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Chapter 3 cells and tissues

Chapter 3

Cell: a vast collection of molecules makes up the cell, the basci functional unit of most living thing.

What is the basic function of cell?
Cells take in oxygen and nutrients, they extract energy from the nutrients for growth, repaire, and reproduction, and they get rid of waste such as carbon dioxide.

What is cell biology?
the study of how cells work.

What is the central theme of physiology?
Coorperation between cells is a central theme of physiology.

What is zygote?A zygote (Greek: ζυγωτόν) is a cell that is the result of fertilization. That is, two haploid cells—usually (but not always) an ovum from a female and a sperm cell from a male—merge into a single diploid cell called the zygote (or zygocyte).
Animal zygotes undergo mitotic cell divisions to become an embryo. Other organisms may undergo meiotic cell division at this time (for more information refer to biological life cycles).Twins and multiple births can be monozygotic (identical) or dizygotic (fraternal).

What is differentiation?
a process that developing cells take on more than 200 different shapes and functions. delective gene expression.

How does differentiation occur?
Each cell inherites the same genetic information in its DNA, but no cell uses all of it. only selected genees are activated. the final shape and size of a cell and its contents reflect its function.

Composition of cell
Cell----cytoplasm, nucleus,cell membrane
Cytoplasm---cytosol, organelles
Organells-----nonmembrancous organells, membranous organells.
Nonmembranous organells: cytoskeleton, centrioles, centerosomes, cilia, flagella, ribosomes, vaults.
Membranous organells: mitochoria, endoplasmic reticuluc, Golgi apparatus,lysosomes, perocisomes.

cell membrane
the selectively permeable cell membrane (or plasma membrane or plasmalemma) is a thin and structured bilayer of phospholipid and protein molecules that envelopes the cell. It separates a cell's interior from its surroundings and controls what moves in and out. Cell surface membranes often contain receptor proteins and cell adhesion proteins. There are also other proteins with a variety of functions. These membrane proteins are important for the regulation of cell behavior and the organization of cells in tissues.
Hydrophlici phophate head, hydrophobic lipi tail.
Some of these proteins simply adhere to the membrane (extrinsic or peripheral proteins), whereas others might be said to reside within it or to span it (intrinsic proteins – more at integral membrane protein). Glycoproteins have carbohydrates attached to their extracellular domains. Cells may vary the variety and the relative amounts of different lipids to maintain the fluidity of their membranes despite changes in temperature. Cholesterol molecules (in case of eukaryotes) or hopanoids (in case of prokaryotes) in the bilayer assist in regulating fluidity

Function of glycoproteins and glycolipids on membrane extracellusr surface.

What is the function of cemm membrane?
1, gateway, 2, barrier 2, regulate exchange between the cell the ECF.

Cytoplasm in cludes cytosl and organells
Cytosol: is semigelatinous substance. contains: 1, dissolved nutrients 2, ions 3, waster products 4, particles of insoluable materials(inclusions) is the internal fluid of the cell, and a portion of cell metabolism occurs here. Proteins within the cytosol play an important role in signal transduction pathways and glycolysis. They also act as intracellular receptors and form part of the ribosomes, enabling protein synthesis.The cytosol is not a "soup" with free-floating particles, but is highly organized on the molecular level. As the concentration of soluble molecules increases within the cytosol, an osmotic gradient builds up toward the outside of the cell. Water flows into the cell, making the cell larger. To prevent the cell from bursting apart, molecular pumps in the plasma membrane, the cytoskeleton, the tonoplast or the cell wall (if present), are used to counteract the osmotic pressure.

Nonmembranous organelles: in direct contact with the cytosl. movement of material between these organeleesa nd the cytosl does not require transport across a membrane. these organelles can be divided into two groups: 1, those made from RNA and protein, 2, those made from insouble protein fiber (cytoskeleton, centrosomes, and centrioles, cilia, and flagelaa)

