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Created: April 06, 2001.
Revised: June 19, 2002.
Most disease involves problems with cells and many begin with problems in the genetic code. Therefore, it is important to have a basic understanding of cells and genetics.
The human body is comprised of individual cells, about 75 trillion (75,000,000,000,000) in total, consisting of about 200 different types. Each of these cells had to be produced from another cell and each cell generally must create new cells. Each cell contains the information needed to produce any type of cell, hence to produce a total human being. This information is contained in the genetic material within each cell, the DNA. As many diseases involve malfunctions of cells and of genetics, this chapter will provide a basic overview of the operation of the cell and of genetics.
There are many types of organisms that only have one cell. In these unicellular organisms, for example bacteria and protozoans, the single cell performs all life functions. In higher organisms, a division of labour has evolved in which groups of cells have differentiated into different cell types and into specialized tissues, which in turn are grouped into organs and organ systems.
Chemical components and reactions:
Cellular level:
-The basic unit of every living thing is the cell. Cells themselves are extremely complex, come in many different shapes and sizes, and serve countless different functions. Cells contain a number of internal structures called organelles that serve different functions.
Tissue Level:
-A group of similar cells gathered together is called a tissue. Tissues, which may be visible to the naked eye, include bone, muscle, fat, and skin.
Organs:
-Different kinds of tissue working together in the same place may form an organ. Organs, like the heart, lungs, eyes, and brain, perform specific tasks necessary for the body's survival.
Systems:
-Several organs can work together in a system. The organs of a system may be close together, or spread across the body. Some examples are the digestive, muscular, reproductive, respiratory, excretory, and nervous systems.
-Some kinds of tissue may be found in more than one system. Muscle tissue, for example, is part of the muscular, respiratory, and circulatory systems. Some organs, like the pancreas are also part of more than one system (in this case, the digestive and endocrine systems).
The circulatory system is the body's transport system. It is made up of a group of organs that transport blood throughout the body. The heart pumps the blood and the arteries and veins transport it. Oxygen-rich blood leaves the left side of the heart and enters the biggest artery, called the aorta. The aorta branches into smaller arteries, which then branch into even smaller vessels that travel all over the body. When blood enters the smallest blood vessels, which are called capillaries, and are found in body tissue, it gives nutrients and oxygen to the cells and absorbs carbon dioxide, water, and waste. This blood, now depleted of oxygen and nutrients, now becomes a waste removal system as it travels through the veins. The liver and kidneys filter the blood and once back in the lungs, carbon dioxide is expelled and a new load of oxygen is picked up.
A sub-component of the circulatory system is the lymphatic system. Lymph is
a watery fluid (containing white blood cells and antibodies) that washes through
all our tissues, passing through lymph node filters and eventually returning
to the blood stream. The lymphatic system is composed of lymph vessels, lymph
nodes, and organs. The functions of this system include the absorption of excess
fluid and its return to the blood stream, absorption of fat (in the villi of
the small intestine) and immune system function. Lymph vessels are closely associated
with the circulatory system vessels. Larger lymph vessels are similar to veins.
Lymph capillaries are scatted throughout the body. Contraction of skeletal muscle
causes movement of the lymph fluid through valves.
Lymph organs include the bone marrow, lymph nodes, spleen, and thymus. Bone marrow contains tissue that produces lymphocytes. B-lymphocytes (B-cells) mature in the bone marrow. T-lymphocytes (T-cells) mature in the thymus gland. Other blood cells such as monocytes and leukocytes are produced in the bone marrow. Lymph nodes are areas of concentrated lymphocytes and macrophages along the lymphatic veins. The spleen is similar to the lymph node except that it is larger and filled with blood. The spleen serves as a reservoir for blood, and filters or purifies the blood and lymph fluid that flows through it.
Summary: The lymphatic system is both part of circulation and also a defense
system for the body. It filters out organisms that cause disease, produces white
blood cells, and generates disease-fighting antibodies. It also distributes
fluids and nutrients in the body and drains excess fluids and protein so that
tissues do not swell. The lymphatic system is made up of a network of vessels
that help circulate body fluids. These vessels carry excess fluid away from
the spaces between tissues and organs and return it to the bloodstream.
