Studied by 1 PersonTags & Description
What is an enzyme
An enzyme is a protein that acts as a catalyst for ONE specific reaction
How do enzymes catalyze reactions?
Enzymes lower the activation energy required for a reaction by holding their substrate in a way that makes the high energy transition state acquirable at lower energy levels, WITHOUT changing the temperature.
DONT change the energy of the reactants or the products of the reaction. (i.e. DONT change the temperature of the cell)
Do enzymes form temporary covalent bonds with substrates?
Yes
Are enzymes changed after catalyzing a reaction?
No
What is a metabolic pathway?
A metabolic pathway is a series of reactions in which the products of one are the reactants of the next, where each reaction can be catalyzed by a different enzyme.
Metabolism
All of the chemical reactions that occur in an organism
What are the 2 types of metabolism and how are they different?
Anabolism and Catabolism
Catabolism = Complex -> Simple
Releases usable energy while some energy is lost as heat
Energetically favorable (spontaneous)
Anabolism = Simple -> Complex
Uses energy to create bonds between two molecules
Energetically unfavorable (nonspontaneous)
What is the second law of thermodynamics?
The entropy of an isolated system always increases
How do cells create order when entropy must always increase?
Cells create order inside themselves by making its environment more disordered leading to an overall increase in entropy in the isolated system (cell + environment)
When cells break chemical bonds some of the energy is captured as _______ energy while the rest is lost as __________.
chemical; heat
What is the ultimate/ primary source of energy?
The Sun because plants convert the energy from the sun to chemical energy which animals consume.
Oxidation reactions
Loss of electrons; Gain of Oxygen; Loss of Hydrogen
Dehydrogenation
Reduction reactions
Gain of electrons; Loss of Oxygen; Gain of Hydrogen
Hydrogenation ( when molecules pick up electrons, they also pick up H+ or protons from the environment resulting in hydrogenation) A + e- + H+ -> AH
Redox reactions
Reactions that involve the transfer of electrons
Can be a complete transfer of electrons or can exist in a covalent bond where electrons are only partially transferred
Spontaneous Reaction
Reaction in which there is a loss of free energy (ΔG < 0) and once started, proceeds without any additional input of energy.
Energetically favorable
Nonspontaneous Reaction
Reaction in which there is a gain in free energy (ΔG > 0) and requires a constant input of energy to proceed.
Energetically unfavorable
What is the behavior of ΔG throughout a reaction?
ΔG tends to decrease in a reaction until it hits 0 at which the reaction is at equilibrium
Reactions tend to proceed until reaching equilibrium.
What is metabolic disequilibrium and why is it important?
Metabolic disequilibrium refers to the ability of cells to keep themselves in a state of constant disequilibrium by either removing products or adding reactants. If cells reach equilibrium they will die as there is no input of energy.
Standard free energy change allows what to be calculated? what is the equation used?
Allows the calculation of free energy change for a reaction with different concentrations of product and reactant.
ΔG = ΔG° + RT ln [Product]/[Reactant]
What is equilibrium constant K?
The ratio of product to reactant concentration for a particular reaction at equilibrium.
The HIGHER the K, the MORE NEGATIVE ΔG
For reactions with only 1 reactant K = [product]/[reactant] For reactions with 2 substrates, K = [Product]/([reactant_1][reactant_2])
What equation can you use to calculate the concentration of products to reactants at equilibrium for a reaction with only 1 reactant?
ΔG° = -1.42 log K
where 1.42 = RT in kcal/mole
For every 1.42 kcal/mol diff in free energy, K is changed by a factor of 10.
What are association and disassociation rates equal to?
association rate is equal to the concentration of reactant 1 MULTIPLIED by the concentration of reactant 2 because the reactant molecules must collide in order to react.
