Life, living matter, cellsSophisticated chemical reactions

synthesis, energy: chemical and solar energy chemical reactions might result in production of heat, motion, light or electricity

Reversible chemical reactions, facilitated by catalysts

Catalysts: enzymes, RNAs extremely good efficiency, at low pressure and temperature

Compartmentalization: restricted domains, membraneslimits and make contact: selective transfer of materialsenrichment of certain components

Membrane-associated catalysts:reduction of dimensions leads to faster reactions (assembly lines)

The energy of the cells is stored in ATP moleculesATP = adenosin triphosphate

Nucleotide triphosphates contain „macroerg” chemical bonds: their synthesis requires much energy, but all this is released or can be used for the synthesis of other compounds, when the bond is hydrolysed

Life, living matter, cells

All living organisms have cells

Cells are produced by cells: no new forms of living matter have been evolved in recent times (billion year)

All living organisms are descendants of the same origin

information carrier molecules are the sameidentical codons, sequence homologies relatedness can be calculatedstructural and functional homologies

On the basis of organization: prokaryotes and eukaryotesprokaryotes are just as highly evolved organisms,same ancestors, different adaptation strategies

Prokaryotic organisms

Highly different niche: 37 és 137 C

Prokaryotes are very versatile and adaptive: they can tolerate high temperatures, very high pressures, extreme pH, high salt concentrations, the presence of toxic compounds.

Scheme of prokaryotic cells

Prokaryotic cell: EM picture

The prokaryotic cell

A single space, limited by plasmamemrane. Contains a cytoplasm and all the molecules carrying genetic information.

Few organelles, no cytoskeleton and cytoplasmic membranes (few exceptions: cyanobacteria). All chemical reaction are carried out in one compartment.

Amazingly large relative surface: high reaction rate. In good conditions extremely high metabolisms and reproduction rate

Prokaryotes are very dependable, adaptable and flexible:short generation time: many generations, large numbershuge variability, exchange of genetic material

The sensitive cell membrane is protected from physical, chemical and biological effects by (layers of) cell wall, capsule, lipids, mucous polymers

The prokaryotic cells

In ideal conditionsone generation takes 30 minutes. One single cells gives rise to 1000 in 5 hours, a mass of 250 g in a day.In 48 hours severalbillion tons would be produced!

The oxigen-rich atmosphere was created by photo-synthetic bacteria eons ago.

The eukaryotic (animal) cellCells of multicellular organismsDifferent tissues have different cell types with many forms and functions.Their size is orders of magnitude (1000x) larger than that of prokaryotic cells.

The large inner space is divided into separate domains, with characteristic pH, redox potential, chemical and physical parameters.

Cytoplasmic membranes limit inner spaces: compartmentalizationOrganized communication and exchange of material between the separated compartments

Cytoskeleton: architectural and traffic functions, cell motility. Continuous reorganization.

Storage and transcription of genetic material in the nuclei

Transport, modification and sorting: vesicular transport, signal sequences (monomeric) G proteins

Endosymbiosis resulted in development of organelles

The eukaryotic (animal) cell

The nucleusCytoplasm of active cells occupies much larger space than that of resting cells. The nucleus of a naiv lymphocyte (arrow) occupies most of the cell.

The nucleusThe nucleus of animal cells is surrounded by a special membrane. (Most of

the) genetic material is found in the nucleus.

During the cell divisions DNA of the nucleus is organized in chromosomes. Transcription of information (from DNA to RNA) also takes place in the nucleus.

Within the nucleus nucleoli can be observed, they are responsible for the organization of certain organelles (eg. ribosomes, lysosomes)

Pores of the nuclear membranes control the traffic of macromolecules into and from the nucleus. The nuclear membrane is physically linked with and forms an integrated system with the membranes of the endoplasmic reticulum

Compartments of the animal cell

DNA of dividing cells is organized into chromosomes

ChromosomesGenes of individual chromosomes are also separated in resting nuclei, but form more compact structure before cell division.The chromosomes can be „painted” with special probes (fluorescent DNA sequences) to help identification of them.

„Painting” of chromosomes helps detection of genetic abnormalities (eg. loss of one chromosome 17 in cells of this patient)

Centrosomes and centriolesThe centrosome is located in the cytoplasm attached to the outside of the nucleus. It is duplicated during S phase. Just before cell division the two centrosomes move apart until they are on opposite sides of the nucleus. As mitosis proceeds, microtubules grow out from each centrosome toward the metaphase plate. These clusters of microtubules are called spindle fibers.

Each centrosome contains a pair of centrioles. Found only in animal cells, these paired organelles are typically located together near the nucleus inthe centrosome.

Pores of the nuclear membrane

The pores allow free diffusion of only small molecules. Traffic of proteins and nucleic acids is strictly regulated by the proteins of the pore complex (see signal sequences, and nuclear translocation).

Endoplasmic reticulum

The ER, which is linked to the nuclear membrane, is a sophisticated system of membrane limited tubes and reaction vessels. ER is the place where proteins and lipids are synthesized.

The lumen and inner surface of the ER is very rich in enzymes (see protein transport, protein modification and maturation).

There is an intensive exchange of materials between the ER and other compartments of the cell. Tubes and vesicles of the ER carry targeted molecules to other destinations (see vesicular transport, and sorting).