The digestive system is made up of organs that break down food into vitamins, minerals, carbohydrates, and fats, which the body needs for energy, growth, and repair. After food is chewed and swallowed, it goes down the esophagus and enters the stomach, where powerful stomach acids further break it down. From the stomach, the food travels into the small intestine where it is again broken down into nutrients that are absorbed into the bloodstream through tiny hair-like projections in the walls of the intestine. Excess food that the body doesn't need or can't digest is turned into waste and is eliminated from the body.
The endocrine system is made up of a group of glands that produce the body's long-distance messengers, or hormones. Hormones are chemicals that control body functions, such as metabolism, growth, and sexual development. The glands, which include the pituitary gland, thyroid gland, parathyroid glands, adrenal glands, thymus gland, pineal body, pancreas, ovaries, and testes, release hormones directly into the bloodstream. The blood transports the hormones to organs and tissues throughout the body.
The immune system is our body's deface system against infections and diseases. Organs, tissues, and cells all work together to respond to intruder organisms (like viruses or bacteria) and other substances that may enter the body from the environment. There are three types of response systems in the immune system: the anatomic response, the inflammatory response, and the immune response. The anatomic response physically prevents threatening substances from entering your body. Examples of the anatomic system include the mucous membranes in the nose and lungs and the skin. If substances do get by, the inflammatory response goes on attack. The inflammatory system works by excreting the invaders from your body. Sneezing, runny noses and fever are examples of the inflammatory system at work. The third line of deface is the immune response. The central part of the immune system is made up of white blood cells, which fight infection by gobbling up antigens. About a quarter of white blood cells, called the lymphocytes, migrate to the lymph nodes and produce antibodies, which fight disease.
The muscular system is made up of tissues that work with the skeletal system to control movement of the body. Some muscles like the ones in your arms and legs are voluntary, meaning that you decide when to move them. Other muscles, like the ones in your stomach, heart, intestines and other organs, are involuntary. This means that they are controlled automatically by the nervous system and hormones you often don't even realize they're at work. The body is made up of three types of muscle tissue: skeletal, smooth and cardiac. Each of these has the ability to contract and relax which allows the body to move and function. Skeletal muscles help the body move. Smooth muscles, which are involuntary, are located inside organs, such as the stomach, blood vessels and intestines. Cardiac muscle is found only in the heart. Its motion is also involuntary.
The nervous system is made up of the brain, the spinal cord, and nerves. The nervous system is your body's control system. It sends, receives, and processes nerve impulses throughout the body. These nerve impulses tell your muscles and organs what to do and how to respond to the environment. There are three parts of your nervous system that work together: the central nervous system, the peripheral nervous system, and the autonomic nervous system. The central nervous system consists of the brain and spinal cord. It sends out nerve impulses and analyses information from the sense organs, which tell your brain about things you see, hear, smell, taste and feel. The peripheral nervous system includes the craniospinal nerves that branch off from the brain and the spinal cord. It carries the nerve impulses from the central nervous system to the muscles and glands. The autonomic nervous system regulates involuntary action, such as respiration, the heart and digestion.
The reproductive system allows humans to produce offspring. Sperm from the male fertilizes the female's egg, or ovum, in the fallopian tube. The fertilized egg travels from the fallopian tube to the uterus, where the fetus develops over a period of nine months.
The respiratory system brings air (oxygen) into the body and removes carbon dioxide. It includes the nose, trachea, and lungs. When you breathe in, air enters your nose or mouth and goes down a long tube called the trachea. The trachea branches into two bronchial tubes, or primary bronchi, which go to the lungs. The primary bronchi branch off into even smaller bronchial tubes, or bronchioles. The bronchioles end in the alveoli, or air sacs. Oxygen follows this path and passes through the walls of the air sacs and enters the blood stream. At the same time, carbon dioxide passes from the blood out into the lungs and is exhaled.
The skeletal system is made up of bones, ligaments and tendons. It shapes the body and protects organs. The skeletal system works with the muscular system to help the body retain its shape and to move. Within bone is marrow, which is a soft, fatty tissue that produces red blood cells, many white blood cells, and other cells important in the immune system.
