© 2012 Pearson Education, Inc. Cell Theory o Developed from Robert Hooke’s research Cells are...

© 2012 Pearson Education, Inc.

Cell Theoryo Developed from Robert Hooke’s research

• Cells are the building blocks of all plants and animals

• All cells come from the division of preexisting cells

• Cells are the smallest units that perform all vital

physiological functions

• Each cell maintains homeostasis at the cellular level


Sex Cells (Germ Cells)

o Reproductive cells

o Male sperm

o Female oocyte (a cell that develops into an egg)

Somatic Cells

o Soma = body

o All body cells except sex cells

Plasma membrane

Nonmembranous organelles

Membranous organelles

Secretory vesicles

CYTOSOL

Centrosome and Centrioles

Centrosome

Centrioles

Cytoplasm contains two centrioles at right angles; each centriole iscomposed of 9 microtubule triplets in a 9 0 array

FunctionsEssential formovement ofchromosomesduring cell division;organization ofmicrotubules incytoskeleton

Proteins organized in fine filaments orslender tubes

FunctionsStrength andsupport;movement ofcellular structuresand materials

Plasma Membrane

FunctionsIsolation;protection;sensitivity;support;controls entryand exit ofmaterials

Freeribosomes

Plasma membrane


Membranous organellesMicrofilament

Microtubule

Lipid bilayer containing phospholipids, steroids, proteins, and carbohydrates

Cytosol (distributesmaterials

by diffusion)

Cytoskeleton

Plasma membrane



Microvilli

Membrane extensionscontaining microfilaments

FunctionIncrease surfacearea to facilitateabsorption of extra-cellular materials

Plasma membrane



Proteasomes

Hollow cylinders of proteolyticenzymes with regulatory proteins at their ends

FunctionsBreakdown and recycling of damaged or abnormal intracellular proteins

Cilia

Cilia are long extensionscontaining microtubuledoublets in a 9 2 array (notshown in the model cell)

FunctionMovement of material over cell surface

RibosomesRNA proteins; fixed ribosomesbound to rough endoplasmicreticulum, free ribosomesscattered in cytoplasm

FunctionProtein synthesis

Golgi apparatus

Stacks of flattened membranes(cisternae) containing chambers

FunctionsStorage, alteration, and packaging of secretory products and lysosomal enzymes

Mitochondria

Double membrane, with innermembrane folds (cristae)enclosing important metabolicenzymes

FunctionsProduce 95% of the ATPrequired by the cell

Endoplasmic reticulum (ER)

Network of membranouschannels extendingthroughout the cytoplasm

FunctionsSynthesis of secretoryproducts; intracellularstorage and transport

Rough ERmodifies andpackages newlysynthesized proteins

Smooth ERsynthesizes lipids and carbohydrates

Peroxisomes

Vesicles containingdegradative enzymes

FunctionsCatabolism of fats and otherorganic compounds,neutralization of toxiccompounds generated inthe process

NUCLEUS

Plasma membrane



PeroxisomesVesicles containingdegradative enzymes

FunctionsCatabolism of fats and otherorganic compounds,neutralization of toxic compounds generated in the process

Lysosomes

Freeribosomes

Vesicles containingdigestive enzymes

FunctionsIntracellular removal ofdamaged organelles orpathogens

Plasma membrane



Chromatin

Nuclearenvelope

Nucleolus(site of rRNA

synthesis andassembly of

ribosomalsubunits)

Nuclearpore

NUCLEOPLASM

NUCLEUS

Nucleoplasm containingnucleotides, enzymes,nucleoproteins, andchromatin; surrounded by a double membrane,the nuclear envelope

Functions:Control of metabolism; storage and processing of genetic information;control of proteinsynthesis


Extracellular Fluid (Interstitial Fluid)

o A watery medium that surrounds a cell

o Plasma membrane (cell membrane) separates

cytoplasm from the extracellular fluid

o Cytoplasm

• Cytosol = liquid

• Intracellular structures collectively known as organelles


Functions of the Plasma Membraneo Physical Isolation

• Barrier o Regulation of Exchange with the Environment

• Ions and nutrients enter

• Wastes eliminated and cellular products

released


Functions of the Plasma Membraneo Sensitivity to the Environment

• Extracellular fluid composition

• Chemical signals o Structural Support

• Anchors cells and tissues


Membrane Lipids

o Phospholipid bilayer

• Hydrophilic heads — toward watery environment, both

sides

• Hydrophobic fatty-acid tails — inside membrane

• Barrier to ions and water — soluble compounds


Membrane Proteins

o Integral Proteins

• Within the membrane

o Peripheral Proteins

• Bound to inner or outer surface of the membrane


Membrane Proteinso Anchoring Proteins (stabilizers)

