Section 2

Gene structure

Gene structure in eukaryotes

Operon

Transcription

Transcription

Translation

Protein folding

Micro-organism

Fungi Eukaryotic (have membrane-bound nucleus) Obtain food from other organisms Possess cell walls Composed of Molds – multicellular; have hyphae; reproduce by sexual and asexual spores Yeasts – unicellular; reproduce asexually by budding; some produce sexual spores

Bacteria Unicellular and lack nuclei Much smaller than eukaryotes Found everywhere there is sufficient moisture; some found in extreme environments Reproduce asexually cell walls contain peptidoglycan; some lack cell walls; most do not cause disease and some are beneficial

Algae Unicellular or multicellular Photosynthetic Simple reproductive structures Categorized on the basis of pigmentation, storage products, and composition of cell wall

Protozoa Single-celled eukaryotes Similar to animals in nutrient needs and cellular structure Live freely in water; some live in animal hosts Asexual (most) and sexual reproduction Most are capable of locomotion by Pseudopodia – cell extensions that flow in direction of travel Cilia – numerous, short, hairlike protrusions that propel organisms through environment Flagella – extensions of a cell that are fewer, longer, and more whipl ike than cilia

Archaea Unicellular and lack nuclei Much smaller than eukaryotes Found in extreme environments cell walls composed of polymers other than peptidoglycan

Viruses Not independently living cellular organisms Much simpler than cells- basically a small amount of DNA or RNA wrapped in protein and sometimes by a lipid membrane Individuals are called a virus particle or virion Depend on the infected cell’s machinery to multiply and disperse

Bacteriology Morphology, Classification, Staining Methods

PROKARYOTES BACTERIA ARCHAEA

Background Information Prokaryotes Prokaryotes represent two domains, bacteria and archaea. Archaea live in Earth’s extreme environments. Bacteria are the most abundant and diversified organisms on Earth.

Bacteria Have One of Three Cellular Shapes Rods (bacilli) Coccoid-Shaped Spirilla

Other shapes of bacteria Comma shaped Spirochetes Spirilla

Reproduction Prokaryotic cell division is binary fission. Single DNA molecule that first replicates. Attaches each copy to a different part of the cell membrane. Cell begins to pull apart. Following cytokinesis, there are then two cells of identical genetic composition.

Anatomy of a Bacterial Cell

Anatomy of A Bacterial Cell Outer layer – two components: Rigid cell wall Cytoplasmic (Cell/ Plasma) membrane – present beneath cell wall Cytoplasm – cytoplasmic inclusions, ribosomes, mesosomes and nucleus Additional structures – plasmid, slime layer, capsule, flagella, fimbriae (pili), spores

Structure of Bacteria All cells have 3 main components: DNA (‘nucleoid”) genetic instructions surrounding membrane (“cytoplasmic membrane”) limits access to the cell’s interior cytoplasm, between the DNA and the membrane where all metabolic reactions occur especially protein synthesis, which occurs on the ribosomes Bacteria also often have these features: cell wall resists osmotic pressure flagella movement pili attachment capsule protection and biofilms

Naturally Wall-less Genus Mycoplasma

Cellular coverage Cell wall Plasma membrane Capsule

Capsule & Slime layer Capsule : Viscous layer secreted around the cell wall. Polysaccharide / polypeptide in nature Capsule : sharply defined structure, antigenic in nature Protects bacteria from lytic enzymes Inhibits phagocytosis Stained by negative staining using India Ink Can be demonstrated by Quellung reaction (capsule swelling reaction) Slime layer : loose undemarcated secretion

Cell wall protects the bacterium from damage cell wall acts as a coarse filter prevent bursting from osmotic pressure (called lysis)

Cytoplasmic (Plasma) membrane Thin layer 5-10 nm, separates cell wall from cytoplasm Acts as a semipermeable membrane: controls the inflow and outflow of metabolites Composed of lipoproteins with small amounts of carbohydrates

FLAGELLA Some bacteria are motile Locomotory organelles- flagella Taste environment Respond to food/poison Chemotaxis (is the movement of an organism in response to a chemical stimulus)

Flagella Made of Flagellin Used for Classification Monotrichous: 1 flagella Lophotrichous: having two or more flagella at one end; said of bacterial cells. Amphitrichous: tuft at both ends Peritrichous: all around bacteria

Monotrichous Amphitrichous Lophotrichous Peritrichous

Flagella

Pili (fimbriae) hair-like projections of the cell sexual conjugation adhesion to host epithelium Short protein appendages Smaller than flagella Adhere bacteria to surfaces Used in conjugation for Exchange of genetic information

Other Cytoplasmic Components Ribosomes – protein synthesis Mesosomes – Multilaminated structures formed as invaginations of plasma membrane Principal sites of respiratory enzymes Coordinate nuclear & cytoplasmic division during binary fission More prominent in Gram +ve bacteria Intracytoplasmic inclusions – reserve of energy & phosphate for cell metabolism e.g. Metachromatic granules in diphtheria bacilli

Nucleus No nucleolus No nuclear membrane Genome: single, circular double stranded DNA. Haploid Divides by binary fission

Additional Organelles Plasmid Extra nuclear genetic elements consisting of DNA Transmitted to daughter cells during binary fission May be transferred from one bacterium to another Not essential for life of the cell Confer certain properties e.g. drug resistance, toxicity

Spores Highly resistant resting stages formed during adverse environment (depletion of nutrients) Formed inside the parent cell, hence called Endospores Very resistant to heat, radiation and drying and can remain dormant for hundreds of years. Formed by bacteria like Clostridia, bacillus