Ch03 the Cellular Level of Organization

7/31/2019 Ch03 the Cellular Level of Organization

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Copyright 2009 John Wiley & Sons, Inc.

Chapter 3

The Cellular Level of

Organization


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A Generalized Cell

1. Plasma membrane

- forms the cells outer boundary

- separates the cells internal environmentfrom the outside environment

- is a selective barrier

- plays a role in cellular communication


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A Generalized Cell

2. Cytoplasm

- all the cellular contents between the plasmamembrane and the nucleus

- cytosol - the fluid portion, mostly water

- organelles - subcellular structures havingcharacteristic shapes and specific functions


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A Generalized Cell

3. Nucleus

- large organelle that contains DNA

- contains chromosomes,each of which

consists of a single molecule of DNA and

associated proteins

- a chromosome contains thousands ofhereditary units called genes


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Fig. 3.1 Generalized Body Cell


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Plasma Membrane

Flexible yet sturdy barrier

The fluid mosaic model- the arrangement ofmolecules within the membrane resembles a

sea of lipids containing many types ofproteins

The lipids act as a barrier to certain

substances The proteins act as gatekeepers to certain

molecules and ions


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Structure of a Membrane

Consists of a lipid bilayer - made up ofphospholipids, cholesterol and glycolipids

Integral proteins - extend into or through the

lipid bilayer

Transmembrane proteins - most integralproteins, span the entire lipid bilayer

Peripheral proteins - attached to the inneror outer surface of the membrane, do notextend through it


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Structure of the Plasma Membrane


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Structure of aMembrane

Glycoproteins - membrane proteins with acarbohydrate group attached that protrudesinto the extracellular fluid

Glycocalyx - the sugary coatingsurrounding the membrane made up of thecarbohydrate portions of the glycolipids and

glycoproteins


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Functions of Membrane Proteins

Some integral proteins are ion channels

Transporters - selectively move substancesthrough the membrane

Receptors - for cellular recognition; a ligandis a molecule that binds with a receptor

Enzymes - catalyze chemical reactions

Others act as cell-identity markers


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Figure 3.3


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Membrane Permeability

The cell is either permeable or impermeableto certain substances

The lipid bilayer is permeableto oxygen,

carbon dioxide, water and steroids, butimpermeableto glucose

Transmembrane proteins act as channels

and transporters to assist the entrance ofcertain substances, for example, glucose andions


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Passive vs. Active Processes

Passive processes - substances move acrosscell membranes without the input of anyenergy; use the kinetic energyof individual

molecules or ions Active processes - a cell uses energy,

primarily from the breakdown of ATP, to

move a substance across the membrane, i.e.,against a concentration gradient


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Diffusion

Steepness of

concentrationgradient

Temperature

Mass of diffusingsubstance

Surface area Diffusion

distance


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Simple Diffusion, Channel-mediated

Facilitated Diffusion, and Carrier-mediated

Facilitated Diffusion


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Channel-mediated Facilitated Diffusion of

Potassium ions through a Gated K+ Channel


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Carrier-mediated Facilitated Diffusion of

Glucose across a Plasma Membrane


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Glucosetransporter

Glucosegradient

Glucose

Extracellular fluid Plasma membrane Cytosol

1

Glucosetransporter

Glucosegradient

Glucose


1

2

Glucosetransporter

Glucosegradient

Glucose

Glucose


1

2

3


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Osmosis

Net movement of water through aselectively permeable membrane from anarea of high concentration of water (lowerconcentration of solutes) to one of lower

concentration of water Water can pass through plasma membrane

in 2 ways:

1. through lipid bilayer by simple diffusion

2. through aquaporins, integral membraneproteins


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Tonicity and its effect on RBCS


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Active TransportSolutes are transported across plasma membranes with the use of energy, from an area

of lower concentration to an area of higher Concentration Sodium-potassium pump

1

3 Na+

K+gradient

Na+gradient

Na+/K+ ATPase

Extracellular fluid

Cytosol

1

3 Na+ expelled

3 Na+

ADP

P

K+gradient

Na+gradient

Na+/K+ ATPase

Extracellular fluid

CytosolATP

21

3 Na+ expelled

3 Na+

ADPP

P

K+gradient

Na+gradient

Na+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP2 31

3 Na+ expelled

3 Na+

ADPP

P

2 K+

imported

K+gradient

Na+gradient

Na+/K+ ATPase

Extracellular fluid

Cytosol

2K+

ATP2 3 4


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Transport in Vesicles

Vesicle- a small spherical sac formed by budding offfrom a membrane

Endocytosis - materials move into a cell in a vesicleformed from the plasma membrane

three types: receptor-mediated endocytosisphagocytosisbulk-phase endocytosis (pinocytosis)