• Attach to inside or outside structures o Recognition Proteins (identifiers)

• Label cells as normal or abnormal o Enzymes

• Catalyze reactions


Membrane Proteinso Receptor Proteins

• Bind and respond to ligands (ions,

hormones) o Carrier Proteins

• Transport specific solutes through

membrane o Channels

• Regulate water flow and solutes through

membrane


Membrane Carbohydrateso Proteoglycans, glycoproteins, and glycolipids

• Extend outside cell membrane

• Form sticky “sugar coat” (glycocalyx)

o Functions of the glycocalyx

• Lubrication and Protection

• Anchoring and Locomotion

• Specificity in Binding (receptors)

• Recognition (immune response)

EXTRACELLULAR FLUID

Glycolipidsof glycocalyx

Phospholipidbilayer

Integral proteinwith channel

Hydrophobictails

Peripheralproteins

Hydrophilicheads

2 nmCytoskeleton

(Microfilaments)

Gatedchannel

Cholesterol

CYTOPLASM

Integralglycoproteins

Plasmamembrane


Cytoplasmo All materials inside the cell and outside the nucleus

• Cytosol (intracellular fluid) • Dissolved materials

• Nutrients, ions, proteins, and waste products

• High potassium/low sodium• High protein• High carbohydrate/low amino acid and fat

• Organelles • Structures with specific functions


The Organelleso Nonmembranous organelles

• No membrane

• Direct contact with cytosol

• Include the cytoskeleton, microvilli, centrioles, cilia, ribosomes, and proteasomes

o Membranous organelles

• Covered with plasma membrane

• Isolated from cytosol

• Include the endoplasmic reticulum (ER), the Golgi apparatus, lysosomes, peroxisomes, and mitochondria

Nonmembranous Organelleso Six types of nonmembranous organelles

1. Cytoskeleton

2. Microvilli

3. Centrioles

4. Cilia

5. Ribosomes

6. Proteasomes


The Cytoskeleton

o Structural proteins for shape and strength

• Microfilaments

• Intermediate filaments

• Microtubules


The Cytoskeleton

o Microfilaments — thin filaments composed of the

protein actin

• Provide additional mechanical strength

• Interact with proteins for consistency

• Pair with thick filaments of myosin for muscle movement


The Cytoskeleton

o Intermediate filaments — mid-sized between

microfilaments and thick filaments

• Durable (collagen)

• Strengthen cell and maintain shape

• Stabilize organelles

• Stabilize cell position


The Cytoskeleton

o Microtubules — large, hollow tubes of tubulin protein

• Attach to centrosome

• Strengthen cell and anchor organelles

• Change cell shape

• Move vesicles within cell (kinesin and dynein)

• Form spindle apparatus


The Cytoskeleton

o Thick filaments

• Myosin protein in muscle cells

Microfilaments

Plasma membrane

Terminal web

Mitochondrion

Intermediatefilaments

Endoplasmicreticulum

Microtubule

Secretoryvesicle

The cytoskeleton provides strength andstructural support for the cell and its organelles. Interactions between cytoskeletal components are also important in moving organelles and in changing the shape of the cell.

Microvillus

Microvillus

Microfilaments

Terminal web

The microfilaments andmicrovilli of an intestinal cell.Such an image, produced by a scanning electron microscope, is called a scanning electron micrograph (SEM) (SEM 30,000).

Microtubules (yellow) in a living cell, as seen afterspecial fluorescent labeling(LM 3200).


o Microvilli• Increase surface area for absorption

• Attach to cytoskeleton

o Centrioles in the Centrosome• Centrioles form spindle apparatus during cell division

• Centrosome cytoplasm surrounding centriole

o Cilia• Small hair-like extensions

• Cilia move fluids across the cell surface

Microtubules

Centriole. A centriole consistsof nine microtubule triplets(known as a 9 0 array). A pairof centrioles orientated at rightangles to one another occupiesthe centrosome. Thismicrograph, produced by a transmission electronmicroscope, is called a TEM.

Basal body

Cilium. A cilium contains nine pairs ofmicrotubules surrounding a central pair(9 2 array). The basal body to which the cilium is anchored has a structure similar to that of a centriole.

