.Eukaryotes cell origin, structure

and function

Dr. Ganga Naik. S1st Year Ph.D

Department of Anatomy

Veterinary College

Hebbal, Bangalore -24

. Origin of life - Prokaryotes and Eukaryotes

Difference between prokaryotes and

eukaryotes

Different kind of eukaryotes - Cell structure

and function

almost 2 billionyears of strictlyunicellular life!

.

• .

Our understanding of the origin of life is

incomplete

Hypothesis that organic molecules formed

spontaneously and evolved into molecular

systems with the fundamental properties of life

.

• .

Many laboratory experiments lend support to

an abiotic origin of life through chemical

evolution

Spontaneous generation or abiogenesis.

Abiogenesis -

is the study of how biological life could arise

from inorganic matter through natural processes.

Inorganic compounds are of inanimate, not

biological origin.[1] Inorganic compounds lack

carbon and hydrogen atoms and are synthesized

by the agency of geological systems

Organized living structures have been found in

black shales of the Palaeoproterozoic

Francevillian B Formation in Gabon, dated at

2.1 billion years old. Eukaryotic life could have

evolved at that time.

Fossils that are clearly related to modern groups

start appearing an estimated 1.2 billion years

ago, in the form of a red alga, though recent

work suggests the existence of fossilized

filamentous algae in the Vindhya basin dating

back perhaps to 1.6 to 1.7 billion years ago.

Biomarkers suggest that at least stem eukaryotes

arose even earlier.

The presence of steranes in Australian shales

indicates that eukaryotes were present in these

rocks dated at 2.7 billion years old

Eukaryotes cell origin

The origin of the eukaryotic cell is considered

a milestone in the evolution of life,

since they include all complex cells and

almost all multicellular organisms.

.Miller–Urey experiment

• Demonstrated that most amino acids, were shown to be

racemically synthesized in conditions thought to be similar to

those of the early Earth.

• racemically - relating to, or constituting a compound or

mixture that is composed of equal amounts of dextrorotatory

and levorotatory forms of the same compound and is not

optically active

• In all living things, these amino acids are organized into

proteins, and the construction of these proteins is

mediated by nucleic acids, that are themselves

synthesized through biochemical pathways catalysed by

proteins.

• The experiment used water (H2O), methane (CH4),

ammonia (NH3), and hydrogen (H2). Miller and Urey

observed that as much as 10–15% of the carbon within

the system was now in the form of organic compounds.

Two percent of the carbon had formed amino acids that

are used to make proteins in living cells, with glycine as

the most abundant. Sugars were also formed. Nucleic

acids were not formed within the reaction.

• The Big Bang theory is the prevailing cosmological

model that describes the early development of the

Universe.[1] According to the Big Bang theory, the

Universe was once in an extremely hot and dense state

which expanded rapidly. This rapid expansion caused

the Universe to cool and resulted in its present

continuously expanding state. According to the most

recent measurements and observations, the Big Bang

occurred approximately 13.75 billion years ago,[2][3]

which is thus considered the age of the Universe.[4][5]

After its initial expansion from a singularity, the

Universe cooled sufficiently to allow energy to be

converted into various subatomic particles, including

protons,neutrons, and electrons. While protons and

neutrons combined to form the first atomic nuclei only

a few minutes after the Big Bang, it would take

thousands of years for electrons to combine with them

and create electrically neutral atoms. The first element

produced was hydrogen, along with traces of helium

and lithium. Giant clouds of these primordial elements

would coalesce through gravity to form stars and

galaxies, and theheavier elements would be synthesized

either within stars or during supernovae.

.Endosymbiotic theory

Konstantin Mereschkowski in 1905.

According to this theory, certain organelles

originated as free-living bacteria that were taken

inside another cell as endosymbionts.

The endosymbiotic theory argues that

mitochondria, plastids (e.g. chloroplasts), and

possibly other organelles of eukaryotic cells,

originate through symbiosis between multiple

microorganisms. According to this theory, certain

organelles originated as free-living bacteria that

were taken inside another cell as endosymbionts.

Mitochondria developed from proteobacteria (in

particular,Rickettsiales, the SAR11 clade,[1][2] or close

relatives) and chloroplasts from cyanobacteria.

