The Cell Flashcards
Facultative anaerobes
Bacteria that can toggle between metabolic processes, using oxygen for aerobic metabolism when its present and switching to anaerobic when its not
What are centrosomes?
o Centrosomes are organelles responsible for the organization and nucleation of microtubules in animal cells and also regulate the cell cycle
o Serves as a microtubule organizing center during cell division
How can epithelial cells be classified according to the number of layers they have?
o Simple epithelia have ONE layer of cells
o Stratified epithelia have MULTIPLE layers
o Pseudostratified epithelia APPEAR to have multiple layers due to differences in cell height, but are actually only ONE layer
What is the Golgi Apparatus?
o Consists of stacked membrane-bound sacs
o Materials from the ER are transferred to the Golgi apparatus in vesicles
o Once in the Golgi apparatus, theses cellular products can be modified by the addition of various groups, including carbohydrates, phosphates, and sulfates
o May also modify cellular products through the introduction of signal sequences, which direct the delivery of the product to a specific cellular location
What happens in the SMOOTH ER?
Smooth ER is devoted almost exclusively to the manufacture of lipids and in some cases to the metabolism of them and associated products.
Smooth ER is abundant in the liver, where it contains enzymes that metabolize various lipid-soluble compounds. These detoxifying enzymes inactivate a number of potentially harmful drugs (e.g., phenobarbital) by converting them to water-soluble compounds that can be eliminated from the body in the urine. The smooth ER is thus involved in multiple aspects of the metabolism of lipids and lipid-soluble compounds.
How are mitochondria semi-autonomous? How did this likely come about?
o Mitochondria contain some of their own genes and replicate independently of the nucleus via BINARY FISSION
• They have their own DNA which can replicate INDEPENDENTLY; the mitochondrial DNA produces its own mRNA, tRNA and rRNA
• Keeping these genes that are central to the functioning of the mitochondria in the mitochondria gives the cell a way to individually control the organelle—this local control means that cells can more quickly and efficiently regulate energy production moment-to-moment
• Has a CIRCULAR genome
o Mitochondria are believed to have evolved from an anaerobic prokaryote engulfing an aerobic prokaryote and establishing a symbiotic relationship
The significance of the plasma membrane in prokaryotes is that it?
- it selectively allows some molecules to pass into the
- it prevents movement of molecules out of the organism
- it is the site of protein synthesis–
In bacterial cells, ribosomes are packed into the cytoplasmic matrix and also loosely attached to the plasma membrane.
What are the two major functions of the nucleus?
o The nucleus contains all the genetic material (DNA), and thus stores the cell’s hereditary material
• The genetic material contains coding regions called genes—the linear DNA is wound around organizing proteins known as HISTONES, and is then further wound into linear strands called chromosomes
o The nucleus coordinates the cell’s activities, which include GROWTH, metabolism, protein synthesis, and reproduction (cell division)
How do proteins enter the rough ER?
Proteins can be translocated into the ER either during their synthesis on membrane-bound ribosomes (cotranslational translocation) or after their translation has been completed on free ribosomes in the cytosol (posttranslational translocation). In mammalian cells, most proteins enter the ER co-translationally
Pathogenic Bacteria
Although the vast majority of bacteria are harmless or beneficial, a relatively small list of pathogenic bacteria can cause infectious diseases. Pathogenic bacteria may live intracellularly or extracellularly. For example, Chlamydia trachomatis, a common sexually transmitted infection, lives inside cells of the reproductive tract; Clostridium tetani, the cause of tetanus, lives outside of cells and produces toxins that enter the bloodstream.
What is EPITHELIAL TISSUE?
o Epithelial tissues cover the BODY and lines its cavities, providing a means for protection against pathogen invasion and desiccation
• To remain ONE cohesive unit, epithelial cells are tightly joined to each other and to an underlying layer of connective tissue known as the BASEMENT MEMBRANE
o In certain organs, epithelial cells are involved in ABSORPTION, SECRETION, and SENSATION
o All GLANDS are made up of epithelial cells
o Epithelial layers contain NO BLOOD VESSELS, so they must receive nourishment via DIFFUSION of substances from the underlying connective tissue through the basement membrane
Why are archaea notable for their ability to use alternative sources of energy?
