Cellular Respiration: Biology Review

Glucose

A simple sugar molecule that is the most important energy source in living energy and is a component of many carbohydrates. It has the ability to store chemical energy in a concentrated, stable form. Glucose is the end product of photosynthesis, and is the nearly universal food for life. It has the chemical formula of: C6H12O6 and glucose is the form of energy that is carried onto the blood of living organisms, making up all of the organism's trillions of cells.

Why do organisms need both glucose and ATP?

ATP is used to power cells' life processes. In contrast, glucose is used for energy storage as well as transportation. Glucose is powerful, as it contains a high input of chemical energy.

Autotrophs

Also known as producers, they are able to make their own food, as they use chemical energy in the form of light to produce food through a process known as "photosynthesis". Only three types of organisms are able to produce food through photosynthesis. They are: plants, algae, and some bacteria. Autotrophs are what form the basis of the "Simon food chain".

Heterotrophs

Also knowns as consumers, they get their food/chemical energy by consuming other organisms. Heterotrophs include: fungi, all animals, and many single celled organisms.

Cell Divison in Prokaryotes

Cell division is more complex in eukaryotes than prokaryotes. Prior to dividing, all the DNA in a eukaryotic cell's multiple chromosomes is replicated. Its organelles are also duplicated. Then, when the cell divides, it occurs in two major steps: • The first step is mitosis, a multi-phase process in which the nucleus of the cell divides. During mitosis, the nuclear membrane breaks down and later reforms. The chromosomes are also sorted and separated to ensure that each daughter cell receives a complete set of chromosomes. Mitosis is described in greater detail in Lesson 5.2. • The second major step is cytokinesis. As in prokaryotic cells, during this step the cytoplasm divides and two daughter cells form. Cell division is just one of several stages that a cell goes through during its lifetime. The cell cycle is a repeating series of events that include growth, DNA synthesis, and cell division. The cell cycle in prokaryotes is quite simple: the cell grows, its DNA replicates, and the cell divides. In eukaryotes, the cell cycle is more complicated. Eukaryotic cell cycle: The diagram in Figure 1.3 represents the cell cycle of a eukaryotic cell. As you can see, the eukaryotic cell cycle has several phases. The mitosis phase (M) actually includes both mitosis and cytokinesis. This is when the nucleus and then the cytoplasm divide. The other three phases (G1, S, and G2) are generally grouped together as interphase. During interphase, the cell grows, performs routine life processes, and prepares to divide. These phases are discussed below. Interphase of the eukaryotic cell cycle can be subdivided into the following three phases, • Growth Phase 1 (G1): during this phase, the cell grows rapidly, while performing routine metabolic processes. It also makes proteins needed for DNA replication and copies some of its organelles in preparation for cell division. A cell typically spends most of its life in this phase. • Synthesis Phase (S): during this phase, the cell's DNA is copied in the process of DNA replication. • Growth Phase 2 (G2): during this phase, the cell makes final preparations to divide. For example, it makes additional proteins and organelles. Control of the Cell Cycle If the cell cycle occurred without regulation, cells might go from one phase to the next before they were ready. What controls the cell cycle? How does the cell know when to grow, synthesize DNA, and divide? The cell cycle is controlled mainly by regulatory proteins. These proteins control the cycle by signaling the cell to either start or delay the next phase of the cycle. They ensure that the cell completes the previous phase before moving on. Regulatory proteins control the cell cycle at key checkpoints, which are shown in Figure 1.4. There are a number of main checkpoints. • The G1 checkpoint, just before entry into S phase, makes the key decision of whether the cell should divide. • The S checkpoint determines if the DNA has been replicated properly. • The mitotic spindle checkpoint occurs at the point in metaphase where all the chromosomes should have aligned at the mitotic plate. Cancer is a disease that occurs when the cell cycle is no longer regulated. This may happen because a cell's DNA becomes damaged. Damage can occur due to exposure to hazards such as radiation or toxic chemicals. Cancerous cells generally divide much faster than normal cells. They may form a mass of abnormal cells called a tumor (see Figure 1.5). The rapidly dividing cells take up nutrients and space that normal cells need. This can damage tissues and organs and eventually lead to death.

Cell Division

Cell division is the process in which one cell, called the parent cell, divides to form two new cells, referred to as daughter cells. How this happens depends on whether the cell is prokaryotic or eukaryotic. Cell division is simpler in prokaryotes than eukaryotes because prokaryotic cells themselves are simpler. Prokaryotic cells have a single circular chromosome, no nucleus, and few other organelles. Eukaryotic cells, in contrast, have multiple chromosomes contained within a nucleus and many other organelles. All of these cell parts must be duplicated and then separated when the cell divides.

Chromosomes

Chromosomes are coiled structures made of DNA and proteins. Chromosomes are the form of the genetic material of a cell during cell division. During other phases of the cell cycle, DNA is not coiled into chromosomes. Instead, it exists as a grainy material called chromatin. The vocabulary of DNA: chromosomes, chromatids, chromatin, transcription, translation, and replication is discussed at http://www.youtube.com/user/khanacademy#p/c/7A9646BC5110CF64/6/s9HPNwXd9fk (18:23).

