Anatomy & Physiology IChapter 3

All organisms composed of cells and cell products.The cell is the smallest structural and functional unit of life. An organism’s structure and functions are due to the activities of its cells.Cells come only from preexisting cells, not from nonliving matter.Cells of all species have many fundamental similarities in their chemical composition and metabolic mechanisms.

Over 200 different types of human cellsTypes differ in size, shape, subcellular components, and functions

Squamous - thin and flat with nucleus creating bulgePolygonal - irregularly angular shapes with 4 or more sidesStellate – starlike shapeCuboidal – squarish and about as tall as they are wideColumnar - taller than wideSpheroid to Ovoid – round to ovalDiscoid - disc-shapedFusiform - thick in middle, tapered toward the endsFibrous – threadlike shape

Squamous

Polygonal

Cuboidal Columnar

Spheroid

Discoid Fusiform (spindle-shaped)

Stellate

Fibrous

Fibroblasts

Erythrocytes

Epithelial cells

(d) Cell that fights disease

Nerve cell

Fat cell

Sperm

(a) Cells that connect body parts, form linings, or transport gases

(c) Cell that storesnutrients

(b) Cells that move organs and body parts

(e) Cell that gathers information and control body functions

(f) Cell of reproduction

SkeletalMusclecell

Smoothmuscle cells

Macrophage

All cells have some common structures and functions Human cells have three basic parts:

Plasma membrane—flexible outer boundaryCytoplasm—intracellular fluid containing organellesNucleus—control center

ZOOMING IN• What is attached to the ER to make it look rough?• What is the liquid part of the cytoplasm called?

Regulates the movement of substance into and out of the cellEncloses cell contentsSeparates intracellular fluid (ICF) from extracellular fluid (ECF)

Interstitial fluid (IF) = ECF that surrounds cellsParticipates in cellular activitiesBilayer structure

Phospholipids CholesterolProteins

75% phospholipids (lipid bilayer)Phosphate heads: polar and hydrophilicFatty acid tails: nonpolar and hydrophobic

5% glycolipidscontributes to glycocalyx – carbohydrate coating on thecells surface

20% cholesterolIncreases membrane stability and fluidity

ZOOMING IN • How many layers make up the main substance of the plasma membrane?

Chemicalmessenger

Breakdownproducts

Ions CAM ofanother cell

(a) Receptor A receptor that binds to chemical messengers such as hormones sent by other cells

(b) EnzymeAn enzyme thatbreaks downa chemicalmessenger andterminates itseffect

(c) Ion ChannelA channel proteinthat is constantlyopen and allowsions to passinto and out ofthe cell

(d) Gated ion channelA gated channelthat opens andcloses to allowions throughonly at certaintimes

(e) Cell-identity markerA glycoproteinacting as a cell-identity markerdistinguishing thebody’s own cellsfrom foreign cells

(f) Cell-adhesionmolecule (CAM)A cell-adhesionmolecule (CAM)that binds onecell to another

Unique fuzzy coat external to the plasma membrane

carbohydrate moieties of membrane glycoproteins and glycolipidsunique in everyone, but identical twins

Functionsprotection - cell adhesionimmunity to infection - fertilizationdefense against cancer - embryonic developmenttransplant compatibility

Structures projecting from the cell surface used for motionCiliaFlagellum

Cilia

10 m

Motile cilia – respiratory tract, uterine tubes, ventricles of the brain, efferent ductules of testes

beat in wavessweep substances across surface in same directionpower strokes followed by recovery strokes

MucusSaline layer

Epithelial cells

1 2 3 4 5 6 7Power stroke Recovery stroke

Saline layer at cell surface due to chloride pumps move Cl- out of cell. Na+ ions and H2O followCystic fibrosis – hereditary disease in which cells make chloride pumps, but fail to install them in the plasma membrane

chloride pumps fail to create adequate saline layer on cell surface

thick mucus plugs pancreatic ducts and respiratory tractinadequate digestion of nutrients and absorption of oxygenchronic respiratory infectionslife expectancy of 30 Mucus