Some archaea are PHOTOSYNTHETIC while others are CHEMOSYNTHETIC, meaning they are able to generate energy from INORGANIC COMPOUNDS, including sulfur and nitrogen-based compounds, like ammonia
What kind of fatty acid tail would contribute MOST to the stability of the cell membrane of a thermophilic bacterium?
o Thermophile: an organism that thrives at relatively HIGH temperatures
o In order to tolerate high temperatures, a thermophilic bacterium must have fatty acid tails that decrease the fluidity of its cell membrane
o Saturated fatty acid tails (no double bonds) have STRONGER Van der Waals interactions and thereby DECREASE the fluidity of cell membranes
o Longer fatty acid tails have greater SURFACE AREA for Van der Waals interactions, so they also decrease the fluidity of cell membranes
Why are capsules important in colonies?
Many prokaryotes secrete another sticky protective layer of polysaccharide or protein, the capsule, outside the cell wall. They glue together the cells of those prokaryotes that live as colonies.
How are new virions created?
When viruses infect a cell, they use the cell’s ribosomes, tRNA, amino acids and enzymes to translate the viral genome into proteins; most of these proteins are STRUCTURAL CAPSID PROTEINS which are then used to create new virions in the cytoplasm of the host cell. Once the viral genome has been replicated ,it can be packaged within the capsid.
The VIRAL GENOME must be returned to its ORIGINAL FORM before packaging.
A single virus may create hundreds or thousands of virions within a single host cell
What are colonies?
“Prokaryotes are also single-celled organisms, meaning that each cell must be able to perform all of the functions necessary for life on its own. However, prokaryotes may live in colonies with other cells and may signal these cells to share information about the environment.”
Some species may aggregate transiently or form true colonies, showing division of labor between specialized cell types.
While prokaryotes are considered strictly unicellular, most can form stable aggregate communities. When such communities are encased in a stabilizing polymer matrix (“slime”), they may be called “biofilms”. Cells in biofilms often show distinct patterns of gene expression (phenotypic differentiation) in time and space. Also, as with multicellular eukaryotes, these changes in expression often appear to result from cell-to-cell signaling, a phenomenon known as quorum sensing.
What are PRIONS?
Prions are INFECTIOUS PROTEINS and are thus, NON-LIVING THINGS
Why is antibiotic compliance a big problem?
Many patients fail to complete an entire course of antibiotics, often discontinuing the treatment because they feel better. Unfortunately, this breeds antibiotic resistance by killing off the bacteria that are nonresistant and leaving behind bacteria that are more resistant.
These resistant bacteria then reproduce, resulting in recurrence of the infection. Over time, this practice has led to bacteria that are resistant to multiple antibiotics, making common infections more difficult to treat.
Why is bacterial genetic recombination important, and what are the three kinds of recombination?
Genetic recombination helps increase bacterial diversity and thus permits EVOLUTION of bacterial species over time.
Recombination processes include: TRANSFORMATION, CONJUGATION, and TRANSDUCTION
What is BOILING POINT ELEVATION?
Boiling-point elevation describes the phenomenon that the boiling point of a liquid (a solvent) will be higher when another compound is added, meaning that a solution has a higher boiling point than a pure solvent. This happens whenever a non-volatile solute, such as a salt, is added to a pure solvent, such as water.
A solution will boil at a higher temperature than the pure solvent.
What does it mean for a symbiotic relationship to be obligate as opposed to facultative?
Some symbiotic relationships are obligate, meaning that both symbionts entirely depend on each other for survival. For example, many lichens consist of fungal and photosynthetic symbionts that cannot live on their own.
Others are facultative (optional): they can, but do not have to live with the other organism.
What is the purpose of gas vesicles in bacteria?
Gas vesicles are found in Cyanobacteria, which are photosynthetic and live in aquatic systems. In these lakes and oceans, the Cyanonbacteria want to control their position in the water column to obtain the optimum amount of light and nutrients.
Gas vesicles are aggregates of hollow cylindrical structures composed of rigid proteins. They are impermeable to water, but permeable to gas. The amount of gas in the vacuole is under the control of the microorganism.
