02/16/09 What must all cells do to LIVE? What is a Prokaryotic Cell? What are the different kinds of Prokaryotic cells? What is a Cell? Where do Prokaryotic cells live? How are the life functions of Prokaryotic Cells different from Eukaryotic Cells and each other? How are the structures of Prokaryotic Cells different from Eukaryotic Cells and each other? 1 What do ALL need to to carry out life processes? 2 I. General Characteristics of Prokaryotic Cells A. Bacterial Cells 1. 2. Size Shapes and arrangements B. Archaeal Cells 1. 2. Size Shapes and arrangements II. Cell Structures A. Plasma Membrane 1. Bacterial and Eukaryal (what?!) Plasma Membrane Structure 2. Archaeal Plasma Membrane Structure 3. Functions of the Plasma Membrane B. Cell Wall 1. Bacterial Cell Walls 2. Archaeal Cell Walls C. Structures External to the Cell Wall 1. Glycocalyx 2. Movement Appendages 3. Attachment Appendages 4. Cell Surface Molecules 5. Prokaryotic only! DNA Exchange Appendages D. Structures Internal to the Plasma Membrane 1. Cytoplasm 2. Genetic Material- DNA 3. Ribosomes 4. Inclusions 5. Endospores 3 Prokaryotic Cells Bacteria Archaea 4 I. Three Primary Types of Cells Bacteria1 Archaea2 Gram Positive, Spirochaetes, Purple bacteria (Proteobacteria), Cyanobacteria, Flavobacteria/Bacteroides, Green Sulfur Bacteria, Green Nonsulfur Bacteria, Thermatogales 3-5 groups tentatively identified, but include the following: Methane-producers, Extreme Halophiles, Thermoacidophiles Eukarya Plants, Animals, Fungi (molds and yeast), and Protists (algae, protozoans, slime molds, etc.) http://en.wikipedia.org/wiki/Bacteria http://en.wikipedia.org/wiki/Archaea 5 I. General Characteristics of Prokaryotic Cells A. Bacterial Cells 1. Size: Most bacteria range from 0.2 micrometer to 3.0 micrometers in diameter and 1-20 micrometers in length 2. Shapes and Arrangement a. Cocci http://student.ccbcmd.edu/courses/bio141/lecguide/ unit1/shape/u1coccus.html -Cocci: More resistant to drying than rods. Streptococcus pneumoniae (diplococcus) 6 b. Bacilli The following structures discussed in the lecture guide are not listed on this diagram: glycocalyx slime layer, axial filaments, plasmids, inclusions, endospore Single bacilli are common. http://www.cellsalive.com/cells/bactcell.htm http://student.ccbcmd.edu/courses/bio141/lecguide/unit1/shape/rod.html Single rods -Rods: Increased surface area, so can more easily take in dilute nutrients from the environment. 7 c. Curved 1) Spirochetes: Both syphilis and Lyme disease are caused by these bacteria, and other species are important symbionts in the stomachs of cows and other ruminants. They are very thin, flexible, spiral-shaped bacteria that move by means of structures called axial filaments. Most spirochetes are free living (in muds and sediments), or live in associations with animals (e.g. in the oral cavity or GI tract). A few are pathogens of animals (e.g. leptospirosis in dogs, Syphilis in humans and Lyme Disease in dogs and humans). 2) Spirilla have a helical or spiral shape. Unlike spirochetes, they have a rigid cell wall and are motile by means of ordinary polar flagella. Two pathogens of humans are found among the spirilla. Campylobacter jejuni is an important cause of bacterial diarrhea, especially in children. The bacterium is transmitted via contaminated food, usually undercooked poultry or shellfish, or untreated drinking water. Helicobacter pylori is able to colonize the gastric mucosal cells of humans, i.e., the lining of the stomach, and it has been fairly well established as the cause of peptic ulcers. -Spiral: Corkscrew motion & therefore less resistant to movement. 3) Vibrio: The name Vibrio derives from the Latin because these curved rods possess a single polar flagellum and appear "to vibrate". They are often implicated in foodborne diseases. V. cholerae. Gastrointestinal symptoms and the presense of a rice water stool are presumptive for cholera. Direct examination of the feces may indicate vibrios. V. vulnificus. Persons who are immunocompromised, especially those with chronic liver disease, are at risk for V. vulnificus when they eat raw seafood, particularly oysters. A recent study showed that people with these pre-existing medical conditions were 80 times more likely to develop V. vulnificus bloodstream infections than were healthy people. The bacterium is frequently isolated from oysters and other shellfish in warm coastal waters during the summer months. Since it is naturally found in warm marine waters, people with open