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The Cell
The significance of cells All body functions depend on the integrity of the cell
structure and function. Understanding cellular biology is necessary to understand
disease. At the heart of cellular biology, in cellular communication or cellular cross
talk. This is how messages are originate and are transmitted, received, interpret,
and used by the cell. The key topics that we will be talking about include eukaryote
cell components and functions, cell to cell adhesions, cellular communication and
signal transduction, cellular metabolism, membrane transport, cellular intake and
output, and cellular reproduction or the cell cycle and tissue and tissue formation.
Cell structure and function.
Our body functions depend on the integrity of cells. Therefore, an understanding of
cellular biology is intrinsically necessary for an understanding of disease. An
overwhelming amount of information is revealing how cells behave as a
multicellular social organism. At the heart of cellular biology, cellular
communication or cellular cross talk. How messages originate and are transmitted,
received, interpreted, and used by the sale. The streamline conversation between,
among and within sales maintains the cellular function and specialization.
Intercellular signals allow each sale to determine its position. And specialized role.
Cells must demonstrate a chemical fondness for other cells and their surrounding
environment to maintain the integrity of the entire organism. When they no longer
tolerate this fondness, a conversion breaks down and cells either adapt or become
vulnerable to isolation, injury, disease, or even death. Living cells are divided into
two major classes. Prokaryotes versus eukaryotes. Cells of higher animals and
plants are eukaryotes, as are the single-cell organisms, fungi, protozoa, and most
algae. The prokaryotes have a nucleus, but they do not have any organelles. These
consist of cyanobacteria, regular bacteria, and rickettsia, complex cells, the
eukaryotes have a complex cellular organization. They have membrane-bound
organelles. They're well-defined nucleus, and these belong to the higher animals,
plants, fungi and protozoa.
Cell differentiation and specialized cellular functions. Human cells are not all the
same. Each cell has a specific calling or purpose. Cells become specialized through
the process of differentiation or maturation, so that some cells eventually perform
one kind of function and other cells perform other functions. That a specialized
cellular functions are movement, conductivity, metabolic absorption, secretion,
excretion, respiration, reproduction and communication. And movement is a
generated force to produce motion. Muscle cells of the blood vessels on in the
bladder are examples. Conductivity. These are waves of excitation, electrical
potential passed along the cell surface. For example, nerve cells, metabolic
absorption, all cells take in nutrients. Cells of the intestines and kidneys are
specialized to absorb secretion. These are mucus gland cells and they secrete, as do
adrenal glands, testes, and the ovary cells excretion. All cells rid themselves of
waste. For example, lysosomes and then respiration. All cells absorb oxygen to form
ATP.
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Communication. All cells communicate. For example, the pancreatic cells release
insulin, signal muscle cells to absorb glucose for energy. Structure and function of
the cellular components of eukaryotic sales. The general components include
cytoplasma. Cytoplasmic organelles, which include the nucleus and the plasma
membrane. The plasma membrane is the bi-layer of lipids and proteins. This
encloses the cells and controls the movement of substances across it. It influences
metabolic pathways. The cytoplasma fills the space between the nucleus and the
plasma membrane and houses the intracellular organelles. The intracellular
organelles are suspended in the cytoplasma, and this includes the nucleus. The
nucleus. The structure is a nuclear envelope with nuclear pores. It has nucleo
plasma. The nucleus consist of RNA, DNA. And what is happening in the nucleus, the
DNA replicates, repairs and also there's transcription. Note histone proteins package
the DNA. The functions of the nucleus include cell division, control of genetic
information, DNA replication, and repair and RNA processing.
Cytoplasmic organelles. Cytoplasm is a aqueous solution that feels the cytoplasmic
matrix, which is the space between the nuclear envelope and the plasma
membrane. This includes the cytoplasma of ribosomes, the endoplasmic reticulum,
which is rough and smooth. The Gogli complex, an apparatus, lysosomes,
peroxisomes, mitochondria, the cytoskeleton, and the nucleus. Cytosol is the liquid
matrix found inside cells. It occurs in both eukaryotic, plant and animal and
prokaryotic bacteria cells. In eukaryotic cells, it includes the liquid enclosed within
the cell membrane, but not the cell nucleus. Organelles are fluid contained within
organelles. It is a component of the cytoplasma, the structure. It is a gelatinous,
semi liquid portion of the cytoplasm, 55 percent of the total cells volume and its
functions. An intermediary metabolism involving enzymatic biochemical reactions,
ribosomal protein synthesis and storage. Cytoplasm It's an aqueous solution that
feels the cytoplasmic matrix, which is the space between the nuclear envelope and
the plasma membrane. The cytoplasma encompasses all of the material in the cell
membrane, including the organelles, but excluding the nucleus. So the liquid within
the mitochondria, the chloroplasts and the vacuoles is part of the cytoplasm, but is
not a component of Cytosol.
