Photosynthesis BIO I Assignment
mattymatt121
Mason_UB3e_ch07_PPT_final_Accessible.pptxChapter 7 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.®
The Chemical Building Blocks of Life
Chapter 7
© Creatas/PunchStock RF
© McGraw Hill
‹#›
Life driven by energy
Organisms can be classified based on how they obtain energy:
Autotrophs
Able to produce their own organic molecules through photosynthesis
Heterotrophs
Live on organic compounds produced by other organisms
All organisms use cellular respiration to extract energy from organic molecules
© McGraw Hill
‹#›
3
Extracting Potential Energy
Potential energy stored in organic molecules resides largely in C—H bonds
Most foods contain a variety of energy-rich organic compounds
Carbohydrates, proteins, and fats
The reactions that break down these molecules are all oxidation reactions
The process by which energy is harvested is cellular respiration
© McGraw Hill
‹#›
4
Cellular respiration 1
Cellular respiration is a series of reactions
Oxidized – loss of electrons
Reduced – gain of electron
Dehydrogenation – lost electrons are accompanied by protons
A hydrogen atom is lost (1 electron, 1 proton)
© McGraw Hill
‹#›
5
Redox Reactions
During redox reactions, electrons carry energy from one molecule to another
Nicotinamide adenosine dinucleotide (NAD+)
An electron carrier
NAD+ accepts 2 electrons and 1 proton to become NADH
Reaction is reversible
© McGraw Hill
‹#›
6
Figure 7.1
© McGraw Hill
‹#›
7
Cellular respiration 2
Overall cellular respiration
Dozens of redox reactions take place
Number of electron acceptors including NAD+
In the end, high-energy electrons from initial chemical bonds have lost much of their energy
Transferred to a final electron acceptor
© McGraw Hill
‹#›
8
Types of respiration
Aerobic respiration
Final electron acceptor is oxygen (O2)
Anaerobic respiration
Final electron acceptor is an inorganic molecule (not O2)
Fermentation
Final electron acceptor is an organic molecule
© McGraw Hill
‹#›
9
Aerobic respiration
Free energy = – 686 kcal/mol of glucose
Free energy can be even higher than this in a cell
This large amount of energy must be released in small steps rather than all at once.
© McGraw Hill
‹#›
10
Electron carriers
Many types of carriers used
Soluble, membrane-bound, move within membrane
All carriers can be easily oxidized and reduced
Some carry just electrons, some electrons and protons
NAD+ acquires 2 electrons and a proton to become NADH
© McGraw Hill
‹#›
11
Figure 7.2
© McGraw Hill
‹#›
12
ATP
Cells use ATP to drive endergonic reactions
ΔG (free energy) = –7.3 kcal/mol
Two mechanisms for synthesis
Substrate-level phosphorylation
Transfer phosphate group directly to ADP
Occurs during glycolysis
Oxidative phosphorylation
ATP synthase uses energy from a proton gradient
© McGraw Hill
‹#›
13
Figure 7.3
© McGraw Hill
‹#›
14
Substrate-level phosphorylation
Phosphoenolpyruvate (PEP) has a high-energy phosphate (P) bond similar to the bonds in ATP.
PEP’s phosphate group is transferred enzymatically to ADP to create ATP.
© McGraw Hill
‹#›
Oxidation of Glucose
The complete oxidation of glucose proceeds in stages:
Glycolysis
Pyruvate oxidation
Citric acid cycle
Electron transport chain & chemiosmosis
© McGraw Hill
‹#›
16
Figure 7.5
© McGraw Hill
‹#›
17
Glycolysis
10-step biochemical pathway
Occurs in the cytoplasm
Converts 1 glucose (6 carbons) to 2 pyruvate (3 carbons)
Net production of 2 ATP molecules by substrate-level phosphorylation
2 NADH produced by the reduction of NAD+
© McGraw Hill
‹#›
Figure 7.6
© McGraw Hill
‹#›
Figure 7.7
© McGraw Hill
‹#›
NADH must be recycled
For glycolysis to continue, NADH must be recycled to NAD+ by either:
Aerobic respiration
Oxygen is available as the final electron acceptor
Produces significant amount of ATP
Fermentation
Occurs when oxygen is not available
Organic molecule is the final electron acceptor
© McGraw Hill
‹#›
Fate of pyruvate
Depends on oxygen availability.
