Cells: Structure and Function Notes PDF

# Cells - The basic structural and functional units of every organism - **All Cells:** - Are bound by a plasma membrane - Contain cytosol - Contain chromosomes - Contain ribosomes ## Types of Cells: - **Prokaryotes:** - Domains: Bacteria and Archaea - DNA is in the nucleoid...

# Cells - The basic structural and functional units of every organism - **All Cells:** - Are bound by a plasma membrane - Contain cytosol - Contain chromosomes - Contain ribosomes ## Types of Cells: - **Prokaryotes:** - Domains: Bacteria and Archaea - DNA is in the nucleoid region - Generally smaller in size than eukaryotes - **Eukaryotes:** - Protists, fungi, animals, and plants - DNA is in the nucleus - Contain membrane-bound organelles ## Organelles - Membrane bound structures in eukaryotes - **Two classifications:** - **Endomembrane organelles:** - Nuclear envelope - Endoplasmic reticulum - Golgi complex - Lysosomes - Vesicles/Vacuoles - Plasma membrane - **Energy organelles:** - Mitochondria - Chloroplasts ## Compartmentalization - Organelles allow for different metabolic reactions to occur in different locations - **Increases surface area for reactions** - Prevents interfering reactions from occurring in the same location ## Unique Cell Components ### Plants - Chloroplasts - Central vacuole - Cell wall - Plasmodesmata ### Animals - Lysosomes - Centriole - Flagella # Nucleus - Contains chromosomes (genetic information) - Enclosed by the nuclear envelope - Double membrane - Has pores - Pores regulate entry and exit of materials - Contains a nucleolus - Dense region of the nucleus where ribosomal RNA (rRNA) is synthesized - rRNA is combined with proteins to form large and small subunits of ribosomes - Subunits exit via nuclear pores - Assemble into ribosomes - Ribosomes translate messages found on mRNA into the primary structure of polypeptides # Ribosomes - Comprised of ribosomal RNA and protein - Function: synthesize proteins - Note: some texts do not classify ribosomes as organelles because they are not bound by a membrane # Ribosomes - Can be found in two locations: - **Cytosol:** - Proteins produced here generally function only within the cytosol (i.e., enzymes) - Known as "free ribosomes" - **Bound to the endoplasmic reticulum or nuclear envelope:** - Proteins produced here can be secreted from the cell - Leave via transport vesicles # Endoplasmic Reticulum - A network of membranous sacs and tubes - **Functions:** - Synthesizes membranes - Compartmentalize the cell to keep proteins formed in the rough ER separate from those of free ribosomes # Endoplasmic Reticulum - **Rough ER:** - Contains ribosomes bound to the ER membrane - **Smooth ER:** - Contains no ribosomes - Synthesizes lipids, metabolizes carbohydrates, and detoxifies the cell # Golgi Complex - Contains flattened membranous sacs called cisternae - Separate the sacs from the cytosol - Each cisternae is not connected - Has directionality - **Cis face:** Receives vesicles from the ER - **Trans face:** Sends vesicles back out into cytosol to other locations or to the plasma membrane for secretion - **Functions:** - Receives transport vesicles with materials from the ER (cis face) - Modifies the materials - Sorts the materials - Adds molecular tags - Ensures newly formed proteins are folded correctly or modified correctly - Packages materials into new transport vesicles that exit the membrane via exocytosis # Lysosomes - Membranous sac with hydrolytic enzymes - **Function:** - Hydrolyzes macromolecules in animal cells - **Autophagy:** lysosomes can recycle their own cell's organic materials - Allows the cell to renew itself - **Peroxisomes:** - Similar to lysosomes - Membrane bound metabolic compartment - Catalyze reactions that produce H₂O₂ - Enzymes in peroxisomes then break down H₂O₂ to water # Vacuoles - Large vesicles that stem from the ER and Golgi - Selective in transport - **Types:** - **Central vacuole** - Found in plants - Contains inorganic ions and water - Important for turgor pressure - **Food vacuole** - Form via phagocytosis (cell eating) and then are digested by lysosomes - **Contractile vacuole** - Maintain water levels in cells # The Endosymbiont Theory - Explains the similarities mitochondria and chloroplasts have to a prokaryote - **Theory states that an early eukaryotic cell engulfed a prokaryotic cell:** - Prokaryotic cell became an endosymbiont (cell that lives in another cell) - Became one functional organism # Endosymbiont Theory - **Evidence:** - Two membranes - Ribosomes (prokaryotic) - Circular DNA - Capable of functioning on their own - Can only reproduce on their own - The cell can't make more if removed # Mitochondria - Site of cellular respiration - **Structure of the double membrane:** - Outer membrane is smooth - Inner membrane has folds called cristae - Divides the mitochondria into two internal compartments and increases the surface area for cellular respiration reactions # Mitochondria - **Intermembrane Space:** space between inner and outer membrane - **Mitochondrial matrix:** central chamber enclosed by inner membrane - Location for the Krebs cycle - **Contains:** - Enzymes that catalyze cellular respiration and produce ATP - Mitochondrial DNA (circle) - Ribosomes # Mitochondria - The number of mitochondria in a cell correlates with metabolic activity - Cells with high metabolic activity have more mitochondria - Example: cells that move/contract # Chloroplast - Specialized organelles in photosynthetic organisms - Site of photosynthesis - Contains the green pigment chlorophyll - **Inside of its double membrane:** - **Thylakoids:** Membranous sacs that can organize into stacks called grana - Light dependent reactions occur in grana # Chloroplast - **Stroma:** fluid around thylakoids - Location for the Calvin cycle - Uses chemical energy to build carbohydrates - **Contains:** - Chloroplast DNA (circle) - Ribosomes - Enzymes # The Cytoskeleton - A network of fibers throughout the cytoplasm - Give structural support (especially for animal cells) and mechanical support: - Anchor organelles - Allow for movement of vesicles and organelles and/or the whole cell - Movement occurs when the cytoskeleton interacts with motor proteins # Microtubules - Hollow rod-like structures made of the protein tubulin - Grow from the centrosome - Assist in microtubule assembly - **Functions:** - Serve as structural support (think: tracks) for the movement of organelles that are interacting with motor proteins - Assist in the separation of chromosomes during cell division - Cell motility (i.e., cilia and flagella) # Microfilaments - Thin solid rods made of the protein actin - **Functions:** - Maintain cell shape - Bear tension - Assist in muscle contraction and cell motility - Actin works with another protein called myosin to cause a contraction - Division of animal cells - Contractile ring of the cleavage furrow # Intermediate Filaments - Fibrous proteins made up of varying subunits - Permanent structural elements of cells - **Functions:** - Maintain cell shape - Anchor nucleus and organelles - Form the nuclear lamina - Lines the nuclear envelope