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A&P I, Chap. 4

Biology of a Cell

Size of erythrocyte 7-8 nm
Size of oocyte 120 nm
Functions of plasma membrane - 1 Establishes a flexible boundary, protects cellular contents and supports cell structure. Phospholipid bilayer separates substances inside and outside the cell.
Functions of plasma membrane - 2 Selective permeability. Regulates entry and exit of ions, nutrients and waste molecules through the membrane.
Functions of plasma membrane - 3 Electrochemical gradients. Establishes and maintains an electrical charge difference across the plasma membrane.
Functions of plasma membrane - 4 Communication - Contains receptors that recognize and respond to molecular signals
Passive processes of membrane transport Does not require energy, depends on substances moving down concentration gradient.
Two types of passive transport Diffusion, facilitated diffusion and osmosis
Active processes of membrane transport Requires energy, ex: movement of a substance against its concentration gradient, release of a membrane bound vesicle
Vesicular transport Release of membrane-bound vesicle
Diffusion Substance moving from high to low concentration.
Environmental factors affecting diffusion Steepness of concentration gradient and temperature
Steepness of concentration gradient The steeper the gradient, the faster the diffusion rate
Temperature - diffusion Higher temperature, higher movement, faster rate of diffusion
Facilitated diffusion Transport process for small charged or polar solutes, requires assistance from plasma membrane proteins, maximum rate of transport determined by number of channels and carriers
Two types of facilitated diffusion Channel-mediated, carrier-mediated
Ions move down their concentration gradient through..... water filled channels, either Na or K leak channels
Carrier proteins change shape to transport.... molecules across the plasma membrane
Aquaporin Permeable to water
Osmosis Cell gains or loses water, resulting in change of cell volume and osmotic pressure
Tonicity Ability of a solution to change the volume or pressure of the cell by osmosis
Isotonic solution Solution inside and outside are equal. No loss or gain of water.
Hypotonic solution Solution outside of cell is less concentrated than inside the cell. Osmosis occurs resulting in hemolysis.
Hypertonic solution Solution inside cell is higher than solution outside of cell. Osmosis occurs resulting in crenation of cell. (shrinking)
Ion pumps Active transport proteins that move ions across membrane, helps cell maintain internal concentration of ions.
Symporter Substances move in the same direction.
Antiporter Substances move in opposite directions.
Vesicular transport Requires vesicles (membrane bound sac filled with materials), requires energy to transport vesicles, via exocytosis and endocytosis
Exocytosis Substance is released OUTSIDE of the cell, ex: secretion of saliva
Endocytosis Substance is released INSIDE the cell, intake of large substances from the environment, used for digestion, maintaining membrane protein composition.
Receptor mediated endocytosis Receptors are located on the outside of the plasma membrane which will signal the endocytosis process when a substance has been taken in by a receptor.
Primary Active Transport Pumps are powered directly by splitting an ATP molecule.
Secondary Active Transport Pumps are powered by energy harnessed as a second substance and moves through a channel down a concentration gradient.
Immune system cells Direct contact is important for function, destroys unhealthy and foreign cells, communicate through contact, recognizes healthy vs. unwanted, determines if cells have normal glycocalyx (cell coating), unhealthy/foreign cells are destroyed
Channel-linked receptors Permit ion passage into or out of cells, occurs in response to neurotransmitter binding, helps initiate electrical changes in muscle and nerve cells.
