Chemical Reactions in Cells - PowerPoint PPT Presentation

1 / 33
About This Presentation
Title:

Chemical Reactions in Cells

Description:

Spontaneity of a reaction depends on free. energy change. G ... If is negative, free energy is released and the reaction is spontaneous. G ... – PowerPoint PPT presentation

Number of Views:142
Avg rating:3.0/5.0
Slides: 34
Provided by: santamo
Learn more at: http://homepage.smc.edu
Category:

less

Transcript and Presenter's Notes

Title: Chemical Reactions in Cells


1
Chemical Reactions in Cells
  • Energetics, Enzymes and Metabolic Reactions

2
Energy
  • Energy is the capacity for work or change.
  • Kinetic Energy energy of movement
  • Potential Energy stored energy
  • 1st Law of Thermodynamics
  • Energy can be transferred and transformed from
    one form to another but it cannot be created or
    destroyed.

3
Energy
  • 2nd Law of Thermodynamics
  • Energy transfer or transformation increases the
    entropy of the universe
  • Increase in entropy randomness
  • Energy conversions result in a loss of useful
    energy

4
Free Energy Energy Useful for Change
5
Free Energy Energy Useful for Change
6
Chemical Reactions
  • Involve the breaking and formation of chemical
    bonds
  • Reactants are converted to products.
  • Two types of reactions based on energy use
  • Exergonic free energy released
  • Endergonic free energy consumed

7
Exergonic Reactions
Burning glucose (sugar)an exergonic reaction
Activation energy neededto ignite glucose
Glucose O2
Energy released byburning glucose
C O2 H2O
8
Endergonic Reactions
Photosynthesisan endergonic reaction
Glucose
Net energycaptured bysynthesizingglucose
Activationenergy fromlight capturedby
photosynthesis
CO2 H2O
9
Applying Your Knowledge
  1. Endergonic Reaction
  2. Exergonic Reaction

A. Which type of reaction would be spontaneous?
B. For which type of reaction will the products
have a higher energy than the reactants?
C. Which type of reaction releases energy?
10
ATP Provides Energy for Cellular Reactions
11
Short-Term Energy Storage
  • Chemical Energy is stored in the bonds of ATP
  • ATP adenosine triphosphate
  • ADP adenosine diphosphate
  • to store energy
  • ADP Phosphate Energy? ATP
  • to release energy
  • ATP ? ADP Phosphate Energy

12
Coupled Reactions
  • Pairing of an Exergonic reaction, often
    involving ATP, with an Endergonic reaction

Note that overall free energy change is negative
13
Metabolic Reactions
  • Anabolic
  • link simple molecules to produce complex
    molecules (eg. dehydration synthesis of starch)
  • require energy
  • Catabolic
  • break down complex molecules to release simple
    ones (eg. hydrolysis of starch? sugars)
  • release energy stored in chemical bonds

14
Metabolic Pathways
InitialReactants
Intermediates
FinalProducts
B
C
A
Enzyme 1
Enzyme 2
Enzyme 3
Enzyme 4
Pathway 1
F
G
Pathway 2
Enzyme 5
Enzyme 6
15
Enzymes Assist in Biological Reactions
  • Enzymes are biological catalysts.
  • biological composed of protein or, rarely, RNA
  • catalyst speeds up a reaction without being
    changed by the reaction

16
Properties of Enzymes
  • Enzymes speed up biological reactions by lowering
    the activation energy for the reaction.
  • Enzymes provide a surface where the catalysis
    takes place
  • The reaction reaches equilibrium more rapidly

17
Activation Energy Controls Rate of Reaction
Amount of energy required for reaction to occur
transition state
Activationenergy withoutcatalyst
Activationenergy withcatalyst
18
Properties of Enzymes
  • Enzymes are SPECIFIC for the reactants
    (substrates) in the reactions that they catalyze.
  • Only substrates that fit the active site of the
    enzyme can bind and complete the reaction
  • active site region on enzyme where substrates
    bind

19
Enzyme-Substrate Interactions
Substrate
Substrate
1 Substrates enter active site
ActiveSite
2 Shape change promotes reaction
Enzyme
  1. Product releasedenzyme ready again

20
Chemical Events at Active Sites
  • Enzymes hold substrates in the proper orientation
    for the reaction to take place

21
Chemical Events at Active Sites
  • Enzymes induce strain in the substrate to produce
    a transition state favorable to reaction
  • Active site provides a microenvironment that
    favors the chemical reaction

22
Chemical Events at Active Sites
  • Active site directly participates in the reaction
  • covalent bonding can occur between enzyme and
    substrate
  • R groups of the enzymes amino acids can
    temporarily add chemical groups to the substrates

23
Molecules that Assist Enzymes
  • Cofactors inorganic ions that bind to enzymes,
    eg. zinc
  • Coenzymes small organic factors that temporarily
    bind to enzymes, eg. biotin, NAD, ATP
  • Prosthetic groups non-protein factors that are
    permanently bound an enzyme, eg. heme

24
Factors Influencing Reaction Rate
Rate no longer increases since the active sites
of all enzymes are saturated with substrate
  • Substrate Concentration

Rate is more rapid
Rate is proportional to substrate concentration
25
Factors Influencing Reaction Rate
  • Competitive Inhibitors Bind at the active site,
    compete for binding with substrate
  • Irreversible form covalent bond with amino acids
    in the active site

26
Factors Influencing Reaction Rate
  • Competitive Inhibitors Bind at the active site,
    compete for binding with substrate
  • Reversible molecule similar to substrate
    occupies active site but does not undergo reaction

27
Factors Influencing Reaction Rate
  • Non-Competitive Inhibitors Bind to a different
    site, cause a conformational change in the enzyme
    that alters the active site
  • Reversible

28
Factors Influencing Reaction Rate
  • Allosteric Regulation
  • Conversion between active and inactive forms of
    an enzyme due to binding of regulatory molecules
    at an allosteric site
  • Activators stabilize the active form
  • Allosteric inhibitors stabilize the inactive form

29
Factors Influencing Reaction Rate
  • Allosteric Regulation
  • Cooperativity a substrate causing induced fit in
    one enzyme subunit can cause a change to the
    active form in all the other subunits

30
Enzyme Regulation Feedback Inhibition
Commitment step
D
C
B
A
Enz. 5
Enz. 4
Enz. 3
Enz. 2
Enz. 1
Threonine(substrate)
Isoleucine(end product)
Feedback Inhibition The product of a pathway
inhibits an initial step in the pathway to
decrease its own production
31
Properties of Enzymes
  • Three dimensional structure of an enzyme
    preserves its ACTIVE SITE
  • Conditions that can affect three dimensional
    structure include heat, pH (acid/base balance)
    and other chemicals (salt, charged ions)

32
Effects of Temperature and pH on Enzymatic
Activity
33
Applying Your Knowledge
  1. Active Site
  2. Activation Energy
  3. Allosteric Site
  4. Commitment step
  5. Induced fit
  1. Where can an inhibitor bind to stabilize the
    inactive form of an enzyme?
  2. Where do the substrates bind?
  3. Enzymes (raise or lower) the (1, 2, 3, 4 or 5) of
    a reaction.
  4. What is the model for a shape change caused by
    substrate binding to the enzyme?
Write a Comment
User Comments (0)
About PowerShow.com