Compendium Review Unit 1

Table of Contents

• • Introduction
• Life and biology
  • Molecules of life
  • Cell as fundamental unit
  • Cell organization and function
  • Cell metabolism
  • Cells organized into tissues
  • Cell junctions
• Organ systems
• Conclusion
  
  

Introduction

You should know right off that I do not consider myself a “scientific” kind of girl. Sure the world is a fascinating place and I like learning new things, but when I watched the introductory video and heard Professor Frolich go on about cells and how they worked, I must admit that I felt a little intimidated. However, once I got into the material I began to gain a real appreciation for the “fundamental unit of life” and the universe that it contains.

Life and Biology

• What is Life
  

The topic heading “What is life?” seemed kind of silly to me when I first saw it. It seemed so elementary. I thought to myself, “Of course I know this, everyone knows it.” Upon further reflection however, I realized that the definition of life was not something I had given much thought to. Biology is the study of life, and I am taking this course to gain a better understanding of human life, therefore it makes sense to start off with the basics. So what exactly constitutes life? Here is a short list, living things:

• Need energy
• Reproduce
• Grow and develop, beginning at fertilization and ending at death
• Respond to stimulus
• Are Homeostatic- maintain a stable internal condition
• Are highly organized
• Have an evolutionary history
  
• Evolution and the relationship between humans and other animals

In the slide show Professor Frolich stated that human beings “are living systems, no different from any other.” Life is organized hierarchically beginning at the smallest unit, the atom, all the way up to the biosphere. This is illustrated quite clearly in this graph, taken from our text book, Human Biology by Sylvia S. Mader.

Levels of biological organization, page 3-Human Biology, Sylvia S. Mader

This organization is explained in the text book through evolution, the process by which a species changes, evolves, over time. Although I understand that humans are simply living organisms like any other, I still see a difference. The text book talks about our cultural heritage and how we threaten the biosphere. It seems to me that this sets us apart. Also the incredible “organization” described in these chapters makes me think of intelligent design, it seems obvious to me, but that is all I will say on that subject.

All living things are classified under three domains, Eukarya, Archaea, and Bacteria. As far as classification, humans are vertebrates in the kingdom Animalia, of the domain Eukarya. Vertebrates are characterized by a nerve cord surrounded by a segmented vertebral column.

• Science

The scientific process is the way in which scientists study the natural world. The scientific method involves steps including: Observation, hypothesis, experiment/observation, conclusion and theory. Science uses this method to gain data in forming a theory. A scientific principle is a theory largely accepted as valid by an overwhelming number of scientists. Another way of collecting data is through a controlled study. In this “information age” we are often bombarded by new theories and scientific studies, but it is important to consider the source. Scientific journals are a great source as the information they contain goes through a rigorous review process and generally come directly from the scientist(s) who conducted the study.

Molecules of Life

• Atoms to molecules
  

This section blew my mind! Today I was mixing lemonade for Sunday school and was distracted by the thought of all the different molecules involved in the mixture, or should I say solution? I will never look at a pitcher of lemonade the same again! Molecules are made up of atoms that have bonded together to form a chemical unit. For example, water is the most abundant molecule in living organisms and is formed by one oxygen and two hydrogen atoms. Water usually makes up about 60-70% of total body weight, and is essential to life.

• The four molecules of life
  

The four molecules of life are carbohydrates, lipids, proteins, and Nucleic acid or DNA/ RNA.

• Carbohydrates

Carbohydrates are made up of simple sugars and are broken up in the mitochondria for energy. There are simple carbohydrates, monosaccharides like glucose, and complex carbohydrates, polysaccharides, like starches.

• Lipids

Lipids are fats and oils. Fats usually come from animals, and oils usually come
from plants. In mammals and other vertebrates Lipids function as long term
energy storage. Phospholipids are also especially important in forming cell
membranes. Cell membranes are important because they separate the cell from its
environment.

The above graphic shows three different ways to depict
phospholipids. This diagram comes from http://bioweb.wku.edu/courses/BIOL115/Wyatt/Biochem/Lipid/Lipid_2.asp

Although too much fat can be a problem, humans still need fat to be healthy. Unsaturated fatty acids that have double bonds in the carbon chain, for example cooking oils, are liquid at room temperature. Saturated fatty acids do not have double bonds between carbon atoms, for example butter, and are more or less solid at room temperature. Reading nutrition facts on food products helps consumers know how much fat is in a product.

• Proteins

The primary importance of proteins is in the structure and function of cells. Proteins are composed of amino acids. The amino acids are linked together with peptide bonds, forming a chain. The level of organization in proteins is very complicated. As far as I can understand, there are at least three levels of protein organization, the primary structure, secondary structure, and tertiary structure. Correct folding in the amino acid chain is very important. Improper folding or change in shape can result in diseases such as Alzheimer’s. The Blue Gene IBM Project is using a super computer to try to solve this problem. It seemed to me to be an innovative and creative way to do this.

