Prokaryotic vs. Eukaryotic Cells

• Microbiology is the study of microorganisms; “micro” means small and biology" refers to the study of living things.
• A microbe/microorganism is a microscopic organism that comprises either a single cell, cell clusters, or multicellular relatively complex organisms.
• Microbiology studies microscopic organisms like bacteria, viruses, archaea, fungi, and protozoa.

Types of Microorganisms

• Microorganisms are bacteria, archaea, protozoa, algae, fungi, viruses, and multicellular animal parasites (helminths).
• Each microorganism type has characteristic cellular composition, morphology, and reproduction.
• Microorganisms can produce oxygen, decompose organic material, and provide nutrients for plants.
• Some microorganisms are pathogenic and cause diseases in plants and humans.
• Bacteria are unicellular organisms described as prokaryotic because they lack a nucleus
• Fungi (mushroom, molds, yeasts) are eukaryotic cells with a true nucleus and most fungi are multicellular with a cell wall of chitin
• Viruses are noncellular entities consisting of a nucleic acid core (DNA or RNA) surrounded by a protein coat and are not considered living organisms.
• Parasites are a helminth group of eukaryotic organisms consisting of flatworms and roundworms.
• Algae, also called cyanobacteria or blue-green algae, are unicellular or multicellular eukaryotes that obtain nourishment by photosynthesis.
• Protozoa are unicellular aerobic eukaryotes with specialized structures that obtain nourishment by absorption or ingestion.

Three Domains of Life

• Bacteria (prokaryotes)
• Archaea (prokaryotes)
• Eukarya (eukaryotes), including animals, fungi, protozoans, and parasites

Characteristics of Prokaryotic and Eukaryotic Cells

• Prokaryotes are always single-celled organisms that lack a defined nucleus
• Eukaryotes can be single-celled or multicellular organisms
• Characteristics shared by eukaryotic and prokaryotic cells
• Include performing the same basic functions
• Surrounded by a plasma membrane to control what enters and leaves
• Contain cytoplasm
• Contain ribosomes to make protein
• Contain DNA to give the general instructions for cell life

Differences Between Prokaryotic and Eukaryotic Cells by DNA and Nucleus

• Eukaryotic DNA is contained within a distinct nucleus, which is a membrane-bound organelle. This nuclear membrane serves to protect the genetic material and regulate the flow of substances in and out of the nucleus, thus playing a vital role in cellular function and gene expression.
• In contrast, prokaryotic DNA is located in a region known as the nucleoid. This area is not surrounded by a membrane, which makes the organization of genetic material within prokaryotic cells less compartmentalized compared to eukaryotes. This fundamental difference is reflective of the overall complexity and efficiency of cellular processes in each type of organism.
• Eukaryotic cells typically possess multiple chromosomes that are organized in pairs, which play a crucial role in sexual reproduction and genetic diversity. Each pair contains one chromosome from each parent.
• Prokaryotic cells, on the other hand, generally harbor a single, circular chromosome that governs all essential functions, and this simplicity distinguishes them significantly from eukaryotic cells.
• Furthermore, eukaryotic cells contain histone proteins that assist in the packaging and organization of DNA into a compact structure known as chromatin, enabling proper regulation of gene expression. Prokaryotic cells lack these histones, reflecting their simpler organizational structure.

Differences Between Prokaryotic and Eukaryotic Cells by Structure

• Prokaryotic cells, which include bacteria and archaea, lack membrane-bound organelles and do not possess a defined nucleus, consequently resulting in the absence of a cell wall structure akin to those found in eukaryotic organisms. This unique cellular organization allows for rapid reproduction and adaptation to diverse environments.
• In prokaryotic cells, the cell wall is primarily composed of peptidoglycan, a complex polymer consisting of sugars and amino acids. This peptidoglycan layer provides structural integrity and protection against osmotic pressure, making it vital for maintaining the shape and stability of the cell.
• Plant cells possess a rigid cell wall made from cellulose, a polysaccharide that provides strength and support, while fungal cells contain chitin, another structural polysaccharide that offers durability. These components play crucial roles in maintaining the cell's shape and protecting against environmental stresses.
• In contrast, animal cells do not have a cell wall; instead, they are surrounded by a flexible plasma membrane. This lack of a rigid structure allows for greater variability in cell shapes, as well as facilitating cellular communication and movement, which are essential for the various functions that animal cells perform in multicellular organisms.

