Membrane-Bound Organelles Section 4.5

Learning Objectives Distinguish between smooth and rough endoplasmic reticulum in terms of structure and function Trace the path of protein synthesis in rough ER from creation to delivery to final destination Compare the functions of lysosomes, vacuoles, and peroxisomes Contrast the functions of mitochondria & chloroplasts & compare their structure

Endomembrane System A series of interacting organelles that exchange materials through small membrane-enclosed containers Involved in making & modifying lipids & proteins for the cell Made up of all organelles found in the cytoplasm except mitochondria and chloroplasts

Interactions among organelles keep the cell alive

Endoplasmic Reticulum (ER) ER = a complex network of membranes expanding from the nuclear envelope that has various functions and structures 2 main types: Rough ER and Smooth ER One function in both types is storage of calcium ions for cell signaling

Rough Endoplasmic Reticulum Also called Rough ER An extension of the nuclear envelope Has ribosomes attached to it Makes it look bumpy or rough Function is making proteins

Smooth Endoplasmic Reticulum Also called Smooth ER An extension of the nuclear envelope Has no ribosomes on it Functions: Makes lipids Makes hormones Breaks down drugs and toxins Can cause cells to make more smooth ER so they can break it down faster

Golgi Complex Also called Golgi apparatus or Golgi body Makes changes to proteins and lipids received from other parts of the cell Finished lipids & proteins are then sorted & packaged for delivery by vesicles to other parts of the cell Makes lysosomes

Vesicles Vesicle = Membrane bound sac or container Transport materials around the cell Move along cytoskeleton tracks or “roads”

Lysosomes Lysosomes are made in the Golgi apparatus Contain enzymes that break down organic molecules Also breaks down worn out or damaged cell parts Only found in animal cells

If lysosomes are missing an enzyme then materials can build up in the cells Eventually causes the cell to die Cause of some diseases (ex. Tay-Sachs Disease)

Vacuoles Vacuoles are larger than vesicles Can form when vesicles fuse together Function in the storage of materials Store water, waste, sugars, toxins, etc. Some protists have contractile vacuoles Helps remove extra water from the cell

Plants have a very large Central Vacuole Filled with stored food, salts, pigments, wastes, and lots of water Pushes on the cell wall to give the cell strength

Peroxisomes Peroxisomes are created in the Smooth ER Breaks down fatty acids & toxins Contains the enzyme catalase Changes hydrogen peroxide (which is toxic to cells) into water and oxygen Found in both plant & animal cells

Cells Store Energy as ATP Energy enters cells as chemical energy stored in food molecules or as light energy Must be converted into a form of energy the cell easily use and store (such as ATP) Organelles involved in energy conversion Mitochondria Chloroplasts

Mitochondria Mitochondria are organelles with: Function is making ATP Double-membrane Inner membrane has many folds called cristae Its own DNA & ribosomes Function is making ATP Break down glucose Also involved in apoptosis Programmed cell death

Plastids Plastids have a double membrane Function in producing and storing food materials Found in plant & algal cells 3 common types: Amyloplasts Chromoplasts Chloroplasts

Plastids Amyloplasts – store starch Have no pigment (color) Chromoplasts – make and store pigments that are not chlorophyll Attracts animals to act as pollinators or seed dispersers

Chloroplast Chloroplast = plastid specialized for photosynthesis Has a double membrane (outer membranes) Have their own DNA & ribosomes Third highly folded inner membrane called the thylakoid membrane Fluid filled space surrounding thylakoid membrane is the stroma Function is to capture light energy to make sugars from water and CO2

Parts of a Chloroplast

Theory of Endosymbiosis Why do mitochondria & chloroplasts have their own DNA & ribosomes? They are very similar to certain species of bacteria Scientists think their ancestors were free-living bacteria that were ingested by eukaryotic cells The bacteria were then allowed to live within the cell & produce sugar or ATP for it