Membrane Structure and Function, Enzymes (14-17) Flashcards
Functions of membrane proteins (4)
Transport
Enzyme Activity
Signal transduction
Cell-cell recognition
Functions of membrane proteins: TRANSPORT
control movement of molecules through membrane
Functions of membrane proteins: ENZYME ACTIVITY
enzymes that function on lipid substrates
Functions of membrane proteins: SIGNAL TRANSDUCTION
bind chemical signals like hormones and cause a biochemical change within the cell
Functions of membrane proteins: CELL-CELL RECOG
interact with neighbors and extracellular components
Definitions of types of membrane transport: PASSIVE transport
move down concentration gradient (high to low), does not require energy, polar and charged molecules require integral membrane protein
Type of Passive Transport: Simple Diffusion
small nonpolar molecules
Type of Passive Transport: Facilitated Diffusion
use of integral membrane protein for polar/charged molecules
Channel - pore
Carrier - bind and change conformation
Transporter
Definitions of types of membrane transport
ACTIVE transport
requires energy from ATP hydrolysis to move up the concentration gradient (low to high)
Channel Protein
Hydrophilic pore across lipid bilayer
Highly selective based on size of pore and amino acid residues lining the pore
Can be open or closed in response to signals
Example: aquaporin - water specific channel
Carrier Protein
Binds the molecule they transport Undergoes conformational change to expose the bound molecule to the other side Example: GLUT transporter Binds glucose (polar) outside of cell Conformational change Release glucose inside cell
active transport by Na+/K+ pump key features:
Na+ (high/low) (inside/outside cell)
K+ (high/low) (inside/outside cell)
Na+ high outside cell
K+ high inside cell
Na+/K+ pump uses energy from ___ _______ to move molecules against/up their concentration gradient
ATP hydrolysis
Na+/K+ Pump Step By Step (y’all just watch a video or something this is a lot)
Binding pocket open to inside cell (cytosol)
3 Na+ bind
Pump binds ATP and phosphate is attached
Conformational change so binding pocket face outside of cell
Reduced affinity for Na+ causes it to be released outside the cell
Phosphorylated pump has increased affinity for K+ so 2 K+ bind
Phosphate is cleaved
Protein returns to original conformation facing the inside of cell and K+ is released
cAMP role
cAMP initiates pathways (activates glycogen phosphorylase) to release glucose from glycogen stores to provide fuel for muscles
** for “ex of receptors and cell signal, insulin and glucose and epinephrine and degradation of glycogen”
look at the study guide
How acetylcholine transmits a nerve signal
ACh is a neurotransmitter that controls skeletal muscle
ACh crosses a synapse and binds receptors on the postsynaptic neuron
Results in change in permeability or ions on the postsynaptic neuron which initiates a nerve impulse
What is an enzyme and why is it specific?
Enzyme is a protein that catalyzes a biochemical reaction
Specific for substrate, reaction, and type of reaction based on the geometry and chemical complementarity of the the active site and substrate
Enzymes are good catalysts because (4)
Proximity effect
Orientation effect
Catalytic effect
Energy effect
Proximity effect
- bring substrate and active site close together
Orientation effect
- hold substrate at exact distance needed for catalysis
Catalytic effect
- provide acidic, basic, or other groups necessary for catalysis
Energy effect
- lower energy barrier by weakening substrate bonds
Six types of enzymes, reactions they catalyze (BE ABLE TO RECOGNIZE - she has hard examples on the problem sets)
-
Types of enzymes / reactions: Oxidoreductase
catalyze redox reaction
Usually add or remove O or H
Can involve NAD+ reduced to NADH
Require coenzymes that are reduced or oxidized as the substrate is oxidized or reduced
Types of enzymes / reactions: Transferase
transfer functional group from one molecule to another
Require energy
Kinase - transfer a phosphate
Types of enzymes / reactions: Isomerase
catalyze isomerization, rearrangement
Types of enzymes / reactions: Hydrolase
break bonds by addition of H2O
Types of enzymes / reactions: Ligase
bond together 2 substrates
Types of enzymes / reactions: Lyase
add/remove grp from double bond (same as hydrolase but no H2O or ox/redoc)
Oxidoreductase Equation
Transfer electrons from molecule A to B or B to A
A + B: → or ← A: + B
Ex: pyruvate + NADH → ← lactic acid + NAD+
