BIO 201: Chapter 2 Anatomy of a Representative Cell

Components of the Plasma Membrane

(1) Phospholipids - the plasma membrane is called the phospholipid bilayer - consists of the hydrophilic heads and hydrophobic tails (2) Proteins - there are 2 general types of membrane proteins: peripheral proteins and integral proteins - Peripheral proteins: attached to either the inner or outer membrane surface, depending on their function - Integral proteins (transmembrane proteins): embedded in the membrane - some integral proteins from channels that let water molecules, ions, and small water-soluble substances into or out of the cell - communication between the interior and exterior of the cell occurs through these channels - some of the channels are gated channels that can open or close to regulate recognition or as catalysts or receptor sites (3) Glycolipids - inner and outer surfaces of the plasma membrane differ in protein and lipid composition - the carbohydrate (glco-) component of the glycolipids and glycoproteins that extend away from the outer surface of the plasma membrane form a viscous, superficial coating known as the glycocalyx (calyx, cup) (4) Sterols - stabilize the membrane structure and maintain its fluidity - most common sterol in the plasma membrane of human cells is cholesterol

List the three active processes.

- active transport - endocytosis - exocytosis

plasma membrane (cell membrane)

Composition - lipid bilayer, containing phospholipids, steroids, proteins, and carbohydrates Function - isolates - protects - senses - supports - controls entrance/exit of materials

Nonmembranous Organelle: Microvilli

Composition - membrane extensions containing microfilaments Function - increase surface area to facilitate absorption of extracellular materials

Define anucleate.

(a-, without) - lack a nucleus - a cell without a nucleus will survive only 3 to 4 months (Ex): mature red blood cells

Membranous Organelle: Lysosomes

(lyso-, dissolution, + soma, body) Composition - vesicles containing digestive enzymes - vesicles filled with digestive enzymes formed by the RER and then packaged within the lysosomes by the Golgi apparatus - Primary lysosomes: contain inactive enzymes - Secondary lysosomes: contain activated enzymes, form when a primary lysosome fuses with another membrane-bound vesicle Function - removes damaged organelles or pathogens - defending against disease - perform essential cleanup and recycling activities inside the cell - Using the process of endocytosis, cells remove bacteria, fluids, and organic debris from their surroundings and isolate them within vesicles. Primary lysosomes fuse with these vesicles, forming secondary lysosomes, and the digestive enzymes within the secondary lysosomes break down the contents. Reusable substances such as sugars or amino acids are released into the cytosol, and the remaining wastes are eliminated by exocytosis. In this way, the cell not only protects itself against pathogens (disease-causing organisms) but also obtains valuable nutrients. - When muscle cells are inactive, lysosomes gradually break down their contractile proteins--this process accounts for the decreased muscle mass that occurs with aging or disuse. - If muscle cells become active once again, the destruction ceases. - In a damaged or dead cell, lysosomes disintegrate and release active enzymes into the cytosol. These enzymes rapidly destroy the proteins and organelles of the cell, a process called autolysis (auto-,self) - Because the breakdown of lysosomal membranes can destroy a cell, lysosomes have been called cellular "suicide packets"

Define multinucleate.

(multi-, many) - contain many nuclei (Ex): skeletal muscle cells

Nonmembranous Organelle: Cilia

(plural, cilia); (singular; cilium) Composition - membrane extensions containing microtubule doublets in a 9 + 2 array - composed of 9 groups of microtubule doublets surrounding a central pair of microtubules, an arrangement known as a 9 + 2 array - anchored to a compact basal body located just beneath the cell surface Function - move materials over cell surface - "beat" rhythmically to move fluids or secretions across the cell surface (Ex): Cilia lining the respiratory tract beat in a coordinated manner to move sticky mucus and trapped dust particles toward the throat and away from delicate respiratory surfaces. If the cilia damaged due to smoking or a metabolic problem, the irritant stay in the lungs and chronic respiratory develop.