• Nucleic Acids

Nucleic acids are the DNA and RNA. A strand of DNA is known as a nucleotide composed of phosphate, deoxyribose, and bases. A single DNA strand is extremely complex and contains the genetic information on an organism. DNA replicates itself in order to pass on information. It also undergoes transcription to mRNA to be transcribed into proteins. DNA can be identified by its double helix structure.

Model of a Eukaryotic animal cell, page 45- Human Biology, Sylvia S. Mader

Cell as fundamental unit

Cells and all their parts are made up of the molecules discussed earlier, carbohydrates, lipids, proteins, and nucleic acids. There are two kinds of cells prokaryotic and eukaryotic. Prokaryotic cells are small and relatively simple without a nucleus. An example would be bacteria. The first life was cellular life and the prokaryotic cell is thought to be evidence of this. Eukaryotic calls are complex, and much larger. They are internally organized with a nucleus and organelles. All multi cellular organisms, like plants and animals are made out of eukaryotic cells.

Eukaryotic cells can do a number of things. First of all they are able to maintain homeostasis by separating themselves from the outside environment. The plasma membrane controls what goes in and what comes out. These cells can also, produce proteins, catalyze chemical reactions, breakdown sugars in the mitochondria to produce energy, organize the distribution of molecules, and move. I will describe the organization of eukaryotic cells, their parts and how they function in the next section.

Cell organization and function

• Plasma Membrane
  

This part of the cell has a bylayer of phospholipids and is embedded with proteins. This membrane is essential for the life of the cell. The plasma membrane is "selectively permeable," in other words it allows some things in and keeps others out. The ways that things move across the plasma membrane are diffusion, osmosis, facilitated transport, active transport, endocytosis, and exocytosis.

Selective permeability: This picture from our text book illustrates how certain substances cannot cross the plasma membrane, The arrows crossing the membrane indicate substances that can diffuse across the membrane. Page 46- Human Biology, Sylvia S. Mader

Diffusion is where the molecules basically distribute themselves in equal concentration. Osmosis is the diffusion of water over the membrane. Certain solutions can effect cell in specific ways depending on their tonicity. An isotonic solution has the same concentration of nondiffusible solutes and water on either side of the plasma membrane. Hypertonic and hypotonic solutions can cause cells to shrivel or swell respectively, depending on the concentration of solute.

Sometimes molecules are transported across the plasma membrane by protein carriers. When this occurs at a higher rate than usual from the site of higher concentration to lower, it is called facilitated transport. This means of transport is passive and does not require an expenditure of energy. Active transport is pretty much the opposite, molecules are transported across the membrane from areas of lower concentration to higher. This action does require energy through the breakdown of ATP.

An excellent illustration of Endocytosis and Exocytosis. Page 48- Human Biology, Sylvia S. Mader

When I read about endocytosis and exocytosis I also learned the word "invaginate." I had to look it up. It means "To insert or receive as into a sheath,; To fold or draw back within itself; To form a pocket by turning in." This definition along with the pictures and animation from the web links helped me to get a better handle of this concept. So basically in endocytosis, a part of the plasma membrane "invaginates" to surround a particular substance. Then this pocket that is formed by the membrane pinches off and forms a endocytic vesicle inside the cell. Some White blood cells do this when they encounter pathogens. Exocytosis is the opposite, a vesicle fuses to the plasma membrane, the membrane opens to the outside and releases the substance. Very cool!

• Nucleus

The nucleus of the cell is where the genetic information is stored. Inside the nucleus is chromatin which coils into chromosomes. Chromosomes contain a DNA molecule and certain proteins. There is also the nucleolus which contains rRNA. I should point out that red blood cells do not have a nucleus. The nucleus is separated from the cytoplasm by a porous nuclear envelope which connects with the endoplasmic reticulum which is part of the endomembrane system.

• The endomembrane system
  

This system includes the nuclear envelope, endoplasmic reticulum, the Golgi Apparatus, lysosomes, and vesicles. The endoplasmic reticulum has two parts, the rough ER and the smooth ER. The rough ER is studded with ribosomes on the outside of the membrane facing the cytoplasm (the semi fluid medium containing organelles). Ribosomes are organelles, structures within the cytoplasm that perform specific functions. Ribosomes are composed of protein and rRNA. They perform protein synthesis. proteins enter the interior of the ER and undergo processing and modification. Some of these proteins are for export and some are incorporated into the membrane. The smooth ER does not have ribosomes and synthesizes the phospholipids for the membranes. The smooth ER can have other functions depending on the cell.

