Chapter 6 – A Tour of the Cell How small is a cell anyway? Scientists were able to discover more about the cell as better microscopes were developed… Light microscope 1600s Mid 1800s – cell theory = all living things are made of cells, and cells come from other cells 1950s – Electron microscope Scanning electron Microscope (see detailed surface of specimen) Transmission electron microscope (study details of internal cell structure) New techniques in all fields of microscopy continue to improve our ability to study cells Magnification and Resolution Electron Microscopy Why are cells so small? Why are cells so small? How about other shapes? • Large sphere with radius 3 units vs 27 small spheres with radius 1 unit • To reiterate: Surface area-to-volume ratios affect the ability of a biological system to obtain necessary resources, eliminate waste products, acquire or dissipate thermal energy, and otherwise exchange chemicals and energy with the environment. How do materials get through the cell membrane? Eukaryotes Prokaryotes • https://www.youtube.com/watc h?v=Pxujitlv8wc&ab_channel=A moebaSisters Prokaryotes Eukaryotes Protists, fungi, plants, and animals Nucleus Membrane-bound organelles Plants have cell walls, not animals Much larger (about 10x average prokaryotic cell) Bacteria and archaea -Chromosomes No nucleus – nucleoid (genetic Ribosomes are somewhat chemically material) different than eukaryotes -Ribosomes Most have cell wall (make proteins) -Cytoplasm Some have sticky outer coat called a capsule Much smaller (average about 1/10 the size of eukaryotic cells) Eukaryotes and Prokaryotes What are archaea, bacteria, protists, and fungi anyways? • https://www.youtube.com/watch?v=VGcT1XaWgk&ab_channel=AmoebaSisters • https://www.youtube.com/watch?v=zK7Ckmxxqds &ab_channel=AmoebaSisters Keep in mind when studying cell parts that living cells and components are always moving, interacting, and changing Cellular metabolism – essential chemical activities that occur inside cells – performed in specialized organelle membranes, fluidfilled spaces, and structures Membrane-bound organelles – each organelle (means “little organ”) bound by a lipid and protein membrane that fits its function Eukaryotic cells are divided into functional compartments…some introductory notes (1)Genetic control - The nucleus and ribosomes carry out the genetic control of the cell. 4 General Categories (2) “Endomembrane system” - Organelles involved in the manufacture, distribution, and breakdown of molecules include the endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, and peroxisomes. (3) Energy Processing - Mitochondria in all cells and chloroplasts in plant cells function in energy processing. (4) Structural support, movement, and communication between cells are the functions of the cytoskeleton, plasma membrane, and plant cell wall. Nucleus • Chromosomes • Chromatin • Nuclear envelope – double membrane, each a phospholipid bilayer with embedded proteins • Nuclear pores • Regulate movement in and out of the nucleus • Nuclear pores – regulate the movement of large molecules • Link with ER Nucleus Ribosomes • Protein making machinery • Cells that make a lot of proteins, like insulin producing pancreas cells, have a lot • Free ribosomes • Make proteins that function in the cytoplasm • EX: enzymes that catalyze the first steps of sugar breakdown. • Bound ribosomes • make proteins that will be inserted into membranes, packaged in certain organelles, or exported from the cell Endoplasmic Reticulum • Smooth ER • • • • No ribosomes Synthesize lipids Process toxins Store calcium ions • Rough ER • Produce phospholipids – makes more membrane, which buds off as vesicles and can join other structures • The bound ribosomes attached to the rough ER produce proteins that will be inserted into the growing ER membrane, transported to other organelles, or secreted by the cell. Golgi Apparatus • Series of flattened membranous sacks • Modifies and distributes products of the ER • Materials move into the golgi, between sacs, and leave the golgi via vesicles. Lysosome • Membranous sack of digestive enzymes • Digest food particles, recycle old or damaged organelles, invading bacteria Vacuoles and Peroxisomes • Vacuoles • Large vesicles that perform a variety of functions, mostly storage • Ex: water, food, pigments • Peroxisomes • metabolic compartments that do not originate from the endomembrane system • Some break down fatty acids to be used as cellular fuel or detoxify harmful compounds • Create hydrogen peroxide (H2O2) as a byproduct, other enzymes in the peroxisome quickly convert this toxic product to water—another example of the importance of a cell’s compartmental structure. Mitochondria • Cellular respiration • Double phospholipid membrane • Intermembrane space • Inside the inner membrane – mitochondrial matrix – contains mitochondrial DNA and ribosomes and enzymes that catalyze cellular respiration reactions • Inner membrane • Cristae • Embedded proteins active in ATP synthesis Chloroplasts • Double membrane, thin intermembrane space • Stroma contains DNA, ribosomes, and enzymes • Thylakoids, thylakoid space, grana • chlorophyll • Site of the light dependent reactions of photosynthesis Endosymbiont theory • This theory states that an early ancestor of eukaryotic cells engulfed an oxygen-using prokaryotic cell, which eventually evolved into mitochondria. • At least one of these cells may have then taken up a photosynthetic prokaryote, becoming the ancestor of eukaryotic cells that contain chloroplasts. • Evidence – mitochondria and chloroplasts contain: • • • • Double membranes Ribosomes circular DNA molecules autonomous (somewhat independent) organelles that grow and reproduce within the cell Cytoskeleton • Network of protein fibers that function to provide structure and motility 1. Microfilaments 2. Intermediate filaments 3. Microtubules - Readily dissembled and reassembled elsewhere in the cell - Grow out of a “microtubule organizing center” region near the nucleus that contains a pair of centrioles - Movement – form tracks for organelles, chromosomes, make up cilia and flagella - 3D network just inside the plasma membrane that helps support the cell’s shape - Also involved in cell movements - Actin and myosin in muscle cells - Amoeboid movement - Cytoplasmic streaming in large plant cells - Reinforce cell shape - Anchor organelles - Ex: nuclear lamina - more permanent fixtures of cells than are microfilaments and microtubules Cilia and flagella • Cilia – some protists, cells lining respiratory tract • Flagella – other protists, sperm cells • Composed of microtubules wrapped in an extension of the plasma membrane • 9+2 pattern, 9 triplets for basal body (and centrioles) • Cilia and flagella bend through dynein “walking” • Some non-motile cilium act as signal receiving “antennae” Extracellular Matrix • helps hold cells together in tissues and protects and supports the plasma membrane • Glycoproteins – structure • Integrins are proteins that span the cell membrane and transmit signals between the ECM and cytoskeleton Cell Junctions • Tight junctions - tightly pressed against each other and knit together by proteins. Forms a seal, prevents leakage • Anchoring junctions – fasten cells into strong sheets. Intermediate filaments made of sturdy keratin proteins. Common in tissues under more mechanical stress. • Gap junctions - channels that allow small molecules to flow through protein-lined pores between cells Cell Walls • Made of fibers of cellulose embedded in a matrix of other polysaccharides and proteins • Plasmodesmata • Primary wall – thin and flexible, allows the growing cell to continue to enlarge • Secondary wall – thicker more rigid wall deposited in laminated layers • Wood • Pectin - between adjacent cells is a layer of sticky polysaccharides Animal vs plant cells