ER with attached ribosomes is rough ER, without them it is called smooth ER

The „rough” ER (RER)

RER fluoresces in yellow on the photo (top): its close association with the nucleus is evident

On this electron microscopic (EM) picture ribosomes are small, dark spots associated withe membranes of the ER. The lumen of the ER – due to the high level of enzymes – looks darker (more electron dense), than the rest of the cytoplasm.

Membrane bound ribosomes of the ERAbove the nucleus the ER is very rich in ribosomes (polysomes).

On the sides one can see the tubes and vesicles of the smooth ER.

Golgi

The ER and the Golgi apparate have fairly similar structures. The function of the Golgi is modification and sorting of proteins and lipids. Vesicles generated by this organell deliver proteins and lipids into other locations within the cell.There is an intensive exchange of material between Golgi and other compartments. Golgi is responsible for the identification and separation of defective proteins and sending them to lysosomes for recycling.

The Golgi apparat (green fluorescence) around the nuclei (blue)

Vesicular transport between the ER and Golgi

Important components of the ER are transported to the Golgi along with the freshly synthesized proteins and lipids. These components get back to the ER with the return pathway.

Mitochondria

There are a large number of mitochondria in the cells. Mitochondria produce energy for the cell. They are surrounded by an outer and an inner membrane. The inner membrane has the characteristics of a prokaryotic membrane. Generally, the more energy a cell needs, the more mitochondria it contains.

Mitochondria

The origin of mitochondria (and chloroplasts)

plants

animals

Ribosomes

Ribosomes are complexes of proteins and RNA molecules. Ribosomes carry out the synthesis of proteins. Soluble proteins are synthesized by cytoplasmic ribosomes, while membrane proteins and proteins produced for export are made by ribosomes of the endoplasmic reticulum (RER).

Peroxisome

Peroxisomes are small, membrane vesicles, full with enzymes which are able to degrade peroxides and free radicals. Frequently, enzymes of the peroxisomes are found in crystalline form. The number of peroxisomes are very different in different cell types, in different metabolic states.

Proteasome and lysosomesProteasomes are enzyme complexes degrading proteins. Lysosomes are acidic vesicles, containing digestive enzymes (which cleave proteins, nucleic acids, lipids and polysaccharides). Proteins are degraded for several reasons:

misfolded (abnormal) proteins are destroyed some proteins are made only for short periods of timeenzymes, regulatory proteins are degraded, when not neededfragments of proteins are produced for „presentation” to immune

cellsproteins are degraded, when cells are starving for amino acids

There are „labels”, which identify protein molecules to be degraded.

lysosome

Cytoskeleton

tubulin

actin

Cytoskeletal structures (microtubules and fibers) provide support for the cell,They participate in vesicular transport, cell movement and signal transduction, in cell division (distributing the chromosomes in the daughter cells).

actin

Organelle Structure/Function I• Cell Membrane (Plasmamembrane) The cell membrane keeps the

cell together by containing the organelles within it. Cell membranes are selectively-permeable, allowing materials to move both into and outside of the cell.

• CentrosomesThe centrosomes contain the centrioles, which are responsible for cell-division.

• Cytoplasm Cytoplasm is a jelly-like substance that is sometimes described as "the cell-matrix". It holds the organelles in place within the cell.

• Goli Apparatus The goli apparatus of a cell is usually connected to an endoplasmic reticulum (ER) because it stores and then transports the proteins produced in the ER.

• Lysosomes Lysosomes are tiny sacs filled with enzymes that enable the cell to utilize its nutrients. Lysosomes can also destroy the parts of the cell (autophagia), there are some circumstances (diseases/conditions) in which lysosomes begin to 'break-down' living cells.

Organelle Structure/Function II• Microvilli "Microvilli" is the pural form; "Microvillus" is the singular

form. Microvilli are finger-like projections on the outer-surface of the cell. Not all cells have microvilli. Their function is to increase the surface area of the cell, which is the area through which diffusion of materials both into, and out of, the cell is possible.

• Mitochondria "Mitochondria" is a plural term; which is appropriate as these are not found alone. The quantity of mitochondria within cells varies with the type of cell. These are the energy producers within the cell. They generate energy in the form of Adenosine Tri-Phosphate (ATP). Generally, the more energy a cell needs, the more mitochondria it contains.

• Nuclear Membrane The nuclear membrane separates the nucleus and the nucleolus from the rest of the contents of the cell.

• Nuclear Pore Nuclear pores permit substances (such as nutrients, waste) to pass both into, and out of, the nucleus. They also control the entrance and exit of macromolecules and cellular information.

Organelle Structure/Function III• NucleolusThe nucleolus is responsible for the cell organelles (e.g.

lysosomes, ribosomes, etc.).• Nucleus The nucleus is the "Control Center" of the cell, which

contains DNA (genetic information) in the form of genes, and also information for the formation of proteins. Information is carried on chromosomes, which are a compact, organized form of DNA.

• Ribosomes Ribosomes interpret cellular information from the nucleus and so synthesize appropriate proteins, as required.

• Rough Endoplasmic Reticulum (RER) "Rough" indicates that there are ribosomes attached to the surfaces of the endoplasmic reticulum. The endoplasmic reticulum is where proteins and lipids are produced (and modified), and is also responsible for the transport of these materials within the cell.

• Smooth Endoplasmic Reticulum (SER) "Smooth" indicates that there are no ribosomes attached to the surfaces of the endoplasmic reticulum.