Lecture 7B Flashcards
why do cells need enzymes?
to speed up the reactions
what is an enzyme?
a catalyst or catalytic protein that speeds up the rate of a reaction without being consumed or altered by the reaction
what is activation energy?
the amount of energy required to convert the reactants into products.
EA
what is the unstable state of a chemical reaction?
the transition state
what does thermal energy do to a reaction?
it increases the movement/speed of molecules causing them to collide more often thus breaking the bonds between them to which will allow new bonds to form.
energy is released when new bonds are formed
heat speeds up a reaction allowing the reactants to reach the transition state
why is using thermal energy inappropriate for biological systems?
- high temperatures denatures proteins
- heat would speed up all cells and not just the necessary ones.
how to enzymes catalyze a reaction?
they catalyze by lowering the activation energy barrier which will allow the reactants to absorb the sufficient amount of energy to reach the transition state even at moderate temperatures.
what type of reaction is the hydrolysis of sucrose?
it is an exergonic reaction and a catabolic reaction
exergonic = spontaneous
- The reaction however is slow
- The change in free energy stays the same
- Lowered activation energy
can enzymes turn an endergonic reaction into an exergonic reaction?
No enzymes cant, but they can speed up this process of conversion.
what is an enzymes substrate?
the reactant an enzyme acts on
what is the enzyme-substrate complex?
enzyme + substrate/reactant = enzyme + product
can enzymes work both forward and reversed?
yes
what is the active site?
region where the enzyme binds to the substrate
A pocket/groove on surface of protein formed by amino acids
Needs to be compatible fit between the shape of the active site and the shape of the substrate.
what is the substrate held by?
hydrogen and ionic bonds
what is the induced fit?
the interaction between the substrate and amino acids to cause a change in structure of the active site so that it can fit properly with the substrate
It brings chemical groups into positions that increase the rate
How do enzymes lower the rate?
- be a template for substrate molecules to come together
- stress the substrate molecule bonds
- participates in the chemical reactions (at times)
- provides favorable microenvironments for the reaction
how do enzymes stress the substrate?
they stress the substrate by stretching the substrate molecules towards the transition state.
Sometimes enzymes are involved in brief covalent bonding between an active site R-group and the substrate.
what is a good example that presents an enzyme as a good microenvironment?
an active site composed of amino acids with acidic R groups creating a pocket of low pH in neutral cell.
what are the five steps to an enzyme catalysis?
1) substrate binds to the active site of an enzyme
2) enzyme-substrate complex if formed
3) reaction proceeds and the products are formed
4) product leaves
5) enzyme returns to original shape.
Name factors that influence the rate of a reaction?
- subtrate concentration (the greater the concentration of substrate molecules the more they will will reaction and interact with the enzymes active site
-enzyme concentration ( can be saturated with subtrate ) - temperature
- pH
- the presence of other chemicals
what does the rate of reaction give you?
provides you with the slope of the amount of products formed per unit of time.
this is dependent on the initial subtrate concentration
what does it mean when the enzyme is saturated?
this is when all the active sites of the enzyme is taken up by substrates
This is the subtrate concentration
What does high enzyme concentration mean for a reaction?
This means that there needs to be a high substrate concentration to saturate the enzymes and ensure a maximum reaction rate is higher.
A higher enzyme concentration will lead to a higher Vmax
what is Km?
the measure of affinity of the enzyme for the substrate
1/2 Vmax
affinity = the tendency of the substrate binding to the enzyme
high Km= low affinity = needs a higher concentration of substrate to achieve Vmax
How does a cell regulate its metabolic pathways?
Does this by controlling when and where enzymes are active.
What are the two ways in which an enzyme can regulate metabolic pathways?
1) regulating activity of that enzyme (enzyme activators = molecule that promotes enzyme function, enzyme inhibitors = molecule that interferes or prevents an enzyme from functioning
2) Switching genes that code for the making of an enzyme on/off to increase/decrease the number of enzyme molecules present.
what are cofactors (prosthetic groups)?
organic or inorganic molecules that allow the enzyme to function properly
Non-protein part of the enzyme
Coenzymes= organic cofactors
zinc, copper, iron = inorganic enzymes
What is the protein part of an enzyme?
apoenzyme
What is the holoenzyme?
the apoenzyme + the cofactor
What makes a enzyme reaction irreversible?
when the inhibitor attaches to the enzyme by covalent bonds
what makes an enzyme reaction reversible?
when the inhibitor attaches to the enzyme by weak interactions
What do competitive inhibitors do?
- bind to the same site as the substrate on the enzyme
- blocks substrates from entering active sites which reduces the productivity of an enzyme
- be overcome by increasing the substrate concentration so that as active sites become available, more substrate molecules than inhibitor molecules are around to gain entry to the sites
What do non-competitve inhibitors do?
- bind to a different site on the enzyme than the substrate
- causes the enzyme molecule to change conformation so that the active site becomes less effective at catalyzing the conversion of substrate to product.
How can you overcome a competitive inhibitor?
By adding more substrate
Vmax stays the same but Km increases
A noncompetitve inhibitor cannot be overcome by adding substrate which means Vmax decreases but Km remains the same.
what is an allosteric site of an enzyme?
a site other than the active site of an enzyme
what happens when molecules bind to a allosteric site?
causes a conformational change in the enzyme which may result in an inhibition or stimulation of the enzymes activity.
causes the entire enzyme complex to move between active and inactive
what is a conformational change?
when one subunit is transmitted to the entire complex.
allosteric regulation
what is cooperativity?
the binding of one substrate molecule to one active site which may affect the other active sites in the complex.
Feedback inhibition is what type of common control?
metabolic control
- pathway is shut off by its own end-product
- the end-product of the pathway becomes the inhibitor to an enzyme that acts early in the pathway
- prevents the cell from wasting resources by avoiding making more product than needed
what is an example of feedback inhibition?
cellular respiration:
- inhibited by ATP
- stimulated by AMP
what is gene regulation?
slower but long term method of regulating the speed a metabolic pathway occurs.
Makes more enzymes, stops making enzymes
example: enzymes in the liver = cytochrome P450
what is a multi-enzyme complex?
facilitates the product from one enzyme into becoming the substrate for the next enzyme in line.
often found in the plasma membrane as organelles like the mitochondria
