Wednesday, December 17, 2008

Review for Final!

Hey girls! Here's one last review of Cellular Respiration and Photosynthesis. I’ve included several diagrams to help prepare you for the exam and I hope all of you do well!

Cellular Respiration:

The ATP-generating process that occurs within cells. Energy is extracted from glucose to form ATP from ADP and Pi:
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + energy

Anaerobic Respiration is cellular respiration in the presence of oxygen. There are three components of anaerobic respiration:
  • Glycolysis: the decomposition of glucose to pyruvate; this process occurs in the cytosol. Here is a summary of the steps:
    • 2 ATP are added (the first several steps require the input of energy)
    • 2 NADH are produced (NADH forms when NAD+ combines with two electrons and H+) (NADH is a very energy-rich molecule)
    • 4 ATP are produced
    • 2 pyruvate are formed
  • Krebs Cycle: details what happens the pyruvate after glycolysis. Here is a summary of the steps:
    • Pyruvate to acetyl CoA (this is a step leading up to the actual Krebs cycle, pyruvate combines with coenzyme A to produce acetyl CoA, also producing 1 NADH and 1 CO2)
    • Acetyl CoA combines with OOA to form citrate (producing 3 NADH and 1 FADH2, and releasing CO2)
  • Oxidative Phosphorylation: the process of extracting ATP from NADH and FADH2.
    • Electrons from NADH and FADH2 pass along an electron transport chain
    • Along each step of the chain, the electrons give up energy used to phosphorylate ADP to ATP
      • NADH generates about 3 ATP
      • FADH2 generates about 2 ATP
    • The final electron accept is oxygen. The O2 accepts the two electrons and with 2 protons, forms water
Below is a diagram of the process of Cellular Respiration:

The two major processes of Cellular Respiration, the Krebs Cycle and Oxidative Phosphorylation, occur in the Mitochondria.
The Mitochondria has four distinct areas:
    • Outer Membrane: double phospholipid bilayer
    • Intermembrane Space: narrow area between the inner and outer membranes where protons accumulate
    • Inner membrane: double phospholipid bilayer that has convulsions called cristae (this is where oxidative phosphorylation occurs). Within this membrane, the electron transport chain removes electrons from NADH and FADH2 and transports protons from the matrix tot he intermembrane space.
    • Matrix: the fluid material that fills the inner membrane (this is where the Krebs cycle and the conversion of pyruvate the acetyl CoA occur)
Below is a diagram of a mitochondria: Chemisosmosis is the mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane. Here is a description of this process during oxidative phosphorylation in mitochondria.
• The Krebs Cycle produces NADH and FADH2 in the matrix and CO2 is generated and substrate level phosphorylation occurs

• Substrate level phosphorylation occurs when a phosphate group and its associated energy is transferred to ADP to form ATP. The substrate molecule donates the high energy phosphate group

• Electrons are removed from NADH and FADH2. These electrons move along the electron transport chain, from one protein complex to the next

• Protein complexes transport H+ ions from the matrix to the intermembrane compartment
• As H+ are transferred, the pH in the intermembrane space decreases, and the pH in the matrix increases.

• ATP synthase generates ATP

Here are some questions about Cellular Respiration:

1. The final electron acceptor of the electron transport chain that functions in anaerobic respiration is:

a) NAD+

c) pyruvate

d) oxygen

e) ADP

2. Which of the following processes occur in the Mitochondria?

a) glycolysis
b) Krebs Cycle
c) Oxidative Phosphorylation

d) all of the above

e) only b and c

3. Glycolysis occurs in the:

a) Outer Membrane of the Mitochondria

b) Cytosol
c) Inner Membrane of the Mitochondria

d) Intermembrane Space of the Mitochondria

e) Matrix of the Mitochondria

1. d 2. e 3. b

The process of converting energy in sunlight to energy in chemical bonds, especially glucose. The general chemical equation for photosynthesis is:
6 CO2 + 6 H2O + light ->C6H12O6 + 6O2

Here is a diagram showing the main components of Photosynthesis:

