The mass number and atomic number therefore determines how an atom behaves.
We can therefore summarize the chemical behavior of atom as being due to interactions between electrons. Electrons of an atom remain within certain, predictable electron configurations. These configurations are determined by the mechanics of electrons in the electric energy potential of the atom. The numbers determines particular electron shells with distinct energy levels. Usually the higher the energy level of a shell, the further it is from the nucleus. The electron configuration is actually the arrangement of
electrons in an atom, molecule or other body. A molecule is the smallest particle of a pure chemical substance that still retains its composition and chemical properties. It is a sufficiently stable, electrically neutral entity composed of two or more atoms. When two or more atoms join together, they form a molecule. There are also some molecules that have only one element. An example is the molecular nitrogen (N2) with two atoms. There are also the molecules of compounds that consist of two or more elements in an unvarying proportion. A Given example is water which has one molecule of oxygen atom and two molecules of hydrogen atoms.
The chemical configuration therefore influences the chemical behavior of an atom in the form of a chemical reaction. Chemical reaction is a process that is the result of a chemical change and it yields one or more products which are different from the reactants. This encompasses changes that strictly involve the motion of electrons in the forming and breaking of chemical bonds. The electrons in the outermost shell, called the valence electrons, have the greatest influence on chemical behavior. Core electrons (those in the outer shell) play a role, but it is usually in terms of a secondary effect due to screening of the positive charge in the atomic nucleus. There are different types of chemical reactions. They include endergenic reaction and endergenic reactions.
Endergenic reaction is characterized as having products with more stored energy in them than the reactants have. An example is photosynthesis. Energy is stored for later use.
Exergenic reactions release stored energy to do work in the cell. An example is respiration. Cells stay alive by coupling energy inputs to energy outputs with ATP. ATP (adenosine triphosphate) is where energy is stored for use, a little at a time. ATP is composed of an adenine base, a ribose sugar and three phosphate groups. ATP couples endergonic and exergenic reactions in the cell. When ATP breaks down to ADP, a phosphate is transferred to another molecule. This is known as energy transfer.
Phosphate transfer is called phosphorylation and gives energy to another molecule.
: Four organelles or structures that all eukaryotic cells have in common.
Introduction.
The cell as it has been known is the structural and functional unit of all living organisms. According to the cell theory, all living organisms are made up of cells and all cells come from pre-existing cells. There are two basic types of cells; prokaryotic cells and eukaryotic cells. The prokaryotic cells include bacteria. Although prokaryotic cells have DNA, they are not isolated from the rest of the cell inside a nucleus. (Prokaryotic cells do not have nucleus).
Eukaryotic cells are cells that contain membrane-bound compartments in which specific metabolic activities take place. Eucharyotes include humans, animals, plants and fungi and a variety of other micro-organisms called protests. The protests include parasites.
Eukaryotes, along with archaea-bacteria and eubacteria, make up the three major branches of living organisms. Euchariotic cells are usually distinguished from other forms of life by the presence of nucleus and the presence of a cytoskeleton. The most important compartments of a eukaryotic cell is the nucleus which houses the eukaryotic cell’s DNA. DNA is genetic information which are organized into discrete chromosomes and contained within a membrane-bounded compartment. The nucleus from the pictures that I have seen is spherical in shape and separated from the cytoplasm by a double membrane structure called the nuclei envelope. All DNA replication and RNA synthesis occur in the nucleus. The cytoskeleton is a complex array of proteins which provides the structural framework for the eukaryotic cell and its components.
Eukaryotic cells also have other specialized, membrane bounded structures called organelles. Organelles are small structures within cells that perform dedicated functions.
Apart from the nucleus and cytoskeleton, all eukaryotic cells have other organelles or structures in common. Some of these structures or organelles include cytoplasm, mitochondria, cell membrane, and ribosome just to name at least four.
The cytoplasm is actually a jelly-like matrix that surrounds the nucleus of a cell and is bounded by the cell membrane. It includes the organelles of the cell as well as the sugars, amino acids, and proteins that cell uses for growth and reproduction. The cytoplasm also contains dissolved nutrients and salts, and helps dissolve waste products. It also facilitates the movement of materials around the cell through the process of cytoplasmic streaming.
