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PROKARYOTES ARCHAEA Cells that lack peptidoglycan, tend to live in harsh environments. Extremophiles: a)Methanogens: produce methane as a result of respiration.

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Presentation on theme: "PROKARYOTES ARCHAEA Cells that lack peptidoglycan, tend to live in harsh environments. Extremophiles: a)Methanogens: produce methane as a result of respiration."— Presentation transcript:

1 PROKARYOTES ARCHAEA Cells that lack peptidoglycan, tend to live in harsh environments. Extremophiles: a)Methanogens: produce methane as a result of respiration b)Halophiles: live in areas of extreme salinity c)Thermophiles: live in extremely hot water d)Others can survive in extremes of pH

2 Bacterial Cell Structure Structure Cell wall Cytoplasmic membrane Chromosome Relative functions Protect cells against osmotic shock (most important) and physical damage Regulation of substance transport into and out of cells. Contain genome.

3 Structure Plasmid Ribosome Flagella Relative functions Contain supplemental genetic information such as resistance to antibiotics, production of toxins and tolerance to toxic environment. Take part in protein synthesis. Movement of cells.

4 Structures Inclusion body Pili Endospore Relative functions Mineral storage of cells. Attachment to host, bacterial exchange of genetic material. Tough, heat resistance structure that help bacteria survive in adverse conditions.

5 Cell Wall The cell wall of bacteria protects the cell from osmostic shock and physical damage. In addition, it also confers rigiditiy and shape of bacterial cells. Gram Negative: consist of a thin layer of peptidoglycan surrounded by an outer membrane composed of lipids, lipoproteins, and a large molecule known as lipopolysaccharide (LPS). LPS can play a protective role and can also act as an endotoxin, causing some of the symptoms characteristic of gram-negative bacterial infections; there are no teichoic acids in gram-negative cell walls. Gram Positive: consist of a thick layer of peptidoglycan and large amounts of teichoic acids

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7 Plasma Membrane Cytoplasmic membrane The cytoplasmic membrane encloses the cytoplasm. It regulates the specific transport of substance between the cell and the environment. The cytoplasmic membrane contains 2 main components: lipid and protein. The lipid component of the bacterial cell is phospholipid bilayer. Thickness: 6-8nm. Unit: amphipathic phospholipid, consisting of 1 phosphate group (hydrophilic ) and unbranched fatty acid chains (hydrophobic). Distribution of 2 portions: hydrophilic heads are exposed to the external environment or the cytoplasm. The fatty acid chains point inward, facing each other due to hydrophobic effects (staying away from water).

8 Plasma Membrane Membrane proteins are located in various positions within the membrane, through specific interactions with phospholipid molecules. These proteins consist of 3 main groups: integral proteins, outer-surface proteins and inner- surface proteins. They play distinctive roles in cellular activities. Integral proteins: firmly embedded in the membrane, transport substance across the cytoplasmic membrane in 3 main mechanisms known as uniport, symport and antiport. Outer-surface proteins: usually in Gram-negative bacteria, interact with periplasmic proteins in the transport of large molecules into the cells. Inner-surface proteins: cooperate with other proteins in enery yeilding reactions and also other important cellular functions.

9 How Do Bacteria Store Genetic Information? Genetic information in bacteria is stored in the sequence of DNA in two forms, that is bacterial chromosome and plasmid.

10 How Do Bacteria Attach To Surfaces? Glycocalyx: Structure: Polysaccharide layers; can be thick and stable like capsule or loosely attached to cell wall like slime layer. Function: Assist cells in adhesion to solid surface, and also protect pathogenic bacteria from the attack of the host's immune system. Encapsulated streptococci 

11 How Do Bacteria Attach To Surfaces? Pili: Structure: Short, thin, straight, hairlike projections form surface of some bacteria. Composed of protein pilin, carbohydrate and phosphate. Pili are usually few. Function: Take part in adhesion of pathogen to specific host tissues. Sex pili are involved in genetic material exchange between mating bacterial cells.

12 How Do Bacteria Attach To Surfaces? Fimbriae: Structure: Similar to pili, but shorter and more abundant on the cell surface. Function: Adhesion of cells to surface and formation of pellicles (biofilms) containing thin sheets of cells on a liquid surface.

13 Movement of Bacteria Motility of most bacteria is away from or toward a stimulus. Chemotaxis – chemical stimuli Phototaxis – light stimuli Magnetotaxis – movement along the Earth’s magnetic field. Occurs in bacteria that contain magnetosomes including iron.

14 Structure of flagella Long filamentous appendages containing a filament, hook and basal body. Filament: consists of protein flagellin. Hook: single type of protein, connects filament to the basal body. Basal body: contains a rod and several rings in gram-negative bacteria. ( Gram-positive bacteria only have the inner pair of rings). This contributes to rotation of flagella, using energy from the activity of proton pumps.

15 Most bacteria can locomote to different parts of their environment, which helps them to find new resources to survive. This process is due to flagellum (plural, flagella) pushing or pulling the cell through a liquid medium. Types of Flagella distribution Monotrichous flagella: one flagellum, if it originates from one end of the cell, it is called polar flagellum. Rapid swimming caused by the rotation of flagella. Peritrichous flagella: flagella surround the cell. Bundled peritrichous flagella give rise to slower forward motion than polar flagella. Amphitrichous flagella: groups of flagellum at each end of the cell. Lophotrichous flagella: two or more at one end.

16 The SLEEPING Bacteria An endospore, a heat-resistant and non-growing structure, can retain its viability over long periods of time under adverse environmental conditions. When the environment becomes more favourable, the endospore then germinates to a vegetative cell.

17 The SLEEPING Bacteria Endospore structure Exosporium: Outer-most layer consisting of protein. Spore coat: Several layers of spore-specific proteins. Cortex: Loosely cross-linked peptidoglycan. Core: Core wall, cytoplasmic membrane, cytoplasm, nucleoid, ribosomes and other cellular compartments. Additionally. dipicolinic acid-calcium complex maintains dehydrated conditions inside the spore and helps to stablise DNA against heat denaturation.

18 Genetic Material Prokaryotic – Genetic material not enclosed within a membrane, generally a singular circular chromosome Eukaryotic – Genetic material (DNA) found in the nucleus as multiple chromosomes Anatomy of a Cell The differences and similarities of prokaryotic and eukaryotic cells.

19 DNA Prokaryotic – DNA is not associated with histones Eukaryotic – DNA is associated with chromosomal proteins called histones and non- histones. Histones help coil and shorten chromosomes

20 Organelles Prokaryotic – Lack membrane enclosed organelles Eukaryotic – Most organelles are membrane enclosed Cell Walls Prokaryotic – Contain complex polysaccharide peptidoglycan Eukaryotic – Chemically simple (if present)

21 Cell Division Prokaryotic – Generally divide by binary fission Eukaryotic – Generally divide by mitosis (Sexual reproduction involves meiosis) Cell Size Prokaryotic – 0.2 to 2.0 µm diameter Eukaryotic – 10 to 100 µm diameter

22 Flagellum Prokaryotic – Consist of two protein building blocks Eukaryotic – Are complex consisting of multiple microtubiles Plasma Membrane Prokaryotic – No carbohydrates, few sterols Eukaryotic – Includes carbohydrates and sterols as receptors


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