A Tour to Cell

8/13/2019 A Tour to Cell

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Biology of the Cell(A Tour of the Cell)

Compiled by:

Herbert Sipahutar

Universitas Negeri Medan2013


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A Tour of the Cell

How cells are studied Overall view of cell Nucleus & ribosomes Endomembrane system

Mitochondria and Chloroplasts Cytoskeleton Cell surfaces and junctions


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How cells are studied

Cells / cellular objects are small Need to be magnified to be seen Microscopy


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Size range of cells

Most are 1 - 100m

Copyright 2005 Pearson Education, Inc., publishing as Benjamin Cummings


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Size range of cells



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Size rangeof cells



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Size rangeof cells



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Microscopy

Two important parameters magnification

ratio of apparent size of an object to itsreal size

resolving power minimum distance two points that can be

separated and still be distinguished


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Microscopy

Light Microscopes visible light passing through glass lenses

magnification - up to 1000X resolution - 0.2m


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Different Types of Light Microscopy

Brightfield(unstained)

Brightfield(stained)

Fluorescence

Phase-contrast

Nomarski(differential-interference-contrast)

Confocal



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Electron Microscopy

Uses a beam of electrons instead of light Can visualize sub-cellular objects

magnification - resolution - 2nm (0.002 m)


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Electron Microscopy

Transmission (TEM) electron microscope Thin sections of the specimen

Scanning (SEM) electron microscope Surface of the specimen


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Electron micrographs of rabbit trachea

A) transmission electronmicrograph - TEM

B) scanning electronmicrograph - SEM



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How cells are studied

Cell Fractionation Separate cell constituents

assign function to a specific component

Ultracentrifugation

130,000 rpm up to 1 x 10 6 g


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Cell Fractionation

Break cells open and separateinto component parts

ULTRACENTRIFUGE >100,000 rpm up to 1 x 10 6 g



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A Tour of the Cell

How cells are studied Overall view of cell Nucleus & ribosomes Endomembrane system

Mitochondria and Chloroplasts Cytoskeleton Cell surfaces and junctions


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Two Types of Cells

Prokaryotic before nucleus

lacking a membrane- bound nucleus Eukaryotic

true nucleus

Both types are surrounded by a PlasmaMembrane


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A Prokaryotic Cell



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Eukaryotic Cell

Larger than prokaryotic cells bacteria - 1 - 10 m in diameter

eukaryotic cells - 10-100m in diameter Chromosomes located within nucleus,

membrane bound organelle

Cytoplasm is region between plasmamembrane and nucleus Contains other cell components

(cytosol and organelles)


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Limits to Cell Size

Upper limits to cell size volume of cell increases faster than its

surface area!

for a sphere -

Volume = 4/3 r 3 Surface Area = 4 r 2


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Surface area to volume of cells

Smaller objects have agreater ratio of surfacearea to volume thanlarger ones


6 1.2 6


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Limits to Cell Size

Larger organisms have more cells, rather than larger cells


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Plasma Membrane

Boundary of every cell Functions as a selective barrier

Oxygen, nutrients, and wastes must passthrough plasma membrane.

Cell needs a large surface area to volume

ratio for efficient transfer of substances


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The Plasma Membrane


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Animalcell overview


nucleusnucleolus

chromatin

plasmamembrane

Golgi apparatus

lysosome

mitochondrion

ribosome

peroxisomemicrovilli

microtubules

smooth ER

flagellum

rough ER

intermediatefilaments

microfilaments

centrosome

l ll


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Plant cell overview



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Animal / Plant Cell Differences

Not in Animal cell Not in Plant cell

ChloroplastsTonoplastCentral Vacuole

Plasmodesmata

LysosomesCentriolesFlagella

(but in some plant sperm)


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A Tour of the Cell

How cells are studied Overall view of cell Nucleus & ribosomes Endomembrane system Mitochondria and Chloroplasts Cytoskeleton Cell surfaces and junctions


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Nucleus

Largest organelle ~5m in diameter

contains most of the genetic material chromosomes surrounded by a double membrane

nuclear envelope

Lined by a scaffolding of proteinfilaments called nuclear lamina


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Nucleus and its envelope



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Double membrane structure - 20-40nm space


Nuclear Envelope


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Nucleus

Nuclear lamina network of protein fibers on nuclear side

of membrane maintain shape of nucleus

Nuclear contents Chromatin = DNA + protein

Organized into chromosomes Nucleolus - one or more

Site of ribosome component synthesis


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Site for protein synthesis - Contain rRNA and protein


