Early History of Earth What was early Earth like? Some scientists suggest that it was probably very...

Early History of Earth

What was early Earth like?

Some scientists suggest that it was probably very hot.

The energy from colliding meteorites could have heated its surface, while both the compression of minerals and the decay of radioactive materials heated its interior.

Early History of Earth

Volcanoes might have frequently spewed lava and gases, relieving some of the pressure in Earth’s hot interior. These gases helped form Earth’s early atmosphere.

The Origin of Life – Early Ideas

In the past, the ideas that decaying meat produced maggots, mud produced fishes, and grain produced mice were reasonable explanations for what people observed occurring in their environment.

Such observations led people to believe in spontaneous generation — the idea that nonliving material can produce life.

In 1668, an Italian physician, Francesco Redi, disproved a commonly held belief at the time—the idea that decaying meat produced maggots (immature flies).

• Redi’s well-designed, controlled experiment successfully convinced many scientists that maggots, and probably most large organisms, did not arise by spontaneous generation.

Control group

Experimental group

Time

Time

The Origin of Life – Early Ideas

However, during Redi’s time, scientists began to use the latest tool in biology—the microscope (invented by Anton Van Leeuwenhoek )

Although Redi had disproved the spontaneous generation of large organisms, many scientists thought that microorganisms were so numerous and widespread that they must arise spontaneously-probably from a vital force in the air.

In the mid-1800s, Louis Pasteur designed an experiment that disproved the spontaneous generation of microorganisms.

Pasteur set up an experiment in which air, but no microorganisms, was allowed to contact a broth that contained nutrients.

Pasteur’s experiment showed that microorganisms do not simply arise in broth, even in the presence of air.

From that time on, biogenesis, the idea that living organisms come only from other living organisms, became a cornerstone of biology.

Pasteur’s ExperimentEach of Pasteur’s broth-filled flasks was boiled to kill all microorganisms.

Microorganisms soon grew in the broth, showing that they come from other microorganisms.

The flask’s S-shaped neck allowed air to enter, but prevented microorganisms from entering the flask.

Pasteur tilted a flask, allowing the microorganisms to enter the broth.

The Evolution of Cells

Fossils indicate that by about 3.4 billion years ago, photosynthetic prokaryotic cells existed on Earth. But these were probably not the earliest cells. The first forms of life may have been prokaryotic forms that evolved from a “protocell”.

Because Earth’s atmosphere lacked oxygen, scientists have proposed that these organisms were most likely anaerobic.

• For food, the first prokaryotes probably used some of the organic molecules that were abundant in Earth’s early oceans.

• Over time, these heterotrophs would have used up the food supply.

• Heterotrophs are organisms which obtain their food from other heterotrophs or autotrophs (plants).

The First True Cells

Autotrophs are organisms that can make their own food (i.e. plants). These first autotrophs were probably similar to present-day archaebacteria.

• Archaebacteria are prokaryotic and live in harsh environments, such as deep-sea vents and hot springs.

•The earliest autotrophs probably made glucose by chemosynthesis rather than by photosynthesis.

•In chemosynthesis, autotrophs release the energy of inorganic compounds, such as sulfur compounds, in their environment to make their food (they use chemicals instead of sunlight). Bill Nye Video Segment

– Life As We Know It

The Endosymbiont Theory (Endosymbiosis)

Complex eukaryotic cells probably evolved from simple prokaryotic cells.

The endosymbiont theory, proposed by American biologist Lynn Margulis in the early 1960s, explains how eukaryotic cells may have arisen.

The endosymbiont theory proposes that eukaryotes evolved through a symbiotic relationship between ancient prokaryotes.

New evidence from scientific research supports this theory and has shown that chloroplasts and mitochondria have their own ribosomes that are similar to the ribosomes in prokaryotes.

In addition, both chloroplasts and mitochondria reproduce independently of the cells that contain them.

The fact that some modern prokaryotes live in close association with eukaryotes also supports the theory. (i.e. E.coli in human gut)

The Discovery of Cells

Anton Van Leeuwenhoek = Dutch scientist who invented the first light microscope.

Robert Hooke = English scientist who identified and named the “cell” while observing cork cells with a light microscope.

Robert Brown = English scientist who identified and named the nucleus of the cell.

Matthias Schleiden = German scientist that noted all plants are made of cells.

Theodor Schwann = German scientist who noted that all animals are made of cells.

Rudolf Virschow = Russian scientist who stated that cells come from pre-existing cells.

The Cell Theory

All plants are made of cells.