Enzymatic receptors Protein kinase enzymes, activated to phosphorylate other enzymes within the cell, provides mechanism for altering enzymatic activity
Ligand receptor signaling Indirectly activate protein kinase enzymes
Membrane bound organelles Surrounded by membrane, functions of organelle are able to run in isolated environment, differ in shape, membrane composition, enzymes, include: ER, golgi apparatus, lysosome, peroxisome, mitochondra
Endoplasmic reticulum (ER) Extends from nuclear membrane to plasma membrane, point of attachment for ribosomes (with ribosomes is called rough ER, without is called smooth ER)
Rough ER Glycogen is stored, protein production by ribosomes,plentiful in cells producing proteins, peroxisomes produced here
Smooth ER Continuous with rough ER, plentiful in cells of testes (produce testosterone), plentiful in liver, functions - synthesis, transport and storage of lipids, carbohydrate metabolism, detoxification of drugs, alcohols and poisons
Golgi apparatus Composed of several elongated, saclike membranous structures, "warehouse" of cell
Functions of Golgi apparatus Modification, packaging and sorting of proteins, transport of material from cis- to trans-, formation of secretory vesicles and lysosomes
Lysosome "Digestive system" of organelle, contains digestive enzymes made by Golgi apparatus, participation in digestion of unnecessary substances, digests contents of endocytosed vesicles
Peroxisomes Membrane-enclosed sacs smaller than lysosomes, pinched off vesicles from rough ER, contain oxidative enzymes, serve in detoxification (produce H2O2), engage in beta oxidation of fatty acid, abundant in liver
Mitochondria Oblong shaped organelles with a double membrane, contain genes for producing its proteins, active in aerobic cellular respiration, "powerhouses" of the cell, used in DNA identification, complete digestion of fuel molecules to synthesize ATP
Ribosomes (non-membrane bound), contain protein and RNA, made with nucleolus and assembled in cytoplasm, bound ribosomes attached to ER "rough", free floating in cytosol
Cytoskeleton functions Intracellular support, organization of organelles, cell division, movement of materials, anchors proteins in plasma membrane,
Components of cytoskeleton Includes micro- and intermediate filaments as well as microtubules
Microfilament characteristics Smallest component of cytoskeleton, actin protein monomers in two twisted filaments, form interlacing network on cytoplasmic side of membrane
Microfilament functions Maintain shape of cell, internal support of microvilli, separate two cells during cytokinesis, facilitate cytoplasmic streaming, muscle contraction
Intermediate filament characteristics Intermediate-sized components of the cytoskeleton, more rigid than microfilaments
Intermediate filament functions Support cells structurally, stabilize cell junctions, varied protein composition between cells, ex: keratin, in skin, hair and nails
Microtubules characteristics Largest components of the cytoskeleton, hollow cylinders, long chains of tubulin protein, impermanent structures elongated or shortened as needed
Microtubule functions Maintain cell shape, organize and move organelles, form components of cilia and flagella, participate in cellular vesicle transport, separate chromosomes during cell devision
Centrosome characteristics Close proximity to nucleus, contains pair of perpendicularly oriented cylindrical centrioles, surrounded by protein
Centrosome functions Organizes microtubules within the cytoskeleton, best known for function in cell division (forms mitotic spindle)
Proteasome characteristics Large, barrel-shaped protein complexes, protein-digesting organelles, located in cytosol and cell nucleus
Proteasome functions Degrade cell proteins through cell ATP-dependent pathway (housekeeper), proteins marked with ubiquitin tag for disposal, may be unable to remove proteins as it ages
Cilia characteristics Found on exposed surfaces of specific cells, ex: respiratory tract, many in number
Cilia function Moving substances along surface
Flagella characteristics Similar to cilia in structure, longer and usually singular
Flagella functions Helps propel an entire cell, ex: human sperm cell
Microvilli characteristics Microscopic extensions from surface of plasma membrane, much smaller than cilia, densely packed, lack powered movement, supported by microfilaments
Microvilli functions Form extensive plasma membrane surface, increase surface area for nutrient absorption ex: small intestine
Tight junction characteristics Encircle certain types of cells near exposed surface, completely attach cells to neighbors, fused plasma membrane proteins of neighboring cells
Tight junction functions Prevent substances passing between epithelial cells (decreases permeability), ex: small intestine - prevent digestive enzymes from moving between cells, in urinary bladder - prevention of urine exiting through urinary wall
Desmosome characteristics Like snaps between adjacent cells, web of intermediate filaments anchored across cells, found in cells exposed to stress, ex: external layer of skin
Desmosome functions Hold cells together at a single point
Gap junction characteristics Formed across intercellular space between cells, gap bridged by proteins called connexons
