Cell structure

Morphology and ultra structures of plant, animal and bacterial cells

S C KunduBiotechnology

Microscopy

This is an aid to naked eye for mainly magnifying the image and to improve resolution of object.•Dyes and stains•Need for staining

– Difference in transparency and refractive index

•Fixation•Effect of fixing solutions

– Prevents bacterial decay– Prevents autolysis– Makes cell contents insoluble– Reduces shrinkage of the cells– Minimizes distortion– Increases the visibility of the cell

components– Prepares the cell components for

staining

Resolution• The ability to distinguish between

very closely positioned objects• The resolution of a microscopic lens

is numerically equivalent to ‘D’, the minimum distance between 2 objects (smaller the value of ‘D’, better the resolution)

– D =

Where, λ= electromagnetic wavelength N= refractive index of the

medium α= Half angle of the cone

of light entering the lens

Theoretically limit of resolution = = 0.22 µm

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sin

61.0

N

4.1

5.061.0 m

Types of Microscopy

• Dissecting microscope• Stereo-zoom microscope• Compound microscope• Bright field microscope• Dark field microscope• Phase contrast microscope• Interference microscope• Fluorescence microscope• Confocal microscope• Electron microscope• Transmission electron microscope• Scanning electron microscope

For cutting ultra-thin sections Ultramicrotomy

Microscopes to view ultrastructures• Electron Microscope

– Electromagnetic lens– Focus high velocity electron beam (wavelengths, from 10 -13 centimeter to infinity)– Ultra high vacuum

• Transmission electron microscope– Used to view very thin sections (50-100nm)– Electrically heated tungsten cathode as electron

source– Electrons transmitted from sample are projected on

photographic film

• Scanning electron microscope– To view the surfaces of unsectioned specimens– Samples are fixed, dried– Coated with heavy metals like – Excitedly released secondary electrons are focused

onto Scintillation detector– Magnification (up to 6 orders of magnitude from

about 10 to 500,000 times)

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Differences between prokaryotic and eukaryotic cellsParameters Prokaryotes Eukaryotes• Age differences First life forms on earth 2 billion years later the formation (3.5 billion years ago) of prokaryots• Structural difference

– Differentiation Unicellular Multicellular

– DNA arrangements DNA floats freely around in a   Held within the nucleus (linear)

unorganized manner (circular)

– Cellular organelles Ribosomes (70S) Nucleus, Ribosomes (80S), ER, golgi bodies, chloroplast,

mitochondria

– Size Smaller than eukaryotes Ten times larger than prokaryotic cells

– Cell wall Composed of peptidoglycan Some have cell wall but none

(amino acid and sugar) made of peptidoglycan

– Chromosome One-but not true chromosome: More than one chromosome

Plasmid

– DNA wrapping on Not present Present

proteins

– Lysosomes and Not present Present

peroxisomes

– Special Structures Mesosome, carboxysome, magnetosome Absent

What is Ultrastructure?• Structures can be seen under electron microscope• Structures having dimensions below limit of resolution of an optical microscope (~0.2 µm)

What is a Cell?• Structural and functional unit of living system

Optical Microscopic RBC (6 – 8 µm) WBC monocyte (14 – 20 µm) Plant cells (30 – 200 µm) Ostrich egg (15 – 20 cm) E.coli (0.2-1.5 X 2-6 µm) S cerevisiae (5-40 µm) Mycoplasma (0.1-0.5 µm) Human hair ( European - 40 µm)

(African - 250 µm)

Electron Microscopic Plasma membrane (6 – 10 nm) Pseudomembrane (~ 3.5 nm) Organells Cytoskeleton

Vacuole (0.1-50 µm) Microtubule (25 nm wide)

Chloroplast (4-6 µm) Microfilament (4-6 nm “) Mitochondria (< 0.1 µm) Flagella Lysosomes (0.4 µm) (12-18 nm wide) Ribosomes (20-25 nm) Pilli Magnetosome (400-1000 A) (4-35 nm wide) Carboxysome (50-500 nm)

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Ultrastructure of a plant cell (Eukaryotic)

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Organelle of a plant cell

Cell wall Morphology

Middle lamella (Outermost layer rich in pectins, forms the interface between adjacent plant cells and glues them together.)

