Cell and Tissue Characteristics

Chapter 4: Cell and Tissue Characteristics 1

Eina Jane & Co. 2009.

I. Cell A. Smallest functional unit necessary for life B. Can organize into larger units (tissues) based on embryonic origin then

into body structures organs C. Exchange materials, obtain NRG from organic nutrients, synthesize complex

molecules, replicate themselves D. Understanding of cell process is crucial to understand of disease process

because most disease processes are initiated at cellular level *** diseases affect 1. Single organ 2. Particular tissue type 3. Entire organism

II. Functional components of cell A. Protoplasm: internal matrix of cell B. Composed of

1. Water (70‐85%) 2. Proteins (10‐20%): cell structures, enzymes for cell reactions,

nucleoproteins, glycoproteins, lipoproteins 3. Lipids (2‐3%): phospholipids, cholesterol for cell membrane and

membranous barriers that separate different cell compartments; fat cells can have 95% triglycerides occupying the cell mass for stored energy that can be mobilized and used whenever needed

4. Carbohydrates: few found in cell, serve primarily as rapid source of energy vs. fats

5. Electrolytes: cell metabolism, transmission of electrochemical impulses in nerve and muscle cells a. Intracellular potassium, magnesium, phosphate, sulfate,

bicarbonate b. Small intracellular: Sodium, chloride, calcium

C. 2 distinct regions 1. Cytoplasm: outside the nucleus 2. Karyoplasm / nucleoplasm: inside nucleus

III. Nucleus A. Control center of the cell; contains most of the hereditary material B. All eukaryotic cells at least have one nucleus, prokaryotic have none C. Contains DNA genes that encode necessary information for synthesis of

proteins, enzymes, carbohydrates, lipids, and individual units of inheritance that transmit transformation from one generation to another

D. Site for synthesis of 3 types of ribonucleic acid (RNA) that move to cytoplasm and carry out the actual synthesis of proteins 1. Messenger RNA (mRNA) copies and carries the DNA instructions for

proteins synthesis to cytoplasm 2. Ribosomal RNA (rRNA) is the site of protein synthesis 3. Transfer RNA (tRNA) transports amino acids to the site of proteins

synthesis for incorporation into protein being synthesized



E. Chromatin: term indicating the complex structure of DNA and DNA‐associated proteins dispersed in the nuclear matrix 1. Heterochromatin: condensed inactive form of chromatin 2. Euchromatin: extended more active form of chromatin 3. Heterochromatic regions of nucleus stain more intensely compared to

euchromatin, nuclear staining can be a guide to cell activity F. Nuclear envelope: surrounds nucleus G. Formed by (outer and inner) nuclear membranes containing a perinuclear

cisternal space between them 1. Inner nuclear membrane supported by rigid network of protein filaments

that bind to chromosomes and secure their position in nucleus 2. Outer nuclear membrane resembles membrane of endoplasmic reticulum

and is continuous with it H. Contains many structurally complex circular pores where the two

membranes fuse to form a gap filled with a thin protein diaphragm 1. Molecules: fluids, electrolytes, RNA, some proteins, hormones can move

in both directions through nuclear pores 2. Pores regulate the bidirectional exchange of molecules between the

cytoplasm and the nucleus IV. Cytoplasm and Its Organelles

A. Cytoplasm 1. Surrounds the nucleus; where the work of the cell takes place 2. Colloidal solution of water, electrolytes, proteins, fats, glycogen 3. Pigments: melanin (skin), bilirubin (bile excess skin, sclera

jaundice) 4. Embedded in cytoplasm are organelles organs of the cell: ribosomes,

endoplasmic reticulum, Golgi complex, mitochondria, lysosomes B. Organelles

1. Ribosomes a. Site for protein synthesis; small particles of nucleoproteins (rRNA and

proteins) held together by strand of mRNA to form polysomes (polyribosomes) that exists as isolated clusters of free ribosomes within cytoplasm or attached to membrane of endoplasmic ER

b. Free ribosomes: involved in synthesis of proteins, enzymes aid in control of cell function

c. Attached to ER: translate mRNAs that code for proteins secreted from cell or stored within cell

