Biology Chapter 1: The Cell PDF

BIOLOGY Chapter 1: The Cell Cell Theory 4 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 preexisting cells ○ Cells carry genetic info in the form of DNA. This ge...

BIOLOGY Chapter 1: The Cell Cell Theory 4 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 preexisting cells ○ Cells carry genetic info in the form of DNA. This genetic material is passed on from parent to daughter cell. Viruses are not considered living things b/c they are acellular, cannot reproduce w/o assistance of a host cell, and may use RNA as their genetic material Eukaryotic Cells Eukaryotes have membrane-bound organelles, a nucleus, and may form multicellular organisms Cell membrane and membranes of organelles contain phospholipids which organize to form hydrophilic interior and exterior surfaces w/ a hydrophobic core Cytosol suspends organelles and allows diffusion of molecules to cell Eukaryotic Organelles Nucleus Contains DNA organized into chromosomes Surrounded by nuclear membrane/envelope Double membrane that contains nuclear pores for 2-way exchange of materials b/t nucleus and cytosol DNA is organized into coding regions called genes Nucleolus Subsection of nucleus in which ribosomal RNA (rRNA) is synthesized Mitochondria Outer membrane forms barrier w/ cytosol Inner membrane is folded into cristae and contains enzymes for ETC B/t the membranes is intermembrane space Inside inner mitochondrial membrane is mitochondrial matrix Mitochondria can divide independently of the nucleus via binary fission and can trigger apoptosis by releasing  mitochondrial enzymes into cytoplasm Lysosomes Contain hydrolytic enzymes that can break down substances ingested by endocytosis and cellular waste products When these enzymes are released, autolysis of cell can occur Endoplasmic Reticulum (ER) A series of interconnected membranes and is continuous w/ nuclear envelope Rough ER (RER) is studded w/ ribosomes, which permit translation of proteins destined for secretion Smooth ER (SER) is used for lipid synthesis and detoxification Golgi Apparatus Consists of stacked membrane-bound sacs in which cellular products can be modified, packaged, and directed to specific cellular locations Peroxisomes Contain hydrogen peroxide and can break down very long chain fatty acids via β-oxidation Also participate in phospholipid synthesis and pentose phosphate pathway Cytoskeleton provides stability and rigidity to overall structure of cell, while also providing transport pathways for molecules w/i the cell Microfilaments Composed of actin Provide structural protection for cell and can cause muscle contraction through interactions w/ myosin Help form cleavage furrow during cytokinesis in mitosis Microtubules Composed of tubulin Create pathways for motor proteins like kinesin and dynein to carry vesicles Contribute to structure of cilia and flagella where they are organized into 9 pairs of microtubules in a ring w/ 2 microtubules at the center (9+2  structures) Centrioles are found in centrosomes and are involved in microtubule organization in the mitotic spindle Intermediate filaments Involved in cell-cell adhesion and maintenance of the integrity of the cytoskeleton Help anchor organelles ○ EX: keratin and desmin Epithelial tissues cover the body and line its cavities, protecting against pathogen invasion and desiccation Some absorb or secrete substances or participate in sensation ○ In most organs, epithelial cells form the parenchyma, or the functional parts of the organ ○ They may be polarized, w/ one side facing a lumen of the outside world, and the other side facing blood vessels and structural cells ○ Epithelia can be classified by the number of layers Simple epithelia have one layer Stratified epithelia have many layers Pseudostratified epithelia appear to have multiple layers d/t diff in cell heights but actually only have one layer ○ Epithelia can also be classified by the shapes of the cells Cuboidal cells are cube-shaped Columnar cells are long and narrow Squamous cells are flat and scale-like Connective tissues support the body and provide a framework for epithelial cells ○ In most organs, connective tissues form the stroma or support structure by secreting materials to form an extracellular matrix ○ Bone, cartilage, tendons, ligaments, adipose tissue, and blood are all connective tissues Classification and Structure of Prokaryotic Cells Prokaryotes do not contain membrane-bound organelles They contain their genetic material in a single circular molecule of DNA located in the nucleoid region There are 3 overarching domains of life (prokaryotes account for 2 of these) Archaea Often extremophiles, living in harsh enviro (high temp, high salinity, no light) and often use chemical sources of energy (chemosynthesis) rather  than light (photosynthesis) They have similarities to both eukaryotes (start translation w/ methionine, similar RNA polymerases, histones) and bacteria (single circular chromosome, divide by binary fission or budding) Bacteria Have many similar structures to eukaryotes and have complex relationships w/ humans, including mutualistic symbiosis and pathogenesis Eukarya The only non-prokaryotic domain Bacteria can be classified by shape ○ Spherical bacteria are called cocci ○ Rod-shaped bacteria are called bacilli ○ Spiral-shaped bacteria are called spirilli Bacteria can be classified based on metabolic processes ○ Obligate aerobes require oxygen for metabolism ○ Obligate anaerobes cannot survive in oxygen-containing enviro and can only carry out anaerobic metabolism ○ Facultative anaerobes can survive in enviro w/ or w/o oxygen and will toggle b/t metabolic processes based on the enviro ○ Aerotolerant anaerobes cannot use oxygen for metabolism, but can survive in an oxygen-containing enviro The cell wall and cell membrane of bacteria form the envelope. Together, they control the movement of solutes into and out of the cell ○ Bacteria can be classified by the color of their cell walls turned during Gram staining w/ a crystal violet stain, followed by a counterstain w/ safranin. Gram-positive bacteria turn purple, while gram-negative bacteria turn pink-red ○ Gram-positive bacteria have a thick cell wall composed of peptidoglycan and lipoteichoic acid ○ Gram-negative bacteria have a thin cell wall composed of peptidoglycan and an outer membrane containing phospholipids and lipopolysaccharides Bacteria may have 1, 2, or many flagella that generate propulsions to move the bacterium toward food or away from immune cells ○ Moving in response to chemical stimuli is called chemotaxis ○ Bacterial flagella contain a filament composed of flagellin, a basal body that anchors and rotates the flagellum, and a hook that connects the two Prokaryotes carry out the ETC using the cell membrane Prokaryotic ribosomes are smaller than eukaryotic ribosomes (30S and 50S, rather than 40S and 60S) Genetics and Growth of Prokaryotic Cells Prokaryotes multiply through binary fission, in which the chromosome replicates while the cell grows in size, until the cell wall begins to grow inward along the midline of the cell and divides it into 2 identical daughter cells In addition to the single circular chromosome in prokaryotes, extrachromosomal material can be carried in plasmids ○ Plasmids may contain antibiotic resistance genes or virulence factors ○ Plasmids that can integrate into the genome are called episomes Bacterial genetic recombination increased bacterial diversity Transformation Occurs when genetic material from the surroundings is taken up by a cell, which can incorporate this material into it genome Conjugation The transfer of genetic material from one bacterium to another across a conjugation bridge A plasmid can be transferred from F+ cells to F- cells, or a portion of the genome can be transferred from an Hfr cell to a recipient Transduction The transfer of genetic material from one bacterium to another via a bacteriophage vector Transposons Genetic elements that can insert into or remove themselves from the genome Bacterial growth follows a predictable pattern ○ The bacteria adapt to new local conditions during the lag phase ○ Growth then incr exponentially during the exponential (log) phase ○ As resources are reduced, growth levels off during the stationary phase ○ As resources are depleted, bacteria undergo a death phase Viruses and Subviral Particles Viruses contain genetic material, a protein coat (capsid), and sometimes a lipid-containing envelope Viruses are obligate intracellular parasites, meaning that they cannot survive and replicate outside of a host cell ○ Individual virus particles are called virions Bacteriophages are viruses that target bacteria  ○ In addition to the other structures, they contain a tail sheath, which injects the genetic material into a bacterium, and tail fibers, which allow the bacteriophage to attach to the host cell Viral genomes may be made of various nucleic acids ○ May be composed of DNA or RNA and may be single- or double-stranded ○ Single-stranded RNA viruses may be positive sense (that can be translated by the host cell) or negative sense (which requires a complementary strand to be synthesized by RNA replicase before translation) ○ Retroviruses contain a single-stranded RNA genome, from which a complementary DNA strand is made using reverse transcriptase The DNA strand can then be integrated into the genome Viruses infect cells by attaching to specific receptors, and can then enter the cell by fusing w/ the plasma membrane, being brought in by endocytosis, or injecting their genome into the cell The virus reproduces by replicating and translating genetic material using the host cell’s ribosomes, tRNA, amino acids, and enzymes Viral progeny are released through cell death, lysis, or extrusion Bacteriophages have 2 specific life cycles Lytic Cycle The bacteriophage produces massive numbers of new virions until the cell lyses Bacteria in the lytic phase are termed virulent Lysogenic Cycle The virus integrates into the host genome as a provirus or phophage, which can then reproduce along w/ the cell The provirus can remain in the genome indefinitely, or may leave the genome in response to a stimulus and enter the lytic cycle Prions are infectious proteins that trigger misfolding of other proteins, usually converting an ⍺-helical structure to a β-pleated sheet ○ This decr the solubility of the protein and incr its resistance to degradation Viroids are plant pathogens that are small circles of complementary RNA that can turn off genes, resulting in metabolic and structural changes and, potentially, cell death