Cell Biology Significance and History

• Organisms consist of roughly 37 trillion cells of around 200 distinct types.
• As physicians need to grasp the anatomy and physiology from which chemistry, biochemistry, biophysics, genetics, and molecular biology stem.

Cells as the Basic Unit of Life

• Living organisms are single cells or comprised of cells.
• Striated muscle and giant algae are atypical occurrences as cells.

History of Cell Biology

• 1595: First light microscope was invented by ((Jansen)).
• 1655: Hooke discovered 'cells' in cork.
• 1674: Leuwenhoek observed protista (animalcules).
• 1833: Brown identified the cell's nucleus from the orchid.
• 1839: Schleiden & Schwann proposed the cell theory where all organisms comprise of cells.
• 1857: Pasteur discovered lactobacillus, stating bacteria are also cells.
• 1858: Rudolf Virchow stated all cells develop from pre-existing cells through cell division (omnis cellula e cellula).
• 1859: Darwin introduced the theory of evolution (The origin of species).
• 1866: Mendel became known as the Father of Genetics
• 1874: Flemming described chromosome behaviour during mitosis.
• 1882: Koch discovered mycobacterium tuberculosis, establishing the bacterias pathogenic role.
• 1894: Altmann first described mitochondria.
• 1898: Golgi described the Golgi apparatus.
• 1951: the HeLa cell line was developed
• Cell culturing, biophysical, and molecular biology tools are used for observation and manipulation.
• 2010: Creation of a bacterial cell controlled by a chemically synthesized genome was achieved.

Evolution and Basic Properties of the Cell

• In most general terms, life involves a system of enzyme catalyzed anabolic and catabolic processes with the ability of self-reproduction.
• RNA molecules, functioning as ribozymes (RNA polymerase, splicing, polypeptide synthesis, reverse transcriptase), suggest the RNA world preceded the protein world.
• By coupling the systems of RNA and protein synthesis via the aminoacyl-tRNA synthetases – the universal genetic code evolved.

Modern Cell Theory

• All living entities consist of cells, the fundamental structural and functional units.
• Cells arise from pre-existing cells by division, not through spontaneous generation.
• Cells contain hereditary information passed on during cell division.
• Cells share similar chemical compositions.
• Cells sustain their organized structure through energy investment.
• Catabolic and anabolic processes occur within cells, balancing energy production and consumption.

Origins and Main Features of Life

• Info is coded in DNA (genotype)
• The flow of information occurs: DNA → RNA → protein
• There is a universal genetic code
• Ribosomes are present
• The phenotype is primarily determined by proteins.

Prokaryotes vs. Eukaryotes

• Prokaryotes (arche- and eubacteria):
  • Contain a nucleoid.
  • Has circular DNA (0.75-5 Mbp).
  • Usually have no introns.
  • Possess one membrane-attached chromosome.
  • Has no inner compartmentalization.
  • Has no cytoskeleton.
  • Does not undergo endocytosis or exocytosis.
  • Undergo metabolism: aerob/anaerob
  • Is usually unicellular
• Eukaryotes:
  • Unicellular: protists, yeast
  • Multicellular: plants, animals
  • Possess a nucleus (with RNA and protein synthesis separated).
  • Contain a nucleolus and histons.
  • Have linear DNA (15 Mbp).
  • Have introns in genes.
  • Have several nucleoskeleton-anchored chromosomes
  • Contains mitochondrium, chloroplasts, ER, Golgi, lysosomes, peroxisomes
  • Contains µtubules, µfilaments, intermedier filaments
  • Can undergo endocytosis and exocytosis
  • Is Usually aerobic
  • Is usually multicellular, and undergo differentiation

Cell Biological Differences Chart: Prokaryotes vs. Eukaryotes

Bacteria-like Organelles in Eukaryotes

• The Endosymbiotic Theory postulates how bacteria-like organelles evolved in eukaryotes.
• Mitochondria likely descended from close relatives of typhus-causing bacteria.
• During evolution, a eukaryotic organism equipped with cytoskeleton and internal membrane systems, engulfed/phagocytosed a prokaryotic organism, leading to a mutually beneficial co-existence.
• Mitochondria arose when an aerobic prokaryote performing oxidative phosphorylation was internalized.
• Chloroplasts derive from prokaryotes performing photosynthesis, origin of peroxysomes is probably similar.
• The alternative definition suggests an organism, possibly an archaea, with cytoskeleton and membrane elements engulfed a prokaryotic organism for mutual benefit.

