Cell Diversity - Biology Notes PDF

Cell diversity Cells internal organisation: Prokaryotes: Baceteria and Archaea Pro = before, Karyon = nucleus Prokaryotes cell lacks a nucleus and most other organelles Eukaroytes: Fungi, protozans and plants and animals Eu = true Karyon = nu...

Cell diversity Cells internal organisation: Prokaryotes: Baceteria and Archaea Pro = before, Karyon = nucleus Prokaryotes cell lacks a nucleus and most other organelles Eukaroytes: Fungi, protozans and plants and animals Eu = true Karyon = nucleus Eukaryotes nucleus+ membrane bound organelles Where did it all start? All life on earth is believed to have originated from a common ancestor. At some point, an evolutionary divergence was observed, leading to the branch of organisms we refer to as Eubacteria (More commonly known as Bacteria), as  well as the Archaea The next divergence point is the point at which eukaryotes acquired mitochondria, with a smaller subset acquiring chloroplasts (Plants). Mitochondria are essentially the same in plants, animals, and fungi, and therefore were presumably acquired before these lines diverged. Due to these similarities, they are all included within the Eukaryota. Although all organisms in the eubacterial and Archaean lineages are prokaryotes, archaea are more similar to eukaryotes than to eubacteria (“true” bacteria) in some respects. Archaean and eukaryotic genomes encode homologous histone proteins, which associate with DNA Eubacteria lack histones RNA and protein components of Archaean ribosomes are more like those in eukaryotes than those in bacteria. Both of these characteristics have provided a picture of how life diverged from the initial common ancestor. Prokaryotes: 2 distinctions: Eubacteria + Archaea Prokaryotes are distinguished by a number of unique properties: - DNA is not contained within a membrane bound pocket, contained in a nucleoid - Cell division achieved by binary fission or budding - Prokaryotic chromosomes are haploid in nature, and usually circular - Cytoplasmic membrane reinforced with hopanoids (not Archaea) Chemistry of prokaryotic cells – Lack of specialised cellular compartments has necessitated the development of specialised membranes required for certain biochemical pathways. Cell walls of prokaryotes are highly diverse, with a variety of cell wall constructions seen in both Eubacteria and Archaea. Despite classified as prokaryotes are classed as unicellular and they are capable of forming discreet organised multicellular structures Bacterial shape: Bacterial classification: Gram staining differentiates between bacteria through the detection of peptidoglycan The main components of a gram stain are crystal violet (Purple) and safranin (Pink counter stain) and an organic solvent (usually alcohol) Other characteristics of Prokaryotes: In addition to their morphology and colony formation characteristics, prokaryotes may also have: Plasmids: Small accessory rings of DNA.  Genes not related to basic life functions (e.g. antibiotic resistance) Transferred from one bacterial cell to another Capsule or a slime layer. Mediate adherence Protect from engulfment (protozoa or phagocytes) Protect from attack by antimicrobial agents Soil bacteria: protect from effects of drying Reserves of carbohydrate for subsequent metabolism. Flagella: This is the most common means of locomotion for prokaryotes, and is achieved via the rotation of the flagella working as a propeller. They are composed of the protein flagellin. Motor proteins are buried within the basal body of the plasma membrane, a drive shaft is attached to the filament by means of a flexible hook Flow of hydrogen ions through a the complex promotes promotive force, allowing the bacteria to swim (chemotaxis). Fimbriae: This is the most common means of locomotion for prokaryotes, and is achieved via the rotation of the flagella working as a propeller. They are composed of the protein flagellin. Motor proteins are buried within the basal body of the plasma membrane, a drive shaft is attached to the filament by means of a flexible hook Flow of hydrogen ions through a the complex promotes promotive force, allowing the bacteria to swim (chemotaxis). Pili: Longer than fimbriae Single/pairs Adhere to another bacterium during DNA transfer This takes the place of more sophisticated sexual reproduction found in eukaryotes  It is a means of bacteria generating genetic diversity via an alternative means to spontaneous mutation. The process allows bacteria to respond to environmental stimuli at a much faster rate than spontaneous mutation would allow for. Heterotrophic: get energy by consuming organic molecules made by other organisms Chemo-heterotrophs – E.coli 1 Organisms which obtain energy from chemical sources that they take from the surrounding environment They are not able to produce their own carbon sources. Photo-heterotrophs – Rhodobacter sphaeroides 2 Generates energy using light but cannot use carbon dioxide as its sole carbon source. Like other heterotrophs, they take carbon from the surrounding environment. Autotrophic: get energy by making their own food in inorganic molecules Lithio-autotrophs – Eg:Thiobacillus denitrificans 1 Derives energy from reduced compounds of mineral origin. Photo-autotrophs – Nostoc pruniforme 2 Nitrogen fixing bacteria, use light energy to fix atmospheric nitrogen under anoxic conditions (Atmospheric nitrogen lacking) ARCHEA: 3 classifications of archaea  Methanogens Produce methane as a metabolic byproduct in anaerobic conditions Halophiles “salt loving” Halophiles are found in environments with high salt concentration such as the great salt lake or soil with a high salt concentration Thermophiles “Heat loving” Thermophiles live in hot environments such as hot springs and hydrothermal vents Eukaryotes Cyto-architecture: Nucleus: Surrounded by double membrane: nuclear envelope Communicates with cytosol via nuclear pores Nuclear pores perforate the envelope Contains main genome  DNA and RNA synthesis Chromatin: DNA and Proteins Nucleolus: Chromatin and ribosomal subunits Nucleoplasm: Semi fluid medium inside nucleus Outer nuclear membrane continuous with membrane of endoplasmic reticulum (ER) Endoplasmic Reticulum: System of interconnected sacs and tubes of membrane Extends across the cell – synthesis of lipids/proteins Rough ER – Ribosomes synthesies proteins – delivered into ER lumen Smooth ER – no ribosomes, its highly developed for preforming functions, such as steroid hormone synthesis in adrenal glandm or sequesters Ca2+ from the cytosol.  