Endoplasmic Reticulum (ER): cisternae

(singular, cisterna, a reservoir for water) - hollow tubes, flattened sheets, and rounded chambers

Microtubules: Flagella

(singular, flagellum, "whip") Microtubule Organization - same as cilia - resemble cilia but are much longer Location - at cell surface Function - propel sperm cells through fluid - a flagellum moves a cell through the surrounding fluid, rather than moving the fluid past a stationary cell (Ex): The sperm cell is the only cell in the human body that has a flagellum; it moves the cell along the female reproductive tract. If a man's sperm flagella are paralyzed or abnormal, the man is sterile because immobile sperm cannot reach and fertilize an oocyte (a female sex cell).

Membranous Organelle: Mitochondria

(singular, mitochondrion; mitos, thread, + chondrion, small granules) - double membrane, with inner membrane folds (cristae) enclosing metabolic enzymes - cristae: inner membrane contains numerous folds - matrix: these cristae surround the fluid contents and provide a large surface area for the organization of the enzymes that produce most of the ATP - control their own maintenance, growth, and reproduction Function - produce 95% of the ATP required by cell - produce ATP by breaking down organic molecules in a series of reactions that consume oxygen (O2) and generate carbon dioxide (CO2) Location - Red blood cells lack mitochondria because they obtain energy in other ways - Skeletal muscle cells typically contain as many as 300 mitochondria

Nucleus: nucleoli

(singular, nucleolus) - nuclear organelles that synthesize the components of ribosomes - a nucleolus contains histones, enzymes, and RNA - forms around a chromosomal region containing the genetic instructions for producing ribosomal proteins and RNA - most prominent in cells that manufacture many proteins, such as liver cells and muscle cells, because these cells need large numbers of ribosomes

Nucleus: chromosome

- DNA strands form complex structures - contains DNA strands bound to special proteins called histones - direct control over the synthesis of RNA - the nucleus of each of your somatic cells contains 23 pairs of chromosomes; one member of each pair came from your mother and one from your father.

Nucleus: Nucleoplasm

- a jelly-like fluid substance within the nucleus - contains a network of fine filaments, the nuclear matrix, which provides structural support and may help regulate genetic activity - ions, enzymes, proteins, small amounts of RNA and DNA are also suspended within the nucleoplasm

Define permeability.

- a membrane determines its effectiveness as a barrier - the greater the permeability, the easier it is for substances to cross the membrane

Cytoskeleton: Microtubules

- all cells posses microtubules - a small, hollow tubes built from the protein tubulin - a microtubule forms temporarily from a collection of tubulin molecules, but then disassembles into individual tubulin molecules once again - microtubular array is centered in a region called the centrosome - microtubules radiate outward from the centrosome into the edge of the cell. Functions: - form the main components of the cytoskeleton, giving the cell strength and rigidity and anchoring major organelles - as microtubules assemble and disassemble, they change the shape of the cell and may help the cell move - attach to organelles and other intracellular materials and move them around within the cell - during cell division, microtubules form the spindle apparatus that distributes the duplicated chromosomes (genetic material) to opposite ends of the dividing cell - form structural components of organelles such as centrioles, cilia, and flagella (nonmembranous organelles)

Define and describe cytoplasm.

- all the material found inside the cell - contains more proteins than extracellular fluid; protein account for 13-30% of the weight of the cell Two Major Components (1) Cytosol (intracellular fluid) - contain dissolved nutrients, ions, soluble and insoluble proteins, and wastes - plasma membrane separates the cytosol from the surrounding extracellular fluid (2) Organelles - intracellular structures that have specific functions

Nucleus: nucleosome

- at intervals, the DNA strands wind around the histones, forming a complex called a nucleosome - entire change of nucleosomes may coil around other histones - the degree of coiling determines whether the chromosome is long and thing or short and fat - in dividing cells, chromosomes are tightly coiled and clearly visible in light or electron micrographs - in cells that are not dividing, the chromosomes are loosely coiled, forming a tangle of fine filaments known as chromatin

What are the groups of microtubules in the cytoskeleton?