Exocytosis - vesicles fuse with the plasmamembrane, releasing their contents into theextracellular fluid

Transcytosis - a combination of endocytosis andexocytosis


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Receptor-Mediated Endocytosis

1 Binding

1 Binding

1 Binding

1 Binding

1 Binding

1 Binding


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1

Clathrin-coatedpit

Binding

Receptor

Receptor-LDLcomplex

LDL particle Plasmamembrane

Invaginated plasmamembrane

1

Clathrin-coatedvesicle

Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex



2

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Uncoating



2

3

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Fusion with

endosome

Uncoating



Endosome

2

3

4

Transportvesicle

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicleTransportvesicle

Fusion with

endosome

Recyclingof receptorsto plasmamembrane

Uncoating



Endosome

2

3

4

5

Transportvesicle

1


Clathrin-coatedpit

Binding

Vesicle formation

Receptor

Receptor-LDLcomplex

Uncoated vesicle

Degradationin lysosome

Lysosome

Transportvesicle

Transportvesicle

Fusion with

endosome

Recyclingof receptorsto plasmamembrane

Uncoating



Endosome

Digestiveenzymes

2

3

4

5

6


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Phagocytosis


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Bulk-phase Endocytosis


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Cytoplasm - 2 components

1. Cytosol - intracellular fluid, surrounds the organelles

- the site of many chemical reactions

- energy is usually released by these reactions

- reactions provide the building blocks for cell maintenance,

structure, function and growth

2. Organelles

Specialized structures within the cell

The cytoskeleton - network of protein filaments throughout the

cytosol-provides structural support for the cell

-three types according to increasing size: microfilaments,intermediate filaments, and microtubules


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The Cytoskeleton


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Organelles

Centrosome - located near the nucleus,consists of two centrioles and pericentriolarmaterial (Fig. 2.7)

Cilia - short, hair-like projections from the cellsurface, move fluids along a cell surface

Flagella - longer than cilia, move an entire

cell;only example is the sperm cells tail (Fig.2.8)


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The Centrosome


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Cilia and Flagella


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Organelles

Ribosomes - sites of protein synthesis

Endoplasmic reticulum - network of membranes inthe shape of flattened sacs or tubules

- Rough ER -connected to the nuclear envelope, aseries of flattened sacs, surface is studded withribosomes, produces various proteins

-Smooth ER- a network of membrane tubules, does

not have ribosomes, synthesizes fatty acids andsteroids, detoxifies certain drugs


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Ribosomes


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Endoplasmic Reticulum


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Organelles

Golgi complex - consists of 3-20 flattened,membranous sacs called cisternae

- modify, sort, and package proteins for

transport to different destinations

- proteins are transported by variousvesicles

Lysosomes - vesicles that form from the Golgicomplex, contain powerful digestive enzymes


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Golgi Complex


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Processing and Packaging


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Lysosomes


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Organelles

Peroxisomes - smaller than lysosomes,detoxify several toxic substances such asalcohol, abundant in the liver

Proteasomes - continuously destroyunneeded, damaged, or faulty proteins, foundin the cytosol and the nucleus


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Organelles

Mitochondria - the powerhouses of the cell

Generate ATP

More prevalent in physiologically active cells: muscles, liverand kidneys

Inner and outer mitochondrial membranes

Cristae- the series of folds of the inner membrane

Matrix- the large central fluid-filled cavity

Self-replicate during times of increased cellular demand or

before cell division


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Mitochondria


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Organelles - Nucleus

Spherical or oval shaped structure

Usually most prominent feature of a cell

Nuclear envelope- a double membrane thatseparates the nucleus from the cytoplasm

Nuclear pores- numerous openings in the nuclear

envelope, control movement of substances betweennucleus and cytoplasm

Nucleolus- spherical body that produces ribosomes

Genes- are the cells hereditary units, control

activities and structure of the cell Chromosomes- long molecules of DNA combined

with protein molecules


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Packing of DNA into a Chromosome of a

Dividing Cell


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Overview of Gene Expression


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Transcription


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Translation


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Somatic Cell Division - Mitosis

The cell cycle is a sequence of events inwhich a body cell duplicates its contents anddivides in two

Human somatic cells contain 23 pairs ofchromosomes (total = 46)

The two chromosomes that make up eachpair are called homologous chromosomes

(homologs) Somatic cells contain two sets of

chromosomes and are called diploid cells


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Cell Division

Interphase - the cell is not dividing

- the cell replicates its DNA

- consists of three phases, G1, S, and G2,

replication of DNA occurs in the S phaseMitotic phase - consists of a nuclear division(mitosis) and a cytoplasmic division

