Biology 110

Tri-County Technical College

Pendleton, SC

Chapter 3

Cells and Tissues

Generalized Cell

• No one cell type exactly like all others• Do have same basic parts and certain

functions common to all cells• GENERALIZED CELL constructed to

demonstrate these typical features• We will concern ourselves with

generalized eukaryotic (eucaryotic) cell

General Areas of Eukaryotic Cell

In general, eukaryotic cells have 3 main regions

NUCLEUS located near center of cellCYTOPLASM is semifluid material that

surround nucleus and extends to the PLASMA MEMBRANE which forms the outer boundary of the cell

Organelles

“little organs” Specialized cellular COMPARTMENTS

designed to perform SPECIFIC job Most bounded by membrane (some bilayer) Compartmentalization crucial to their ability to

perform specialized functions ER, Golgi apparatus, lysosomes,

mitochondria, peroxisomes, cytoskeleton

Functions and Parts of Nucleus

• Control cell for cell containing its DNA• Surrounded by bilayer nuclear membrane• Has three distinct regions (structures)• NUCLEAR MEMBRANE• NUCLEOLUS (nucleoli)• CHROMATIN

The Nuclear Membrane

• Bilayer of phospholipids with nuclear pores

• Semipermeable– Controls what enters and exits the nucleus

• Encloses the nucleoplasm– Jellylike fluid in which the nucleoli and

chromatin are suspended

The Nucleolus• May only be one, but some cells have

several

• Stains darker than other regions of DNA

• Is site where ribosomal RNA is transcribed off info in DNA

• Combined with protein(s) to form functional ribosome

• Review: ribosomes are actual site of protein synthesis

DNA and its Forms

• CHROMATIN is loose network of threads of DNA– Unwound, not supercondensed or supercoiled– Easy for replication and transcription to occur

• Must be duplicated in S of interphase• In dividing cells, chromatin condenses into

CHROMOSOMES (X—well, kind of)

The PM and more…much more

• Bilayer of phospholipids with proteins and other molecules floating in layer

• Review: fluid mosaic model• Pores, carriers, transporters, receptors,

& enzymes • Cholesterol and glycoproteins in layers• GPs determine blood type; act as

receptors for certain bacteria, viruses, or toxins; & play role in cell-to-cell interactions

The PM, continued

• Specializations (epithelial cells lining hollow body cavities such as small intestine) occur as MICROVILLI and/or MEMBRANE JUNCTIONS

• MICROVILLI increase surface area of cell so absorption can occur more quickly

• Membrane junctions vary structurally depending on their role

Types of Membrane Junctions• Tight junctions are impermeable junctions

that bind cells into leakproof sheets– Stomach and small intestine best examples

• Desmosomes are anchoring junctions that prevent cells subjected to mechanical stress from being pulled apart– Button-like thickenings of PM connected by fine

protein filaments

• Gap junctions allow for communication– Heart and between embryonic cells– Neighboring cells connected by CONNEXONS– Composed of protein that span entire width of

abutting membranes

Cytoplasm

• Cellular material outside nucleus and inside PM

• Site of most cellular activities• Has 3 major components• CYTOSOL is semitransparent fluid that

suspends other elements• ORGANELLES (already defined)• INCLUSIONS are nonfunctioning units

– Most are stored nutrients or cell products– Fat droplets, glycogen, pigments (melanin) mucus,

secretory products, and various kinds of crystals

The Mitochrondrion

• “Powerhouse of the cell”• Important in aerobic respiration

– Krebs cycle and chemiosmosis

• Important parts: outer membrane, inner membrane highly folded (CRISTAE)

• Gelatinous fluid inside the cristae called the MATRIX

Ribosomes

• Composed of rRNA and proteins• Actual site of translation (protein synthesis)• Some float free in cytoplasm while others

attached to endoplasmic reticulum (RER)• Functional ribosome composed of two

subunits• 80S and & 70S and never the twain will meet

Endoplasmic Reticulum• System of fluid-filled cisterns in cytoplasm• Rough ER studded with ribosomes

– Very important in manufacturing proteins destined for export from the cell

– Enzymes that catalyze membrane lipid synthesis reside on outer surface of RER

• Smooth ER has no ribosomes– Cholesterol synthesis and breakdown, fat

metabolism, and is detox center for the cell– Liver cells and cells that synthesize steroid-based

hormones packed with SER

Golgi Apparatus• Stack of flattened membranous sacs

associated with swarms of tiny vesicles• Traffic director for cellular proteins• UPS of the cell

– Receives, modifies, packages, and ships cellular products

• Transport vesicleGolgisecretory vesicles

• Most SVs exit cell by exocytosis (mucus and digestive enzymes)

• Also produces lysosomes

Lysosomes• Breakdown bodies filled with potent digestive

enzymes• Recycle old/worn-our cellular structures;

digest most foreign substances that enter cell• Are cell’s demolition sites• Especially abundant in WBCs that engulf

bacteria & other harmful substances • Lysosomal enzymes made by ribosomes and

packaged by Golgi apparatus

Peroxisomes

• Membranous sacs containing oxidase enzymes to detoxify harmful/poisonous substances

• MOST important function is to neutralize “free radicals” (by product of respiration)– Unpaired electrons = electron stealing

• Superoxide radical & hydrogen peroxide• CATALASE converts hydrogen

peroxide to water and oxygen• Numerous in liver and kidney cells

Cytoskeleton• Elaborate network of protein structures

extending throughout cytoplasm• “Bones and muscles” which furnish

internal framework that determine cell shape, supports other organelles, and provides machinery needed for intracellular transport and various types of cellular movements