Golgi Apparatus: Golgi Apparatus – known as Golgi body, of the endomembrane system contained within the cytoplasm of eukaryotic cells GA – composed of stacked curved saccules comprised of membrane enclosed vesicles Receives proteins and lipids from ER this location of post- translational modification of proteins within the cell GA – organises and packages proteins within the cell for secretion or delivery to other areas within the cell Transport of these proteins via 3 main ways: Exocytotic Vesicles – Vesicles involved in the packaging and delivery of proteins destined for extracellular release. Vesicles bud off the GA, and move immediately to the plasma membrane. They fuse with the membrane and release contents into the  extracellular space Secretory Vesicles – Similar to Exocytotic vesicles, however there are important variations. Proteins are packaged, bud off in vesicles but are stored prior to release. Release is mediated by stimulation from a cell signalling pathway Lysosomal Vesicles – Contains proteins and ribosomes destined for the lysosome, ready for degradation at the lysosome. Lysosomes and Endosomes- Lysosomes Spherical organelles (vesicles) produced by the Golgi apparatus. Single membranes Contain hydrolytic enzymes and are involved in intracellular digestion (food particles, invading objects, worn out cell parts) Endosomes Sort ingested molecules, recycle some back to plasma membrane Peroxisomes – Peroxisomes are enclosed by a single membrane, and contain a number of enzymes responsible for a number of metabolic reactions Peroxisomes contain catalase, and provides a defense against hydrogen peroxide (A marker of oxidative stress) Peroxisomes provide protection against other cellular toxins, like uric acid. They are able to break down fatty acids, an important part of energy production. Fatty acid breakdown in yeasts and plant cells occurs exclusively within the peroxisomes. Within animal cells, fatty acids can be broken down in both peroxisomes and mitochondria. Mitochondria and Chloroplasts Peroxisomes are enclosed by a single membrane, and contain a number of enzymes responsible for a number of metabolic  reactions Peroxisomes contain catalase, and provides a defence against hydrogen peroxide (A marker of oxidative stress) Peroxisomes provide protection against other cellular toxins, like uric acid. They are able to break down fatty acids, an important part of energy production. Fatty acid breakdown in yeasts and plant cells occurs exclusively within the peroxisomes. Within animal cells, fatty acids can be broken down in both peroxisomes and mitochondria. Mitochondria Most eukaryotic cells Folded membrane within an outer membrane Folds of the inner membrane are called cristae This double membrane surrounds fluid-filled matrix The matrix contains enzymes that break down carbohydrates Cristae houses protein complexes that produce ATP (Cellular respiration) Chloroplasts: Most eukaryotic cells Folded membrane within an outer membrane Folds of the inner membrane are called cristae This double membrane surrounds fluid-filled matrix The matrix contains enzymes that break down carbohydrates Cristae houses protein complexes that produce ATP (Cellular respiration) Vacuoles and Vesicles Vacuoles (large) and vesicles (small) are membranous sacs in the cell that store substances. Very large in plants  Storage of nutrients, water, plant pigments, toxins Vesicles bud from one membrane and fuse with another, carrying membrane components and soluble proteins between cell components Plastids Three types of plastids in plant cells: Chloroplasts Chromoplasts: synthesise and store pigments Leucoplasts: store food such as starches, proteins, and lipids Cytoskeleton: Network of filaments and tubules that extends from the nucleus to the plasma membrane. Support system for organelles Contains three types of elements responsible for cell shape, movement within the cell, and movement of the cell: Actin filaments Microtubules Intermediate filaments  Actin filaments Bundles or mesh-like networks Structural role in intestinal microvilli, interact with motor molecules, such as myosin Microtubules: Small hollow cylinders made of tubulin Microtubule assembly controlled by centromere Maintains shape of cell and act as tracks along which organelles can move Intermediate filaments: Ropelike assemblies of fibrous polypeptides Support plasma membrane and nuclear envelope Plant Cell Wall –  Plant cell walls are composed of 3 layers Primary cell wall Generally thin, and are present to accommodate for increasing cellular size during growth phase. Secondary cell wall Production begins once the growth phase has ended. Usually constitutes a hardening/thickening of the primary cell wall, or by deposition of new layers underneath old ones. Middle lamella Pectin rich layer, forming the outermost layer forming the interface between adjacent plant cells Fungal Cell Walls Chitin: a long linear homopolymer of beta-1,4-linked N- acetylglucosamine is a structurally important component of fungal cell walls. Glucan: Glucose based polymers that provide fungi with protection from a number of anti-fungal agents Mannoproteins – Mannose based polymers providing rigidity, and has a role in biofilm production protecting cells from antifungal agents.