Understanding Requirements for Life and Cell Theory - Biology

The R group is a side chain connected to the central carbon atom in an amino acid. The central carbon atom of an amino acid can bind to four other groups. In an amino acid, the central carbon will always bind to a carboxyl group, and amine group, and a hydrogen atom. The fourth bond, however, will be different for each amino acid, linking the central carbon to the R group.

Waxes provide skin with a waterproof coating. Waxes are made out of fats.

Hemoglobin is a protein responsible for transporting oxygen. DNA polymerase repairs DNA molecules. Amylase is the protein that helps convert starch to glucose.

Proteins are synthesized through dehydration synthesis reactions, which is the removal of water between two amino acids. In this case, two hydrogen atoms are removed from the amine group and one oxygen is removed from the carboxyl group, forming a peptide bond between the carbon atom of one amino acid and the nitrogen atom of the other amino acid.

The sequence of amino acids is called a protein's primary structure. Each protein has a unique sequence of amino acids. A difference of just one amino acid in a chain of hundreds can be deadly to the organism. For example, mutation leading to a single amino acid change is responsible for sickle cell anemia.

A helix is formed when Hydrogen bonds occur between the amino group in one peptide bond and the carboxyl group of another in the same polypeptide chain.

The cell theory has three basic parts: all living things are made of cells, the cell is the smallest unit of life, and all cells come from preexisting cells. Prokaryotic cells are indeed cells and they do not contradict any tenets of the cell theory. However, they do not contain nuclei; rather, their genetic material is contained in the cytoplasm.

The pH of a solution is defined as the the concentration of H+ ions in the solution. The pH of a solution declines as H+ concentration increases. On the pH scale, ranging from 0 to 14, 7 is neutral. Substances below 7 are more acidic, 0 being the most acidic. Substances above 7 are more basic, 14 being the most basic.

“Composed of plutonium” is not a characteristic of a living organism. The other three choices are characteristics of living organisms. Organisms use energy in their metabolic processes. Organisms reproduce either asexually or sexually to make offspring for the next generation. Organisms from the simplest prokaryote to the human species contain DNA—the universal genetic code.

All amino acids contain carbon, hydrogen, oxygen, and nitrogen. These elements create a carboxylic acid group and an amine group, which can fuse to form a peptide bond. Peptide bonds hold amino acids together and generate the primary structure of the protein.

Cysteine, a specific amino acid, also contains sulfur. Thus, the correct answer is that carbon, oxygen, hydrogen, nitrogen, and sulfur can all be found in amino acids.

Phosphorus is never found in amino acids, but plays an important role in the structure of nucleic acids, such as DNA, and in the modification and activation of proteins.

All life forms must be able to uptake or produce energy to survive (metabolism), grow, and reproduce to propagate the species. While having a safe place to live is an ideal for most species, it is not a requirement of life.

These criteria can be tested by thinking of a single cell. A single cell requires energy, and can metabolize it via glycolysis (even in an anaerobic environment). A cell can grow, and does so during the G1 phase of the cell cycle. A cell is also capable of reproducing via mitosis. A single cells does not, however, require shelter; some cells live in highly extreme environments.

An object is considered as 'living' if it is able to grow through metabolism, adapt to the environment, and reproduce. All organisms are also composed of cells.

Ability to interact with other life forms is not a requirement for life.

The tertiary structure of a protein is created by various interactions between the R groups in the chain. This makes the protein fold three-dimensionally.

One example would be ionic bonds forming between a positively charged R group and a negatively charged R group. Covalent disulfide bonds will create a tertiary shape between two cysteine amino acids. Hydrophobic R groups will also contribute to the structure, bending toward one another to avoid contact with the aqueous environment.

A quaternary protein structure is made up of two or more polypeptide chains that fit together based on their shape and polarities, like a jigsaw puzzle. The subunits also fit together by forces of attraction between positively charged regions and negatively charged regions. Not all proteins have quaternary structure.

Active transport is used to carry amino acids from the lumen of the small intestine into the blood stream. Active transport requires the use of energy (ATP) in order to transport molecules. In this case, amino acids are large, blulky, and frequently polar. All of these characteristics make them hard to transport across a plasma membrane.

Steroids are derived from cholesterol, which is a lipid.

Many hormones are are classified as peptide hormones, and are made of protein. Keratin is a hard structural protein found in hair and nails. Enzymes are catalytic proteins that facilitate biochemical reactions in the body.

When a protein is exposed to extreme conditions, such as high temperature or acidity, the interactions that provide protein structure are disrupted. The result is denaturation, or the loss of structure.

When conditions are returned to optimal levels, the protein can often return to its normal structure and remain functional. Denaturation affects the interactions that give the protein shape, but does not affect the peptide bonds that hold amino acids together.

The four basic biological macromolecules carry out virtually every metabolic process of living organisms. Keep in mind that these molecules work together to achieve common goals. For example, enzymes (proteins) are used to help break down glucose (carbohydrate) in glycolysis. One product of glycolysis is energy in the form of ATP. ATP can be used to polymerize nucleotides (nucleic acids) to copy DNA.

The functions of specific types of macromolecules are highly dependent on their structures. For example, firbous proteins are used to provide structural support, while globular proteins are better suited to catalyze reactions as enzymes. The variety of macromolecular structures is directly related to the multitude of functions these molecules can facilitate.

All of these answers are characteristics of life. All organisms are capable of reproduction, respond to their surrounding environmental stimuli, process chemical energy, and grow and develop. This is true of organisms are any level, from animals like humans, down to the simplest prokaryotic bacteria.

DNA—deoxyribonucleic acid—is found in chromosomes within a cell’s nucleus. A complete set of DNA (i.e. 46 chromosomes) is called a genome. DNA contains instructions that make humans different from other species and other individuals. DNA provides instructions for all the proteins that the body makes and is passed from adults to offspring. DNA cannot get out of the nucleus; however, RNA can. RNA is used to get the instructions from DNA out of the nucleus and into the site of protein synthesis: the ribosomes within the cytoplasm. Proteins are made of amino acids and determine the structure and function of all of the body’s cells; therefore, this process can be simplified into “DNA to RNA to protein.”