• Can be assembled and disassembled as needed – Some components fairly permanent

Cytoskeleton Components

• Intermediate filaments help form desmosomes and important to internal stability

• Microfilaments (actin/myosin) involved in cell motility and cell shape changes

• Microtubules determine overall shape of cell and distribution of organelles– **very important in cell division

Centrioles

• Paired centrioles lie close to nucleus in animal cells

• Rod-shaped and lie at right angles to each other

• Composed of microtubules• Direct formation of mitotic spindle• Responsible for cilia and flagella

Organelles of Locomotion

• Cilia and Flagella

• Cilia responsible for moving substances across cell’s surface

• Flagella responsible for moving the cell itself

• Respiratory tract and oviduct have cells with cilia

• Only flagellated human cell is a sperm cell

Major aspects of cell physiology

• Most cells have ability to metabolize– Use nutrients to build new cell material,

break down substances, and make ATP

• Also have ability to digest food, dispose of wastes, reproduce, grow, move, and respond to a stimulus (irritability)

• We like to think of the human entity as “total or complete” but all of items above OCCUR at the cellular level

Body’s Fluid Compartments• INTRACELLULAR fluid (nucleoplasm

and cytosol) is solution containing small amts of gases, nutrients, and salts

• INTERSTITIAL FLUID is fluid that bathes the exterior of cells– Rich, nutritious, and unusual soup

• Contains 1000s of ingredients—nutrients (amino acids, sugars, fatty acids, vitamins), regulatory substances (hormones/neurotransmitters), salts, and wastes products

Selective Permeability

• Means barrier that allows some substances to pass through while excluding others

• PM of cell is selective permeable

• Allows nutrients to enter cell but keeps many undesirable products out

• Keeps valuable cell proteins and other substances within cell

• Allows wastes to pass out of cell

Passive Processes• Cell does NOT have to invest any

energy for passive transport processes• Simple diffusion and filtration• Review on diffusion: available space;

kinetic energy; and down [ ] gradient• Affected by size of molecule and

temperature• Review: PM bilayer structure• Unassisted diffusion of solutes through

PM = simple diffusion• Lipid soluble, O2, CO2, some small ions

Facilitated Diffusion• Substances too large for pores require

“transport protein” in PM• **still moving down their [ ] gradient• Glucose (lipid insoluble and too large for

pores)• Binds to transport protein causing

change in its shapetransported into cellreleased insidetransport protein returns to its original shape

• **REMEMBER: simple diffusion and facilitated diffusion are PASSIVE processes

Water, water, everywhere….

• Osmosis defined as movement of water through a selectively permeable membrane

• Not quite accurate, but close enough• Remember water is POLAR

– Does pass through pores created by proteins– Aquaporins

• Movement determined by [ ] gradient• Greater [ ] of nonpermeable solutes in

solution, the lower the water [ ] of that solution and the greater the osmotic pressure

Osmosis, continued

• Water always tends to diffuse toward solutions of greater osmotic pressure

• Ability of solution to change size and shape of cells by altering amount of water they contain is called TONICITY

• HYPERTONIC, HYPOTONIC, ISOTONIC• ISOTONIC: Ringers lactate, 5% dextrose,

0.9% saline solution• KEY: water will move (if it can) from hypotonic

to hypertonic solution

Filtration

• Process by which water and solutes are forced through membrane (or capillary wall) by fluid (hydrostatic) pressure

• Passive process and gradient is involved

• Gradient involved is PRESSURE GRADIENT– From higher to lower pressure

• Filtration necessary for kidneys to do their job

Active Transport Processes

• Active transport occurs when cell uses ATP to move substances across membrane

• Substances may be too large, nonlipid soluble, charged, or may have to move AGAINST their [ ] gradient

• Best two examples of active transport are SOLUTE PUMPING and BULK TRANSPORT

Solute Pumping

• Requires transport proteins in membrane and expenditure of ATP

• Amino acids, some sugars, and most ions transported via SP

• Sodium-potassium pump necessary for normal transmission on nerve impulses

• SP provides way for cell to be very selective in cases where substances cannot pass by diffusion

Bulk Transport• Endocytosis-processes by which cell takes

up, or engulfs, extracellular substances by enclosing them in small membranous vesicle

• If large particles engulfed, endocytosis process called PHAGOCYTOSIS (to eat)– WBCs

• If cell takes in liquids that contain dissolved fats/proteins, or ions, endocytosis called PINOCYTOSIS (to drink)– Pinocytosis regular activity for most cells (small

intestine lining and kidney tubule cells

Bulk Transport, continued

• EXOCYTOSIS moves things out of the cell• Hormones, mucus, cellular products, or

cellular wastes• Product to be released packaged by Golgi

apparatus into small vesicles which migrate to PM, fuses with PM, releases product to outside of cell

Mitosis and Cytokinesis

• Mitosis is nuclear division process that KEEPS THE COUNT THE SAME

• Cytokinesis process that divides the cytoplasm and organelles

• Mitosis produces “clones” barring a mutation• KEY: Mitosis produces two daughter cells and

keeps the chromosome count the same

Cell Cycle

• Chalk-talk time on cell cycle• G1, S, G2, mitosis/meiosis, cytokinesis• G1, S, G2 collectively called Interphase• Chromatin is replicated during S phase• Mitosis/Meiosis consists of Prophase,

Metaphase, Anaphase, and Telophase• KEY EVENTS OF EACH

Protein Synthesis• Transcription and Translation

• DNA, mRNA, tRNA, and rRNA

• Initiation, elongation, and termination

• Codons and anticodons

• Genetic code

• Chalk talk time on protein synthesis

• GENES are sections of DNA that code for functional products (carries info for building one protein/one polypeptide