.Endosymbiotic theory

Mitochondria developed from proteobacteria

(Rickettsiales)

chloroplasts from cyanobacteria.

cenancestor, is the most recent organism from

which all organisms now living on Earth descend.[1]

Thus it is the most recent common ancestor

(MRCA) of all current life on Earth. The LUA is

estimated to have lived some

3.5 to 3.8 billion years ago

The Proteobacteria are a major group (

phylum) of bacteria. They include a wide

variety of pathogens, such as Escherichia,

Salmonella, Vibrio, Helicobacter, and many

other notable genera. [2] Others are free-living,

and include many of the bacteria responsible

for nitrogen fixation.

• Cyanobacteria (/sa æno bæk t əriəɪˌ ʊ ˈ ɪ /), also

known as blue-green bacteria, blue-green

algae, and Cyanophyta, is a phylum of

bacteria that obtain their energy through

photosynthesis.[3] The name "cyanobacteria"

comes from the color of the bacteria (Greek

: κυανός (kyanós) = blue).

• The ability of cyanobacteria to perform

oxygenic photosynthesis

• the last universal ancestor (LUA), also called

the last universal common ancestor(LUCA),

or the cenancestor, is the most recent

organism from which all organisms now living

on Earth descend.[1] Thus it is the

most recent common ancestor (MRCA) of all

current life on Earth. The LUA is estimated to

have lived some 3.5 to 3.8 billion years ago

(sometime in the Paleoarchean era).[2][3]

.Endosymbiotic theory

Many separate organisms may have contributed

for development of cenancestor (

most recent common ancestor).

is the most recent organism from which all organisms

now living on Earth descend.[1] Thus it is the

most recent common ancestor (MRCA) of all current

life on Earth. The LUA is estimated to have

Mitochondria and chloroplasts

Surrounded by two membranes

Possess their own DNA

Possess ribosomes

70S (bacterial), 80S (eukaryotic)

Self replication

The Proteobacteria are a major group (phylum

) of bacteria. They include a wide variety of

pathogens, such as Escherichia, Salmonella,

Vibrio, Helicobacter, and many other notable

genera. [2] Others are free-living, and include

many of the bacteria responsible for

nitrogen fixation.

• Cyanobacteria (/sa æno bæk t əriəɪˌ ʊ ˈ ɪ /), also

known as blue-green bacteria, blue-green

algae, and Cyanophyta, is a phylum of bacteria

that obtain their energy through photosynthesis.

[3] The name "cyanobacteria" comes from the

color of the bacteria (Greek: κυανός (kyanós) =

blue).

• The ability of cyanobacteria to perform

oxygenic photosynthesis

• the last universal ancestor (LUA), also called

the last universal common ancestor(LUCA),

or the cenancestor, is the most recent organism

from which all organisms now living on Earth

descend.[1] Thus it is the

most recent common ancestor (MRCA) of all

current life on Earth. The LUA is estimated to

have lived some 3.5 to 3.8 billion years ago

(sometime in the Paleoarchean era).[2][3]

EARLIEST LIFE

Life arose - 3.8 billion years ago

The earliest cells were prokaryotic

• .

Prokaryotes

Contains

1. Nucleoid region – Contain

DNA

2. Cell membrane & Cell wall

3. Ribosomes

4. (no membrane) to make

proteins in their cytoplasm

Ancient prokaryotes fromWestern Australia.

Filamentous “Cyanobacteria”

3.5 BYA

Cyanobacteria are one of the earliest life forms known to have existed on Earth

Earliest filamentous microfossils 3.23 BYA

FROM: Rasmussen 2000 NATURE

Microfossils are fossils generally not larger than four millimeters, and commonly smaller than one millimeter, the study of which requires the use of light or electron microscopy. Fossils which can be studied with the naked eye or low-powered magnification, such as a hand lens, are referred to as macrofossils. Obviously, it can be hard to decide whether or not some organisms should be considered microfossils, and so there is no fixed size boundary

Microfossil Cyanobacteria

Evolution of Eukaryotes

• As early as 2.1 Bya eukaryotic cells appear as fossils

Figure 01A: Microfossils of probable eukaryotic cells

Reproduced from Schopf, J.W., Scientific American 239 (1978): 111-138. Courtesy of J. William Schopf, Professor of Paleobiology & Director of IGPP CSEOL

Figure 01B: Microfossils of probable eukaryotic cells

Figure 01C: Microfossils of probable eukaryotic cells

Origin of the Eukaryotes

Two theories to explain the origin of

membrane bound organelles

1. Endosymbiosum

2. Invagination

• a type of symbiosis in which one organism lives inside the

other, the two typically behaving as a single organism. It is

believed to be the means by which such organelles as

mitochondria and chloroplasts arose within eukaryotic

cellsendosymbiotic adj

• Invagination is the infolding of one part within another

part of a structure

• Both mitochondria and chloroplasts were once free living

organisms

– Engulfed by early eukaryotic cells

– Maintained rather than being digested

– “Endosymbionts”

• Most genes have been lost or transferred to the nucleus

– A few genes are retained

• ENDOSYMBIOSIS

Mitochondria and chloroplasts -

“Endosymbionts”

At present, host cells cannot live without

their endosymbionts,

these endosymbionts cannot live without

their host cell

Other organelles are likely

endosymbionts also

• .

