The Cell Cell theory: first unifying theory of biology. Cells: fundamental units of life All organisms are composed of cells All cells come from preexisting cells.
The Cell Most cells are tiny, in order to maintain a good surface area-to-volume ratio. The volume of a cell determines its metabolic activity relative to time The surface area of a cell determines the number of substances that can enter or leave the cell
The cellTwo types of microscopes to visualize small cells:Light microscopes²use glass lenses and light Resolution = 0.2 ȝmElectron microscopes²electromagnets focus an electron beam Resolution = 2.0 nm
The CellPlasma membrane: Selectively permeable barrier . Allows cells to maintain a constant internal environment Important in communication and receiving signals Has proteins for binding and adhering to adjacent cells
The cellTwo types of cells:Prokaryotes are without membrane-enclosed compartments.Eukaryotes have membrane- enclosed compartments called organelles, such as the nucleus.
Prokaryotic Cells Do Not Have a Nucleus Prokaryotic cells Enclosed by a plasma membrane DNA located in the nucleoid The rest of the cytoplasm consists of: Cytosol (water and dissolved material) and suspended particles Ribosomes²sites of protein synthesis
Prokaryotic Cells Bacteria cell walls contain peptidoglycans Other bacteria have a slimy layer of polysaccharides, called the capsule. Some prokaryotes swim by means of flagella Some rod-shaped bacteria have a network of actin-like protein structures to help maintain their shape.
Eukaryotic Cells Have a Nucleus and Other Membrane-Bound CompartmentsEukaryotic cells have a plasma membrane, cytoplasm, and ribosomes, also membrane-enclosed compartments called organelles.Each organelle plays a specific role in cell functioning.
Eukaryotic Cells Ribosomes: sites of protein synthesis Occur in both prokaryotic and eukaryotic cells and have similar structure²one larger and one smaller subunit. Each subunit consists of ribosomal RNA (rRNA) bound to smaller protein molecules
Eukaryotic cell. Ribosomes Not membrane-bound organelles In eukaryotes: free in the cytoplasm, attached to the endoplasmic reticulum, or inside mitochondria and chloroplasts. In prokaryotic cells, ribosomes float freely in the cytoplasm.
Eukaryotic Cell. The Nucleus Usually the largest organelle. Location of DNA and of DNA replication Site where DNA is transcribed to RNA Contains the nucleolus, where ribosomes begin to be assembled from RNA and proteins.
Eukaryotic Cells. The Nucleus Surrounded by two membranes that form the nuclear envelope. Nuclear pores control movement of molecules between nucleus and cytoplasm. In the nucleus, DNA combines with proteins to form chromatin in long, thin threads called chromosomes.
Eukaryotic Cell. The endomembrane system The endomembrane system includes The nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes. Tiny, membrane-surrounded vesicles shuttle substances between the various components, as well as to the plasma membrane.
Endoplasmic Reticulum (ER) Network of interconnected membranes in the cytoplasm, with a large surface area The ER has two distinct regions: Smooth ER, which lacks ribosomes Rough ER, with ribosomes
Smooth ERRough ER Nuclear envelopeER lumenCisternae Ribosomes Transitional ER Transport vesicle 200 nm Smooth ER Rough ER
Endoplasmic Reticulum Smooth ER Rough ER Synthesizes Has bound lipids and ribosomes, secrete steroids glycoproteins Metabolizes Distributes carbohydrates transport Detoxifies vesicles, proteins poisons surrounded by Stores calcium membranes Glycogen Is a membrane degradation site factory for the cell
The Golgi Apparatus The Golgi apparatus consists of flattened membranous sacs called cisternae ³Shipping and Receiving Center´ Functions of the Golgi apparatus: Modifies products of the ER Manufactures certain macromolecules (polysaccharides in plants) Sorts and packages materials into transport vesicles
cis face(³receiving´ side of Golgi 0.1 µmapparatus) Cisternae trans face (³shipping´ side of Golgi TEM of Golgi apparatus apparatus)
Lysosomes Primary lysosomes originate from the Golgi apparatus. contain digestive enzymes Site where macromolecules are hydrolyzed into monomers.
Lysosomes Isolate Digestive Enzymes from the Cytoplasm
Eukaryotic Cells. Mitrochondria In eukaryotes, molecules are first broken down in the cytosol. The partially digested molecules enter the mitochondria, here chemical energy is converted to energy-rich ATP. Cells that require a lot of energy often have more mitochondria.
Eukaryotic Cells. Mitochondria Two membranes: Outer membrane: porous Inner membrane: extensive folds called cristae, to increase surface area The fluid-filled matrix inside the inner membrane contains enzymes, DNA, and ribosomes.
Eukaryotic Cells. Plastids Plant and algae cells contain plastids that can differentiate into organelles² some are used for storage. Chloroplast contains chlorophyll and is the site of photosynthesis. Photosynthesis converts light energy into chemical energy.
Eukaryotic Cells. Other organelles Specialized functions. Peroxisomes collect and break down toxic by-products of metabolism, such as H2O2, using specialized enzymes. Glyoxysomes, found only in plants, are where lipids are converted to carbohydrates for growth.
Eukaryotic Cell. VacuolesMainly in plants and fungi, functions:Storage of waste products and toxic compoundsStructure for plant cells²water enters the vacuole by osmosis, creating turgor pressure
Eukaryotic Cell. VacuolesReproduction: vacuoles in flowers and fruits contain pigments whose colors attract pollinators and aid seed dispersalCatabolism²digestive enzymes in seeds¶ vacuoles hydrolyze stored food for early growth
The Cytoskeleton Provides Strength and Movement The cytoskeleton Supports and maintains cell shape Holds organelles in position Moves organelles Involved in cytoplasmic streaming Interacts with extracellular structures to anchor cell in place
The Cytoskeleton Provides Strength and Movement Three componentsMicrofilaments:Help a cell or parts of a cell to moveDetermine cell shapeMade from actin
The Cytoskeleton Provides Strength and Movement Intermediate filaments: At least 50 different kinds Tough, ropelike protein assemblages, more permanent than other filaments Anchor cell structures in place Resist tension, maintain rigidity
The Cytoskeleton Provides Strength and Movement Microtubules: The largest diameter components, two roles: Form rigid internal skeleton for some cells or regions Act as a framework for motor proteins to move structures in the cell
The Cytoskeleton Provides Strength and Movement Microtubules line movable cell appendages. Cilia²short, usually many present, move with stiff power stroke and flexible recovery stroke Flagella²longer, usually one or two present, movement is snakelike
Extracellular Structures Allow Cells to Communicate with the External Environment Extracellular structures are secreted to the outside of the plasma membrane. In eukaryotes, these structures have two components: A prominent fibrous macromolecule A gel-like medium with fibers embedded
Extracellular Structures Allow Cells to Communicate with the External Environment Plant cell wall²semi-rigid structure outside the plasma membrane The fibrous component is the cellulose. The gel-like matrix contains cross- linked polysaccharides and proteins.
Extracellular Structures in animal cells extracellular matrices in animal cells Hold cells together in tissues Contribute to physical properties of cartilage, skin, and other tissues Filter materials Orient cell movement during growth and repair
Extracellular Structures Cell junctions specialized structures that protrude from adjacent cells and ³glue´ them together Tight junctions Desmosomes Gap junctions