Anatomy & Physiology (I)

생체의공학 개론김 태 성

경희대학교 생체의공학과

Introduction

• Biomedical Engineering = Engineering + Life Sciences• Need to understand the basic components of the body and how they function. That is Anatomy and Physiology• Anatomy = internal and external structures of the body and their physical relationships• Physiology = study of the functions of the structures

Cellular Organization

Organization of the Cell• Two major parts: nucleus

and cytoplasm• Nuclear membrane:

separates nucleus from the cytoplasm

• Cell membrane: separates cytoplasm from the surrounding fluid

• The rest are called protoplasm (water, electrolytes, proteins, lipids, and carbohydrates)

Composition of Protoplasm I• Water: 70~85 percents of the cell. Cellular chemicals

dissolved. Others suspended• Ions: Most important (potassium, magnesium, phosphate,

sulfate, bicarbonate). Small quantities of sodium, chloride, and calcium. The ions provides inorganic chemicals for cellular reactions. Also necessary for operations of some of the cellular control mechanisms.

• Proteins: Most abundant substances. 10~20 percent of the cell mass. Two types (structural proteins and globular proteins)• Structural proteins: In the forms of long thin filaments (polymers of

many basic proteins molecules). Provides the contractile mechanism of all muscles. Other types of filaments are organized into microtubules that provides the cytoskeletons of cilia, nerve axons, and etc.

• Globular proteins: Composed of individual protein molecules. Mainly the enzymes. Often soluble in the cell fluid. Adherent to membranous structures in the cell.

Composition of Protoplasm II

• Lipids: Common property of being soluble in fat solvents. Most important lipids are phospholipidsand cholesterol (two are insoluble in water, and, therefore, are used to form the cell membrane as well as intracellular membranous barriers that separate the different cell compartments.• Some cells contain large quantities of triglycerides (or

neutral fat). These fat cells store fat as the body’s main storehouse of energy-giving nutrient.

• Carbohydrates: Little structural functions, but play a major role in nutrition of the cell. Human cells do not maintain large stores of carbohydrates (1~3 percents of the cell mass)

Physical Structure of the Cell• A cell contains the internal organellesin the cytoplasm and in the nucleus.• Ex) Without mitochondria, more than 95 percent of the cell’s energy supply stops.

Cell Membrane I• Most organelles of the cell are covered by membranes composed primarily of

lipids and proteins.• The lipids of the membranes provide a barrier that prevents movement of

water and water-soluble substances from one cell compartment to the other (why? The water is not soluble in the lipids)

• Protein molecules often penetrate all the way through the membrane, thus providing specialized pathways called pores.

• Cell membrane is a thin, pliable, elastic structure only 7.5 to 10 nanometers thick (55% proteins, 25% phospholipids, 13% cholesterol, 4% other lipids, 3% carbohydrates)

Cell Membrane II• Lipid Barrier of the Cell Membrane Prevents Water

Penetration• Basic structure is a lipid bilayer• The bilayer is composed of phospholipid molecules. One end is

hydrophilic (soluble in water), the other is hydrophobic (soluble only in fats)

• Which side is hydrophilic and hydrophobic?• Water-soluble substances (ions, glucose, urea) are impermeable to

the usual water-soluble substances. Fat-soluble substances (oxygen, carbon dioxide, alcohol, cholesterol) can penetrate the cell membrane with ease.

• Cell Membrane Proteins• Two types: integral proteins (protrude all the way through the

membrane) peripheral proteins (attached only to one surface of the membrane and do not penetrate)

• Integral proteins provide structural channels (pores). Water and water-soluble molecules (ions) can diffuse through

• Some integral proteins acts as carrier proteins for transporting substances. Sometimes against diffusion gradients (called active transport)

Cytoplasm and Its Organelles

• Cytoplasm is filled with both minute and large particles and organelles. • Cytosol: clear fluid portion of the cytoplasm in which contains dissolved proteins, electrolytes, and glucose • Dispersed in the cytoplasm are neutral fat globules, glycogen (insoluble polymer of glucose) granules, ribosomes, secretory vesicles, and five most important organelles (endoplasmic reticulum, Golgi apparatus, mitochondria, lysosomes, and peroxisomes)

Endoplasmic Recticulum• A network of tubular and flat vesicular structure• The tubules and vesicles interconnect with one another• The space inside the tubules and vesicles is filled with endoplasmic

matrix (a watery fluid medium)• Mainly conduction system: substances enter the space and conducted

to other parts of the cell• Vast surface area and multiple enzyme systems are attached to the

membrane to share metabolic functions of the cell.