Ribosomes: is an organelle composed of rRNA and ribosomal proteins (known as a Ribonucleoprotein). It translates mRNA into a polypeptide chain (e.g., a protein). It can be thought of as a factory that builds a protein from a set of genetic instructions. Ribosomes can float freely in the cytoplasm (the internal fluid of the cell) or bind to the endoplasmic reticulum, or to the nuclear envelope. Since ribosomes are ribozymes, it is thought that they might be remnants of the RNA world.
Ribosomes consist of two subunits (Figure 1) that fit together (Figure 2) and work as one to translate the mRNA into a polypeptide chain during protein synthesis (Figure 3). Each subunit consists of one or two very large RNA molecules (known as ribosomal RNA or rRNA) and multiple smaller protein molecules. Crystallographic work has shown that there are no ribosomal proteins close to the reaction site for polypeptide synthesis. This suggests that the protein components of ribosomes act as a scaffold that may enhance the ability of rRNA to synthesise protein rather than directly participating in catalysis.
1, (polyribosome)Free ribosomes usually produce proteins used in the cytosol or organelle in which they occurthey are free in solution and not bound to anything within the cell.
2, (fixed ribosomes) certain proteins are synthesized by a ribosome they can become "membrane-bound". The newly produced polypeptide chains are inserted directly into the ER by the ribosome and are then transported to their destinations. Bound ribosomes usually produce proteins that are used within the cell membrane or are expelled from the cell via exocytosis.

Three sizes of protein fibers in the cytoplasm:
The protein fibers in the cytoplasm are classified by their diameter. the thinnest, microfilament--actin(protein); larger intermediate filament----myosin(muscle protein), Keratin (hair and sking_ and neurofilament (nerve cell); Thick filaments-----intermediate myosin filaments combine; microtubules ---tubulin.
microtubules combine to form more compex structures of centrioles, cilia, and flagelaa.

The important functions of cytoskeleton
1, mechanical strength to the cell, determing the shape of the cell. the cytoskeleton helps to support microvilli to increase the surface for absorption.
2, the fibers stabilized the positions of organelles.
3, transport materials into the cell and within the cytoplasm.
4,fibers of the cytoskeleton connect with protein fibers in the extracellular space, linking cells to each other and to support material outside the cell, allow transfer of information from one cell to another.
5, enables certain cells to move, (white cell and squeeze out of blood vessels and travel to sites of infection.

Centrosomes and centriole ( associated with microtubules)
centrosomes: regions of darkly staining material close to nucleus. act as cell's microtubule-organizine center, where tubulin molecules are assembled into microtubules.
centrosome contain two centrioles: each centriole is a cylindrial bundle of 27 microtubules, arranged in nine triplet. Cells that can't not undergo cell division, lack centrioles.

Cillia and flagella (movable hairlike structures)
cilia: short, hair like structures projecting from the cell surface.the surface of a cilium is a continuation of the cell membrane, and its core contains nine pairs of microtubules surrounding a central pair. the microtubules terminate inside the cell at the basal body. its movement creats currents and sweep fluids or secretions across the surface.
flagella: same microtubules arrangement but larger. only one or two flagela. are found on free-floating single cell. the function is to push the cell through fluid with wave like movements of the flagellum.

Many membranous organelle's membrane have lumen(cavity of a hollow tube)

What is the function of those membranes?
1, the membrane barrier allows the organells to contain substances that might be harmful to the cell if they were free.
2, It also allows the cell to separate different funtions.

Mitochondria(ATP production): are small sperical to elliptical organelles with an unusual double wall. The outer membrane of the wall gives the mitochondrion its shape. the inner membrane if folded into leaflet called cristae. They are studded with proteins, including ATP synthase and a variety of cytochromes. The cristae provide more surface area for chemical reactions to occur within the mitochondria. This allows cellular respiration (aerobic respiration since the mitochondria requires oxygen) to occur. matrix contains enzyme, ribosomes, granuels, and DNA. intermembrane space space between the outer and inner memberanes is a region plays an important role in the production of ATP. The number of mitochondria is depend on the energy a cell needs.

Why mitochondira is unusual?
1, in matrix, they have their own DNA, this mitochondrial DNA, along with the ribosomes, means it can produce their own proteins. why? because, mitchodira are the descendants of bacteria that invaded cells millions of years ago. the bacteria developed a mutual relationship with host and becomme an integral part of the host cell.
2, their ability to replicate themselves even when the cell not undergoing cell division. this process is aided by the presence of mitochondrial DNA that allows the organeels to direct their own duplication. small daugher mitochondria pinching off an enlarged parent. then produces more engery with the duplicated mitochonrial.

The endoplasmic reticulum( the site of protein and lipid synthesis)
ER, is a netword of interconnected membrane tubes. that are a continuation of the outer nuclear membrane. 1, Rought ER(with ribosomes) and2, Smooth ER.
Three major functions: 1, synthesis, 2, storage 3, transport of biomolecules.