Evolution of Life Forms

• Earth is 4.5 billion years old.
• Life arose on Earth 3.5-4 billion years ago.
• Pro/eukaryotes emerged 3 billion years ago.
• Plants, animals, and yeasts appeared 1.5 billion years ago.
• Mutations, selection, and endosymbiosis drive evolution.
• Evolution occurs in leaps.

Main Features of Life's Evolution

• Prebiological evolution led to "organic soup," with RNA leading to DNA.
• Catalyzed chemical reactions, trigger, cascade, feedback regulation and linked reactions are important.
• Mutability and selection occur
• Trait propagation involves self-reproductive capacity.
• E. coli divides every 20-40 minutes.
• Mutations are buffered by other proteins
• Compartmentalization is present
• Changes occur in leaps: phagocytic capacity, splicing, sex
• Metabolism evolved from anaerobic to aerobic, with use of ATP.

Cell Size

• Cells need a large surface area-to-volume ratio, which limits its size.

Cell functions:

• self-maintenance, housekeeping
• motility
• growth, proliferation
• cell-cell communication
• differentiation, morphogenesis
• all determined by gene expression

Genome Size

• Mycoplasma gene count is ~ 300.
• E. coli gene count is ~ 4000.
• Yeast gene count is ~ 6000.
• C. elegans gene count is ~ 20000.
• Humans have ≥ 20000 genes.
• Mycoplasma genome size is ~5 million bp.
• E. Coli genome size is ~5 million bp
• Yeast genome size is ~12 million bp.
• C. elegans genome size is 100 million bp.
• Human genome size is ~3000 million bp.

Gene Expression

• In prokaryotes, transcription and translation occur simultaneously.
• In eukaryotes, transcription occurs in the nucleus, and translation in the cytosol.
• Alternative splicing increases protein diversity which enables having more proteins than genes.

Eukaryotic Gene Expression Regulation

• humans have 30x more DNA and about the same number of genes as in C. elegans
• Expression is regulated in eukaryotes by, protein factors, and RNAs
• IncRNAs (long non-coding RNA).
• MiRNAs (micro RNA) and circular RNAs.

Keywords

• arche-, eubacteria
• prokaryotes, eukaryotes
• Escherichia coli
• Caenorabditis elegans
• protist (protozoa)
• yeast
• cell culture
• Phagocytosis
• endosymbiosis (in evolution)
• exon, intron, splicing
• transcription, translation
• ribosomes
• genotype
• phenotype
• metabolism
• anabolic, catabolic
• heterotrophic
• autotrophic
• anaerobic, aerobic
• photosynthesis
• chemosynthesis
• glycolysis
• oxidative phosphorylation
• protist (protozoa)

Revision

• Plants have mitochondria. *
• Bacteria have ribosomes.
• Mitochondria and Chloroplasts had originated by endosymbiosis?
• E. coli codes for roughly 4000 genes.
• Exons, introns, alternative splicing
• A solid grasp of the size range, using the order of magnitude, concerning various organic entities is expected.
• The approximate volume, span, tempo, alongside density spectrum of various biologically relevant items and processes needs addressing
• Typical plant cell 10-100 μm
• Trypanosoma (protozoan) 25 µm long
• Chlamydomonas (green alga) 5-6 μm
• Human red blood cell 7-8 µm diameter
• Escherichia coli (bacterium) 1-5 µm long
• poliovirus 30 nm
• HIV 100 nm
• DNA 2mm
• T4 bacteriophage 225 nm long
• Tobacco mosaic virus 300 nm long
• Cell membrane: 4-10 nanometers.
• Average protein: 3-6 nanometers.
• Water molecule: 0.3 nanometers

Test your knowledge of cell biology's importance, historical milestones, and key scientists. Explore cell theory, the significance of HeLa cells, and the relationship between cell biology, genetics, and molecular biology. Assess your understanding of cellular components and the Miller experiment.