Plasma membrane

Microtubules

Power stroke Return stroke

Ciliary movement. Action of a single cilium. During the power stroke, the cilium isrelatively stiff; during the return stroke, itbends and returns to its original position.


o Ribosomes• Build polypeptides in protein synthesis

• Two types

1. Free ribosomes in cytoplasm

• Manufacture proteins for cell

2. Fixed ribosomes attached to ER

• Manufacture proteins for secretion

o Proteasomes• Contain enzymes (proteases)

• Disassemble damaged proteins for recycling


Membranous Organelles

o Five types of membranous organelles

1. Endoplasmic reticulum (ER)

2. Golgi apparatus

3. Lysosomes

4. Peroxisomes

5. Mitochondria


Endoplasmic Reticulum (ER)

o Endo- = within, plasm = cytoplasm, reticulum = network

o Cisternae are storage chambers within membranes

o Functions

1. Synthesis of proteins, carbohydrates, and lipids

2. Storage of synthesized molecules and materials

3. Transport of materials within the ER

4. Detoxification of drugs or toxins



o Smooth endoplasmic reticulum (SER)

• No ribosomes attached

• Synthesizes lipids and carbohydrates

• Phospholipids and cholesterol (membranes)

• Steroid hormones (reproductive system)

• Glycerides (storage in liver and fat cells)

• Glycogen (storage in muscles)



o Rough endoplasmic reticulum (RER)

• Surface covered with ribosomes

• Active in protein and glycoprotein synthesis

• Folds polypeptide protein structures

• Encloses products in transport vesicles

Cisternae

The three-dimensional relationships between the rough and smooth endoplasmic reticula are shown here.

Ribosomes

Rough endoplasmicreticulum with fixed

(attached) ribosomes

Smoothendoplasmic

reticulum

Nucleus

Rough endoplasmicreticulum with fixed

(attached) ribosomes

EndoplasmicReticulum

Smoothendoplasmic

reticulum

Rough endoplasmicreticulum and freeribosomes in thecytoplasm of a cell.

TEM 111,000

Freeribosomes


Golgi Apparatuso Vesicles enter forming face and exit maturing face

o Functions

1. Modifies and packages secretions• Hormones or enzymes

• Released through exocytosis

2. Renews or modifies the plasma membrane

3. Packages special enzymes within vesicles for use in the cytoplasm

Secretoryvesicles

Secretoryproduct

TransportvesiclesHere is a three-dimensional

view of the Golgi apparatuswith a cut edge.

This is a sectional view of the Golgiapparatus of an active secretory cell.

Golgi apparatus TEM 42,000


Lysosomeso Powerful enzyme-containing vesicles

• Lyso- = dissolve, soma = body

o Primary lysosome

• Formed by Golgi apparatus and inactive enzymes

o Secondary lysosome

• Lysosome fused with damaged organelle

• Digestive enzymes activated

• Toxic chemicals isolated


Lysosomeso Functions

1. Clean up inside cells

2. Autolysis

Clean Up inside Cells

o Break down large molecules

o Attack bacteria

o Recycle damaged organelles

o Eject wastes by exocytosis


Autolysis

o Auto- = self, lysis = break

o Self-destruction of damaged cells• Lysosome membranes break down

• Digestive enzymes released

• Cell decomposes

• Cellular materials recycle

Golgiapparatus

Autolysis liberatesdigestive enzymes Primary

lysosome

Reabsorption Endosome

Damaged organelle

Secondarylysosome

Reabsorption

Secondarylysosome

Endocytosis

Extracellularsolid or fluid

Exocytosisejects residue

Exocytosisejects residue

The lysosomal membranebreaks down during autolysisfollowing injury to, or death of,the cell

A primary lysosome fuses withan endosome containing fluidor solid materials from outsidethe cell

A primary lysosome fuses withthe membrane of anotherorganelle, such as a mitochondrion

Activation of lysosomesoccurs when:


Peroxisomes

o Are enzyme-containing vesicles

• Break down fatty acids, organic compounds

• Produce hydrogen peroxide (H2O2)

• Replicate by division


Membrane Flow

o A continuous exchange of membrane parts by vesicles

• All membranous organelles (except mitochondria)

• Allows adaptation and change


Mitochondriao Have smooth outer membrane and inner membrane

with numerous folds (cristae)

o Matrix

• Fluid around cristae

o Mitochondrion takes chemical energy from food

(glucose)

