Chapter 2: Molecules and Cells Flashcards
Describe cell membrane
Forms functional compartments from phospholipid bilayers which are fluid.
-physically compartmentalize systems in functionally essential ways.
Describe epithelium
Sheet of cells that covers a body surface or organ, or lines a cavity.
- similar to membranes, but a larger scale.
- compartmentalize body regions by forming boundaries
Explain basis and significance of membrane fluidity
Phospholipid bilayer is fluid; heads are hydrophilic and tails are hydrophobic. Phospholipid molecules are not covalently bonded so they move relative to each other and are flexible. Fluidity depends on saturation of hydrocarbon tails.
Channel membrane protein
diffusion of solutes through the membrane
Transporter proteins
actively binds to molecules and move them across membrane
Enzyme proteins
catalyze chemical reactions
Receptor protein
binds to molecules and changes membrane permeability
structural protein
anchors molecules in membrane; form structural relations
tight junctions
(occluding junctions) - place where cell membranes of adjacent cells are tightly joined, no intercellular space.
septate junction
(occluding junctions) - instead of tight junctions, invertebrates have these. Look like a double helix.
Gap junctions
localized spot where cytoplasm’s of cell communicate through tiny pores
Four factors that influence chemical reaction
- number of active enzyme molecules present; they must be able to react with substrate to catalyze reaction
- concentration of substrate molecules; hyperbolic/sigmoid kinetics
- catalytic effectiveness; how fast chemical reaction will occur
- enzyme substrate affinity; how likely enzyme is to stick to substrate
relate half-saturation constant to enzyme substrate affinity and reaction velocity
half saturation constant (km) is concentration required to attain half the reaction velocity, which is how fast substrate is converted to product. The enzyme substrate affinity is how likely the enzyme will bind to the substrate.
-lower km mean greater affinity. reaction velocity increases as substrate concentration increases until they reach vmax.
Explain how molecular flexibility relates to cooperativity and allosteric modulation
cooperativity is a change in the affinity for one ligand once another has bound, allosteric modulation occurs when a ligand binds and changes catalytic activity or substrate affinity. Molecular flexibility allows these enzymes to function.
How is regulation of processes accomplished by enzymes?
- The type and amount of enzyme depends on gene expression and enzyme degradation
- modulation of enzyme molecules permits fast regulation of cell function
- rate limiting reaction set the rate of reaction for entire pathway, branch point reaction effect rapid metabolic regulation
- amplification occurs because each molecules of kinase can catalyze the activation of many molecules of the enzyme following it.
Ligand-gated channel
receptor protein that opens to permit ions to pass through when they bind to their ligands. Ions alter the electrical charge across the membrane.
-Hydrophilic inorganic ions are commonly transported
G protein-coupled receptor
interacts with two other cell membrane proteins to activate intracellular enzyme catalytic sites. Movement depends on membrane fluidity
Enzyme-enzyme linked receptor
interacts directly with other membrane proteins that are enzymes. Binding with the ligand activates a catalytic site on the same molecule, activation causes the production of second messenger cyclic GMP
Intracellular receptor
only effective for ligands that can dissolve in and diffuse through the lipid bilayer of the membrane
How are membrane protein diverse?
- provide functionality
- primary structure is maintained by covalent bonds
- secondary structure maintained by hydrogen bonds.
Apical surface
facing into cavity or open space
Basal surface
facing toward the underlying tissue to which the epithelium is attached
catabolism
breaking down chemical compounds to release energy
anabolism
building up chemical compounds from smaller building blocks, using energy
Lactate dehydrogenase
key enzyme in production of ATP.
end product inhibition
type of regylation and a form of negative feedback control
-end product is a ligan that binds with ENz to allosterically inhibit it.
protein kinases
enzymes that catalyze phosphorylation of other enzymes
protein kinase 1
activated by one of various chemical mechanisms, catalyzes phosphorylation of protein kinase 2
protein kinase 2
activated by phosphorylation, catalyzes phosphorylation of final target enzyme
protein kinase 3
activated by phosphorylation, catalyzes critical metabolic process such as rate limiting or branch point reaction
Five secondary messenger systems
- Cyclic AMP, Cyclic GMP, Ca+, DAG, IP3
- all participate in cell signal transduction
- immediate intracellular affect is to activate a protein kinase that is already present in the cell in an inactive form.
