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Physiology 1
LECTURE 1 NOTES
By Dr. Tom Madayag
THE CELL AND ITS FUNCTIONS
Organization of the Cell
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Nuclear membrane separates the nucleus from the cytoplasm
The cell membrane separates the cytoplasm from the surrounding fluids
All substances in the cell are collectively called the protoplasm
Composition of the Protoplasm
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Water
Electrolytes
Proteins
Lipids
Carbohydrates
Water
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Principal fluid medium of the cell
Consists of 70-75% of the cellular composition
Electrolytes/Ions
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Includes potassium, magnesium, phosphate, sulfate, bicarbonate and small amounts of sodium,
chloride, and calcium
Electrolytes provide inorganic chemicals for cellular reactions
Allows for transmission of electrochemical impulses in nerve and muscle fibers
Proteins
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After water the most abundant substances in the cell
Constitute 10-20% of cell mass
Two types of proteins:
o Structural
 In the form of long filaments
 To form microtubules (cytoskeletons) of cellular organelles, nerve axons, mitotic
spindles for cell division
 Fibrillar proteins found outside the cell especially in collagen and elastin fibers
of connective tissues and in blood vessel walls, tendons, ligaments
o Functional
 Combinations of a few molecules in tubular glandular form
 These proteins are mainly the enzymes of the cells
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Mobile in the cell fluid
Lipids
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Soluble in fat solvents
Examples are phospholipids and cholesterol
Constitute 2% of the cell mass
Mainly insoluble in water and therefore are used to form the cell membrane and intracellular
membrane barriers that separate the different compartments
Some cells contain large amounts of triglycerides (also called neutral fat)
Carbohydrates
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Have little structural functions
Major role is nutrition of the cell
About 1% is stored in cells, 3% in muscle cells and 6% in liver
Stored glucose is in the form of glycogen; when needed is depolymerized and used rapidly to
supply energy needs of the cell
Physical Structure of the Cell
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Organized physical structures are called intracellular organelles
Membranous structures
o Consist mainly of lipids and proteins
o These structure are: cell membrane, nuclear membrane, membranes of the
endoplasmic reticulum, membranes of the mitochondria, lysosomes, and Golgi
apparatus
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Protein molecules in the membrane often penetrate all the way through the membrane
(specialized pathways—PORES) for passage of specific substances through the
membrane
Some of these membranes are actually enzymes that catalyze chemical reactions
The Cell Membrane (plasma membrane)
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Envelopes the cell
Composed mainly of proteins and lipids
 Proteins 55%
 phospholipids 25%
 cholesterol 13%
 other lipids 4%
 CHO 3%
Functions
 Impedes penetration by water-soluble substances
 Is a lipid bi-layer
 Interspersed are large globular proteins
The lipid-bilayer
 Composed of three types of lipids
 Phospholipids- most abundant
o Contains a hydrophilic head (soluble in water)
o Other end is soluble only in fats (hydrophobic)
o Phosphate end is hydrophilic, fatty acid portion is hydrophobic
 Sphingolipids
o Present in small amounts especially in nerve cells
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o Protects from harmful environmental factors, transmits signals,
o Serves as adhesion sites for extracellular proteins
Cholesterol
o They have a steroid nuclei are highly fat soluble
o These are dissolved in the bilayer of the membrane
o They help in the determining degree of permeability of the bilayer
o Controls the fluidity of the membrane
Integral & Peripheral Cell Membrane Proteins
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Proteins (globular) that float in the lipid bilayer (mainly glycoproteins)
Two types of cell membrane proteins
o Integral proteins Protrude all the way through the membrane.
 Functions:
 To provide structural channels (or pores) through which water
molecules and water-soluble substances, especially ions, can diffuse
between the extracellular and intracellular fluids.
 To act as carrier proteins
 To act as enzymes
 To serve as receptors for water-soluble chemicals
 Act as second messengers, relaying the signal from the extracellular part
of the receptor to the interior of the cell
o Peripheral proteins Attached only to one surface of the membrane and DO NOT penetrate all the
way
 Attached to integral proteins
 Functions
 Act as enzymes or as controller of substances through the cell
membrane “pores”
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Membrane Carbohydrates—the Cell Glycocalyx
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CHO occur in combination with proteins or lipids in the form of glycoproteins or
glycolipids
Glyco portion of the molecule protrudes to the outside of the cell in addition to
proteoglycans (CHO bound to small protein cores)
The entire outside force of the cell has a loose CHO coat called the Glycocalyx
Functions of the CHO attached to the outside of the cell
o Many of them are negatively charged, thus repels other negatively charged ions
o Attaches one cell to another through the Glycocalyx
o Act as receptor substances for binding hormones (e.g. Insulin). When attached,
this activates internal proteins
o Has an immune function
The Cytoplasm and its Organelles
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Cytosol- jelly-like fluid portion of the cytoplasm
What are suspended in the cytosol
o Neutral fat globules
o Glycogen granules
o Ribosomes
o Secretory vesicles
o 5 organelles
1. Endoplasmic reticulum
2. Golgi apparatus
3. Mitochondria
4. Lysosomes
5. Peroxisomes
Endoplasmic Reticulum (ER)
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Helps process molecules made by the cell and transports them to their specific destinations
inside or outside of the cell
Synthesizes lipids (especially phospholipids & cholesterol which are incorporated into the lipid
bilayer of the ER itself (mainly in the smooth ER)
Space inside the ER is connected with the space between the two membrane surfaces of the
nuclear membrane
Contributes to several enzyme systems to maintain metabolic functions of the cell
ER are of two kinds
o Granular- contains Ribosomes
o Agranular (smooth) – Functions
 synthesis of lipid substances
 provides enzymes that control glycogen breakdown
 provides enzymes capable of detoxifying substances (drugs) that might be
dangerous to the cell
Golgi Apparatus
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Composed of four or more stack layers of thin, flat enclosed vesicles lying near one side of the
nucleus
Functions
o In association with the ER
o Synthesis of certain CHO (e.g., hyaluronic acid & chondroitin sulfate)
o Transported substances from the ER are processed by the Golgi
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Lysosomes
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Vesicular organelles
Functions: Provides an intracellular digestive system to
1. Digest damaged cellular structures
2. Process food particles ingested by the cell (converts protein to form amino acids;
glycogen to glucose; lipids to fatty acids & glycerol)
3. Digest unwanted matter such as bacteria, dead cells. If entire cell is damaged, kills the
entire cell in process called autolysis
4. Autophagy- “to eat oneself”. A housekeeping process by which obsolete organelles and
large protein aggregates are degraded and recycled.