When oxygen is present, pyruvate is oxidized to acetyl-CoA which enters the citric acid cycle
Aerobic respiration
Without oxygen, pyruvate is reduced in order to oxidize NADH back to NAD+
Fermentation
© McGraw Hill
‹#›
Figure 7.8
© McGraw Hill
‹#›
Pyruvate Oxidation
In the presence of oxygen, pyruvate is oxidized
Occurs in the mitochondria in eukaryotes
multienzyme complex called pyruvate dehydrogenase catalyzes the reaction
Occurs at the plasma membrane in prokaryotes
© McGraw Hill
‹#›
Products of pyruvate oxidation
For each 3-carbon pyruvate molecule, the following are produced:
1 CO2
Decarboxylation by pyruvate dehydrogenase
1 NADH
1 acetyl-CoA which consists of 2 carbons from pyruvate attached to coenzyme A
Acetyl-CoA proceeds to the citric acid cycle
© McGraw Hill
‹#›
Figure 7.9
© McGraw Hill
‹#›
Citric acid cycle 1
Oxidizes the acetyl group from pyruvate
Occurs in the matrix of the mitochondria
Biochemical pathway of 9 steps in three segments
Acetyl-CoA + oxaloacetate → citrate
Citrate rearrangement and decarboxylation
Regeneration of oxaloacetate
© McGraw Hill
‹#›
Figure 7.10
© McGraw Hill
‹#›
Citric acid cycle 2
For each Acetyl-CoA entering the citric acid cycle:
2 molecules of CO2 are released
3 NAD+ are reduced to 3 NADH
1 FAD (electron carrier) is reduced to FADH2
1 ATP is produced
Oxaloacetate is regenerated
© McGraw Hill
‹#›
Figure 7.11
© McGraw Hill
‹#›
At this point
Glucose has been oxidized to:
6 CO2
4 ATP
10 NADH
2 FADH2
NADH and FADH2 are electron carriers and proceed to the electron transport chain
Electron transfer has released 53 kcal/mol of energy by gradual energy extraction
Energy will be put to use to manufacture ATP
© McGraw Hill
‹#›
Electron Transport Chain (ETC)
ETC is a series of membrane-bound electron carriers
Embedded in the inner mitochondrial membrane
Electrons from NADH and FADH2 are transferred to complexes of the ETC
In each complex:
A proton pump creates a proton gradient
Electrons are transferred to next carrier
© McGraw Hill
‹#›
Figure 7.12
© McGraw Hill
‹#›
Chemiosmosis
Uses a proton gradient to make ATP
Accumulation of protons in the intermembrane space drives protons into the matrix via diffusion
Membrane is relatively impermeable to ions
Most protons can only reenter matrix through ATP synthase
Energy gradient makes ATP from ADP + Pi
© McGraw Hill
‹#›
Figure 7.15
© McGraw Hill
‹#›
Figure 7.14
© McGraw Hill
‹#›
Energy Yield of Respiration
Theoretical energy yield
32 ATP per glucose for bacteria
30 ATP per glucose for eukaryotes
© McGraw Hill
‹#›
Figure 7.16
© McGraw Hill
‹#›
Regulation of Respiration
Example of feedback inhibition
Two key control points
In glycolysis
Phosphofructokinase is allosterically inhibited by ATP and/or citrate
In pyruvate oxidation
Pyruvate dehydrogenase inhibited by high levels of NADH
Citrate synthetase inhibited by high levels of ATP
© McGraw Hill
‹#›
Figure 7.17
© McGraw Hill
‹#›
Oxidation Without O2
Anaerobic respiration
Use of inorganic molecules (other than O2) as final electron acceptor
Many prokaryotes use sulfur, nitrate, carbon dioxide or even inorganic metals
Fermentation
Use of organic molecules as final electron acceptor
© McGraw Hill
‹#›
Anaerobic respiration
Methanogens
CO2 is reduced to CH4 (methane)
Found in diverse organisms including bacteria in the digestive system of cows
Sulfur bacteria
Inorganic sulphate (SO2) is reduced to hydrogen sulfide (H2S)
Early sulfate reducers set the stage for evolution of photosynthesis
© McGraw Hill
‹#›
Figure 7.18
(a): © Wolfgang Baumeister/Science Source; (b): National Park Service, photo by Jim Peaco
© McGraw Hill
‹#›
Fermentation
Reduces organic molecules in order to regenerate NAD+
Ethanol fermentation occurs in yeast
CO2, ethanol, and NAD+ are produced
Lactic acid fermentation
Occurs in animal cells (especially muscles)
Electrons are transferred from NADH to pyruvate to produce lactic acid
© McGraw Hill
‹#›
Figure 7.19
© McGraw Hill
‹#›
Catabolism of Protein
Amino acids undergo deamination to remove the amino group
Remainder of the amino acid is converted to a molecule that enters glycolysis or the citric acid cycle
Alanine is converted to pyruvate
Aspartate is converted to oxaloacetate
© McGraw Hill
‹#›
Figure 7.21
© McGraw Hill
‹#›
Catabolism of Fat
Fats are broken down to fatty acids and glycerol
Fatty acids are converted to acetyl groups by b-oxidation
Oxygen-dependent process
The respiration of a 6-carbon fatty acid yields 20% more energy than 6-carbon glucose.