Overall, the excretory system regulates the chemical composition of body fluids by removing metabolic wastes (waste products created as metabolism occurs) and retaining the proper amounts of water, salts, and nutrients. Waste products are created inside cells. Cells use amino acids to construct proteins and other nitrogen-containing molecules. Amino acids can also be oxidized for energy or converted to fats or carbohydrates.
When amino acids are oxidized or converted to other kinds of molecules, the amino (NH2) group must be removed. The nitrogen-containing compounds produced as a result of protein breakdown are toxic and must be removed by the excretory system. Nitrogenous wastes of animals are excreted in form of ammonia, urea, or uric acid.
Components of this system in humans include:
Kidneys: During circulation, blood passes through the kidneys in order to deposit used and unwanted water, minerals, and a nitrogen-rich molecule called urea. The kidneys filter the wastes from the blood, forming a liquid called urine. The kidneys funnel the urine into the bladder along two separate tubes called ureters. The bladder stores the urine until muscular contractions force the urine out of the body through the urethra. Each day, your kidneys produce about 1.5 liters of urine. All of it needs to be removed from your system. This occurs through urination.
Liver: Some proteins and other nitrogenous compounds are broken down in the liver by a process called deamination. As a result of these reactions, a nitrogen containing waste called urea is formed.
Lungs: Secrete and expel carbon dioxide.
Skin: Sweat comes out of pores in your skin. Sweat is a mixture of three metabolic wastes: water, salts, and urea. So as you sweat, your body accomplishes two things: 1) sweating has a cooling effect on the body, and 2) metabolic wastes are excreted.
Above based on http://www.factmonster.com/ipka/A0774536.html
http://www.uvm.edu/~inquiryb/webquest/fa06/mvogenbe/
Cell Theory:
Modern biology rests on some core assumptions about cells described in Cell Theory. Its major tenets are: 1) All living things are composed of one or more cells; 2) Chemical reactions take place within cells; 3) All cells originate from preexisting cells; and 4) Cells contain hereditary information, which is passed from one generation to another.
Cells can be separated into two major groups: prokaryote cells that do not have a central nucleus, for example, bacteria. Prokaryote cells are among the earliest and most primitive forms of life on earth. The second, larger group, are eukaryote cells, characterized by a cell nucleus (center). All organisms, other than bacteria, consists of one or more eukaryotic cells. Prokaryotes are smaller in size and simpler in internal structure than eukaryotes and are believed to have evolved much earlier.
All cells share a number of common properties; they store information in genes made of DNA, they use proteins as their main structural material; they build proteins using the information encoded in the DNA; they use a chemical called adenosine triphosphate (ATP) as the means of transferring energy for the cell's internal processes; and they are enclosed by a cell membrane, composed of proteins and a double layer of lipid (fat) molecules, that controls the flow of materials into and out of the cell.
The parts of a cell are called organelles (like organs in the body). Each organelle has a specific function within the cell. There are three main parts of a typical cell: the cell membrane holding the cell together, the cytoplasm containing the cytoskeleton and the various organelles of the cell and the nucleus, the center of the cell housing the DNA.
Based on: http://www.rkm.com.au/CELL/organelles/
Also see an excellent illustration at: www.rkm.com.au/CELL/animalcell.html
-Cell membrane: The cell membrane has proteins embedded in it, with the ends protruding out on the cell surface. This is an important feature as many of these proteins act as flags on the cells surface helping to identify it and interact with other cells, while others act as transport portals into and out of the cell. The cell membrane separates the cell from its surroundings and comprises a double molecular layer. It has an "oily" interior while both surfaces are attracted to water. The cell membrane is effectively continuous with the endoplasmic reticulum and the nuclear membrane.
-Centriole(s): bundles of microtubules. During cell division, the centrioles go to opposite sides of the cell and organize the microtubules that drag the chromosomes apart (so that one set each of the duplicated chromosomes end up in each daughter cell).
-Centrosome: generates microtubules.
-Chromatin: The substance of which eukaryotic chromosomes are composed.
-Cytoplasm: the area outside the nucleus but inside the cell membrane.
-Cytosol {SIGHT-oh-sol}: the salty semi-fluid filling the cytoplasm. Contains soluble elements and cytoskeletal structural elements. Water makes up to 60-65% of the cell.