All animals are made of cells

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

Schleiden

Schwann

The Cell Theory

1. All organisms are made of one or more cells.

2. The cell is the basic unit of structure and organization of organisms.

3. All cells come from pre-existing cells.

Modern Additions:

4. All cells contain hereditary information which is passed from cell to cell during cell division.

5. All cells are basically the same in chemical composition.

6. All energy flow (metabolism and biochemistry) of life occurs within cells.

Two Fundamentally Different Types of Cells

A prokaryotic cell

A eukaryotic cell

Comparing Cells

PROKARYOTES• All lack a nucleus• Contain DNA• Contain cytoplasm• All lack organelles• All have a cell membrane• Only bacteria are made of prokaryotic cells

EUKARYOTES• All have a nucleus• All contain organelles• All contain cytoplasm• All have a cell membrane• All contain DNA inside a nucleus

“Us vs. Them” - Eukaryotes and Prokaryotes

CELLS!

CELLS!

PROKARYOTE vs. EUKAROTECommon Features

EUKARYOTES

★ Greek = “true nucleus” ★ Compartmentalized with organelles (membrane-bound

structures) ★ Eukaryotic cells include: plant, animal, fungi, protist

EUKARYOTES

PLANT vs. ANIMAL

Electron Micrograph

EUKARYOTIC ORGANELLESPLANT ANIMAL

★ Cell Wall ★ Centriole★ Chloroplast ★ Cilia or Flagella★ Large central vacuole ★ Many small vacuoles★ Cell/Plasma Membrane ★ Cell/Plasma Membrane★ Cytoplasm/Cytosol ★ Cytoplasm/Cytosol★ Mitochondria ★ Mitochondria★ Ribosomes ★ Ribosomes★ Nucleus ★ Nucleus★ Nucleolus ★ Nucleolus★ Nuclear Envelope/Membrane★ Nuclear Envelope/Membrane★ Rough Endoplasmic Reticulum (E.R.) ★ Rough

Endoplasmic Reticulum★ Smooth E.R. ★ Smooth E.R.★ Lysosomes ★ Lysosomes★ Golgi Body/Apparatus ★ Golgi Body/Apparatus★ Cytoskeleton ★ Cytoskeleton

Animal vs. Plant Cells – Chloroplasts Are a Big Part of the Difference

Two Other Unique Features of Plant Cells

The central vacuole may occupy 90% of a plant cell.

EUKARYOTIC ORGANELLES

Structure Description FunctionNucleus

Nucleolus

Endoplasmic Reticulum

(Smooth & Rough)

Golgi Apparatus

Lysosomes

Mitochondria

Chloroplasts(Plant)


Structure Description FunctionCentrioles(Animal)

Cytoskeleton

Flagella/Cilia(Animal, fungi and

some protists)

Central Vacuole (Plant)

Cell Wall(Plant)

Cytoplasm/Cytosol

Ribosomes


THE NUCLEUS★ Latin = “kernel” or “nut”

★ First described by Robert Brown (1831)

★ Most eukaryotic cells contain one central nucleus

★Fungi have many nuclei

★ Contains Nucleolus (where synthesis of ribosomal RNA takes place)

★ Nucleus protected by Nuclear Envelope/Membrane (which contains nuclear pores)Structure Description Function

Nucleus Usually spherical surrounded by double membrane that contains chromosomes

Control center of cell; directs protein synthesis and cell reproduction.

Nucleolus Site of genes for ribosomal RNA (rRNA) synthesis

Assembles ribosomes


THE NUCLEUS

http://www.cartage.org.lb/en/themes/Sciences/Zoology/AnimalPhysiology/Anatomy/AnimalCellStructure/Nucleus/Nucleus.htm

http://www.frontiers-in-genetics.org/en/pictures/nucleus_1.jpg

The Nucleus

“The Control

Center of the Cell”

Think of the nucleus as the cell’s control center.

Two meters of human DNA fits into a nucleus that’s 0.000005 meters across.

• Regulates all cell activity• Contains chromatin composed of DNA.


THE ENDOPLASMIC RETICULUM★ Endoplasmic = “within the cytoplasm” Reticulum = Latin for “a little net” Usually connected to nuclear envelope

★ ROUGH E.R.: Contain many ribosomes, which appear pebbly or “rough”, and are destined to be exported from the cell; synthesizes, moves and proofreads proteins.