© McGraw Hill
‹#›
Figure 7.22
© McGraw Hill
‹#›
Figure 7.20
© McGraw Hill
‹#›
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 7.1 - Text Alternative
Return to parent-slide containing images.
In metabolism, food molecules store energy in electron in C-H bonds. When the food is metabolized by enzymes, these molecules are oxidized, releasing these electrons. The electrons are captured by NAD+ forming NADH.
© McGraw Hill
‹#›
Figure 7.2 - Text Alternative
Return to parent-slide containing images.
In the electron transport chain electrons move from high energy to low energy. In the diagram this is shown as the electrons bouncing down a set of stairs, showing that the energy is released in small steps which allows the cell to capture the energy to form ATP. In the end the electrons are used to form water from hydrogen and oxygen.
© McGraw Hill
‹#›
Figure 7.3 - Text Alternative
Return to parent-slide containing images.
NAD is reduced when it gains two electrons forming NADH. The electrons are stored in a C-H bond. When those electrons are released NADH is oxidized to form NAD+.
© McGraw Hill
‹#›
Figure 7.5 - Text Alternative
Return to parent-slide containing images.
In aerobic metabolism, glucose is first converted to pyruvate in the cytoplasm. The pyruvate then enters the mitochondria where it is oxidized to acetyl CoA releasing a molecule of carbon dioxide. The acetyl CoA enters the citric acid Cycle and is further metabolized are two more carbon dioxides are released. At each step electrons that are released are collected by NAD+ forming NADH. These electrons are then delivered to the electron transport chain where ATP are formed.
© McGraw Hill
‹#›
Figure 7.6 - Text Alternative
Return to parent-slide containing images.
In glycolysis, glucose is first primed with two ATP to form an activated molecule. This is then cleaved into two three carbon sugars with a phosphate attached. After several more reactions, four ATP and two NADH are formed for a net production of two ATP and two NADH. The final molecules in the glycolytic pathway are two 3 carbon pyruvates.
© McGraw Hill
‹#›
Figure 7.7 - Text Alternative
Return to parent-slide containing images.
In glycolysis, glucose is first primed with two ATP to form fructose 1.6-bisphosphate. This is then cleaved into two three carbon glyceraldehyde 3-phosphate molecules. The next reaction is an oxidation producing NADH and 1,3 pisphosphoglycerate. One of the phosphates is then released producing ATP from ADP and forming 3-phosphoglycerate. After a few rearrangements, the high energy phosphoenolpyruvate is formed which can direct a phosphate directly to ADP forming ATP and is converted into pyruvate in the process.
© McGraw Hill
‹#›
Figure 7.8 - Text Alternative
Return to parent-slide containing images.
During metabolism of glucose a lot of NAD+ is required to accept electrons forming NADH. The electron transport chain will regenerate NAD+ in the presence of oxygen. However, in the absence of oxygen, NAD+ levels drop which would shut down metabolism and ATP production. In response anaerobic metabolism is activated and NADH will donate its electrons to pyruvate producing lactate or ethanol.
© McGraw Hill
‹#›
Figure 7.10 - Text Alternative
Return to parent-slide containing images.
Citrate is then oxidized to a 5 carbon molecule with the electrons being captured by NAD+ and releasing CO2. The 5 carbon molecule is then oxidized to a 4 carbon molecule with the electrons being captured by NAD+ and releasing CO2. The 4 carbon molecule goes through 3 rearrangement reactions generating 1 NADH, 1 FADH2, and one ATP in the process. One turn of the citric acid cycle generates 3 NADH, 1 FADH2, and one ATP.
© McGraw Hill
‹#›
Figure 7.11 - Text Alternative
Return to parent-slide containing images.
