cell structure and function
DESCRIPTION
Cell Structure and Function. Anatomy & Physiology I Chapter 3. Modern Cell Theory. 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. - PowerPoint PPT PresentationTRANSCRIPT
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Anatomy & Physiology IChapter 3
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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.
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Over 200 different types of human cellsTypes differ in size, shape, subcellular components, and functions
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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
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Squamous
Polygonal
Cuboidal Columnar
Spheroid
Discoid Fusiform (spindle-shaped)
Stellate
Fibrous
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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
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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
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ZOOMING IN• What is attached to the ER to make it look rough?• What is the liquid part of the cytoplasm called?
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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
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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
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ZOOMING IN • How many layers make up the main substance of the plasma membrane?
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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
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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
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Structures projecting from the cell surface used for motionCiliaFlagellum
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Cilia
10 m
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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
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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
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tail of the sperm - only functional flagellum
whiplike structuremuch longer than cilium
movement is more snakelikeno power stroke or recovery stroke as in cilia
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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
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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
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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
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Chromatin (condensed)
Nuclear envelope Nucleus
Nuclear pores
Nucleolus
Cisternae of rough ER
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DNA and RNA have similar structuresFour nucleotides
Adenine (A)Guanine (G)Cytosine (C)Thymine (T) or uracil (U)
SugarRibose or deoxyribose
PhosphateNitrogen base
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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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
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Nuclearpores
mRNA
Pre-mRNARNA Processing
Transcription
Translation
DNA
Nuclearenvelope
Ribosome
Polypeptide
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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
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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
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Defines changes from formation of the cell until it reproducesIncludes:
InterphaseCell division (mitotic phase)
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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
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G1
Growth
SGrowth and DNAsynthesis G2
Growth and finalpreparations fordivisionM
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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
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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
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The stages of mitosis. ZOOMING IN • If the original cell shown has 46 chromosomes, how many chromosomes will each new daughter cell have?
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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
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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
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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.
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Active transport
Carrier-mediated Active TransportVesicular (Bulk) Transport
EndocytosisPhagocytosisPinocytosis
Exocytosis
Active transport mechanisms consume ATP.
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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
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Extracellular fluid
Lipid-solublesolutes
Cytoplasm
Simple diffusion of fat-soluble molecules directly through the phospholipid bilayer
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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.
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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
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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.
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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)
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Watermolecules
Lipidbillayer
Aquaporin
(d) Osmosis, diffusion of a solvent such as water through a specific channel protein (aquaporin) or through the lipid bilayer
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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
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(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
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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
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When osmosis occurs, water enters or leaves a cellChange in cell volume disrupts cell function
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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
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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).
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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
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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
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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
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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.
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Taking in droplets of ECF occurs in all human cells
Membrane caves in, then pinches off into the cytoplasm as pinocytotic vesicle
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Certain mutations may cause changes in cellsUncontrolled reproduction of cellsCells spread (metastasize), producing cancerCancer cells form tumors, crowding out normal cells
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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