Photosynthesis BIO I Assignment
mattymatt121
Mason_UB3e_ch06_PPT_final_Accessible.pptxChapter 6 Lecture Outline
Understanding Biology
THIRD EDITION
Kenneth A. Mason
Tod Duncan
Jonathan B. Losos
© 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution permitted without the prior written consent of McGraw Hill.
Because learning changes everything.®
Energy and Metabolism
Chapter 6
©Robert Caputo/Cavan Images
© McGraw Hill
‹#›
Flow of Energy 1
Life requires a constant flow of energy within and between organisms to do the work of living.
Energy – capacity to do work
Two states
Kinetic – energy of motion
Potential – stored energy
Many forms – mechanical, heat, sound, electric current, light, or radioactivity
Heat the most convenient way of measuring energy
1 calorie = heat required to raise 1 gram of water 1ºC
calorie or Calorie?
© McGraw Hill
‹#›
3
Figure 6.1
© McGraw Hill
‹#›
4
Flow of Energy 2
Energy flows into the biological world from the sun
Photosynthetic organisms capture this energy
Stored as potential energy in chemical bonds
© McGraw Hill
‹#›
5
Redox reactions
Oxidation–reduction reactions transfer energy
Oxidation
Atom or molecule loses an electron
Reduction
Atom or molecule gains an electron
Higher level of energy than oxidized form
Oxidation-reduction reactions (redox)
Reactions always paired
© McGraw Hill
‹#›
6
Figure 6.2
© McGraw Hill
‹#›
7
Laws of thermodynamics 1
Thermodynamics
Branch of chemistry concerned with energy changes
Cells are governed by the laws of physics and chemistry
© McGraw Hill
‹#›
8
Laws of thermodynamics 2
First law of thermodynamics
Energy cannot be created or destroyed
Energy can only change from one form to another
Total amount of energy in the universe remains constant
During each conversion, some energy is lost as heat
Living systems cannot create the energy needed for life, they must acquire it
© McGraw Hill
‹#›
9
Laws of thermodynamics 3
Second law of thermodynamics
Energy cannot be transformed from one form to another with 100% efficiency
Entropy (disorder) is continuously increasing
Energy transformations proceed spontaneously to convert matter from a more ordered/less stable form to a less ordered/ more stable form
© McGraw Hill
‹#›
10
Figure 6.3
© McGraw Hill
‹#›
11
Free energy
G = Energy available to do work
G = H – TS
H = enthalpy, energy in a molecule’s chemical bonds
T = absolute temperature (Kelvin scale)
S = entropy, unavailable energy
© McGraw Hill
‹#›
“molecule’ s” – close up # after apostrophe
12
∆G = ∆H − TS
∆G = change in free energy
Positive ∆G
Products have more free energy than reactants
H is higher or S is lower
Not spontaneous, requires input of energy
Endergonic
Negative ∆G
Products have less free energy than reactants
H is lower or S is higher or both
Spontaneous (may not be instantaneous)
Exergonic
© McGraw Hill
‹#›
13
Figure 6.4
© McGraw Hill
‹#›
14
Activation energy
Extra energy required to destabilize existing bonds and initiate a chemical reaction
Exergonic reaction’s rate depends on the activation energy required
Larger activation energy proceeds more slowly
Rate can be increased two ways
Increasing energy of reacting molecules (heating)
Lowering activation energy
Equilibrium exists between the relative amounts of reactants and products
© McGraw Hill
‹#›
“Exergonic reaction’ s …” Close up # after apostrophe.
Fix # in No. list from No. to entry?
15
ATP
Adenosine triphosphate
Chief “currency” all cells use
Composed of
Ribose – 5 carbon sugar
Adenine
Chain of 3 phosphates
Key to energy storage
Covalent bonds between the phosphates is unstable
ADP – 2 phosphates
AMP – 1 phosphate – lowest energy form
© McGraw Hill
‹#›
16
Figure 6.5
© McGraw Hill
‹#›
17
ATP cycle
ATP hydrolysis drives endergonic reactions
Coupled reaction results in net – ∆G (exergonic and spontaneous)
ATP not suitable for long-term energy storage
Fats and carbohydrates better
Cells store only a few seconds worth of ATP
© McGraw Hill
‹#›
18
Figure 6.6
© McGraw Hill
‹#›
19
Catalysts
Substances that influence chemical bonds in a way that lowers activation energy
Activation energy is the energy needed to destabilize chemical bonds
Cannot violate laws of thermodynamics
Cannot make an endergonic reaction spontaneous
Do not alter the proportion of reactant turned into product
© McGraw Hill
‹#›
20
Figure 6.8
© McGraw Hill
‹#›
21
Enzymes: Biological Catalysts
Most enzymes are protein
Some are RNA
Enzymes lower the activation energy
Shape of enzyme stabilizes a temporary association between substrates
Enzyme not changed or consumed in reaction
Carbonic anhydrase
200 molecules of carbonic acid per hour made without enzyme
600,000 molecules formed per second with enzyme
© McGraw Hill
‹#›
22
Active site
Pockets or clefts for substrate binding
Precise fit of substrate into active site
Forms enzyme–substrate complex
Induced fit
Applies stress to distort particular bond to lower activation energy
© McGraw Hill
‹#›
23
Figure 6.10
© McGraw Hill
‹#›
24
Figure 6.9
© McGraw Hill
‹#›
25
Enzyme function
Rate of enzyme-catalyzed reaction depends on concentrations of substrate and enzyme
© McGraw Hill
‹#›
26
Enzymes
Enzymes may be suspended in the cytoplasm or attached to cell membranes and organelles
Multienzyme complexes – subunits work together to form molecular machine
Product can be delivered easily to next enzyme
Unwanted side reactions prevented
All reactions can be controlled as a unit
© McGraw Hill
‹#›
27
Nonprotein enzymes
Ribozymes
1981 discovery that certain reactions catalyzed in cells by RNA molecule itself
Two kinds
Intramolecular catalysis – catalyze reaction on RNA molecule itself
Intermolecular catalysis – RNA acts on another molecule
