The Cell Flashcards
1
Q
Cell Theory
A
- All living things are composed of cells.
- The cell is a basic functional unit of life.
- Cells arise only from pre-existing cells.
- Cells carry genetic information in the form of DNA, and this genetic material is passed on from parent to daughter cell.
2
Q
Nucleus
A
- Contains all the genetic material necessary for replication of the cell.
- Enclosed by Nuclear Membrane (double membrane that separates nuclear environment from cytoplasm) containing Nuclear Pores that allow selective two-way exchange of materials (small polar molecules, ions, proteins, and RNA) between cytoplasm and nucleus.
- Coding regions of DNA are called Genes.
- Linear DNA is wound around Histones and is then further wound into Chromosomes.
- Nucleus keeps DNA transcription separate from RNA translation.
- Nucleolus is a subsection of the nucleus where ribosomal RNA (rRNA) is synthesized. Identified as darker spot in nucleus.
3
Q
Mitochondria
A
- Site of aerobic respiration. Anaerobic respiration occurs in cytoplasm.
- Outer Mitochondrial Membrane serves as a barrier between the cytosol and the inner environment of the mitochondrion and contains cholesterol and pores that increase permeability to small proteins and ions.
- Inner mitochondrial membrane is arranged into numerous infoldings called Cristae that contain the molecules and enzymes of the ETC and contains very little cholesterol, reducing its permeability and increasing its selectivity.
- Space between the membranes is called the Intermembrane Space, and the space enclosed by the inner membrane is called the Matrix.
- Mitochondria are semi-autonomous; they contain some of their own genes and replicate independently of the nucleus via binary fission (example of Cytoplasmic/Extranuclear Inheritance).
- Serial Endosymbiosis Theory: Posits that mitochondria (in animals), chloroplasts (in plants), and organelles of motility (in bacteria) were formed by the engulfing of an aerobic prokaryote by an anaerobic prokaryote and the establishment of a symbiotic relationship.
- Responsible for apoptosis of cell via release of ETC enzymes.
4
Q
Lysosomes
A
- Contains hydrolytic enzymes that are capable of breaking down ingested substrates (such as phagocytosed pathogen or macromolecules) and cellular waste products (intracellular debris and worn-out organelles).
- Function in conjunction with Endosomes which transport, package, and sort sell material traveling to and from the cell membrane. Endosomes can transport materials to the Golgi for modification, the cell membrane for secretion, or to the lysosome for degradation.
- Can release its enzymes in a process called Autolysis, which results in apoptosis.
5
Q
Endoplasmic Reticulum
A
- Series of interconnected membranes contiguous with the nuclear envelope.
- Double membrane is folded into numerous invaginations creating complex structures with central lumen.
- Rough endoplasmic reticulum is studded with ribosomes which permit translation of proteins destined for secretion directly into its lumen.
- Smooth endoplasmic reticulum utilized primarily for lipid synthesis (such as phospholipids for cell membrane) and detoxification of certain drugs and poisons; SER also transports proteins from RER to the Golgi apparatus.
6
Q
Golgi Apparatus
A
- Consists of stacked membrane-bound sacs.
- Responsible for modifying, sorting, and packaging cellular products.
- Receives materials from ER in vesicles, and these cellular products may be modified either by addition of groups like carbohydrates, phosphates, and sulfates or through introduction of signal sequences which direct the delivery of the product to a specific cellular location.
- Modified cellular products are repackaged in vesicles and then directed to the correct cellular location. If destined for secretion, contents are released via exocytosis.
7
Q
Peroxisomes
A
- Contain hydrogen peroxide to break down very long chain fatty acids via beta-oxidation.
- Participates in the synthesis of phospholipids and contains some of the enzymes involved in the pentose phosphate pathway.
8
Q
Cytoskeleton
A
- Provides structure to the cell and helps it to maintain its shape.
- Microfilaments: Solid polymorized rods of Actin protein, which uses ATP to generate force for movement by interacting with Myosin in muscle contraction. Important in Cytokinesis (division of materials between daughter cells), as microfilaments form Cleavage Furrow during mitosis.
- Microtubules: Hollow polymers of Tubulin protein, which provide the primary pathways along which motor proteins like Kinesin and Dynein carry vesicles. Main component of Cilia (such as in respiratory epithelial cells) and Flagella (such as in sperm cells); only eukaryotic cilia and flagella have 9+2 microtubule structure. Centrioles (found in the Centrosome) are organizing centers for microtubules and help form Mitotic Spindle during mitosis; the microtubules emanating from the centrioles attached to the chromosomes via Kinetochores to pull apart the sister chromatids.