2. Endoplasmic Reticulum (ER) a. Extensive system of paired membranes and flat vesicles that connects

various parts of inner cell between ER membranes is a fluid‐filled space called matrix i. Matrix connects membranes of nuclear envelope, cell membrane,

and various cytoplasmic organelles ii. Functions as tubular communication system for transporting

various substances from part of the cell to another



b. 2 forms of ER: rough and smooth i. Rough: studded with ribosomes attached to specific binding sites

on membrane proteins produced by RER become components of lysosomes and other organelles

ii. Smooth: free of ribosomes, continuous with RER; does not participate in protein synthesis o Enzymes involved in lipid molecules, regulation of intracellular

calcium, metabolism and detoxification of hormones and drugs (smoother ER of liver involved in glycogen storage and metabolism of lipid‐soluble drugs)

o Site of lipid, lipoprotein, steroid hormone synthesis 3. Golgi Complex aka Golgi apparatus

a. Stacks of thin, flattened vesicles or sacs found near nucleus and function in association with ER large proteins are modified by the Golgi complex and packages them into secretory/smaller granules or vesicles

b. Insulin, synthesized as a large, inactive proinsulin molecule that is cut apart to produce a smaller, active insulin molecule within the Golgi complex of the beta cells in the pancreas

c. Produce large carbs + proteins from rough ER = glycoproteins d. Can receive proteins and other substances from cell surface by

retrograde transport mechanism retrograde pathway has been exploited by several bacterial toxins, such as Shiga and cholera toxins, and plant toxins, such as ricin, that have cytoplasmic targets

4. Lysosomes and Peroxisomes a. Lysosomes

i. Digestive system of the cell; small, membrane‐enclosed sacs that contain powerful hydrolytic enzymes

ii. Break down excess and worn‐out cell parts as well as foreign substances that are taken into the cell

iii. All lysosomal enzymes are acid hydrolases = require acidic environment Maintain pH of 5 in their interior pH of cytoplasm 7.2, serves to protect other cellular structures from acidity

b. Peroxisomes i. Smaller than lysosomes, spherical membrane‐bound organelles ii. Contain special enzyme that degrades peroxides (e.g. hydrogen

peroxide) iii. Unlike lysosomes, peroxisomes are not formed by the Golgi

apparatus o Peroxisomes are self‐replicating like mitochondria and are

initially formed by proteins produced by free ribosomes o Function in the control of free radicals



Unless degraded, these highly unstable chemical compounds would otherwise damage other cytoplasmic molecules

For example, catalase degrades toxic hydrogen peroxide molecules to water

o Peroxisomes also contain the enzymes needed for breaking down very‐long‐chain fatty acids, which mitochondrial enzymes ineffectively degrade In liver cells, peroxisomal enzymes are involved in

formation of bile acids 5. Mitochondria

a. Power plants of cell transform organic compounds into energy that is easily accessible to the cell

b. Do not make energy, but extract it from organic compounds store energy as high‐energy phosphate bonds such as ATP

c. Contain enzymes needed for capturing energy in food and converting it into cellular energy multistep process known as cellular respiration that requires oxygen

d. Mitochondria contain own DNA and ribosomes and are self replicating mtDNA inherited matrilineally (from the mother) which provides basis for familial lineage studies

V. Cell (Plasma) Membrane A. One of the most important parts of the cell semi‐permeable structure that

separates intracellular and extracellular environments 1. Provides receptors for hormones and other active substances 2. Participates in electrical events that occur in nerve and muscle cells 3. Aids in regulation of cell growth and proliferation

B. Dynamic and fluid structure consisting of lipids, carbohydrates and proteins 1. Main structural component: lipid bilayer

a. Phospholipids, glycolipids, cholesterol b. Basic fluid structure of membrane and serves as relatively

impermeable barrier to all but lipid‐soluble substances 2. Approx 75% of lipids are phospholipids, each with hydrophilic (water‐

soluble) head and hydrophobic (water‐insoluble) tail 3. Phospholipid molecules with glycolipids are aligned such that their

hydrophilic heads face outward on each side of the membrane and their hydrophobic tails project toward the middle of the membrane a. Hydrophilic heads retain water help cells stick to each other b. At normal body temp, viscosity of lipids of membrane is the same as

olive oil presence of cholesterol stiffens the membrane C. Proteins carry out specific functions

