BIOl 2051 Chapter 1 Notes

Robert Koch provided the first clear demonstration that a bacterium, Bacillus anthracis and Mycobacterium tuberculosis (Microbes in Focus 1.1), was the cause of a specific disease, anthrax, in livestock.(respectively) Know what Koch (pronounced Coke) discovered

-His work with anthrax helped sheepherders and cattle ranchers avoid costly animal losses. -This basic rules Koch established made it possible for other to determine which microbes caused which diseases. They are still in use to this day. -These rules (Koch's postulates) will be discussed in more detail in Ch. 18.

PPT: But what about separating interior from exterior?

-A single lipid layer known as a micelle may have been an early form of plasma membrane. -This could have formed a crude way of separating interior contents from the external environment. How did the first membranes form? Be able to answer the proposed model. We know that hydrocarbons coupled to charged groups, such as phosphates, form polar lipids, which can spontaneously organize into micelles and even bilayer membranes that close back upon themselves to form a sealed compartment (Figure 1.14). Perhaps such primitive membranes initially formed around fragments of minerals, such as FeS2, that also happened to serve as surfaces for the aggregation of organic molecules, as just discussed. If a membrane encapsulated an informational molecule and a catalytic molecule, like a ribozyme, then something like a cell would have been formed.

PPT: So how do microbes obtain energy?

-It depends on whether a microbe is a heterotroph (ingesting preformed organic molecules) or an autotroph (producing organic molecules). -Early oxygen-producing autotrophs helped change the Earth's early atmosphere over time

The importance of RNA in the basic information flow of modern cells highlights their prehistoric importance.

-DNA is transcribed into a "working copy" in the form of messenger (m)RNA. -mRNA is translated into the proteins needed to make a cell work. -Other form of RNA (tRNA, rRNA) are also important, showing the versatility of RNA molecules for life processes.

So, one idea of how microbial life arose on Earth is:

-Early conditions formed RN A and micelles. o These came together into a primitive cell using RNA for storing genetic info and coding. o Primitive cells eventually changed from using RNA to DNA instead for storing their genetic information.

Okay, but how do we use this information to study the genetics of microbes today?

-Knowing the way the systems work allows us to examine microbial genomes from two different perspectives: 1. Examining effects of single mutations in DNA individually 2. Studying and comparing pieces of genomes to each other (bioinformatics) across domains

In 1958, Robert Whittaker

Advocated further separation of eukaryotic microorganisms into kingdoms, Fungi and Protista but kept prokaryotic cells in a single kingdom called Monera. This five-kingdom taxonomic system— Animalia, Plantae, Fungi, Protista, and Monera- became the accepted standard for the next few decades until DNA and protein sequences between widely accessible.

Aristotle categorized life into just two fundamental groups,_____

Animals and plants, and this categorization persisted until the dawn of microbiology as a science.

PPT: But molecules alone aren't life—so how did early organic molecules change into the four macromolecules of cells today?

Early iron-containing surfaces may have helped provide the right environments by sticking the molecules to their surfaces. But any early life would still need to have genetic information, the ability to catalyze biochemical reactions, and a way of separating the cell interior from the external environment. Are there molecules or structures that might satisfy those requirements? Perhaps the organic molecules would have required a surface on which to accumulate rather than simply floating in the open ocean. Günter Wächtershäuser has theorized that life evolved on iron-containing surfaces, such as iron pyrite (FeS2), an insoluble, positively charged surface with affinity for organic compounds. What you need to take from this is what type of molecules may have been used for the first metabolic processes before oxygen.

When/how did eukaryotes appear?

Endosymbiotic theory: Primitive prokaryotic microbes ingested other microbes, starting a symbiotic relationship, forming the first basic eukaryotes. -Ingested microbes that could use oxygen for a respiratory process to produce chemical energy became mitochondria. -Ingested microbes that could fix carbon dioxide into organic molecules using light energy became chloroplasts.

polymerase chain reaction (PCR)

a technique that allows researchers to quickly amplify specific pieces of DNA and the development of rapid, cost-effective DNA sequencing techniques, we now have a richer and more accurate phylogenetic tree.

first to come?

aerobic photosynthesis **

best metabolic pathway

aerobic respiration

Günter Wächtershäuser has theorized that life evolved on

iron-containing surfaces, such as iron pyrite (FeS2), an insoluble, positively charged surface with affinity for organic compounds. Metabolic processes that occur in modern cells could have evolved from reactions among surface-bound organic compounds. Many modern proteins, such as cytochromes and hemes, bind iron and other metallic atoms; many enzymes, including DNA polymerases, require bound metals for activity. These interactions with metals may reflect a very ancient relationship.

