cell hierarchy & chemical composition -...
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The Cell
1.The cell – the basic structural and functional unit of living organisms
2.Prokaryotic and Eukaryotic Cells
3.Cellular organization:
� external morphology – cell size, shape and color
� internal structure – cell compartments
4.Chemical composition of living cells
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Prof. Dr. Nikolai Lazarov
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Levels of organization
� Levels of organization:cell � tissue � organ � organ system � organism
� The cell:� the basic structural and
functional unit of all known living organisms
� the smallest unit of life –the building block of body
� Major cell abilities:� reproduction by cell division� the functioning of a cell
depends upon its ability to extract and use chemical energy stored in organic molecules
� response to stimuli such as changes in temperature, pHor levels of nutrients
� cell contents are contained within a cell surface membrane
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Prof. Dr. Nikolai Lazarov
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� Prokaryotic cells(Gr. πρό- (pro-) "before" + καρυόν(karyon) “nut or kernel", referring to the cell nucleus)
� bacteria and archaea
� Eukaryotic cells – "true nucleus"(Gr. eυ- (eu), "good", "true")� multicellular organisms� internal compartmentalization
The cell –evolutionary levels
The biological universe consists of two cell types:
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Prokaryotes and Eukaryotes
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� 200 different cell types that come in an astounding
assortment of shapes and sizes:
� size – 5-200 µm
� small-sized – up to 10 µm
� medium-sized – 10-20 µm
� large-sized – > 20 µm
� shape – related to their function:
� spherical
� spindle-shaped
� squamous, cuboidal ...
� color:� colorless
� pigmented
The cell –external morphology
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� nucleus (Lat., nux, nut)
� cytoplasm (Gr. kytos, cell + plasma, thing formed)
� organelles (“little organs”)� universal and specialized� membranous
(membrane-limited)� nonmembranous
� cytoplasmic inclusions� deposits of carbohydrates,
lipids, and pigments
� cytosol (cytoplasmic matrix)
Basic cellular architecture
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� cytosol (intracellular fluid,cytoplasmic matrix), Lat. mold� ~70 % of the cell volume� final supernatant produced
by differential centrifugation� translucent fluid, pH 6.8� delicate 3D microtrabecular
lattice (cytoskeleton) –intermediate and filaments of actin, microtubules
� substratum for cytoplasmic functions
� water (up to 90%)� macromolecules:
� proteins (20-25%), incl. soluble enzymes
� all machinery to synthesize proteins (rRNA, mRNA, tRNA, enzymes)
� carbohydrates� salts and electrolytes
Cell components
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� essential elements: � macroelements – 98-99%
of the cell mass - C, N, O, H
� microelements – up to 0.000001% - Cu, Zn, Mg
� ultra trace elements –≤0.000001% - Hg, Ag, U, Ra
� water – 70-80%� exogenous – ⅔� endogenous – ⅓
� inorganic molecules:� free – ions� bound with
organic molecules
� organic compounds:� carbohydrates� lipids� proteins� nucleic acids
The cell –chemical composition
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� Water – features: � essential for all life to
exist� 99% of the molecules
inside living cells arewater molecules
� 70-80% of the totalwet-weight of the cell
� functions:� “a matrix of life”� solvent for nutrients� helps the body
�maintain a constant temperature
� eliminate waste products from the cell
� water channels:� aquaporins – Peter Agre
The cell –water composition
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� Carbohydrates:
�monosaccharides
�pentoses
�hexoses
�disaccharides
�polysaccharides
The cell –organic compounds
saccharide (Gr. sakchar, sugar)
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� Lipids (Gr. lipos, fat)
The cell –organic compounds
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� general features: � very large molecules of linked
subunits called amino acids� 60% of cell dry mass
(15% on a wet-weight basis)� determine the shape and
structure of the cell� serve as main instruments of
molecular recognition and catalysis
� classification – ~10000 different types:
� structurally:� simple proteins – albumins,
globulins, histones, collagen� compound proteins
• glycoproteins• lipoproteins• nucleoproteins• metalloproteins
� functional classes:� structural proteins� enzymes � transport proteins� storage proteins� defense proteins� contractile proteins
The cell –organic compounds
� Proteins (Gr. πρώτος (prótos), first, original)
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� amino acids: � 20 different amino acids:
� “essential”� “nonessential”
� major function:� protein building blocks� smallest units of proteins
� non-protein functions:� precursors for the
biosynthesis of some biological molecules
� forming parts of coenzymes� metabolic intermediates� neurotransmitters:
• excitatory• inhibitory
Building blocks of proteins
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� Four levels of structural organization:� Primary structure:
� the amino acid sequence
� Secondary structure:� regularly repeating local structures
stabilized by hydrogen bonds
� Tertiary structure:� formation of protein subunits
by folding
� Quaternary structure:� the assembly of subunits –
the structure formed by several protein molecules (polypeptide chains)
Protein structure
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� Nucleic acids:�DNA�RNA
�ribosomal RNA (rRNA)�transfer RNA (tRNA)�messenger RNA (mRNA)
The cell –organic compounds
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Prof. Dr. Nikolai Lazarov
16Thank you…