- centrioles - cilia - flagella

Cytoskeleton: Thick Filaments

- composed of myosin protein subunits - abundant in muscle cells, where they interact with actin filaments to produce powerful contractions

List the nonmembranous organelles.

- cytoskeleton - microvilli - centrosome - cilia - flagella - ribosomes

List the three passive processes.

- diffusion - osmosis - facilitated diffusion

Define extracellular fluid.

- fluid outside the cell - cells float in a watery medium

Define cytoskeleton.

- internal framework of fibers - filaments are grouped into bundles, forming a framework that makes the cytoplasm strong and flexible

What are the four major components of cytoskeleton?

- microfilaments - intermediate filaments - thick filaments - microtubules

List the membranous organelles.

- mitochondria - nucleus - endoplasmic reticulum - Golgi apparatus - lysosome - peroxisome

Describe plasma membrane and its functions.

- outer boundary of a cell - also called cell membrane or plasmalemma - extremely thin and delicate Four Important Functions (1) Physical isolation - lipid bilayer of the plasma membrane forms a physical barrier separating the inside of the cell from the surrounding extracellular fluid (2) Regulation of exchange with the environment - the plasma membrane controls the entry of ions and nutrients, the elimination of wastes, and the release of secretory products (3) Sensitivity - the plasma membrane is the first part of the cell affected by changes in the extracellular fluid - contain a variety of receptors that allow the cell to recognize and respond to specific molecules in the environment and to communicate with other cells - any alteration in the plasma membrane affects all cellular activities (4) Cell-to-cell communication, adhesion, and structural support - specialized connections between adjacent plasma membranes or between plasma membranes and extracellular materials allow cells to communicate with and attach to each other and give tissues a stable structure.

Define selectively permeable.

- permits some substances to cross freely but restricts others from crossing (Ex): plasma membranes

Nucleus: histones

- proteins associated with the DNA of the nucleus, and around which the DNA strands are wound.

Cytoskeleton: Microfilaments

- slender strands composed of the protein actin Two major functions (1) anchor the cytoskeleton to integral proteins of the plasma membrane - stabilizes the position of the membrane proteins, strengthens the cell, and attaches the plasma membrane to the underlying cytoplasm (2) actin microfilaments interact with other microfilaments or larger structures composed of the protein myosin - this interaction allows part of the cell to move or changes the shape of the entire cell

Extensions of the Plasma Membrane: Microvilli

- small, finger-shaped projections of the plasma membrane - found in cells that absorb materials from the extracellular fluid, such as in the small intestine and kidneys - promote absorption by increasing the surface area exposed to the extracellular environment - a network of microfilaments stiffens each microvillus and anchors it to the terminal web, a dense supporting network within the underlying cytoskeleton Cytoskeleton - the cell's internal framework of filaments and fibers - interactions between these microfilaments and the cytoskeleton produce a waving or bending action - movement of the microvilli circulate fluid close to the plasma membrane, bringing dissolved substances into contact with receptors on the membrane surface

Cytoskeleton: Intermediate Filaments

- stabilizes organelles - transport materials within the cytoplasm - provide strength (Ex): specialized intermediate filaments in nerves called neurofilaments support the axons, which are cellular processes that may be up to a meter in length

What can cause the differences of permeability?

- substance's size, electrical charge, molecular shape, solubility, or any combination of these factors - the permeability of the plasma membrane varies depending on the organization and characteristics of the lipids and proteins within it - a substance may pass through the membrane by a passive or active process

cytosol

Component - fluid component of cytoplasm - may contain inclusions of insoluble materials Functions - distributes materials by diffusion - stores glycogen, pigments, and other materials

Nonmembranous Organelle: Ribosomes

Composition - RNA and proteins - attached ribosomes bound to rough endoplasmic reticulum - free ribosomes scattered in cytoplasm - each ribosome, which is composed of about 60% RNA (a macromolecule) and 40% protein, consists of two subunits that interlock as protein synthesis begin Function - synthesize protein - manufacture proteins using information provided by the DNA (the carrier of genetic information) of the nucleus. When protein synthesis is complete, the subunits separate. There are 2 major types of ribosomes. (1) Free ribosomes are scattered throughout the cytosol. - Proteins manufactured by free ribosomes enter the cytosol. (2) Attached ribosomes are temporarily attached to the endoplasmic reticulum, a membranous organelle. - Proteins manufactured by attached ribosomes enter the lumen, or internal cavity, of the endoplasmic reticulum, where they are modified and packaged for export.