1. Integral proteins span entire lipid bilayer a. Essentially part of membrane b. Also called transmembrane proteins because most of integral proteins

pass directly through the membrane



2. Peripheral proteins bound to one or the other side of the membrane a. Does not pass into the lipid bilayer b. Removal of the peripheral proteins from the membrane damages the

membrane D. Manner in which proteins are associated with the cell membrane often

determines their function 1. Peripheral proteins associated with functions involving inner or outer

side of membrane where they are found 2. Several peripheral proteins serve as receptors or are involve in

intracellular signaling systems 3. By contrast, only transmembrane proteins can function on both sides of

membrane or transport molecules across it E. Glycocalyx

1. Fuzzy‐looking layer surrounding the cell surface; the cell coat 2. Consists of long, complex carbohydrate chains attached to protein

molecules that penetrate the outside portion of the membrane (glycoproteins); outward‐facing membrane lipids (glycolipids); carbohydrate‐binding proteins called lectins

3. Participates in cell‐to‐cell recognition and adhesion a. Contains tissue transplant antigens that label cells as self or nonself b. Cell coat of red blood cell contains the ABO blood group antigens

4. An intimate relationship exists between the cell membrane and the cell coat. If the cell coat is enzymatically removed, the cell remains viable and can generate a new cell coat, but damage to the cell membrane usually results in cell death

VI. Integration of Cell Function and Replication A. Cell Communication: important to coordinate function and control growth

1. Direct communication between adjacent cells through gap junctions, autocrine and paracrine signaling, endocrine, synaptic signaling

2.



3. Autocrine signaling: cell releases chemical into extracellular fluid that affects its own activity

4. Paracrine signaling: enzymes rapidly metabolize the chemical mediators, and therefore they act mainly on nearby cells.

5. Endocrine signaling: relies on hormones carried in the bloodstream to cells throughout the body

6. Synaptic signaling occurs in the nervous system, where neurotransmitters act only on adjacent nerve cells through special contact areas called synapses

7. In some parts of the body, the same chemical messenger can function as a neurotransmitter, a paracrine mediator, and a hormone secreted by neurons into the bloodstream

B. Cell Receptors 1. Signaling systems consist of receptors that reside in cell membrane

(surface receptors) or within cells (intracellular receptors) 2. First messengers: receptors activated by variety of extracellular signals

neurotransmitters, proteins hormones, growth factors, steroids, chemical messengers

3. Second messengers: additional intracellular mechanisms in the pathway many molecules involves in signal transduction are proteins proteins can change their shape which allows them to change their functions in the cell proteins often accomplish these conformational changes through enzymes called protein kinases that catalyze the phosphorylation of amino acids in the protein structure

C. Cell Surface Receptors: G‐protein linked, ion‐channel linked, enzyme linked 1. Number of proteins increase or decrease according to the needs of the

cells a. Down regulation: when excess chemical messengers are present, # of

active receptors decrease b. Up regulation: when there is a deficiency, # of active receptors

increase 2. G‐Protein‐Linked Receptors

a. Largest family of cell surface receptors b. Rely on the intermediary activity of a separate class of membrane‐

bound regulatory proteins to convert external signals (first messengers) into internal signals (second messengers)

c. Because these regulatory proteins bind to guanine nucleotides such as guanine diphosphate (GDP) and guanine triphosphate (GTP), they are called G proteins. G‐protein‐linked receptors mediate cellular responses for numerous types of first messengers, including proteins, small peptides, amino acids, and fatty acid derivatives such as the prostaglandin

d. All have a ligand‐binding extracellular receptor component, which functions as a signal discriminator by recognizing a specific first



messenger, and they all undergo conformational changes with receptor binding that activates the G protein

e. All G proteins are found on the cytoplasmic side of the cell membrane, and all incorporate the GTPase cycle, which functions as a molecular switch that exists in two states. In its activated (on) state, the G protein has a high affinity for GTP, and in its inactivated (off) state, it binds GDP