SMOOTH E.R.: Relatively few or no ribosomes; may contain enzymes which can 1) storage and synthesis of lipids and steroids (testes, intestine, and brain) or; 2) carry out detoxification of drugs (liver)

Structure Description Function

Endoplasmic Reticulum(Smooth & Rough)

Network of highly folded phospholipid membranes within the cytoplasm

Forms compartments and vesicles; participates in protein and lipid synthesis; transports synthesized proteins


THE ENDOPLASMIC RETICULUM

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/rougher.htm

http://www.ccs.k12.in.us/chsBS/kons/kons/eukaryotic%20cell/cytoplasm_and_its_associated_str_files/image002.jpg


THE GOLGI BODY/APPARATUS★ Flattened stacks of tubular membranes

★ Smooth, membranous structure located near the middle of the cell

Receives proteins and lipids from the E.R. Modifies and sorts proteins Creates lysosomes

★ Packages proteins into membrane-bound structures, called vesicles, to be sent to appropriate destinations

★ Similar to a “post office”Structure Description Function

Golgi Body/ApparatusFlattened stacks of tubular membranes

Sorts, packages and transports proteins for export from the cell


THE GOLGI BODY/APPARATUS

http://www.bu.edu/histology/i/20303ooa.jpg

http://media-2.web.britannica.com/eb-media/52/116252-004-9615DB80.jpg


THE CENTRIOLES★ Important in animal Cell Division

★ Composed of 9 triplets of microtubules

★ Microtubules = long, hollow cylinders which influence cell shape, move the chromosomes in cell division, and provide structure for flagella and cilia

★ Barrel-shaped organelles found in animals and most protists

★ Plants and fungi lack centrioles

★ Occur in pairs, usually at right angles


CentriolesOccur in pairs and made of microtubules; in animal cells and most protists

Important in cell division, cell shape and structure for flagella and cilia


CENTRIOLES

http://upload.wikimedia.org/wikipedia/commons/4/49/Plagiomnium_affine_laminazellen.jpeg

http://images.protopage.com/view/721389/3ydo50yjpdnqy8ag4flqbd1un.jpg


THE LYSOSOME★ Membrane-bounded digestive vesicles

★ Arise from the Golgi Apparatus

★ Contain degrading enzymes which break down (recycle) old organelles

★ Enzymes also function to eliminate harmful or foreign cells through phagocytosis

Called “suicide sacs” In plants, called peroxisomes


LysosomeVesicles derived from Golgi apparatus that contain digestive enzymes

Digests worn-out organelles and foreign or harmful cells; acts like a “garbage disposal”; plays a role in cell death (“suicide sacs”)


THE LYSOSOME

http://www.stolaf.edu/people/giannini/cell/lys/autophag.jpg

http://www.cartage.org.lb/en/themes/sciences/zoology/AnimalPhysiology/Anatomy/AnimalCellStructure/Lysosomes/lysosome.jpg


Endocytosis = into the cell Exocytosis = exiting the cell

The Lysosome

The Lysosome

This bacterium is about to be eaten by a white blood cell and will spend the last minutes of its existence within a lysosome.


FLAGELLA/CILIA★ Made of microtubules

Aid the cell in locomotion or feeding Motion is similar to that of oars in a rowboat Flagella are longer projections that move with a whip-like

motion Cilia are shorter, numerous projections that look like hairs. Some protists use a pseudopod (“false foot”) to crawl; similar

to squeezing a water balloon at one end forces the balloon to bulge out at the other end.


Flagella/CiliaCellular extensions made up of pairs of microtubules

Aid the cell in locomotion (movement) or feeding


CILIA FLAGELLAhttp://www.ibri.org/RRs/RR051/51cytoskeleton.gif

Cilia = tiny hairs (move like oars in a boat)

Flagella = tails (move with whip-like action)


THE MITOCHONDRION★ Plural = Mitochondria

★ Peanut-shaped with outer membrane and highly folded inner membrane (cristae)

★ Have their own DNA (mitochondrial DNA or mDNA) important for oxidative metabolism (inherited by you mother)

★ Supply ATP (energy) to the cell; “powerhouse” of the cell Similar to a battery, generator or power plant Where cellular respiration occurs

★ Cells have many mitochondria (ex: liver cells have up to 2000!)

★ Each time the cell divides, a mitochondrion divides in twoStructure Description Function

MitochondriaPeanut shaped structure with double membrane (outer membrane and highly folded inner membrane called cristae)

“Powerhouse” of the cell; sites of oxidative metabolism


MITOCHONDRIA

http://academic.brooklyn.cuny.edu/biology/bio4fv/page/mito.gif

The Mitochondrion

* Responsible for Apocytosis = programmed cell death

* 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.