The structure, Cytosol equals aqueous solution. Cytoskeleton or the bones and
muscles of the cells. And this houses the cytoplasmic organelles are the little
organs. The functions are protein synthesis, transport, and deep gradation, waste
elimination, biochemical metabolic processes. And it's a storage unit for fat,
carbohydrates and secretory vesicles. Ribosome's endoplasmic reticulum and
protein folding. Ribosomes is a complex molecular machine found inside the living
cells that produce protein from amino acids during the process called protein
synthesis or translation. The structure, ribonucleic acid protein or RNA complexes.
They are free versus attached ribosomes. The function is again to synthesize
protein. The endoplasmic reticulum is a network of tubular or sac like channels.
They can be smooth or rough. Endoplasmic reticulum is attached to the nuclear
envelope. The function is the site of protein synthesis, quality and control, and it
senses cellular stress.
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The endoplasmic reticulum again synthesizes and transport protein and lipid.
Responsible for quality and control of protein. Protein folding and sensing sales
stress. Proteins exist and an unfolded state and after the process of translation, they
produce a folded protein. Protein folding occurs in the endoplasmic reticulum, ER, or
cell stress. Mutations, errors during protein synthesis can decrease the folding
amount or rate of falling. Insults to folding may include viral infections, toxins, and
mutations. There are protective mechanisms, for example, chaperones that help
facilitate folding and prevent miss formations. Misfolded proteins can result in cell
death and are recognized as a part of some diseases such as Alzheimer's,
Parkinson's, ALS, diabetes, and sepsis, and accelerated age-related dysfunction.
Golgi complex. This is a network of flattened, smooth membranes and vesicles
frequently located near the nucleus. Golgi complex are also termed as Golgi
apparatus. It is a membrane-bound organelle which is mainly composed of a series
of flattened or stack patches called subarray. This cell organ now is primarily
responsible for transporting, modifying, and packaging proteins and lipids to
targeted destinations. Lysosomes are membrane enclosed organelles are saclike
filled items enzymes that digest molecules. They defunct intracellular organelles
and particles engulfed from outside the cell by endocytosis. Again, the structure is a
saclike structure that originate from the Golgi. They contain digestive, digestive
enzymes. They can be primary, which is not active, versus secondary, which is
active lysosomes. Their functions are intracellular digestive system hydrolases of 60
digestive enzymes. They have a role in auto-digestion and autophagy. And there is
four degradation pathways Endocytosis, Phagocytosis, micropinocytosis, an
autography.
Peroxisomes are membrane-bound organelles that contains several oxidative
enzymes. Their functions, they are the major site of oxygen utilization. They
detoxify compounds and fatty acids. They break down substances into harmless
products. and they synthesize specialized phosphorlipids for nerve cell myelination.
Mitochondria are organelles found in large numbers and most cells. They are
responsible for cellular respiration and energy production. Their structure, they are
surrounded by a double membrane and they have an increased inner membrane
surface area which is provided by cristae. Their functions again, they are
responsible for cellular respiration and energy production. This is essential to
oxidative phosphorylation. Vaults are cytoplasmic organelles and are also called
ribonucleoproteins. They are thought to function as cellular trucks carrying
messenger ribonucleic acid from the nucleus to the ribosomal site of protein census.
Cytoskeleton - This is an elaborate and specialized internal structure in the cytosol
that provides the bones and muscles of the cell. It maintains the cell shape and
internal organization. It permits movement of substances within the cell. and
movement of external projections, Mechanotransduction, microtubules, which
provides strength, and then microfilaments such as actin. Plasma membrane and
structures. Membranes define the cells boundaries, whether they surround the cells
or enclose an intracellular organelle. Membranes are crucial to normal physiologic
function because they control the composition of the space or compartment they
enclose. The main components of cell membranes are lipids and proteins.