3. Enzyme‐Linked Receptors a. Transmembrane proteins with ligand‐binding site on outer surface of

cell membrane b. Enzyme‐linked receptors mediate cellular responses such as calcium

influx, increased sodium‐potassium exchange, and stimulation of glucose and amino acid uptake

c. Signaling cascades generated by the activation of tyrosine kinase receptors are also involved in the function of growth factors signals cell replacement and cell growth cytokines for immune system, colony‐stimulating factor for WBC and RBC growth factors stimulate the transcription of many genes that were silent in resting cells, and they regulate the entry of cells into the cell cycle and their passage through the cell cycle

4. Ion‐Channel‐Linked Receptors a. Involved in rapid synaptic signaling between electrically excitable

cells neurotransmitters b. Transiently opening or closing ion channels formed by integral

proteins in cell membrane involved in transmission of impulses in nerve and muscle cells

D. Intracellular Receptors 1. Messengers (thyroid and steroid hormones) that do not bind to

membrane receptors but move directly across lipid layer of cell membrane and are carried to cell nucleus, where they influence DNA activity

2. Bind to cytoplasmic receptor receptor‐hormone complex is carried to nucleus binds to DNA increasing transcription of mRNA mRNA translated in ribosomes, with production of increased amounts of proteins that alter cell function

VII. Cell Cycle and Cell Division A. Cell cycle: life cycle of the cell five phases G0, G1, S, G2, M

1. G0: state of inactivity leave the cell cycle or reenter cell cycle any time cancer has no G0, keeps growing nonstop

2. G1: prepares for mitosis DNA and protein synthesis, increase in organelle and cytoskeletal elements

3. S: synthesis phase DNA replication, centrioles replicate 4. G2: premitotic, similar to G1 in terms of RNA activity and protein synthesis 5. M: cell mitosis occurs; 1‐3 hours followed by cytokinesis or cell division;

P, prophase M, metaphase A, anaphase T, telophase



B. Nondividing cells, such as neurons and skeletal and cardiac muscle cells, have left the cell cycle and are not capable of mitotic division in postnatal life

C. Mitosis: cell division, process when parent cell divides and each daughter cell receives a chromosomal karyotype identical to parent cell 1. Replaces cells that have limited life 2. Increases tissue mass during periods of growth 3. Tissue repair and wound healing 4. Divided into 4 stages: prophase, metaphase, anaphase, telophase

a. Interphase: phase cell not undergoing division b. Prophase: chromosomes become visible, increased coiling of DNA,

microtubles of mitotic spindle appear between 2 pairs of centrioles; later in prophase, nuclear envelope and nucleolus disappear

c. Metaphase: organization of chromosome pairs in midline of cell and formation of mitotic spindle compose of microtubules

d. Anaphase: separation of chromosome pairs, microtubules pulling one member of each pair of 46 chromosomes toward opposite cell pole

e. Telophase: mitotic spindle vanishes, nuclear membrane develops, encloses each complete set of chromosomes, cell division/cytokinesis occurs

VIII. Cell Metabolism and Energy Sources A. Energy = ability to do work B. Cells use oxygen to breakdown products of foods into energy C. Energy metabolism = processes by which fats, proteins, and carbohydrates

from foods we eat are converted into energy in the form of ATP 1. Catabolism: breaking down stored nutrients and body tissues to produce

NRG 2. Anabolism: constructive process in more complex molecules are formed

from simpler ones D. ATP = carrier for cellular energy; adenosine triphosphate, high energy E. Two types of energy production: anaerobic and aerobic

1. Anaerobic: without oxygen, glycolytic pathway a. Glycolysis: NRG from glucose, important for cells that lack

mitochondria, or when oxygen delivery is impaired b. Converts glucose pyruvate ATP from ADP one glucose, 2 ATP