Gas vesicles regulate the buoancy of the microbes by changing the amount of gas contained within them. Release of gas from the vesicle causes the bacteria to fall in the water column, while filling the vesicle with gas increases their height in the water.
How does actin polymerize?
The first step in actin polymerization (called nucleation) is the formation of a small aggregate consisting of three actin monomers. Actin filaments are then able to grow by the reversible addition of monomers to both ends, but one end (the plus end) elongates five to ten times faster than the minus end. The actin monomers also bind ATP, which is hydrolyzed to ADP following filament assembly. Although ATP is not required for polymerization, actin monomers to which ATP is bound polymerize more readily than those to which ADP is bound. ATP binding and hydrolysis play a key role in regulating the assembly and dynamic behavior of actin filaments.
What is autolysis?
o Autolysis, commonly known as SELF-digestion, refers to the destruction of a cell through the action of its OWN enzymes, especially those released by lysosomes
o When lysosomes release their hydrolytic enzymes, it results in apoptosis→the released enzymes DIRECTLY lead to the degradation of cellular components
What are the dynamic properties of actin filaments? Does polymerization require energy?
- assemble (polymerize) and disassemble (depolymerize) by noncovalent, reversible, additions/loss of actin monomers at the ends of filaments
- polymerization requires energy by ATP hydrolysis, releasing energy to the filaments that creates a type of dynamic activity called treadmilling
What is cytoplasmic streaming?
Cytoplasmic streaming is the directed flow of cytosol (the liquid component of the cytoplasm) and organelles around fungal and plant cells. This movement aids in the delivery of organelles, nutrients, metabolites, genetic information, and other materials to all parts of the cell. Cytoplasmic streaming occurs as myosin-coated organelles move along actin filaments in the cytoskeleton of the cell, causing the cytosol to move as well.
What are the four basic tenets of cell theory?
- All living things are composed of cells
- The cell is the basic functional unit of life
- Cells arise only from pre-existing cells
- Cells carry genetic information only in the form of DNA→genetic material is passed from parent to daughter cell
How and why does the lysogenic cycle revert to a lytic cycle?
Environmental factors (radiation, light, or chemicals) can cause the provirus to LEAVE the genome and revert to a lytic cycle. The prophage exits the bacterial chromosome to initiate the lytic cycle. The virus remains dormant until host conditions deteriorate, perhaps due to depletion of nutrients; then, the endogenous phages (known as prophages) become active. At this point they initiate the reproductive cycle, resulting in lysis of the host cell. As the lysogenic cycle allows the host cell to continue to survive and reproduce, the virus is reproduced in all of the cell’s offspring.
What are the two “faces” of the Golgi Apparatus?
Each Golgi stack has two distinct ends, or faces. The cis face of a Golgi stack is the end of the organelle where substances enter from the endoplasmic reticulum for processing, while the trans face is where they exit in the form of smaller detached vesicles. Consequently, the cis face is found near the endoplasmic reticulum, from whence most of the material it receives comes, and the trans face is positioned near the plasma membrane of the cell, to where many of the substances it modifies are shipped. The chemical make-up of each face is different and the enzymes contained in the lumens (inner open spaces) of the cisternae between the faces are distinctive.
Proteins, carbohydrates, phospholipids, and other molecules formed in the endoplasmic reticulum are transported to the Golgi apparatus to be biochemically modified during their transition from the cis to the trans poles of the complex. Enzymes present in the Golgi lumen modify the carbohydrate (or sugar) portion of glycoproteins by adding or subtracting individual sugar monomers. In addition, the Golgi apparatus manufactures a variety of macromolecules on its own, including a variety of polysaccharides.
What is an HFR (high frequency recombination) bacterial cell?
A high-frequency recombination cell (Hfr cell) (also called an Hfr strain) is a bacterium with a conjugative plasmid (for example, the F-factor) integrated into its chromosomal DNA. The integration of the plasmid into the cell’s chromosome is through homologous recombination.
What role do bacteria play in producing vitamins?
Bacteria perform ESSENTIAL functions for human beings, including the production of VITAMIN K in the intestine. Vitamin K is required for the production of PLASMA PROTEINS necessary for blood clotting. Beneficial bacteria in the human intestine produce about 75% of the vitamin K the body absorbs each day, with the other 25% coming from dietary sources.