Photosystem

Group of molecules, including chlorophyll, in the thylakoid membrane of a chloroplast that captures light energy

Why the hell do living things need energy for anyways?

Inside every cell of all living things, energy is needed to carry out life processes. Energy is required to break down and build up molecules and to transport molecules into plasma membranes. A lot of energy is also lost to the environment as heat.

Grana

It is located within the chloroplast, as it consists of sac-like membranes, known as thylakoid membranes

Food

Its the energy that organisms need. Food stores energy in their chemical bonds and are build-up of organic molecules. In terms of obtaining food for energy, there are two types of organisms: Autotrophs and Heterotrophs.

The Stages Of Photosynthesis

Photosynthesis occurs in two stages, Stage 1 is known as the light reactions, as it uses water and changes light energy from the sun into chemical energy stored in ATP and NADH (another energy-carrying molecule). This first stage releases oxygen as a waste product. Stage 2 is called the calvin cycle/dark reactions (no light is necessary, and it can occur by day). This stage combines carbon from carbon dioxide in the air and uses the chemical energy found in ATP and NADH to make glucose. It takes place in the stroma surrounding the thykaloid membranes of the chloroplast.

How does photosynthesis differ from cellular respiration?

Photosynthesis: 1. Takes place in a chloroplast 2. Carbon dioxide and water react, using light energy, to produce glucose and oxygen. 3. Light energy from the sun changes to chemical energy in glucose. Cellular Respiration: 1. Takes place in a mitochondrion 2. Glucose and oxygen react to produce water, carbon dioxide and energy in the form of ATP molecules 3. Chemical energy in glucose changes to chemical energy in ATP.

Calvin Cycle

Second stage of photosynthesis in which carbon atoms from carbon dioxide are combined, using the energy in ATP and NADH to make glucose

electron transport chain

Series of electron-transport molecules that pass high-energy electrons from molecule to molecule and capture their energy

Stroma

Space outside the thylakoid membrane of a chloroplast that captures light energy

ATP (Adenosine Triphosphate)

A compound consisting of an adenosine molecule bounded to three phosphate groups, present in all living tissue. The breakage of one phosphate linkage (to form ADP) provides energy for physiological purposes. i.e. : Muscle contraction as well as basic body functions. It is made during the first half of photosynthesis and is used as energy by cells.

chlorophyll

A green pigment inside a chloroplast which absorbs sunlight in the light reactions of photosynthesis.

Cellular Respiration

A process in which Glucose is broken down and ATP is made. Cellular Respiration occurs in ALL cells of ALL living organisms, wether if they are autotrophs or heterotrophs. Chemical Formula: C6H12O6+6O2=6CO2+6H2O+Chemical Energy as ATP

Chemosynthesis

A process in which some bacteria use chemical energy/compounds to produce their own food. (One example is Hydrogen Sulfide) One "animal" that does this are tube-worms.

Chromatid

DNA condenses and coils into the familiar X-shaped form of a chromosome, shown in Figure 1.6, only after it has replicated. (You can watch DNA coiling into a chromosome at the link below.) Because DNA has already replicated, each chromosome actually consists of two identical copies. The two copies are called sister chromatids.

Anaphase

During anaphase, sister chromatids separate and the centromeres divide. The sister chromatids are pulled apart by the shortening of the spindle fibers. This is like reeling in a fish by shortening the fishing line. One sister chromatid moves to one pole of the cell, and the other sister chromatid moves to the opposite pole. At the end of anaphase, each pole of the cell has a complete set of chromosomes. Telophase

Energy

Energy is defined to be the property of matter that is manifest as the capacity to perform work.

Thylakoid membrane

Membrane in a chloroplast, where the light reactions of photosynthesis occur

Cell Division in Prokaryotes

Most prokaryotic cells divide by the process of binary fission. Binary fission can be broken down into a series of three steps, although it is actually a continuous process. The steps are described below and also illustrated in Figure 1.2. They include DNA replication, chromosome segregation, and cytokinesis. • Step 1: DNA Replication. Just before the cell divides, its DNA is copied in a process called DNA replication. This results in two identical chromosomes instead of just one. This step is necessary so that when the cell divides, each daughter cell will have its own chromosome. • Step 2: Chromosome Segregation. The two chromosomes segregate, or separate, and move to opposite ends (known as poles) of the cell. • Step 3: Cytokinesis. A new plasma membrane starts growing into the center of the cell, and the cytoplasm splits apart, forming two daughter cells. This process is called cytokinesis. The two daughter cells that result are genetically identical to each other and to the parent cell.

Chloroplast

Note: Found in plats and algae, it holds everything inside a plant's cell (including its organelles)

Simon's Food Chain

The Simon food chain is a food chain that shows how energy and matter flow from producers to consumers. Matter is recycled, but energy must keep flowing into the system.

Photosynthesis

The flow of energy through living organisms begins through this process, as this process stores energy from sunlight in the chemical bonds of glucose. By breaking these chemical bonds, cells are able to release the stored energy and make the ATP they need. Chemical Formula: 6CO2+6H2O+light energy=C6H12O6 (Glucose is the main product) Photosynthesis and Cellular respiration recycle oxygen in earth's atmosphere.