• Produces energy molecule ATP


Mitochondrial Energy Productiono Glycolysis

• Glucose to pyruvic acid (in cytosol)

o Citric acid cycle (also known as the Krebs cycle and the

tricarboxylic acid cycle or TCA cycle)

• Pyruvic acid to CO2 (in matrix)

o Electron transport chain

• Inner mitochondrial membrane

Mitochondrial Energy Productiono Called aerobic metabolism (cellular respiration)

• Mitochondria use oxygen to break down food and

produce ATP

• Glucose + oxygen + ADP carbon dioxide + water

+ ATP

Organic moleculesand O2

Inner membrane

Matrix Cristae

Shown here is the three-dimensional organization and acolor-enhanced TEM of a typical mitochondrion in section.

Enzymes

Outermembrane

Mitochondrion

Cytoplasm of cell

TEM 46,332

Cristae Matrix

Outermembrane

CYTOPLASM

MATRIX

Pyruvate

Glycolysis

Glucose

Citric AcidCycle

ADP phosphate

Enzymesand

coenzymesof cristae

MITOCHONDRION

This is an overview of the role of mitochondria in energy production. Mitochondria absorb short carbon chains (such as pyruvate) and oxygen and generate carbon dioxide and ATP.


Nucleuso Largest organelle

o The cell’s control center

o Nuclear envelope• Double membrane around the nucleus

o Perinuclear space• Between the two layers of the nuclear envelope

o Nuclear pores• Communication passages

Nucleoplasm

Chromatin

Nucleolus

Nuclear envelope

Nuclear pore

Important nuclear structures are shown here.

Nucleus TEM 4800

Nuclear pore

Perinuclear space

Nuclear envelope

A nuclear pore is a largeprotein complex that spansthe nuclear envelope.

Nuclear pores

Inner membrane ofnuclear envelope

Broken edge ofouter membrane

Outer membrane ofnuclear envelope

Nucleus Freeze fracture SEM 9240

This cell was frozen and then broken apart to make itsinternal structures visible. The technique, called freezefracture or freeze-etching, provides a unique perspectiveon the internal organization of cells. The nuclear envelopeand nuclear pores are visible. The fracturing process broke away part of the outer membrane of the nuclear envelope, and the cut edge of the nucleus can be seen.


Contents of the Nucleuso DNA

• All information to build and run organismso Nucleoplasm

• Fluid containing ions, enzymes, nucleotides,

and some RNAo Nuclear matrix

• Support filaments


Contents of the Nucleuso Nucleoli

• Are related to protein production

• Are made of RNA, enzymes, and histones

• Synthesize rRNA and ribosomal subunitso Nucleosomes

• DNA coiled around histones


Contents of the Nucleuso Chromatin

• Loosely coiled DNA (cells not dividing)

o Chromosomes

• Tightly coiled DNA (cells dividing)

Nucleus

Cell preparedfor division

Nondividing cell

DNAdouble

helixNucleosome

Histones

Chromatin innucleus

Centromere

Telomeres of sister chromatids

Kinetochore

Visiblechromosome

Supercoiledregion


Information Storage in the Nucleuso DNA

• Instructions for every protein in the bodyo Gene

• DNA instructions for one proteino Genetic code

• The chemical language of DNA instructions

• Sequence of bases (A, T, C, G)• Triplet code

• 3 bases = 1 amino acid


The Role of Gene Activation in Protein Synthesis

o The nucleus contains chromosomes

o Chromosomes contain DNA

o DNA stores genetic instructions for proteins

o Proteins determine cell structure and function



o Gene activation – uncoiling DNA to use it

• Promoter

• Terminator

o Transcription

• Copies instructions from DNA to mRNA (in nucleus)

• RNA polymerase produces messenger RNA (mRNA)



o Translation

• Ribosome reads code from mRNA (in cytoplasm)

• Assembles amino acids into polypeptide chain

o Processing

• RER and Golgi apparatus produce protein


The Transcription of mRNA

o A gene is transcribed to mRNA in three steps

1. Gene activation

2. DNA to mRNA

3. RNA processing


Step 1: Gene activation

• Uncoils DNA, removes histones

• Start (promoter) and stop codes on DNA

mark location of gene

• Coding strand is code for protein

• Template strand is used by RNA polymerase

molecule


o Step 2: DNA to mRNA

• Enzyme RNA polymerase transcribes DNA

• Binds to promoter (start) sequence

• Reads DNA code for gene

• Binds nucleotides to form messenger RNA (mRNA)