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Plasma membranes functions. The first one is structure. It contains all of the cellular
organelles. Protection. It's a barrier to toxins, foreign organisms and cells. Activation
of the cells, such as hormones which regulates cellular activity, mitogens which are
involved in cellular division and antigens and antibody synthesis, growth factor for
proliferation and the differentiation, transport for diffusion and active transport, and
cell to cell interaction or receptor. So it has a relationship with the extracellular
matrix. The membrane composition. The main components of cell membranes are
lipids and proteins. The basic structure of cell membranes is the lipid bilayer. The
lipid bilayer provides the basic cell structure of the membrane. And it's mostly an
impermeable barrier to water-soluble molecules.
Most membrane proteins span the lipid bi-layer and mediate most of the functions
of the membrane, including transport of molecules across the membrane and ATP
census. Cell membranes may contain many different lipid classes, but in animals,
the main ones are phospholipids, cholesterol, and glycolipids. Phospholipids are key
for repairing the membrane. Proteins perform most of the plasma membrane
specific task. The amounts and types of proteins in a membrane. Very a protein
that's made from a chain of amino acids known as polypeptides and are vital to the
cell. They are the workhorse of the cell. Proteins have a role and a plethora of
cellular structures and functions. Proteins move from one compartment to another.
Graded transport, protein translocation, or vesicular transportation.
Proteostasis is a state of cell balance of the processes of cell protein synthesis,
folding and degradation. Proteases are enzymes that cause a breakdown of protein.
And protein synthesis is the process by which cells make protein folding. Protein
folding occurs in the endoplasmic reticulum and error-free folding is vital. Each
protein in an unfolded state after translation, amino acid reactions produce a three-
dimensional structure called a folded protein.
ER stress mutations, errors impact protein folding process. Pathologic processes
impact that ER, that in turn call it cause imbalances in proteins synthesis.
Chaperones help with protein folding. Misfolded proteins not repaired is seen in
some diseases or can lead to cell death. In the ER, an unfolded protein response is
an adaptive mechanism that is associated with inflammation. Protein degradation is
break down or protein, also known as the proteolytic cascade. And this will be
discussed on the next slide. Proteolytic cascade, tightly orchestrated sequence of
events that cause the breakdown of protein. There's four major cascades. The
Caspase mediated apoptosis or cell death, the Blood coagulation cascade, the
Matrix metalloproteinases cascade, and the Complement cascade. Cellular
receptors are protein molecules on the plasma membrane in the cytoplasm or in the
nucleus capable of recognizing and binding smaller molecules called ligands. They
recognize and bind with ligands which are smaller molecules like hormones. At a
binding site. Drug receptors on the membrane include anesthetics, opioids,
endorphins, antibiotics, chemotherapeutic agents, and others.
Cell-to-cell adhesions. Cells are small and squishy, not like bricks. They are enclosed
only by a flimsy membrane. Yet the cell depends on the integrity of this membrane
for its survival. Plasma membranes not only serve as the outer boundaries of all
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cells, but also allow groups of cells to be held, to gather robustly and cell-to-cell
adhesions to form tissues and organs. This is accomplished by three different
means.
An extracellular matrix, cell adhesion molecules in the plasma membrane and
specialized cell junctions. The extracellular matrix includes three types of protein
fibers. These are collagen, elastin, and fibronectin. The matrix helps regulate cell
growth and differentiation. The functions include mechanical support, control of cell
proliferation, tissue regeneration, and tissue microenvironments. The basement
membrane is a specialized type of extracellular tissue. It's also known as the basal
lamina. It's a thin tissue layer underlying many organs. It is thin, tough and flexible,
that lies below the epithelial cells and surrounds individual muscle cells. fat sales.
and Schwann cells wrap around the peripheral nerve cell axons.
Cell adhesion molecules, or CAMs, cell surface proteins that bind to adjacent cells
and are components of the E, C, M. The four main protein families are integrins,
which are receptors in the ECM that interacts with collagen, fibronectin, and
fibrinogen. The cadherins, which are calcium-dependent glycoproteins, Selectins
They bind certain carbohydrates, specifically mucins, and the immunoglobulin
superfamily, which binds integrins and other immunoglobulins.
