Most Familiar organisms are made from Eukaryotic Cells e.g. plants animal fungi – including yeasts protists – protozoa (animal-like single celled) e.g. paramecia -algae (plant-like single/multi celled) e.g. algae
OrganelleP/A?Function Nucleus (nuclear pore Nucleolus) Nucleus Controls the cell, contains DNA in the form of chromsomes (chromatin) Nucleolus Manufactures ribosomes, contains a lot of rRNA Nuclear pore Allows transfer of materials between nucleus and cytoplasm (esp. mRNA Mitochondrion Site of aerobic respiration Cristae Electron transfer chain, produces majority of ATP Matrix KREB’s Cycle Rough Endoplasmic Reticulum R.E.R. Transports proteins synthesized on the ribosome around cell in particular to Golgi for packaging for secretion Ribosome Site of protein synthesis, mRNA translation Smooth Endoplasmic reticulum Site of synthesis of some other macromolecules in particular lipids Golgi Body Packaging of macromolecules, especially proteins (enzymes, hormones, neurotransmitters) for excretion from the cell Lysosome Contain digestive enzymes (e.g lysozyme), low pH, Digest macromolecules, involved in autophagy. Centriole Found in pairs, made of microtubules, Organizes spindle fibres on which chromsomes align during cell division. Chloroplast Site of photosynthesis Light reactions –grana (thylakoid) membranes, Dark reaction – stroma Large Vacuole Large storage vesicle, containing cell salts, pigments.
Plasmodesmata are channels found in plant cells which allow direct cytoplasmic connection between adjacent plant cells. Middle Lamella –layer of “glue” between adjacent plant cells which holds them together. Contains pectins. Nucleosome – DNA string wrapped around a histone protein bead. Necessary to allow DNA to be packaged efficiently into the small volume of the nucleus
Helicobacter pylori- Stomach uclers Mycobacterium tuberculosis – Tuberculosis Nesseiria meningitiis – Meningitis Yersinia pestis – Black death (plague) Bacteria 0.5-100 m, Eukaryotes 10- 100 m Streptomyces coelicolor. The bacterium and its relatives produce most of the natural antibiotics in current use, including tetracycline and erythromycin. They also generate compounds that are used to treat cancer and suppress the immune system.
An Electron Micrograph of a bacterium Bacteria are much more simply constructed – no membrane bound organelles
COMMON BACTERIA SHAPES Spherical (coccus) Rod shaped (bacillus) Spiral (spirochaetes, helicobacter)
BASIC BACTERIAL STRUCTURES flagellae cytoplasm pili (fimbriae)
Major difference between prokaryotic cells and eukaryotic cells
PLASMA MEMBRANE Same as all membranes (bilipid layer) Phospholipid composition may differ between bacteria and eukaryotic cells.
The Cytoplasm No compartmentalisation (no internal mebranes ie. No ER) All chemical reactions occur within it. Efficient regulation of biochemistry needed (Jacob Monod). Contains ribosomes (free floating) responsible for protein synthesis – different from eukaryotic ribosomes – antibiotics (chloramphenicol, tetracycline, streptomycin) can specifically target them.
The Bacterial “Chromosome” - Nucleoid A single, circle of DNA. Packaged by folding – to reduce volume. Functions Contains genetic information. Codes for bacterial proteins.
Replication Bacteria reproduce by dividing (asexual) DNA must be replicated DNA simply copied (no MITOSIS - no chromosomes).
Extrachromosomal DNA – Plasmids Structure Circular DNA, smaller than nucleoid. Size ~ 1000 - 200, 000 bp (c.f. 4,000,000 base pairs) 1-700 copies. Function Not normally essential, Gives some advantage e.g. antibiotic resistance. e.g. conjugative plasmids - Allow exchange of DNA between bacteria – antibiotic resistance can jump from one bacterial species to another.
The Cell Wall General Properties Cell wall resists swelling due to osmotic entry of water Prevents osmotic lysis Maintains shape Structure and synthesis unique to prokaryotes.
The chemical structure of peptidoglycan The NAM, NAG and amino acid side chain form PEPTIDOGLYCAN Covalently bonded (strong) to form a repeating polymer. The polymer is further strengthened by covalent cross links (peptide bridges) between amino acids. NAM – N acetyl muramic acid NAG – N acetyl glucosamine
Two basic types of bacterial cell wall structures – GRAM +ve Gram +ve cells peptidoglycan is: heavily cross-linked very thick (peptidoglycan accounting for 50% of weight of cell and 90% of the weight of the cell wall) 20-80 nm thick.
Two basic types of bacterial cell wall structures – GRAM -ve In GRAM –ve (G-) bacteria peptidoglycan much thinner 15-20% of the cell wall intermittently cross-linked.
Gram positive (G+) cells are purple and Gram negative (G-) cells are red. GRAM STAINING
Lysozyme ( tears and saliva) -attacks peptidoglycan. It hydrolyzes the NAM - NAG linkage. Cell Wall Freely permeable to solutes, the openings in the mesh are large and all types of molecules can pass through them. Penicillin inhibits cells wall synthesis. The G+ cell wall is very sensitive to the action of lysozyme and penicillin. Penicillin is antibiotic of choice for infections caused by G+ organisms. e.g. Streptococcus pyrogenes which causes strep throat. Bleu D’avergne
BACTERIAL MOTILITY Flagellum (ae) – used for movement
Fimbriae/ pili –concerned with cell adhesion Special SEX pili – enable transfer of plasmids from one bacteria to another – can on occasion cross species. e.g staphylococcus - MRSA
SUMMARY No true membrane bound nucleus – rather a nucleoid (folded) No membrane bound organelles/ no compartmentalisation Many free floating ribosomes Cell walls made of peptidoglycan (G+/ G-) Mucilaginous capsule can be present Flagellae (movement) Pili./ Fimbrae are other extracellular protrusions (adhesion/ transfer)