Newborn infants are not yet COLONIZED by bacteria and so cannot produce vitamin K and therefore lack CLOTTING factors, putting them at risk for hemorrhage (bleeding). When babies are born they are given injections of vitamin K to aid in production of clotting factors until they have been colonized by bacteria.
What is the difference between prokaryotic and eukaryotic cells?
o Eukaryotic cells contain a true nucleus enclosed in a membrane, while prokaryotic cells do not contain a nucleus
o Prokaryotic cells are SMALLER and simpler than eukaryotic
What role do mitochondria play in apoptosis?
o The mitochondria are capable of killing the cell by release of enzymes from the ETC; this release kick-starts a process known as APOPTOSIS, or programmed cell death
o Mitochondrial outer membrane permeabilization is often required for activation of the caspase proteases that cause apoptotic cell death; caspase proteases dismantle cells and signal efficient phagocytosis of cell corpses
What are some prion diseases?
Bovine Spongiform Encephalopathy (BSE/MAD COW)
Creutzfeldt-Jakob Disease, Classic (CJD)
Familial Fatal Insomnia
Historically, Archaea were considered extremophiles. What does this mean?
Extremophiles are organisms that thrive in physically or geochemically EXTREME conditions that are detrimental to MOST life on earth–these organisms are most commonly found in HARSH environments with extremely high temperatures, high salinity, or NO LIGHT
What are the three domains into which all life is classified?
BACTERIA
ARCHAEA
EUKARYA
What is the DEATH PHASE in bacterial growth?
After the bacteria have exceeded the ability of the environment to support the number of bacteria, a death phase occurs as resources in the environment have been depleted.
At death phase (decline phase), bacteria die. This could be caused by lack of nutrients, environmental temperature above or below the tolerance band for the species, or other injurious conditions.
Which kind of viruses live longer, enveloped or non-enveloped? WHY?
The envelope is very sensitive to heat, detergents, and desiccation, making enveloped viruses easier to kill.
Viruses that do not have an envelope are more resistant to sterilization and are likely to persist on surfaces for an extended period of time.
Why are retroviruses so dangerous?
Because the integration of the genetic material of the virus into the HOST CELLS GENOME allows for the cell to be infected INDEFINITELY–the only way to cure the infection is to kill the infected cell itself.
What comprises microtubules?
o Microtubules are HOLLOW polymers of tubulin proteins; they are cylindrical tubes built by the assembly of dimers of alpha tubulin and beta tubulin
*Microtubules are the largest scaffold proteins with a diameter of 25 nm
o Microtubules radiate throughout the cell, providing the primary pathway along which motor proteins like KINESIN and DYNEIN carry vesicles
• Motor proteins like kinesin and dynein are classic examples of NONENZYMATIC proteins, along with binding proteins, cell adhesion molecules, IG, and ion channels
• Motor proteins often travel along cytoskeletal structures to accomplish their function
o Microtubules act as a scaffold to determine CELL SHAPE and provide a set of tracks for cell organelles and vesicles to move on
o When arranged in geometric patterns inside flagella and cilia, they are used for locomotion
What composes the sugar component of peptidoglycan?
The sugar component consists of alternating residues of β-(1,4) linked N-acetylglucosamine and N-acetylmuramic acid. Attached to the N-acetylmuramic acid is a peptide chain of three to five amino acids. The peptide chain can be cross-linked to the peptide chain of another strand forming the 3D mesh-like layer
What composes the membrane of eukaryotic cells?
o Membranes of eukaryotic cells consists of a PHOSPHOLIPID BILAYER
• Surfaces are HYDROPHILIC (water-lovng)→can electrostatically interact with the aqueous environment inside & outside the cell
• Inner portions are HYDROPHOBIC→hydrophobicity helps provide a highly selective BARRIER between the interior of the cell and the EXTERNAL environment
What is the serial endosymbiosis theory?
