11.27.07
Friday, November 30, 2007 Prompts
1)
There are three stages to aerobic cellular respiration: glycolysis, the Krebs Cycle, and oxidative phosphorylation. Each of these three stages is essential to the energy flow and chemical recycling in ecosystems that cellular respiration is responsible for.
The first stage is glycolysis. In the term glycolysis, ”glyco” means sweet whereas “lysis” means to split; the whole term can be taken to mean a sweet split of glucose. This stage takes place in the cytosol where glucose is partially metabolized into two pyruvate molecules. It is a catbolic pathway in which a 6-carbon glucose is split into two 3-carbon sugars and are rearranged to form two pyruvates. In glycolysis, no oxygen and no carbon dioxide is used because all carbon found in the glucose goes into the produced pyruvates. Lastly, there are two phases of glycolysis: the energy-investment phase and the energy-yielding phase. In the energy-investment phase cells use ATP to phorporylate compounds while in the energy-yielding phase each molecule of glucose yields 2 ATP and 2 NADH are produced.
The next stage of cellular respiration is the Krebs Cycle, or the Citric Acid Cycle. This stage takes place in the mitochondria matrix and completes the metabolism of glucose. In this stage pyruvate is transformed into acetyl coenzyme, or CoA. In this stage there is also a release carbon dioxide during respiration by removing pyruvate’s carboxyl group. The remaining fragment left after the carboxyl group is removed is then oxidized and forms the compound acetate. This transfers theextracted electrons to NAD+ and then stores energy in the form of NADH. Lastly, CoA is formed because coenzyme A is attached to the acetate in an unstable bond. All these reactions are products of glycolysis and the Citric Acid Cycle actually acting together. Also in the Krebs Cycle, electrons are transferred to FAD, which is later tranformed into FADH2 and along with NADH moves electrons from food to the electron transport chain.
Lastly, oxidative phosphorylation is the final sage in respiration. It occurs in the mitochondria membrane and 90% of ATP is produced in this stage, making this stage very efficient to respiration. Redox reactions come into play in oxidative phosphorylation. In these reactions electron donors transfer electrons to electron acceptors like oxygen. This releases energy and produces ATP. Redox reactions are carried out by protein complexes called electron transport chains. When energy is released when flowing through a transport chain it is called chemiosis. Also, ATP synthase produces ATP from ADP.
2)
The relationship between photosynthesis and cellular respiration is a very similar one. For instance, the summary equation for cellular respiration is the summary for photosynthesis, only backwards. This being said, photosynthesis must be performed before cellular respiration can take place. Photosynthesis produces glucose and oxygen gas which are essential to the life of a plant and also all other forms of life. In cellular respiratation glucose and oxygen gas are broken down into carbon dioxide, water, and energy. These are also essential to the life of plants and the universe.
3)
Common scientific knowledge can tell one that the mitochondria is the “powerhouse of the cell.” Found in the cytoplasm of most eukaryotic cells, the mitochondria is involved in energy production and allows multicellular organsims to survive. The mitochondria has an outer and inner membrane, much like a cell itself. It also consists of an inner membrane, the matrix, and the cristae, which allow reactions to take place and along with the matrix increases surface area in the organelle.
11.14.07
Friday, November 16, 2007 Prompts
1) In photosynthesis light reactions take place in the thylakoid space of a chloroplast. During a light reaction light energy gets changed into ATP and NADPH, but no sugar is made. In fact, light and water are taken into the thylakoid space. Water is split into hydrogen and more importantly, oxygen gas, which is released through the tiny pores of a chloroplast called stomata.
In the light reaction there are three things involved: two photosystems referred to as Photosystem I and Photosystem II, two electron transport chains, and ATP synthase. The photosystems play a big part in the production of NADPH, as electrons from Photosystem I are passed down a transport chain and added to NADP+ to make NADPH. Photosystem II passes electrons down the remaining electron chain to pump hydrogen ions from the stroma into thylakoid compartments. The photosystems replenish their electrons once water is split in a light reaction. ATP is made by ATP synthase, the enzyme that takes synthase and makes it ATP.
2) The Calvin Cycle of photosynthesis occurs in the stroma of the chloroplast. It uses energy from the light reaction to reduce carbon dioxide, which is called carbon fixation, and also to produce a molecule of G3P. When two molecules of G3P combine to make glucose. The energy used in the Calvin Cycle is formed by photophosphorylation. The goal of the Calvin Cycle is not only to produce glucose, but also other organic compounds.
3) Chloroplasts are found in the mesophyll of the leaf. The chloroplast consists of an outer membrane and also an inner membrane to insure safety in a cell. Inside the inner membrane a dense liquid surrounds the tissue called stroma as well as oval-shaped sacs called thylakoids, which are actually an elaborate membrane system. The interior of the thylakoids is called the thylakoid space, and stacks of thylakoids are called granum.
11.11.07
Plant Pigments Summary
To start off, a pigment is any substance that absorbs light. Photosynthetic pigments can absorb certain wavelengths of light and change light energy to chemical energy, which is what determines the color that a pigment appears as. This makes them very important to autotrophs and other organisms that make their own food through photosynthesis. Pigments have three main classifications: chlorophylls, carotenoids, and phycobilins.
Chlorophylls are green pigments that contain a porphyrin ring. The most important chlorophyll is chlorophyll “a”, because it makes photosynthesis possible. It appears as a yellowish-green in plant leaves. Chlorophyll “b” appears as a greenish-blue and is an accessory pigment. Carotenoids are red, yellow, or orange pigments that are referred to specifically as accessory pigments. Carotene and Xanthrophyll are accessory pigments, Carotene appearing orange and Xanthrophyll appearing yellow. Chlorophyll “b” is obviously an acception to the accessoy pigments rule, seeing as it belong in the chlorophyll group while still being an accessory pigment. The final classification of pigments is phycobilins. Phycobilins are water soluble pigments that are found in the stroma of the chloroplast. They only occur in Cynobacteria and Rhodophyta, helping them to absorb light engery
11.02.07
Friday, November 2, 2007 Questions
1) The size of the cells pores affects the permeability of a cell membrane. If the molecules of a solution are too large they will not pass through a cell membrane, just as the starch in the dialysis bag lab did not diffuse through the bag. Also, whether a substance is hydrophobic or hydrophilic setermines what crosses the membrane, as well as the molarity of the solution, which contributes to the rate at which diffusion occurs across the cell membrane.
2) The membrane protein allows large molecules such as hydrophilic substances and charged ions to cross a cell membrane, acting as an door for them since they cannot normally pass through the selectively permeable barrier.
3) The lipids are hydrophilic and this causes an inability to pass through the phospholipids of the cell membrane. Their large size does not make it possible for them to pass through the membrane’s pores.
4) The cell membrane, or plasma membrane, and its permeabilty is what determines what enters and exits a cell.
