the molecule to which the receptor binds -may be on the plasma membrane or within the cell
signal transduction
the events within the cell that occur in response to a signal
Direct contact (cell communication)
molecules on the surface of one cell are recognized by receptors on the adjacent cell
Paracrine signaling
signal released from a cell has an effect on neighboring cells
Endocrine signaling
hormonesreleased from a cell affect other cells throughout the body
Synaptic signaling
nervecells release the signal (neurotransmitter)which binds to receptors on nearby cells
Phosphorylation
acommon way to change the activity of a protein.
protein kinase
an enzyme that adds a phosphate to a protein
phosphatase
an enzyme that removes a phosphate from a protein
cell surface receptor
receptor – located on the plasma membrane to bind a ligand outside the cell
channel linked receptors
ion channel that opens in response to a ligand
enzymatic receptors
– receptor is an enzyme that is activated by the ligand
G protein-coupled receptor
a G-protein (bound to GTP) assists in transmitting the signal
G-protein-coupled receptor (GPCRs)
– receptors bound to G proteins
G-protein
activatesan effector protein (usually an enzyme)
g protein second messenger
generates the cellular response to the original signal
steroid hormones
have a nonpolar, lipid-soluble structure usuallyaffect regulation of gene expression
major histocompatibility complex
proteins are used by cells to distinguish “self” from “non-self”
glycolipids
are commonly used as tissue-specific markers
tight junctions
createsheets of cells
anchoring junctions
connect the cytoskeletons of adjacent cells
communicating junctions
permit small molecules to pass between cells
gap junctions
in animal cells
plasmodesmata
in plant cells
globular proteins
inserted in the lipid bilayer
phospholipids
arranged in a bilayer
glycerol
a3-carbon polyalcohol acting as a backbone for the phospholipid
2 fattyacids/ phosphate group
attached to the glycerol
Peripheral membrane proteins
anchored to a phospholipid in one layer of the membrane -possess nonpolar regions that are inserted in the lipid bilayer -are free to move throughout one layer of the bilayer
Integral membrane proteins
span the lipid bilayer (transmembrane proteins) -nonpolar regions of the protein are embedded in the interior of the bilayer -polar regions of the protein protrude from both sides of the bilayer
transmembrane domain
regionof the protein containing hydrophobic amino acids
b-barrel
interior is polar and allows water and small polar molecules to pass through the membrane
Passive transport
is movement of molecules through the membrane in which -no energy is required -molecules move in response to a
Diffusion
ismovement of molecules from high concentration to low concentration
Selective permeability:
integral membrane proteins allow the cell to be selective about what passes through the membrane.
Channel proteins
have a polar interior allowing polar molecules to pass through.
Carrier proteins
bind to a specific molecule to facilitate its passage.
ion channels
allow the passage of ions (charged atoms or molecules) which are associated with water
gated channels
are opened or closed in response to a stimulus
Facilitated diffusion
is movement of a molecule from high to low concentration with the help of a carrier protein.
Osmosis
is the movement of water from an area of high to low concentration of water
hypertonic solution
has a higher solute concentration
hypotonic solution
has a lower solute concentration
osmosis water through------ard the hypertonic solution.
aquaporins
Some cells use --------- in which water is ejected through contractile vacuoles.
extrusion
---------------keeping the cell isotonic with their enviroment
Isosmotic regulation
Plantcells use -to push the cell membrane against thecell wall and keep the cell rigid
turgorpressure
Active transport
requiresenergy – ATP is used directly or indirectly to fuel active transport
uniporters
– move one molecule at a time
symporters
move two molecules in the same direction
antiporters
movetwo molecules in opposite directions
Sodium-potassium (Na+-K+) pump
an active transport mechanism -uses an antiporter to move 3 Na+ out of the cell and 2 K+ into the cell
Coupled transport
uses the energy released when a molecule moves by diffusion to supply energy to active transport of a different molecule -a symporter is used
endocytosis
– movement of substances into the cell
exocytosis
movement of materials out of the cell
pinocytosis
thecell takes in only fluid
receptor-mediated endocytosis
specificmolecules are taken in after they bind to a receptor
Surface area-to-volume ratio
as a cell increases in size, the volume increases 10x faster than the surface area
Light microscopes
canresolve structures that are 200nm apart
Electron microscopes
canresolve structures that are 0.2nm apart
Probe microscopes
canresolve structures to the atomic size.
Prokaryotic cells
lacka membrane-bound nucleus.
Archaean
cellwalls lack peptidoglycan
DNAis organized with proteins to form -and further packaged into-
nucleosomes
chromatin
Ribosomes
thesite of protein synthesis in the cell
Rough endoplasmic reticulum (RER)
synthesis of proteins to be secreted, sent to lysosomes or plasma membrane
Smooth endoplasmic reticulum (SER)
-relatively few ribosomes attached -functions: -synthesis of membrane lipids -calcium storage -detoxification of foreign substances
Golgi apparatus
flattened stacks of interconnected membranes -packaging and distribution of materials to different parts of the cell
Lysosomes
destroycells or foreign matter that the cell has engulfed by phagocytosis
Vacuoles
membrane-bound structures with various functions depending on the cell type
Peroxisomes
contain oxidative enzymes and catalase
Chloroplasts
organelles present in cells of plants and some other eukaryotes -contain chlorophyll for photosynthesis
thylakoids
are membranous sacs within the inner membrane
grana
are stacks of thylakoids
Endosymbiotic Theory
proposedthat eukaryotic organelles evolved through a symbiotic relationship
9-2 structure
9pairs of microtubules surrounded by 2 central microtubules
Extracellular matrix (ECM)
composed of glycoproteins and fibrous proteins such as collagen -connected to the cytoplasm via integrin proteins present in the plasma membrane