• .

.

• .

Origin of the Eukaryotes

.• .

CYTOSKELETON

MITOCHONDRION

CENTRIOLES

LYSOSOME

GOLGI BODY

SMOOTH ER

ROUGH ER

RIBOSOMES

NUCLEUS

PLASMA MEMBRANE VESICLE

CYTOPLASM

Eukaryotes cells

Differences between Prokaryotic Cells and Eukaryotic cells

Prokaryotic Cells Eukaryotic cells

small cells (< 5 mm) larger cells (> 10 mm)

always unicellular often multicellular

no nucleus or any membrane-bound organelles

always have nucleus and other membrane-bound organelles

DNA is circular, without proteins DNA is linear and associated with proteins to form chromatin

ribosomes are small (70S) ribosomes are large (80S)

no cytoskeleton always has a cytoskeleton

cell division is by binary fission cell division is by mitosis or meiosis

reproduction is always asexual reproduction is asexual or sexual

Include most cells (other than bacteria)

1.Plants

2. Fungi

3. Animals

A fungus ( / f ŋ əsˈ ʌ ɡ /; plural: fungi[3] or funguses

[4]) is a member of a large group of eukaryotic

organisms that includes microorganisms such

as yeasts and molds(British English: moulds), as

well as the more familiar mushrooms.Fungal cells are most similar to animal cells, with the following exceptions:A cell wall that contains chitinLess definition between cells; the hyphae of higher fungi have porous partitions calledsepta, which allow the passage of cytoplasm, organelles, and, sometimes, nuclei. Primitive fungi have few or no septa, so each organism is essentially a giant multinucleate supercell; these fungi are described as coenocytic.Only the most primitive fungi, chytrids, have flagella.

Eukaryotes

Eukaryotic Cell

Contain 3 basic cell structures:

1.Nucleus

2.Cell Membrane

3.Cytoplasm with

organelles

Types of Eukaryotic Cells

Plant Cell Animal Cell

Plant CellPlant Cell

Made of cellulose which

forms very thin fibers

Gives shape to the cell

Strong and rigid

In plant cells only

– Protects and supports the

cell

– Gives shape to the cell

– A dead layer, ∴freely

permeable

– Resists entry of excess

water into the cell

• Cell wall

– Lies immediately against

the cell wall

– Made of protein and lipid

� ∴Selectively permeable

– Can control the movement

of materials into and out of

the cell

• Cell membrane

Plant CellPlant Cell

–Jelly-like substance

enclosed by cell membrane

–Contains organelles and granules

•e.g. chloroplast

•e.g. mitochondrion

–Contains the green pigment

chlorophyll

•To trap light energy, to

make food by

photosynthesis

•Contains starch grains

(products of

photosynthesis)

•Provide a medium for chemical reactions to take place

has specific functions

in cytoplasm–Non-living granules

–Starch granules

–Oil droplets

–Crystals of insoluble wastes

– large central vacuole– Contains cell sap

•a solution of chemicals (sugars, mineral salts, wastes, pigments)

• Cytoplasm

Plant CellPlant Cell

Nucleus

– Bounded by a nuclear membrane

– 1.Controls the normal activities of the cell

2. For heredity

– Contains thread-like chromosomes

– Each cell has fixed number of chromosomes

• Chromosomes carry genes

–genes control cell characteristics

Plant Cell

.