Specialized cell junctions. These are cells and direct physical contact with
neighboring cells. And they're often linked together at specialized regions of their
plasma membrane called cell junctions. They are classified by function. The tight
junctions hold cells together forming a tight seal. The desmosomes are adherens
junctions and they provide strong mechanical attachments. And number three is the
gap junctions and they provide special chemical communications. Cellular
communication. Cells need to communicate with each other to maintain a stable
internal environment or homeostasis.
The three main mechanisms are contacts, signaling, remote signaling, and to form a
gap junction such as protein channel. That image shows cells communicating in
three different ways. They display plasma membrane-bound signaling molecules,
which are receptors that affect the cell itself and other cells and direct physical
contact to our receptor proteins inside the target cell. And the signal molecule has
to enter the cell to bind to them. And number three, they form protein channels that
directly coordinate the activities of adjacent cells. Cellular communication primary
modes that occurs by contact dependent signaling through the plasma membrane
bound receptors and gap junctions. Paracrine signaling, which is also autocrine
signaling, hormonal signaling, neuro hormonal signaling, and through
neurotransmitters. Signal transduction. Extracellular first messengers.
Extracellular first messengers convey instructions to the cell's interior. They
transfer, amplify, distribute, and modulate signal transduction or channel
regulation. This opens and closes the gate depending on the first messenger.
There's two important second messengers. They are cyclic adenosine
monophosphate and calcium. Cellular metabolism. All the chemical task of
maintaining essential cellular functions are referred to as cellular metabolism. It
provides the cell with energy and it can cause anabolism, which is energy using and
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catabolism, which is energy releasing. Cellular metabolism. The role of ATP, best
known about ATP, is its role as a universal fuel inside living cells. This fuel or energy
drives biologic reactions necessary for cells to function. ATP is created from the
chemical energy contained in organic molecules. ATP is used in the synthesis of
organic molecules, muscle contraction and active transport. Cellular metabolism,
the food and production of cellular energy. The first phase is digestion, are large
molecules are broken down into their smaller subunits. Phase two is glycolysis and
oxidation. The small molecules enter cells and are further broken down into the
cytoplasm.
Phase 3 is the citric acid cycle. It's called the Krebs cycle or the tricarboxylic acid
cycle. Oxidative phosphorylation occurs in the mitochondria. It is a mechanism by
which energy produced from carbohydrates, fats, and protein and is transferred to
ATP. Membrane transport, cellular intake and output. Cellular survival and growth
depend on the constant exchange of molecules with their environment. The
transport mechanisms include passive transportation for water and small neutral
molecules occurs, and this requires no energy.
It's done by diffusion, hydrostatic pressure, and osmosis. Active transportation is
larger complex molecules. And this requires cell energy. And also there can be a
combination and known as mediated, where there's active or passive. But first,
basics about Saljuqs. Body fluids are composed of two types of solutes, electrolytes,
which are electrically charged and dissociate into constituent ions when placed in a
solution and non-electrolytes. The electrolyte are cations which are positive, or
anions which are negative. They're measured in milli, equivalents per liter or
milligrams per deciliter. And then non-electrolytes, which include glucose, urea, and
creatinine. And these do not disassociate when placed in a solution. Membrane
transport, or passive transport, occurs when water and small electrically uncharged
molecules move through membrane pores. It does not require energy. And this
includes diffusion, passive mediated transport, filtration, and osmosis such as
osmotic or oncotic pressure. Membrane transport, cellular intake and output.
Tonicity is the osmolarity of a solution. Osmolarity is the measure of the number of
millimoles per liter of solution or the concentration of molecules per volume of
solution. Osmolarity is the measure of the number of millimoles per kilogram of
water with a concentration of molecules. per weight of water, isotonic has the same
osmolarity or concentration of particles as the intracellular fluid or extracellular fluid
hypertonic. There's a concentration of more than 285 to 294. And the hypotonic is a
lower concentrate or more dilute than body fluids. Membrane transport, cellular
intake and output mediated transport can be passive or active. Examples include
the movement of two molecules simultaneously in one direction. Or in the opposite
direction, also includes the movement of a single molecule in one direction.
Membrane transport, active transport. Larger molecules and molecular complexes
are moved into the cell. This requires the cell expenditure of energy that moves
molecules across a concentration gradient. It's protein mediated. And one example
of active transport pump is ion channels with a carrier such as the potassium
sodium pump.
