Unit 7 Flashcards
Metabolism (4)
- life-sustaining chemical reactions in an organism
- converts food to energy
- converts food to monomers of proteins, lipids, and carbs
- elimination of nitrogenous wastes
What do the chemical reactions of our metabolism require?
an initial input of energy to take place
activation energy
amount of energy reactants must absorb to start a chemical reaction
How can we increase the rate of chemical reactions?
enzymes
What is another name for enzyme?
biological catalysts
enzyme functions (3)
- catalyze/speed up reactions
- mostly proteins (some RNA)
- reduce activation energy
How do enzymes work?
by binding to reactants and speeding up their conversion to products
substrate
reactant which binds to enzyme
active site
region where substrate bind and undergoes a chemical reaction
enzyme-substrate complex
temporary association between enzyme and substrate
enzyme facts (3)
- must COLLIDE with reactants for binding to occur
- remain UNCHANGED after they release products
- are REUSABLE
What types of reactions to enzymes catalyze? (2)
- hydrolysis
- condensation
sucrase
breaks down sucrose
proteases
break down proteins
lipases
break down lipids
DNA polymerase
builds DNA adds nucleotides to DNA strand
What is an important characteristic of enzymes?
they are highly specific
Why are enzymes substrate-specific? (2)
- active sites have 3D shapes that determine which substrate can bind
- active sites hold substrates in the optimum position to carry out reactions
The shape of the active site is…(2)
- determined by the tertiary structure of the protein
- complementary to the substrate and facilitates binding
What do R groups have to do with enzyme-substrate specificity? (2)
- R groups lining the enzyme active sites use chemical attraction to facilitate substrate biding
- R group interactions temporarily hold the substrate in active site
How are substrates held in place?
by weak interaction between amino acids
What weak reaction hold substrates in place? (3)
- hydrogen bonds
- hydrophobic interactions
- ionic interactions
Hexokinase
catalyzes first step of glycolysis (cellular respiration)
How does hexokinase lower activation energy? (3)
- glucose and ATP are both negatively charged
- it takes energy to bring 2 negatively charged objects together
- hexokinase lowers this energy barrier with positive charges in its active site
Substrates are held in the active site of hexokinase through which interaction?
Ionic
What about hexokinase facilitates the binding of the enzyme and its substrates?
the shape of the active site is complementary to the shape of the substrate molecule
Lock and Key Hypothesis (2)
- active site and substrate have complementary shapes like puzzle pieces
- enzymes specifically react with only one or a very few substrates
Analogy for Lock and Key Hypothesis
only the correctly sized key fits into the keyhole of the lock
What does the lock and key hypothesis explain phenomena wise? (2)
- enzyme specificity
- activity loss when enzymes denature/change shape
Why can’t the lock and key hypothesis explain all experimental evidence?
in the lock and key hypothesis, the active site is not favorable to product formation
What does the induced fit hypothesis say?
when a substrate binds with an enzyme, it causes the enzymes active site to change shape and form products
Change in shape of active site lowers activation energy and favors product formation by… (3)
- Providing a favorable microenvironment for active site to attract the substrate
- Orienting substrates correctly for the reaction to occur
- Straining substrate bonds & stabilizing transition state
What are the steps of the induced fit hypothesis? (3)
1) The complementary shapes and weak interactions between substrate and active site lead to initial binding.
2) The enzyme and substrate change their shape to facilitate a stronger bond, favoring product formation.
3) Products are released from the active site and active site goes back to original conformation
Lactose
disaccharide produced in lactating mammals as an energy source for newborns
Lactase (enzyme)
breaks down lactose into glucose and galactose in the small intestine
lactose intolerance
inability to digest and absorb lactose that results in gastrointestinal symptoms when consumed
What are causes for lactose intolerance?
a reduction or complete loss of lactase activity
What happens to lactose when an individual does not have lactase?
lactose will pass into the large intestine, where it is broken down by bacteria
What are some symptoms of lactose intolerance? (4)
- Abdominal bloating
- Abdominal cramps
- Gas
- Nausea
What are treatments for lactose intolerance? (3)
- Removing milk from diet
- Add lactase to milk or take in capsule/chewable form
- Consume lactose-free milk products (lactose-free milk is sweeter)
Lactose-Free milk can be produced by… (2)
- placing lactase from yeast directly into milk
- attaching lactase to immobilized alginate beads and repeatedly passing milk over the enzyme
Alginate
natural polymer extracted from seaweed that forms a gel beads that holds lactase
What are advantages of using immobilized alginate beads bound with lactase for producing lactose-free milk? (3)
- Enzymes are conserved and can be reused
- high concentrations of enzymes can be used for a faster rate of reaction
- enzymes can be recycled, reducing costs
Where can immobilized enzymes be applied?
industrial practices
What are the advantages of converting lactose to glucose and galactose? (4)
- as a source of dairy for lactose-intolerant individuals
- a means of increasing sweetness without artificial sweeteners
- as a way of reducing the crystallization of ice-creams
- as a means of reducing production time for cheeses and yogurts
How is enzyme activity measured?
reaction rate
reaction rate
products formed OR substrates used up in a given amount of time
What happens to a graph showing the relationship between reaction rate and time when there are no enzymes present?
increasing reactant concentration increases reaction rate
How does substrate concentration affects reaction rate? (2)
- as ↑ substrate = ↑ reaction rate
- reaction rate levels off when enzyme is saturated
What can cause proteins to denature? (2)
- high temperatures
- changes in pH
What can denatured proteins lead to?