Performed by lactate dehydrogenase
Transferase Equation
A + BX → AX + B
Isomerase Equation
One substrate and one product
One is converted to its isomer
A → B
Occurs in glycolysis: glucose-6-P → fructose-6-P
Hydrolase Equation
A + H2O → B + C
Ligase Equation
A + B = AB
(like DNA 2 polymers coming into one strand by DNA ligase
Lyase Equation
A → B + C
In order to accomplish their goals, lyase generate either a double bond or a ring structure in a molecule between two atoms
At low substrate concentration,
the rate is directly proportional to the substrate concentration
With increasing substrate concentration,
the reaction rate slows
Rate of enzyme catalyzed reaction is dependent on the overall efficiency of the enzyme (depends on the enzyme’s affinity for the substrate)
Rate at which they combine is the limiting factor
Occurs in enzyme substrate complex
Reaction rate reaches maxim when enzyme is saturated (active sites filled)
Reaction rate can increase again by increase enzyme concentration
Enzymes function best at body temperature
Rate decreases if below this temperature
Rate increase with increased temperature but will decrease once too high and protein denatures
Enzymes function best at pH of body fluid where they act
Rate will decrease if above or below this pH
Enzyme Regulation: Feedback
product of pathway effects earlier step
Enzyme Regulation: Inhibition
decreases enzyme activity
Enzyme Regulation: Allosteric
bind allosteric site and alter enzyme activity
Positive - increase activity
Negative - decrease activity
Enzyme Regulation: Covalent Modification
add or remove covalently bonded portion
Zymogen - need part cleaved to be active
Blood clotting factors
Enzyme Regulation: Genetic Control
hormones control the synthesis of enzymes until they are needed
Example: lactase not synthesized til lactose is present
Reversible Enzyme Inhibition
inhibitor can leave restoring the enzymes activity
Irreversible Enzyme Inhibition
inhibitor remains permanently bound and enzyme is permanently inhabited
Competitive Enzyme Inhibition
inhibitor binds active site and prevents the substrate from binding
Inhibitor looks like substrate
Noncompetitive Enzyme Inhibition
inhibitor binds allosteric site and substrate less likely to bind the enzyme
Noncompetitive inhibition (can/cannot) be overcome by increasing substrate concentration
CANNOT. since the inhibitor binds a site different from the active site (they are not competing)
A noncompetitive inhibitor will slow the reaction rate and it will not be able to reach the maximum
Competitive inhibition (can/cannot) be overcome by increasing substrate concentration
CAN.
Increasing the substrate concentration makes it more likely to bind the active site than the inhibitor
A competitive inhibitor will slow the reaction rate but it is still able to reach the maximum
No inhibition
rate increase with substrate concentration and reaches maximum when enzyme is saturated
Zymogens
enzymes synthesized in an inactive form, not activated till they are needed
Activation requires chemical reaction to cleave part of the molecule (covalent modification)
Ex: enzymes that digest proteins or act as blood clotting factors
Covalent modification
add or remove a covalently bonded portion of an enzyme in order to activate it when it is needed
Ex: phosphorylation - addition of a phosphate by kinase to activate an enzyme
How covalent modification of the enzyme that catalyzes glycogen breakdown influences glucose levels
Phosphorylation by kinase
Glycogen phosphorylase becomes more active when phosphorylated
Glycogen phosphorylase breaks down glycogen stores to release glucose to be used by muscles
Vitamins are
Essential in trace amounts, must be consumed
Water soluble vitamins are vitamins _ and _
B and C
Water soluble vitamins
Can’t be stored, Can’t overdose because excreted in urine
Water sol vitamins: Important for coenzymes - help facilitate enzyme catalysis (important in redox reactions)
Coenzyme structure derived from these vitamins
Ex: niacin and NAD+
Ex: riboflavin and FADH2
Fat soluble include _, _, _ and _
A, D, E, and K.
Fat soluble vitamins are stored __ _____ ______ and it is possible to _____.
stored in fat deposits
possible to overdose
Vitamin A
growth and development, eyesight, immune response
Vitamin D
calcium uptake
Vitamin E
antioxidant
Vitamin K
blood clotting/bone
NAD+
electron acceptor
Can be reduced to NADH
NADH
electron carrier, form of stored chemical energy
Can be oxidized to produce ATP
