Upload
zulema
View
16
Download
0
Tags:
Embed Size (px)
DESCRIPTION
CELLS @ WORK. Cell Metabolism and ATP. ATP is the energy molecule of the cell. Billions are used and reassembled every second!! Endergonic Rxn – Requires energy (ie. Photosynthesis) Exgergonic Rxn – releases energy (ie.Cellular Respiration) Glucose = 1 dollar ATP = 1 penny. Enzymes. - PowerPoint PPT Presentation
Citation preview
CELLS @ WORKCELLS @ WORK
Cell Metabolism and ATPCell Metabolism and ATP• ATP is the energy molecule
of the cell.• Billions are used and
reassembled every second!!• Endergonic Rxn – Requires
energy (ie. Photosynthesis)
• Exgergonic Rxn – releases energy
(ie.Cellular Respiration)• Glucose = 1 dollar• ATP = 1 penny
EnzymesEnzymesOur “Key” to Biochemical
Reactions
ENZYMESENZYMES
• Proteins that accelerate chemical reactions
• Almost all processes in the cell need enzymes in order to occur – Cellular Respiration, Photosynthesis, food digestion etc.
• Are extremely selective – very specific to certain reactions
ENZYMESENZYMES
• For Example:For Example:
Lysozyme digests bacterial cell walls, and is found in human tears, egg-white, etc
ENZYMESENZYMES
• Enzymes are known to catalyze about 4,000 reactions in the human body
• Named according to the reaction they catalyze … “ase” is added to the name of the substrate
• Ex: Lactase breaks down lactose
HOW ENZYMES WORK:HOW ENZYMES WORK:
• By providing a lower activation energy for a reaction and dramatically accelerating its rate
• For example… (Do not copy)– the reaction catalysed by orotidine-
phosphate decarboxylase will consume half of its substrate in 78 million years if no enzyme is present. However, when the decarboxylase is added, the same process takes just 25 milliseconds
HOW ENZYMES WORK:HOW ENZYMES WORK:
EnzymeEnzymeSUBSTRATE PRODUCT(S)
Eg:Eg:
SucraseSucraseSucrose + Water Glucose + Fructose
Enzymes help a reaction to occur … without being directly involved!!!
Check these out!Check these out!
• http://www.yellowtang.org/animations/enzymes.swf
• http://www.yellowtang.org/animations/enyme_action_final.swf
Enzymes lower the activation Enzymes lower the activation energy of a reactionenergy of a reaction
Final energy state of products
Initial energy stateof substrates
Activation energyof uncatalysed reactionsActivation energy
of enzyme catalysedreaction
Progress of reaction (time)
Ene
rgy
leve
ls o
f m
olec
ules
Enzymes lower activation energy by Enzymes lower activation energy by forming an enzyme/substrate complexforming an enzyme/substrate complex
Substrate + Enzyme
Enzyme/substrate complex
Enzyme/product complex
Product + Enzyme
In anabolic reactions enzymes bring the substrate molecules together.
In catabolic reactions the enzyme active site affects the bonds in substrates so they are easier to break
HOW ENZYMES WORK:HOW ENZYMES WORK:
• ““Lock and Key” Model:Lock and Key” Model:
HOW ENZYMES WORK:HOW ENZYMES WORK:
Lock-and-key hypothesis assumes the Lock-and-key hypothesis assumes the active site of an enzyme is rigid in its active site of an enzyme is rigid in its
shapeshape
How ever crystallographic studies indicate proteins are flexible.
The Induced-fit hypothesis suggests the The Induced-fit hypothesis suggests the active site is flexible and only assumes its active site is flexible and only assumes its catalytic conformation after the substrate catalytic conformation after the substrate molecules bind to the site.molecules bind to the site.
When the product leaves the enzyme the active site reverts to its inactive state.
Enzyme Reaction RatesEnzyme Reaction Rates
Rates of enzymesRates of enzymes
• Rate of enzyme action is dependent on number of substrate molecules present
Vmax = maximum rate of reaction
Vmax approached as all active sites become filled
Some active sites free at lower substrate concentrations
Substrate concentration
Rat
e of
Rea
ctio
n (M
)
Temperature -Enzymes denature at Temperature -Enzymes denature at 6060ooCC
Temperature
Rat
e of
rea
ctio
n
Rate doubles every 10oC
Enzyme denaturing and losing catalytic abilities
Optimum temperature
Some thermophilic bacteria have enzymes with optimum temperatures of 85oC
pH - affects the formation of hydrogen pH - affects the formation of hydrogen bonds and sulphur bridges in proteins bonds and sulphur bridges in proteins and so affects shape.and so affects shape.
pepsintrypsin cholinesterase
2 4 8 106pH
Rat
e of
Rea
ctio
n (M
)
In Summary...In Summary...• Work at optimal concentrations, temp.
& pH
• If it is too hot, an enzyme can become DENATURED… and will no longer function properly
Define the following terms:Define the following terms:1. Anabolic reactions:
2. Catabolic reactions:
3. Metabolism:
4. Catalyst:
5. Metabolic pathway:
6. Specificity:
7. Substrate:
8. Product:
Reactions that build up molecules
Reactions that break down molecules
Combination of anabolic and catabolic reactions
Sequence of enzyme controlled reactions
Only able to catalyse specific reactions
The molecule(s) the enzyme works on
Molecule(s) produced by enzymes
A substance that speeds up reactions without changing the produced substances
Competitive InhibitorsCompetitive Inhibitors
• A molecule similar in shape to the substrate bonds with the enzyme’s active site and inhibit its function.
• Can be reversible or irreversible
• Poisons: cyanide and arsenic bind to key enzymes in this manner…death may result!
Non-Competitive Non-Competitive InhibitorsInhibitors
• Attach to a binding site on the enzyme other than the active site...causing the shape to change.
• The enzyme loses affinity for substrate
Allosteric RegulationAllosteric Regulation
• Inhibits or stimulates enzyme activity
• Enzyme can be turned on or off...therefore cellular reactions are controlled through feedback.
The switch: Allosteric The switch: Allosteric inhibitioninhibition
Allosteric means “other site”
E
Active site
Allosteric site
Switching offSwitching off
• These enzymes have two receptor sites
• One site fits the substrate like other enzymes
• The other site fits an inhibitor molecule
Inhibitor fits into allosteric site
Substratecannot fit into the active site
Inhibitor molecule
The allosteric site the The allosteric site the enzyme “on-off” switchenzyme “on-off” switch
E
Active site
Allosteric site
emptySubstratefits into the active site
The inhibitor
molecule is absent
Conformational change
Inhibitor fits into
allosteric site
Substratecannot fit into the active site
Inhibitor molecule
is present
E
Negative Feedback Negative Feedback InhibitionInhibition
This example demonstrates how an end product can inhibit the first step in its production.
1.Isoleucine binds to the allosteric site of threonine deaminase and prevents threonine from binding to the active site because the shape of the active site is altered. 2.When the level of isoleucine drops in the cell’s cytoplasm, the isoleucine is removed from the allosteric site on the enzyme, the active site resumes the activated shape and the pathway is “cut back on” and isoleucine begins to be produced.
Example!Example!
• http://www.yellowtang.org/animations/feedback_inhibition.swf
The End!!!The End!!!