- Intermediate Filaments: Filamentous proteins (such as keratin, desmin, vimentin, and lamins) which are involved in cell-cell adhesion, anchoring of organelles, and maintenance of the overall integrity of the cytoskeleton.
9
Q
Types of Tissues
A
- Epithelial Tissue: Covers the body and lines its cavities; involved in protection, absorption, secretion, filtration, and sensation. Tightly joined to each other and to underlying layer of connective tissue called the Basement Membrane. Constitute the Parenchyma of organs, the functional part of the organ (such as nephrons in kidney, hepatocytes in liver, acid-producing cells in stomach). Are polarized, with one side facing a lumen or the outside world and another side interacting with underlying blood vessels and structural cells (such as in intestinal cells). Classified as simple epithelia (one layer), stratified epithelia (multiple layers), pseudostratified epithelia (one layer with cells of different height), and cuboidal, columnar, squamous.
- Connective Tissue: Supports the body and provides a framework for the epithelial cells to carry out their functions. Constitute the Stroma of organs, the support structure. Cells in connective tissues produce and secrete materials (such as collagen and elastin) to form Extracellular Matrix. Includes bone, cartilage, tendons, ligaments, adipose tissue, and blood.
10
Q
Prokaryotes
A
- Do not contain organelles.
- Genetic material organized into single circular molecule of dsDNA in Nucleoid Region.
• Archaea: Extremophiles (high temp, high salinity, no light) and use alternative sources of energy (chemosynthetic). Similar to eukaryotes by metabolic pathways, DNA-histone association, initiation of translation with methionine, and lack of peptidoglycan in cell wall. Similar to bacteria by single circular chromosome, binary fission and budding, and overall structure.
- Bacteria: Some have flagella (different structure to eukaryotic flagella) or fimbriae (similar to cilia). Bacterial flagella composed of Flagellin permit Chemotaxis. Also contain primitive cytoskeleton.
- Prokaryotes have 70S ribsome (50S subunit and 30S subunit), which is significantly smaller in comparison to eukaryotic 80S ribsome (60S subunit and 40S subunit).
- Prokaryotes lack mitochondria; cell membrane is used instead for the electron transport chain and generation of ATP.
- Prokaryotic cell wall and plasma membrane together are called Envelope.
- Gram-Positive Bacteria have thick peptidoglycan-rich cell walls that appear deep purple after Gram staining. Also contain Lipoteichoic Acid in cell wall, which activates human immune system.
- Gram-Negative Bacteria have thin cell walls (separated from plasma membrane by periplasmic space) with less peptidoglycan that appear pink-red after Gram staining. Also contain Lipopolysaccharides in cell wall, which trigger stronger immune responses in humans.
- Bacteria can be beneficial mutualistic symbiotes or harmful pathogens/parasites and can exist as Cocci (spherical, like strep and staph), Bacilli (rod-shaped, like escherichia and mycobacterium), Spirilli (spiral-shaped, like treponema and leptospira). Can be Obligate Aerobes (require oxygen for metabolism), Obligate Anaerobes (cannot survive in oxygen-containing environment), Facultative Anaerobes (utilize both aerobic and anaerobic metabolism depending on oxygen availability), or Aerotolerant Anaerobes (cannot use oxygen for metabolism but are not harmed by its presence).
11
Q
Prokaryote Reproduction
A
• Binary Fission: Rapid form of asexual reproduction in which the circular chromosome replicates and migrates to opposite sides of the elongating cell and then the plasma membrane and the cell wall begin to grow inward along the midline of the cell (forming a septum) to produce two identical daughter cells.
- Genetic Recombination: Plasmids are small circular structures that carry extrachromosomal/extragenomic material (DNA from external sources) that is not necessary for survival of the prokaryote and is thus not considered part of its genome but may confer advantages like antibiotic resistance; plasmids may also carry Virulence Factors that increase pathogenicity, such as toxin production, attachment projections, or features that permit evasion of host’s immune system. Episomes are Plasmids that are capable of integrating into the genome of bacterium. Three types of bacterial genetic recombination.
- Transformation: Integrating foreign (environmental) genetic material into bacterial genome; usually from nearby lysed bacteria. Competent cells can readily undergo transformation.
- Conjugation: Sexual reproduction in which two cells form a Conjugation Bridge that facilitates the unidirectional transfer of genetic material from Donor Male (+) to Recipient Female (-). Conjugation Bridge made from a donor male’s Sex Pilus; donor male must contain plasmids known as Sex Factors to form pilus. F (fertility) Factor in E. coli is best-studied sex factor. During conjugation, an F+ cell (bacteria possessing F factor) replicates its F factor plasmid and donates the copy to an F- cell, converting the F- cell into an F+ cell. 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. An Hfr cell (High Frequency of Recombination) is an F+ cell that has integrated its sex factor into its genome (via transformation) such that it no longer exists freely in the cytoplasm as a plasmid; during conjugation, Hfr cell transfers its sex factor along with part of its genome to the recipient cell.