SER: the main site for the synthesis of fatty acid, steroids, and lipids. Phospholipids for the cell memrabne are procued here, cholesterol is modified into steroid hormones, such as the sex homones. the SER of liver and kiney cells detoxifies or inactivate drugs.

RER: main site for the synthese of protein. protein assembled on ribosomes attached to the surfaced of RER, then inserted into the lumen, where they undergo chemical modification. most of these proteins are packaged into vesicles that pinch off from the RER, then scross the cytosol to the Golgi apparatus.

Golgi apparatus( package protein into membrane-bound vesicles)
1, consists of 5 or 6 hollow curved sacs stacked on top of each other and conncected so that they share a single lumen.
2, the convex side of the stack faces the RER and receives the transport vesicles from it.
3, these transport vesicles fuse with the membranes of the golgi sac and discharge their contents into its lumen.
4, as the proteins move through teh sac, they may be modified by enzymes. long proteins into smaller protein, or carbohydrates attached to proteins to make glycoproteins.
5,the processed proteins are enclosed in a membrane-bound vesicles thatp inch off from the concave face of the golgi and move out into the cytosole.

Vesicles: 1, secretory vesicles: contain proteins that will be exported to other parts of the body. Secetion is the process by which a cell release a substance into the extracelluar space.
2, storage vesicles: never leave the cytoplasm, lysosomes are the major storage vesicles of the cell.

Lysosomes: intracelluar digestive system.
small, spherical storage vesicles that membrane-bound granules. they contain powerful enzymes and act as the digestive system of the cell.
1, they take up bacteria or old organelles, such as mitochondria, and use enzyme to break down them into component molecules. those molecules that can be reused are reabsorbed into the cytosole, while the rest are dumped out of the cell.
2, the digestive enzymes are not always kept ioslated within the membranes of the organelles. lysosomes release their enzymes to dissovle extracelluar support material, the inappropriate release of lysosomal enzymes has been implicated in certain diease state.
3, cells allow that enzymes of their lysosomes to come in contact with the cytoplasm, leading to self digestion of all or part of the cell.

Why enzyme do not destory the cell that contains them?
Because these enzymes are activated only by very acid conditions, 100times more acid than the normal cytoplasm. when lysosome first pinch off from the Golgi appratus, their pH is the same as that of the cytosol, 7.0-7.3. the enzyme then is inactive. it only activate at 4.8-5.0

What is lysosomal storage disease?
lysosomes are effective because they lack specific enzymes. Tay-Sachs disease. Infant with that disease have defective lysosomes that fail to break down glycolipids in nerve cell. al=ccumulation of the glycolipid in the cells cause the nervous system dysfunction, including blindness and loss of coordination.

Peroxisomes( contain enzymes that neutralize toxin)
They are storage vesicles that smaller than lysosomes. the main function:1, degrade long-chain fatty acids and 2, potentially toxin foreign molecules. Perixisomes get their name from the breakdown of fatty acids generate hydrogen peroxide. (H2)2), a toxic moledcule. Peroxisome convert this peroxide to oxygen and water by using the enzyme catalase. its disorders disrupt the normal processing of lipids and disrupt the normal function of the nervous system by altering the structure of nerve cell membranes.

Nucleus ( control center)
contains: DNA, genetica material controls all cell processes.
Nuclear envelope: two membrane structure that separates the nucleus from the cytoplasmic compartment. the outer membrane is connected with the ER, and both memebranes of the envelope are pierced by pores. communication between the nucleus and cytosol occurs through the nuclear pore complexes large protein complexes with a central channel. ions and small molecules move freely through this channel when it is open, but proteins and RNA must be transported by a process that uses energy. this requirment allows the cell to restric large molecules such as DNA to the nucleus and enzymes to nucleus and cytoplasm.

Chromatin: celling that are not dividing, most DNA appears as randowmly scatteded granular material.
A nucleus also contain from 1 to 4 larger dark-staining bodies of DNA, RNA, and protein called nucleoli. which contain the genes and proteins that control the synthesis of RNA for ribosomes.

TISSUE
Tissue:cells assemble into larger untis called tissues.

Cell junction: collections of cells held together by specialized connection called cell junctions.

Histology: study of tissues structure and function is known as histology.
1, shape and size of the cells
2, how the cells are arranged in the tisseus( scattered, layers)
3, how the cells are connected to each other
4, the amount of extracellular material that is present in the tissues.

