Bacteria
60 flashcards covering Bacteria for the MCAT Biology & Biochemistry section.
Bacteria are microscopic, single-celled organisms that lack a nucleus and are found almost everywhere on Earth, from soil and water to inside our bodies. They come in various shapes like rods, spheres, or spirals and reproduce rapidly through binary fission. While some bacteria cause diseases such as tuberculosis or food poisoning, others play essential roles in processes like nutrient cycling, digestion, and even biotechnology. Understanding bacteria is fundamental to biology because they represent one of the earliest forms of life and influence ecosystems, human health, and medical treatments.
On the MCAT, bacteria frequently appear in biology and biochemistry questions, often testing knowledge of their structure, metabolism, genetics, and interactions with hosts. Expect multiple-choice questions on topics like cell wall composition, antibiotic resistance, or bacterial reproduction, as well as passage-based scenarios involving pathogenicity or symbiosis. Common traps include confusing bacteria with viruses or archaea, so watch for questions that probe subtle differences in cell structure and energy sources. Focus on key concepts like Gram staining, DNA replication, and ecological roles to excel.
A concrete tip: Always review bacterial classification systems to quickly identify key features in exam questions.
Terms (60)
- 01
Bacterium
A single-celled microorganism that lacks a nucleus and membrane-bound organelles, belonging to the domain Bacteria, and can be found in diverse environments, playing roles in nutrient cycling and disease.
- 02
Prokaryotic cell
A type of cell, such as in bacteria, that lacks a true nucleus and membrane-bound organelles, with genetic material in a nucleoid region, allowing for rapid reproduction and metabolic diversity.
- 03
Peptidoglycan
A polymer in the bacterial cell wall that provides structural support and shape, composed of sugars and amino acids, and is thicker in Gram-positive bacteria, making it a target for certain antibiotics.
- 04
Gram staining
A laboratory technique used to classify bacteria based on their cell wall properties, where Gram-positive bacteria retain the crystal violet dye and appear purple, while Gram-negative bacteria do not and appear pink.
- 05
Coccus
A spherical shape of bacterial cells, which can occur singly, in pairs, chains, or clusters, influencing how the bacteria move and interact with their environment.
- 06
Bacillus
A rod-shaped bacterial cell, which allows for efficient nutrient absorption and can form endospores for survival in harsh conditions.
- 07
Spirillum
A spiral-shaped bacterium that often uses flagella for movement, enabling it to navigate through viscous environments like mucus in hosts.
- 08
Flagellum
A whip-like appendage on some bacteria that provides motility by rotating like a propeller, allowing the cell to move toward favorable conditions or away from harm.
- 09
Pili
Short, hair-like structures on bacterial surfaces that facilitate attachment to host cells or other bacteria, and in some cases, enable genetic exchange through conjugation.
- 10
Capsule
A gelatinous layer surrounding some bacterial cells that protects against phagocytosis by immune cells and helps in adhesion to surfaces.
- 11
Cell membrane in bacteria
A phospholipid bilayer in bacterial cells that regulates the passage of substances in and out, and contains proteins for transport and energy production.
- 12
Binary fission
The asexual reproduction process in bacteria where a single cell divides into two identical daughter cells after DNA replication and cell elongation.
- 13
Generation time
The time required for a bacterial population to double in number under optimal conditions, typically ranging from 20 minutes to several hours depending on the species.
- 14
Bacterial growth curve
A graphical representation of bacterial population growth over time, consisting of lag, exponential, stationary, and death phases, reflecting changes in environmental adaptation.
- 15
Lag phase
The initial stage of bacterial growth where cells adapt to new conditions by synthesizing enzymes and repairing damage, resulting in little to no increase in population.
- 16
Exponential phase
The period in bacterial growth where cells divide at the maximum rate, leading to rapid population increase, as long as nutrients are plentiful and conditions are ideal.
- 17
Stationary phase
The growth stage where the bacterial population stabilizes due to nutrient depletion or waste accumulation, with cell division balancing cell death.
- 18
Death phase
The final stage of bacterial growth where the population declines as cells die from lack of nutrients, toxic buildup, or environmental stress.
- 19
Aerobic bacteria
Bacteria that require oxygen for cellular respiration to generate energy, using it as a final electron acceptor in their metabolic pathways.
- 20
Anaerobic bacteria
Bacteria that can grow and produce energy without oxygen, either by fermentation or using other molecules as electron acceptors, and may be killed by oxygen exposure.
- 21
Fermentation pathway
A metabolic process in some bacteria that converts sugars into acids, gases, or alcohol without oxygen, allowing energy production in anaerobic conditions.
- 22
Nitrogen fixation
The biological process by which certain bacteria convert atmospheric nitrogen gas into ammonia, which can be used by plants and other organisms for growth.
- 23
Rhizobium
A genus of bacteria that forms symbiotic relationships with leguminous plants, fixing nitrogen in root nodules and aiding plant nutrition in exchange for carbohydrates.
- 24
Plasmid
A small, circular piece of DNA in bacteria separate from the chromosomal DNA, often carrying genes for antibiotic resistance or other adaptive traits.
- 25
Conjugation
A process of horizontal gene transfer in bacteria where genetic material is directly transferred between cells via a pilus, often spreading resistance genes.