If two organisms were closely related, these researchers reasoned, then the amino acid sequence of a common protein in the organisms should be very similar. Conversely, if two organisms were distantly related, then the amino acid sequence of a common protein should be more divergent.

Woese and colleagues began to focus not on protein sequences, but on RNA sequences. Woese reasoned that the ribosomal RNAs (rRNAs), because of their universal presence in all cells, could be excellent molecules to compare.

Can studying the genetics of microbes help us to use them to benefit humans?

YES! -By altering the genomes of microbes, we can mass-produce molecules that humans want. -A classic example of this is the production of human insulin by inserting the gene into E. coli cells (done in 1978 by Genentech in San Francisco)

polypeptides

polymers of amino acids, constitute the most abundant class of macromolecules. Polypeptides, also often referred to as proteins, fold into elaborate structures and can execute a vast array of important jobs. Some proteins function as enzymes, macromolecules that catalyze chemical reactions within the cell (Figure 1.5). Other proteins may facilitate the movement of material into or out of the cell. Still other proteins comprise critical structures such as microfilaments that facilitate cell movement (Table 1.2).

Members of Ehrlich's research group discovered an organic arsenic-containing compound, arsphenamine, which in 1910 became the first effective commercial drug for the treatment of Treponema pallidum,

the bacterium that causes the sexually transmitted disease syphilis (Figure 1.11). Because it also exhibited toxicity to host cells, arsphenamine, known by its trade name Salvarsan, was abandoned in the 1940s in favor of penicillin, the first widely used antibiotic capable of killing many different kinds of bacteria.

In the 1970s, DNA sequencing was used to compare sequences of ribosomal RNA genes in different organisms (see Mini-Paper)

*This led to a new scheme of organizing life into three domains: Bacteria, Archaea, and Eukarya.

Why are microbes used for research models?

-Many are easily cultivated in the lab using inexpensive equipment; they grow rapidly to high cell density on cheap nutrient sources. -They facilitate the production of enzymes, other proteins, and various biomolecules for industrial and medical uses. -Most have relatively small numbers of genes to analyze. Even the largest bacterial and archaeal genomes are smaller than the smallest eukaryal genomes, and eukaryal microorganisms have substantially fewer genes than complex multicellular eukarya. -Many can be genetically manipulated much more easily than complex eukarya. Microbes as model organisms Microbes have been used extensively in research. Because they replicate quickly, are cheap to grow, and have relatively simple structures, they have been used extensively to study basic cellular processes like DNA replication, transcription, and translation. Two of the most-studied microbial model organisms are a. the bacterium Escherichia coli and b. the eukarya Saccharomyces cerevisiae, a yeast.

How do microbes interact with the world around them?

-Microbes can also help in biogeochemical cycling as they interact with the environments. -This is a process by which inorganic molecules are cycled to organic molecules and back again.

BE CAREFUL! Microbes are not individual cells/ populations Microbes live in diverse groups in nature, with many different members forming a microbial community and ecosystem.

-Microbes in the intestines -Plaque in teeth -Slime on rocks on beaches -Mold growths on bathroom surfaces

Where has this reduction of deaths from from?

-Prevention of infection through -Use of antiseptics (Joseph Lister) -Sanitation improvements (sewage treatment) -Food/water safety (pasteurization) -Personal hygiene improvements -Vaccination -Treatment of infections (antibiotics!)

PPT: RNA world hypothesis

-Some RNA molecules have the ability to catalyze reactions (these are known as ribozymes, a combination of ribonucleic acid and enzymes). -This means RNA could serve the dual purpose of genetic information storage and catalyzing reactions! -Conversely, recent research points to the idea that the first genetic material was likely made of both RNA and DNA subunits. that information was initially stored in RNA molecules rather than DNA, leading to the RNA world hypothesis for the origins of life. We now know that certain RNA molecules, ribozymes, can catalyze chemical reactions, much like the protein-based enzymes with which we are more familiar. Early in the history of life, then, RNA may have had dual functions, serving as the primary informational molecule and catalyzing important reactions. So what molecule has been proposed as one that can both give rise to proteins and DNA? Is this a hypothesis or a theory? Why?

