CELL ANATOMY

Cell Anatomy

byDr.Arun Naragund

Asst.prof.

Shri.j g c h s a m cghataprabha

The Cell Theory

All organisms are composed of one or more cells.

Cells are the smallest living things.

All organisms living today are descendents of an ancestral cell.

Cells arise only by division of previously existing cells.

The cell theory (proposed independently in 1838 and 1839) is a cornerstone of biology.

Schleiden

Schwann

Cells are Us

A person contains about 100 billion cells. That’s 100,000,000,000 or 1 x 1011 cells.

There are about 200 different cell types in mammals (one of us).

Cells are tiny, measuring on average about 0.002 cm (20 um) across. That’s about 1250 cells, “shoulder-to-shoulder” per inch.

nerve cell

Red and white blood cells above vessel-forming cells.

Two Fundamentally Different Types of Cells

A prokaryotic cell

A eukaryotic cell

Us vs. Them -Eukaryotes and Prokaryotes

Structure of Animal Cells

Cell Video

Cellular Anatomy

Major Divisions of the Eukaryotic Cell

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3.2: A Composite Cell

• Also called a ‘typical’ cell• Major parts include:

• Nucleus• contains DNA

• Cytoplasm• cellular contents between plasma

membrane &nucleus

• Cell membrane• selective barrier

Microtubules

Flagellum

Nuclear envelope

Basal body

Chromatin

Ribosomes

Cell membrane

Mitochondrion

Cilia

Microtubules

Microtubule

Centrioles

Microvilli

Lysosomes

Nucleolus

Nucleus

Phospholipid bilayer

SmoothEndoplasmicreticulum

RoughEndoplasmicreticulum

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Golgiapparatus

Secretoryvesicles

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• Outer limit of the cell

• Controls what moves in and out of the cell

• Selectively permeable

• Phospholipid bilayer • Water-soluble “heads” form surfaces (hydrophilic)• Water-insoluble “tails” form interior (hydrophobic)• Permeable to lipid-soluble substances

• Cholesterol stabilizes the membrane

• Proteins:• Receptors• Pores, channels and carriers• Enzymes• CAMS• Self-markers

Cell Membrane

Plasma Membrane

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The Cytoskeleton• Maintains cell shape

• Assists in movement of cell and organelles

• Three types of macromolecular fibers

– Actin Filaments

– Intermediate Filaments

– Microtubules

• Assemble and disassemble as needed

A Cytoskeleton Gallery

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The Cytoskeleton:Actin Filaments

• Extremely thin filaments like twisted pearl necklace• Dense web just under plasma membrane maintains

cell shape• Support for microvilli in intestinal cells• Intracellular traffic control

– For moving stuff around within cell– Cytoplasmic streaming

• Function in pseudopods of amoeboid cells• Pinch mother cell in two after animal mitosis• Important component in muscle contraction (other is

myosin)

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The Cytoskeleton: Actin Filament Operation

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The Cytoskeleton:Intermediate Filaments

• Intermediate in size between actin filaments and microtubules

• Rope-like assembly of fibrous polypeptides• Vary in nature

– From tissue to tissue– From time to time

• Functions:– Support nuclear envelope– Cell-cell junctions, like those holding skin cells tightly

together

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The Cytoskeleton:Microtubules

• Hollow cylinders made of two globular proteins called and tubulin

• Spontaneous pairing of and tubulin molecules form structures called dimers

• Dimers then arrange themselves into tubular spirals of 13 dimers around

• Assembly:– Under control of Microtubule Organizing Center

(MTOC)– Most important MTOC is centrosome

• Interacts with proteins kinesin and dynein to cause movement of organelles

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The Cytoskeleton: Microtubule Operation

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Microtubular Arrays:Centrioles

• Short, hollow cylinders– Composed of 27 microtubules– Microtubules arranged into 9 overlapping triplets

• One pair per animal cell– Located in centrosome of animal cells– Oriented at right angles to each other– Separate during mitosis to determine plane of division

• May give rise to basal bodies of cilia and flagella

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Centrioles

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Microtubular arrays:Cilia and Flagella

• Hair-like projections from cell surface that aid in cell movement

• Very different from prokaryote flagella– Outer covering of plasma membrane– Inside this is a cylinder of 18 microtubules arranged in

9 pairs– In center are two single microtubules– This 9 + 2 pattern used by all cilia & flagella

• In eukaryotes, cilia are much shorter than flagella– Cilia move in coordinated waves like oars– Flagella move like a propeller or cork screw

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Cytoplasm

• Cytosol = water

• Organelles = solids

Cytoplasm is really like a Jello fruit salad where the Jello is the cytosol and the fruits (oranges, grapes, bananas,

maybe walnuts, etc.) are the organelles.

Cytoplasm

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Organelles

Endoplasmic Reticulum (ER)• Connected, membrane-bound sacs, canals, and vesicles• Transport system• Rough ER

• Studded with ribosomes• Smooth ER

• Lipid synthesis• Added to proteinsarriving from rough ER

• Break down of drugs

Ribosomes• Free floating or connected to ER• Provide structural support and enzyme activityto amino acids to form protein (protein synthesis)

Membranes

Ribosomes

Membranes

(b) (c)


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Organelles

Golgi apparatus• Stack of flattened, membranous sacs• Modifies, packagesand delivers proteins

Vesicles• Membranous sacs• Store substances Inner membrane

Outer membrane

Cristae

(a) (b)


a: © Bill Longcore/Photo Researchers, Inc.