Begins with light-absorbing pigment in plant cells. A pigment molecule is able to absorb the energy from light only within a narrow range of wavelengths. Different pigments, capable of absorbing different wavelengths, act together to optimize energy absorption. These pigments include the green chlorophyll a and chlorophyll b and the carotenoids, which are red, orange or yellow. When the light is absorbed into one of these pigments, the energy from the light is incorporated into electrons within the atoms that make up the molecule. These energized electrons are unstable and almost immediately re-emit the absorbed energy. The energy is then reabsorbed by electrons of a nearby pigment molecule. This process continues, with the energy bounding from one pigment molecule to another. The process ends when the energy is absorbed by one of two special chlorophyll a molecules, P680 and P700 (the numbers represent the wavelengths at which they absorb their maximum amounts of light: 680 and 700 nanometers). Chlorophyll P700 forms a pigment cluster called photosystem I (PS I) and chlorophyll P680 forms photosystem II (PS II)

Photophosphorylation is the process of making ATP from ADP and phosphorylation using energy derived from light. There are two kinds of photophosphorylation:
  • Noncyclic Photophosphorylation: takes the energy in light and the electrons in H2O to make the energy-rich molecules ATP and NADPH. Noncyclic photophosphorylation begins with PS II and follows these steps:
    • Electrons trapped by P680 in photosystem II are trapped by light
    • Two energized electrons are passed to a molecule called the primary electron acceptor.
    • Electrons pass through an electron transport chain consisting of proteins that pass electrons from one carrier protein to the next
    • The two electrons move down the electron transport chain, losing energy. This energy is used to phosphorylate, about 1.5 ATP molecules
    • The electron transport chain terminates with PS I (P700). Here, the electrons are again energized by sunlight and passed to a primary electron acceptor
    • The two electrons pass through a short electron transport chain and then combine with NADP+ and H+ to form NADPH (a coenzyme)
    • The loss of the two electrons from PS II is replaced when H2O is split into two electrons, 2 H+ and 1/2 O2. The two electrons from H2O replace the lost electrons from PS II, one of the H+ provides the H in NADPH and the 1/2 O2 contributes to the oxygen gas that is released
  • Cyclic Photophosphorylation: occurs simultaneously with Noncyclic Photophosphorylation to generate addition ATP. Cyclic Photophosphorylation occurs when the electrons energized in PS I are "recycled".
    • Energized electrons from PS I join with protein carriers and generate ATP
    • Electrons then return to PS I, where they can be energized again to participate in cyclic or noncyclic photophosphorylation
Calvin Cycle: takes chemically unreactive, inorganic CO2 and incorporates it into an organic molecule that can be used in biological systems. The function of the pathway is to produce a single molecule of glucose (C6H12O6), and in order to accomplish this, the Calvin Cycle must repeat six times and use 6 CO2 molecules.
The Calvin cycle is referred to as C3 photosythensis because the first produce formed, PGA contains three carbon atoms.
No light is directly used in the Calvin cycle, however, this process cannot occur in the absense of light.
Here is a summary of the steps (only the most important molecules are mentioned and the molecules involved have been multiplied by 6):

  • Carboxylation: the enzyme rubisco catalyzes the merging of CO2 and RuBP
    • 6 CO2 combine with 6 RuBP to produce 12 PGA
  • Reduction: the energy in the ATP and NADPH molecules is incorporated into G3P. ADP, Pi and NADP+ are released and then re-energized in noncyclic photophosphorylation
    • 12 ATP and 12 NADPH are used to convert 12 PGA to 13 G3P
  • Regeneration: Regenerating the 6 RuBP originally used to combine with 6 CO2 allows the cycle to repeat
    • 6 ATP are used to convert 10 G3P to 6 RuBP
  • Carbohydrate Synthesis: The two remaining G3P are used to build glucose or other monosaccharides
In summary, the Calvin cycle takes CO2 from the atmosphere and the energy in ATP and NADPH to create a glucose molecule.
Below are some diagrams of the Calvin cycle:

The reactions of photosynthesis take place in the Chloroplasts.
Chloroplasts consist of the following areas:
  • Outer Membrane: double layer of phospholipids
  • Intermembrane Space: narrow area between the inner and outer membranes
  • Inner Membrane: double phospholipid bilayer
  • Stroma: fluid material that fills the area inside the inner membrane; where the Calvin cycle occurs
  • Granum: stacks of pancake-like membranes (each individual membrane is a thylakoid). The membranes of the thylakoids contain the protein complexes and other electronc arriers of light-dependent reactions
  • Thylakoid Lumen: inside of the thylakoid, where protons accumulate
Below is a diagram of a chloroplast:

is the mechanism of ATP generation that occurs when energy is stored in the form of a proton concentration gradient across a membrane. Here is a description of this process during photophosphorylation in chloroplasts.
• Protons accumulate inside the thylakoids and protons are acarred from the tromas into the lumen by a cytochrome

• A pH and electrical gradient across the thylakoid membrane is created (the pH inside the thylakoid decreases and the pH in the stroma increases)

• ATP synthases generate ATP
• The Calvin Cycle produces G3P using NADPH and CO2 and ATP

There are two other types of Photosynthesis: C4 Photosynthesis and CAM Photosynthesis

C4 Photosynthesis: Improving on photosynthetic efficiency, some plants have evolved a special "add-on" feature to C3 photosynthesis.
  • When CO2 enters the leaf, it is absorbed by the usual photosynthesizing cells, the mesophyll cells.
  • Instead of being fixed by rubisco into PGA, the CO2 combines with PEP to form OAA
  • OAA has four carbon atoms thus the name C4 photosynthesis
  • OAA is then converted to malate, which is shuttled through plasmodesmata to the bundle sheath cells
  • Here, the mala is converted to pyruvate and CO2 and then shuttled back to the mesophyll cells where one ATP is required to convert the pyruvate back to PEP
  • This process then repeats
The purpose for moving CO2 to bundle sheath cells is to increase the efficiency of photosynthesis. Because the bundle sheath cells rarely make contact with an intercellular space, very little oxygen reaches them. When malate delivers CO2 to a bundle sheath cell, rubisco begins the Calvin cycle (C3 photosynthesis).
In order for photosynthesis to occur stomata must be open to allow CO2 to enter; however when the stomata are open, H2O can escape. The higher rate of photosynthesis among C4 plants allows them to reduce the time that the stomata are open, thereby, reducing H2O loss. Therefore, C4 plants are found in hot, dry climates.
Below is a diagram of C4 Photosynthesis:

CAM Photosynthesis: another "add-on" feature to C3 Photosynthesis; the physiology of this pathway is almost identical to C4 photosynthesis.
  • PEP carboxylase still fixes CO2 to OAA
  • OAA is converted to malic acid
  • Malic acid is shuttle to the vacuole of the cell
  • At night, stomata are open, PEP carboxylase are active and malic acid accumulates in the cell's vacuole
  • During the day, stomata are closed, malic acid is shuttled out of the vacuole and converted back to OAA, releasing CO2
  • CO2 is fixed by rubisco and the Calvin cycle proceeds
Advantage of CAM is that photosynthesis can proceed during the day while the stomata are closed, greatly reducing H2O loss. CAM provides an adaptation for plants that grow in hot, dry environments with cool nights.
Below is a diagram of CAM photosynthesis:

Here are some questions about Photosynthesis:

1. The reaction-center chlorophyll of photosystem I is known as P700 because
a) there are 700 chlorophyll molecules in the center
b) this pigment is best at absorbing light with a wavelength of 700 nm
c) there are 700 photosystem I components to each chloroplast
d) it absorbs 700 photons per microsecond
e) the plastoquinone reflects light with a wavelength of 700 nm

2. What are the products of noncyclic photophosphorylation?
a) heat and fluorescence
b) ATP and P700
c) ATP and NADPH
d) ADP and NADP
e) P700 and P680

3. Where does the Calvin Cycle take place?
a) stroma of the chloroplast
b) thylakoid membrane
c) cytoplasm surrounding the chloroplast
d) chlorophyll molecule
e) outer membrane of the chloroplast

1. b) 2. c) 3. a)

Finally, I thought it would be helpful to see the relationship between photosynthesis and cellular respiration, so, I have included two diagrams and a chart showing the similarities and differences between the two.

I hope this has helped and good luck!!!

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