Saline layer

Epithelial cells

tail of the sperm - only functional flagellum

whiplike structuremuch longer than cilium

movement is more snakelikeno power stroke or recovery stroke as in cilia

Located between plasma membrane and nucleusCytosol

Water with solutes (protein, salts, sugars, etc.)Cytoplasmic organelles

Metabolic machinery of cellInclusions

Granules of glycogen or pigments, lipid droplets, vacuoles, and crystals

Nucleus - Contains chromosomes (DNA) and nucleolusRough ER - Manufactures all secreted proteinsSmooth ER – Synthesize steroids and other lipids; manufactures all membranes of the cellRibosomes - Site of protein synthesisMitochondria – cellular respiration (ATP production)Golgi apparatus – Storage warehouses of the cell; carbohydrate synthesisLysosomes - contain digestive enzymes; Digest ingested bacteria, viruses, and toxinsPeroxisomes - Detoxify harmful or toxic substances; Neutralize dangerous free radicals Centrioles - play role in cell division

Largest organelle in a cellGenetic library with blueprints for nearly all cellular proteinsResponds to signals and dictates kinds and amounts of proteins to be synthesizedMost cells are uninucleateRed blood cells are anucleateSkeletal muscle cells, bone destruction cells, and some liver cells are multinucleate

Chromatin (condensed)

Nuclear envelope Nucleus

Nuclear pores

Nucleolus

Cisternae of rough ER

DNA and RNA have similar structuresFour nucleotides

Adenine (A)Guanine (G)Cytosine (C)Thymine (T) or uracil (U)

SugarRibose or deoxyribose

PhosphateNitrogen base

DNA – deoxyribonucleic acid - a long threadlike molecule with uniform diameter, but varied length

46 DNA molecules in the nucleus of most human cells

DNA and other nucleic acids are polymers of nucleotides

Each nucleotide consists ofone sugar - deoxyribose one phosphate groupone nitrogenous base

A, T, G or C

HC

N C

N

NH2

NH

C

C

CH

N

H

CH2OHO

O

OH

P

H

HOH

HH

O

Adenine

Phosphate Deoxyribose

Molecular shape is a double helix (resembles a spiral staircase)

each sidepiece is a backbone composed of phosphate groups alternating with the sugar deoxyribose.

steplike connections between the backbones are pairs of nitrogen bases

A T

A T

T A

A T

AT

G C

G

G

C

C

G C

Sugar–phosphate backbone

G

A

C

T

T

GC

A

Sugar–phosphate backbone

Nitrogenous bases united by hydrogen bonds

a purine on one backbone with a pyrimidine on the otherA – T two hydrogen bondsC – G three hydrogen bonds

DNA base pairing A – T C – G

Law of Complementary Base Pairing

one strand determines base sequence of other

GC

Sugar–phosphatebackbone

Sugar–phosphatebackbone

G

A

C

T

AT

AT

GC

Genes – genetic instructions for synthesis of proteins

Gene – segment of DNA that codes for a specific protein

Genome - all the genes of one personhumans have estimated 25,000 to 35,000 genes

2% of total DNAother 98% is noncoding DNA

plays role in chromosome structureregulation of gene activityno function at all – “junk” DNA

chromatin – fine filamentous DNA material complexed with proteins

occurs as 46 long filaments called chromosomesin nondividing cells, chromatin is so slender it cannot be seen with light microscopehistones – disc-shaped cluster of eight proteinsDNA molecule winds around the clusterappears to be divided into segments - nucleosomes

nucleosome consists of :core particle – histones with DNA around themlinker DNA – short segment of DNA connecting core particles