The larger the values of K, the __________ the binding b/w 2 substrates by ___________ bonds.
stronger, noncovalent
At higher value of K, the shape of the 2 substrates are ___________ complementary, because they have _____________ binding.
more; stronger
The more 2 substrates bind together complementarily, the ___________ negative the value of ΔG for the reaction.
more
Similarly to Hess's Law for Changes in enthalpy, changes in free energy for sequential reactions are _______________.
additive
How can sequential reactions allow unfavorable reactions to occur?
Unfavorable reactions can occur when there is a favorable reaction right after it that uses the products as its reactants and has a negative enough ΔG that it makes the overall ΔG negative.
"Siphons" the products of the unfavorable reaction by quickly converting the products of the unfavorable reaction to products of the favorable reaction, making the amount of reactant concentration of the unfavorable reaction always higher than the product concentration, therefore lowering the ΔG of the unfavorable reaction.
What does Enzyme catalyzation rate depend on?
How fast and how often enzyme collides with its substrate
Increase in substrate concentration increases catalyzation rate
Increase in temperature increases catalyzation rate
How fast the products form and diffuse away
How is the rate of catalysis of enzymes measured?
Michaelis Constant
What is Vmax?
V max refers to the rate of catalysis by an enzyme at which enzymes are fully saturated with substrate molecules
No real way to determine this value
What is Michaelis Constant?
KM = The concentration of substrate at which the enzyme is functioning at half its maximum speed.
Concentration at 1/2 Vmax
What is the relationship between KM and the strength of binding b/w substrate and enzyme?
Large KM = Weak binding because it take a larger concentration of the substrate to reach half of the enzymes max saturation
Small KM = Strong binding because it takes less concentration of substrate to reach half of the enzymes max saturation
Enzymes catalyze the forward and backward reactions the same amount
T/F
True
The net distance a molecule travels through the cytosol via diffusion is relatively short in comparison with the total distance it may need to travel. This is because movement governed by diffusion alone is a __________ process that is most effective for the dispersion of small molecules over short distances.
slow
Seed oils are often dehydrogenated and added back into processed foods. The new fatty acids have an increased number of carbon-carbon double bonds. The dehydrogenation reaction could also be described as a/an __________ reaction.
Oxidation
When there is an excess of nutrients available in the human body, insulin is released to stimulate the synthesis of glycogen from glucose. This is a specific example of a/an __________ process, a general process in which larger molecules are made from smaller molecules.
Anabolic
The energy used by the cell to generate specific biological molecules and highly ordered structures is not stored in the form of ______________. (choose all that apply).
Brownian Movement
Heat
Light Waves
Chemical Bonds
Brownian Movement, Heat, Light Waves
The study of enzymes also includes an examination of how the activity is regulated. Molecules that can act as competitive inhibitors for a specific reaction are often similar in shape and size to the enzyme's substrate. Which variable or variables used to describe enzyme activity will remain the same in the presence and absence of a competitive inhibitor?
Vmax
Chemical reactions carried out by living systems depend on the ability of some organisms to capture and use atoms from nonliving sources in the environment. The specific subset of these reactions that use protein to build muscle is
Anabolic
What is the name of the catalysts used by cells to lower the activation energy of a given reaction?
Enzymes
The equilibrium constant for complex formation between molecules A and B will depend on their relative concentrations, as well as the rates at which the molecules associate and dissociate. The association rate will be larger than the dissociation rate when complex formation is favorable. The energy that drives this process is referred to as __________ energy.
Binding
Your body extracts energy from the food you ingest by catalyzing reactions that essentially "burn" the food molecules in a stepwise fashion. What is another way to describe this process?
Oxidation
Oxidation is a favorable process in an aerobic environment, which is the reason cells are able to derive energy from the oxidation of macromolecules. Once carbon has been oxidized to _, its most stable form, it can only cycle back into the organic portion of the carbon cycle through _.
CO2; Photosynthesis
Activated carriers (such as ATP and NADH/NADPH) serve as sources of what for biosynthetic reactions?
Energy and Chemical Groups
Plants can produce O2 from H2O despite it being an unfavorable chemical reaction. How are plants able to do this?