Nonmembranous Organelle: Centrosome

Composition - cytoplasm containing two centrioles, at right angles - each centriole is composed of nine microtubule triplets - a clear region of cytoplasm that contains this pair of centrioles Function - essential for movement of chromosomes during cell divisions - organizes microtubules in cytoskeleton

Membranous Organelle: Endoplasmic Reticulum (ER)

Composition - network of membranous channels extending throughout the cytoplasm - a network of intracellular membranes forming hollow tubes, flattened sheets, and rounded chambers called cisternae - Rough ER: has ribosomes bound to membranes - Smooth ER: lacks attached ribosomes Functions (1) ER - synthesizes secretory products - intracellular storage and transport - synthesis: the ER contains specialized regions that manufacture lipids, proteins, and carbohydrates; the cisternae of the ER store these manufactured products - storage: the ER stores synthesized molecules and substances absorbed from the cytosol without affecting other cellular operations - transport: substances travel from place to place within the cell inside the ER - detoxification: the ER absorbs drugs and toxins and neutralizes them with enzymes - functions as a combination workshop, storage area, and shipping depot; newly synthesized proteins undergo chemical modification and are packaged for export to their next destination, the Golgi apparatus (2) Rough ER (RER) - modifies and packages newly synthesized proteins - outer surface contains attached ribosomes - ribosomes synthesize proteins using instructions provided by a strand of RNA - as the polypeptide chains grow, they enter the cisternae of the ER, where they are further modified - the proteins and glycoproteins produced by the RER are packaged into small membrane sacs that pinch off the edges or surfaces of the ER; these transport vesicles deliver the proteins to another organelle called the Golgi apparatus. (3) Smooth ER (SER) - synthesizes lipids, steroids, and carbohydrates; stores calcium ions - lacks ribosomes - removing and inactivating toxins (Ex): Pancreas cells manufacturing digestive enzymes contain extensive RER and little SER. The situation is reversed in cells synthesizing steroid hormones in reproductive organs.

Membranous Organelle: Nucleus

Composition - nucleoplasm containing nucleotides, enzymes, nucleoproteins, and chromatins - surrounded by a double-layered membrane (nuclear envelope) containing nuclear pore - nucleolus: dense region in nucleoplasm containing DNA and RNA - consists of nuclear envelope, nucleolus, and nuclear pore - nuclear envelope: a double-layered membrane that encloses a narrow perinuclear space (peri-, around). - nuclear pores: chemical communication between the nucleus and cytosol occurs through here; a complex of proteins that regulates the movement of macromolecules into and out of the nucleus; these pores account for about 10% of the surface of the nucleus, permit the movement of water, ions and small molecules but regulate the passage of large proteins, RNA, and DNA Functions (1) nucleus - controls metabolism - stores and processes genetic information - controls protein synthesis - control center for cellular operations - determines the structural and functional characteristics of the cell by controlling which proteins are synthesized, when they are synthesized, and in what amounts (2) nucleolus - site of rRNA synthesis and assembly of ribosomal subunits

Nonmembranous Organelle: Cytoskeleton

Composition - proteins organized in filaments or slender tubes - consists of microtubules and microfilaments Functions - strengthens and supports - moves cellular structures and materials

Membranous Organelle: Peroxisome

Composition - vesicles containing degradative enzymes - smaller than lysosomes and carry a different group of enzymes - formed by free ribosomes and are inserted into the membranes of pre-existing peroxisomes - new peroxisomes result from the cell recycling older, pre-existing peroxisomes that no longer contain active enzymes Functions - catabolizes fats and other organic compounds - neutralizes toxic compounds generated in the process - one group of enzymes, oxidases, breaks down organic compounds into hydrogen peroxide (H2O2), which is toxic to cells - catalase, another enzyme within peroxisomes, then converts hydrogen peroxide to water and oxygen - peroxisomes also absorb and break down fatty acids - peroxisomes are most abundant in liver cells, which remove and neutralize toxins absorbed in the digestive tract.