The stages of cellular respiration

The reactions of cellular respiration can be grouped into three stages, they are: Glycolysis, the krebs cycle (also known as the citric acid cycle), and electron transport. Glycolysis: It is the first stage and takes place in the cytosol of the cytoplasm. In this stage, glucose is broken down to two molecules of pyruvate (also known as pyruvic acid). In glycolysis, glucose (C6) is split into two 3-carbon (C3) pyruvate molecules. This releases energy, which is then transferred to ATP. Glycolysis splits the glucose molecule into two pyruvate molecules. These two molecules then go to stage 2 of cellular respiration. During this stage high-energy electrons are also transferred to molecules of NAD+ to produce two molecules of NADH, another energy-carrying molecule. NADH is used in stage III of cellular respiration to make more ATP. Krebs Cycle/Citric-Acid cycle: Recall that glycolysis produces two molecules of pyruvate (pyruvic acid). These molecules enter the matrix of a mitochondrion, where they start the Krebs cycle. High-energy electrons are also released and captured in NADH. Results of the Krebs Cycle After the Krebs cycle, the original glucose molecule has been broken down completely. All six of its carbon atoms have combined with oxygen to form carbon dioxide. The energy from its chemical bonds has been stored in energycarrier molecules. These molecules are: • ATP • NADH • FADH2 Scientists think that glycolysis evolved before the other stages of cellular respiration. This is because the other stages need oxygen, whereas glycolysis does not, and there was no oxygen in Earth's atmosphere when life first evolved about 3.5 to 4 billion years ago. Cellular respiration that proceeds without oxygen is called anaerobic respiration. Then, about 2 or 3 billion years ago, oxygen was gradually added to the atmosphere by early photosynthetic bacteria. After that, living things could use oxygen to break down glucose and make ATP. Today, most organisms make ATP with oxygen. They follow glycolysis with the Krebs cycle and electron transport to make more ATP than by glycolysis alone. Cellular respiration that proceeds in the presence of oxygen is called aerobic respiration. Electron-Transport: Electron transport is the final stage of aerobic respiration. In this stage, energy from NADH and FADH2, which result from the Krebs cycle, is transferred to ATP. High-energy electrons are released from NADH and FADH2, and they move along electron transport chains, like those used in photosynthesis. The electron transport chains are on the inner membrane of the mitochondrion. As the high-energy electrons are transported along the chains, some of their energy is captured.

Centromere

They are attached to one another at a region called the centromere. A remarkable animation can be viewed at http://www.h hmi.org/biointeractive/media/DNAi_packaging_vo2-sm.mov.

Anaerobic Respiration

Today, most living things use oxygen to make ATP from glucose. However, many living things can also make ATP without oxygen. This is true of some plants and fungi and also of many bacteria. These organisms use aerobic respiration when oxygen is present, but when oxygen is in short supply, they use anaerobic respiration instead. Certain bacteria can only use anaerobic respiration. In fact, they may not be able to survive at all in the presence of oxygen. An important way of making ATP without oxygen is called fermentation. It involves glycolysis but not the other two stages of aerobic respiration. Many bacteria and yeasts carry out fermentation. People use these organisms to make yogurt, bread, wine, and biofuels. Human muscle cells also use fermentation. This occurs when muscle cells cannot get oxygen fast enough to meet their energy needs through aerobic respiration. There are two types of fermentation: lactic acid fermentation and alcoholic fermentation. In lactic acid fermentation, pyruvic acid from glycolysis changes to lactic acid. This is shown in Figure 3.12. In the process, NAD+ forms from NADH. NAD+, in turn, lets glycolysis continue. This results in additional molecules of ATP. This type of fermentation is carried out by the bacteria in yogurt. It is also used by your own muscle cells when you work them hard and fast. In alcoholic fermentation, pyruvic acid changes to alcohol and carbon dioxide. This is shown in Figure 3.13. NAD+ also forms from NADH, allowing glycolysis to continue making ATP. This type of fermentation is carried out by yeasts and some bacteria. It is used to make bread, wine, and biofuels. Have your parents ever put corn in the gas tank of their car? They did if they used gas containing ethanol. Ethanol is produced by alcoholic fermentation of the glucose in corn or other plants. This type of fermentation also explains why bread dough rises. Yeasts in bread dough use alcoholic fermentation and produce carbon dioxide gas. The gas forms bubbles in the dough, which cause the dough to expand. The bubbles also leave small holes in the bread after it bakes, making the bread light and fluffy. Aerobic respiration evolved after oxygen was added to Earth's atmosphere. This type of respiration is useful today because the atmosphere is now 21% oxygen. However, some anaerobic organisms that evolved before 78 www.ck12.org Chapter 3. Photosynthesis and Cellular Respiration the atmosphere contained oxygen have survived to the present. Therefore, anaerobic respiration must also have advantages. One advantage of anaerobic respiration is obvious. It lets organisms live in places where there is little or no oxygen. Such places include deep water, soil, and the digestive tracts of animals such as humans