Plants absorb light which provides energy to convert H2O into O2
What is a common method for cells drive a reaction with a positive ΔG?
Couple the reaction to another reaction with a negative ΔG
If the reaction X-> Y is followed by the sequential energetically favorable reaction Y-> Z, is the equilibrium constant for the X-> Y reaction changed? Why or why not?
It is not because the equilibrium concentrations is kept constant since as the Y disappears, more X is converted to Y keeping the concentration ratio of product to reactant constant.
The only chemical reactions that are possible are those that ___________ the disorder of the UNIVERSE
increase
What molecule is often hydrolyzed in an energetically favorable reaction, to power unfavorable reactions?
ATP
What are activated carriers?
Organic molecules that can contain READILY TRANSFERRABLE high energy bonds or high energy electrons, that store chemical energy used to power nonfavorable reactions
Activated carrier activation is an energetically ______________ process that is often coupled with an energetically ______________ process that powers it
unfavorable; favorable
Such as the oxidation of food molecules.
The most widely used activated carrier is
ATP
ATP hydrolysis can be coupled with a __________ reaction through 2 steps: activation and condensation.
condensation reaction
1st step: OH group on the molecule that will undergo condensation is replaced by the phosphate group released upon hydrolysis of ATP
2nd Step: Phosphoanhydride bond holding the phosphate to the molecule is broken and the energy released is used to replace the phosphate group with some other moelcule.
How is the amino acid glutamate formed?
First, the OH on glutamic acid is replaced with a phosphate group, then the phosphate group is replaced by an NH3 group.
What are the two popular activated carriers that transfer electrons
NADH and NADPH
How do NADH and NADPH differ in structure and function?
NADH and NADPH differ in the presence of a phosphate group, which NADPH has and NADH does not.
NAD+ in the body is used as an oxidizing agent for many catabolic reactions (breaking down food molecules) while NADPH is used as a reducing agent for many anabolic reactions (building molecules)
The cell wants to keep (more/less) of NAD+ than NADH and (more/less) of NADPH than NADP+.
The cell wants to keep MORE of NAD+ and MORE of NADPH
Activated carriers are made up of what 2 parts?
Transferrable group and the handle
What do handles often contain and what is a theory for why this is?
Handles often contain nucleotides and a theory that explains this is that the early catalysts were RNA molecules (ribozymes)
The condensation reaction that connects monomers to make macromolecules is coupled with the hydrolysis of ATP by first converting the monomer to a ________________.
high energy intermediate
Similar to synthesis of glutamine
Hydrolysis of ATP has approximately what free energy change?
-13 kcal/mol
When the hydrolysis of ATP does not produce enough energy to power an unfavorable reaction, ATP can be hydrolyzed into _____________ and ___________ instead.
AMP and Pyrophosphate
The pyrophosphate is then hydrolyzed into two inorganic phosphates.
The hydrolysis of ATP to AMP and Pyrophosphate produces __________ as much energy as hydrolysis of ATP to ADP and P.
twice
The rule that oxidation reactions release energy and reduction reactions require energy is true of all reactions. T/F
False. This is only true for cells because the unique environment of cells permits this.
High energy electrons in activated carriers are (tightly/loosely) associated with the atomic nucleus.
loosely, because they are readily transferable
Are all biological enzymes proteins?
No
Vmax (is/is not) changed in the presence of competitive inhibitors and (is/is not) changed in the presence of noncompetitive inhibitors
is not; is
What is the difference between competitive and noncompetitive inhibition?
Noncompetitive inhibition cannot be overcome by increasing substrate concentration while competitive inhibition can be.
Changes in Free energy are_______
additive
Biosynthesis
Energy requiring reactions -> building molecules ("synthesis)
Which of the following are possible functions of plasma membrane proteins?
All of these are true. Transporters Anchors Receptors Enzymes
All of these are true.