Describe cytosol.

Composition of cytosol differs from extracellular fluid in 3 ways... (1) contains high concentration of potassium ions; net excess of negative charge (2) contain high concentration of dissolved and suspended proteins; these proteins give the cytosol a consistency ranging from that of thin maple syrup to that of almost-set gelatin (3) contains small quantities of carbohydrates and large amounts of amino acids and lipids - the cell breaks down carbohydrates for energy - uses amino acids to manufacture proteins - uses the lipids to maintain plasma membrane and provide energy when carbohydrates are unavailable - contain masses of insoluble substances known as inclusions, or inclusion bodies - most common inclusions are stored nutrients, for example, glycogen granules in liver or skeletal muscle cells and lipid droplets in fat cells

Microtubules: Cilia

Microtubule Organization - nine groups of long microtubule doublets form a cylinder around a central pair Location - at cell surface Function - propel fluids or solids across cell surface

Microtubules: Centrioles

Microtubule Organization - nine groups of microtubule triplets form a short cylinder Location - in centrosome near nucleus Function - organize microtubules in the spindle to move chromosomes during cell division

Describe organelles.

Subdivided into.. (1) Nonmembranous organelles are always in contact with the cytosol. - includes the cytoskeleton, centrioles, cilia, flagella, and ribosomes (2) Membranous organelles are surrounded by membranes that isolate their contents from the cytosol.

Cells that can divide contain...

a pair of centrioles arranged at right angles to each other.

Membranous Organelle: Golgi Apparatus

aka. Golgi complex Composition - stacks of flattened membrane discs (cisternae) containing chambers - typical Golgi apparatus consists of 5 to 6 cisternae - flattened membrane discs, or cisternae, of the Golgi apparatus communicate with the ER and with the cell surface by the formation, movement, and fusion of vesicles Functions - stores, alters, and packages secretory products and lysosomal enzymes (1) Package enzymes for use in the cytosol - among the vesicles that are packaged by the Golgi and remain in the cytoplasm are lysosomes, which are filled with enzymes that break down engulfed foreign material or pathogens as well as damaged membranous organelles (2) Renew or modify the plasma membrane - as the Golgi apparatus loses membrane through the generation of vesicles at the maturing (or trans) face, it gains membrane by the fusion of transport vesicles at the forming (or cis) face - when Golgi-generated vesicles fuse with the plasma membrane, it adds to the surface area of the cell, balancing the membrane loss that occurs during endocytosis - over time, this process can change the sensitivity and functions of the cell - in an actively secreting cell the change can be rapid, and the entire plasma membrane may be replaced every hour (3) Synthesize and package secretions - at the maturing face, vesicles form that carry materials away from the Golgi apparatus - vesicles containing material that will be secreted from the cell are called secretory vesicles - when a secretory vesicle fuses with the plasma membrane, its content are released into the extracellular fluid; this process is known as exocytosis SYNTHESIS AND PACKAGING OF SECRETIONS: STEPS (1) Protein and glycoprotein synthesis occurs in RER. Some of these proteins and glycoproteins remain within the ER. (2) Secretory products are packaged into transport vesicles that eventually bud off from the ER. These transport vesicles then fuse to create the forming (cis) of the Golgi apparatus. (3) Each cisterna physically moves from the forming face to the maturing face, carrying with it its associated proteins. This process is called cisternal progression. (4) The maturing (trans) face generates vesicles that carry modified proteins away from the Golgi apparatus.

Define freely permeable.

all substances cross without difficulty

Define intracellular.

inside the cell

Cells that do not divide, such as...

mature red blood cells and skeletal muscle cells, lack centrioles.

Define impermeable.

nothing crosses a membrane