Cell Physiology Flashcards
Functions of Plasma Membranes
- Physical barrier
- Cell to Cell communication
- Structural support
- Transport
Phospholipid Bilayer
Spontaneously form bilayer
Polar head faces aqueous environment
Nonpolar tails from hydrophobic core
Steroids
Cholesterol maintains membrane fluidity
Glycolipids
Lipids with CHO chain attached Outer leaflet of plasma membrane Amphipathic Forms glycocalyx -layer of carbs linked to lipids -identification + interaction between cells
Desmosomes
Adhering junctions that anchor cells together in tissues subject to considerable stretching or mechanical stress
Maintain the structural integrity of tissue
Cadherins link cells together
Tight Junctions
Occludins form nearly impermeable junctions that link adjacent cells together and limit the movement of molecules between cells
Gap Junctions
Links cytoplasm of adjacent cells with connexions
Communicating Junctions
Electrically and metabolically couple cells
Nucleus Function
Transmission of genetic information and contains information for protein synthesis
Nucleus Structure
Nuclear envelope is made of 2 phospholipid bilayers and has pores that allow molecules to move in and out of the nucleus
Chromatin
DNA and associated proteins
Nucleolus
Site of synthesis of ribosomal RNA
Ribosome Function
protein synthesis
Ribosome Structure
Composed of large and small subunit that are not functional when separated
Rough Endoplasmic Reticulum Function
Synthesizes proteins and performs post-translational modifications needed for a functional protein
Rough Endoplasmic Reticulum Structure
Flattened sacs with ribosomes attached to outer surface
Smooth Endoplasmic Reticulum Function
Synthesizes lipids, stores calcium, drug detoxification
Smooth Endoplasmic Reticulum Structure
Branched tubular structure with no ribosomes attached to outer surface
Golgi Apparatus Function
Modifies proteins made at RER, sorts and packages proteins into vesicles, sends proteins to where it needs to be
Golgi Apparatus Structure
Composed of cisternae
Lysosomes
Contains hydrolytic enzymes which break large molecules into small subunits
Active at pH of 5
Peroxisomes
Contains oxidative enzymes which uses oxygen to remove hydrogen from molecules, breaking them down
Breaks down fatty acids, alcohol, drugs
byproduct is H2O2
Mitochondria
Makes energy for the cell
contains double phospholipid membrane
Have own DNA
Cytoskeleton Function
Maintain cell shape, position of organelles in cell
Cytoskeleton Structure
Composed of protein/cytoskeletal filaments
Microfilaments = actin
Intermediate filaments
Microtubules = tubulin
Phagocytosis
Uses extensions of the plasma membrane called pseudopodia to surround material being brought into the cell
Brings in large particles
Pinocytosis
Plasma membrane indents below the particles to be brought into the cell
Nonspecific process
Brings in small molecules like ions and nutrients
Receptor-mediated Endocytosis
Specific process - involves receptors that bind specific ligands brought into the cell
Involves clathrin
-concentrates
-clathrin-coated vesicle is formed
Exocytosis
Release content from cell using vesicles
- hormones
- waste products
Chemical Driving Force
Chemical driving is due to the concentration gradient of the substance
Electrical Driving Force
Electrical driving is due to the membrane potential
Electrochemical Driving Forces
The sum of the electrical and chemical driving forces acting on an ion - depends on net direction of both
Simple Diffusion
Passive movement of molecules through bilayer
Doesn’t require energy
Moves in concentration gradient
What can move by diffusion?