-Endoplasmic reticulum (ER): Two types: smooth ER, rough ER. The smooth ER is continuous with the rough ER but has different functions. It is used in lipid synthesis, detoxification and other metabolic processes. The rough ER is used in protein synthesis.
-Golgi complex: Acts as a transport station, packaging materials (such as proteins from the ER) into vesicles and sending them off either to other organelles or for excretion (removal) from the cell. Also: The Golgi receives proteins synthesized in the rough endoplasmic reticulum. These are ferried to the Golgi by transfer vesicles. The proteins are then processed by the Golgi for export, membrane use or for inclusion in lysosomes.
-Lysosome(s): A sac similar to a vacuole containing powerful digestive enzymes used to break down large food particles within the cell and do other cell maintenance, for example, to destroy invading matter and unwanted cellular material (waste byproducts). Lysosomes originate from the Golgi and they contain a variety of powerful enzymes (hydrolases) that break down material. Aside: Prions (the rogue proteins associated with Mad Cow Disease) are resistant to degradation by lysosomal enzymes and so accumulate in the cell.
-Membrane: There are several important membranes in the cell, including the membrane surrounding the whole cell. These membranes are generally a fatty fluid like material that is semi permeable, meaning that some materials are able to pass in and out through the membranes.
-Microtubules: form a structure within the cell (like a scaffold) called the cytoskeleton. Also move things within the cell (like a pipeline).
-- production of energy
--Mitochondria play a special role in the cell and in disease.
--They are found in all eukaryotic cells.
--Mitochondria are small bodies floating in the cytoplasm, having a double membrane surrounding them.
--Production of energy takes place in the mitochondria via cellular respiration - the process by which organic molecules are broken down to release energy (in the form of heat and work) which the cell can store for later use. Sugar molecules (glucose) are broken down in a cellular "fuel" molecule called adenosine triphosphate (ATP).
--Each cell in our body contains, on average, between 500 and 2,000 mitochondria.
--Mitochondria have a small amount of their own DNA (called mtDNA), separate from the cell's DNA. mtDNA is inherited only form the mother.
--Mitochondria can create their own proteins and reproduce to form new mitochondria.
--Evidence suggests that perhaps mitochondria were once separate living organisms that somehow became incorporated into eukaryotic cells.
--Singular term: mitochondrion.
--When the mitochondria aren't functioning properly, an "energy crisis" can develop in tissues such as muscle, brain and heart, which normally are heavy energy consumers.
--Mutations in mitochondrial DNA (mtDNA) have been implicated or cause a number
of diseases including: Alzheimer's Disease, Parkinson's Disease, Exercise Intolerance,
Diabetes Mellitus, and Mitochondrial Myopathy.
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Mitochondrial Myopathy: -A number of biochemical defects in mitochondria have been discovered. -There is no single entity that can be diagnosed as a "mitochondrial myopathy." -In those mitochondrial defects in which a defective oxidative metabolism exists, a common result is a tendency for the muscles to generate large amounts of lactic acid. This is a consequence of needing to provide energy from the non-oxidative breakdown of the glycogen stored in the muscle. -In the same way that a car can show many different signs of engine problems, mitochondrial diseases - of which hundreds of varieties have been identified -- can cause a complex variety of symptoms. These include muscle weakness, muscle cramps, seizures, food reflux, learning disabilities, deafness, short stature, paralysis of eye muscles, diabetes, cardiac problems and stroke like episodes, to name a few. The symptoms can range in severity from life threatening to almost unnoticeable, sometimes taking both extremes in members of the same family. -Because some people have specific subsets of these symptoms, clinical researchers have grouped those that occur together into "syndromes," producing a complicated array of descriptive acronyms such as MELAS (mitochondrial encephalomyopathy with lactic acidosis and stroke like episodes) or MERRF (myoclonus epilepsy with ragged red fibers). -You may also hear the terms "mitochondrial myopathy" (indicating muscle involvement) or "mitochondrial encephalomyopathy" (indicating brain and muscle involvement). -The mitochondrial encephalomyopathies and myopathies are typically caused by defects in a part of the mitochondrion known as the respiratory chain or the electron transport chain. -MDA covers diseases in both of these categories, which include many different syndromes. The MDA website contains excellent information on these topics: http://www.mdausa.org/ |
-Nuclear envelope: A double layer that surrounds the nucleus and separates the interior of the nucleus from the rest of the cell. It is bridged by numerous nuclear pores and its outer layer is continuous with the membrane of the rough endoplasmic reticulum.
