Download Chapter 3 Energy for Cells SECTION 3.1 Cells, Matter, and Energy

Chapter 3 Energy for Cells
SECTION 3.1 Cells, Matter, and Energy
Recall that all the energy on Earth comes from the sun. That solar energy is used by plants to produce food.
Plants are eaten by other organisms which in turn are eaten by other organisms. The general food chain is as follows:
photosynthesizers -> herbivores -> carnivores -> top carnivores
At any point along this food chain, if an organism dies, it is eaten by decomposers. Throughout the food chain,
energy is being transferred from one organism to the next and the matter is recycled (water cycle, carbon cycle, nitrogen
cycle, phosphate cycle, ...).
Energy is the capacity to do work. Potential energy is stored energy in an object (a rock on the edge of a cliff).
Kinetic energy is the energy of motion (the rock falling off the cliff). Chemical energy is the potential energy stored in
the bonds of compounds. When the bonds are broken, atoms are allowed to move freely (kinetic energy). The Law of
Conservation of Energy states that energy can not be created or destroyed. It can only be transformed from one form to
another.
The chemical reactions of life simply transform energy from one form to another. Some of these reactions will
break large molecules to simpler ones and release energy. Other reactions build complex compounds from simpler ones
but must use energy to do this. Theses two opposing types of reactions make up metabolism. For example,
photosynthesis converts solar energy and the chemical energy of carbon dioxide and water into the chemical energy of
glucose and oxygen. Cellular respiration on the other hand releases the chemical energy in glucose and stores it in other
molecules.
Energy Cycle
Adenosine Triphosphate (ATP) is an energy rich compound which stores the energy released from cellular respiration.
Adenosine Diphosphate (ADP) is a lower energy compound which results from the loss of one phosphate from ATP.
phosphorylation - the removal of a phosphate from one molecule (ATP) and transferring it to another compound
Oxidation-Reduction Reactions
Oxidation is a chemical change in which an atom or molecule loses electrons. The molecule which loses the
electrons is said to be oxidized. Usually, the oxidized molecule loses energy as well.
Reduction is a chemical change in which an atom or molecule gains electrons. The molecule which gains the
electrons is said to be reduced. Usually, the reduced molecule gains energy.
-> LEO the lion says GER
Hydrogen Acceptors
Along the biochemical pathway of cellular respiration, when a molecule is oxidized, the electron is lost along with
a proton (in the form of a hydrogen atom). The hydrogen is bonded to a special type of coenzyme. Two coenzymes
which accept hydrogen in cellular respiration are:
1)
nicotinamide adenine dinucleotide (NAD)
NAD + 2H -> NADH2
2)
flavin adenine dinucleotide (FAD)
FAD + 2H -> FADH2
These coenzymes are temporarily carrying more energy when they have the hydrogens bonded to them. The
energy is released in another series of reactions.
SECTION 3.2 The Process of Photosynthesis
Photosynthesis
photosynthesis - the process by which sunlight is captured and transformed into chemical energy (food)
e.g. 6 CO2 + 12 H2O + sunlight -> 6 O2 + C6H12O6 + 6 H2O
net-> 6 CO2 + 6 H2O + sunlight -> 6 O2 + C6H12O6
Light Energy
Light energy is a form of energy called radiation. There are two theories on light energy.
1) Light travels in the form of waves in which the wavelength is the distance between the crest of one wave and the next.
The shorter the wavelength, the more energy it carries.
Visible light to the human eye is only a small range of the radiation spectrum. It includes wavelengths between
400-770 nanometres (1 nm = 1/1,000,000 of a mm). The 7 colors of the visible spectrum are red (770 nm), orange,
yellow, green, blue, indigo, and violet (400 nm). Sunlight is called white light because it is a mixture of all these
wavelengths.
2) Light exists as a particle called a photon.(light with shorter wavelengths or higher frequency have more energy in their
photons).