What are four primary tissues types in human body?
1, epithelial 2, connective 3, muscle 4, neural or nerve

Matrix: is extracelluar material that is synthesized and secreted by the cells of a tissues. When matrix proteins attach to proteins in the cell membrane, they provides a means of communication between the cell and its external environment. the amount of matrix in a tissues caries. nerve and muscle have little matrix, but the connective tisseus, cartilage, bone and blood have matrix that occupies as much volume as their cells. the consistency of matrix varies from watery (blood and lymph) to rigid (bone) . in many tissues, matrix is composed of comeplex glycoprotein molecules mixed with insoluable protein fibers. the protein fibers provide strength and anchor cells to the matrix.

CAMs: membrane proteins known as cell adhesion molecules.

Cell junction hold cells together to form tissues: 1, adhesive junction 2, tight junctions 3, gap junctions.

Adhesive junction: are recognizable by the dense glycoprotein bodies: plaques. lie just inside the cell membranes in the region where the two cells connect. the protein linkage of adesive cell junction is very strong, it allows sheets of tissue in skin and lining body cavities to resist damage from stretching and twisting. however, it can be broken. a blister results: fluid accumulates in the resulting space and the payer separate. 1, desmosomes 2, adherens junctions. desmosomes: created by membrane spanning protein called cadherins that connenct each other across the intercellular space. and link to intermediate filaments of the cytoskeleton. it may be small points of contact( spot desmosomes) or bands that encircle the entire cell (belt desmosomes). Hemidesmosomes: use integrins to anchor cell to matrix glycoproteins . Adherens junction, similar to semosomes but not as strong. also use caherins.

Tight junction: serve to prevent the movement of material past the cells they link. cells fuse together with occludins. thereby making a barrier. occur next to adherens junction. the combination is called a junction complex.(tight and adherens).

Comparision between tight and adherens: tight junction: very little can pass from one side of the wall to other. adherens, allow material to pass.

Gap junction: create cytoplasmic bridges between adjacent cells so that chemical and electrical signal pass rapidly from one cell to the next. uses protein connexins, resemble holow revet with narrow channels throught their centers. Small molecules and ions move through the channels from cell to cell. very important in cell to cell communication in many tissues, including liver, pancrease...

Function of epithelial tissues.
1, act as a barrier to keep water in the body and invaders such as bacteria out.
2, control the movement of material between the external environment and the extracellular fluid of the body. nutrients, gasses, and wastes much often across several different epithelia in their passage beteen cells and outside world.
3, is specialized to manufacture and secret chemicals into the blood or to the external environment. sweet and saliva are substances secreted by epithelia into the environment. hormones, signal molecules used to maintain hoeostasis, are secreted into the blood.

Structure of epithelia:
1, a thin layer of extracellular matrix that lies between the cells and their underlying tissues: basal lamina, basement membrane. : a network of fine protein filaments embedded in glycoprotein. the filaments hold the epithelial cells to the underlying cell layer.
2, cell junction in epithelia: leaky : adhesive junctions leave gaps or pore and allow molecules to pass across the epethelium cells. (capillary blood vessels) tight: selective to what can pass and what can not pass. (liver)

Types of epithelia:
1: sheets of tissues that lie on the surface of the body or that line the inside of tubes and hollow organs : a, simple (one cell think) b, squamous: (three cells) c, columnar.
2, secretory epithelia that synthesize and release substances into the extracelluar space.

Five functional types of epithelia:
1, exchange epithelia: permit rapid exchange of material, gases.
2, transport epethelia: selective in the intestinal tract, and the kidney
3, ciliated epithelia: in the airway of the respiratory system and in the female reproductive tract. (nontransporting ,moving fluid and particles)
4, protective epithelia: surface of the body and inside the openings of the body cavities. prevent exchange, stratified, toughened by keratin.many layers.short life span.
5, secretory epithelia: synthesize and release substances into the extracelluar space or into blood.

What are the characteristics of transporting epethelia?
1, one layer cell, but much thicker. mostly cuboidal or columnar in shape.
2, the apical membrane is the surface of the cell that faces the lumen. has microvilli.increase the surface area for transport. basolateral membrane face the ECF also increase the cell's surface area.
3, cells are tight to very tight junctions. means that material must move into an epithlial cell on one side of the tissue and out of the cell on the other in order to cross the epithelium.
4, most cell that transport material have numersou mitochondria to provide energy for transport.

