Biology

5 Biology



Chapter outline


Biology Basics

Water

Biologic Molecules

Metabolism

The Cell

Cellular Respiration

Photosynthesis

Cellular Reproduction

Genetics

DNA

Review Questions

Answers to Review Questions


Key terms


Alleles


Amino Acids


Binary Fission


Chromosomes


Codon


Cytokinesis


Deoxyribonucleic Acid (DNA)


Electron Transport Chain


Glycolysis


Golgi Apparatus


Heterozygous


Homozygous


Interphase


Krebs Cycle


Meiosis


Messenger RNA (mRNA)


Metabolic Pathway


Metaphase Plate


Mitosis


Organelles


Phagocytosis


Phospholipids


Photosynthesis


Punnett Square


Ribonucleic Acid (RNA)


Rough ER


Smooth ER


Steroids


Stop Codon


Transcription


Transfer RNA (tRNA)


Biology is the scientific study of life. Members of the health professions naturally deal with biology, whether it requires knowing the structure of a cell, understanding how a molecule will react to a medication or treatment, or comprehending how certain organisms in the body function. Prospective students desiring to enter one of the health professions should have a basic knowledge of biology.


This chapter reviews the structure and reactions of cells and molecules. The concepts of cellular respiration, photosynthesis, cellular reproduction, and genetics are also presented.



Biology Basics


In biology, there is a hierarchic system of organization. The system is most inclusive as kingdom and least as species. The order is as follows:


• Kingdom

• Phylum

• Class

• Order

• Family

• Genus

• Species

Most scientists agree that the core theme in biology today is the idea of evolution. Charles Darwin first introduced this notion in 1859 in his book On the Origin of Species. He proposed that current species arose from a process he called “descent with modification.”


Science is a process. For an experiment to be performed, the following steps must be taken:


• The first step is hypothesis, which is a statement or explanation of certain events or happenings.

• The second step is the experiment, which is a repeatable procedure of gathering data to support or refute the hypothesis.

• The final step in the scientific process is the conclusion.


Water


Water is the substance that makes life possible. The molecule itself is simply two hydrogen atoms covalently bonded to one oxygen atom. The most significant aspect of water is the polarity of its bonds.


It is the polar nature of water that allows for hydrogen bonding between molecules. This type of intermolecular bonding has several resulting benefits. The first of these is water’s high specific heat.


The specific heat of a molecule is the amount of heat necessary to raise the temperature of 1 gram of that molecule by 1° Celsius. Water has a relatively high specific heat value, which allows water to resist shifts in temperature. One powerful benefit is the ability of oceans or large bodies of water to stabilize climates.


Hydrogen bonding also results in strong cohesive and adhesive properties. Cohesion is the ability of a molecule to stay bonded or attracted to another molecule of the same substance. A good example is how water tends to run together on a newly waxed car. Adhesion is the ability of water to bond to or attract other molecules or substances. When water is sprayed on a wall, some of it sticks to the wall. That is adhesion.


When water freezes, it forms a lattice, which actually causes the molecules to spread apart, resulting in the phenomenon of floating. Most molecules, when they are in the solid form, do not float on the liquid form of the substance. If ice did not float, lakes would freeze from the bottom to the top. Life could not exist as we know it.


The polarity of water also allows it to act as a versatile solvent. Water can be used to dissolve a number of different substances (Figure 5-1).


image

Figure 5-1 Water as a solvent. The polar nature of water (blue) favors ionization of substances in solution. Sodium (Na+) ions (pink) and chloride (Cl−) ions (green) dissociate in the solution.


(From Patton KT, Thibodeau GA: Anatomy and physiology, ed 7, St Louis, 2010, Mosby.)



Biologic Molecules


There are multitudes of molecules that are significant to biology. The most important molecules are carbohydrates, lipids, proteins, and nucleic acids.



Carbohydrates


Carbohydrates are generally long chains, or polymers, of sugars. They have many functions and serve many different purposes. The most important of these are storage, structure, and energy.



Lipids


Lipids are better known as fats, but specifically they are fatty acids, phospholipids, and steroids.



Fatty Acids


Fatty acids vary greatly but simply are grouped into two categories: saturated and unsaturated. Saturated fats contain no double bonds in their hydrocarbon tail. Conversely, unsaturated fats have one or more double bonds. As a result, saturated fats are solid, whereas unsaturated fats are liquid at room temperature. Saturated fats are those the general public considers detrimental; cardiovascular problems are likely with diets that contain high quantities of saturated fats.