• mRNA duplicates DNA coding strand, uracil

replaces thymine


o Step 3: RNA processing

• At stop signal, mRNA detaches from DNA

molecule• Code is edited (RNA processing)

• Unnecessary codes (introns) removed

• Good codes (exons) spliced together

• Triplet of three nucleotides (codon) represents one amino acid

DNA

Templatestrand

Gene

Promoter

Triplet 1

Triplet 3

Triplet 2

Triplet 4

Co

mp

lem

enta

rytr

iple

ts

Codon1

1

RNAnucleotide

After transcription, the two DNA strands reassociate

KEY

Adenine

Guanine

Cytosine

Uracil (RNA)

Thymine (DNA)

Codon2

Codon3

Codon 4(stop codon)

mRNAstrand

11

2 2

3

4

3

4

Codingstrand

RNApolymerase

Codon


Translationo mRNA moves:

• From the nucleus through a nuclear pore

o mRNA moves:

• To a ribosome in cytoplasm surrounded by amino acids

o mRNA binds to ribosomal subunits

• tRNA delivers amino acids to mRNA


Translationo tRNA anticodon binds to mRNA codon

• 1 mRNA codon translates to 1 amino acid

o Enzymes join amino acids with peptide bonds

• Polypeptide chain has specific sequence of amino acids

o At stop codon, components separate

NUCLEUS

mRNA

Amino acid

tRNA

Anticodon

tRNA binding sites

Smallribosomal

subunit

Start codon mRNA strand

The mRNA strand binds to thesmall ribosomal subunit and isjoined at the start codon by thefirst tRNA, which carries theamino acid methionine. Binding occurs between complementary base pairs of the codon and anticodon.

KEY

Adenine

Guanine

Cytosine

Uracil

Large ribosomalsubunit

The small and largeribosomal subunitsinterlock around the mRNA strand.

A second tRNA arrives at theadjacent binding site of theribosome. The anticodon ofthe second tRNA binds to the next mRNA codon.

Stopcodon

The first amino acid isdetached from its tRNA and isjoined to the second aminoacid by a peptide bond. Theribosome moves one codonfarther along the mRNA strand;the first tRNA detaches asanother tRNA arrives.

Peptidebond

Small ribosomalsubunit

The chain elongates until thestop codon is reached; thecomponents then separate.

Completedpolypeptide

Large ribosomal

subunit


How the Nucleus Controls Cell Structure and

Function

1. Direct control through synthesis of:

• Structural proteins

• Secretions (environmental response)

2. Indirect control over metabolism through enzymes


Membrane Transport

o The plasma (cell) membrane is a barrier, but:

• Nutrients must get in

• Products and wastes must get out

o Permeability determines what moves in and out of a cell, and

a membrane that:

• Lets nothing in or out is impermeable

• Lets anything pass is freely permeable

• Restricts movement is selectively permeable


Membrane Transporto Plasma membrane is selectively permeable

• Allows some materials to move freely

• Restricts other materials

o Selective permeability restricts materials based on:

• Size

• Electrical charge

• Molecular shape

• Lipid solubility


Membrane Transporto Transport through a plasma membrane can be:

• Active (requiring energy and ATP)

• Passive (no energy required)

o Diffusion (passive)

o Carrier-mediated transport (passive or active)

o Vesicular transport (active)


Diffusiono All molecules are constantly in motion

o Molecules in solution move randomly

o Random motion causes mixing

o Concentration is the amount of solute in a solvent

o Concentration gradient

• More solute in one part of a solvent than another


Factors Influencing Diffusiono Distance the particle has to move

o Molecule Size

• Smaller is faster

o Temperature

• More heat, faster motion

o Concentration Gradient

• The difference between high and low concentrations

o Electrical Forces

• Opposites attract, like charges repel


Diffusion across Plasma Membraneso Can be simple or channel mediated

• Materials that diffuse through plasma

membrane by simple diffusion• Lipid-soluble compounds (alcohols, fatty acids,

and steroids)

• Dissolved gases (oxygen and carbon dioxide)