wounds can be exposed to V. vulnificus through direct contact with seawater. There is no evidence for person-to-person transmission of V. vulnificus. There are exceptions to the usual bacterial shapes : Some examples are Trichome (also referred to as palliside or picket-fences), sheathed, stalked, filamentous, square, star-shaped, spindleshaped, lobed, and pleomorphic (def). http://student.ccbcmd.edu/courses/bio141/lecguide/unit1/shape/shape.html 8 B. Archaeal Cells Archaea include some truly weird microbes that thrive in extremely salty water, as well as microbes that live in temperatures of hundreds of degrees. Even more recently, scientists have begun finding archael cells in an increasing array of habitats, such as the ocean surface, deep ocean muds, salt marshes, the guts of animals, and even in oil reserves deep below the surface of the Earth. Archaea have gone from obscurity to being nearly ubiquitous in only 25 years! http://www.ucmp.berkeley.edu/archaea/archaeasy.html 1. Size: Less than 1 micron-15 microns. 2. Variety of shapes: coccus (regular spheres, lobed, lumpy), bacillus, spiral, or other (triangular, square) Basic Archaeal Shapes : At far left, Methanococcus janaschii, a coccus form with numerous flagella attached to one side. At left center, Methanosarcina barkeri, a lobed coccus form lacking flagella. At right center, Methanothermus fervidus, a short bacillus form without flagella. At far right, Methanobacterium thermoautotrophicum, an elongate bacillus form. http://www.ucmp.berkeley.edu/archaea/archaeamm.html -Square shapes help cope with high salinity environments. 9 II. Cell Structures Structure Plasma Membrane Cell Wall Glycocalyx Movement Appendages Attachment Appendages Cell Surface Molecules DNA Exchange Appendages Genetic Material-DNA Ribosomes Inclusions Endospores Cytoskeleton Chloroplasts Mitochondria ER & Golgi Body Lysosomes & Peroxisomes Vesicles & Vacuoles Centrioles Bacteria Arachaea Eukaryote 10 A. Plasma Membrane 1. Bacterial and Eukaryal Plasma Membrane Structure Inverted phospholipid bilayer containing proteins Phospholipid 11 2. Archaeal Plasma Membrane Structure Archaeal cell membranes are chemically different from all other living things. Notice branching Archaea Side chains Bacterial, Eukaryal No branching a. Glycerol component (found with the phosphate in the ‘head’) is a ‘mirror image’ (stereoisomer) of bacterial and eukaryal cell membrane glycerol. b. Linkage (type of bond) between the glycerol and side chains (‘tails’) is different. This results in different properties. c. Side chains are not fatty acids in Archaea. Isoprenes are common. Isoprenes are a large and diverse group of lipids (they are not fatty acids) http://www.cem.msu.edu/~reusch/VirtualText/lipids.htm 12 3. Functions of the plasma membrane: a. Regulation of the movement of materials into and out of the cell; the plasma membrane is SEMIPERMEABLE (selectively permeable) 1) How do molecules move across the plasma membrane? a) Diffusion Simple (passive) o Special example: osmosis Facilitated b) Active transport c) Group translocation d) Cytosis b. Other (see p. ) 13 a) Diffusion: (def.) Concentration: Gradient: 14 Simple (Passive) Diffusion -No energy is used. -Transmembrane protein channels may be required. Osmosis: Movement of water across a membrane by simple diffusion in response to the concentration of molecules that cannot cross the membrane (impermeable). -Water is a solvent (dissolver) for many molecules (solutes; for example salts and sugars). 15 Note: The solution refers to the surrounding environmental solution outside of the cell. 1) Isotonic solution: If solute concentration outside of the cell is the same as that inside, the solution is isotonic. 2) Hypotonic solution: a solution with a lower solute concentration than that inside the cell is hypotonic. 3) Hypertonic solution: a solution with a higher solute concentration than that inside the cell is hypertonic. 16 Facilitated Diffusion -Movement WITH (along) the concentration gradient. -No energy is used. -Transmembrane ‘carrier’ proteins are required. b) Active Transport -Movement AGAINST the concentration gradient. -Energy is required. -Transporter protein(s) are required. c) Group Translocation -Only occurs in prokaryotes, not eukaryotes. Transported substance is chemically altered during passage through the membrane. Examples: Carbohydrates, fatty acids, some nucleic acid building blocks. In E. coli, glucose outside the cell is phosphorylated during transport into the cell. -Energy is utilized. -Enzymes are required. 