© McGraw Hill
‹#›
28
Cofactors
Enzyme function is often assisted by chemical components known as cofactors
Metal ions
Make bonds less stable and easier to break
Coenzyme
Nonprotein organic molecule
Vitamins
© McGraw Hill
‹#›
29
Enzyme activity
Cell conditions determine enzyme activity
Chemical and physical factors can alter an enzyme’s three-dimensional shape
Temperature
pH
Binding of regulatory molecules
© McGraw Hill
‹#›
30
Figure 6.12
© McGraw Hill
‹#›
31
Inhibitors and Activators
Inhibitor – substance that binds to enzyme and decreases its activity
Competitive inhibitor
Competes with substrate for active site
Noncompetitive inhibitor
Binds to enzyme at a site other than active site (allosteric site)
Causes a change in the shape of the active site that makes enzyme unable to bind substrate
© McGraw Hill
‹#›
32
Figure 6.13
© McGraw Hill
‹#›
33
Allosteric Enzymes
Allosteric enzymes – enzymes exist in active and inactive forms
Most noncompetitive inhibitors bind to allosteric site – chemical on/off switch
Allosteric inhibitor – binds to allosteric site and reduces enzyme activity
Allosteric activator – binds to allosteric site and increases enzyme activity
© McGraw Hill
‹#›
34
Metabolism
Total of all chemical reactions carried out by an organism
Anabolic reactions/anabolism
Expend energy to build up molecules
Catabolic reactions/catabolism
Harvest energy by breaking down molecules
© McGraw Hill
‹#›
35
Biochemical pathways
Biochemical pathways organize chemical reactions in cells
Reactions occur in a sequence
Product of one reaction is the substrate for the next
Many steps take place in organelles
© McGraw Hill
‹#›
36
Figure 6.14
© McGraw Hill
‹#›
37
Feedback inhibition
End-product of pathway binds to an allosteric site on enzyme that catalyzes first reaction in pathway
Shuts down pathway so raw materials and energy are not wasted
© McGraw Hill
‹#›
38
Figure 6.15
© McGraw Hill
‹#›
39
End of Main Content
© 2021 McGraw Hill. All rights reserved. Authorized only for instructor use in the classroom.
No reproduction or further distribution permitted without the prior written consent of McGraw Hill.
Because learning changes everything.®
www.mheducation.com
Accessibility Content: Text Alternatives for Images
© McGraw Hill
‹#›
Figure 6.4 - Text Alternative
Return to parent-slide containing images.
Two graphs of free energy on the Y-axis and course of the reaction on the X-axis. In an endergonic reaction, the curve trends upwards as there is more energy in the products than the reactants. In an exergonic reaction, the curve trends downwards as there is more energy in the reactants than the products.
© McGraw Hill
‹#›
Figure 6.6 - Text Alternative
Return to parent-slide containing images.
When ATP is hydrolyzed energy and a phosphate are released, forming ADP. ATP is synthesized when energy is used to join the ADP and phosphate together.
© McGraw Hill
‹#›
Figure 6.8 - Text Alternative
Return to parent-slide containing images.
In an exergonic reaction, the reactants have more energy than the products, so energy is released as the reaction proceeds. However, to get the reaction started activation energy is added, so the reaction curve initially slopes upwards before dropping. Catalysts work by lowering the activation energy, but the starting energy of the reactants and final energy of the products do not change with a catalyst.
© McGraw Hill
‹#›
Figure 6.9 - Text Alternative
Return to parent-slide containing images.
In this example the disaccharide sucrose is the substrate and it is hydrolyzed to form glucose and fructose in the active site of the enzyme.
© McGraw Hill
‹#›
Figure 6.12 - Text Alternative
Return to parent-slide containing images.
Graphs of the rate of an enzymatic reaction on the Y-axis and temperature or pH are shown. In each case two curves are shown. For temperature, the curves for a human enzyme and that from a prokaryote from a hotspring are graphed, with the human enzyme having an optimal temperature near 40C, or body temperature. The prokaryotic enzyme curve peaks at 70C, the temperature of the hot spring. In the pH curve, pepsin has maximum activity at pH 3, similar to that found in the stomach, while trypsin has maximum activity at pH 7, similar to that found in the intestines.
© McGraw Hill
‹#›
Figure 6.13 - Text Alternative
Return to parent-slide containing images.
Competitive inhibitors bind to the active site of an enzyme while noncompetitive inhibitors bind to a different allosteric site on the enzyme. In both cases, binding of the substrate is blocked.
© McGraw Hill
‹#›
Figure 6.14 - Text Alternative
Return to parent-slide containing images.
In a biochemical pathway a series of reactions occur in which the product of one reaction becomes the substrate of the next reaction. In this example there are 4 enzymes and an initial substrate is sequentially converted into intermediates A, B and C before finally being converted into the final product by the last enzyme in the pathway.
© McGraw Hill
‹#›
Figure 6.15 - Text Alternative
Return to parent-slide containing images.
In feedback inhibition the product at the end of a pathway goes back and inhibits the first step of the pathway. A biochemical pathway a series of reactions occur in which the product of one reaction becomes the substrate of the next reaction. In this example there are 3 enzymes and an initial substrate is sequentially converted into intermediates A and B before finally being converted into the final product by the last enzyme in the pathway. The final product then goes back and inhibits the first enzyme in the pathway.
© McGraw Hill
‹#›