-Nuclear pore(s): Controls transport in and out of nucleus.
-Nucleus {New-CLEE-us}: Controls the cell's activities. The center of the cell containing the genetic material (DNA). The nucleus sits roughly in the middle of the cell and contains the cell's genetic information encoded in DNA. A double membrane, the nuclear envelope, which segregates the nuclear contents from the rest of the cell, surrounds the nucleus. Molecular portals, called nuclear pores, permit certain traffic in and out of the nucleus.
-Nucleolus {New-CLEE-ah-lus}: The nucleolus is a structure within the nucleus where the components of ribosomes are manufactured. These ribosomal components exit through the nuclear pores and enter the cytoplasm where they assemble into ribosomes.
-Peroxisome {per-OX-ah-some}: located in the cytoplasm, its function is to oxidize materials and then dispose of the resulting hydrogen peroxide.
-Proteasomes: use enzymes to disassemble and destroy proteins.
-Ribosomes (Two types): Bound or attached ribosomes are attached to the exterior (cytoplasmic side) of the rough endoplasmic reticulum. These ribosomes are busy with protein synthesis. Stringing them together is messenger RNA that directs protein manufacture as it passes through the ribosomes. The growing proteins project into the cavity (lumen) of the rough ER, which in places is continuous with the lumen of the nuclear envelope.
Free ribosomes float free in the cytoplasm. Messenger RNA threads into ribosomes. In addition, necklace-like arrangements represent polysomes (polyribosomes). Polysomes are variable in length and are strings of ribosomes joined by messenger RNA. As the mRNA feeds through these ribosomes, so proteins are synthesized. The proteins synthesized by these free ribosomes pass into the cytoplasm.
-Vacuoles: small sacks within the cell made up of a single-membrane, used for storage. They can contain various substances including proteins, water, carbohydrates and many other nutrients.
-Vesicles: very small vacuoles. Often vesicles are formed at a Golgi body and used to carry proteins either to other organelles or to the cell membrane.
Relative sizes:
-1 nm (nanometre) = one billionth of a metre (one thousandth of a micrometre)
-1 um (micrometre) = one millionth of a metre
-0.1 nm diameter of a hydrogen atom
-0.8 nm Amino Acid
-A one nanometre cube of diamond contains 176 diamond atoms
-2 NM Diameter of a DNA Alpha helix
-4 NM Globular Protein
-6 NM microfilaments
-10 NM thickness of cell membranes
-11 NM Ribosome
-25 NM Microtubule
-50 NM Nuclear pore
-100 NM Large Virus
-200 NM Centriole
-200 NM (200 to 500 NM) Lysosomes
-200 NM (200 to 500 NM) Peroxisomes
-(1 - 10 um) the general sizes for Prokaryotes
-1 um Diameter of human nerve cell process
-2 um E.coli - a bacterium
-3 um Mitochondrion
-5 um length of chloroplast
-6 um (3 - 10 micrometers) the Nucleus
-9 um Human red blood cell
-(10 - 30 um) Most Eukaryotic animal cells
-(10 - 100 um) Most Eukaryotic plant cells
-90 um Amoeba
-100 um Human Egg
-1 mm (1 millimetre, 1/10th of a centimetre)
-1 mm Diameter of the squid giant nerve cell
-2 mm Diameter of a frog egg
http://niko.unl.edu/bs101/notes/sizes.html
The various elements that make up the cell are:
-59% Hydrogen (H)
-24% Oxygen (O)
-11% Carbon ( C)
-4% Nitrogen (N)
-2% Others - Phosphorus (P), Sulphur (S), etc.
The molecules that make up the cell:
-50% protein
-15% nucleic acid
-15% carbohydrates
-10% lipids
-10% Other
http://www.cbc.umn.edu/~mwd/cell_www/cell_intro.html
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