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Membrane transport, active transport. And we're going to talk about transport by
vesicular formation. Endocytosis is the taking in. This is an internalizing process
during which a section of the plasma membrane in full substances from outside the
cell and invaginate and separates them from the plasma membrane, forming a
vesicle that moves inside the cell. Pinocytosis is cell ingestion of ECF and its
contents. Phagocytosis. Large molecular substances are engulfed by the plasma
membrane and enter the cell wall so that these substances can be isolated and
destroyed by lysosomal enzymes. Endocytosis continued. It can be clathrin
mediated. It's rapid and enables to sail to ingest large amounts of specific ligand. It
can be caveolae-mediated, where it functions as uptake vesicles, but are also
important sites for signal transduction. Can be clathrin-caveolin independent And
then there's exocytosis, which is expelling movement of electrical impulses. All body
cells are electrically polarized with the inside of the cell more negatively charged
than the outside. The resting membrane potential is the difference in voltage across
the plasma membrane.
That action potential consist of depolarization, threshold potential, repolarization, or
refractory period, which is absolute and relative. And hypo polarization and hyper
polarization. Cellular reproduction, the cell cycle, this is the continuity of life that
depends on constant rounds of cell growth and division. Cellular reproduction and
the body tissues involves mitosis and cytokinesis. Only mature cells are capable of
division. Maturation occurs during a state of cellular life called interphase or the
growth phase. The cell cycle is the reproductive process that begins after interphase
in all tissues with cellular turnover. The four phases of the cell cycle are the G1
phase, which is a gap between the M phase and the start of DNA synthesis. The S
phase, which is DNA synthesis in the cell nucleus, and the G2 phase, which is RNA
and protein synthesis. Cell division again is either Mitosis where there's nuclear
division or Cytokinesis where there is cytoplasmic division. M phase includes mitosis
and cytokinesis. This involves a prophase, metaphase, and anaphase and telophase.
Cell division begins with the prophase. This is where the chromosomes appear.
Chromatids are seeing connected at the centromere, nuclear membranes disappear.
Spindle fibers are formed. Then there's the metaphase where the chromosomes line
up in the center of the sale. Spindle fibers attach to the chromosomes anaphase,
where the spindle fibers pull chromosomes to opposite sides of the sale. And then
the telophase membranes form around the two new group of chromosomes and
cytokinesis occurs, creating two daughter cells within 46 chromosomes, each.
Cellular reproduction, the rates of cellular division are different. A completed cycle
takes approximately 12 to 24 hours and different rates occur in different phases.
There's the cell cycle control system. This is the Cyclin which is dependent on
kinases and the cyclins molecules that control cell division and growth, or the
mitogens, that growth factor and the survival factors. And then there's DNA
damage, which equals cell cycle arrest. Tissue formation. Cells of one or more types
are organized into tissues and different types of tissue composed organs. Organs
are organized to function as tracks or system. Tissue formation is dependent upon
intracellular recognition, communication, adhesion, and memory. The four basic
types of tissue are epithelial, muscle, neural, and connective tissues.
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Epithelial tissue. This covers most internal and external body surfaces. It can be
simple versus stratified. It can be Squamous or Cuboidal, Columnar or
Pseudostratified. The structures include cilia and microbial line. The functions are
protection, absorption, secretion and excretion. Connective tissue. This binds
various tissues and organs together, supporting them and their locations and
serving as storage sites for excess nutrients. The structure is a ground structure. It
has fibers, which are collagenous, elastic, and reticular, and they can be loose and
dense connective tissue. Examples include cartilages, bone, vascular, adipose, and
organs. Its functions are to form a framework for organs binding, supporting, and
storing excess nutrients. Muscle tissue. Its structure is composed of myocytes.
Examples would include smooth, skeletal, and cardiac. And its functions are
contract out tissue enabling both voluntary and involuntary movement. Neural
tissue, the structure involves neurons which are highly specialized cells, which
receive and transmit electrical impulses very rapidly across synapses. Synapses are
points of functional contact between neurons. There's the cell body, axons, which
are long prolongations of the cell body. And every nerve has one axon and then
dendrites. These are structures that extend from the cell body. A nerve cell can
have many dendrites. The main difference between axon and dendrite is that axon
carries nerve impulses away from the cell body. where dendrites carry nerve
impulses from synapses to the cell body. The functions are to receive and transmit
electrical impulses very rapidly across junctions called synapses. And this also
involves the neurotransmitters. This slide shows the references. Thank you for being
attentive today.
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