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

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

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:

Prof. Dr. Nikolai Lazarov

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Prokaryotes and Eukaryotes

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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� Carbohydrates:

�monosaccharides

�pentoses

�hexoses

�disaccharides

�polysaccharides

The cell –organic compounds

saccharide (Gr. sakchar, sugar)

Prof. Dr. Nikolai Lazarov

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� Lipids (Gr. lipos, fat)

The cell –organic compounds

Prof. Dr. Nikolai Lazarov

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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)

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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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

Prof. Dr. Nikolai Lazarov

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� Nucleic acids:�DNA�RNA

�ribosomal RNA (rRNA)�transfer RNA (tRNA)�messenger RNA (mRNA)

The cell –organic compounds

Prof. Dr. Nikolai Lazarov

16Thank you…