o In this theory, a bacterium (which is aerobic) is engulfed by an ancestral eukaryote (anaerobic), and multiplies within it (primitive mitochondria formed)
o CHLOROPLASTS: engulfed cyanobacterium becomes an endosymbiont and multiplies; new cells can make ATP using energy from SUNLIGHT
o The prisoner prokaryotes might have provided crucial nutrients (in the case of the primitive chloroplast) or helped to exploit oxygen for extracting energy (in the case of the primitive mitochondrion); the prokaryotes, in turn, would have received PROTECTION and a steady environment in which to live
What is the role of the nuclear envelope in regards to transcription and translation?
o It separates the nucleus from the cytoplasm and thus allows for COMPARTMENTALIZATION of transcription (formation of hnRNA from TNA, which is then processed to form mRNA), and TRANSLATION (mRNA made into a peptide/protein)
Which intermolecular process primarily drives the formation of a bilayer when phospholipids are added to water?
o Lipids cause water to arrange in an ordered, unfavorable cage-like structure. Forcing lipids into a bilayer reduces this effect
• The formation of a phospholipid bilayer is PRIMARILY driven by an increase in entropy of surrounding water molecules
• Lipids cause water to arrange in an ordered, unfavorable, cage-like structure called a CLATHRATE cage
o Several intermolecular forces contribute to and subtract from the favorability of a phospholipid bilayer
• These include STRONGER Van der Waals forces between hydrophobic phospholipid tails (favorable), INCREAED entropy of water molecules (favorable), decreased entropy of phospholipid molecules (unfavorable), and stabilization by hydrogen bonds (favorable)
• Systems tend towards increased entropy; a disordered state is MORE favorable than an ordered state
*Phospholipids are amphipathic molecules with two hydrophobic fatty acids and a hydrophilic phosphate-containing group linked to glycerol. When placed in an aqueous solution, water forms a shell around the hydrophobic lipid, a situation that not only prevents water from making hydrogen bonds with other water molecules, but also reduces freedom of movement, making the water molecules more ordered.
How are Archaea similar to eukaryotes?
Both eukaryotes and Archaea start TRANSLATION with METHIONINE, contain RNA POLYMERASES, and associate their DNA with HISTONES. Due to the similarities of Archaea with eukaryotes, it is believed that hey share a COMMON ORIGIN
How do viroids cause disease/problems?
Viroids can BIND to a large number of RNA sequences and will silence genes in the plant genome. This prevents synthesis of necessary proteins and can subsequently cause METABOLIC and STRUCTURAL DERANGEMENTS in the plant cell.
During conjugation, what happens in regards to the F factor for E. Coli bacteria?
The (F+) cell replicates its F factor and donates the copy to the recipient, converting it from an (F-) cell to an (F+) cell. This process enables the cell obtaining the new plasmid (in this case the F plasmid) to then transfer copies to OTHER CELLS.
This method of genetic recombination allows for RAPID acquisition of antibiotic resistance or virulence factors throughout a colony because other plasmids can also be passed through the conjugation bridge.
What are the relative sizes of viruses, prokaryotes and eukryotes?
Viruses may be as small 20nm or as large as 300nm.
Prokaryotes are 1-10 um, and eukaryotes are about ten times larger.
Transformation (bacterial genetic recombination)
Results from the integration of foreign genetic material into the host GENOME.
Genetic material often comes from other bacteria that, upon lysing, spill their contents in the vicinity of a bacterium capable of transformation.
Many gram-negative RODS are capable of transformation.
Pathogens
A bacterium, virus, or other microorganism that can cause disease.
In sequential order, what are the phases of bacterial growth?
- LAG PHASE
- EXPONENTIAL PHASE/LOG PHASE
- STATIONARY PHASE
- DEATH PHASE
What is the STATIONARY PHASE in bacterial growth?
As the number of bacteria in the colony grows, resources are often reduced. The reduction of resources slows reproduction, and the stationary phase results.
The stationary phase is often due to a growth-limiting factor such as the depletion of an essential nutrient, and/or the formation of an inhibitory product such as an organic acid. Stationary phase results from a situation in which growth rate and death rate are equal. The number of new cells created is limited by the growth factor and as a result the rate of cell growth matches the rate of cell death. The result is a “smooth,” horizontal linear part of the curve during the stationary phase.
Conjugation (bacterial genetic recombination). How does this process work?
The bacterial form of MATING (sexual reproduction).