Animal cell

Animal cell

No cell wall and chloroplast

Small vacuoles

Stores glycogen granules and oil droplets

in the cytoplasm

mitochondrion

nucleus

glycogen granule

cell membrane

cytoplasmAnimal cellAnimal cell

vacuole

Different kinds of animal cells

white blood cell

red blood cell

cheek cellssperm

nerve cell

muscle cell

Amoeba

Paramecium

Structure Animal cells Plant cellscell membrane Yes yes

nucleus Yes yesnucleolus yes yesribosomes yes yes

ER yes yesGolgi yes yes

centrioles yes nocell wall no yes

mitochondria yes yescholorplasts no yes

One big vacuole no yescytoskeleton yes Yes

.Cytoplasm involved in

1. Energy formation and release

2. Protein synthesis

.Cytoplasm• Subdivided into

1.Cytocentrum

2. Endocentrum

3.Ectoplasm

.Cytoplasm

1.Cytocentrum• ER

• Pair of centriole

• Cytoskeletal

element

.Cytoplasm

2.Endocentrum• Largest

• Most of structural

components

.Cytoplasm

3. Ectoplasm• Narrow band

PLASMA MEMBRANE/Cell membrane

Surrounds the entire cytoplasm

Provides a selective barrier

regulates the transport of materials into

and out of the cell.

PLASMA MEMBRANE/Cell membrane

All membranes including the membranous

organelles are composed

1. Lipid and protein - mainly

2. Carbohydrate - small amount

.

Organelles

1. Rough Endoplasmic Reticulum

2. Smooth Endoplasmic Reticulum:

3. Golgi Complex:

4. Mitochondria:

5. Lysosomes:

6. Peroxisomes Or Microbodies:

.

Cytoskeletal

Elements And

Cytoplasmic

Matrix

a) Microtubules:

b) Centrioles Or

Diplosomes

c)Microfilaments:

.NUCLEUS

The nucleus is found in all cells except

mammalian red blood cells and platelets,

.NUCLEUS

It has DNA,

which is the storehouse of genetic information

controls protein synthesis in the cells.

,

Granular endoplasmic reticulum /

Rough endoplasmic reticulum / Ergatoplasm /

chromidial substance:

E/M defined as a system of

interconnecting membrane bound

channels or cavities,

Granular endoplasmic reticulum

The membrane bound channels are either

a. Cistarnae (flattened sacs)

b. Tubular or

c. Vesicles

The membrane bound channels attached with

ribosomes on their outer surface.

May communicate with the nuclear envelope

.Granular endoplasmic reticulum

Ribosomes

are Rnp granules (Ribonuclear

protein),

the sites of synthesis of proteins from

amino acids.

Basophilia of the endoplasmic

reticulum is due to RNA of

ribosomes

and not due to membranes of EPR.

In nerve cells closely packed

flattened sacs of RER are called

Tigroid bodies or Nissl bodies.

Functions:

1. Contributed to the mechanical support of

cytoplasm

2. Synthesis of proteins for export

Ribosomes:

.

Ribosomes:

Occur in two forms.

1. Associated with endoplasmic reticulum

2. Occur free in cytoplasm

Ribosomes:

• Under E/M appear as small electron dense

particles 150Ǻ diameter formed by 2 subunits one

large and one small.

• have a characteristic sedimentation coefficient of

80s (sedgberg unit) with the larger heavier unit

having 60s and the smaller subunit having 40s

unit.

•

.

Several ribosomes associated with

endoplasmic reticulum synthesis proteins,

These proteins are meant for external

use.

Eg. Enzymes.

.

• Several ribosomes are attached to each other by a

strand of mRNA forming polysomes or

polyribosomes.

.

Polyribosomes

Synthesize proteins

intracellular use

Eg. Hemoglobin formed in red blood cells.

:

SMOOTH ENDOPLASMIC RETICULUM

SMOOTH ENDOPLASMIC RETICULUM:

Under electron microscope appear as three

dimensional network of membrane bound

tubules with no cisternae and lack ribosomes.

It may communicate with RER or with

nuclear envelope.

.

• .

Functions:

Production of steroid hormone, in

steroid secreting cells, adrenal cortex,

testes, ovary.

GOLGI COMPLEX:

GOLGI COMPLEX:

• Supranuclear position in secreting cells

• Multiple in number in hepatocyte (liver cells).

Forms a network around the nucleus in nerve cells,

.

• E/M appear as lamellae (3-12 in number) of

parallely arranged flattened curved membranous

sacs, vacuoles or vesicles.

Function:

Condensation and packing of secretory product by

loss of water.

Formation of lysosomes and peroxisomes in

leukocytes.

DNA directs RNA synthesis RNA exits nucleus

through a nuclear pore ribosome protein is

made proteins with proper code enter RER

proteins are modified in RER and lipids are made

in SER vesicles containing the proteins and

lipids bud off from the ER

ER vesicles merge with Golgi body proteins and

lipids enter Golgi each is fully modified as it

passes through layers of Golgi modified

products are tagged, sorted and bud off in Golgi

vesicles …

Golgi vesicles either merge with the plasma

membrane and release their contents OR remain

in the cell and serve a purpose

Completes the processing substances received from

the ER

Sorts, tags and packages fully processed proteins

and lipids in vesicles

.MITOCHONDRIA:

.