(cytokinesis) to form two identical cells


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The Cell Cycle


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DNA Replication


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Nuclear Division: Mitosis

Prophase- the chromatin fibers change intochromosomes

Metaphase - microtubules align the centromeres ofthe chromatid pairs at the metaphase plate

Anaphase- the chromatid pairs split at thecentromere and move to opposite poles of the cell;the chromatids are now called chromosomes

Telophase- two identical nuclei are formed aroundthe identical sets of chromosomes now in theirchromatin form


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Cytoplasmic Division: Cytokinesis

Division of a cells cytoplasm to form twoidentical cells

Usually begins in late anaphase

The plasma membrane constricts at itsmiddle forming a cleavage furrow

The cell eventually splits into two daughtercells

Interphase begins when cytokinesis iscomplete

1

Pericentriolar materialCentrioles

Centrosome:

1


Centrosome:

1


Centrosome:

1


Centrosome:

1


Centrosome:

1


Centrosome:


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NucleolusNuclear envelopeChromatinPlasma membrane

Cytosol

(a) INTERPHASE

all at 700xLM

LateEarly


Cytosol

Chromosome(two chromatidsjoined atcentromere

(a) INTERPHASE

(b) PROPHASE

Fragments ofnuclear envelope

Mitotic spindle(microtubules)

Kinetochore

2

all at 700xLM

Centromere


Cytosol

Metaphase plate

(a) INTERPHASE

(c) METAPHASE

2

3

LateEarly(b) PROPHASE



Kinetochore

all at 700xLM


Centromere

EarlyLate(d) ANAPHASE


Cytosol

Chromosome

(a) INTERPHASE

(c) METAPHASE

2

3

4

Cleavagefurrow




Kinetochore

Metaphase plate

all at 700xLM


Centromere



Cytosol

(a) INTERPHASE

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

2

3

4

5

Cleavagefurrow




Kinetochore

Metaphase plate

Chromosome

all at 700xLM


Centromere



Cytosol

(a) INTERPHASE

(f) IDENTICAL CELLS IN INTERPHASE

Cleavage furrow

(e) TELOPHASE

(c) METAPHASE

Cleavagefurrow

2

3

4

5

6




Kinetochore

Metaphase plate

Chromosome

all at 700xLM

Centromere



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R d i C ll Di i i


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Reproductive Cell Division

During sexual reproduction each new organism isthe result of the union of two gametes (fertilization),one from each parent

Meiosis - reproductive cell division that occurs inthe gonads (ovaries and testes) that producesgametes with half the number of chromosomes

Haploid cells - gametes contain a single set of 23

chromosomes Fertilization restores the diploid number of

chromosomes (46)

R d i C ll Di i i


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Reproductive Cell Division

Meiosis occurs in two successive stages:meiosis I and meiosis II

Each of these two stages has 4 phases:prophase, metaphase, anaphase, and

telophase Summary - Meiosis I begins with a diploid cell

and ends with two cells having the haploidnumber of chromosomes; in Meiosis II, each

of the two haploid cells divides, the net resultis four haploid gametes that are geneticallydifferent from the original diploid starting cell


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Leptotene stage condensation of chromatin


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Leptotene stage- condensation of chromatinfibers into long, threadlike structures, similarto what occurs at the beginning of mitosis.

Zygotene stage- individual chromosomesbecome distinguishable and homologouschromosomes become closely paired with

each other via synapsis.


Pachytene stage crossing over or the


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Pachytene stage- crossing over, or theexchange of DNA segments between thehomologous chromosomes.

This accounts for genetic recombination.

Each chromosome undergoes compactingprocess where the size is reduced to less

than of its previous length.



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Diplotene stage- homologous chromosome


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Diplotene stage- homologous chromosomebegin to separate from each other particularlynear the centromere. They however, remainattached by connections known aschiasmata.

Chiasmata regions where exchange of DNA

materials has occured. Diakinesis- chromosomes recondense to

their maximally compacted state. Nucleoli

disappear, the spindle forms and the nuclearenvelope breaks down.



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Cellular Diversity


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Cellular Diversity

The average adult hasnearly 100 trillion cells

There are about 200different types of cells

Cells come in a varietyof shapes and sizes

Cellular diversity

permits organization ofcells into more complextissues and organs

E d f Ch 3


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End of Chapter 3

Copyright 2009 John Wiley & Sons, Inc.All rights reserved. Reproduction or translation of this work beyond that

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Ch03 the Cellular Level of Organization

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