Diffusion across Plasma Membraneso Channel-mediated diffusion

• Water-soluble compounds and ions

o Factors in channel-mediated diffusion

• Size

• Charge

• Interaction with the channel – leak channels

Plasma membrane

EXTRACELLULAR FLUID

CYTOPLASM

Lipid-soluble moleculesdiffuse through theplasma membrane

Channelprotein

Small water-solublemolecules and ionsdiffuse throughmembrane channels

Large molecules that cannotdiffuse through lipids cannotcross the plasma membraneunless they are transportedby a carrier mechanism


Osmosis: A Special Case of Diffusiono Osmosis is the diffusion of water across the cell

membrane• More solute molecules, lower concentration of water

molecules

• Membrane must be freely permeable to water, selectively permeable to solutes

• Water molecules diffuse across membrane toward solution with more solutes

• Volume increases on the side with more solutes

Volume increased

Originallevel

Volumedecreased

Watermolecules

Solutemolecules

Selectively permeable membrane

Appliedforce

Volumesequal

Two solutions containing differentsolute concentrations are separatedby a selectively permeable membrane. Water molecules (small blue dots) begin to cross the membrane toward solution B, the solution with the higher concentration of solutes (large pink dots)

Watermolecules

Solutemolecules

Selectively permeable membrane

At equilibrium, the soluteconcentrations on the two sides ofthe membrane are equal. Thevolume of solution B has increasedat the expense of that of solution A.

Volume increased

Originallevel

Volumedecreased

Osmosis can be prevented by resistingthe change in volume. The osmoticpressure of solution B is equal to theamount of hydrostatic pressurerequired to stop the osmotic flow.

Appliedforce

Volumesequal


Osmosis: A Special Case of Diffusion

o Osmotic pressure

• Is the force of a concentration gradient of water

• Equals the force (hydrostatic pressure) needed to block

osmosis


Osmolarity and Tonicityo The osmotic effect of a solute on a cell

• Two fluids may have equal osmolarity, but different

tonicity

o Isotonic (iso- = same, tonos = tension)

• A solution that does not cause osmotic flow of water

in or out of a cell

o Hypotonic (hypo- = below)

• Has less solutes and loses water through osmosis

o Hypertonic (hyper- = above)

• Has more solutes and gains water by osmosis


Osmolarity and Tonicity

o A cell in a hypotonic solution:

• Gains water

• Ruptures (hemolysis of red blood cells)

o A cell in a hypertonic solution:

• Loses water

• Shrinks (crenation of red blood cells)

Solutemolecules

Watermolecules

SEM of normal RBCin an isotonic solution

SEM of RBC in ahypotonic solution

SEM of crenated RBCsin a hypertonic solution

Solutemolecules

Watermolecules

In an isotonic saline solution, noosmotic flow occurs, and thesered blood cells appear normal.

SEM of normal RBCin an isotonic solution

SEM of RBC in ahypotonic solution

Immersion in a hypotonic salinesolution results in the osmoticflow of water into the cells. Theswelling may continue until theplasma membrane ruptures, orlyses.

SEM of crenated RBCsin a hypertonic solution

Exposure to a hypertonic solutionresults in the movement of waterout of the cell. The red blood cellsshrivel and become crenated.


Carrier-Mediated Transporto Of ions and organic substrates

• Characteristics• Specificity

• One transport protein, one set of substrates

• Saturation Limits • Rate depends on transport proteins, not substrate

• Regulation • Cofactors such as hormones


Carrier-Mediated Transporto Cotransport

• Two substances move in the same direction at the same

time

o Countertransport

• One substance moves in while another moves out


Carrier-Mediated Transporto Facilitated Diffusion

• Passive

• Carrier proteins transport molecules too large to fit through channel proteins (glucose, amino acids)

• Molecule binds to receptor site on carrier protein

• Protein changes shape, molecules pass through

• Receptor site is specific to certain molecules

EXTRACELLULARFLUID

CYTOPLASM

Glucose releasedinto cytoplasm

Carrierprotein

Glucosemolecule

Receptor site


Carrier-Mediated Transporto Active Transport (Primary or Secondary)

• Active transport proteins• Move substrates against concentration gradient

• Require energy, such as ATP

• Ion pumps move ions (Na+, K+, Ca2+, Mg2+)

• Exchange pump countertransports two ions at the same time


Carrier-Mediated Transport

o Primary Active Transport

• Sodium–potassium exchange pump

• Active transport, carrier mediated

• Sodium ions (Na+) out, potassium ions (K+) in

• 1 ATP moves 3 Na+ and 2 K+

EXTRACELLULARFLUID

Sodiumpotassiumexchange

pump

CYTOPLASM


Carrier-Mediated Transport

o Secondary Active Transport

• Na+ concentration gradient drives glucose transport

• ATP energy pumps Na+ back out

Glucosemolecule

Sodiumion (Na)