17 Other Functions of the Plasma Membrane b. Proteins (enzymes) catalyze reactions involved in... 1) Nutrient breakdown 2) Molecule secretion 3) Environmental monitoring/Cell communication (signaling) 4) Cell wall synthesis Bacteria and Archaea only: 5) Respiration and fermentation (reactions to acquire usable energy) 6) Photosynthesis 7) Chemosynthesis (utilizing inorganic chemicals as an E source) 18 B. Cell Wall 1. Bacterial Cell Walls: All the members of domain Bacteria, with the exception of four genera (Mycoplasma, Ureaplasma, Spiroplasma, and Anaeroplasma) contain cell walls. If a bacterium has a cell wall, it will contain peptidoglycan. a. Examples of functions: 1) Prevents the cell from bursting (lysis). 2) Maintains shape. 3) Protection from the environment. However, the cell wall is not a regulatory structure like the cell membrane. Although it is porous, it is not selectively permeable and will let anything pass that can fit through its gaps. b. Bacterial Cell Wall Components: 1) 2) All bacterial cell walls contain a compound called peptidoglycan. Peptidoglycan is composed of a glycan (sugar) component and a peptide (bonded amino acids) component: Glycan (sugar, carbohydrate) component: 2 monosaccharides 1) NAG (N-acetylglucosamine) 2) NAMA (or NAM; N-acetylmuramic acid) There is an alternating sequence of NAG and NAMA. Peptide component: Each NAG-NAM layer is connected, or crosslinked, to the other by a ‘bridge’ made of amino acids. The particular amino acids vary among different species. The crosslinked peptidoglycan molecules form a network which covers the cell like a grid. http://medic.med.uth.tmc.edu/path/00001438.htm 19 Peptidoglycan can be thought of as a strong, woven mesh that holds the cell shape and prevents it from bursting. It is not a barrier to small molecules, the openings in the mesh are large and all types of molecules can pass through them. Gram positive vs. Gram negative 20 Bacterial Cell Walls c. Gram positive cell walls A distinguishing factor among Gram-positive bacteria is that roughly 90% of their cell wall is comprised of peptidoglycan, and a Gram-positve bacteria can have more than 20 layers of peptidoglycan stacked together to form the cell wall (comprising ~50% of the weight of the entire cell). Examples of common Gram-positive cells are Staphylococcus aureus and Streptococcus cremoris, a bacterium used in dairy production. Another chemical in the G+ cell wall is teichoic acid. Teichoic acid is covalently bonded to NAMA and links various layers of the peptidoglycan mesh together. Self-reading: The cell wall is the site of action of many important antibiotics and antibacterial agents. Penicillin inhibits cells wall synthesis. Lysozyme an enzyme found in tears and saliva-attacks peptidoglycan. It hydrolyzes the NAG - NAMA linkage. 21 Bacterial Cell Walls d. Gram negative cell walls Gram negative cell walls have a more complicated structure; but it is comprised of only 20% peptidoglycan. Outside of the plasma (cytoplasmic) membrane is an open area called the periplasmic space. Beyond this is a thin layer of peptidoglycan. External to the peptidoglycan is an additional membrane, the outer membrane (OM). (OM) -Electron micrograph of a Gram negative cell wall. The Outer Membrane (OM) OM is beneficial to the bacterium. The outer membrane is beneficial to the bacterial cell because it may be able to restrict substances which may damage or prevent the synthesis of peptidoglycan (for example, certain antibiotics). OM is bad for us. The OM is similar to the inner, cell membrane, but it also contains lipopolysaccharides (LPS-endotoxins). Many species of Gram- bacteria are pathogenic usually due to these lipopolysaccharides. The Black Plague which wiped out a third of the population of Europe was caused by the tiny G- rod, Yersinia pestis. Many enteric (intestinal/bowel related) illnesses can also be attributed to this group of bacteria, such as Salmonella food poisoning. http://medic.med.uth.tmc.edu/path/00001443.htm 22 Bacterial Cell Walls Gram negative cell wall Outer Member (OM) of the Gram- cell wall. Lipo-proteins strongly bind the peptioglycan to the outer membrane. Periplasmic space. Cell Membrane proteins. o The side of the OM that faces the outside contains the lipopolysaccharide. o Porins are proteins that form pores in the outer membrane wide enough to allow passage of most small hydrophilic molecules. This allows migration of these molecules into the periplasmic