- Transduction: The only genetic recombination process that requires a Vector (virus that carries genetic material from one bacterium to another). Bacteriophages can accidentally incorporate a segment of host DNA during assembly and then release it when the bacteriophage infects another bacterium; the transferred DNA can then be integrated into the genome, giving the new host additional genes.
- Transposon: Genetic element capable of inserting and removing itself from the genome, possibly in a new location on the genome; if transposon is inserted within a coding region of a gene, the gene may be disrupted.
12
Q
Bacterial Growth
A
- Bacteria reproduce by binary fission, implying that all are exactly the same in a local colony (assuming no mutations or genetic recombination).
- Lag Phase: In a new environment, bacteria first adapt to the new local conditions.
- Exponential (Log) Phase: After adapting, the number of bacteria in the colony exponentially increases.
- Stationary Phase: Reproduction slows down due to reduced resources.
- Death Phase: After the bacteria have exceeded the ability of the environment to support them and exhausted all available resources, the colony dies off.
13
Q
Viruses
A
- Obligate intracellular parasites, as they cannot reproduce independently.
- Acellular, and therefore non-living.
- Composed of genetic material (circular or linear, single-stranded or double-stranded, DNA or RNA); Capsid (protein coat); and sometimes Envelope (made of phospholipids and virus-specific proteins, enveloped viruses easier to kill as envelope is very sensitive to heat, detergents, desiccation; non-enveloped viruses are more resistant to sterilization).
- Viral genetic information must be expressed and replicated in host cell, as viruses lack ribosomes for protein synthesis. After hijacking host cell’s machinery, Virions (viral progeny) are produced, which can then infect other cells.
- Bacteriophages do not enter bacterium but instead use Tail Fibers to recognize and connect to host cell and use a syringe-like Tail Sheath to inject genetic material into bacterium.
- ssRNA viruses can be Positive Sense (RNA genome can be directly translated to functional proteins by host ribosomes) or Negative Sense (RNA strand used as template for complimentary strand synthesis, which can then be used for protein synthesis, ssRNA must therefore carry RNA Replicase for complementary RNA strand synthesis).
- Retroviruses are enveloped ssRNA viruses that carry Reverse Transcriptase, which synthesizes dsDNA from ssRNA in cytoplasm, and Integrase, which integrates viral dsDNA into host DNA genome in nucleus; integrated viral DNA is replicated and transcribed as if host’s own DNA. Difficult to kill as a result (such as HIV).
14
Q
Viral Life Cycle
A
- Infection: Viruses can only infect a specific set of cells, because they must bind to specific receptors on host cell. Enveloped viruses (like HIV) fuse with plasma membrane, while bacteriophages anchor themselves to plasma membrane and inject their genome into host cell through the tail sheath (leaving capsid outside the cell).
- Translation and Progeny Assembly: Viral DNA travels to nucleus for transcription into mRNA, and then viral mRNA travels to cytoplasm for translation. RNA viruses remain in cytoplasm for protein synthesis. Translation of viral mRNA produces capsid proteins and any necessary enzymes in cytoplasm for virion assembly. Viral genome returned to its original form is then packaged into capsids.
- Progeny Release: Viral progeny can be released via initiating cell death in host cell, lysing host cell due to host cell being filled with extremely large number of virions, or Extrusion (fusing with cell membrane of host cell). Virus that uses extrusion for progeny release is said to be in a Productive Cycle.
• Lytic Cycle: Bacteriophage maximizes the 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. Viruses in the lytic phase are termed Virulent.
• Lysogenic Cycle: Virus is integrated into host genome as Provirus or Prophage, does not lyse the bacterium, and will be replicated as the bacterium reproduces indefinitely (because virus is now a part of the host’s genome). Environmental factors (such as radiation, light, or chemicals) may cause the Provirus/Prophage to leave the genome and revert to a lytic cycle; provirus may extract bacterial genes as it leaves genome, allow transduction of genes from one bacterium to another. Infection with one strain of phage makes the bacterium less susceptible to Superinfection (simultaneous infection) with other phages.
15
Q
Prions and Viroids
A
- Prions: Infectious proteins that trigger misfolding and aggregation of other proteins.
- Viroids: Very short circular ssRNA that silences genes in plants.