Carl Woese *know what Carl Woese did and how this change the basis of classfication. WHat molecule is used to compare create phylogenic relationships?

-Studied at University of Illinois -focused his attention on the structure and sequence of one of the RNA molecules that serves as a scaffold for assembly of the ribosome—the small subunit (SSU) ribosomal RNA. This molecule is a critical component of the ribosome in all living organisms and interacts with the messenger RNA during translation -his work paved the way for a revolution in thinking about phylogeny --- or evolutionary history of organisms -because of his work we categorise organisms in three domains -fascinated by group of prokaryotes known as "archaebacteria" -In the 1970s, microbiologists studying some prokaryotes noted that their molecular machinery resembled that of eukaryotes more than it did other prokaryotes. Leading the way in these studies was Dr. Carl Woese of the University of Illinois.

What do we know about the physiology, genetics, and cultivation of microbes?

-The very early environment on Earth was drastically different than it is today. -There was little oxygen in the atmosphere, and the surface of the planet was a soup of chemicals in liquid form. -This early atmosphere and environment led to the initial synthesis of the first forms of macromolecules (and their use in primitive single-celled life). -Multicellular fossils dating to about 0.5 billion ybp (years before present) have been found—meaning microbes dominated the planet for approximately 3.5 billion years! Some microbial fossil records do exist, largely in fossilized mats discovered in Australia.

Why study microbes at all if they're so hard to see?

-Very fast, cheap, and easy to grow -can produce enzymes and other molecules for industrial/medical uses -most of them have smaller numbers of genes, making them simple to study - genetic manipulation of single-celled bacteria is usually much easier than multicellular eukarya

1.4 Microbes and Disease people still did not understand that microbes could be transmitted from person to person. Rather, many assumed that microbes arose from inanimate materials, a process known as spontaneous generation. This belief negated a need to even consider the transmission or prevention of microbial diseases. If microbes arose spontaneously, then there was no reason to investigate how a person became infected. How are microbes associated with disease?

-We didn't always believe that microbes caused disease or existed around us unseen. -People used to believe that disease was associated with angry gods or bad air. -Even when microbes were known to exist, people thought they could spontaneously form as life from nonliving matter (the spontaneous generation theory) -It took the work of many people to debunk these ideas, but two were very important: Louis Pasteur and Robert Koch.

Bacteria (and humans) today use double-stranded DNA (not single-stranded RNA) for storage of genetic information. Why the change? For now, know what DNA and RNA are composed of and what do they do as well as what the letters stand for.

-dsDNA provides a "backup copy" of the genetic information in case of a problem. -DNA is more stable than RNA. -DNA is an elegant, albeit enormously long, molecule whose structure is beautifully suited for information storage and replication

The method of _______ has greatly enhanced the speed and ease of doing these DNA sequence examinations

polymerase chain reaction (PCR)

*If microbiology is the study of life, what is the basis for life?

. First, living organisms are composed of cells (cellular composition), the smallest units of life as we know it. Second, living organisms are capable of: • Metabolism: A controlled set of chemical reactions that extract energy and nutrients from the environment and transform them into new biological materials. • Growth: An increase in the mass of biological material. • Reproduction: The production of new copies of the organism. To accomplish these tasks, organisms contain a biological instruction set to guide their actions. These instructions need to be reproduced as the organism itself reproduces. Other features that living organisms share include: • Genetic variation, allowing the possibility of evolution, or inherited change within a population, through natural selection over the course of multiple generations. • Response/adaptation to the external environment — Response to external stimuli and adaptation to the local environment (within genetic and physiological constraints). • Homeostasis(maintaining internal organization and order usually by expending energy): Active regulation of their internal environment to maintain relative constancy.

In 1953, Stanley Miller described the first laboratory investigation intended to simulate prebiotic Earth. Miller, then a graduate student at the University of Chicago, designed a reactor with his mentor, Harold Urey, to test for abiotic production of biologically relevant molecules. The Miller-Urey experiment revolutionized the thinking of many scientists, and a fair number of non-scientists as well, about the origin of life on Earth.