Peroxisomes
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Similar to lysosomes but differs in two ways
1. Formed by self-replication rather than from the Golgi
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2. Contain oxidases (capable of combining oxygen with hydrogen ions) rather than
hydrolases
Function: to catabolize long chain fatty acids
Secretory Vesicles
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Contains products from ER or Golgi in the form of storage vesicles
Example: pancreatic enzymes
Mitochondria
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Powerhouses of the cell
Number dependent on the type of cell (numerous in cardiac tissue)
Has infoldings or shelves called cristae
Cristae provides a large surface area for chemical reactions
Nutrients + O2= energy (ATP- adenosine triphosphate)
Mitochondria are self-replicating (contains DNA similar to that in the nucleus)
Functions
o Foodstuff react with oxygen to convert CHO to glucose, proteins to amino acids and fats
to fatty acids to form ATP
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Cell Cytoskeleton—Filament & Tubular Structures
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Consists of fibrillary proteins organized into filaments or tubules
In muscle cells, actin and myosin filaments organized into contractile machine
Tubulin- specialized filament constructs microtubules (like flagella)
Functions
o Provides support for the cell membrane (actin filaments in the outer zone of the
cytoplasm (Ectoplasm). Act as a cytoskeleton (determines cell shape)
o Participates in cell division
o Allows cells to move
o As a track that directs the movement of organelles to move in the cell
Nucleus
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Control center of the cell
Sends messages to the cell to grow and mature, to replicate, or to die
Contains large quantities of DNA which comprise the genes
Parts of the Nucleus
o Nuclear membrane
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 Continuous with the ER
 Has pores
Nucleoli
 The nuclei contains highly staining structures called nucleoli
 Does not have a limiting membrane
 Contains RNA
Functional Systems of the Cell
https://www.youtube.com/watch?v=lh6V4zbut7w
Ingestion by the Cell—Endocytosis
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Two kinds
o Pinocytosis
 Ingestion of minute particles of extracellular fluid & minute particles
 Forms vesicles by invagination
 Releases vesicles by energy of ATP
o Phagocytosis
 Ingestion of large particles (bacteria, whole cells or degenerating tissues)
 Attaches to antibody (created by bacterial invasion)
 Attaching to the antibody is known as opsonization
Pinocytic and phagocytic foreign substances are digested inside the cell by lysosomes. Those not
digested (called residual bodies) are excreted out of the cell by exocytosis
Regression of tissues is a function of lysosomes (e.g., uterus after pregnancy, mammary gland
after lactation, muscles after long periods of inactivity)
Chemical Processes in the Formation of ATP
https://www.youtube.com/watch?v=-Gb2EzF_XqA
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Glucose + enzymes in the cytoplasm
converted to pyruvic acid (process is called
glycolysis). Converts to ADP to ATP or
In mitochondria (95% of it is produced here): pyruvic acid converted to compound acetylcoenzyme A (CoA)
enzymatic reactions in the citric acid cycle (Krebs cycle) splits
acetyl-CoA into hydrogen and carbon dioxide. Carbon dioxide excreted (diffusion). The hydrogen
atoms combine with oxygen, converting ADP to ATP
release of water + energy
Functions of ATP for Cellular Function
o Transport substances through multiple membranes in the cell
o Synthesis of chemical compounds throughout the cell
o Supply energy for special cells to perform mechanical work (e.g., muscle fibers require
ATP; locomotion of cells such as ciliary and ameboid motion)
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Locomotion of Cells
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Ameboid Movement
o Examples: movement of WBC, fibroblasts, embryonic cells (fertilization of an ovum)
o Steps
 Protrusion of a pseudopodium
 Pseudopodium anchors in a new area
 Pulls rest to new area
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Cilia and Ciliary Movement
o Whip like movement
o Example: flagellum of a sperm
o Whip like strokes