2 nm

11 nm

Nucleosome

Linker DNA

300 nm

30 nm

700 nm

700 nm

Core particle

In dividing cells only

ChromatidsCentromere

1

2

3

4

5

6

30 nm fiber isthrown intoirregular loopsto form a fiber300 nm thick

Nucleosomesfold accordion-like into zigzagfiber 30 nm indiameter

DNA windsaround coreparticles to formnucleosomes11 nm indiameter

DNA double helix

In dividingcells, loopedchromatin coilsfurther into a700 nm fiber toform eachchromatid

Chromosomeat the midpoint(metaphase) ofcell division

RNA much smaller cousin of DNA (fewer bases)messenger RNA (mRNA) over 10,000 basesribosomal RNA (rRNA)transfer RNA (tRNA) 70 - 90 basesDNA averages 100 million base pairs

one nucleotide chain (not a double helix as DNA)

ribose replaces deoxyribose as the sugar

uracil replaces thymine as a nitrogenous base

Essential functioninterprets code in DNAuses those instructions for protein synthesisleaves nucleus and functions in cytoplasm

A segment of DNA that carries the code for a particular protein

The segment of DNA first codes for the production of a molecule of RNA The molecule of RNA then plays a role in synthesizing one or more proteins (protein synthesis)

The amino acid sequence of a protein is determined by the nucleotide sequence in the DNA

Genome – all the DNA in one 23-chromosome set3.1 billion nucleotide pairs in human genome

46 human chromosomes comes in two sets of 23 chromosomes

one set of 23 chromosomes came form each parenteach pair of chromosomes has same genes but different versions (alleles) exist

body can make millions of different proteins, all from the same 20 amino acids, and encoded by genes made of just 4 nucleotides (A,T,C,G)

Genetic code – a system that enables these 4 nucleotides to code for the amino acid sequence of all proteins

minimum code to symbolize 20 amino acids is 3 nucleotides per amino acid

Base triplet – a sequence of 3 DNA nucleotides that stands for one amino acid

codon - the 3 base sequence in mRNA64 possible codons available to represent the 20 amino acids

61 code for amino acidsStop Codons – UAG, UGA, and UAA – signal the ‘end of the message’, like a period at the end of a sentenceStart Codon – AUG codes for methionine , and begins the amino acid sequence of the protein

process of protein synthesisDNA mRNA protein

transcription – step from DNA to mRNA

occurs in the nucleus where DNA is located

translation – step from mRNA to protein

most occurs in cytoplasm

15-20% of proteins are synthesized in the nucleus

DNA too large to leave nucleus and participate directly in cytoplasmic protein synthesis

necessary to make a small mRNA copy that can migrate through a nuclear pore into the cytoplasm

Transcription – copying genetic instructions from DNA to RNA

translation – the process that converts the language of nucleotides into the language of amino acidsribosomes - translate sequence of nucleotides into the sequence of amino acids

occur mainly in cytosol, on surface of rough ER, and nuclear envelope

Nuclearpores

mRNA

Pre-mRNARNA Processing

Transcription

Translation

DNA

Nuclearenvelope

Ribosome

Polypeptide

1

2

3

4

5

6

DNA double helix

Seven base triplets on thetemplate strand of DNA

The corresponding codons ofmRNA transcribed from theDNA triplets

The anticodons of tRNA thatbind to the mRNA codons

The amino acids carried bythose six tRNA molecules

The amino acids linked into apeptide chain

One gene can code for more than one protein

Gene (DNA)

Pre-mRNA Intron Exon

mRNA 2mRNA 1 mRNA 3

Protein 2Protein 1 Protein 3

Transcription1

Translation3

Splicing2

A B C D E F

A C D A E FB D E

Defines changes from formation of the cell until it reproducesIncludes:

InterphaseCell division (mitotic phase)

Period from cell formation to cell divisionNuclear material called chromatinSubphases:

G1 (gap 1)—vigorous growth and metabolismS (synthetic)—DNA replicationG2 (gap 2)—preparation for division