Mitochondria• Membranous sacs with inner partitions• Generate energy

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Organelles

Lysosomes• Enzyme-containing sacs• Digest worn out cell parts or unwanted substances

Peroxisomes• Enzyme-containing sacs• Break down organic molecules

Centrosome• Two rod-like centrioles• Used to produce cilia and flagella• Distributes chromosomes during cell division

(a) (b)

Centriole(cross-section)

Centriole(longitudinal section)


a: © Don W. Fawcett/Visuals Unlimited

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Organelles

Cilia• Short hair-like projections• Propel substances on cell surface

Flagellum• Long tail-like projection• Provides motility to sperm

(a)


a: © Oliver Meckes/Photo Researchers, Inc.

© Colin Anderson/Brand X/CORBIS

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Microfilaments and microtubules• Thin rods and tubules• Support cytoplasm• Allows for movement of organelles

Organelles

Inclusions

• Temporary nutrients and pigments

Microtubules

Microfilaments


© M. Schliwa/Visuals Unlimited

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Ribosomes• Serve in protein synthesis• Composed of rRNA

– Consists of a large subunit and a small subunit– Subunits made in nucleolus

• May be located:– On the endoplasmic reticulum (thereby making it

“rough”), or– Free in the cytoplasm, either singly or in groups called

polyribosomes

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Figure 4.9

Ribosome

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Endomembrane System• Restrict enzymatic reactions to specific

compartments within cell• Consists of:

– Nuclear envelope– Membranes of endoplasmic reticulum– Golgi apparatus– Vesicles

• Several types• Transport materials between organelles of system

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The Endoplasmic Reticulum

• Rough ER– Studded with ribosomes on cytoplasmic side– Protein anabolism

• Synthesizes proteins• Modifies proteins

– Adds sugar to protein– Results in glycoproteins

• Smooth ER– No ribosomes– Synthesis of lipids

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Endoplasmic Reticulum

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The Golgi Apparatus

• Golgi Apparatus– Consists of 3-20 flattened, curved saccules

– Resembles stack of hollow pancakes

– Modifies proteins and lipids• Packages them in vesicles

• Receives vesicles from ER on cis face

• Prepares for “shipment” in vesicles from trans face– Within cell

– Export from cell (secretion, exocytosis)

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Golgi Apparatus

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Endomembrane System: A Visual Summary

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Lysosomes

• Membrane-bound vesicles (not in plants)– Produced by the Golgi apparatus– Low pH– Contain lytic enzymes

• Digestion of large molecules• Recycling of cellular resources• Apoptosis (programmed cell death, like tadpole losing tail)

• Some genetic diseases– Caused by defect in lysosomal enzyme– Lysosomal storage diseases (Tay-Sachs)

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Lysosomes

The Lysosome

Cell suicide (suicide is bad for cells, but good for us!)

Recycling cellular components

Functions:

Digesting food or cellular invaders

(The lysosome is not found in plant cells)

This bacterium

about to be eaten by an

immune system cell

will spend the last minutes of its existence

within a lysosome.

Mitochondrion

• A cellular organelle probably of endosymbiotic origin that resides in the cytosol of most nucleated (eurkaryotic) cells.

• This organelle produces energy by oxidising organic acids and fats with oxygen by the process of oxidative phosphorylation and generates oxygen radicals (reactive oxygen species ROS )as a toxic by-product

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Mitochondrial Structure

The Mitochondrion

A class of diseases that causes muscle weakness and neurological disorders are due to malfunctioning mitochondria.

Worn out mitochondria may be an important factor in aging.

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Energy-Power House:Mitochondria

• Bounded by double membrane

– Cristae – Infoldings of inner membrane that encloses matrix

– Matrix – Inner semifluid containing respiratory enzymes

• Involved in cellular respiration

• Produce most of ATP utilized by the cell

Mitochondrial Genetics

• Each cell contains many mitochondria, each of which contains multiple copies of 16.5-k-b circular DNA molecule

• The mitochondrial genome is subject to a number of peculiarities of inheritance

Mitochondrial Genetics

• Interest in mitochondrial genetics comes mostly from:

• interest in diseases caused by mutations in mDNA

• interest in human history

• Doug Wallace.(mitochondrial enthusiast)

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Peroxisomes• Similar to lysosomes

– Membrane-bounded vesicles– Enclose enzymes

• However– Enzymes synthesized by free ribosomes in cytoplasm

(instead of ER)– Active in lipid metabolism– Catalyze reactions that produce hydrogen peroxide

H2O2• Toxic• Broken down to water & O2 by catalase

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Peroxisomes

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Cell Nucleus

• Is the control center of the cell

• Nuclear envelope• Porous double membrane• Separates nucleoplasm from cytoplasm

• Nucleolus• Dense collection of RNA and proteins• Site of ribosome production

• Chromatin• Fibers of DNA and proteins• Stores information for synthesis of proteins


Nucleus

Nucleolus

Chromatin

(a)

Nuclearpores

Nuclearenvelope

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Nucleus• Command center of cell, usually near center• Separated from cytoplasm by nuclear envelope

– Consists of double layer of membrane– Nuclear pores permit exchange between nucleoplasm

& cytoplasm• Contains chromatin in semifluid nucleoplasm

– Chromatin contains DNA of genes– Condenses to form chromosomes

• Dark nucleolus composed of rRNA– Produces subunits of ribosomes

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Why Study Cell Biology?

“ The key to

every

biological

problem must

finally be

sought in the

cell, for every

living

organism. ”

Thank you

Education

CELL ANATOMY