Primary cell wall (thin, flexible and extensible layer, forms during cell growth)

Secondary cell wall (thick layer inside the primary cell wall. Contains xylem. Made of lignin, which strengthens and waterproofs the wall.)

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Organelle of a plant cell

Chloroplast Key features

• Photosynthesis• Contain the

chlorophyll pigment• Members of plastids• Plastid

transformation in genetically modified plants

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Ultrastructure of an animal cell (Eukaryotic)

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Organelle of an animal cellLysosome

Key features

• Contains acid hydrolase enzymes to break down waste materials and cellular debris

• They are created by the addition of hydrolytic enzymes to early endosomes from the Golgi apparatus

• Some important enzymes found within lysosomes include:

– Lipase, which digests lipids– Amylase, which

digests amylose, starch, and maltodextrins

– Proteases, which digest proteins– Nucleases, which digest nucleic acids– Phosphoric acid monoesters

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Some common organelle of eukaryotic cellsMitochondria Morphology

Contains outer and inner membranes composed of phospholipid bilayers and proteins

Five distinct compartments: The outer mitochondrial membrane

Porins forms channels Associated with the ER membrane

The intermembrane space (the space between the outer and inner membranes)

The inner mitochondrial membrane Contains proteins with five types of functions

Those that perform the redox reactions of oxidative phosphorylation

ATP synthase, which generates ATP in the matrix Specific transport proteins that

regulate metabolite passage into and out of the matrix

Protein import machinery. Mitochondria fusion and fission protein

The cristae space (formed by infoldings of the inner membrane)

The matrix (space within the inner membrane) Mitochondria-associated ER membrane Pyruvate and the citric acid cycle NADH and FADH2: the electron transport chain

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Some common organelle of eukaryotic cellsNucleus Morphology

Contains Nuclear envelope and pores Nuclear lamina Chromosomes Nucleolus Other subnuclear bodies

AnucleatedHuman red blood cell

Multinucleated cells Acantharean species of protozoa and

some fungi in mycorrhizae Intestinal parasites in the genus Giardia (2

nuclei per cell) Humans, skeletal muscle cells,

called myocytes (More than 2 nuclei per cell) Function

Gene expression Cell compartmentalization Processing of pre-mRNA

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Some common organelle of eukaryotic cellsRibosome Key features

• Synthesizes protein chains from mRNA molecules (Translation)

• Made of Ribonucleoproteins • Contains two subunits

– The smaller subunit binds to the mRNA– Larger subunit binds to the tRNA and

the amino acids• Free ribosome (in cytosol)• Membrane bound ribosome (with ER)• Prokaryotes have 70S ribosomes

– consisting of a small (30S) – a large (50S) subunit

• Eukaryotes have 80S ribosomes– each consisting of a small (40S)– large (60S) subunit

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Some common organelles of eukaryotic cellsEndoplasmic Reticulum and Golgi Apparatus

Morphology

• The endoplasmic reticulum (ER) is the transport network for molecules targeted for certain modifications and specific destinations

– Rough ER– Smooth ER

• The primary function of the Golgi apparatus is to process and package the macromolecules such as proteins and lipids that are synthesized by the cell

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Some common organelle of eukaryotic cellsPeroxysome and centrosome Features

• Peroxisomes have enzymes that rid the cell of toxic peroxides. The cell could not house these destructive enzymes if they were not contained in a membrane-bound system

• The centrosome produces the microtubules of a cell – a key component of the cytoskeleton.

– It directs the transport through the ER and the Golgi apparatus.

– Centrosomes are composed of two centrioles, which separate during cell division and help in the formation of the mitotic spindle.

– A single centrosome is present in the animal cells.

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Peroxysome

Centrosome

Ultrastructure of a bacterial cell (Prokaryotic)

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Ultrastructure of a typical bacterial cell

Organells Magnetosomes (Magnetic crystals

Fe3O4 ) impart a permanent dipole moment to the cell swim along the geomagnetic field (magnetotaxis – movement in response to magnetic field of earth) 35-120 nm

Carboxysomes Ribulose 1,5-bisphosphate carboxylase or RuBisCo (CO2 fixation)

PHB (Polyhydroxy Butyrate) A raw material for making biodegradable plastic

Chlorophyll Containing vesicle in photosynthetic bacteria [having chloroplast equivalent to eukaryotic cells]

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