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What is Life ?

Overwhelming diversity of the living world

Life has been viewed as an intangible property that defies simple explanation

Described in operational term: Movement, Reproduction, Adaptation, Responsiveness to external stimuli

Despite the rich diversity of living organisms, from the blue whale to the smallest of microorganisms, all obey the same chemical and physical laws that rule the universe.

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Visualization of

PhagocytosisMoving Amoeba

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Life is complex and dynamic

All organisms are primarily composed of organic (carbon-based) molecules that have three dimensional shapes

Their methods for sustaining biological processes are similar

Living processes (growth and development) involve thousands of chemical reactions.

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Visualization of

3D Molecular structure

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Life is organized and self sustaining

Living organisms are hierarchically organized systems (each level is based on the one below)

The molecules that make up living organisms, referred to as Biomolecules

In multicellular organisms levels of organization: tissues, organs and organ systems

At each level of organization the whole is greater than the sum of the parts

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Life is organized and self sustaining

Emergent properties (Hemoglobin)

Continuous acquisition of both energy and matter and removal waste molecules.

These tasks are accomplished by hundreds of biochemical reactions that are catalyzed by enzymes

The sum total of all reactions in a living organism is referred to as Metabolism

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Life is cellular

Cells differ widely in structure and function

Each is surrounded by a membrane that controls the transport of some chemical substances into and out of the cell.

The membrane mediates the response of the cell to components of the extracellular environtment.

Cells arise only from the division of existing cells.

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Life is information-based

Organization requires information

Living organisms can be considered to be information-processing systems

Interacting molecules within cells, between cells and generation of future cells

Genetic information specifies the linear sequence of amino acids in proteins and how and when those proteins are synthesized

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Most living organisms are single cells,others are multicellular,which perform specialized functions and are linked by intricate systems of communication.Whole organisms has been generated by cell divisions from a single cell.Single cell is the vehicle for the hereditary information that defines the species.All cells store their hereditary information in the same linear chemical code (DNA)

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DNA is made from simple subunits nucleotides,each consists of two parts *sugar (deoxyribose) with a phosphate group attached.* base which maybe either adenine (A),guanine (G),cytosine (C),or thymine (T).

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Life adapts and evolves

All life on earth has a common origin, with new forms arising from other forms

DNA mutations can be repaired or have no effect on the functioning of the organism

On rare occasions mutations may contribute to an increased ability of the organism to survive, to adapt to new circumstances and to reproduce

The interplay of environtmental change and genetic variation can lead to favorable traits and different forms of life.

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Form and Function

Life is based on morphological units known as cells (1838)

Two major classifications of cells:

the Eukaryotes( plants,fungi,animals) and Prokaryotes (bacteria)

Eukaryotes keep their DNA in nucleus and prokaryotes have no distinct nucleus to keep their DNA.

Prokaryotes have relatively simple structures and unicellular (they may form colonies)

Viruses, are not classified as living because they lack the metabolic apparatus to reproduced outside their host cells

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The tree of life has three primary branches : Bacteria, Archaea ( procaryotes) and Eucaryotes.

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Form and Function

Prokaryotes are the most numerous and widespread organism on Earth

Highly adaptable metabolism suit them to an enormous variety of habitats

Certain types of bacteria may thrive in or even require conditions that are hostile to eukaryotes (chemical environments, high temperature and lack of oxygen)

Rapid reproductive rate and ability of many bacteria to form spores

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Form and Function

Prokaryotes have relatively simple anatomies (cell membrane, cell wall, capsule, cytoplasm chromosome, RNA enzymes and ribosomes)

Prokaryotes employ a wide variety of metabolic energy sources (autotrophs, chemolithotrophs, photoautotrophs, heterotrophs, obligate aerobes and obligate anaerobes, organotrophs)

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Prokaryotic classification

Taxonomy are inaplicable to prokaryotes because the relatively simple structures provide little indication of their phylogenetic relationships

Based on cell wall properties: 3 major types: Mycoplasma, Gram-positive bacteria and Gram-negative bacteria

Mycoplasmas are the smallest of all living cells and possess ~20% of the DNA of an E.coli

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In general are bigger and more elaborate than prokarryotic cells. Eukaryotes cellular architecture

Structural complexity allows sophisticated regulation of living processes

They have internal membrane-enclosed organelles.

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Structure of cells

Plasma Membrane

Endoplasmic Retikulum

Golgi Apparatus

Lysosome

Mitochondrion

Cytoplasm

Nucleus membrane

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Eukaryotic phylogeny and differentiation

One of the most remarkable characteristics of eukaryotes is their enormous morphologial diversity, on both the cellular and organismal levels (an amoeba, an oak tree and a human being)

Taxonometric schemes based on gross morphology as well as on protein and nucleic acid sequences: three kingdoms (Fungi, Plantae, Animalia, Protista)

Anatomical comparisons among living and fossil organisms indicate that the various kingdoms of multicellular organisms independently evolved from Protista

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Eucaryotes originated as predators, suggested by :

Eucaryotic cells keep their DNA in nucleus,their cells are typically 10 times bigger and 1000 times larger in volume than procaryotes.

cytoskeleton together with many proteins that attach to them for movement,elaborate intracellular compartments for digestion and secretion.

Capacity to engulf other cells (phagocytosis)-- protozoa.

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Metabolism that depends on the oxidation of organic molecules by mitochondria.

Eucaryotic cells evolved from symbiosis.

Aerobic eubacteria were engulfed by anaerobic eubacteria.

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We cannot hope to determine exactly how life aroseThe development of life occupied three stages:

Chemical evolution

The self organization

Biological evolution

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The unique properties of Carbon

Elements (C, H, O, N, P and S) form covalent bonds, comprise ~92% of the dry weight of living things.

Carbon has the unique ability to form a virtually infinite number of compounds as a result of its capacity to make as many as four highly stable covalent bonds combined with its ability to form covalently linked C-C chains of unlimited extent

Over 17 million chemical compounds, nearly 90% are organic (carbon containing) substances.

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Chemical evolution

We are far from certain as to how life arose .

Earths atmosphere contain significant quantities of O2, H2O, N2, CO2 and smaller amounts of CO, CH4, NH3, SO2 and possibly H2.

UV radiation from the sun or lightning discharges caused the molecules to react to form simple organic compounds such as amino acids, nucleic acids bases and sugars.

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The rise of living systems

Living systems have the ability to replicate themselves

The inherent complexity of such a process is such that no manmade device has even approached having this capacity.

There is an infinitesimal probability that a collection of molecules can simply gather at random to form a living entity.

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