After a few days of continuous operation, Miller observed that the water in the flask was changing color. Within a week, the solution in the flask had turned a deep red and had become turbid. Miller examined the solution after a week and found that the solution contained organic molecules, or molecules containing carbon-hydrogen bonds. Most notably, the simple amino acids glycine and alanine were readily detectable, along with aspartic acid. These amino acids are among the 20 primary amino acids used by life on Earth for protein synthesis and presumably were abundant as life evolved. Miller's flask provided the first evidence that such molecules could be synthesized from inorganic precursors under conditions believed to mimic primordial Earth, where energy inputs could have included electrical discharge from lightning strikes as well as heat from both the sun and Earth's crust.

Microbes

Are forms of life too small to be seen with the naked eye (bacteria, archaea, fungi, Protozoa, and algae) The field examines how microbes interact with humans, with food, and how they can be used by humans (among other aspects).

You have found a novel microbe and wish to classify it at the domain level. The new microbe has a single RNA polymerase activity, no organelles and standard plasma membrane structure. Which other features are likely displayed by this microbe? (Select all that apply) A) RNA pol II B) RNA pol II-like polymerase C) RNA pol III D) Single RNA Polymerase E) Nuclear membrane

B) RNA pol II-like polymerase D) Single RNA Polymerase

The Domains of Life

Bacteria, Archaea, and Eukarya

*The slime mold

Dictyostelium discoideum, for instance, exists as a rather typical unicellular organism when food is readily available.

*This will be the basis for our material on metabolism.

FIGURE 1.18 Glycolysis, fermentation, and aerobic respiration In almost all organisms, glucose can be converted to pyruvate, resulting in the production of some ATP. The process of aerobic respiration allows cells to generate much more ATP from pyruvate. In plants, animals, and many bacteria, respiration occurs in the presence of oxygen (aerobic respiration) and results in the generation of CO2 and H2O. Some bacteria undergo anaerobic respiration, utilizing a terminal electron acceptor other than oxygen. If respiration cannot occur, some organisms undergo fermentation reactions. Two well-studied types of fermentation result in the production of lactate or ethanol. These products of fermentation generally are toxic to the microorganism but may be helpful to humans.

Regardless of how they get organic molecules, they are then broken down by microbes to harness chemical energy (ATP).

Fermentation doesn't need oxygen but doesn't yield much energy for microbes. Aerobic respiration does require oxygen but yields much more energy!

By 3.8 billion ybp, life clearly had gained a permanent foothold. The first microorganisms appeared as life transformed from a semiorganized set of chemicals and reactions to a true cellular form. By 3.5 billion ybp, microbial cells were abundant on Earth, as is evident from fossilized stromatolites containing cyanobacteria-like structures (Figure 1.13).

Given that multicellular algae and marine invertebrates are not evident in the fossil record until 0.5 billion ybp, it appears that microbial life ruled Earth for over 3(.5) billion years. Only during the last 500 million years has Earth seen the rise of plants and animals! Some microbial fossil records do exist, largely in fossilized mats discovered in Australia.

PPT: So how did the first microbial life arise?

In the 1950s, a grad student named Stanley Miller worked with his mentor, Harold Urey, to simulate the "spark" that might have started forming organic molecules from the primordial soup.

Vaccination against smallpox was occasionally practiced in eighteenth-century Europe, but it was the famous experiment of English physician Edward Jenner in 1796 that popularized the procedure.

Jenner used material from a cowpox infection of a milkmaid to inoculate a boy, who was later shown to be immune to smallpox (Figure 1.31). We now know that cowpox virus is closely related to the smallpox virus, explaining why exposure to it generated immunity to smallpox. Thanks to the smallpox vaccine, in fact, no naturally occurring cases of smallpox have occurred since 1977. In one of the greatest achievements in medical history, we have eliminated this scourge from the face of Earth. Vaccines also have had an enormous impact in reducing the sickness and death associated with infectious diseases. Vaccination involves exposing a person to an inactivated or weakened version of a microbe, or even just a part of the microbe, to create immunity to a disease.

Pasteur added nutrient broths to swan-necked flasks and then boiled the broths to kill any contaminating microorganisms. He then observed the broths for signs of microbial growth (Figure 1.26). With this approach, Louis Pasteur reasoned, outside air could enter the flask. Bacteria present in the outside air, though, would become trapped in the neck of the flask, never coming in contact with the sterile broth. No bacteria, he hypothesized, would grow. If the flask were tilted such that the broth traveled to the neck of the flask and then returned to the upright position, however, bacteria trapped in the neck would flow back into the nutrient broth and growth would occur. In other words, microbial life in the broth could result only from microbial life present in the neck of the flask; it did not arise spontaneously. Make sure you understand how Pasteur disproved spontaneous generation. What is he has used regular shaped flasks? What did Leuwenhoek do?