Ribosomes

Ribosomes canbe free ormembrane-bound


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A Tour of the Cell



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The Endomembrane System

Physically continuous or transferredsegments of membranes as vesicles

Endoplasmic Reticulum (ER) Golgi Apparatus Lysosomes

Vacuoles


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Endoplasmic reticulum (ER)


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Smooth ER Functions

Diverse metabolic functions Lipid synthesis

phospholipids, oils and steroids (sex hormones) Carbohydrate metabolism

mobilization of glucose from glycogen in liver

Detoxification of drugs/poisons in liver Calcium ion storage


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Smooth ER Functions

Diverse metabolic functions Muscle cells contain enzymes that pump

calcium ions from the cytosol to the cisternae. When a nerve impulse stimulate a musclecell, calcium rushes from the ER into thecytosol, triggering contraction.

The enzymes then pump the calcium back,readying the cell for the next stimulation.


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Rough ER Functions

Protein secretion Glycoproteins

carbohydrates attached to proteins

Contained within lipid vesicles Transport vesicles Move to Golgi Apparatus before secretion

Membrane Production Phospholipid synthesis Membrane protein synthesis


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Physically continuous or transferredsegments of a membrane


Vacuoles


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ER products are modified, sorted &stored, then sent to other destinations

The Golgi Apparatus


Vesicles toor from ER cis-face

trans-faceSome vesiclesmove backward

TEM of Golgi

0.1m


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The Golgi Apparatus

Flattened membranous sacs Cisternae pita bread Has distinct polarity

cis face - receiving side (from ER) trans face - shipping side

May modify ER products Alters carbohydrate of glycoproteins

Synthesizes certain polysaccharides For secretion


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Vacuoles


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Lysosomes

Membrane bounded sac of digestiveenzymes

Breakdown all macromolecules Acidic environment - pH = 5


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Lysosome -phagocytosis


Lysosome


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Lysosome -autophagy



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Inherited diseases and Lysosomes

defective gene produces defective enzyme substrate cant be digested and builds to toxic

levels Pompes disease

Acid Maltase Deficiency progressive muscle weakness

Tay-Sachs disease in the brain lipid (GM2) accumulation leads to death of

neurons - death by age 2 or 3


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Vacuoles


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Large membrane -bound sacs

Various functions& types

Food vacuole Central vacuole Contractile vacuole


Vacuoles


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Functions of Vacuoles

Food vacuoles Formed by phagocytosis

Contractile vacuoles found in freshwater protists pump excess water out of the cell.


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Functions of Vacuoles

Plants have a large central vacuole Enclosed by tonoplast (membrane) Storage compartment

Proteins in cells of seeds Inorganic ions (K +, Cl -, etc.) Pigments Toxic metabolic by-products

Role in Plant Growth increases surface area to volume ratio

R i f l ti hi ll f


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Review of relationships among organelles ofthe endomembrane system

Nuclear envelope is connected to rough ERRough ER is continuous with SER.

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Vesiclestransportmaterials fromER to Golgi

Golgi sortsand packages

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Vesicles from transface of Golgi becomelysosomes or aresecretory vesicles


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A Tour of the Cell



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Other Organelles

Mitochondrion

Chloroplast

Peroxisome


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Mitochondrion

One to thousands in a cell Two membranes

Outer - smooth Inner - convoluted Cristae - folds in inner membrane

Increases membrane surface area

Intermembrane space Matrix - enclosed by inner membrane


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Mitochondrion

Inner membrane is site of respiration ATP synthesis


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The mitochondrion, site of respiration

1-10m in length


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Chloroplasts

One of several types of plastids Amyloplast - stores starch Chromoplasts - store pigments

Double membrane around chloroplast Internal membrane

Thylakoid - flattened sacs Grana - stacked thylakoids Stroma - cytosol of chloroplast Thylakoid space - inside thylakoid sacs

The chloroplast, site of


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Thylakoid space - inside membraneous sacs


p ,photosynthesis


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Peroxisome

Bound by single membrane Does not arise from endomembrane

system arise from lipids and proteins in the cytosol


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Peroxisome

Specialized metabolic compartment some types break down fatty acids

some detoxify compounds (alcohol, etc.) produce H 2O 2 as by-product

have catalase to remove H 2O 2

P i


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Peroxisome

crystal of catalase


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A Tour of the Cell

How cells are studied Overall view of cell

Nucleus & ribosomes Endomembrane system Mitochondria and Chloroplasts Cytoskeleton Cell surfaces and junctions


