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MCB 450: Exam 2
Glycolipid |
-sugar containing lipid derived from sphingosine
-sugar residues attached via linkage at 1-OH group of sphingosine
-one sugar: cerebroside
-two or more: gangliosides |
Facilitated Diffusion
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- proteins facilitate net movement of solutes only in thermodynamically favorable direction
- proteins display measurable affinity for transported solute
- saturable
- graph looks like x=y^2 |
Passive Diffusion
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- transported species moves across membrane in thermo. favored direction w/o help of specific transport system or protein |
Ways proteins interact with membrane bilayer
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- bind to surfaces of integral proteins
- transverse the lipid bilayer
- interact with the hydrocarbon region of the bilayer
- tightly anchor themselves to the membrane via covalently attached lipid molecule |
Hydrolase
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- enzyme that speeds up process of hydrolysis
-cleave by addition of water
-ex: chymotrypisin, trypsin 3.4.21.4 |
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Induced fit model
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Feedback inhibition
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inhibition of allosteric enzyme by the end product of the pathway controlled by the enzyme
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Red box: first order
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Noncompetitive Inhibition
- inhibitor and substrate can bind simultaneously to enzyme at different bonding sites
-works by decreasing overall # of active enzymes bound to substrate
-cannot be overcome by increase in substrate concentration
ESI complex |
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Uncompetitive Inhibition
- inhibitor binds only to enzyme-substrate complex
- inhibitors' binding site created only when enzyme binds substrate
- cannot be overcome by addition of more substrate
- ex. Round Up
- ES complex. then ESI complex |
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Competitive Inhibition
- inhibitor resembles substrate and binds to active site of enzyme
- substrate prevented from binding
- diminishes rate of cataylsis by reducing proportion of enzyme molecules bound to a substrate
-relieved by increase in substrate concentration |
Hemoglobin's oxygen binding properties affected by:
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- change in concentration of hydrogen ions
- pH
-increased concentration of 2,3- biphosphoglycerate
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carbonic anhydrase
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- catalyst to rxn of carbon dioxide with water to form carbonic acid
- occurs inside red blood cell |
Melting point of fatty acid determined by:
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- # van der Waals interactions between hydrocarbon chains
- chain length
- # of methylene groups |
Lower melting temp correlates with
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more fluidity
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Fatty Acids
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- Stored for fuel as triacylglycerides
- found in linear, branched, and cyclic forms
- mostly with even number of carbons |
Fatty acids are:
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- stored for fuel as triacylglycerides
- found in linear, branched, and cyclic forms
- even number of carbons |
Enzymes
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- proteins, RNA
- catalyze metabolic rxns
- may use cofactors
- form metabolic pathways
- have substrate and rxn specificity
- present in small amounts (not consumed by rxn)
- Integrate metabolic (ana/catbolic) fcns
- regulated: sensor of cell needs |
What enzymes do
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- provide alternate pathway of lower activation energy
- does not change free energy of reactants and products |
Oxidoreductase
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redox rxns
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transferases |
transfer of functional groups between molecules
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lyases
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modifies double bonds
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isomerases |
move groups within molecule
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ligases |
join two molecules by ATP cleavage
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Phospholipids |
- oriented in membrane in tail-to-tail fashion
- within each bilayer membrane, phospholipid comp of inner and outer leaflets is difference
- main component of membranes
- composed of three components:
-backbone (gylcerol or sphingosine)
-two fatty acid chains
-phosphorylated alcohol |
Active Transport
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transported species moves in therm. unfavored direction (low to high)
- energy required
- pump |
Catalytic Power
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ratio of enzyme catalyzed rate to uncatalyzed rate
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Antiporter |
- transport system in which a molecule is carried across a membrane in the direction opposite that of an ion, which in turn is pumped back across the membrane through a pump linked to ATP hydrolysis
- secondary |
Cholesterol is component/precursor of:
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-Vitamin D
- Glucocorticoids
- membranes of intracellular organelles
- animal cell membranes |
Cholesterol Derivatives
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-5 Families of Steroid hormones
-androgens
-estrogens
-progestins
-gulcocorticoids
-mineralocorticoids
-Bile acids (assist in absorption of dietary lipids)
-Vitamin D |
Strategy by which catalysts work
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increase probability of product formation
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Concerted Model
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- allosteric regulation that requires all subunits to be in the same state
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allosteric enzyme
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- enzyme having multiple active sites as well as
distinct regulatory sites that controls the flux of biochemicals through a metabolic pathway
- regulation of catalytic activity is by environmental signals, including the final product of the metabolic pathway regulated by the enzyme |
Some Hemoglobin Stuff
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- hemoglobin displays cooperative behavior
- myoglobin and hemoglobin bind oxygen in heme groups
- hemoglobin binds oxygen cooperatively
- hydrogen ions and CO2 promote dissociation of oxygen from hemoglobin |
homotropic effect
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disruption of the T<-> R equilibruim by substrates
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heterotrophic effect
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disruption of T<-> R equilibrium by regulators
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Why is super market meat red?