space for transport across the cytoplasmic membrane. o Summary of functions of the outer membrane in Gram negative cells: Selective barrier. Keeps enzymes in periplasm (see next page). Stabilizes cells exchanging DNA. Pathogenic properties. Bacteriophage (bacterial virus) receptors - although this is a function the cell would rather not have. 23 Periplasmic space The periplasmic space in-between the inner, cell membrane and peptidoglycan Cell membranes and the peptidoglycan contain many different proteins. These proteins function to detect the environment, and modify, and transport needed nutrients into the cell. Some examples of periplasmic proteins include: A. Hydrolytic enzymes- Examples 1. Proteases - degrade proteins 2. Endonucleases - degrade nucleic acids B. Binding proteins - recognize specific nutrients (for example, sugars and vitamins) and transport them across membrane. C. Chemoreceptors - Helps the cell interpret chemical composition of its environment Summary: Differences between G + and G- cells Property Thickness of wall Gram Positive Gram Negative 20-80 nm 10 nm Number of layers in wall 1 2 Peptidoglycan content >50% 10-20% Teichoic acid in wall + - Lipopolysaccharide 0 13% Sensitive to penicillin + - (not as much) Digested by lysozyme + - (not as much) http://www.bact.wisc.edu/MicrotextBook/BacterialStructure/MoreCellWall.html 24 e. Bacteria Lacking Cell Walls Ex: Mycoplasma pneumoniae Bacteria without cell walls are not affected by penicillin or lysozyme. For most bacterial cells, the cell wall is critical to cell survival, yet there are some bacterial cells without cell walls. Mycoplasma species are one example, and they are very wide-spread. They are the smallest known cells (0.2-0.3 micrometers) – almost as small as the largest viruses (poxviruses). They also have a very small genomeabout 650 genes (about 1/5 the number in E. coli). Mycoplasma are know to cause many plant diseases. Due to the lack of a cell wall, Mycoplasma have unusually tough membranes (3 layers) that are more resistant to rupture than other bacteria. The presence of sterols in the membrane also contributes to their durability. Many Mycoplasma are also pleomorphic (having no defined shape. Bacterial cells that have no cell wall will often be pleomorphic. However, there are also microbes with cell walls that have this property, and the growth state of the microbe sometimes influences this.) Click below for more info on Mycoplasma pneumoniae http://www.emedicine.com/med/topic1540.htm 25 2. Archaeal Cell Walls a. Archaeal cells have more variations in their cell wall chemistries. Examples: Methanosarcina sp. cell walls contain non-sulfated polysaccharides Halococcus sp. contain sulfated polysaccharides similar to Methanosarcina sp. Halobacterium sp. contain negatively charged acidic amino acids in their cell walls which counteract the positive charges of the high Na+ environment. Therefore, cells lyse in NaCl concentrations below 15%. Methanomicrobium sp. & Methanococcus sp. cell walls are exclusively made up of proteins. b. They never contain true peptidoglycan, but a few have a similar molecule (NAG is present but a different molecule replaces NAM). Penicillin is ineffective in inhibiting the synthesis and lysozyme cannot break the bonds in this type of cell wall. c. Some archaea do not have cell walls (eg Thermoplasma). 26 B. Structures External to the Cell Wall (Anchored to the cell wall or the plasma membrane) 1. Glycocalyx: Substances that completely surround the outside of the cell wall. a. Functions 1) Attachment to surfaces. Most prokaryotic cells adhere to each other. Some bacteria adhere to rocks (aquatic bacteria) and other solid surfaces. Some pathogenic bacteria adhere to animal tissues (ex: respiratory tract). Some are involved in plaque formation leading to dental caries. 2) Protection from environment (slows dehydration). 3) Entrapment of nutrients. b. Bacterial Glycocalyx: (Capsules and Slime layers) Usually the capsule is chemically polysaccharides. It is thick and firmly attached to the cell wall, very dense. Found in pneumonia causing pathogens such as Streptococcus pneumoniae, Haemophilus influenzae, and Klebsiella pneomoniae. Capsulated variants are pathogenic whereas non-capsulated variants of the same species are non-pathogenic. Capsules protect the bacteria against human white blood cells that engulf and digest the bacterial cells. -Ex: Streptococcus pneumoniae 27 Notes: 28 Notes: 29 c. Slime layers: Chemically similar to capsules but less firmly attached, thinner, and less dense. Functions: Basically the same as the capsule but they are not associated with pathogenicity. d. Archaeal cells also have a sticky glycocalyx which functions for: cellto-cell attachment, cell recognition, or strengthening of cell surface. 