Chapter 9 . Energy in A Cell. The Need for Energy. Energy is Essential in life The major energy source molecule of the cell is ATP . This complex molecule is critical for all life from simplest to the most complex .
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Energy in A Cell
All fuel sources of nature, all foodstuffs of living things produce ATP which in turn powers virtually every activity of the cell and organism.
ATP is an abbreviation for Adenosine Triphosphate. ATP contains the purine base adenine and the sugar ribose which together form the nucleotide adenosine.
An even greater amount of energy is required to force a third charge phosphate group close enough to the other two to form a bond. When this bond is broken energy is released.
When the chemical bond between the second and third phosphate groups in ATP is broken, energy is released and the resulting molecule is broken. At this point ADP can form ATP again by bonding with another phosphate group.
Many proteins have a specific site where ATP can bind. When the phosphate is bond is broken and the energy released, the cell can use the energy for activities such as making a protein or transporting molecules through the plasma membrane.
Light dependent reactions depend on two major collections of light harvest pigments chlorophyll molecules are called photosystem II and photosystem I
What happens is that energy in the form of light is absorbed by special pigments called chlorophyll. They pass this energy on to one of the reactions center and that reaction center molecule can actually lose a couple of electrons and those electrons carry energy away.
So this reaction center flings this high energy electrons to do things. If you keep removing electrons from molecules those electrons are being used to form bonds of those molecules. So if that happens the molecules will pull apart . So we need to get replacements and that’s the job of the photosystem II where there is a special enzyme that can grab electrons from water. Which makes the water fall apart into hydrogen ions and oxygen gas. Now those hydrogen ions have a positive charge because we took away their electrons
Now the chloroplasts have a electron transport system. Well this system has a bunch of molecules sort of acting like wires which allow passage of electrons. Right in the middle of the light dependent reaction where is a pump that grabs hydrogen ions outside of the thylakoid and shoves them inside the thylakoid.
Remember you have already hydrogen ions inside the thylakoids so we are forcing more into the membrane and this requires energy to force them in because there is a high positive charged.
That’s why it requires energy to pull them in. Eventually those electrons have lost their energy because its been used to do something.
So photosystem 1 also at the same time has been absorbing light and giving its energy from that light to some high energy electron carrier NADPH+. If you give them two electrons it becomes negatively charge and it grabs hydrogen ion from outside and becomes NADPH. That is one of the two things that is required by the Calvin Cycle for it to operate and to do carbon fixation.
The last thing we need to generate is for the Calvin Cycle is ATP. That is where all these hydrogen ions that we have been building up inside the thylakoids membrane come into play. These high concentrations of hydrogen ions give us the ability to do some work.
This difference from hydrogen ions on one side to the other side is called a chemiosomitic gradient. Its more than just a concentration gradient because all these hydrogen ions adding to one side and removing from the other side they have a charge. They have a positive region inside compared to the outside regions is negative. For this reason they are attracted to the other side as well as repelling each other.
The last part of the light independent reactions is collection of molecules called ATP synthase. It’s a specialized channel that as hydrogen ions go zipping down their gradient. Hydrogen ions go through the ATP synthase they force it to literally spin and while its spinning its grabs a ADP and a Phosphate and rams them together make ATP. The ATP floats away to the Calvin Cycle.
Carbon fixation is the building of glusose or other sugars by using carbon dioxide in the air. The Calvin cycle takes place in the stroma of the chloroplast. It is using the energy in the ATP molecules and the energy of the electrons being carried by NADPH that were being provided to the stroma by light dependent reactions.
The light dependent reactions occur on the thylakoidmembrane and they send their materials, ATP and NADPH to the stroma
The ATP and NADPH and those are being consumed by the Calvin Cycle as it takes in Carbon Dioxide for the air (carbon fixation) and spits out some sugars.
Notice that’s a cycle that starts off with some building materials adds the CO2 to them. Builds some glucose but has to recycle a lot of materials in order to have your starting materials from the beginning again. It send the used up NADP+ and ATP back to the thylakoid membrane
The Calvin cycle begins with 5 carbon molecules called ribulose biphosphate (RuBP). The Bid- just means that is has two phosphates on the end of this 5 carbon ribulose molecule. The P represents the phosphate.
So we have our 5 carbon RuBP and we ram it to together the CO2 that is brought in from the outside to make it a 6 carbon molecule. It falls apart immediately because its unstable. It breaks apart into a pair of these phosphogylcerate (PG) molecules.
For every 6 ribulose biphosphate that I add 6 carbons to that will give me 12 RuBP. This molecules needs to be energized in order to make the chemical changes that we want to make it. So we add a phosphate at the opposite end. It already has a phosphate and since we added another, now it is called biphophate glycerate (BPG).
Now we can make some major changes and we can add some additional electrons from NADPH. These are special electrons have lots of energy . These high energy electrons allows to make major alterations turn the biophosphoglycerate into a different molecules called Glyceraldehyde(G3P)
There are 12 of these 3 carbon molecules if you count up the carbons you have 36. You have 36 carbons but we need to recycle so we can go back to the beginning. Keep 30 of the carbons to keep the cycle going. So I can use 6 carbons to make glucose . C6H12O6.
ATP comes along adds some energy and a bunch of enzymes to help this process happens and we recycle our way back to our staring material.
The process by which mitochondria break down food molecules to produce ATP is called cellular respiration.
Glucose—energy C6H12O6+6O2----6CO2+6H2O+energy= heat and energy
ATP is the energy currency for our biological systems.
Glycolysis needs 2 ATPS and generates 4 ATP’s. It generates 2 net ATP’s. And then the pyruvic acid gets pulled onto Krebs Cycle and generates 2 more ATP. After glycolysis and the Krebs Cycle then you have the electron transport chain which gets credit for producing the bulk of the ATP’s 34.
When you start running out of oxygen some these by products of glycolysis instead of going into the Krebs Cycle of electron transport chain where they go through a side process called Fermentation. For some organism these process of fermentation takes your by products glycolysis and literally produces alcoholic fermentation and for humans it produces lactic acid fermentation.
Glycolysis and Krebs Cycle are constantly taking NAD+ and adding hydrogen to it to form NADH. For 1 molecule of glucose this happens to 10 NAD+ to become NADH. These two things drive the electron transport chain.
FADH2 and NADH get oxidized (combine with having a chemical reaction with oxygen) in the electron transport system to make ATP.
10 NADH (1 NADH make 3 ATP)= 30
2 FADH2 (1 FADH2 make 2 ATP)= 4
You have a total of 38 ATP’s