Louis Pasteur performed a simple yet elegant experiment to disprove spontaneous generation theory in the late 1800s. About 200 years after van Leeuwenhoek's first observations of microbes (and just 15 years after Pasteur showed that microorganisms do not arise by spontaneous generation)

All cells are built from

Macromolecules

Macromolecules

Make up over 90% of a cell's dry weight, or the weight obtained after the removal of all water.

As we mentioned in the previous section, the evolution of photosynthesis resulted in the increased level of atmospheric oxygen that makes our existence possible. In later chapters, we will see that microbes affect biogeochemical cycling of many other chemicals, from nitrogen to carbon to phosphorus. They interact not only with chemicals, but also with each other and with various macroscopic organisms.

Microbes have been intimately involved in modulating conditions within the biosphere, those regions of Earth that can support life. Not only did microorganisms, through photosynthesis, create the oxygen-rich atmosphere on which most life on Earth relies, but they are also involved in biogeochemical cycling, the transitioning of various chemicals between organic and inorganic forms. The amount of carbon contained within living bacteria on Earth, for instance, is estimated to be nearly as great as the amount of carbon in all the multicellular organisms combined. Photosynthetic cyanobacteria convert CO2 from the atmosphere into organic molecules. Microbial metabolism ultimately converts much of this organic carbon back into CO2. As we saw in Section 1.1, nucleic acids and polypeptides, two important categories of cellular macromolecules, contain nitrogen. Only certain types of bacteria and archaea can convert nitrogen gas (N2) from the atmosphere into forms that can be readily used by other organisms to form these molecules. This nitrogen fixation is accomplished by both free-living bacteria and bacteria living in symbiotic associations with plants (Figure 1.24).

What changed the O2 and CO2 concentrations so dramatically since life began?

Microbial activities over the past 4 billion years are part of the answer.

How did complex cells arise?

Most biologists now agree that mitochondria and chloroplasts, two of the most distinctive organelles in eukaryal cells (Figure 1.16), are derived from bacterial cells through a process known as "endosymbiosis." What is the endosymbiotic theory and what evidence supports this? When/how did eukaryotes appear? Endosymbiotic theory: Primitive prokaryotic microbes ingested other microbes, starting a symbiotic relationship, forming the first basic eukaryotes. -Ingested microbes that could use oxygen for a respiratory process to produce chemical energy became mitochondria -Ingested microbes that could fix carbon dioxide into organic molekcules using light energy became chloroplasts.

*4 major types of macromolecules (KNOW examples of each)

Polypeptides, nucleic acids, lipids, polysaccharides

*Does this list represent a complete description of what it means to be alive? (know the arguments for viruses. Are viruses living by the traditional standards of a living organism?)

Probably not. It's easy to come up with situations that challenge these criteria. Consider the curious case of bacterial endospores, specialized, metabolically inert cells produced by some bacterial species under highly stressful conditions. After shutting down metabolism, growth, and reproduction, endospores can remain dormant for long periods of time, even thousands of years, awaiting a favorable environment to germinate. Is an endospore alive during this state of suspended animation? These spores have all the components of living cells and, when conditions are appropriate, they will again develop into cells that meet the criteria listed above. What about Nanoarchaeum equitans, an archaeon that we will explore in Chapter 4? Apparently, it can survive only when in contact with a host cell. As we will see later in this section, viruses—subcellular microbes—represent an even more interesting anomaly to the standard definition of life. These microbes replicate and evolve. We could argue that they respond to external stimuli. Does the presence of these properties make them alive? Most likely, our definition of life should be applied holistically; an organism may not exhibit all of these traits at all times.

In 1868, two centuries after van Leeuwenhoek's discovery of microbial life, German biologist Ernst Haeckel

Proposed at third fundamental group, or kingdom, Protista, for microscopic life-forms.

In 1938, Hebert Copeland suggested that microorganisms should actually be divided into two kingdoms,

Protista and Bacteria Therefore, recognized the difference between eukaryotic and prokaryotic cells

These polymers, as we noted, contain information and carry out cellular functions. Some researchers, including Carl Woese, have suggested that information was initially stored in

RNA molecules, ribozymes, can catalyze chemical reactions, much like the protein-based enzymes with which we are more familiar. Early in the history of life, then, RNA may have had dual functions, serving as the primary informational molecule and catalyzing important reactions.

