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Enzymes

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Josefina Lozano

on 30 October 2015

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Transcript of Enzymes

What are they?
Proteins

Tertiary structure

Globular shape. Very specific

Activation energy
Enzymes accelerate reactions by lowering the activation energy. But there is no alteration of products nor reactants.



Reactions are faster because less energy is needed for the reaction to occur.

Parts of the enzyme
Enzyme:
Globular protein that increases the rate of reaction by lowering the activation energy threshold.
Active Site:
Region that binds to a particular substrate(s). Catalysis takes place.
Enzyme-substrate specificity
Active site and substrate complement each other in terms of both shape and chemical properties.

Binding to the active site creates an enzyme-substrate complex.

The enzyme catalyzes the conversion of the substrate into a product(s), creating an enzyme-product complex.

As the enzyme is not consumed in the reaction, it can continue to work once the product dissociates.
Metabolic Pathways
Most chemical changes in a cell results from chains and cycles of reactions, with each step controlled by a separate specific enzyme

This allows for a far greater level of control and regulation of metabolic pathways (such as photosynthesis and cell respiration)
Induced-fit model
When enzymes and substrates bind, the active site may undergo a conformational change in shape to better fit the substrate. Substrate plays a role in determining the final shape of the enzyme. The enzyme is partially flexible

This conformational change may increase the reactivity of the substrate and be necessary for the enzyme's catalytic activity.

Broad specificity: Ability to catalyze several different substrates.
Enzymes
Thank you!
Molecule composed of polymers of amino acids joined together by peptide bonds
Tertiary (3°) Structure:
Coiled polypeptide. Forms a complex molecular shape
Caused by interactions between R groups;
H-bonds
disulphide bridges, ionic bonds
hydrophilic / hydrophobic

HL
Metabolism:
Sum of all chemical reactions that occur in a living organism's body.

Inhibition
A molecule may affect the activity of the enzyme.
End-product inhibition
Prevents the cell from wasting chemical resources and energy.
Form of negative feedback. Increased levels of product decrease the rate of product formation.

Assembly line type of process.

When the end-product is present in a sufficient quantity, the the action of the enzyme is inhibited by the end product. When its concentration is low, enzyme is reactivated.

Example:

E. coli.
End product:
isoleucine
amino acid. If added to the growth medium, threonine (allosteric enzyme) is inhibited.
Lowering the activation energy explanation
Endergonic:
If more energy is in the products than the reactants, energy is lost.
Anabolic reaction: the energy is being used up in bond formation between two substrate molecules.

Exergonic:
If more energy is in the reactants than the products, excess energy is released.
Catabolic reaction: the energy is released from the broken bonds within molecules.
Explain control of metabolic pathways
End-product inhibition is a form of negative feedback.

The product can regulate the rate of its own production by inhibiting an allosteric enzyme because of metabolic pathways.

Non-competitive inhibition changes active site.

Enzyme can not currently function. Rate of product formation decreases.

Inhibition controlled by concentration.
Competitive inhibition
A molecule (inhibitor) similar to the substrate binds to the active site of the enzyme.
The active site blocks and thus prevent substrate binding. (competes for the active site)

Its effect can be reduced by increasing substrate concentration

Example:
Relenza is a competitive inhibitor of neuraminidase (influenza virus enzyme), preventing the release of virions from infected cells.
Non-competitive inhibition
An inhibitor that's not similar to the substrate and binds to the allosteric site.

This causes a conformational change in the active site, making it non-functional.

Its effect cannot be reduced by increasing substrate concentration.
Example:
Cyanide (CN-) inhibits enzymes (cytochrome oxidase) in the electron transport chain by breaking disulphide bonds within the enzyme.
Prevents reduction of oxygen to water, therefore the synthesis of ATP.
Allosteric
enzyme
Example:
Regulation of ATP formation by phosphofructokinase (enzyme in glycolysis)

High ATP levels inhibit phosphofructokinase so glucose is not broken down but stored.

Low ATP levels reactivate phosphofructokinase.
References
Audesirk,T., Audesirk, G., & Byers, B.E. Biology: Life on Earth. University of Colorado Denver. Pearson Education, Inc.
Lock and Key Model
Enzymes and substrates share specificity.

Only the correctly sized key (substrate) fits into the key hole (active site) of the lock (enzyme).
Ophardt, Charles E.
Virtual Chembook
. Elmhurst College. 2003.
<http://www.elmhurst.edu/~chm/vchembook/571lockkey.html>
Factors influencing enzyme-catalyzed reactions
Low temperatures result in insufficient thermal energy for the activation of a given enzyme-catalyzed reaction to be achieved

Increasing the temperature will increase the speed, motion and collisions of both enzyme and substrate, resulting in higher enzyme activity

At an optimal temperature, the rate of enzyme activity will be at its peak

Higher temperatures
:
Stability decreases.
Hydrogen bonds holding the enzyme together are disrupted.
Enzyme loses its shape.
Denaturation
pH alters the charge of the enzyme, and may change the shape of the molecule.

Changing the shape or charge affects active site and diminish its ability to bind to the substrate. Leads to denaturation.

Enzymes have an optimum pH.

High concentration:
More chance that the enzyme and substrate collide and react.

More reactions will occur and more products will be formed.

After a certain point, the rate of reaction will cease to rise because of saturation. = (Vmax)
Temperature
pH
Substrate Concentration
Denaturation
Structural change in a protein that results in the loss of its biological properties

Cause: Heat and pH
Lactose free milk
Lactose
: disaccharide of glucose and galactose
Its broken down by the
enzyme lactase.

Decrease in lactase production leads to lactose intolerance.

Lactose-free milk can be produced by purifying lactase and binding it to an inert substance, which can provide increased resistance to changes in external conditions.

Milk passed over this immobilized enzyme will become lactose-free.
Use of lactose-free milk:

Milk for lactose-intolerant individuals.
Increase the sweetness of milk.
Reducing the crystallization of ice-creams.
Faster fermentation.

Principal enzymes

Lysozyme
– chemically damages many pathogens. Attacks the cell walls of certain bacteria.

Elastase
- important for killing various bacteria.


Amylase:
Helps in breaking down carbohydrates. It is found in saliva,
pancreas and intestinal juices.

Proteases:
Helps in digestion of proteins.
It is present in the stomach, pancreatic and intestinal juices.

Lipases:
Assist in digestion of fats. It is seen in the stomach, pancreatic juice and food fats.

Cellulase
– breaks down cellulose, plant fiber; not found in humans
Enzymes for
digestion:
Enzymes for
immune system
Enzymes for DNA replication and transcription
Helicase:
Initiates separation into two strands of DNA.

DNA Polymerase:

Catalyzes the formation
of covalent bonds
between adjoining
nucleotides





RNA polymerase
:
Catalyzes the creation of
mRNA molecule from one
DNA strand.
Enzymes for DNA cloning:
Endonucleases
: restriction enzyme that finds and recognizes specific base pair sequences.

DNA ligase
: recognizes parts of base sequences that must be bonded together.(sticky ends)
Damon, Alan. McGonegal, Randy. Tosto, Patricia. Ward, William. Biology: developed specifically for the IB diploma. Standard Level. Pearson. 2007.
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