Cells Flashcards
Cell membrane
Small nonpolar polar molecules move through the membrane easily e.g. oxygen and carbon dioxide. Small, polar molecules can pass by, but much slower. Large, nonpolar molecules are next e.g. benzene. They move very slowly. Large and polar molecules cannot pass through e.g glucose. Charged molecules are so polar that they also can’t pass through the membrane.
Phospholipids in the membrane are diverse and make up most of it. Cholesterol maintains the fluidity of the cell membrane; increasing fluidity when temperatures decrease and vice versa. Proteins: transmembrane/integral, peripheral, lipidbound protein - can act as receptors and transport materials in and out of the cell. Glycolipids/Glycoproteins play a big role in communication and cells recognising each other
Cell membrane proteins and fluidity
Integral proteins are primarily useful for the transport of materials. Channel proteins go down the concentration gradient and don’t require energy. Carrier proteins carry materials into the cell or pump them outside. They can go against the concentration gradient. Glycoproteins are mainly used for signalling.
Factors affecting membrane fluidity:
- temperature: at low temperature, a fluidity decreases and at high temperatures, fluidity increases
- cholesterol: at low temperatures, cholesterol increases the difference between the membrane, increasing fluidity. At higher temperatures, cholesterol makes the molecules come closer together, decreasing fluidity
- unsaturated: for saturated fatty acids, thy are stuck pretty close t each other and so fluidity is low. For unsaturated fatty acids, phospholipids are bent. There’s more space between the molecules and so more fluidity
Longer fatty acid tails also have less fluidity
Membrane dynamics
Uncatalyzed movement:
- transbilayer: outer to inner leaflet, inner to outer leaflet; flip flop; slow
- lateral diffusion: from side to side; pretty fast
Catalysed:
- Flippase: from outer side to inner side requires ATP
- Floppase: also uses ATP; from inner leaflet to outer leaflet
- Scramblase: brings a phospholipid from the outer leaflet to the inner leaflet and vice versa; no ATP
Transport mechanisms
*Potassium leak channel: passive; potassium flows down its concentration gradient out of the cell
*Sodium- Potassium pump: primary active transport because were directly using ATP
*Symport: both molecules in the same direction; secondary active transport because we use energy, but not for this specifically e.g. glucose, sodium transport
*Antiport: molecules move in opposite directions; secondary active transport
*vesicular transport: endocytosis, exocytosis
Phagocytosis
Opsonin receptors: bind bacteria and other particles coated with immunoglobulin G antibodies by the immune system
Scavengers receptors: they bind to molecules that are produced by bacteria
Toll-like receptors: bind to specific molecules produced by bacteria; innate immune system
Requires a lot of energy
Membrane potentials
Concentration gradient makes the potassium leave the cell through leak channels. The anions left unbound to potassium attract the potassium ions back inside (membrane potential). At about -92mV, the K moving out and in are equal.
If positive charge is injected into the cell up to -46mV and so the charge won’t draw the potassium in as strongly as before. There’ll be more potassium leaving the cell, and more anions left unbound. These’ll contribute to the negative charge and will slide back down to -92mV. You only have a membrane potential if you have both a concentration gradient t and permeability
Sodium, potassium ,calcium and chlorine are the major ions that contribute to membrane potentials.
Membrane potentials
Concentration gradient makes the potassium leave the cell through leak channels. The anions left unbound to potassium attract the potassium ions back inside (membrane potential). At about -92mV, the K moving out and in are equal.
If positive charge is injected into the cell up to -46mV and so the charge won’t draw the potassium in as strongly as before. There’ll be more potassium leaving the cell, and more anions left unbound. These’ll contribute to the negative charge and will slide back down to -92mV. You only have a membrane potential if you have both a concentration gradient t and permeability
Sodium, potassium ,calcium and chlorine are the major ions that contribute to membrane potentials.