Conclusion Microbiology is a very diverse field, with many achievements already made and many more possible. Of all of the microbes we can grow in the lab, it's estimated there are many more that can't be grown. Coming chapters will focus on what we know and can prove- but there is much yet to be discovered in this field!

Table 1.4 Selected advances in microbiology

Plague is caused by the bacterium Yersinia pestis, which infects rodents and humans and is transmitted between them by fleas (Figure 1.29).

Some microbial diseases have had a profound impact on humanity- plague, for instance.

Archaebacteria

Strange microorganism found primarily in marginal environments such as anoxia sediments, hyper saline ponds, and hot springs. Produced methane

Photosynthesis and Respiration *What is a heterotroph and an autotroph?

This metabolic diversity allows microorganisms to inhabit a wide range of habitats. Because different microorganisms can utilize various nutrients, they can exist in environments that may be uninhabitable by other organism heterotrophs or "other feeders": ingest organic molecules autotrophs or "self feeders": can produce their own organic molecules from an inorganic carbon source. ex: plants

- are not alive -do not replicate outside of a host cell -(usually) have little to no biochemical activity outside of a host cell - inert and non reactive outside of a host cell -too small to be seen with the naked eye -require host cells for replication *- infect all cellular forms of life. They replicate in various ways, but all depend on using host cell machinery for their replication. This makes them obligate intracellular parasites. We will examine viral replication in Section 9.3.

Virus - an isolated virus has no metabolism- it takes up no nutrients and extracts no energy from its environment - do not respond to stimuli, except perhaps when they bind to receptors on a new host cell -do not maintain internal homeostasis -new virus particles are only assembled after the genetic material has been replicated and the host cell has synthesized new viral proteins

*The Evolution of Life on Earth Have a basic time line on when life first appeared, what was the atmosphere like and what was it's structure.

When Earth formed approximately 4.5 billion years ago (abbreviated ybp, for years before present), it was a hot and sterile place. Oceans of liquid water formed around 4 billion ybp, once the crust and atmosphere had cooled sufficiently for liquid water to condense (Figure 1.12). PPT: What do we know about the physiology, genetics, and cultivation of microbes? -The very early environment on Earth was drastically different than it is today. -There was little oxygen in the atmosphere, and the surface of the planet was a soup of chemicals in liquid form. -This early atmosphere and environment led to the initial synthesis of the first forms of macromolecules (and their use in primitive single-celled life).

Characteristics of the Three Domains

Where is DNA found? What are the different composition of cell walls? (linkage AND sugars!) that make them different from each other. RARE is like unicorns. Unless we discuss the unicorn, don't spend time memorizing this as a difference. So instead make it simple- bacteria do not have membrane organelles

"small subunit (SSU) rRNA" molecules

are critical in the ribosome, helping to bring together the ribosomal structure and interacting with messenger RNA. Not only are ribosomal RNAs universally distributed, but they also have the same function in all cells.

Microorganisms

are microscopic forms of life- organisms that are too small to be seen with the unaided eye

polysaccharides

are polymers of monosaccharides, or sugars. These molecules are composed entirely of carbon, hydrogen, and oxygen, with the general formula of Cm(H2O)n. Some polysaccharides serve as energy storage molecules. Starch and glycogen, for instance, are both polymers of the monosaccharide glucose (C6H12O6). Other polysaccharides serve as structural molecules. Cellulose, the primary structural component of plant cell walls, also is a polymer of glucose monomers. Chitin, the primary structural component of fungal cell walls, consists of a derivative of glucose: N-acetylglucosamine. Many bacterial and archaeal cells use other polysaccharides for their cell walls.

In fact, comparisons of DNA sequences for the small ribosomal subunit are how we can break life into three large groups known as

domains

lipids

hydrophobic hydrocarbon molecules, represent another important class of macromolecules. The primary role of lipids in most cells is to form the foundation of the plasma membrane, a barrier surrounding the cell that, quite simply, separates inside from outside. This membrane restricts the movement of materials into and out of the cell, thereby allowing the cell to capture and concentrate nutrients for metabolism and growth, and prevent the products of metabolism from escaping (Figure 1.6).