• Granular endoplasmic reticulum: ribosomes are attached. Ribosomes are composed of a mixture of RNA (ribonucleic acid) and proteins and they function in the synthesis of new protein molecules

• Agranular (=smooth) endoplasmic reticulum, where no attached ribosomes. It functions in the synthesis of lipid substances.

Golgi Apparatus• Composed of four or more stacked

layers of thin, flat enclosed vesicles lying near one side of the nucleus.

• Functions in association with endoplasmic reticulum (ER)

• ER vesicles (transport vesicles) continually pinch off from the ER and shortly thereafter fuse with the Golgi apparatus. Why? (Substances entrapped in the ER vesicles are transported from ER to Golgi apparatus)

• Substances are processed in the Golgi apparatus to form lysosomes.

Lysosomes

• Vesicular organelles that form by breaking off from the Golgi apparatus and then dispersing throughout the cytoplasm• Lysosomes provide an intracelluar digestive system that allows the cell to digest within itself (1) damaged cellular structures (2) food particles that have been ingested by the cell (3) unwanted matter such as bacteria

Formation of Proteins, Lipids, and Cellular Vesicles

• Major functions of the endoplasmic reticulum and Golgi appratus: formation of proteins, lipids, and cellular vesicles

Peroxisomes

• Similar physically to lysosomes, but different in two important ways (1) they are believed to be formed by self-replication or budding off from the smooth ER (2) they contain oxidases.

• Oxidases are capable of combining oxygen with hydrogen ions to form hydrogen peroxide (H2O2), a highly oxidizing substance

• This is used in association with catalase, another oxidize enzyme in peroxisomes to oxidize many substances that might be otherwise poisonous to the cell

• About half of the alcohol a person drinks is detoxified by the peroxisomes of the liver cells in this manner

Mitochondria

• Powerhouses of the cell• Without mitochondria, the cells would be unable to extract

energy from nutrients• Number varies according to the energy need by the cell• Variable in size and shape• Inner membrane form shelves where oxidative enzymes are

attached. They cause oxidation of nutrients, thereby forming carbon dioxide and water, releasing energy

• Energy is used to synthesize a high-energy substance called adenosine triphosphate (ATP)

• ATP is transported out of mitochondria to wherever it is needed

• Mitochondria are self-replicative (one mitochondrion can form a second one). This means they contain DNA.

Formation of ATP • Cells extract energy when

carbohydrates, fats, and proteins react with oxygen.• Carbohydrates converted

into glucose• Proteins converted into

amino acids• Fats into fatty acids

• Most oxidative reactions occur inside mitochondria to form high energy compound ATP

• ATP = Adenine + Ribose + phosphate

• Citric Acid Cycle or Krebs Cycle

Uses of ATP for Cellular Function• ATP is used to promote three major categories of cellular functions

• Membrane transport: ex) to supply energy for the transport of sodium through the cell membrane

• Synthesis of chemical compounds: ex) to promote protein synthesis by the ribosomes

• Mechanical work: ex) to supply the energy needed during muscle contraction• Energy is also required for membrane transport of potassium, calcium, magnesium,

phosphate, chloride, and etc. Membrane transport is so important to cell function that some cells use as much as 80 percent of the ATP.

• Cells synthesize phospholipids, cholesteriol, etc.

• Muscle contraction of a muscle fiber requires expenditure of tremendous quantities of ATP

• ATP is always available to release its energy rapidly and almost explosively wherever in the cell it is needed

• More than 95 percent of ATP is formed in the mitochondria, the powerhouse of the cell.

Nucleus• The nucleus is the control center of

the cell• The nucleus contains large

quantities of DNA (=genes)• Genes determine the characteristics

of the cell’s protein, including structural proteins as well as the enzymes of the cytoplasm

• Genes control reproduction• Genes reproduce themselves to

give two identical sets of genes. And the cell splits by a special process called mitosis to form two daughter cells.

Nuclear Membrane and nucleoli

• Nuclear membrane is two separate bilayer membranes• The outer membrane is continuous with the ER.• The nuclear membrane is penetrated by several thousand nuclear pores.• Nucleoli (or nucleolus) inside nuclei do not have a limiting membrane• It is an accumulation of large amount of RNA and proteins found in

ribosomes.• Specific DNA genes cause RNA to be synthesized. Some of this is

stored in the nucleoli, but most of it is transported outward and used in conjunction with specific proteins to assemble mature ribosomes.

