Cell Energenics

1
Cell Energenics
2
Cells Engage in Metabolism (Chemical Work)
3
Energy

• Potential Energy The capacity to do work
• The potential energy of molecules is called
  chemical energy.
• Kinetic Energy Energy in motion
• Entropy is the measure of disorder, is wasted
  energy- becomes more random, can be sound or
  light but is mostly heat, everything always moves
  towards entropy
• Energy is measured in units called kilocalories.
  A kilocalorie is a 1000 calories, the amount of
  energy required to raise 1 kg of water 1 degree
  Celsius at standardized pressure.
• All organisms have specific adaptations for
  securing energy from their environment
• Some capture energy from the sun
• Others extract energy from inorganic or organic
  substances in the environment

4
Energy must come from somewhere

• 1st Law of Thermodynamics
• The total amount of energy in the universe
  remains constant. Energy cannot be created nor
  destroyed, it can only change form.
• Your body at rest gives off as much heat as a 100
  watt light bulb. Thermal energy.

• 2nd Law of Thermodynamics
• Every time energy is used some is lost to heat.
• Entropy (measure of worlds systems moving from
  order to disorder)
• So the amount of usable energy decreases as it
  is used and converted. It is lost as heat.
• Overall, energy usually moves in one direction.

5
Endergonic Reactions

• Energy is put into a system
• example C6H12O6 is made from 6CO2 and 12H2O
  So why dont we get as much energy from carbon
  dioxide and water as we do glucose?
• In photosynthetic cells, energy inputs from
  the sun drive reactions that make glucose, the
  result being a net increase of usable energy.
• Endergonic reactions
• 1. Products have a higher energy level than
  reactants
• 2. They must be supplied with energy until they
  are completed- can be supplied by energy from a
  variety of sources including exergonic reactions
  linked together these can form a coupled
  reaction. Transferring energy reactions from one
  reaction to another. Uphill analogy
• Activation energy-is the amount of energy it
  takes to get the reaction going ie. Heat or hot
  plate
• Catalyst- lowers the activation energy, it
  doesnt supply energy.

6
(No Transcript)
7
Exergonic Reactions

• The reverse of endergonic. C6H12O6 to CO2 and
  H2O. Meaning Energy Out
• This kind of reaction normal will proceed on its
  own with a net loss of energy.
• Exergonic reactions-
• 1. products have a lower energy than the
  reactants
• 2. they proceed spontaneously until finished
  (once started)
• 3. give off energy (could be anything)
• Downhill Analogy

8
(No Transcript)
9
Enzymes-are protein catalysts that speed up
chemical reactions by lowering the activation
energy.                                         
                                                  
                         
10
Enzymes

• -protein catalyst
• -has a specific 3d shape that is reactionary
• -works on substrates (each enzyme is specific for
  a given substrate)
• -can be denatured- needs optimal temperature and
  pH
• -active site - binds to what it is work on the
  substrate
• -allosteric site - second site , is a way to turn
  enzymes on and off, like a switch

11
Allosteric Site
12
Enzyme-Substrate Reaction

• Enzymes are substances present in the cell in
  small amounts which speed up or catalyze chemical
  reactions. Enzymes speed up the rate of chemical
  reactions because they lower the energy of
  activation, the energy that must be supplied in
  order for molecules to react with one another.
  Enzymes lower the energy of activation by forming
  an enzyme-substrate complex.

13
(No Transcript)
14
Non-Competitive Inhibitor
15
Competitive Inhibitor
16
(No Transcript)
17
Enzymes dont know when to stop and will run at
full blast, needs a regulator

• Regulating reactions speed
• -limit substrate makes the enzyme hunt for more
  
• regulates the speed of the reaction, slows
  reaction
• 2. -inhibitors interfere with the reaction
• -competitive inhibitors-want to bond in the
  active site- are structurally similar to
  substrate and the greatest concentration
  (substrate vs. inhibitor) will occupy the site.
• -non-competitive inhibitors-occupies the
  allosteric site- changes the shape of the active
  site and/or closes the active site

18
(No Transcript)
19
Allosteric site has a lot of possible functions
depending on the enzyme

• 1. May supply a needed item to the reaction- may
  be something simple like
  an ion- not main substrate- may need this
  substrate to activate the enzyme called
• -cofactor-non organic, mostly a metal ion
• -coenzyme-proteins or vitamins
• 2. may open the active site
• 3. may close the active site ie. Non-competitive
  inhibitor
• Feedback inhibitor- chemical switches that turn
  off and on an enzyme using concentrations of
  substrates to regulate an end product

20
Ways to generate ATP from ADP
-when an enzyme transfers a phosphate group from
a substrate to ADP to make ATP
21

• 1. Coupled reaction- when one reaction drives or
  supplies energy for another reaction to occur
  which is more technically referred to as
  Substrate Level Phosphorylation
• 2. Chemiosmosis - some organelles (mitochondria
  and chloroplasts) can establish a concentration
  gradient of H (hydrogen ions) by splitting a
  hydrogen and transporting the e- (electron) to
  the other side of the membrane. At an enzyme that
  can generate ATP the H are allowed to pass
  through the membrane (down the concentration
  gradient), this is exergonic in nature and its
  energy is used to produce ATP
• -In mitochondria the H build up between the 2
  membranes, then pass back into the matrix and in
  chloroplasts the build up inside the thylakoids a
  pass back to the stroma.