CYTOPLASM

pump


Vesicular Transport (Bulk Transport)

o Materials move into or out of cell in vesicles

• Endocytosis (endo- = inside) is active transport

using ATP

• Receptor mediated

• Pinocytosis

• Phagocytosis


Endocytosis

o Receptor-mediated endocytosis

• Receptors (glycoproteins) bind target molecules (ligands)

• Coated vesicle (endosome) carries ligands and receptors

into the cell


Endocytosis

o Pinocytosis• Endosomes “drink” extracellular fluid

o Phagocytosis• Pseudopodia (pseudo- = false, pod- = foot)

• Engulf large objects in phagosomes

Exocytosis (exo- = outside)

o Granules or droplets are released from the cell

Bloodstream

Cytoplasm

Surrounding tissues

Pinocytosis Color enhanced TEM 20,000

Plasmamembrane

Pinosomeformation

Pinosome fusionand exocytosis

Golgiapparatus

Lysosome

EXOCYTOSIS

Secondarylysosome

Phagosomefuses with alysosome

Bacterium

Pseudopodium PHAGOCYTOSIS

Phagosome


Transmembrane Potential

o Charges are separated creating a potential difference

o Unequal charge across the plasma membrane is

transmembrane potential

o Resting potential ranges from –10 mV to

–100 mV, depending on cell type


Cell Life Cycleo Most of a cell’s life is spent in a nondividing state

(interphase)

o Body (somatic) cells divide in three stages

• DNA replication duplicates genetic material exactly

• Mitosis divides genetic material equally

• Cytokinesis divides cytoplasm and organelles into two

daughter cells


DNA Replicationo Helicases unwind the DNA strands

o DNA polymerase

1. Promotes bonding between the nitrogenous bases of the DNA strand and complementary DNA nucleotides dissolved in the nucleoplasm

2. Links the nucleotides by covalent bonds

o DNA polymerase works in one direction

o Ligases piece together sections of DNA


Interphaseo The nondividing period

• G-zero (G0) phase — specialized cell functions only

• G1 phase — cell growth, organelle duplication, protein

synthesis

• S phase — DNA replication and histone synthesis

• G2 phase — finishes protein synthesis and centriole

replication

INTERPHASEMost cells spend only a small part of theirtime actively engaged in cell division.Somatic cells spend the majority of theirfunctional lives in a state known asinterphase. During interphase, a cellperfoms all its normal functions and, ifnecessary, prepares for cell division.

When the activities of G1 have been completed,

the cell enters the S phase. Over the next 68

hours, the cell duplicates its chromosomes.

This involves DNA replication and

the synthesis of histones and other

proteins in the nucleus.

G1 Normal cell functionsplus cell growth,duplication of organelles, protein synthesis

mo

reh

ou

rs8

or

An interphase cell in the G0 phase is

not preparing for division, but is performing all of the other functions appropriate for that particular cell type. Some mature cells, such as skeletal muscle cells and most neurons, remain in G0 indefinitely and never divide. In contrast, stem cells,

which divide repeatedly with very brief interphase periods, never enter G0.

G0

MITOSIS ANDCYTOKINESIS

CYTO NEKI

SIS

SDNA

replication,synthesis

ofhistones

G2

Proteinsynthesis

Once DNA replication has ended, there is a brief (25-hour) G2 phase

devoted to last-minute protein synthesis and to the completion of centriole replication.

Centrioles incentrosome

Nucleus

InterphaseDuringinterphase,the DNA strandsare looselycoiled andchromosomescannot be seen.

1 to

3 hou

sr

A cell that is ready todivide first enters the G1

phase. In this phase, the cell makes enough mitochondria, cytoskeletal elements, endo-plasmic reticula, ribosomes, Golgi membranes, and cytosol for two functionalcells. Centriole replica-tion begins in G1 and commonly continues until G2. In cells dividing at top speed, G1 may last just 812 hours.Such cells pourall their energyinto mitosis, andall other activitiescease. If G1 lastsfor days, weeks, ormonths, preparationfor mitosis occurs as the cells perform their normal functions.

to6 8 hours

to2

5h

ours

THECELL

CYCLE

MITOSIS

Prophase

MetaphaseAnaphase

Telo

ph

ase

An interphase cell in the G0 phase

is not preparing for division, but is performing all of the other functions appropriate for that particular cell type. Some mature cells, such as skeletal muscle cells and most neurons, remain in G0 indefinitely and never

divide. In contrast, stem cells, which divide repeatedlywith very brief interphase periods, never enter G0.

