Download Cell Physiology

Anatomy & Physiology (I)
생체의공학 개론
김태성
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 phospholipids
and 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 organelles
in 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.
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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 doublestranded 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.