannot pass through the membrane?
volume of one side increases as a result of water movement
eventually the solute concentrations on both sides become equal
Tonicity
depends on concentration of solutes in the extracellular fluid
Isotonic Solution
same solute/water concentration on inside and outside of the cell
water moves both into and out of the cell
no change in cell shape
Hypertonic Solution
higher concentration of solutes outside of the cell
water flows out of the cell
cells shrink
Hypotonic Solution
lower concentration of solutes outside the cell
water flows into the cell
cells expand and burst (lyse)
Assisted Membrane Transport/Active Transport
sometimes cells need ions to go against the concentration gradient
poorly lipid soluble molecules and molecules that are very large need help crossing the plasma membrane
use either carrier mediated transport or vesicular transport
Carrier Mediated Transport
carrier proteins span the plasma membrane
can have binding sites at either side (ECF or ICF)
must display specificity, saturation and competition
can either be by facilitated diffusion or active transport
Specificity
carry one or few substances
Saturation
limited number of binding sites
Competition
several related compounds may compete for transport
Facilitated Diffusion
uses a carrier to assist transport of a substance downhill from high to low concentration
example includes moving glucose into cells because it is an important source of fuel that cannot cross the cell membrane without support
Glucose
big size and density making it difficult to break down
polar molecule
higher concentration in blood than tissues requiring facilitated diffusion
Active Transport
movement of molecules against the concentration gradient from a low to high concentration
requires energy in the form of ATP
example is the uptake of iodine by the thyroid as it must be moved from blood (low concentration) to thyroid (high concentration)
Sodium-Potassium Pump
carrier protein transports 3 sodium ions out of the cell, concentrating it in the ECF
2 potassium ions are picked up outside the cell and transported into the ICF
ATP is used and converted into ADP+P
Vesicular Transport
transport of molecules that cannot cross the membrane includes large polar molecules and ingestion of invading bacteria
molecules are too big for the channels and no carriers exist
energy is used to wrap the molecules in a membrane enclosed vesicle either by endocytosis or exocytosis
Endocytosis
moving substances into the cell
includes phagocytosis, pinocytosis and receptor-mediated endocytosis
Phagocytosis
large molecules internalized
can be done by phagocytes and certain types of white blood cells
destroys tissue debris and bacteria by being engulfed in the vesicle
Pinocytosis
small droplet of ECF enfolded and sealed by the plasma membrane
can be done by most body cells
also a good way to get rid of extra plasma membrane
Receptor-Mediated Endocytosis
highly selective unlike pinocytosis
enables cells to import specific large molecules needed by the cell such as cholesterol complexes, vitamin B12, insulin and iron
can be exploited by certain viruses
Exocytosis
moving substances out of the cells
can be used for secreting large highly specific molecules such as hormones and neurotransmitters
also used to add components to the plasma membrane including carriers, channels and receptors
Cytoplasm
includes the cytosol and organelles
Cytosol
semitransparent fluid
mostly water with proteins, salts and sugars
Organelles
each carry out specific functions
Mitochondria
energy production
Smooth Endoplasmic Reticulum
lipid production and detoxification
Rough Endoplasmic Reticulum
protein production
Golgi Apparatus
protein modification and export
Lysosome
protein break down/destruction
Nucleus
control center of the cell
provides instructions, mainly for building proteins
most cells have one
skeletal muscle have multiple
red blood cells have none
Nucleus Membrane
selectively permeable
punctuated with nuclear pores
allows some control over what goes in and out