Cell Biology Essentials: Structure, Transport, and Division

HUMAN ANATOMY AND PHYSIOLOGY LECTURE • CHAPTER 3 - CELL BIOLOGY • • • • • • • • CELL Functions o Basic unit of life o Synthesis of molecules o Communication o Cell metabolism and energy release o Reproduction and inheritance (DNA) Cell Structure o Organelles - specialized structures in cells that perform specific functions; Ex. Nucleus, mitochondria, ribosomes, etc. o Cytoplasm - jelly-like substance that holds organelles; cytosol with organelles o Cytosol - liquid portion CELL MEMBRANE Outermost component of a cell Selective barrier Encloses cytoplasm Extracellular - material outside cell Intracellular - material inside cell Structure o Called Fluid Mosaic Model o Made of phospholipids and proteins o Phospholipids form a double layer or bilayer o Phospholipids contain 2 regions: polar and nonpolar o Polar regions: ▪ “heads” ▪ hydrophilic (H2O loving) ▪ exposed to H2O o Nonpolar regions: ▪ “tails” ▪ hydrophobic (H2O fearing) ▪ away from H2O o o • • • • • • • • • • Movement through Cell Membrane o Cell membrane selectively determines what can pass in and out of the cell. o Enzymes, glycogen, and potassium are found in higher concentrations inside the cell. o Sodium, calcium, and chloride are found in higher concentrations outside the cell. Ways Molecules Pass through Cell Membrane o Directly through (diffusion): ▪ O2 and CO2 (small molecules) o Membrane channels: ▪ proteins that extend from one side of cell membrane to other ▪ size, shape, and charge (+/-) determine what can go through ▪ Ex. Na+ passes through Na+ channels • Carrier molecules: ▪ bind to molecules, transport them across, and drop them off ▪ Ex. glucose Vesicles: ▪ can transport a variety of materials ▪ fuse with cell membrane DIFFUSION Movement of molecules from areas of high to low concentration Solution - solid, liquid, or gas that contains one or more solutes Solute - substance added to solvent that dissolves Solvent - substance such as H2O that solute is being added to Ex. Add salt to H2O. H2O =solvent, salt=solute, mixture=solution Concentration gradient o measures conc. difference at 2 points o greater the distance the faster the solute will travel Filtration - movement of fluid through a partition with holes MEDIATED TRANSPORT MECHANISMS Facilitated diffusion: o diffusion with aid of a carrier molecule o requires no ATP Active transport: o moves substances from low to high conc. o requires ATP o Ex. Sodium-potassium pump Osmosis o diffusion of water across a cell membrane o Osmotic pressure - force required to prevent movement of water across cell membrane o Types of Osmotic Solutions: ▪ Hypotonic solution: • lower conc. of solutes outside cell • • higher conc. of H2O outside cell • H2O moves into cell • lysis (burst) ▪ Hypertonic solution: • higher conc. of solutes outside cell • higher conc. H2O inside cell • H2O moves out • crenation (shrinks) ▪ Isotonic solution: • equal conc. of solutes • water doesn’t move • cell remains intact Endocytosis o process that brings materials into cell using vesicles o Phagocytosis - cell eating (solid particles) o Pinocytosis - cell drinking (liquid particles) • • • • • • • Exocytosis o process that carries materials out of cell using vesicles • • • CELL STRUCTURES • • • • • Cytoplasm o Location: inside cell o Characteristic: jelly-like fluid o Function: give cell shape and hold organelles in place Nucleus o center of cell o all cells contain nucleus at some point • • o houses DNA Nuclear envelope: o edge of nucleus Nuclear pores: o surface of nucleus o where materials pass in and out of nucleus Chromosome: o inside nucleus o made of DNA and proteins o part of genetic makeup Chromatin: o inside nucleus o loosely coiled chromosomes Nucleolus o in nucleus o produce ribosomes Ribosome o attached to RER or cytoplasm o produce proteins RER (Rough Endoplasmic Reticulum) o cytoplasm o membranes with ribosomes attached o site of protein synthesis SER (Smooth Endoplasmic Reticulum) o in cytoplasm o membranes with no ribosomes o site of lipid synthesis (Ex. Cholesterol) Golgi apparatus o in cytoplasm o closely, packed stacks of membranes o collect, sort, package, and distribute proteins and lipids Secretory vesicle o in cytoplasm o distributes materials out of cell Lysosome o in cytoplasm o enzymes that digest foreign material Mitochondria o in cytoplasm o contains folds (cristae) o produces ATP Cilia o cell surface o many per cell o move materials across cell’s surface Flagella o cell surface o 1 per cell o move cell, Ex. sperm • • • • • • • • Microvilli o cell surface o shorter than cilia o increase surface area Cytoskeleton o cell’s framework made of proteins o provide support o hold organelles in place o enable cell to change shape o Microtubules: ▪ largest diameter ▪ provide structural support ▪ form cilia and flagella o Intermediate filaments: ▪ medium diameter ▪ maintain cell shape o Microfilaments: ▪ smallest diameter ▪ involved in cell movement WHOLE CELL ACTIVITY A cell’s characteristics are determined by the type of proteins produced Proteins’ function is determined by genetics Information in DNA provides the cell with a code for its cellular processes DNA o double helix in nucleus o composed of nucleotides o contains 5 carbon sugar (deoxyribose, nitrogen base, phosphate) Flow of Genetic Information o Also called Central Dogma o Occurs in three stages: ▪ DNA replication ▪ Transcription ▪ Translation Gene Expression o information in DNA directs protein synthesis o proteins provide code for gene expression o enzymes regulate chemical reactions o uses transcription and translation o Transcription ▪ process by which DNA is “read” ▪ occurs in ribosomes ▪ produces mRNA (messenger RNA) ▪ mRNA contains codons ▪ codons - set of 3 nucleotide bases that code for a particular amino acid o Translation ▪ process by mRNA is converted into amino acids (polypeptides) ▪ produces proteins ▪ ▪ • • • • • codons pair with anticodons anticodons - 3 nucleotide bases carried by tRNA CELL DIVISION formation of 2 daughter cells from single parent cell uses mitosis and meiosis each cell (except sperm and egg) contains 46 chromosomes (diploid) sperm and egg contain 23 chromosomes Mitosis o cell division occurs in all cells except sex cells o forms 2 daughter cells o Chromatid - 2 strands of chromosomes that are genetically identical o Centromere - where 2 chromatids are connected o Centrioles - small organelle composed of 9 triplets o Stages in Mitosis ▪ Interphase: • time between cell divisions • DNA is in strands (chromatin) • DNA replication occurs ▪ Prophase: • chromatin condenses into chromosomes • centrioles move to opposite ends ▪ Metaphase: • chromosomes align ▪ Anaphase: • chromatids separate to form 2 sets of chromosomes • chromosomes move towards centrioles ▪ Telophase: • chromosomes disperse • nuclear envelopes and nucleoli form • cytoplasm divides to form 2 cells