2. Movement Appendages a. Flagella: Protein appendages, anchored in the plasma membrane Some Bacterial, Archaeal, and Eukaryotic species have flagella, but the molecular structure differs between the three groups. Arrangements: b. Axial filaments: Bundles of fibers found beneath an outer sheath but outside of the cell wall. Only found in bacterial spirochete 3. Attachment appendages ‘Attachment Pili’: Attachment for pathogenic bacteria to human tissues (Often, also called fimbriae). Ex. Neisseria gonorrhoeae Other attachment configurations include protein networks to which the cells may anchor themselves in large groups. May act as receptor sites for attachment of some pathogens. 30 4. Cell Surface Molecules 5. DNA Exchange Appendages (Ex. E. coli) Conjugation Pili (‘sex’ pili) 31 D. Structures Internal to the Plasma Membrane 1. Cytoplasm: All components internal to the plasma membrane- Approximately 80% water. Approximately 20% enzymes, organic compounds, dissolved subst., organelles, DNA... 2. Genetic Material- DNA a. Nuclear Region (Nucleoid): Area in the cytoplasm which contains the large, circular bacterial chromosome (s)1 b. Plasmids: Free-floating, smaller, circular5 pieces of DNA that are in no way connected to the large bacterial chromosome in the nucleoid Usually, the genes on plasmids are not essential to the life of the bacteria but benefit the organism in some way. The genetic information supplements the chromosomal genetic information with… c. Plasmids can be copied and transferred to another bacterial cell d. Often bacterial plasmids are used in genetic engineering. *Some species (relatively rare) of bacteria have been known to have linear chromosomes. 32 3. Ribosomes: Sites of protein synthesis a) ~10,000 ribosomes in Archaea & Bacteria depending on growth rates but many more in Eucarya b) Composed of proteins and rRNA c) Comparing Bacterial, Archeal and Eukaryal ribosomes: 1) Bacterial and Archael ribosomes are similar in size to each other (both smaller than eukaryotic ribosomes) but have different rRNA and protein components. 2) All three cell types have different rRNA molecules and proteins. However the archaeal and eukaryal rRNA components are more similar to each other than to bacteria. 3) Because the three cell types have differences in their ribosome size and molecular structure, different chemicals will interfere in protein synthesis. Examples: o Archaea and Eukarya are not sensitive to antibiotics that inhibit bacterial ribosomes: tetracycline, erythromycin, chloramphenicol, streptomycin o However, the diptheria toxin & anisomycin affects ribosomes of archaea but not bacteria. 4. Inclusions: Structures that appear as granules or globules and serve as storage deposits. a) Not separated by membranes. b) Examples of stored materials: Nutrient and Energy reserves (carbon, etc.). Metabolic deposits: Ex: sulfur deposits as a result of metabolism (some photosynthetic bacteria). http://trishul.sci.gu.edu.au/courses/ss12bmi/microbe_structure.html Metachromatic granules. 33 5. Endospores (‘spores’) a. Tough, inner, dormant (‘resting’) structures that allow the bacterium to survive under poor environmental conditions (ex: low in nutrient supplies). b. They are Gram-positive and usually rod-shaped, but there are exceptions. Mainly found in the genera Bacillus and Clostridium. c. Resistant to: heat, acid, radiation, chemicals, disinfectants, dehydration, and lack of nutrients due to the thick coat, dehydrated nature, and a chemical called dipicolinic acid. Example- heat resistance: Species Time required to kill a suspension in C. botulinum: endospore-forming 2-6 hours at 100oC (boiling water) C. tetani: endospore-forming 1-3 hours at 100oC E. coli & S. aureus: non-endospore formers Killed almost immediately at 100oC, 30 minutes at 70o C2 d. The spore can be differentiated into 4 distinct parts: -Core: Only contain a few essentials for life- Nucleic acids, ribosomes, low/no levels of enzyme activity, dipicolonic acid & low water content. -Cortex: Surrounds the core, mainly peptidoglycan -Coat: Surrounds the cortex, mainly protein -Exosporium: The outer-most, thiner layer 2 o F = (1.8 x oC) + 32 34 e. Sporulation and Germination Importance of