Chapter 3 Cells PDF

Chapter 3: Cells Cell theory: A unifying theme in biology and the foundation for Cell Biology Life on earth represents a continuous line of descent from those early cells ○ 3 Principles: All organisms are composed of cells All cells come only from preexisting cells Cells are the smallest structural...

Chapter 3: Cells Cell theory: A unifying theme in biology and the foundation for Cell Biology Life on earth represents a continuous line of descent from those early cells ○ 3 Principles: All organisms are composed of cells All cells come only from preexisting cells Cells are the smallest structural and functional unit of organisms Perspective…1 inch contains 25,400 micrometers Cell size is limited Due to diffusion of substances in and out of the cell. Diffusion Is the movement of molecules without energy from a high concentration to a low concentration Diffusion is affected by Surface Area available (more SA the more diffusion) Temperature (higher temp more molecule vibrating- denature or damage) Concentration Gradient (more conc.- The more movement of molecule because they are trying to reach a state of equilibrium) Distance across the cell (if cell too large it takes more energy to move it) Larger Cells Increased Diffusion Time Need to take in more macromolecules Have larger energy requirements Cells: Surface Area to Volume Ratio Cell surface the only part of the cell that interacts with environment All substances enter and exist via this membrane. The surface-area-to-volume-ratio requires that cells be small Large cells-surface area relative to volume decreases Internal volume is living cytoplasm, which demands nutrients and produces wastes Specialized cells for have modified membranes increase surface area All cells exhibit basic similarities Centrally located genetic material Every cell contains DNA Prokaryotes: singular circular molecule Eukaryotes: DNA in nucleus (true nucleus) All cells have ribosomes The Cytoplasm ( a location) Contains a semifluid matrix known as the cytosol Contain sugars, amino acids, proteins and organelles The plasma membrane Encloses a cell and separates its contents from its surroundings A phospholipid bilayer about 5 to 10 nm thick Responsible for a cells ability to interact with the environment The Two Major Categories of Cells Prokaryotic cells Domains Bacteria and Archaea 3.5 billion years ago Eukaryotic Cells Domain Eukarya Protists and Kingdoms Plantae, Fungi, Animalia 2.1 billion years ago Prokaryotes Are smaller than eukaryotic cells Lack internal structures surrounded by membranes Lack a nucleus Have a rigid cell wall Asexual Reproduction (binary fission) Higher Plant Cells Versus Animal Cells Plants Cell walls Cell plate and plasmodesmata (pores b/w cell walls) Plastids and vacuoles (central) Animals Internal or external skeletons; no cell walls Divide by pinching in two; no cell plate npr plasmodesmata Centrioles present during cell division No plastids nor vacuoles Cell structure and Communication Cell wall surrounds protoplasm Protoplasm consists of all living cell components. ○ Bound by plasma membrane ○ Cytoplasm consists of all cellular components between the plasma membrane and the nucleus Cytosol- Fluid within cytoplasm containing organelles Organelles- Persistent structures of various shapes and sizes with specialized functions Most, but not all, are bound by membranes. Cell Structure and Communication: CELL WALL Cellulose: Main structural component of cell walls (long chains of glucose monomers) Also contain matrix of: Hemicellulose; holds cellulose fibrils together Pectin; Gives stiffness (like in fruit jellies) Glycoproteins; Proteins with associated sugars Middle Lamella; first produced when new cell walls are formed ○ Shared by two adjacent cells Cell Structure and Communication: Cell wall Flexible primary walls laid down on either side of middle lamella Secondary walls produced inside primary walls ○ Derived from primary Walls by thickening an inclusion of lignin ○ Cellulose microfibrils embedded in lignin for strength Plasmodesmata >>> Series of pores that allow cytoplasmic strands to extend between Allow fluids and dissolved substances to pass between cells Cell Components: Plasma membrane Plasma membrane; semipermeable outer boundary of the living part of the cell. Regulates movement of substances into or out of the cell. Phospholipid bilayer with interspersed proteins Composed 4 basic components: Phospholipid bilayer Membrane proteins Interior protein Network Cell surface markers Plastids; Site of manufacture and storage of important chemical compounds used by the cell Many types: Chloroplast ○ Most conspicuous plastid. ○ Bound by double membrane and contain: Grana made up of thylakoids Thylakoid membranes contain chlorophyll First steps of photosynthesis occur on thylakoid membranes Stroma- Matrix of enzymes involved photosynthesis Small circular DNA molecule Encodes for production of certain proteins for photosynthesis Chromoplast ○ Synthesize and accumulate carotenoids (yellow, orange and red) Leucoplast ○ Colorless ○ May synthesize starches (amyloplasts) ○ Or oils (elaioplasts) Gerontoplast Vacuoles Mature cells… 90% of volume may be taken up by central vacuoles Bounded by vacuolar membranes= tonoplasts Filled with called cell-sap (slightly acidic) Acts to maintain pH, cell pressure and is storage for a variety of secondary metabolites Salt, sugars, organic acid, small proteins and anthocyanins( red, blue and purple pigment) Eukaryotic cells arise from endosymbiotic theory Endosymbiotic Theory Protists have membrane bound organelles Endosymbiotic theory suggests that key organelles originated through a symbiosis with aerobic bacteria to become… ○ mitochondria from non-sulfur purple bacteria ○ chloroplast from cyanobacteria Animal Cells Heterotrophic= eats for its energy Organgeeles not found in most plants ○ Contains lysosomes ○ Contains Centrioles ○ Flagella Plant cells Photoautotrophic= creates its food from solar energy Unique to plant cells ○ Contains chloroplasts ○ Central vacuole ○ Cell wall Shared Organelles Nucleus, Nucleolus Rough and Smooth Endoplasmic Golgi apparatus Mitochondria Peroxisomes Cell membranes are Selectively Permeable Regulates the passage of molecules in and out of a cell Allowed cell to control chemical composition despite changing in external environment Some molecules require no energy - ATP to transport it across the cell membrane ○ Small, non-charged molecules such as carbon dioxide, oxygen, glycerol and alcohol ○ Follow the concentration gradient ( gradual change in chemical concentration between two different areas) Others do not require ATP to be transported across the membrane Types of Membrane Transport Passive Transport No ATP requirement Molecules flow with concentration gradient ( HIGH TO LOW) Diffusion, Facilitated Diffusion, Osmosis ○ Simple Diffusion:The movement of small, nonpolar molecules and water through micropores along concentration gradients. ○ Facilitated Diffusion: diffusion of ions and polar molecules with the help of the protein but no energy (The pic below) EX: Aquaporins- protein that allows for quick water transport ○ Osmosis: the diffusion of water cross a selectively permeable membrane Occurs when molecules cannot cross the membrane Water travels from an area of lower solute concentration to area of a higher solute concentration Solute? Solvent? How is this important to cellular life? Water Balance between cells and their surroundings is crucial to organisms. Cells must engage and osmoregulation the control of the water balance Tonicity plays a huge part in osmoregulation Tonicity; The ability of solution to cause a cell to gain or lose water Depends on the concentration of solutes on both sides of the membrane Note: only influenced by the solutes that cannot cross the cell membrane unassisted. ○ Hyper = greater, more ○ Hypo = less than, lower ○ ISO = equal, same Most often tonicity refers to the solution the cell is surrounded by. If the cell is in a… Hypertonic solution - More solutes outside than within the cell Hypotonic solution - less solutes outside than within the cell Isotonic solution - equal number of solutes Active Transport Requires carrier protein (also called Pumps) ○ Sodium-Potassium Pumps Molecules flow against concentration gradient (LOW TO HIGH) Cells with large active transport requirements need a lot of ATP for energy ○ Kidney Cells