- change in active site shape
- inability of substrate to bind to active site
What has to be disrupted to denature proteins?
weak interactions
Which weak interactions do proteins denature when disrupted? (3)
- hydrogen bonds
- ionic interactions
- hydrophobic interactions
What levels of protein structure are disrupted when a protein denatures? (3)
- secondary
- tertiary
- quaternary
Why do primary structures remain intact?
because it is stabilized by
covalent bonds
Why does pH affect enzyme function? (3)
- Changes in pH add or remove H+ from solution
- Changing H+ in solution disrupts interactions between charged amino acids R groups
- Disrupting interactions changes
overall protein shape and active
site shape; disrupts
interactions between substrate
and active site.
optimum pH
pH at which the reaction rate is highest
What are most human enzyme optimal pHs?
between 6-8
Why are there varying optimal pHs for human enzymes?
it depends on localized conditions
Where is pepsin located?
stomach
What is the optimal pH for pepsin?
2-3
Where is trypsin located?
small intestine
What is the optimal pH for trypsin?
8
Optimal temperature
temperature at which the rate of an enzyme-catalyzed reaction is highest
What happens when an enzyme is at optimal temperature?
greatest number of effective collisions between substrate and active site
What happens as temperature increases to optimal?
molecules move faster and collisions increase between substrates & active sites
producing more products
What happens as temperature goes above optimal? (2)
- the increased energy disrupts weak forces that determine active site shape & enzyme/substrate binding
- enzymes start to denature
Why would enzymes have different optimal temperatures?
because there are organisms that live in different environments
What is the optimal temperature for human enzymes?
35-40 degrees C
Why are human enzymes’ optimal temperature in that range?
the human body temp is 37 degrees C
What other factors affect enzyme function? (2)
- activators
- inhibitors
activators (2)
- molecules or ions some enzymes require to function
- These activate enzymes by stabilizing their shape, or by participating in the chemical reaction directly
Inhibitors
molecules that reduce enzyme activity
What are the 2 types of inhibitors?
- competitive inhibition
- noncompetitive inhibition
Competitive Inhibitors (4)
- bind to the active site
- are similar in shape to the substrate
- “compete” to bind to active site against substrate
- bind to an active site reversibly (can unbind)
How can competitive inhibition be overcome?
by increasing substrate concentration
What is are examples of competitive inhibition? (2)
- disulfiram
- ethanol
Disulfiram
treats chronic alcoholism
How is disulfiram a competitive inhibitor? (2)
- Ethanol is metabolized to acetaldehyde, which is further metabolized to acetate by specific enzymes.
- Disulfiram inhibits aldehyde dehydrogenase, causing the accumulation of acetaldehyde with unpleasant side-effects
Ethanol
treats methanol/antifreeze poisoning
How is ethanol a competitive inhibitor? (2)
- Normally, methanol is metabolized (broken down) and its by-products cause blindness
- Ethanol competes with methanol for the same binding site on alcohol dehydrogenase
Noncompetitive inhibitors (3)
- bind to sites other than active sites (do not resemble substrate)
- prevents substrate binding by causing active site to change shape
- can’t be overcome by increases in substrate concentration
What is noncompetitive inhibition a form of?
allosteric regulation
Allosteric regulation
non-substrate molecule binds to a regulatory site (allosteric site) other than active site and changes enzyme shape to prevent substrate binding
What is an example of a noncompetitive inhibitor?
cyanide
Cyanide
causes death by preventing ATP production via aerobic respiration
How is cyanide a noncompetitive inhibitor? (2)
- binds to molecule (cytochrome c) in electron transport chain
- When bound, the electron transport chain cannot function and ATP is not produced via aerobic respiration
What are the rates of the chemical reactions of metabolism regulated by?
enzymes
Catabolic Pathways (3)
- breakdown of complex molecules into simpler, usable forms
- involves hydrolysis of macromolecules into monomers/ digestion
- Energy released can be stored in molecules or released as heat
Anabolic Pathways (3)
- chemical reactions that synthesize complex molecules from simpler molecules
- involves condensation reactions and forming macromolecules from monomers
- typically use energy
Metabolic Pathways
Metabolic pathways are organized into chains or cycles of enzyme-catalyzed reactions with each step controlled by an enzyme.
What is an example of a chain involved in metabolic pathways?
glycolysis
What is an example of a cycle involved in a metabolic pathway?
Krebs cycle
Why are metabolic pathways beneficial? (2)
- ↑ control because of enzymes can be regulated independently
- ↑ efficiency because it allows products to be used in multiple reactions/pathways
Why are chemical reactions broken into steps? (2)
- ↑ control because of enzymes can be regulated independently
- ↑ efficiency because it allows products to be used in multiple reactions/pathways
End Product Inhibition (3)
- final product is inhibitor of earlier step in pathway
- Switches off pathway when product is plentiful
- no unnecessary accumulation of product
What is an example of feedback inhibition?
synthesis of isoleucine from threonine (amino acids)
How is the synthesis of isoleucine from threonine (amino acids) feedback inhibition? (2)
- isoleucine is the allosteric inhibitor(noncompetitive) of the first step
- as product accumulates it collides with enzyme more often than substrate does