THE CYTOSKELETON★ Interior framework of the cell

★ Network of protein fibers that support the shape of the cell and anchor organelles to fixed locations

★ Stretches the plasma membrane like the poles on a circus tent!

★ Allows cells to rapidly alter shape


CytoskeletonNetwork of protein filaments

Provides internal structural support; helps in cell movement


CYTOSKELETON

http://www.noble.org/press_release/plantbio/blancaflornasa/cytoskeleton.jpg

http://www.ibri.org/RRs/RR051/51cytoskeleton.gif

http://migration.files.wordpress.com/2007/07/cytoskeleton02.jpg

The name is misleading. The cytoskeleton is the skeleton of the cell, but it’s also like the muscular system, able to change the shape of cells in a flash.

The Cytoskeleton

An animal cell cytoskeleton

A white blood cell using the cytoskeleton to “reach out” for a hapless bacterium.

The Cytoskeleton in Action


THE CHLOROPLAST★ Greek: chloro = “green”; plasts = “form “ or “entitiy”

★ Commonly in plant cells

★ Contain pigment called chlorophyll (gives plants their green color)

★ Carry out photosynthesis

★ Typically contain one to several hundred

★ Contain two membranes; closed compartment of stacked membranes called grana which have disk-shaped structures called thylakoids ; surrounding thylakoid is a fluid matrix called stroma

★ A type of plastid which contains it’s own DNAStructure Description Function

ChloroplastFlat, disk-shaped green organelle with two membranes; contain chlorophyll, a photosynthetic pigment

Site of photosynthesis; produces food for the cell

The Chloroplast

Think of the chloroplast as the solar panel of the plant cell.

Only plants have chloroplasts, but animals reap the benefits too.


CHLOROPLAST

http://upload.wikimedia.org/wikipedia/commons/4/49/Plagiomnium_affine_laminazellen.jpeg

http://virtualbiologytutor.co.uk/images/chloroplast.jpg

Cells In a Leaf

A Consequence of Cell Walls – the Great Strength of Woody Plants


CENTRAL VACUOLE★ In Plant cells:

Large sac used to store mainly water and other materials (sugars, ions and pigments)

Helps to increase the surface-to-volume ratio by applying pressure to cell membrane.

In Animal cells: contain many small vacuoles for temporary storage


Central VacuoleIn plant cells, large organelle filled with mainly water, and other materials; takes up most of cell

Storage center for water and other materials; helps maintain volume of cell


CENTRAL VACUOLE


Animal Cell

Plant Cell

Animal Cell

VACUOLES

The Central Vacuole Controls Turgor Pressure

wilts

turgid


CELL WALL★ In Plant and bacterial cells:

In plants = Composed of fibers made out of cellulose In bacteria = composed of peptidoglycan Cell walls in plants are thicker and stronger than those in

bacteria (which are primarily made out of protein polysaccharide)

Made up of a primary and secondary wall Also present in fungi and some protists Provide protection and support


Cell WallIn plant cells, outer layer of cellulose; in bacteria, outer layer of protein; also found in fungi and some protists

Protection and support


CELL WALL

http://www.learner.org/courses/essential/life/images/show2.leaf.jpg


http://library.thinkquest.org/C004535/media/cell_wall.gif


CYTOPLASM / CYTOSOL Clear, gelatinous fluid that fills the interior of the cell

excluding the nucleus Contains sugars, amino acids and proteins that the cell uses

to carry out its everyday activities


Cytoplasm/CytosolClear, gelatinous fluid that fills the inside of the cell

Protection and support


CYTOPLASM / CYTOSOL

http://www.cartoonstock.com/lowres/rjo0896l.jpg


http://www2.puc.edu/Faculty/Gilbert_Muth/art0063.jpg


RIBOSOMES Sites of protein synthesis (where the cell produces proteins

according to the directions of DNA) Consist of two subunits (small and large) composed of rRNA

and protein The individual subunits are synthesized in the nucleolus and

then move through the nuclear pores to the cytoplasm, where they assemble.


RibosomesSmall complex assemblies of proteins and RNA, often bound to endoplasmic reticulum

Sites of protein synthesis


RIBOSOMEShttp://www.ibri.org/RRs/RR051/51cytoskeleton.gif

http://www.estrellamountain.edu/faculty/farabee/biobk/BioBookCELL2.html#Ribosomes (Both images)

Animal Plant

Bacteria

EUKARYOTES

•Video: Bioclips•Click on “Marius Explores The Cell” (10 mins.)

CELL ANALOGIES

FACTORY

Cellular Anatomy

Cell Project: Create an analogy of your own!

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