• Energy conversion system by

which chemical energy of food

stuffs is converted into high energy

phosphates (ATP)

MITOCHONDRIA:

.MITOCHONDRIA:

.

E/M –

Double membranous structure with

rounded ends or sausage shaped.

Both membranes have unit

membrane structure.

.Mitochondrial matrix

Electron dense granules

DNA and RNA strands

.

Mitochondrial matrix

DNA and RNA strands

• which directs the synthesis of enzymes of

mitochondria.

Because of the presence of DNA,

are semiautonomous organelles

capable of self replication.Enzyme localization:

1.Matrix: enzymes of Kreb’s cycle

2.Elementary particles: enzymes of oxidative

phosphorylation

3.Inner membrane:

Respiratory chain enzymes,

flavoproteins, dehydrogenases

.

• .

Function – synthesis of ATP3 major pathways involved in ATP production

1. Glycolysis2. Krebs Cycle3. Electron transport system .(ETS)

.

LYSOSOMES

LYSOSOMES

Membrane bound spherical uniformly

granular electron dense bodies.

LYSOSOMES

Present in all cells

but numerous in cells exhibiting phagocytic

activity.

E.g. Macrophages and WBC’s.

LYSOSOMES

• Associated with intracellular digestion and

phagocytosis.

LYSOSOMES• Contain more than 40 hydrolytic enzymes

• active at acid pH.

Eg. Acid phosphatase, Ribonuclease, sulphatase etc.

• If the material is quite large it may remain over in the form

of brownish pigments called lipoprotein pigments.

Seen in neurons,

heart muscles,

liver cells.

Increase in their number with age and are called

Senility pigment.

Residual bodies.

• The large undigested material is retained

• These bodies may be expelled from the cell by a process of

exocytosis as seen in macrophages.

PEROXISOMES OR MICROBODIES:

• .

PEROXISOMES OR MICROBODIES:

• Membrane bound bodies

•

PEROXISOMES OR MICROBODIES:

• Resemble lysosomes

• but do not contain lysosomal enzymes.

PEROXISOMES OR MICROBODIES:

Function :

Hydrogen peroxide is detoxified

Fatty acids are metabolized

They possess enzymes concerned with production

and destruction of hydrogen peroxide.

.

CYTOSKELETAL ELEMENTS

AND

CYTOPLASMIC MATRIX

.CYTOSKELETAL ELEMENTS

• Structure

Interconnected system of

– microtubules,

– microfilaments,

– intermediate filaments

.CYTOSKELETAL ELEMENTS

• Function

– gives cells internal organization, shape, and ability to

move

CYTOSKELETAL ELEMENTS AND CYTOPLASMIC MATRIX

MICROTUBULES:

Slender, hollow, cylindrical un

branched structures

Made of tubulin proteins (globular)

•

CYTOSKELETAL ELEMENTS AND CYTOPLASMIC MATRIX

MICROTUBULES:

Function

Separation of chromosomes during mitosis.

They function both to determine cell shape

and in a variety of cell movements, including

some forms of cell locomotion, the

intracellular transport of organelles, and

–Move chromosomes around during cell division

• Used to make cilia and flagella

•

CENTRIOLES (Diplosome):

• .

CENTRIOLES (Diplosome):

• A is a cylindrically-shaped cell structure

• Found in most eukaryotic cells,

• though it is absent in higher plants and most fungi

• Contained in an area of gelatinous material called

centrosphere.

CENTRIOLES (Diplosome):

• Wall is composed of 9 sets of microtubule triplets.

CENTRIOLES (Diplosome):

Functions:

involved in the organization of the mitotic spindle

in the completion of cytokinesis

Formation of mitotic spindles as asters in cell

division.

MICROFILAMENTS:

• .

MICROFILAMENTS:

1. Actin - 70A°

2. Myosin - 150 A°.

• In muscle cells well organized filamentous

components.

MICROFILAMENTS:

Functions:

Enable cells to change shape and move

(Participate in muscle contraction)

MICROFILAMENTS:

Functions:.

Provide contractile forces to form

cleavage furrow during cell division.

Cilia and flagella (structures for cell motility)

– Move whole cells or materials across the cell surface

– Microtubules wrapped in an extension of the plasma

membrane (9 + 2 arrangement of MT)

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