G1

Growth

SGrowth and DNAsynthesis G2

Growth and finalpreparations fordivisionM

Mitotic (M) phase of the cell cycleEssential for body growth, tissue repair and renewal

Does not occur in most mature cells of nervous tissue, skeletal muscle, and cardiac muscle

Includes two distinct events:1. Mitosis—four stages of nuclear division:

Prophase - Chromosomes become visible

Metaphase - chromosomes are aligned at the equator

Anaphase - Centromeres of chromosomes split simultaneously—each chromatid now becomes a chromosome

Telophase - chromosomes uncoil to form chromatin

2. Cytokinesis—division of cytoplasm by cleavage furrow

The stages of mitosis. ZOOMING IN • If the original cell shown has 46 chromosomes, how many chromosomes will each new daughter cell have?

plasma membrane – a barrier and a gateway between the cytoplasm and ECF

selectively permeable – allows some things through, and prevents other things from entering and leaving the cell

Some molecules easily pass through the membrane; others do notTravel across the membrane is based on several factors:

Molecular sizeSolubilityElectrical charge

Diffusion through lipid bilayerNonpolar, hydrophobic, lipid-soluble substances diffuse through lipid layer

Diffusion through channel proteinswater and charged, hydrophilic solutes diffuse through channel proteins in membrane

Cells control permeability by regulating number of channel proteins or by opening and closing gates

Passive transport mechanisms

Simple DiffusionFacilitated Diffusion

Carrier-mediated facilitated diffusionChannel-mediated facilitated diffusion

OsmosisFiltration

Passive transport mechanisms require no ATP. Random molecular motion of particles provides the necessary energy.

Active transport

Carrier-mediated Active TransportVesicular (Bulk) Transport

EndocytosisPhagocytosisPinocytosis

Exocytosis

Active transport mechanisms consume ATP.

Simple Diffusion – the net movement of particles from area of high concentration to area of low concentration

due to their constant, spontaneous motion

Also known as movement down the concentration gradient – concentration of a substance differs from one point to another

Downgradient

Upgradient

Extracellular fluid

Lipid-solublesolutes

Cytoplasm

Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer

facilitated diffusion - carrier-mediated transport of solute through a membrane down its concentration gradient

does not consume ATP

solute attaches to binding site on carrier, carrier changes confirmation, then releases solute on other side of membrane

ECF

ICF

1 2 3A solute particle entersthe channel of a membraneprotein (carrier).

The solute binds to a receptorsite on the carrier and thecarrier changes conformation.

The carrier releases thesolute on the other side ofthe membrane.

Lipid-insoluble solutes (such as sugars or amino acids)

Carrier-mediated facilitated diffusion

Small lipid-insoluble solutes

Channel-mediated facilitated diffusionmostly ions selected on basis of size and charge

Filtration - process in which particles are driven through a selectively permeable membrane by hydrostatic pressure (force exerted on a membrane by water)

Examplesfiltration of nutrients through gaps in blood capillary walls into tissue fluids

filtration of wastes from the blood in the kidneys while holding back blood cells and proteins

Figure - Blood pressure in capillary forces water and small solutes such as salts through narrow clefts between capillary cells.

Capillary wall

Red bloodcell

Water

Solute

Clefts hold backlarger particlessuch as red bloodcells.

Osmosis - flow of water from one side of a selectively permeable membrane to the other

from side with higher water concentration to the side with lower water concentration

Water diffuses through plasma membranes:Through the lipid bilayerThrough water channels called aquaporins (AQPs)

Watermolecules

Lipidbillayer

Aquaporin

(d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer

Water concentration is determined by solute concentration because solute particles displace water moleculesOsmolarity: The measure of total concentration of solute particles When solutions of different osmolarity are separated by a membrane, osmosis occurs until equilibrium is reached

(a) Membrane permeable to both solutes and water

Solute and water molecules move down their concentration gradientsin opposite directions. Fluid volume remains the same in both compartments.