Pressure
Hydrostatic pressure is the pressure a liquid exerts on its container, and reflects the volume of liquid in space
Osmotic pressure is the pressure required to prevent movement across a semipermeable membrane and reflects the protein content of the blood
Cell junctions
*Tight junctions connect cells tightly; complete fluid barrier (water tight seal) e.g. bladder, intestines, kindey
*Desmosomes are connections that hold two cells together that attach in the cytoskeleton; water and fluids can flow between the connection; found in organs experiencing lots of stress e.g. skin and intestines
*Gap junctions form a tunnel and allow water and ions flow through the gap; often found in cells or tissues that spread action potential e.g cardiac muscle, neurons
Receptors and channels
Membrane receptors are integral proteins that communicate with outside environments. Ligands and receptors are specific - signal transduction: receptors cause intracellular responses to ligands binding. The induced fit is a more flexible version of the lock and key model.
Types of receptors:
*ligand-gated ion channels: transmembrane ion channels that open or close in repossessed to binding of a ligand; respond quickly; create intracellular electrical signal e.g. neurons
*G-protein coupled receptors:
- largest class; 7 transmembrane alpha helices; G-proteins have alpha, gamma and beta subunits bound to the membrane; gamma and beta are bound to each other.
- a signalling molecule complementarily binds to the GPCR which then undergoes a conformational change. The alpha subunit exchanges its GDP for GTP causing the it to dissociate and find a target protein to regulate. The target protein then relays a signal. This process continues as long as the signalling molecule is bound to the GPCR. When GTP is hydrolysed to GDP, the ligand leaves and everything goes back to normal. Regulation can be through the RGS protein.
*Enzyme linked receptors
- extracellular ligand binding domain and intracellular enzyme domain
- receptor tyrosine kinase (RTK): tyrosine is on the intracellular portion: occur in pairs
- signal molecules bind to ligand binding sites bring in both RTKs close to each other and forming cross linking diners which activate the tyrosines. Each RTK in the dimer phosphorylates the tyrosine on the other RTK (cross phosphorylation)
- the intracellular enzyme domain act as docking platforms for proteins involved in signal transduction which often ends in regulating gene transduction. The proteins need to have SH2 to bind to the tyrosines and their phosphates.
- RTKs are common in growth factors (mutations involved in cancers); can bind hormones like insulin
Organelles
Mitochondria: the inner membrane is not permeable to small molecules
SER: makes lipids; metabolised carbohydrates and detoxifies
RER: protein synthesis of proteins secreted or that become integral proteins, post translational modification of proteins
Golgi apparatus: modifies proteins from RER, sorts and sends proteins to correct locations, synthesises molecules for secretion
Lysosomes: autophagy (digest part of cell or other cells) or crinophagy (digest excess secretory products
Peroxisomes: detoxification, lipid breakdown, uses catalase to breakdown hydrogen peroxide to water and oxygen
Animal tissue
- epithelial tissue: inner and outer lining; avascular; can be simple or stratified
- connective: supports, connects and separates tissues; cells + ground substance + fibres; areolar, adipose, fibre, blood, bone, cartilage
- muscle
- nervous
Cytoskeleton
- helps with movement, transport and structural support
- microtubules (25nm):
*mitotic spindle, cilia, flagella, transport; made of
*alpha and beta tubulin that form a dimer and then polymerise into a sheet and then a tube - microtubule organising centres are the centrosome (kinetochore fibres become interpolation microtubules; astral microtubules come from the end of the aster) and basal body (cells with cilia or flagella; 9+2 arrangement; nexin keeps microtubules in place; dynein breaks down ATP)
- intermediate filaments (10nm): structural support, resists mechanical stress
- microfilaments (7nm): gross movement; made of actin;
Prokaryotes/ bacteria
Abiogenesis: life was spontaneously generated from non-life
Archaea: like extreme environments; thermophiles, halophiles, methanogens;
Protista: all live in moist or aquatic environments; photosynthesising (algae) and non photosynthesising (slime mild), protozoa (amoeba)
Bacteria: flagella (flagellin), circular DNA, inclusion body (storage)
Gram staining:
- circular (coccus), rodlike (bacillus), spiral (spirochete/spirilla)
- if it stained purple, it’s gram positive and if it stained pink, it’s gram negative
- gram negative: thinner cell walls; inner membrane, peptidoglycan layer, outer membrane, lipopolysaccharide layer, capsule
- gram positive: plasma membrane, peptidoglycan layer, capsule; keeps purple stain because of thick peptidoglycan layer
Cell theory
- Schleiden and Schwann both discovered individually that all living things are composed of one or more cells.
- exceptions could be mitochondria and chloroplasts