2. Aerobic: with oxygen, involves mitochondria a. Mitochondria + citric acid cycle (Krebs cycle) + electron transport

chain b. Carbon compounds from fats, proteins, carbohydrates from diet are

broken down to form CO2 + H2O + NRG IX. Movement Across Cell Membrane and Membrane Potentials

A. Cell membrane = barrier; controls which substances enter and leave the cell B. Passive Movement

1. Directly influenced by chemical or electrical gradients and does not require an expenditure of NRG



2. Difference in # of particles on either side of membrane creates a chemical gradient and difference in charged particle or ions creates an electrical gradient

3. Electrochemical gradients: linked chemical and electrical gradients 4. Diffusion: small molecules substances move from area of higher to lower

concentration via spontaneous kinetic movements 5. Osmosis: diffusion of water through semi‐permeable membrane from

higher to lower concentration gradient 6. Facilitated Diffusion: occurs through a transport protein that is not linked

to metabolic energy a. Some substances, such as glucose, cannot pass unassisted through the

cell membrane because they are not lipid soluble or are too large to pass through the membrane's pores

b. These substances combine with special transport proteins at the membrane's outer surface, are carried across the membrane attached to the transporter, and then released on the inside of the membrane

c. In facilitated diffusion, a substance can move only from an area of higher concentration to one of lower concentration

d. Rate depends on difference in concentration between 2 sides of membrane and availability of transport proteins and how fast they can bind and release the substance being transported

C. Active Transport 1. Uses energy to go uphill or against concentration gradient 2. Sodium‐potassium pump

a. Sodium from inside cell to extracellular region, where concentration is 14x greater than inside

b. Returns potassium to the inside, where its concentration is 35x greater that outside the cell

3. Primary active transport: source of energy is used directly in transport of substance

4. Secondary active transport: mechanisms harness energy derived from primary active transport of one substance, for the cotransport of a second substance a. Cotransport or symport: sodium ion and solute transported in same

direction b. Countertransport or antiport: sodium ion and solute transported in

opposite direction D. Endocytosis: process by which cells engulf materials from their surroundings

1. Pinocytosis: “cell‐eating”; ingestion of small solid or fluid particles into small, membrane‐surrounded vesicles for movement into cytoplasm transport of proteins and strong solutions of electrolytes

2. Phagocytosis: “cell‐eating”; involves the engulfment and subsequent killing or degradation of microorganisms or other particulate matter phagocytic vesicle or phagosome is formed where it breaks away from



cell membrane and moves into cell membrane into cytoplasm, fuses with lysosome to be ingested by enzymes

E. Exocytosis: mechanism for the secretion of intracellular substances into the extracellular spaces important in removing cellular debris and releasing substances, such as hormones, synthesized in the cell

X. Ion Channels A. Highly selective; sodium, potassium, calcium, chloride ions specific

interactions between ions and the sides of channels produce extremely rapid rate of ion movement between negative and positive charged ions

B. Plasma membrane contains two basic groups of ion channels: leakage channels and gated channels 1. Leakage channels open in unstimulated state, whereas gated channels

open and close in response to specific stimuli 2. Three main types of gated channels

a. Voltage gated: electrically operated channels that open when membrane potential changes beyond certain point

b. Ligand gated: chemically operated and respond to specific receptor‐bound ligand, such as neurotransmitter acetylcholine

c. Mechanically gated: open or close in response to mechanical stimulations as vibrations, tissue stretching, pressure

XI. Membrane Potential A. Electrical potentials (measured in volts) exist across membranes of most

cells in the body B. Changes in the membrane potential are necessary for generation and

conduction of nerve impulses and muscle contraction C. Resting membrane potential = necessary for electrical excitability = present

when cell is not transmitting impulses 1. Maintained by sodium potassium pump which pumps out 3Na+ and 2K+

in 2. This will lead to a slight negative charge around the cell membrane inside

and a slight positive charge around the cell membrane outside XII. Body Tissues

A. Cell differentiation: process controlled by a system that switches genes on and off 1. Embryonic cells must become different to develop into all of the various

organ systems, and they must remain different after the signal that initiated cell diversification has disappeared