G0

THECELL

CYCLE

INTERPHASE

G1

Normal cell functionsplus cell growth,duplication of organelles, protein synthesis

THE CELLCYCLE

8o

rm

ore

ho

urs

When the activities of G1 have been completed, the cell enters the S phase. Over the next 68 hours, the cell duplicates its chromosomes. This involves DNA replication and the synthesis of histones and other proteins in the nucleus.

SDNA

replication,synthesis

ofhistones

THECELL

CYCLE

to6 8 hours

G2

Proteinsynthesis

Once DNA replication has ended, there is a brief (25-hour)G2 phase devoted to

last-minute protein synthesis and to the completion of centriole replication.

THECELL

CYCLE

2 to5

ho

urs


Mitosiso Divides duplicated DNA into two sets of chromosomes

• DNA coils tightly into chromatids

• Chromatids connect at a centromere

• Protein complex around centromere is kinetochore

MITOSIS ANDCYTOKINESIS

CYNE

KI SIS

Centrioles incentrosome

1 to

3 h

ours

THECELL

CYCLE

MITOSIS

Prophase

MetaphaseAnaphase

Telo

ph

ase

InterphaseDuringinterphase,the DNA strandsare looselycoiled andchromosomescannot be seen.

TO

Nucleus


Mitosis

o Prophase

• Nucleoli disappear

• Centriole pairs move to cell poles

• Microtubules (spindle fibers) extend between

centriole pairs

• Nuclear envelope disappears

• Spindle fibers attach to kinetochore

o Metaphase

• Chromosomes align in a central plane (metaphase

plate)

Centrioles(two pairs)

Astral rays andspindle fibers

Chromosomewith two sister

chromatids

Chromosomalmicrotubules

Metaphaseplate

MetaphaseLate prophaseEarly prophase


Mitosiso Anaphase

• Microtubules pull chromosomes apart

• Daughter chromosomes group near centrioles

o Telophase

• Nuclear membranes re-form

• Chromosomes uncoil

• Nucleoli reappear

• Cell has two complete nuclei

Daughterchromosomes

Cleavagefurrow Daughter

cells

Anaphase Telophase Cytokinesis


Cytokinesis

o Division of the cytoplasm

• Cleavage furrow around metaphase plate

• Membrane closes, producing daughter cells

A dividing cell shown heldin place by a sucker pipeto the left and beinginjected with a needlefrom the right.


The Mitotic Rate and Energy Useo Rate of cell division

• Slower mitotic rate means longer cell life

• Cell division requires energy (ATP)

o Muscle cells, neurons rarely divide

o Exposed cells (skin and digestive tract) live only days or

hours – replenished by stem cells


Cell Divisiono Normally, cell division balances cell loss

o Increased cell division• Internal factors (M-phase promoting factor, MPF)

• Extracellular chemical factors (growth factors)

o Decreased cell division• Repressor genes (faulty repressors cause cancers)

• Worn out telomeres (terminal DNA segments)


Cancer Develops in Stepso Abnormal cell

o Primary tumor

o Metastasis

o Secondary tumor


Tumor (Neoplasm)o Enlarged mass of cells

o Abnormal cell growth and division

o Benign tumor • Contained, not life threatening unless large

o Malignant tumor • Spreads into surrounding tissues (invasion)

• Starts new tumors (metastasis)

Abnormalcell

Celldivisions

Primary tumor cells

Growth of bloodvessels into tumor

Invasion

Penetration Escape

Secondary tumor cells

Celldivisions

Circulation


Differentiationo All cells carry complete DNA instructions for all body

functionso Cells specialize or differentiate

• To form tissues (liver cells, fat cells, and neurons)

• By turning off all genes not needed by that cell

o All body cells, except sex cells, contain the same 46 chromosomes

o Differentiation depends on which genes are active and which are inactive

© 2012 Pearson Education, Inc. Cell Theory o Developed from Robert Hooke’s research Cells are...

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Transcript of © 2012 Pearson Education, Inc. Cell Theory o Developed from Robert Hooke’s research Cells are...