small, nonpolar, uncharged = yes
small, polar, uncharged= maybe
large, polar uncharged = no
any molecule with a charge will not move by diffusion
Factors Influencing Rate of Diffusion
- Lipid solubility of the diffusing substance - nonpolar cross easier
- Size + shape of substance - smaller, even shaped cross easier
- Temperature - hotter=greater membrane permeability
- Diffusing distance - how thick distance is
Osmosis
Passive diffusion of water
Moves from area of low solute concentration to area of high solute concentration
Carrier-Mediated Facilitated Diffusion
Involves transport proteins called carriers which have a specific binding site for the substance to be transported
- Bind the substance and move it across plasma membrane from high to low concentration
- no energy required
Channel-Mediated Facilitated Diffusion
Selective for a certain molecule (usually an ion)
Electrochemical gradient determines ion flux
In an open or closed state
-voltage gated
-ligand gated
-mechanically gated
Active Transport
Uses ATP
Involves transport proteins with specific binding sites for the substance transported
Capable of going against concentration gradient
Primary Active Transport
Energy source for the process is ATP
eg. NA+/K+ pump
-maintains membrane potential + concentration gradient of ions
At rest = high Na+ outside of cell and high K+ inside of cell
3 Na+ in and 2 K+ out
Secondary Active Transport
Energy source is movement of an ion down its electrochemical gradient
Couples movement of an ion down it’s electrochemical gradient with another substance moving against its concentration gradient
eg. Na+/Glucose cotransporter or Na+/H+ exchanger
Unsaturable Transport
Simple Diffusion
Saturable Transport
Mediated transport
Signal Transduction
Sequence of events between the binding of a messenger to a receptor and the production of a cellular response
First Messenger
Extracellular chemical messenger that binds to a specific membrane-bound receptor
Second Messenger
Substance that enters or is generated in the cytoplasm of a cell following the binding of the first messenger to its receptor
Properties of Receptors
Receptors have specific binding sites for a specific messenger
Receptors show saturation - defined number of binding sites
Receptors bind different messengers with different affinities
Lipid-soluble Chemical Messengers
Bind to receptors in cytoplasm or nucleus
steriod hormones
alters transcription of mRNA by binding to response element
alters rate of protein synthesis
Water-Soluble Chemical Messengers
Bind to receptors on extracellular surface or plasma membrane
hormones, neurotransmitters
channel, enzyme, G-linked protein receptors
Ligand-gated Ion Channels
Membrane-bound receptor
1. 1st messenger binding to receptor opens ion channel
2. ions cross membrane
3. change in electrical properties of cell
Fast, may be a calcium channel
Enzyme-Gated Ion Channels
Membrane-bound receptor
- proteins that function as a receptor also have intrinsic enzyme activity
- receptor tyrosine kinases
- docking site for cytoplasmic proteins
- autophosphorylates
- activation of cytoplasmic proteins by phophorylation
G-Protein Linked Receptors
Membrane-bound receptors
- cytosolic surface of plasma membrane
- bings guanosine nucleotides
- alpha, beta, gamma subunits - only alpha subunits bind nucleotides
Activation of G-Proteins on Ion Channels
- Binding of 1st messenger to a receptor causes a conformational change in receptor
- Affinity of alpha subunit for GTP increases, GDP dissociates, GTP binds
- GTP-bound alpha subunit dissociates from beta and gamma, moves to ion channel
- Ion channel opens or closes, alters flow of ions across membrane
Activation of G-Proteins on Enzymes
- Binding of 1st messenger to a receptor causes a conformational change in receptor
- Affinity of alpha subunit for GTP increases, GDP dissociates, GTP binds
- GTP-bound alpha subunit dissociates from beta and gamma, moves to enzyme
- Gs protein stimulates enzymes, Gi protein inhibits protein
- Alters production of 2nd messenger in cytosol
cAMP 2nd Messenger System
- Gs activates cAMP 2nd messenger system
- cAMP is converted to noncyclic AMP by phosphodiesterase
- Gi inhibits cAMP 2nd messenger system
Calcium as 2nd Messenger
- Active transporters maintain low cytosolic [Ca2+]
- 1st messenger binds to receptor
- receptor is ligand-gated ion channel or activates G-protein
- Increase in cytosolic [Ca2+]
- Ca2+-induced Ca2+ release
- Ca2+ is a 2nd messenger
- Activates calmodulin
- Calcium-calmodulin complex alters activity of enzymes + proteins