- 26
Transformation
The uptake and incorporation of foreign DNA from the environment into a bacterial cell's genome, allowing for genetic variation and adaptation.
- 27
Transduction
The transfer of bacterial DNA from one cell to another by a bacteriophage virus, which can introduce new genes and contribute to bacterial evolution.
- 28
Endospore formation
A survival mechanism in some bacteria, like Bacillus, where the cell produces a dormant, resistant spore that can withstand extreme conditions until favorable ones return.
- 29
Exotoxins
Proteins secreted by certain pathogenic bacteria that can cause damage to host cells, such as by disrupting membranes or inhibiting protein synthesis.
- 30
Endotoxins
Lipopolysaccharides in the outer membrane of Gram-negative bacteria that are released upon cell death and can trigger a strong immune response, leading to fever and shock.
- 31
Virulence factors
Molecules produced by pathogenic bacteria that enable them to invade host tissues, evade the immune system, and cause disease, such as adhesins or invasins.
- 32
Antibiotic resistance mechanisms
Strategies bacteria use to survive antibiotics, including enzymatic breakdown of the drug, efflux pumps to expel it, or target modification to prevent binding.
- 33
Quorum sensing
A bacterial communication system where cells detect population density via signaling molecules, coordinating behaviors like biofilm formation or virulence.
- 34
Biofilm formation
The aggregation of bacterial cells into a structured community embedded in a matrix, which protects them from antibiotics and the immune system.
- 35
Symbiosis
A close interaction between bacteria and other organisms, which can be mutualistic, commensal, or parasitic, affecting the survival of both parties.
- 36
Mutualism in bacteria
A symbiotic relationship where both the bacterium and its host benefit, such as gut bacteria aiding in digestion while receiving nutrients and protection.
- 37
Commensalism
A type of bacterial symbiosis where one organism benefits, such as by gaining a habitat, while the other is unaffected, like skin bacteria living on humans.
- 38
Parasitism
A relationship where pathogenic bacteria harm their host by causing disease or resource depletion, while benefiting from the host's nutrients.
- 39
Bacterial chromosome
A single, circular DNA molecule in bacteria that contains the essential genes for growth and reproduction, located in the nucleoid region.
- 40
Operon model
A cluster of genes in bacteria under the control of a single promoter, allowing coordinated expression of related functions, such as in metabolism.
- 41
Lac operon
A specific operon in E. coli that regulates genes for lactose metabolism, turning on only when lactose is present and glucose is absent.
- 42
Repressor protein
A regulatory protein in bacterial operons that binds to the operator region to block transcription until an inducer molecule removes it.
- 43
Inducer
A molecule, like allolactose in the lac operon, that binds to a repressor protein, causing it to release from the operator and allow gene transcription.
- 44
Transcription in prokaryotes
The process where bacterial RNA polymerase synthesizes mRNA from DNA, occurring in the cytoplasm and often coupled with translation.
- 45
S ribosome
The bacterial ribosomal complex, composed of 50S and 30S subunits, that translates mRNA into proteins, differing from eukaryotic ribosomes.
- 46
Shine-Dalgarno sequence
A ribosomal binding site in bacterial mRNA that ensures accurate initiation of translation by aligning the ribosome with the start codon.
- 47
DNA replication in bacteria
The semi-conservative process where bacterial DNA is duplicated bidirectionally from a single origin, using enzymes like DNA polymerase III.
- 48
Okazaki fragments
Short segments of DNA synthesized on the lagging strand during bacterial replication, later joined by DNA ligase to form a continuous strand.
- 49
Mutation
A permanent change in a bacterium's DNA sequence, which can result from errors in replication or environmental factors, potentially leading to new traits.
- 50
Horizontal gene transfer
The movement of genetic material between bacterial cells not through reproduction, including conjugation, transformation, and transduction.
- 51
Selective pressure
Environmental factors, like antibiotics, that favor the survival and reproduction of bacteria with certain traits, driving evolution of resistance.
- 52
Minimum inhibitory concentration
The lowest concentration of an antibiotic that prevents visible growth of a bacterial culture, used to determine effective treatment doses.
- 53
Pasteurization
A heat treatment process that kills pathogenic bacteria in liquids like milk without boiling, reducing spoilage and disease risk.
- 54
Autoclaving
A sterilization method using high-pressure steam to kill all bacteria and spores on equipment, essential in medical and lab settings.
- 55
Bacterial vaccines
Preparations containing inactivated or attenuated bacteria that stimulate an immune response, providing protection against specific bacterial diseases.
- 56
Immune response to bacteria
The body's defense mechanism involving innate and adaptive immunity, such as phagocytosis and antibody production, to eliminate invading bacteria.
- 57
Phagocytosis of bacteria
The process by which immune cells engulf and destroy bacteria, using enzymes and reactive oxygen species within phagolysosomes.
- 58
Complement system activation
A cascade of proteins in the innate immune system that coats bacteria for enhanced phagocytosis or directly lyses them, triggered by bacterial surfaces.
- 59
Antibody production against bacteria
The adaptive immune response where B cells produce specific antibodies that bind to bacterial antigens, neutralizing them or marking them for destruction.
- 60
Bacterial metabolism
The chemical processes in bacteria that convert nutrients into energy and building blocks, varying from heterotrophic to autotrophic pathways.