The Golgi Apparatus looks like a stack of pancakes. The Golgi Apparatus receives proteins and lipids from the ER and modifies them. Lysosomes are membranous sacs produced by the Golgi Apparatus and are found in all cells of the body. Vesicles are also bound by membranes and have the role of storing and transporting substances.

• Cytoskeleton
  

The cell's cytoskeleton serves to maintain the cell's shape and also anchors oganelles. The cytoskeleton also assists in movement. Cilia and flagella are composed of microtubules and are used in movement. Cilia are about twenty times shorter than flagella.


Cell Metabolism

In the cell city tour, mitochondria are characterized as the power plants for the cell. Basically, mitochondra take glucose products and convert them into ATP. This process uses up oxygen that gives off carbon dioxide, thus the term, cell respiration. Protein, lipids, and carbohydrates are also involved in cellular respiration. Mitochondrian look like pictures of bacteria to me, which as the book says "supports the hypothesis that they were originally prokaryotes engulfed by a cell."

This picture illustrates the production of ATP during cellular respiration- Human Biology, Sylvia S. Mader

Cells can also produce ATP without oxygen through glycolysis and fermentation. These processes are called anaerobic and produce two ATP. Anaerobic systems occur in the cytoplasm and are helpful for short bursts of energy.


I will say that I visited the site with the with the e coli bacteria and ran my mouse over all the reactions. I did find glycolysis but not the kreb's cycle.

E Coli http://biocyc.org/ECOLI/new-image?type=OVERVIEW&force=t

Cells organized into tissue

Tissues are made up of specialized cells, all of the same type, that perform a common function for the body. There are four major types of tissue.

• Connective tissue

Connective tissue is for binding and supporting body parts. There are lots of kinds of connective tissue. Fibrous connective tissue is found supporting many internal organs like the lungs. Adipose tissue is also fibrous and is used to store fat. Cartilage is a supportive connective tissue and can be found around the nose, and in the outer ear. Bones are the most rigid connective tissue.

I was surprised to learn that blood is a connective tissue, so is lymph.

• Muscular tissue

Muscular tissue serves to move the body. Muscle fibers make up muscular tissue. There are three types of muscular tissue, Skeletal, smooth, and Cardiac. Cardiac muscle tissue is found only in the heart.

• Nervous Tissue

Nervous tissue is composed of neurons and neuroglia. Neurons are nerve cells and neurolgia support and nourish the neurons. These cells form the nervous system.

• Epithelial Tissue

The epithelium is composed of tightly packed cells that form a continuous layer.You will find epithelial tissue lining body cavities and organs.Of particular interest to me was glandular epithelial,. I learned that a gland can be just one epithelial cell or many.This tissue excretes a product which makes it glandular.

Cell junctions

Cell junctions make it possible for tissue to perform a particular function. Cell junctions take place when plasma membranes join in these three ways.

• Tight junctions

At these junctions adjacent plasma membranes actually join, kind of like a zippper. This causes the layer of cells to become an impermeable barrier You will find these junctions in the tissue lining the kidneys.

• Adhesion junctions

Cytoskeletal fibers of one cell firmly attach to another.Adhesion junctions are foulnd in tissues subject to mechanical stress.

• Gap Junctions

When adjacent plasma membranes converge, leaving a tiny gap between them, this is a gap junction. There are gap junctions between cardiac muscle cells.

Organ systems

There are eleven organ systems discussed in the text.

Integumentary system- The skin helps Maintain homeostasis (controls temperature), protects the body, receives sensory imput, and synthesizes vitamin D.

Cardiovascular system-Includes the heart, veins, and arteries. The heart pumps the blood throughout the body.

Lymphatic and immune systems- These systems help defend against disease. They also help absorb fat and control fluid balance.

Digestive system-This system includes the esophagus, intestines, and stomach. These help in digestion.

Respiratory system- Obviously the lungs are part of this system, and help with the intake of oxygen.

Urinary system- Includes kidneys and bladder. THis system excretes wastes.

Skeletal system- The skeletal system supports the body and produces blood cells in the bone marrow.

Muscular system- The muscles move the body, maintain posture, and produce heat.

Nervous system- This system includes the brain, nerves and spinal cord. These organs receive sensory imput, initiate motor output, and help coordinate organ systems.

endocrine system- This system produces hormones, responds to stress, and helps regulate fluid and PH balance.

Reproductive system- The reproductive system produces and transports gametes, It also produces sex hormones.

Conclusion

At the end of his presentation, ProfessorFrolich said that the number of cells in the human body is about one hundred trillion cells (is that more than the national deficit?- I think it is close). Even before learning that number I had already decided that cells blow my mind. Cells are a universe in and of themselves. the more we understand cells and how they work within our bodies, the more equipped we will be to improve our lives.

Sources:

http://biocyc.org/ECOLI/new-image?type=OVERVIEW&force=t

folding.stanford.edu/index.html

Human Biology, Sylvia S. Mader