The portion of the cytoplasm that lies outside organelles and include other cellular components is called cytosol.Cytoplasm also houses the cytoskeleton and contains a network of cytoplasmic filaments responsible for the movement of the cell and which gives the cell its shape. The nucleus often flows with the cytoplasm, changing shape as it moves.
Mitochondria are mobile, self-replicating organelles that occur in various numbers, shapes, and sizes in the cytoplasm of all eukaryotic cells. Mitochondria contain their own genome that is separate and distinct from the nuclear genome of a cell. Mitochondria have two functionally distinct membrane systems separated by a space. The outer membrane, which surrounds the whole organelle, and the inner membrane, which is thrown into folds or shelves that project inward. These inward folds are called cristae. The number and shape of cristae in mitochondria differ, depending on the tissue and organism in which they are found, and serve to increase the surface area of the membrane. Mitochondria are the site of the citric acid cycle, also known as the kreb’s cycle, which is a vital metabolic pathway for generating energy in eukaryotic cells.
Cell membrane is another feature that all eukaryotic cells have in common. Cell membrane is actually the membrane surrounding the cytoplasm of a cell, consisting of a lipid bilayer with embedded proteins. It regulates what enters and leaves the cell, maintains the correct intracellular ph level and provides a means of separating charges so that the cell can generate energy-carrying molecules such as adenosine triphoshate (ATP). (ph is the negative log of the activity of hydrogen ions and represents the activity of hydrogen ions in a solution at a given temperature). Lipid bilayer mentioned here is the structure of a cell membrane in which two layers of phospholipids spontaneously align so that the hydropholic head groups are exposed to water.
The cell membrane is both a physical and chemical barrier which defines the boundary between the individual and its environment.
The next common feature that I mentioned earlier is the ribosome.
Ribosome is a tiny organelle that is the site of protein synthesis in the living cell. Ribosomes are complex, bead-like structures composed of about 40% protein and 60% ribosomal rna. In eukaryotes, ribosomes are made of four strands of RNA and are often attached to the membranes of the endoplasmic reticulum to form rough endoplasmic reticulum. In prokaryotes, they are made of three strands of RNA and occur free in the cytoplasm. Eukaryote ribosomes are produced and assembled in the nucleolus. Three of the strands are produced there, but one is produced outside the nucleolus and transported inside to complete the ribosome assembly. Ribosomal proteins enter the nucleolus and combine with the four strands to create the two subunits that will make up the completed ribosome. The ribosome units leave the nucleus through the nuclear pores and unite once in the cytoplasm. Some ribosome will remain free-floating in the cytoplasm, creating proteins for the cell’s use. Others will attach to the endoplasmic reticulum and produce the proteins that will be exported from the cell. Protein synthesis requires the assistance of two other RNA molecules. Messenger RNA provides instructions from the cellular DNA for building a specific protein. Transfer RNA brings the protein building blocks, amino acids, to the ribosome. Once the protein backbone amino acids are polymerized, the ribosome releases the protein and it is transported to the Golgi apparatus. There the proteins are completed and released inside or outside the cell.
Eukaryotic cell features that would be found in photosynthetic cells.
Although all eukaryotic cells have a lot of common features, there are some features that are distinctive to photosynthetic cells. These features include cell walls, chloroplast and vacuole. However for the purpose of this assignment, I will describe only two these features.
One of the cell features distinct only to photosynthetic cells is the chloroplast. Only the photosynthetic eukaryotic cells have chloroplasts. These organelles convert solar energy into a chemical energy (food) which is the process of photosynthesis. The chloroplast has oval-like shapes. It contains two outer membrane layers that enclose the semi fluid interior called the stroma. There is also an inner membrane, called the thylakoid membrane that is found in the stroma. This thylakoid membrane forms a single sac or compartment. The first process of photosynthesis occurs when many light-trapping pigments, enzymes and other proteins are embedded in the thylakoid membrane. It continues until ATP is formed.
Another feature that is found only in photosynthetic cells is the central vacuole. The central vacuole is fluid-filled organelle that stores amino acids, sugars, ions and toxic wastes. It also helps the cell to grow. As fluid pressures build up inside the cell’s central vacuoles, it forces its pliable wall to enlarge thereby increasing the rate at which water and other substances can be absorbed across the plasma membrane.