Light Energy
http://www.uccs.edu/~mgrabows/pes106/LecNotes/lecture03.htm
When light strikes an object, three possibilities can occur:
reflection
- light bounces off the object
transmission - light goes through the object
absorption
- light enters the object
When light strikes non-transparent matter some of the energy may or may not be absorbed while the rest is
reflected. This material is referred to as a pigment.
e.g.
black pigments absorb all the energy and reflect none
blue objects reflect blue light but absorb all other wavelengths.
When we think of light as photon particles and a photon strikes an object, the matter may absorb some of the
photon’s energy. This energy is then transferred to the electrons of the object, thus raising its level of energy (in the form
of heat).
Plants use pigments to capture this energy to fuel a series of chemical reactions. Chlorophyll is the major pigment
found in plants which can absorb all wavelengths except green which is reflected.
Chloroplasts are organelles found only in green plants which contain the photosynthetic pigments. The pigments
are arranged in the form of flattened sac-like membranes within the chloroplast called thylakoids. The stacks of
thylakoids are called grana (granum -> singular). The region of fluid surrounding the grana within the chloroplast is the
stroma.
Chloroplast Image
http://www.biology.iupui.edu/biocourses/N100H/images/chloroplast.gif
Chemistry of Photosynthesis
6 CO2 + 12 H2O + sunlight -> 6 O2 + C6H12O6 + 6 H2O
This chemical equation represents all of the chemical reactions involved in photosynthesis which is composed of
two sets of reactions:
1) Light Dependent Reactions only take place in presence of sunlight. They lead to the production of energy rich
molecules using sunlight and occur on the membranes of the grana/thylakoids of the chloroplast. The photosynthetic
pigments are packaged into light absorbing centers called photosystems (I and II).
Steps
1) Photons strike photosystem II (PSII) where the energy is used to break water into 2 hydrogen atoms and oxygen. The
hydrogen atoms lose their electrons and become hydrogen ions.
2) The 2 electrons are passed to an acceptor of an electron transport chain. An ETC much like the one in mitochondria.
3) The 2 electrons are passed down the ETC by a series of oxidation-reduction reactions. The energy lost from the
electrons is used to make one ATP molecule.
4) The 2 electrons (low energy) are received by PSI where light energy is absorbed and is used to re-energize the 2
electrons.
5) The 2 electrons are passed to an acceptor which will combine them with the 2 hydrogen ions and a molecule of NADP
(final electron acceptor) to produce NADPH2.
Light and one molecule of water will produce 1 ATP and 1 NADPH2 (energy rich molecules) and ½ O2 molecule.
There are 12 H2O (used in photosynthesis) which will produce 12 ATP, 12 NADPH2 , and 6 O2.
Light Reactions
http://www2.kumc.edu/netlearning/examples/flash/photosyn2.html
2) Light Independent Reactions or Dark Reactions do not require sunlight to occur but do require the energy rich
molecules produced in the light reactions. They lead to the production of food for the plant (glucose) in a process called
carbon fixation. They occur in the stroma of the chloroplast and were discovered by Melvin Calvin. The dark reactions
are also known as the Calvin Cycle for which he won the Nobel Prize in 1961.
The dark reactions are also known as the C3 photosynthetic pathway because the first molecule produced in the
cycle is a 3 carbon chain (phosphoglyceric acid -> PGA). The process is called a cycle because it starts and ends with the
same 5 carbon sugar, ribulose biphosphate (RuBP).
Steps
1) Six CO2 combine with 6 ribulose biphosphate (RuBP) in a 1:1 ratio to produce six 6 carbon chains which are unstable.
These molecules are quickly broken into 12 phosphoglyceric acid (PGA) molecules.
2) The 12 PGA molecules are converted to 12 PGAL phosphoglyceraldehyde molecules. This requires 12 ATP
molecules (made in light reactions) as an energy source to fuel the reactions and the 12 NADPH 2 (made in light reactions)
as a source of energy and hydrogens. Each PGA accepts 2 hydrogens from a NADPH2. The NADPH2 is oxidized to
NADP and PGA is reduced to PGAL.
