Cell Physiology Flashcards
Plasma membrane
surround the cell
- physical barrier between ICF and ECF
- cell-to-cell communication
- structural support
- transport
Structure of plasma membrane
phospholipid bilayer with embedded proteins
Amphipathic molecule and examples
Contains polar and non polar regions
- phospholipids, cholesterol, glycolipids
Structure of phospholipid
Polar head group - hydrophilic
- phosphate attached to glycerol, nitrogen containing group, and glycerol backbone
Nonpolar tail group - hydrophobic
- fatty acid chain saturated or non saturated
Steroids - Cholesterol
- Embedded in phospholipid bilayer
- Amphipathic (non polar - CH rings, polar - hydroxyl group)
- Maintains membrane fluidity
Glycolipids
- Lipids with carbs attached
- Plasma membrane surface
- Form glycocalyx: coating around cell attached to protein and lipids
Membrane proteins
Integral (intrinsic):
- amphipathic, span full membrane, majority of proteins, transporters, channels
Peripheral (extrinsic):
- not amphipathic, do not penetrate bilayer
Desmosomes
- adhering junctions that anchor cells together
- maintain structural integrity of tissue
- made of proteins: plaques, cadherins, intermediate filaments
Plaques, cadherins, intermediate filaments
Plaques: on cytoplasmic surface of cell, anchor cadherins
Cadherins: link cells together
Intermediate filaments: anchor cytoplasmic surface of desmosome to components inside cell
Tight junctions
Epithelial tissue for molecular transport, cells laid together in sheets, made of occludin proteins
Occludins
- form nearly impermeable junctions
- link adjacent cells together
- limit movement of molecules between cells
- limit movement of integral membrane proteins and lipids
Gap Junctions
- transmembrane channels linking cytoplasms of adjacent cells
- made of connexon proteins
- electrically (move ions) and metabolically (move molecules)
Nucleus function
- transmission of genetic info for next generation of cells and info needed for protein synthesis
Nucleus structure
Chromatin - DNA and proteins
Nuclear Envelope - double phospholipid bilayer
Nuclear pores - allow molecules to move in and out
Nucleolus - site of synthesis of ribosomal RNA
Cells with nucleus exceptions
RBC - no nucleus
Skeletal - many nuclei
Ribosome
- protein synthesis
- large and small subunit must join to function
- some are free and some are bound to rough ER
Endoplasmic Reticulum
RER - flattened sacs with ribosomes attached to outer surface, synthesis of proteins
SER - branched tubular structure with no ribosomes attached to outer surface, synthesis of lipids and stores calcium
Golgi apparatus
- cisternae (flattened sac)
- receives protein vesicles and modifies and sorts into packages and secreted
Lysosomes
- vesicle containing hydrolytic enzymes breaking large into small
- degrade EC and IC debris
Peroxisomes
- vesicle containing oxidative enzymes which use oxygen to remove hydrogen
- break down fatty acids alcohol drugs
- produces toxic hydrogen peroxide but catalase breaks that down
Mitochondria
- makes ATP
- double phospholipid membrane, inner membrane is called the cristae
- have own DNA
Cytoskeleton
- protein filaments
- maintain cell shape, maintain position of organelles, and mediate cell motility
Cytoskeleton filaments
Microfilaments - actin
Intermediate filaments - many proteins
Microtubules - tubulin
Endocytosis
materials brought into cell using vesicle
Exocytosis
materials released from cell using vesicle
- secrete hormones
- release waste products
- add to cell membrane
Phagocytosis
- cell eating
- pseudopodia from membrane to surround material
- large materials
Pinocytosis
- cell drinking
- membrane indents and pinches together
- nonspecific small molecules, ions, nutrients
Steps of phagocytosis
Recognition, attachment, pseudopodia, fusion, destruction, release
Receptor-mediated endocytosis
- specific process involving specific receptors to ligands
- protein clathrin
- binding of ligand causes conformation change and clathrin moves to membrane
- clathrin coated pit if formed
- vesicle lined with clathrin and releases clathrin
Chemical driving force
high concentration of molecules to low concentration
concentration gradient
Electrical driving force
- membrane potential (difference in electrical voltage across membrane)
- charged substance experiences attractive and repulsive forces
- membrane potential will push or pull charged substance depending on direction and charge
- neutral particles are unaffected
Electrochemical driving force
sum of electrical and chemical driving force acting on ion, net direction
Simple diffusion
- PASSIVE movement down the gradient
- small polar and nonpolar uncharged particles can cross
Factors influencing simple diffusion rate
- magnitude of driving force
- membrane surface area
- membrane permeability: lipid solubility, size/shape, temperature, thickness
Osmosis
net water movement from high water concentration to low water concentration (low solute to high solute)
Carrier mediated facilitated diffusion
- transport proteins with specific binding site
- passive, move from high to low concentration
- GLUT moves glucose
Channel mediated facilitated diffuion
- selective to specific ions
- depends on electrochemical gradient of that ion, passive
- channels exist either open or closed and can be gated (voltage, ligand, mechanically)
Active transport
- moves against gradient
- needs energy
- proteins have specific binding sitesp
Primary active transport
- ATP driven transport process
- Na+/K+ pump
Secondary active transport
- movement of ion down its electrochemical gradient drives transport process
- Na+/glucose and Na+/H+ cotransporter
Chemical messengers and receptors
- specific binding sites
- show saturation
- bind different messengers with different affinities
- found on plasma membrane, intracellularly, cytosol, nucleus
Intracellular receptors
- lipid-soluble chemical messengers
- some act as transcription factors by biding to the response element on a DNA sequence and alter protein synthesis
Membrane-bound receptors
- water-soluble chemical messengers
- 3 types: channel-, enzyme-, G-protein-
- First messenger: extracellular chemical messenger binds to membrane receptor
- Second messenger: after first messenger binding, substance that enters or is generated in cytoplasm
- Protein kinase: enzyme that phosphorylates another protein (adds phosphate group to protein) which alters activity of another protein
Steps of signal transduction
- first messenger binds to binding sites on receptor
- ion channel in receptor protein opens
- ions move through channel
- alter electrical properties of cell and produce a response
G-protein linked receptors
- link between receptor in plasma membrane and an effector protein (ion channel or enzyme)
- alpha subunit of G-protein binds GDP when inactive and GTP when active
1. binding of first messenger causes conformational change increases affinity for GTP and decreases affinity for GDP
2. G protein dissociates and alpha subunit is activated and separated from beta and gamma
3. Activated alpha subunit moves to effector protein to create a response
4. Alpha subunit is now inactivated and binds to GDP, beta, gama in membrane receptor
cAMP second messenger system
- binding of first messenger causing conformational change increasing affinity of alpha subunit for GTP and decreasing affinity for GDP
- activated alpha subunit of Gs protein separates from beta and gamma and binds to adenylyl cyclase (membrane enzyme cytoplasmic)
- adenylyl cyclase converts cytosolic ATP to cyclic AMP
- Cyclic AMP acts as second messent and diffuses through cytoplasm
- cAMP binds and activates protein kinase A (PKA)
- Activated PKA catalyzes phosphorylation of cell proteins by transferring phosphate group from ATP to cell proteins
- Phosphorylated proteins result in cell response