Phospholipids


Phospholipids consist of two fatty acids of varying length bonded to a phosphate group. The phosphate group is charged and therefore polar, whereas the hydrocarbon tail of the fatty acids is nonpolar. This quality is particularly important in the function of cellular membranes. The molecules combine in a way that creates a barrier that protects the cell.



Steroids


The last of the lipids are steroids. They are a component of membranes, but more important, many are precursors to significant hormones.



Proteins


Proteins are the most significant contributor to cellular function. They are polymers of 20 molecules called amino acids. Proteins are complex, consist of several structure types, and are the largest of the biologic molecules. Enzymes are particular types of proteins that act to catalyze different reactions or processes. Nearly all cellular function is catalyzed by some type of enzyme.



Nucleic Acids


Nucleic acids are components of the molecules of inheritance. Deoxyribonucleic acid (DNA) is a unique molecule specific to a particular organism and contains the code that is necessary for replication (Figure 5-2). Ribonucleic acid (RNA) is used in transfer and as a messenger in most species of the genetic code.


image

Figure 5-2 The DNA molecule. Representation of the DNA double helix showing the general structure of a nucleotide and the two kinds of “base pairs”: adenine (A) (blue) with thymine (T) (yellow) and guanine (G) (purple) with cytosine (C) (red). Note that the G–C base pair has three hydrogen bonds and an A–T base pair has two. Hydrogen bonds are extremely important in maintaining the structure of this molecule.


(From Patton KT, Thibodeau GA: Anatomy and physiology, ed 7, St Louis, 2010, Mosby.)



Metabolism


Metabolism is the sum of all chemical reactions that occur in an organism. In a cell, reactions take place in a series of steps called metabolic pathways, progressing from a standpoint of high energy to low energy. All of the reactions are catalyzed by the use of enzymes.



The Cell


The cell is the fundamental unit of biology. There are two types of cells: prokaryotic and eukaryotic cells. Cells consist of many components, most of which are referred to as organelles. Figure 5-3 illustrates a typical cell.


image image

Figure 5-3 Typical, or composite, cell. A, Artist’s interpretation of cell structure. Note, too, the innumerable dots bordering the endoplasmic reticulum. These are ribosomes, the cell’s “protein factories.” B, Color-enhanced electron micrograph of a cell. Both show the many mitochondria, known as the “power plants of the cell.” Note, too, the innumerable dots bordering the endoplasmic reticulum. These are ribosomes, the cell’s “protein factories.”


(From Patton KT, Thibodeau GA: Anatomy and physiology, ed 7, St Louis, 2010, Mosby. B, Courtesy A. Arlan Hinchee.)


Prokaryotic cells lack a defined nucleus and do not contain membrane-bound organelles. Eukaryotic cells have a membrane-enclosed nucleus and a series of membrane-bound organelles that carry out the functions of the cell as directed by the nucleus. In other words, prokaryotic cells do not have membrane-bound organelles, whereas eukaryotic cells do. The eukaryotic cell is the more complex of the two cell types.


There are several different organelles functioning in a cell at a given time; only the major ones are considered here.



Nucleus


The first of the organelles is the nucleus, which contains the DNA of the cell in organized masses called chromosomes. Chromosomes contain all of the material for the regeneration of the cell, as well as all instructions for the function of the cell. Every organism has a characteristic number of chromosomes specific to the particular species.



Ribosomes


Ribosomes are organelles that read the RNA produced in the nucleus and translate the genetic instructions to produce proteins. Cells with a high rate of protein synthesis generally have a large number of ribosomes. Ribosomes can be found in two locations. Bound ribosomes are those found attached to the endoplasmic reticulum (ER), and free ribosomes are those found in the cytoplasm. The two types are interchangeable and have identical structures, although they have slightly different roles.

Related posts:

  1. Reading Comprehension
  2. Chemistry
  3. Physics
  4. Mathematics

Stay updated, free articles. Join our Telegram channel
Tags:
Apr 10, 2017 | Posted by in NURSING | Comments Off on Biology

Full access? Get Clinical Tree
Get Clinical Tree app for offline access