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Cytoskeleton

Internal framework of cells Network of fibers in cytoplasm

Maintenance of cell shape Provides support for internal organelles Aids in motility (movement)

Movement of cell from place to place Movement of intracellular components


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Cytoskeleton

Three major categories Microtubules

Microfilaments Intermediate Filaments


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Microtubules

Hollow tubes composed of tubulin - a - tubulin and b - tubulin

Largest of the three cytoskeletal fibers 25nm in diameter // 15nm lumen

Functions Maintenance of cell shape

compression resistance Cell motility (cilia or flagella) Chromosome movements in cell division Organelle movements


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Microtubules



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Cytoskeleton in Cell Motility

Microtubules and motor proteins



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Cytoskeleton in Cell Motility

Microtubules and motor proteins



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Animal cells have a pair ofcentrioles in centrosome Centrioles composed of 9 sets of

triplet MTs


Microtubules


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Microtubules

Eukaryotic Cell Movement Structures

Cilia 0.25m diameter and 2-20 m length

Flagella 0.25m diameter and 10-200 m length

Specialized arrangement of MTs


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Comparison of beating of flagella and cilia


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Comparison of beating of flagella and cilia

Common ultrastructure of


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9 + 2 arrangementDynein = motor molecule


flagellum and cilium

D ein alking


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Dyein walkingmoves cilia and flagella



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Dyein walking moves cilia and flagella


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Dyein walking moves cilia and flagella



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Microfilaments

Two intertwined strands of actin 7nm in diameter (thinnest filament) located just inside plasma membrane

Functions Maintenance of cell shape (tension-bearing) Altering cell shape

Muscle contraction Cell motility (pseudopods) and cell division


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Microfilaments



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Microvilli in intestinalepithelial cells arereinforced by

microfilaments


A Structural Role ofMicrofilaments


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Microfilaments and Mobility

Pseudopodia extend and contract through reversibleassembly and contraction of actin subunits intomicrofilaments.

Mi fil d M bili


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Microfilaments and Mobility

In plant cells (and others), actin-myosin interactionsand sol-gel transformations drive cytoplasmic streaming,the circular flow of cytoplasm in the cell.


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Intermediate Filaments

Intermediate in size (~10nm) Fibrous proteins coiled into cables

One of several different proteins - Keratins Functions

Maintenance of cell shape (tension-bearing) Anchorage of nucleus/other organelles

form the nuclear lamina More permanent than MT and MF


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Intermediate Filaments


keratins


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A Structural Role of

IntermediateFilaments

Network of IF throughout

cells


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A Tour of the Cell

How cells are studied Overall view of cell

Nucleus & ribosomes Endomembrane system Mitochondria and Chloroplasts Cytoskeleton Cell surfaces and junctions


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Plant Cell Surfaces

Cell wall Cellulose microfibrils and other components

Proteins Other polysaccharides

Composition differs from species to species


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Plant Cell Surfaces

Cell wall Function

Protects cell, maintains cell shape Prevents excessive uptake of water Supports plant against force of gravity


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Plant Cell Wall Structure

Primary cell wall Relatively thin and flexible wall

Middle lamella rich in pectins (sticky polysaccharides)

glues adjacent cells together Secondary cell wall

synthesized after cell stops growing strong and durable matrix often has a layered structure (laminated)

Plasmodesmata Channels in cell walls between adjacent cells


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Plant Cell Walls


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Animal Cell Surface

Lack a cell wall Have an Extracellular Matrix (ECM)

Mainly glycoproteins Collagen fibers imbedded in network of

proteoglycans (proteins with carbohydrate residuesattached) Fibronectins - connect to integrins in plasma

membrane and to microfilaments of cytoskeleton ECM proteins bind to cell surface receptor proteins

called integrins that span the cell membrane

E ll l M i (ECM)


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Extracellular Matrix (ECM)


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Extracellular Matrix

Major influence on behavior of a cell Transduces signals from outside cell

Mechanical signalling Chemical signalling


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Cell Junctions

Cells can be organized into tissues and /or organs Adjacent cells stuck together and can

communicate with each other

Pl t C ll J ti


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Plant Cell Junctions

Plasmodesma links cell cytoplasm



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Intracellular

junctions

A Tour to Cell

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