Citrate is then oxidized to a 5 carbon alpha ketoglutarate with the electrons being captured by NAD+ and releasing CO2. The alpha ketoglutarate is then oxidized to a 4 carbon succinyl CoA with the electrons being captured by NAD+ and releasing CO2. The succinyl CoA goes through substrate level phosphorylation producing ATP and forming succinate The succinate is oxidized by FAD producing FADH2 and fumarate Fumarate is converted to malate which is then oxidized by NAD+ to produce NADH and regenerating oxaloacetate to start the cycle again. One turn of the citric acid cycle generates 3 NADH, 1 FADH2, and one ATP.
© McGraw Hill
‹#›
Figure 7.12 - Text Alternative
Return to parent-slide containing images.
In the electron transport chain electrons are transferred from NADH or FADH2 to electron carriers in the inner mitochondrial membrane. As the electrons are passed through the electron transport chain, they lose energy and this energy is used to pump protons into the space between the inner and outer mitochondrial membranes. This generates a proton gradient that is used to generate ATP as they move back through ATP synthase. The electrons are used to produce water from hydrogen and oxygen.
© McGraw Hill
‹#›
Figure 7.15 - Text Alternative
Return to parent-slide containing images.
As electrons pass through the electron transport chain they generate a proton gradient. This gradient is used to produce ATP as they pass down their concentration gradient through ATP synthase. The enzyme has a structure with a stalk and rotor that rotates as the H+ ions pass through the ATP synthase.
© McGraw Hill
‹#›
Figure 7.14 - Text Alternative
Return to parent-slide containing images.
Glucose is metabolized by glycolysis and the citric acid cycle oxidizing it to carbon dioxide. In the process the released electrons are trapped in NADH and FADH2. In the electron transport chain electrons are transferred from NADH or FADH2 to electron carriers in the inner mitochondrial membrane. As the electrons are passed through the electron transport chain, they lose energy and this energy is used to pump protons into the space between the inner and outer mitochondrial membranes. This generates a proton gradient that is used to generate ATP as they move back through ATP synthase. The electrons are used to produce water from hydrogen and oxygen.
© McGraw Hill
‹#›
Figure 7.16 - Text Alternative
Return to parent-slide containing images.
In the oxidation of glucose electrons are released at several steps and are captured by NADH and FADH2. These are then used to produce ATP. Each NADH can lead to production of 2.5 ATP while FADH2 produces 1.5 ATP. An additional 4 ATP are produced through substrate level phosphorylation. This gives a net yield of 30-32 ATP per glucose.
© McGraw Hill
‹#›
Figure 7.17 - Text Alternative
Return to parent-slide containing images.
A cell does not want to burn glucose if it does not need more ATP. ATP shows negative feed back inhibition of the enzyme phosphofructokinase in glycolysis. Citrate is an intermediate in the citric acid cycle and if its level increases due to surplus energy in the cell it will also inhibit phosphofructokinase. NADH will inhibit pyruvate dehydrogenase. Finally, low levels of ATP correlate with elevated ADP which stimulates phosphofructokinase to produce more ATP.
© McGraw Hill
‹#›
Figure 7.19 - Text Alternative
Return to parent-slide containing images.
Fermentation is used to produce ATP in the absence of oxygen. Without enough oxygen electron transport chain slows down and NADH levels increase while NAD+ drops. Without NAD+ glycolysis cannot proceed. In response the cell will go through fermentation and donate electrons from NADH to pyruvate regenerating NAD+. The pyruvate is converted into ethanol in yeast or bacteria or lactate in animal cells.
© McGraw Hill
‹#›
Figure 7.22 - Text Alternative
Return to parent-slide containing images.
Fats are metabolized by beta-oxidation. In this process, the third carbon in from the CoA group on a fatty acid is oxidized from C-H to C-OH to C=O, and finally releases the end two carbons as acetyl CoA. Each oxidation step releases electrons which are captured by NADH or FADH2.
© McGraw Hill
‹#›
Figure 7.20 - Text Alternative
Return to parent-slide containing images.
In addition to sugars, nucleic acids, proteins and fats can serve as energy sources for cells. Fats are broken down into acetyl Co A which feeds directly into the citric acid cycle. Proteins are broken into amino acids which can feed into glycolysis or the citric acid cycle. Nucleotides are metabolized into the citric acid cycle. Both proteins and nucleotides also generate ammonia as a waste product.
© McGraw Hill
‹#›
6126222
CHO6O6CO6HO
+®+