3) Two of the PGAL produced are used to produce one glucose molecule.
4) Ten of the PGAL produced are used to produce the 6 RuBP molecules which uses 6 ATP to fuel the reactions (come
from results of cellular respiration).
In the dark reactions, 6 CO2 are used and 1 C6H12O6 and 6 H2O are made.
Dark Reactions Animation
http://www.science.smith.edu/departments/Biology/Bio231/calvin.html
SECTION 3.3 Aerobic Cellular Respiration
cellular respiration -> the process by which energy stored in food is released by a series of biochemical reactions (a
special biochemical pathway)
1) Anaerobic Respiration is a type of cellular respiration which occurs in the absence of free oxygen. Glucose is only
partially oxidized. It occurs in yeast and many bacteria but these cells receive little energy from the glucose.
2) Aerobic Respiration is a type of cellular respiration which occurs in the presence of free oxygen. Glucose is
completely oxidized to form carbon dioxide and water. It occurs in most other cells and they receive the maximum
amount of energy released from glucose.
Cell Cycle and Oxidation-Reduction
http://wps.prenhall.com/wps/media/objects/1109/1135821/7_1.html
Step I
Glycolysis is the breakdown of glucose into pyruvic acid. It occurs in the cytoplasm of the cell.
1)
The glucose molecule accepts 2 phosphates and is said to be “energized.” The phosphates and energy are
provided by ATP.
2 ATP -> 2 ADP + 2 Pi + energy
2)
The glucose molecule is split to form 2 molecules of phosphoglyceraldehyde (PGAL). This is done by an
enzyme.
3)
Each PGAL molecule is oxidized (loses electrons) through the loss of 2 hydrogens from each PGAL (4 in total).
These hydrogens from each PGAL are accepted by NAD molecules to form NADH2. Two NADH2 are made in total.
4)
The oxidation of PGAL means it has lost energy. This energy is used to form ATP. Each PGAL oxidation
reaction will form 2 ATP (4 all together). The loss of hydrogen and phosphate changes PGAL to pyruvic acid.
Glycolysis Animation
http://www.science.smith.edu/departments/Biology/Bio231/glycolysis.html
Step II
Pyruvic Acid Breakdown is a short step in which the pyruvic acid produced from glycolysis enters the mitochondrion
where it is further oxidized and energy is released. It occurs in the mitochondrial matrix.
1) Each pyruvic acid molecule loses a carbon (in the form of carbon dioxide) and 2 hydrogen atoms which are accepted
by NAD to form NADH2. The remaining two carbon chain is called an acetyl group and is bonded to a coenzyme
(coenzyme A-> CoA) to form a molecule called acetyl CoA.
This occurs twice because there were two pyruvic acids made from one glucose molecule.
Step III
Kreb's Cycle is a series of chemical reactions in the mitochondrial matrix that begins with the acetyl CoA formed from
pyruvic acid breakdown. It is also known as the citric acid cycle. Citric acid is the 6 carbon molecule formed at the start
of the cycle. The purpose of Kreb's cycle is to oxidize the citric acid molecule to produce more high energy molecules
(ATP, NADH2, FADH2).
1) Acetyl CoA, a 4 carbon chain called oxaloacetate, and one water molecule join together to form a 6 carbon chain with a
T shape called citric acid. The CoA is released.
2) The citric acid molecule is oxidized by losing 2 hydrogen atoms (picked up by NAD to form NADH2). A carbon is
lost in the form of carbon dioxide.
3) The 5 carbon molecule is oxidized by losing 2 hydrogen atoms (picked up by NAD to form NADH2). A carbon is lost
in the form of carbon dioxide. The energy given off is used to make 1 ATP molecule. A water molecule is added to the
resulting 4 carbon chain.