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- cooking denatures the globin, Fe2+ becomes Fe3+, turning brown
- carbon monoxide is added to meat to keep it red |
Bohr |
hydrogen ions and carbon dioxide promote release of oxygen
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heterotrophic regulators of oxygen binding by hemoglobin
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- carbon dioxide
- H+ |
Membrane formation
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Driving force:
-water's tendency to H-bond
-hydrophobic effect |
Lipids |
-water insoluble molecules but highly soluble in organic solvents
-have polar and non-polar end (amphipathic)
-Several Fcns:
-energy storage
-membrane component
-signal transduction pathway
-hormones |
Five Classes of Lipids
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-Fatty acids: fuel, building blocks of membranes; can be saturated/unsaturated
-Triacylglycerol: storage form of fatty acids, major source of glycerol
-Phospholipids: main component of membranes
-Glycolipids: important membrane constituents
-Steriods: Polycylic |
Cis-Unsaturated Fatty Acids
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always naturally occurring in cis formation
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Fatty acids esterification
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Fatty acids stored as triacylglycerols in which three fatty acids are esterified to one molecule of glycerol
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Triacylglycerols
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Major energy reserve
-most natural plant and animal fat |
Why Triacylglycerols good fuel reserve?
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-richer in energy (more reduced) than carbohydrates
-Tg can be stored more efficiently
-Tg aggregates are inert; no risk of undesired chem rxns w/ other cell comp.
-provide enough storage for 2 weeks |
Membrane Lipids
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Phopholipids
-Glycolipids
-Cholesterol |
Sphingosine
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amino alcohol containing long unsaturated hydrocarbon chain
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Lipid Anchors
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-Palmitoyl Group
-Farnesyl Group
-Glycosylphosphatidylinsotiol anchor |
Eukaryotic Membranes
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-Membranes serve as boundaries that maintain division of labor in cell
-Actively involved in cellular processes
-permeability barriers
-establish compartments |
Characteristics of Membranes
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-sheet like structures
-composed of lipids and proteins
-membrane lipids small amphipathic molecules
-proteins serve to mitigate impermeability of membranes
-noncovalent assemblies
-asymmetric
-fluid structures |
Membrane formation
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Driving force:
-water's tendency to H-bond
-hydrophobic effect |
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endergonic |
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exergonic
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facilitated diffusion
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passive diffusion
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FRAP
fluorescence recovery after photobleaching |
- cell surface fluoresces because of labeled surface component
- fluorescent molecules of small part of surface are bleached by intense light pulse
- fluorescence intensity recovers as bleached molecules diffuse out of region and unbleached diffuse in
-rate of recover depends on diffusion coefficient |
Proteases
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large class of enzymes that catalyze protein breakdown
cleave by hydrolysis |
Catalytic Triad
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- Serine 195
- Histidine 57
- Aspartate 102 |
His residue
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positions Ser side chain & polarize hydroxyl group for deprotonation
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In presence of substrate, His:
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accepts proton from Ser hydroxyl group
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His 57 acts as
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general base catalyst
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Withdrawal of proton from hydroxyl group
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alkoxide ion
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Asp orients His to make better proton acceptor via
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H-bonding
electrostatic effects |
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Effect of heat on enzyme:
increases then eventually sharply decreases |
covalent catalysis
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active site contains nucleophile
briefly covalently modified |
general acid base catalysis
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molecule (not water) donates or accepts proton
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metal ion catalysis
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metal ions function as electrophilic catalyst
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catalysis by approximation and orientation
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enzyme brings two substrates together in orientation that facilitates catalysis
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Enzymatic activity and T
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increases with increase in temp
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pH dependence
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due to presence of ionizable R groups
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Irreversible Inhibitors
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group specific
affinity labels
suicide inhibitors |
apoenzyme |
enzyme without its cofactor
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holoenzyme
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complete catalytically active enzyme
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two main types of
cofactors |
Coenzymes and metals
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Hutchinson Gilford disease
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mutation of lamin, a protein causing
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glycosphingolipid
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ceramide, fatty acid, amide
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sphingomyelin
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myelin (neural) sheath
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The low incidence of protein or lipid flip-flop in a membrane preserves
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membrane asymmetry
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affinity inversely proportional to
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Km
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multiple substrate enzymes
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sequential and double
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affinity label
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substrate analogue
specifically binds to active site
resembles substrate |
Bohr effect..again
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lower pH or high pressure - release of O2 from oxy heomglobin
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Sickle cell anemia
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substitution of valine reside for glutamic acid residue at B6 position
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Tense |
deoxyhemoglobin
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Relaxed |
oxyhemoglobin
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Glycerolphospholipid
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1,2- diacylglycerol and phosphate group
component of membranes
member of phospholipid |
unsaturation |
lowers melting point
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high lysine content
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ionic; hydrophobic
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Triacylglycerols again
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more energy upon oxidation
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FRAP measures
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increase in fluorescence
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Vmax attained when
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all enzyme is bound to substrate
zero order (top of graph) |
same y-int
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competitive
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same slope
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uncompetitive |
same x-int
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noncompetitive
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Transition state analogue
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not: stable chemically and structurally similar molecules to transition state
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negative allosteric effect
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decrease in cooperativity of substrate
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positive allosteric effect
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increase in cooperativity of substrate
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Difference in myoglobin and hemoglobin
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hemoglobin exhibits cooperative binding of O2 while myoglobin does not
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