Two cells form a CONJUGATION BRIDGE between them that allows the transfer of genetic material. The transfer is UNIDIRECTIONAL and goes from the donor male (+) to the recipient female (-).
What is the difference between saturated and unsaturated fatty acids?
o Saturated fatty aids have NO carbon-carbon double bonds (they are SATURATED with HYDROGEN)
o Unsaturated fatty acids have one to three double bonds along the backbone carbon chain—these double bonds introduce KINKS in the carbon chain which have important consequences on the fluid nature of the lipid membranes (increase fluidity)
o Unsaturated fatty acids have LOWER melting points than saturated fatty acids
What happens to centrioles during MITOSIS?
o During mitosis, the centrioles migrate to opposite poles of the dividing cell and organize the MITOTIC SPINDLE
• Basically, the centrosomes move to opposite sides of the cell and begin the initiation of several types of microtubules, some that anchor the centrosomes in the cell at a specific position, and thus positioning the mitotic spindle apparatus
• The second type of microtubule, the KINETOCHORE microtubule, attaches to the kinetochore, which is a protein found on the centromere of the sister chromatid
o The microtubules emanating from the centrioles attach to the chromosome via complexes called KINETOCHORES and can exert force on the sister CHROMATIDS, pulling them apart
o Basically, this entire apparatus of the centrosome and centriole, as well as the microtubules emanating from these structures, comprise the mitotic spindle
What is hnRNA? How is this term distinct from pre-mRNA?
o hnRNA: heterogeneous nuclear RNA→it is the ORIGINAL product of transcription, so no post-transcriptional modifications have occurred→not all of hnRNA becomes an mRNA product
o Pre-mRNA is an incompletely processed single strand of mRNA synthesized from a DNA template; all pre-mRNAs are hnRNAs but NOT all hnRNAs are pre-MRNAs
o HnRNAs are all of the RNA in the nucleus while pre-mRNAs are those RNAs that will become mRNAs after post-transcriptional processing
What are microfilaments?
o Microfilaments are made up of solid polymerized rods of actin
• They are resistant to COMPRESSION and FRACTURE, and thus provide protection for the cell—they form a band beneath the plasma membrane which provides mechanical strength to the cell
•Actin filaments can use ATP to generate force for movement by interacting with MYOSIN (i.e. during muscle contraction)
o Microfilaments can also carry out CELLULAR MOVEMENTS including gliding, contraction, cytoplasmic streaming, and cytokinesis
*Microfilaments are solid rods made of a protein known as actin. When it is first produced by the cell, actin appears in a globular form (G-actin). In microfilaments, however, which are also often referred to as actin filaments, long polymerized chains of the molecules are intertwined in a helix, creating a filamentous form of the protein (F-actin). All of the subunits that compose a microfilament are connected in such a way that they have the same orientation. Due to this fact, each microfilament exhibits polarity, the two ends of the filament being distinctly different. This polarity affects the growth rate of microfilaments, one end (termed the plus end) typically assembling and disassembling faster than the other (the minus end).
*Also have role in extension of pseudopods in amoebae
Why are viruses not quite in accordance with cell theory?
o Viruses violate the third and fourth tenets of cell theory: that cells come from pre-existing cells, and that genetic information in the form of DNA goes from parent to daughter cells (viruses may have RNA)
o Viruses are unable to reproduce on their own→they can only replicate by invading other organisms and taking over that cells machinery
What is CONNECTIVE TISSUE?
o Connective tissue supports the body and provides a framework for the epithelial cells to carry out their functions
o Connective tissues are the main contributors to the STROMA or SUPPORT STRUCTURE
o Bone, cartilage, tendons, ligaments, adipose tissue, lymph and blood are all examples of connective tissues
o Connective tissues develop from the MESODERM
o Most cells in connective tissues produce and secrete materials such as COLLAGEN and ELASTIN to form the extracellular matrix
• Elastin is a protein found in connective tissue that has the actual property of being ELASTIC and is responsible for allowing tissues in the body to “snap back” to their original shape after being stretched or contraction
• COLLAGEN: the main structural protein in the extracellular space in the various connective tissues in animal bodies; it is the most abundant protein in mammals
What is gram-positive bacteria?