Differences Between Prokaryotic and Eukaryotic Cells by Cytoskeleton and Reproduction

• The cytoskeleton is a complex and dynamic network composed of various types of protein fibers, including microtubules, microfilaments, and intermediate filaments. This intricate framework not only plays a crucial role in determining the cell’s shape but also provides mechanical support, ensuring the integrity of the cell structure. Additionally, it facilitates intracellular transport, acts as a scaffold for organelles, and is essential for cell motility by enabling locomotion through processes such as amoeboid movement and muscle contraction. Notably, the absence of a cytoskeleton in prokaryotic cells distinguishes them from eukaryotic cells, which rely heavily on this system for functionality.
• In prokaryotes, reproduction occurs exclusively through a method known as binary fission, a straightforward process wherein a single organism divides into two identical daughter cells. This method allows for rapid population growth under favorable conditions, as the time taken to reproduce can be as short as 20 minutes, depending on the species and environmental factors. The simplicity and efficiency of binary fission exemplify the prokaryotic life cycle.
• Eukaryotes exhibit greater complexity in their reproductive strategies, engaging in both asexual reproduction via mitosis and sexual reproduction through meiosis. Mitosis is a type of cell division that results in two daughter cells with identical genetic material, while meiosis reduces the chromosome number by half, producing gametes for sexual reproduction, thus promoting genetic diversity.
• Prokaryotic cells are generally smaller than their eukaryotic counterparts, with diameters typically ranging from 0.5 to 2.0 µm and lengths that can vary from 1.0 to 60 µm. This small size enables a high surface area-to-volume ratio, which is advantageous for nutrient uptake and waste elimination, critical processes for survival and growth.
• In contrast, eukaryotic cells are larger and structurally more complex. They contain specialized organelles, such as mitochondria for energy production, endoplasmic reticulum for protein and lipid synthesis, and various vesicles for transportation of biomolecules. This compartmentalization allows eukaryotic cells to perform diverse metabolic functions efficiently and maintain homeostasis within a larger cellular structure.

Summary of Differences between Prokaryotic vs Eukaryotic Cells

• Prokaryotic cells are small, less than 5mm versus larger eukaryotic cells greater than 10mm.
• Prokaryotic cells always are unicellular while Eukaryotic are often multicellular.
• Prokaryotic cells do not have a nucleus nor any member-bound organelles.
• DNA is circular and has no proteins in prokaryotic cells.
• Prokaryotic cells are more simple and eukaryotic cells have more variety.
• Ribosomes are small or 70S in prokaryotic cells versus large or 80S in eukaryotic cells.
• Prokaryotic cells have no cytoskeleton - Eukaryotic cells always have a cytoskeleton.
• Prokaryotic cell division is by binary fission vs eukaryotic cells division - by mitosis or meiosis.
• Reproduction is always asexual in prokaryotes versus asexual or sexual in eukaryotic cells.

Classification of Bacteria

• Bacteria are unicellular organisms that are prokaryotic due to lacking a nucleus.
• Bacteria possess a rigid peptidoglycan cell wall, which provides structural support and protection, and reproduce asexually through a process known as binary fission, creating genetically identical daughter cells.
• May possess flagella for motility
• Classified by shape, cell wall, response to gaseous state, and energy acquisition

Bacteria Shape Classifications

• Bacillus (rod-shaped)
• Coccus (spherical-shaped)
• Spirilla (spiral-shaped)
• Vibrio (curved shape)

Cell Wall Classifications

• Can be classified as either Gram-positive or Gram-negative when using the Gram staining technique, which differentiates bacterial species based on the structure of their cell walls and their response to specific staining protocols.