endospores -Some spore-formers are pathogens of animals, usually due to the production of powerful toxins. Bacillus anthracis causes anthrax, a disease of domestic animals (cattle, sheep, etc.) which may be transmitted to humans. Clostridium botulinum causes botulism, a form of food poisoning. Clostridium tetani is the agent of tetanus. -Food industries often heat-treat products to reduce microbial spoilage & kill pathogens; spore-formers are a problem (look for swelling of tins). -Many are found in soils --> where spores may germinate to produce toxins --> infect wounds. -Some strains were being developed for biological warfare e.g., B. anthracis (anthrax). -Some strains produce important biopesticides (biotechnology) e.g., B. thuringiensis produces toxic proteins against mosquito & blackfly larvae. Commercial variants are available which produce toxins towards slightly different insect pests; for example Bt corn (the toxin kills corn borer). -Spores which have ‘germinated’ have been found in 7200 year old temples, mummies, and from the GI tract of a bee preserved in amber (over one-million years old). http://trishul.sci.gu.edu.au/courses/ss12bmi/microbe_structure.html 35 Exam Review 1. Know the 3 domains of life, the major groups within each domain, and the types of information that was used to create this classification scheme. 2. Bacterial Cells: Know the general characteristics of Bacteria (size, shapes, arrangements). Be able to label bacterial structures on a drawing of a bacterial cell. 3. Archaeal Cells: Know the general characteristics concerning Archaeal cells (size, shapes, habitats). 4. Know the chemical composition of the plasma membrane and its functions. Be able to describe the term ‘semipermeable’ or ‘selectively permeable’. 5. Understand the five ways that cells transport substances across the plasma membrane (be able to compare/contrast them). Be able to describe osmosis and isotonic/hypotonic/hypertonic solutions. 6. Know the functions of some of the various proteins in the plasma membrane. 7. Know examples of functions of the cell wall. Be able to describe the chemical components of a bacterial cell wall. 8. Know the differences between Gram positive and Gram negative cell walls. Know the structure and the importance of the outer membrane to Gram negative bacteria. 9. How do the bacterial cell walls affect disease and disease treatment? 10. Be able to give an example of a bacterium without a cell wall. 11. Briefly describe Archaeal cell walls and their differences from bacterial cell walls. 12 Be able to define/describe and list the functions of the glycocalyx. 13. Be able to describe the experiments performed on Streptococcus pneumoniae concerning the capsule and the importance of the experiments concerning knowledge of bacterial gene transfer and the identity of the genetic material. 14. Be able to define/describe and list the functions of the following bacterial structures outside of the cell wall: movement appendages, attachment appendages, cell surface molecules. 15. Compare transformation and conjugation. 36 16. Be able to define/describe the terms cytoplasm, organelle, membrane-bound. 17. Describe Prokaryotic DNA: large chromosome, nucleoid, plasmids. 18. Be able to define/describe and list the functions of prokaryotic ribosomes and inclusions. 19. Know the importance of bacterial plasmids to bacterial gene transfer, resistance, toxins, and genetic engineering. 20. Define and know the characteristics of endospores and examples of spore-forming bacteria. What are endospores resistant to? What is the structure of an endospore, and what is its chemical composition? Know the importance of endospores to disease, food spoilage, wounds, biological warfare, and biotechnology. Define the terms sporulation, germination, vegetative cell. 21Be able to list bacterial structures targeted by antibiotics and other drugs. Why are these structures targeted? Be able to list antibiotics and chemicals that do not affect bacteria but that do affect Archaea and Eukaryal cells. 22. Be able to show similarities and differences between the Archaea and other forms of life. 23. In what way are bacteria more like eukaryotes than archaea? 24. Be able to answer the following type of question: Which (one or more) of the following cellular molecules or structures is primarily involved in the following life process: Response to the environment (example). Why did you choose this response? a. flagellum b. Cell surface molecules c. Ribosomes d. Inclusions 37