A prokaryotic organism is isolated from a glacier, where it was thriving. Based on your knowledge of the plasma membrane, you would expect to find a predominance of
largely saturated fatty acids.
cell wall to define the cell because the cell membrane would not be present.
largely unsaturated fatty acids.
equal amounts of saturated and unsaturated fatty acids, as long as the chain was close to 12 carbons in length.
none of the above
excessive amounts of cholesterol
largely unsaturated fatty acids
Which of the following molecules would not readily cross an intact cell membrane by simple diffusion, but would require a facilitator protein?
oxygen water thyroid hormone glucose fatty acids
Glucose
THINK BEYOND: A colleague gives you two membrane fractions from a plant cell lysate. One contains the plasma membrane fraction, the other the mitochondrial fraction. The tubes are not labeled, but you run the samples anyway, looking at the macromolecule composition of the samples. You know for certain that the second sample contains the mitochondrial fraction simply because it contains insignificant amounts of,
carbohydrates. specifically phospholipids. lipids. protein. None of the above
Carbohydrates
Membranes contain several classes of lipids, such as phospholipids, sphingolipids, sterols, etc. In spite of their many differences, they all
easily react with bases but not with acids. can be easily hydrolyzed. are readily soluble in water at 37C. are soluble in nonpolar solvents. can be reduced by strong reducing agents such as sodium.
are soluble in nonpolar solvents
Which of the following is the most common phospholipid in cell membranes?
Phosphatidylcholine Phosphatidylethanolamine Phosphatidylinositol Phosphatidylserine None of the above
Phosphatidylcholine
Evaluate the ways in which proteins work to keep a membrane selectively permeable.
All of the these are true
Many membrane bound proteins are transporters, each with a specific mechanism to allow for entrance of a molecule into the cell
Many membrane bound proteins are channels, each with a hydrophobic pore across the membrane which allows for diffusion across the membrane
Certain cells can immobilize certain membrane proteins by attaching them to intracellular or extracellular macro molecules
The attached sugar chains on some proteins that are attached to lipids not only act to lubricate the cells, but are also involved in cell-cell recognitions
All of these are true
Cell-cell communication in plants takes place via specialized structures called
cell wall pores. desmids. gap junctions. connexons. plasmodesmata.
plasmodesmata
The most common number of carbons in fatty acid hydrocarbon chains of membrane phospholipids is: (closest answer)
16
Which of the following statements is false regarding the protein Bacteriorhodopsin?
Bacteriorhodopsin is a very large protein.
Bacteriorhodopsin acts as a proton pump.
The polypeptide chain crosses the lipid bilayer at 7 alpha helices.
This protein contains polar amino acid side chains at strategic locations to help guide the movement of the proton.
This protein is found in the plasma membrane of Halobacterium halobium, which lives in salt marshes.
Bacteriohodopsin is a very large protein
TECHNIQUE: Inactivation of a fluorescent dye in a very concentrated spot on a cell so that the fluidity of membranes can be subsequently visualized is called,
liposome formation. ferritin-conjugated lectins. the freeze-fracture technique. SDS-PAGE. photobleaching.
photobleaching
Two cells with different cell-surface markers are fused in the presence of polyethylene glycol (PEG). The cells are then placed at 0°C. What do you expect to observe about the individual cell markers?
Only one marker will disperse, while the other remains stationary.
The markers will be endocytosed by the fused cell and then redistributed as fused markers.
The markers will evenly disperse throughout both membranes.
Both sets of markers will not mix but will migrate to opposite poles from one another.
The markers will essentially remain where they are, with little migration.
The markers will essentially remain where they are with little migration
A glycolipid molecule may do which of the following?
Lateral diffusion on the plane of the membrane Flexion of its fatty acid tails Rotation about its axis All of the these None of the these
All of these
Localized regions of membrane lipids that contain proteins involved in cell signaling are known as, [These are also known by other names too]
homeoviscous adaptations. membrane leaflets. islands of hydropathy. hopanoids. lipid rafts.
Lipid rafts