Response to Gaseous Classifications

• Aerobic: Refers to organisms that require oxygen for their survival and growth. These organisms utilize oxygen for cellular respiration, enabling them to efficiently convert nutrients into energy through aerobic metabolism. This process produces carbon dioxide and water as by-products, which are expelled from the organism's body.
• Anaerobic: Denotes organisms that thrive in environments devoid of oxygen. Instead of utilizing oxygen for respiration, these organisms rely on anaerobic processes, such as fermentation, to generate energy, often resulting in by-products such as lactic acid or alcohol.
• Facultative anaerobes: Describes organisms capable of adjusting to either aerobic or anaerobic conditions. These versatile life forms can switch between oxygen-dependent respiration and anaerobic processes depending on the availability of oxygen, allowing them to adapt to varying environmental conditions for optimal energy production.

Energy Acquisition Classifications

Heterotrophs: These organisms acquire energy by consuming other living entities, which can include plants, animals, and other microorganisms. Heterotrophs play a vital role in ecosystems as they help in the transfer of energy through food webs. They are unable to synthesize their own food and rely on organic matter for nutrition.

Autotrophs: Autotrophs are distinguished by their ability to produce their own food through photosynthesis or chemosynthesis. Photoautotrophs use sunlight to convert carbon dioxide and water into glucose and oxygen, while chemoautotrophs harness energy from chemical reactions involving inorganic substances. Autotrophs form the base of the food chain, serving as primary producers in various ecosystems.

Saprophytes: These are a specific type of heterotroph, primarily bacteria and fungi, that decompose dead organic materials, recycling nutrients back into the ecosystem. By breaking down dead organisms and organic waste, saprophytes play a crucial role in nutrient cycling, ensuring that resources are available for other organisms to utilize.

Aerobic Bacteria

Aerobic bacteria are a category of bacteria that thrive in environments where oxygen is available. They utilize oxygen for cellular respiration, a metabolic process that converts biochemical energy from nutrients into adenosine triphosphate (ATP), which powers cellular activities.

Obligate Aerobic Bacteria

Obligate aerobic bacteria require oxygen to survive and grow. They cannot perform fermentation or anaerobic respiration, which limits their ability to thrive in low-oxygen environments. These bacteria are essential in various ecological processes and can be found in a variety of habitats.

Example: Mycobacterium tuberculosis is a notable example of an obligate aerobic bacterium. It is the causative agent of tuberculosis, a serious infectious disease primarily affecting the lungs but can also impact other parts of the body. The dependence of M. tuberculosis on oxygen for its growth signifies its ecological niche and presents challenges for treatment due to its respiratory nature.

Microaerophilic Bacteria

• Microaerophilic bacteria are organisms that thrive in environments where the oxygen concentration is lower than that of the atmosphere. Typically, they require oxygen levels ranging from 2% to 10% for their metabolic processes. These bacteria have adapted to utilize oxygen for energy production while avoiding the harmful effects of higher concentrations. A well-known example of microaerophilic bacteria is Helicobacter pylori, which is famously associated with stomach ulcers and gastritis.

Anaerobic Bacteria

• Anaerobic bacteria encompass a diverse group of microorganisms that do not require oxygen for their growth and can even find it detrimental. These bacteria thrive in oxygen-free environments, such as deep-sea vents, high-sulfide environments, and in the gut of animals. They rely on fermentation or anaerobic respiration as their primary energy-generating processes. This adaptability allows them to occupy ecological niches that are inhospitable to aerobic organisms.