Lynn Margulis, a biologist who worked at the University of Massachusetts-Amherst, long championed

endosymbiosis as a mechanism for the origins of mitochondria and chloroplasts. Mitochondria probably were added first to a developing eukaryal cell; they are present in most, but not all, modern eukarya. We can imagine that the endosymbiont provided the host with extra ATP. In return, the host provided the endosymbiont with nutrients and a safe place to live. The extra ATP ultimately allowed for an increase in cell size, and for multicellular arrangements. Chloroplasts probably were added later, leading to the evolution of algae and plants. A bacterium capable of photosynthesis, the ability to harvest the energy present in sunlight to produce organic molecules, would provide a host with a new energy source and allow the host to expand into new habitats. Regardless, photosynthesis brought solar power to eukaryal cells. Algae and plants, as a result, have been phenomenally successful, and now account for a major fraction of the biomass on land (plants) and sea (algae). Once these mitochondria and chloroplasts became permanently established in eukaryal hosts, their own genomes degenerated until only a few essential genes were left. By 500 million years ago, multicellular eukarya had begun to dominate the macroscopic landscape of life on Earth. Microbes had set the stage for them PPT -So, one idea of how microbial life aros on Earth is: -Early conditions formed RNA and micelles. -Thsee came together into a primitive cell using RNA for storing genetic info and coding -Primitive cells eventually changed from using RNA to DNA instead for storing their genetic information

Regardless of how organisms acquire organic molecules, all living organisms also need a mechanism of oxidizing those molecules to generate ATP. One of the simplest means of acquiring energy from organic molecules is

glycolysis, the reaction in which glucose is converted to pyruvate, with the subsequent generation of two ATP molecules: Glucose + 2 ADP + 2 Pi + 2 NAD+ → 2 Pyruvate + 2 ATP + 2 NADH + 2 H+

Without mitochondria to power cellular metabolism efficiently,

large multicellular eukaryal organisms would never have appeared

critical as storehouses of genetic information

nucleic acids (DNA/RNA)

nucleic acids

polymers of nucleotides, make up most of the remainder of the macromolecules within a cell. This category includes deoxyribonucleic acid (DNA), a polymer of deoxyribonucleotides, and ribonucleic acid (RNA), a polymer of ribonucleotides. Individual nucleotides are composed of a sugar molecule (deoxyribose in DNA, ribose in RNA), a phosphate moiety, and one of four nitrogen-containing bases (abbreviated A, T, C, and G in DNA; A, U, C, and G in RNA). In all cells, DNA constitutes the main informational molecule, containing instructions for the production of RNA molecules. These RNA molecules fulfill numerous functions within the cell, most of which are associated with protein production.

these macromolecules help the cell control the movement of materials into and out of the cell

polypeptides and polysaccharides with are associated with the membrane polysaccharides and polypeptides can be embedded in a lipid bilayer, forming a cell's plasma membrane. This separates the external environment from the interior of the cell.

two types of cells

prokaryotes and eukaryotes The term eukaryote is derived from Greek roots meaning "true kernel," in contrast to the term prokaryote, which translates as "before kernel." The "kernel" refers to the membrane-enclosed nucleus of eukaryal cells. The nucleus contains the genetic material of the eukaryal cell during most of the cell cycle Prokaryotes and eukaryotes also differ strikingly in the organization of their genetic material. Prokaryotes usually contain a single circular chromosomal DNA molecule. In contrast, eukaryotes usually contain multiple linear DNA molecules. At some point in their life cycle, most eukaryal organisms have two copies, or a 2n complement, of their genetic material. Most prokaryotes, in contrast, possess a single copy of their genetic material.

Research on the biology of microbial cells has virtually unlimited practical applications. For example, to understand how some antimicrobial drugs work against their microbial targets while sparing host cells, we need to understand differences in structure between bacterial and eukaryal cells, or perhaps between fungal and human cells. Paul Ehrlich, a towering figure in the history of medicine and immunology, was among the first to

recognize that such differences had medical implications. From his experience in the field of histology, Ehrlich was familiar with dyes that differentially stained bacterial and human cells. Based on this observation, he speculated that molecular "magic bullets" that specifically target microbial invaders were feasible. He had little knowledge of the actual structures present on or in cells of any kind, but this concept that certain drugs may adversely affect specific types of cells, while sparing other types of cells, remains at the heart of our drug development initiatives today

What is microbiology?

the study of microbes