4) The 4 carbon molecule is oxidized by losing 2 hydrogen atoms (picked up by FAD to form FADH2).
5) Water is added to the 4 carbon molecule.
6) The 4 carbon molecule is oxidized by losing 2 more hydrogen atoms (picked up by NAD to form NADH2). The 4
carbon molecule is now oxaloacetate (the molecule that is "recycled" in this process).
Two rounds of Kreb’s Cycle occurs from each glucose molecule because one glucose produces 2 acetyl-CoA.
Pyruvic Acid Brakdown & Kreb’s Cycle
http://www.science.smith.edu/departments/Biology/Bio231/krebs.html
NET ENERGY PRODUCTION FROM AEROBIC RESPIRATION SO FAR
STEP I GLYCOLYSIS
STEP II PAB
STEP III KREB'S CYCLE
TOTAL SO FAR
ATP
2 made
0
2 made
4 ATP
NADH2 FADH2 CO2
2 made
0
2 made
0
6 made
2 made
10 NADH2
2 FADH2
H2O
0
2 made
4 made
6 CO2 MADE
O2
0
0
6 used
6 H2O USED
0
0
0
0
Step IV
Electron Transport Chain - a series of proteins along the inner membrane of the mitochondria which carry out numerous
oxidation-reduction reactions to produce ATP from the energy stored in NADH2 and FADH2.
1) Each NADH2 and FADH2 molecule that was produced gives up its 2 hydrogen atoms to release NAD and FAD.
2) Each hydrogen atom will give up its single electron. Each hydrogen acceptor gives up 2 hydrogen atoms, therefore
each hydrogen acceptor would give up 2 electrons. Each hydrogen forms an H+ ion when it loses its electron.
3) The 2 electrons are passed down the electron transport chain in a series of oxidation-reduction reactions.
4) As the electrons move down the chain, energy is lost which is used to produce ATP (1 NADH2 -> 3 ATP,
1 FADH2 -> 2 ATP).
5) At the end of the chain, the 2 electrons are accepted by the 2 H+ ions they were released from originally and react with
oxygen to form water.
2e- + 2H+ + 1/2O2 -> H2O
This equation is multiplied by 12 because there were 10 NADH2 and 2 FADH2 which means that this process occurs 12
times for each glucose molecule.
24e- + 24H+ + 6O2 -> 12H2O
ETC Video
http://www.stolaf.edu/people/giannini/flashanimat/metabolism/mido%20e%20transport.swf
NET ENERGY PRODUCTION FROM AEROBIC RESPIRATION (1 glucose)
ATP
NADH2 FADH2 CO2
H2O
O2
STEP I GLYCOLYSIS
2 made
2 made
0
0
0
STEP II PAB
0
2 made
0
2 made
0
STEP III KREB'S CYCLE
2 made
6 made
2 made
4 made
6 used
TOTAL SO FAR
4 ATP
10 NADH2
2 FADH2
6 CO2
- 6 H2O 0
STEP IV ETC
34 made
-10 NADH2
-2 NADH2
0
12 made
TOTAL
38 MADE
0
0
6 MADE
6 MADE
Chemical equation for aerobic respiration:
C6H12O6 + 6 O2 + 6 H2O -> 6 CO2 + 12 H2O + 38 ATP
Net chemical equation for aerobic respiration:
C6H12O6 + 6 O2 -> 6 CO2 + 6 H2O + 38 ATP
0
0
0
6 used
6 USED
However, there are only 36 ATP produce from the aerobic respiration of 1 glucose molecule. This is because the
2 NADH2 produced in glycolysis can not get to the ETC in the mitochondria. These 2 molecules release their 4 hydrogen
atoms which can enter the mitochondria. Once inside, they bond to 2 FAD molecules (making 2 FADH2) which go to the
ETC to produce 4 ATP rather than the 6 ATP that should have been made from the original 2 NADH2.