2. Process of cell differentiation is controlled by cell memory, which is maintained through regulatory proteins contained in the individual members of a particular cell type

3. Cell differentiation normally moves forward, producing cells that are more specialized than their predecessors not revert to an earlier stage of differentiation

B. Stem cells are still capable of cell division and serve as a reserve source for specialized cells throughout the life of the organism



1. Major source of cells that make regeneration possible in some tissues 2. Stem cells of the hematopoietic (blood) system have the greatest

potential for differentiation recreate blood and immune system, bone marrow transplants

C. Organization of Cells into Tissues 1. Cells with a similar embryonic origin or function are often organized into

larger functional units called tissues, and these tissues in turn associate with other, dissimilar tissues to form the various organs of the body

2. Four types: a. Epithelial: every lining in body, skin b. Connective: bones, joints c. Muscle d. Neural

3. Epithelial tissue a. Forms sheets that cover the body's outer surface, lines internal

surfaces, and forms glandular tissue b. Supported by a basement membrane c. Avascular, and must receive nourishment from capillaries in

supporting (underlying) connective tissues d. Classified according to number of layers present: simple, stratified,

pseudostratified e. Classified according to shape: squamous, cuboidal, columnar

4. Connective tissue a. Most abundant tissue of the body b. Found in a variety of forms, ranging from solid bone to blood cells that

circulate in the vascular system c. Types

i. Loose or areolar: soft and pliable; supports epithelial tissues and provides means by which these tissues are nourished

ii. Adipose: fatty tissue; shape body, thermal insulation, keeps organs in place

iii. Reticular: network of fibroblasts that synthesize type III collagen fibers and macrophages

iv. Dense o Irregular: consists of the same components found in loose

connective tissue, but exhibits a predominance of collagen fibers and fewer cells. This type of tissue can be found in the dermis of the skin (i.e., reticular layer), the fibrous capsules of many organs, and the fibrous sheaths of cartilage (i.e., perichondrium) and bone (i.e., periosteum). It also forms the fascia that invests muscles and organs

o Regular: rich in collagen fibers; form the tendons and aponeuroses that join muscles to bone or other muscles and ligaments that join bone to bone



5. Muscle tissue a. Contains actin (thin filaments) and myosin (thick) filaments b. Allow it to contract and provide

i. Locomotion and movement of skeletal structures (skeletal muscle)

ii. Pumping of blood through the heart (cardiac muscle) iii. Contraction of blood vessels and visceral organs (smooth muscle)

c. Three types: skeletal, cardiac, and smooth i. Skeletal (40‐45%) and cardiac = striated muscles actin and

myosin are arranged in large, parallel arrays in bundles, giving muscle fibers a striped or striated appearance = no mitosis

ii. Smooth muscle lacks striations = involuntary muscles = can undergo mitosis

6. Nervous tissue a. Consists of two cell types

i. Nerve cells or neurons o Consist of 3 parts

Soma: cell body Dendrites: multiple elongated processes, receive and carry

stimuli from the environment, from sensory epithelial cells, and from other neurons to the cell

Axon: single cytoplasm‐filled process, is specialized for generating and conducting nerve impulses away from the cell body to other nerve cells, muscle cells, and glandular cells

o Classified as afferent and efferent neurons according to their function Afferent or sensory neurons carry information toward the

CNS involved in the reception of sensory information from the external environment and from within the body

Efferent or motor neurons carry information away from the CNS they are needed for control of muscle fibers and endocrine and exocrine glands

ii. Glial or supporting cells o Form myelin, and have trophic and phagocytic functions o Four types of neuroglia are found in the CNS: astrocytes,

oligodendrocytes, microglia, and ependymal cells b. Distributed throughout the body serves as the body's

communication system c. Nervous system is divided anatomically into the central nervous

system (CNS), which consists of the brain and spinal cord, and the peripheral nervous system (PNS), which is composed of nerve tissue outside the CNS

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Cell and Tissue Characteristics