Gap junction functions Form tiny, fluid-filled tunnels, provide direct passageway for substances to travel between cells, ex: flow of ions between cells in cardiac muscle
Nucleus characteristics Largest structure in cell, typically one per cell (exceptions - erythrocytes with no nuclei, skeletal cells) mimics shape of cell, cell's control center
Nuclear envelope characteristics Double phospholipid membrane enclosing nucleus, separates cytoplasm from fluid within nucleus (nucleoplasm), externally continuous with rough ER, contains channel-like open passageways, "nuclear pores", allow passage in and out of nucleus
Nucleolus characteristics Dark staining, spherical shape, not membrane bound, composed of protein and RNA, not present in all cells, many in nerve cells, absent in sperm cell
Nucleolus function Produces small and large ribosome subunits
DNA characteristics Housed in nucleus, composed of repeated monomers, looks like a spinal ladder (double helix), sugar and phosphates make up vertical part, nucleotide pairs make up horizontal part (connected by hydrogen bond)
The four DNA nitrogenous bases Adenine, Guanine, Thymine, Cytosine
The four RNA nitrogenous bases Adenine, Guanine, Uracil, Cytosine
Human has how many double stranded DNA molecules? 46
DNA packaging Wound around nuclear proteins - nucleosomes, loose form when not dividing - chromatin, tightly formed when dividing - chromosone
Directed by DNA Cellular activities dependent upon protein synthesis
Transcription Ribonucleic acid copy of a gene formed from DNA in the nucleus
Translation Uses RNA for synthesis of protein by ribosomes in cytoplasm, mRNA threaded through ribosome, code in nucleotide sequence of mRNA translated, converted into amino acids to produce protein, takes place at ribosomes within cytoplasm
Transcription requirements DNA, large numbers of RNA building blocks, RNA polymerase
Produced during transcription mRNA, tRNA, rRNA
Three events of transcription initiation (beginning), elongation (during), termination (end)
Transcription initiation DNA unwound by specific enzymes, makes itself accessible to RNA polymerase, attaches to strand and locates promoter, bonds broken between DNA and region of expansion, DNA strand copied (template strand), other is the coding strand
Transcription elongation Free ribonucleotides base-paired, RNA polymerase assisting, new phosphodiester bonds between ribonucleotides, RNA polymerase moving down DNA
Transcription termination RNA polymerase released at terminal region of gene, hydrogen bonds broken between DNA and new mRNA strand, rewinding of DNA into double helix
Translation requirements Includes ribosomes, mRNA, tRNA, amino acids, rRNA embedded in structure of ribosome, mRNA transcribed from genes, read three bases at once (codons), tRNA
Start codon A U G
Stop codon where mRNA reading ends
tRNA brings specific amino acids to a specific mRNA codon, cloverleaf shaped, contains anticodon, base pairs of complimentary codon in mRNA, has amino acid receptor region
Amino acids 20 found in proteins of living things, building blocks for protein synthesis
DNA Responsible for directing the synthesis of proteins (over 10,000 different proteins in the human body), controls synthesis of enzymes
Two forms of cell division Mitosis, meiosis
Mitosis cell division that occurs in somatic cells (cells other than sex cells)
Meiosis (organism reproduction) cell division in sex cells
Forms of DNA in cells Nucleus w/ 46 DNA molecules, chromosome - most compact form of organized genetic material, Chromatin - loosely coiled form of DNA, transcription possible in this form
Cell division Cell divides in order to reproduce more cells, results in daughter cells
Interphase, mitotic phase Two major phases in cell cycle
Interphase Time between cell divisions, stage that cell spends most of its time, cell maintenance, DNA in loosely coiled chromatin, three phases (G1, S and G2)
Prophase Chromatic supercoiled into chromosomes with sister chromatids, nucleolus is broken down, microtubules growing from centrioles, centriole pairs pushed apart to opposite poles, dissolution of nuclear envelope
Metaphase Chromosomes aligned on equatorial plate of cell, spindle fibers extending from centriole attach at centromere of chromosome, total array termed mitotic spindle
Anaphase Starts as spindle fibers move sister chromatids apart toward opposite poles, each chromatid now a chromosome of one DNA helix
Telophase Chromosomes at each pole, begin to uncoil and return to chromatic, new nucleolus formed in each cell, mitotic spindle broken up, new envelope forms around chromosomes, cleavage begins to form
Cytokinesis Division of cytoplasm between two newly formed cells, other major event in mitotic phase, may overlap with anaphase and telophase, definition of cleavage and separation of daughter cells
G1 Growth phase
S Synthesis phase - DNA replication and growth
G2 Growth, preparing for prophase
Apoptosis When cells are no longer needed, they self-destruct, occurs to promote proper development, occurs to remove harmful cells, occurs more frequently with cells that have DNA damage
Created by: daydreamer67



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