Gland: secretory cells group together to form a multicellular gland. :1, exocrine glands 2, endocrine glands.

Exocrine glands: release their secretion into the external enironment. most exocrine glands release their products through open tubes as ducts. Typical exocrine glands include sweat glands, salivary glands, mammary glands and many glands of the digestive system.

What are the two types of secretion exocrine glands secrete?
1, serous secretion: watery solutions, many of them contain enzymes.tears, sweats and digestive enzymes.
2, mucous secretions: sticky solution containing glycoproteins and proteoglycan. Goblet cells are single exocrine cells that produce mucus.

Endocrine glands:ductless glands that secrete chemical messengers called hormones that circulate within the body via the bloodstream to affect distant organs. Hormones act as "messengers", and are carried by the bloodstream to different cells in the body, which interpret these messages and act on them.
The endocrine system links the brain to the organs that control body metabolism, growth and development, and reproduction.The endocrine system regulates its hormones through negative feedback. Increases in hormone activity decrease the production of that hormone. The immune system and other factors contribute as control factors also, altogether maintaining constant levels of hormones. (pituiary gland, throid gland, pancreas.)

Connective tissues provide rupport and barriers.
the distinguishing characteristic if the presence of extensive extracelluar matrix containing widely scattered cells. the cells secrete and modify the matrix of the tissue.

Stucture of connective tissue
1, the matrix of connective tissue if a ground substance of glycoproteins and water in which insoluble fiberous protein fibers are aaranged. ( one can me watery matrix of blood, the other is the hardened matrix of bone, inbetween are solutions of glycoproteins that vary in consistency from syrupy to gelatinous)
2, the cells lie embedded within the extracellular matrix. fixed : if cells remain in one place, they are responsible for local maintenance, tissue repair, and energy storgage. mobile : if cells can move from place to place, mainly for defense.
3, cells can modify the matrix by adding, deleting , or rearranging molecules. -blast: on a connective tissue cell indicates a cell that is either growing or secreting extracelluar matrix. cells that breaking down matrix are --clast. cells that are neither growing, secreting nor breaking ---cyte(cell).
4, connective cells produce fibers of the matrix. 1: collagen: most abundant protein in human, 1/3 of human dry weight. most diverse. 2, elastin: coiled, wavy protein that returns to original length after being stretched. 3, fibrillin: elastin combines to form filaments and sheets of elastic fibers. 4, fibronectins: important in would healing and blood clotting.

Types of connective tissues
1, loose 2, dense.

Loose connective tissues: elestic tissues that underlie skin and provide support for small glands.

Dense connective tissues: primary function is strength or flexibility.: tendons, ligaments, and sheath that surround muscle and nerves. collagen fibers are the dominant type.

Tendons:muscule to bones.

Ligaments: bone to bone. because contains elastic fibers in addition to collagen fiber.

Adipose tissue: make up of adipocytes or fat cells. white fat: a single enormous lipid droplet, adult, brown fat: multiple lipid droplet, infant.

Blood : watery matrix. lack insoluble protein but contains soluble proteins.

Cartilage and bone: supporting connective tissues,: dense ground substances contains closely packed fibers. Cartilage: solid, flexible lack of blood supply, nutrients and oxygen must reach the cells of cartilage by diffusion. very slow. Bone: matrix is calcified because it contains mineral deposits which gave strength and rigidy.

Why muscle and neural tissues called the excitable tissues?
because their ability to generate electrical signals called action potentials.

Muscle: contract and produce force and movement. 1, cardiac muscle 2, smooth muscle 3, skeleton muscle

Neural tissues: 1 neurons: carry information in the form of chemical and electrical signals from one part of thte body to another. concentrated in the brain and spinal cord, also include a network that extends to every part of the body. 2, Glial cells, support cells for neurons.

Growth: is a process that most people associate with the period from birth to adulthood..

Cell death occur two ways: one messay and one tidy.
Necrosis: cells die from physical trauma, toxin, lack of oxygen when their blood supply is cut off.
Apoptosis: programmed cell deaeth. cell suicide, a complex process regulated by multiple chemical signals.

If cells in adult body are constanting dying, where do their replacement come fomr?
in most case, they come from mature cells of the same tyep that are still able to make mitosis.
the exceptions are blood cells and nerve and mucels cells. blood cells are formed from unddifferntiated precursor cells called stem cells, that are found in the bone marrow.

posted by C-T @ 12:02 PM