Obligate Anaerobic Bacteria

• Obligate anaerobic bacteria are particularly sensitive to oxygen and cannot survive or grow in its presence. Exposure to oxygen can lead to their death or inhibit their growth. An example of obligate anaerobes includes Clostridium tetani, the bacterium that causes tetanus, and Clostridium perfringens, which is often responsible for food poisoning and gas gangrene. These bacteria play various roles in both human health and disease, highlighting their significance in microbiology.

Facultative Anaerobic Bacteria

• Facultative anaerobic bacteria possess the remarkable ability to adapt to both oxygen-rich and oxygen-poor environments. They can grow and divide in the absence of oxygen, but when oxygen is available, they prefer to utilize it for more efficient ATP production through aerobic respiration. A classic example of facultative anaerobes is E. coli, a key organism found in the intestines of humans and animals, serving both beneficial and pathogenic roles.

Aerotolerant Bacteria

• Aerotolerant bacteria are organisms that cannot utilize oxygen to grow, but their survival is not adversely affected by its presence. They primarily rely on anaerobic metabolic processes, such as fermentation, to generate energy. This characteristic allows them to coexist with aerobic organisms, and they can be found in diverse environments where oxygen levels fluctuate.

Shape of Bacteria

• Cocci are characterized by their spherical or oval shape, which allows them to efficiently resist osmotic pressure. Their round morphology can be advantageous in microbial environments as it minimizes the surface area-to-volume ratio, aiding in nutrient absorption. There are significant variations of cocci, including those that are formed within a specific arrangement which can often indicate particular evolutionary adaptations.
• Bacilli have a distinct rod-like structure that enables them to cover more surface area and can also facilitate movement in certain environments. This shape can be found in various species, some of which play crucial roles in nutrient cycling within ecosystems. Their elongated form allows them to utilize their surroundings more effectively in search of resources.
• Vibrios, which resemble comma shapes, thrive in aquatic environments and are known for their mobility. Their unique shape may allow them to navigate through liquid media with ease and helps them to colonize and survive within various ecological niches.
• Spirilla are rigid and have a corkscrew shape, which can confer motility advantages in viscous environments. They often inhabit environments where traditional bacilli might struggle, such as sediments where they can more readily drill through the media.
• Spirochetes are flexible in structure, allowing them to move with a twisting motion that aids in their ability to penetrate host tissues. This adaptability is a critical feature for pathogens that require invasion of host tissues for effective infection.
• Actinomycetes are notable for their branching, filamentous appearance, reminiscent of fungal hyphae. This structure is fundamental to their reproductive strategies, as they can form spores that are highly resistant to environmental stress, thus playing an essential role in soil ecology and the degradation of organic materials.

Arrangement of Bacteria: Cocci

• Cocci can reproduce and arrange themselves in various formations. When cocci occur in pairs, they are referred to as Diplococcus, which is crucial in identifying certain pathogenic species.
• When cocci align in chains, the term used is Streptococcus. This arrangement is characteristic of particular strains that can lead to infections and illnesses ranging from strep throat to skin infections.
• In clusters, cocci are known as Staphylococcus, with this arrangement being critical for the pathogenicity of several strains, such as Staphylococcus aureus, which can lead to serious health complications like MRSA infections.
• A tetrad arrangement features a grouping of four cocci, while the sarcina arrangement consists of eight cocci, both of which demonstrate how bacteria can maintain structural integrity in varied environments.

Arrangement of Bacteria: Bacilli

• Coccobacilli represent a hybrid shape and include organisms such as Gardnerella vaginalis and Haemophilus influenzae. These bacteria can have profound clinical implications, being implicated in conditions such as bacterial vaginosis and respiratory infections.
• In the case of Diplobacilli, these bacilli can be found in pairs, exemplified by Klebsiella rhinoscleromatis, which is responsible for chronic nasal infections in humans. The formation of these pairs can facilitate more effective infection strategies.
• Streptobacillus moniliformis is another example that appears in chains; it is known as the causative agent of rat-bite fever, highlighting the importance of understanding these arrangements in terms of zoonotic diseases.
• Palisade bacteria, typified by Corynebacterium diphtheriae, take on a characteristic angular arrangement. These organisms are famously known for causing diphtheria, a severe respiratory illness.