The Genes• The genes located in the nuclei of all cells of the

body, control heredity from parents to children• Also the same genes control day-to-day function

of all the body’s cells• The genes control cell function by determining

which substances are synthesized within the cell• There are about 100,000 different genes in each

cell, it is theoretically possible to form a vary large number of different cellular proteins.

• Some of the cellular proteins are structural proteins to form various intracelluar organelles.

• Majority of proteins are enzymes that catalyze different chemicals reactions in the cells.

The Genes• The genes are attached in long double-

stranded helical molecules of DNA• Basic building blocks of DNA include (1)

phosphoric acid, (2) deoxyribose, and (3) four bases (two purines, adenine and guanine, and two pyrimidines, thymine and cytosine)

• The purine base adenine (A) of one strand always bounds with the pyrimidine base thymine (T) of the other strand

• The purine base guanine (G) always bonds with the pyrimidine base cytosine (C).

Genetic Code• Fig. 3-6• The importance of DNA lies in its ability to control the formation of proteins in the cell (genetic code)• In Fig. 3-6, the top strand of DNA carries its own genetic code. Reading from left to right, the genetic code is GGC, AGA, CTT, the triplets being separated from one another by arrows.• In Figs. 3-7 and 3-8, these three triplets are responsible for successive placement of the three amino acids, proline, serine, and glutamic acid

Genetic Code

Transcription:Transfer of DNA Code to an RNA Code

• DAN genes of the nucleus control the chemical reactions of the cytoplasm through RNA.• RNA formation is also controlled by DNA• In Fig. 3-7, the code is transferred to the RNA through the process called transcription. • The RNA then diffuses from the nucleus through the nuclear pores into the cytoplasmic compartment, where it controls protein synthesis

Synthesis of RNA• During synthesis of RNA, two strands of DNA molecules

separate temporarily; one of these strands is used as a template for synthesis of the RNA molecules.

• The code triplets in the DNA cause the formation of complementary code triplets (called codons) in the RNA; these codons in turn control the sequence of amino acids in a protein to be synthesized later in the cytoplasm

• When one strand of DNA is used in the manner to cause the formation of RNA, the opposite strand remains inactive.

• Basic building blocks of RNA are almost same as DNA, but the sugar deoxyribose is not used in the formation of RNA, instead ribose (R) is used. And thymine (T) is replaced by another pyrimidine, uracil (U).

• RNA contains the bases adenine (A), guanine (G), cytosine (C), and uracil (U). Note these are the same as the bases in DNA except for one of them; the uracil (U) in RNA replaces the thymine (T) in DNA

• Activation of the RNA nucleiotides in the synthesis of RNA is by RNA polymerase.

Types of RNA• Messenger RNA: carries the genetic code to the cytoplasm for controlling the formation of the proteins• Transfer RNA: transports activated amino acids to the ribosomes to be used in assembling the protein molecules.• Ribosomal RNA: forms the ribosomes. The ribosomes are the physical and chemical structures on which protein molecules are actually assembled.

Translation:Formation of Proteins on Ribosomes

• Shows the functional relation of messenger RNA to the robosomes and the manner in which the ribosomes attach to the membrane of the endoplasmic reticulum

• The process of translation occurring in several ribosomes at the same time in response to the same strand of messenger RNA.

• The newly forming polypeptide (protein) chains passing through the endoplasmic reticulum membrane into the endoplasmic matrix.

Other DNA-Genetic Functions

• Genetic Regulation: activities of the genes themselves are controlled• Cell Reproduction: Genes and their regulatory mechanism determine the growth characteristics of the cells and also when or whether these cells divide to form new cells• Cell Mitosis: Actual process by which the cell splits into two new cells• Cell Differentiation: A special characteristics of cell growth and cell division. That is the cells proliferate in the embryo to form the different bodily structures and organs.

What is Cancer?

• Cancer is caused by mutation or abnormal activation of cellular genes that control cell growth and cell mitosis

• Abnormal genes are called oncogenes: as many as 100 different oncogenes are discovered

• Antioncogenes suppress the activation of specific oncogenes

• Loss of or inactivation of antioncogenes allows activation of oncogenes that lead to cancer

• Characteristics of cancer cells• The cancer cell does not respect usual cellular growth limits• Cancer cells often are far less adhesive to one another than

are normal cells. Thus wander through the tissues.• Some cancers produce angiogenic factors that cause formation

of new blood vessels into the cancer.