A hydrogen ion (H) is very strong
because gtchemically - more hydrogen on one
side gtelectrically - more positive on one
side gtpH - more acidic on the H side
22
Coupled Oxidation-Reduction Reactions
In biological systems, a coupled
oxidation-reduction reaction is one in which one
substance is oxidized (loses electrons) while a
second is reduced (gains electrons). An example
of one such reaction is the conversion of lactate
to pyruvate.
The conversion of lactate to pyruvate is
enzymatically catalyzed by lactate dehydrogenase.
In this reaction lactate loses two electrons
(becomes oxidized) and is converted to pyruvate.
NAD gains two electrons (is reduced) and is
converted to NADH. The coupling of
oxidation-reduction reactions is often depicted
in the following manner.
Both lactate and NAD bind to the active site of
the enzyme lactate dehydrogenase and both lactate
and NAD participate in the catalysis reaction.
In fact, catalysis could not occur unless the
coenzyme NAD bound to the active site.
23
(No Transcript)
24
Participants in metabolic pathwaysMost
substances enter or leave by orderly,
enzyme-mediated sequences

• 1. Substrates are substances that enter reactions
  
• ( Reactants Precursor).
• 2. Intermediates are the compounds formed between
  the start and the end of a pathway.
• 3. End products are the substances present at the
  conclusion of a pathway.
• 4. Energy carriers are mainly ATP.
• 5. Enzymes are proteins that catalyze (speed up)
  reactions.
• 6. Cofactors are small molecules and metal ions
  that help enzymes by carrying atoms or electrons.
• 7. Transport proteins are membrane-bound proteins
  that participate in adjusting concentration
  gradients that will influence the direction of
  metabolic reactions.

25
Anabolic Pathways(biosynthetic)

• Often small molecules are used to build larger
  molecules of higher bond energies, such as
  complex carbohydrates, complex lipids, and
  proteins.
• Need energy inputs to proceed
• The main biosynthetic pathway is photosynthesis

26
Catabolic Pathways(Degradation)

• Degradative pathways are exergonic.
• They breakdown larger molecules into smaller
  products with lower bond energies.
• Aerobic respiration is the main catabolic
  pathway.

27
Which Way Will a Reaction Run?

• Proceed from reactants to products, which, if
  they are allowed to accumulate, will convert back
  to reactants
• Forward - High concentration of reactants
• Equilibrium - Rate of  forward reaction
  equals reverse
• Reverse - High concentration of products

28
Types of Reaction Sequences

• Linear
• Cyclic
• Branching

B
C
A
D
E
F
29
Chemical Equilibrium
Highly Spontaneous
Highly Spontaneous
Most reactions can run forward and reverse
30
No Vanishing Atoms at the End of the Run

• 1. Law of conservation of mass states that the
  total mass of all substances entering a reaction
  equals the total mass of all the products.
• 2. "Balanced" a chemical equation having  equal
  number of atoms of each element on both sides of
  the arrow.

31
Electron Transport Chain

• The vast majority of the energy derived from the
  breakdown of the foodstuffs is captured by the
  cell in the reactions of the electron transport
  chain.

32
ENZYMES
33
Features of Enzymes

• 1. Proteins - globular
• 2. Catalysts
• a. Accelerate chemical reactions
• b. Enzymes can be reused
• 3. Enzymes can be regulated
• 4. Enzymes are very selective about the
  substrates to which they will bind and thereby
  bring about change
• 5. Enzymes recognize both reactants and products
  in order to catalyze a reaction in both directions

34

• Enzyme-Substrate Interactions
• 1. Lower the energy of activation
• a. Energy required to cause molecules to react
• b. Without enzymes, energy must be added in the
  form of heat to initiate a reaction

• Enzyme-Substrate Complexes
• 1. Speed reactions by forming a complex with
  substrates at their active site
• a. Small region of substrate binding
• 2. Induced fit model
• a. Enzyme changes shape at binding
• b. Change in enzyme shape stresses covalent
  bonds in substrate

35
Enzyme Rates

• Enzymatic reactions rapid 2H202 --gt 2H2O O2
• 2. Affected by Temperature, Ph, Enzyme
  concentration Inhibition Pro-enzyme formation
• 3. Temperature
• a. Increase temp. increases rate Increases
  number of molecular collisions
• b. Excessive temperature denatures, disrupts 3D
  configuration
• 4. Each enzyme has an optimal pH
• a. Maintains its normal configuration
• b. Change alters side chain ionization and
  eventually denatures enzyme
• 5. Amount of enzyme limits rates
• a. Law of limiting factor Enzymes have an
  inherent rate
• b. Cells limit the amount of enzymes (genetic)
• 6. Inhibition
• a. Competitive Product or Analog competes for
  active site
• b. Non-competative
• i. Allosteric binding
• ii. Binding of a substance on an enzyme at a
  spot other than the active site
• iii. Can activate or inhibit 
• c. Feedback

36
Bioluminescence

• 1. Animals such as fireflies generate light via
  the oxidation of a small molecule called a
  luciferin, catalysed by a luciferase enzyme.
  Different luciferins produce different colours.
  So, for example, the luciferin in luminous
  beetles produces green, yellow or red light. But
  marine creatures that use the most common
  luciferin in the sea emit violet, blue or green
  light.  Luciferase  Luciferin O2 cofactors
  ?oxyluciferin light 2. The environment created
  by the luciferase protein when it binds to the
  luciferin during this process also affects the
  colour of the emitted light. In fact all the
  luciferase does is create a solvent cage around
  the luciferin, allowing one and only one oxygen
  atom in, and keeping water out (both oxygen and
  water quench electronically excited states).
• 3. The transfer of energy from a donor molecule
  in one protein to an acceptor in another is
  another way of generating bioluminescence. The
  most famous example of this is the transfer of
  energy from a normally blue emitting photoprotein
  or luciferase to a fluorescent protein called
  green fluorescent protein (GFP), resulting in the
  emission of green light.