Cocci in Clusters

• Staphylococcus aureus, which can be magnified up to 5,400x, is particularly notable for its role as a pathogen, with variations that can lead to different diseases such as skin infections, pneumonia, and endocarditis. Understanding its morphological characteristics can direct diagnostic methods and treatment approaches effectively.

Cocci in Chains

• Streptococcus pyogenes is recognized as the predominant bacterial cause of acute pharyngitis, making it clinically significant. Its prevalence accounts for approximately 15-30% of cases in children and 5-10% in adults, underscoring the necessity for swift diagnosis and antibiotic intervention in cases of suspected infection.

Gram-Positive Diplococci

• Streptococcus pneumoniae, presenting as gram-positive diplococci, shows notable morphology with cells that taper at the ends. This "lancet" shape is distinctive and assists in the identification of this bacterium in laboratory settings. Understanding its morphology is important for medical professionals when diagnosing conditions related to pneumonia.
• This bacterium can lead to a variety of severe infections, impacting not only the lungs (causing pneumonia), but also the ears (otitis), sinuses (sinusitis), and more critically, the central nervous system (resulting in meningitis), in addition to bacteremia, highlighting the diverse range of its pathogenic effects.

Gram-Negative Diplococci

• Gonorrhea, caused by infection with the Neisseria gonorrhoeae bacterium, remains a significant public health challenge. The organism can readily adhere to and infect the mucous membranes of the reproductive tract in individuals. This highlights the need for efficient screening and treatment strategies to combat the spread of this sexually transmitted infection.
• The infection process involves the colonization of mucous membranes, occurring in women in the cervix, uterus, and fallopian tubes, while in men, it commonly infects the urethra. The implications of such infections can range from asymptomatic cases to serious complications such as pelvic inflammatory disease and infertility.

Bacilli

• Lactobacillus acidophilus is a beneficial species found in various human body sites, such as the mouth, intestine, and vagina. It is essential for maintaining the balance of healthy microbiota in these regions, playing a key role in preventing pathogenic overgrowth.
• This bacterium is known for producing lactic acid, which contributes to the acidic environment that limits the growth of harmful bacteria. Its existence is critical not only for digestion but also for fostering a healthy immune response.
• Lactobacillus acidophilus enhances the breakdown of food, promoting the absorption of essential nutrients, and it aids the body’s defense against harmful organisms that can induce various diseases. Notably, it is commonly included in probiotic supplements and fermented products like yogurt, further underlining its significance in dietary health.

Escherichia Coli (E. Coli)

• The majority of E. coli strains are harmless, thriving in the gastrointestinal tracts of healthy individuals, where they aid in digestion and nutrient absorption. However, the pathogenic variant E. coli O157:H7 is notorious for causing severe gastrointestinal illness characterized by severe stomach cramps, bloody diarrhea, and vomiting, demonstrating the diverse effects of various strains on human health.
• Exposure to pathogenic strains of E. coli often occurs through the consumption of contaminated water or undercooked foods, particularly raw vegetables and undercooked or poorly handled beef, emphasizing the necessity for safe food handling practices.
• Typically, healthy adults can expect to recover within a week following an infection with E. coli O157:H7; however, vulnerable populations, including young children and older adults, are at an increased risk of developing life-threatening complications, such as hemolytic uremic syndrome, which can result in acute kidney failure.
• Klebsiella pneumoniae infections pose another risk, known primarily for causing bacterial pneumonia, illustrating how various bacteria can contribute to significant respiratory diseases. Understanding the morphology, behavior, and pathogenic potential of these bacteria is crucial for effective medical interventions.

Explore the fundamental differences between prokaryotic and eukaryotic cells. This quiz covers cell structure, reproduction, metabolism, and DNA organization. Test your knowledge of cell biology.