Leftcompartment:Solution withlower osmolarity

Rightcompartment:Solution with greater osmolarity

Membrane

H2O

Solute

Solutemolecules(sugar)

Both solutions have thesame osmolarity: volumeunchanged

Figure 3.8b

(b) Membrane permeable to water, impermeable to solutes

Both solutions have identicalosmolarity, but volume of thesolution on the right is greaterbecause only water is free to move

Solute molecules are prevented from moving but water moves by osmosis.Volume increases in the compartment with the higher osmolarity.

Leftcompartment

Rightcompartment

Membrane

Solutemolecules(sugar)

H2O

When osmosis occurs, water enters or leaves a cellChange in cell volume disrupts cell function

Tonicity - ability of a solution to affect fluid volume and pressure in a cell; depends on concentration and permeability of solute

Hypotonic solution has a lower concentration of nonpermeating solutes than intracellular fluid (ICF)

high water concentrationcells absorb water, swell and may burst (lyse)

Hypertonic solution has a higher concentration of nonpermeating solutes

low water concentrationcells lose water + shrivel (crenate)

Isotonic solution concentrations in cell and ICF are the samecause no changes in cell volume or cell shape

Cells retain their normal size andshape in isotonic solutions (samesolute/water concentration as insidecells; water moves in and out).

Cells lose water by osmosis and shrink in a hypertonic solution (contains a higher concentration of solutes than are present inside the cells).

(a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions

Cells take on water by osmosis untilthey become bloated and burst (lyse)in a hypotonic solution (contains alower concentration of solutes thanare present in cells).

active transport – carrier-mediated transport of solute through a membrane up (against) its concentration gradientATP energy consumed to change carrier Examples of uses:

sodium-potassium pump keeps K+ concentration higher inside the cell

each pump cycle consumes one ATP and exchanges three Na+ for two K+

keeps the K+ concentration higher and the Na+ concentration lower with in the cell than in ECF

necessary because Na+ and K+

constantly leak through membranehalf of daily calories utilized for Na+ - K+ pump

2 K+ in

Extracellularfluid

Intracellular fluid

+

ATP

P iADP +

3 Na+ out

Vesicular Transport – processes that move large particles, fluid droplets, or numerous molecules at once through the membrane in vesicles – bubblelike enclosures of membrane

Endocytosis –vesicular processes that bring material into the cellphagocytosis – “cell eating” - engulfing large particles

macrophages

pinocytosis – “cell drinking” taking in droplets of ECF containing molecules useful in the cell

Exocytosis – discharging material from the cell

Keeps tissues free of debris and infectious microorganisms.

Particle

Pseudopod

Nucleus

Residue

Phagosome

LysosomeVesicle fusingwith membrane

Phagolysosome

1

2

3

45

6

7

A phagocytic cell encounters aparticle of foreign matter.

The cell surroundsthe particle with itspseudopods.

The particle is phagocytizedand contained in aphagosome.

The phagosome fuseswith a lysosome andbecomes a phagolysosome.

The indigestibleresidue is voided byexocytosis.

The phagolysosomefuses with theplasma membrane.

Enzymes from thelysosome digest theforeign matter.

Taking in droplets of ECF occurs in all human cells

Membrane caves in, then pinches off into the cytoplasm as pinocytotic vesicle

Certain mutations may cause changes in cellsUncontrolled reproduction of cellsCells spread (metastasize), producing cancerCancer cells form tumors, crowding out normal cells

Certain forces increase the chances of developing cancer

Heredity – individuals are more likely to develop certain types of cancers if they have a family history of cancer.

Chemical carcinogens in cigarettes, foods, drugs, etc.

Ionizing radiation from x-rays, UV rays and radioactive substances

Continued physical irritation – increased cell division increases the chance of mutation

Diets high in fats and low in fiber, fruits and vegetables make individuals more susceptible to digestive cancers

Viruses trigger some cancers: cervical cancer, lymphomas, leukemias, liver cancer