Gram-positive cell walls contain a THICK LAYER of peptidoglycan, a polymeric substance made of amino acids and sugars.
In addition to peptidoglycan, gram-positive cell walls also contain LIPOTEICHOIC ACID–function unknown. Potentially this acid that activates the immune system of humans
What does it mean that an equilibrium exists between actin monomers and actin filaments?
Because actin polymerization is reversible, filaments can depolymerize by the dissociation of actin subunits, allowing actin filaments to be broken down when necessary. Thus, an apparent equilibrium exists between actin monomers and filaments, which is dependent on the concentration of free monomers. The rate at which actin monomers are incorporated into filaments is proportional to their concentration, so there is a critical concentration of actin monomers at which the rate of their polymerization into filaments equals the rate of dissociation. At this critical concentration, monomers and filaments are in apparent equilibrium.
What is vapor pressure LOWERING?
Vapor pressure lowering is a colligative property of solutions. The vapor pressure of a pure solvent is greater than the vapor pressure of a solution containing a non volatile liquid. This lowered vapor pressure leads to boiling point elevation.
The force that is driving the solvent molecules to the vapour phase is the difference between the entropy of the liquid and the vapour phases: when the molecule escape the liquid there is an entropy gain. Adding a non-volatile solute will increase the entropy of the liquid phase without having an effect on the entropy of the vapour phrase (given that the solute is non-volatile). This will lower the difference in entropy between the two phases, which is the driving force that make vaporisation happen, therefore there will be a lower number of solvent particles in the vapour phase and a consequent lower vapour pressure.
Another reason could be because molecules in solution, like NaCl, will break up and these ions will attract water molecules so water will be surrounding these ions or other polar molecules (like if sugar is added), so they will be less likely to escape because they are attracted to the solute.
Another reason: since some of the solute molecules will take up spaces at the surface of the liquid, this will limit the number of solvent molecules at the surface. Since only solvent molecules located at the surface can escape (evaporate), the sheer presence of the solute lowers the number of solvent molecules coming and going and therefore lowers the equilibrium vapor pressure.
In regards to osmosis, what does isotonic, hypertonic and hypotonic mean?
If the osmotic concentration of two solutions are equal, the solutions are ISOTONIC. When solutions have unequal osmotic concentrations, the solution with the higher concentration of solutes is HYPERTONIC, while the solution with the lower concentration of solutes is HYPOTONIC.
What is a lytic cycle?
In the LYTIC CYCLE, bacteriophages make MAXIMAL use of the cell’s machinery with little regard for the survival of the host cell. Once the host is SWOLLEN with new virions, the cell LYSES, and other bacteria can be infected.
Bacteria in the lytic phase are termed VIRULENT.
Why are prokaryotic cell walls so significant?
The Cell wall forms the outer barrier of the cell and serves to protect the organism from its environment. It provides STRUCTURE and CONTROLS the movement of solutes into and out of the bacterium. This allows the cell to maintain CONCENTRATION GRADIENTS relative to the environment.
The cell wall may also aid a pathogen by providing protection from a host organism’s immune system.
Transduction
A form of genetic recombination that requires a VECTOR, a virus that caries genetic material from one bacterium to another.
Viruses are OBLIGATE INTRACELLULAR PATHOGENS so they need host cell machinery to reproduce themselves; because of this, bacteriophages can trap a segment of host bacterial DNA during viral assembly. Then when that virus infects another bacterium, it can release this trapped DNA into the NEW host cell, and then that transferred DNA can integrate into the genome, giving the host new additional genes.
What are bacteriophages?
Bacteriophages are viruses that specifically target BACTERIA. They do not ENTER bacteria but rather inject their GENETIC MATERIAL, leaving the remaining structure outside the infected cell.
What are the four most common bacterial cell shapes?
The three most common bacterial cell shapes are cocci (spherical, from the Greek word for seed/berry), bacilli (rod-shaped, from the Greek word for staff), and spirilla (curved shape, from spiral), and Vibrio – comma-shaped.
What are flagella and how are they used in bacteria?
Flagella are LONG, WHIPLIKE structures that can be used for propulsion.
Bacteria may have ONE, TWO, or MANY flagella depending on the species.
They can be used to move TOWARD food or AWAY from toxins or immune cells.
