4.5-4.19 ORGANELLES OF THE ENDOMEMBRANE SYSTEM 4.5: The nucleus The nucleus is the cell's genetic control center The nucleus contains the cell's DNA Controls cellular activities by directing protein synthesis Forms long fibers of chromatin (loose, threadlike form of DNA) that make up chromosomes (made of scrunched up DNA and proteins and are ONLY seen during active cell division)

The nucleus is separated from the cytoplasm by the nuclear envelope—which is a double membrane Pores in the envelope control flow of materials in and out Ribosomes are synthesized in the nucleolus

Main functions of the Nucleus Contain DNA and pass it to daughter cells during cell division Build ribosomes (occurs in the nucleolus) Copy DNA instructions to mRNA (messenger RNA) mRNA leaves the nucleus through nuclear pores and then travels to ribosomes where it is translated into the amino acid sequences of proteins

LE 4-5 Nucleus Chromatin Two membranes of nuclear envelope Nucleolus Pore Rough endoplasmic reticulum Ribosomes

4.6 Overview of Organelles Many cell organelles are connected through the endomembrane system The endomembrane system is a collection of membranous organelles. The system is aided by vesicles (sacs made of membane that transfer membrane segments). Divide the cell into compartments Work together in the synthesis, storage, and export of molecules Prime example: Endoplasmic reticulum (ER) A continuous network of flattened sacs and tubes

There are two regions of ER: rough and smooth They differ in function, but the membranes that form them are continuous. The rough ER is also continuous with the nuclear envelope.

4.7 Smooth ER Smooth endoplasmic reticulum has a variety of functions; most of its activity results from enzymes embedded in its membrane Smooth endoplasmic reticulum (smooth ER) lacks attached ribosomes Synthesizes lipids—including fatty acids, phospholipids, and steroids Processes materials such as toxins and drugs in liver cells Stores and releases calcium ions in muscle cells, regulating muscle contractions

LE 4-7 Smooth ER Rough ER Nuclear envelope Ribosomes Smooth ER TEM 45,000

Rough endoplasmic reticulum makes more membrane and modifies proteins 4.8 Rough ER Rough endoplasmic reticulum makes more membrane and modifies proteins Rough endoplasmic reticulum (rough ER) is studded with ribosomes (looks “rough” in electron micrographs) Manufactures more membrane Modifies and packages proteins that will be Transported to other organelles Secreted by the cell (like insulin) See page 59

Transport vesicle buds off Secretary Ribosome (glyco-) protein inside trans- port vesicle Ribosome Sugar chain Glycoprotein Polypeptide Rough ER

4.9 The Golgi apparatus finishes, sorts, and ships cell products The Golgi apparatus consists of stacks of flattened membranous sacs Receives and modifies substances manufactured by ER Ships modified products to other organelles or the cell surface

LE 4-9 Golgi apparatus Golgi apparatus “Receiving” side of Transport vesicle from ER New vesicle forming “Shipping” side of Golgi apparatus TEM 130,000  Transport vesicle from the Golgi

Animation: Lysosome Formation 4.10 Lysosomes are digestive compartments within a cell Lysosomes are sacs of enzymes that form from the Golgi apparatus Function in digestion within a cell Destroy bacteria that have been ingested into white blood cells Recycle damaged organelles Animation: Lysosome Formation

LE 4-10a Rough ER Transport vesicle (containing inactive hydrolytic enzymes) Plasma membrane Golgi apparatus Engulfment of particle Lysosome engulfing damaged organelle “Food” Lysosomes Food vacuole Digestion

4.11 Abnormal lysosomes can cause fatal diseases CONNECTION 4.11 Abnormal lysosomes can cause fatal diseases Lysosomal storage diseases Result from an inherited lack of one or more lysosomal enzymes Seriously interfere with various cellular functions

Video: Paramecium Vacuole 4.12 Vacuoles function in the general maintenance of the cell Plant cells contain a large central vacuole Has lysosomal and storage functions Some protists have contractile vacuoles Pump excess water out of cell Video: Paramecium Vacuole Video: Chlamydomonas

Animation: Endomembrane System 4.13 A review of the endomembrane system The various organelles of the endomembrane system are interconnected structurally and functionally Animation: Endomembrane System

Transport vesicle from Golgi to plasma membrane Rough ER from ER to Golgi Transport vesicle from Golgi to plasma membrane Rough ER Plasma membrane Nucleus Vacuole Lysosome Smooth ER Nuclear envelope Golgi apparatus

ENERGY-CONVERTING ORGANELLES 4.14 Chloroplasts convert solar energy to chemical energy Chloroplasts are found in plants and some protists Are the site of photosynthesis Have a complex membranous structure for capturing and converting light energy

LE 4-14 Stroma Chloroplast Inner and outer membranes Granum TEM 9,750 Intermembrane space

4.15 Mitochondria harvest chemical energy from food Mitochondria are found in nearly all eukaryotic cells Divided into two membranous compartments Intermembrane space Second compartment enclosed by inner membrane Contains fluid mitochondrial matrix Membrane folded into cristae

Carry out cellular respiration Convert the chemical energy in food to ATP for cellular work

LE 4-15 Mitochondrion Outer membrane Intermembrane space Inner Cristae TEM 44,880 Matrix

THE CYTOSKELETON AND RELATED STRUCTURES 4.16 The cell's internal skeleton helps organize its structure and activities The cytoskeleton is network of three types of protein fibers Microfilaments Rods of globular proteins Enable cells to change shape and move

Intermediate filaments Ropes of fibrous proteins Reinforce the cell and anchor certain organelles Microtubules Hollow tubes of globular proteins Give the cell rigidity Anchor organelles and act as tracks for organelle movement

4.17 Cilia and flagella move when microtubules bend Eukaryotic cilia and flagella are locomotor appendages that protrude from certain cells Move whole cells or materials across the cell surface

The structure and mechanism of cilia and flagella are similar Microtubules wrapped in an extension of the plasma membrane 9 + 2 arrangement Extend into basal bodies Movement of dynein arms produces microtubule bending

CELL SURFACES AND JUNCTIONS 4.18 Cell surfaces protect, support, and join cells Cells interact with their environments and each other via their surfaces Many cells are protected by more than the plasma membrane

Plant cell walls Made largely of cellulose Provide protection and support Connect by plasmodesmata, channels through the wall

Walls of two adjacent plant cells Vacuole Plasmodesmata Layers LE 4-18a Walls of two adjacent plant cells Vacuole Plasmodesmata Layers of one plant cell wall Cytoplasm Plasma membrane

Connect by cell junctions Animal cells Embedded in an extracellular matrix that binds cells together in tissues Connect by cell junctions Tight junctions bind cells into leakproof sheets Anchoring junctions link cells into strong tissues Gap junctions allow substances to flow from cell to cell

LE 4-18b Tight junctions Anchoring junction Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells

FUNCTIONAL CATEGORIES OF ORGANELLES 4.19 Eukaryotic organelles comprise four functional categories Eukaryotic organelles fall into four functional categories that work together to produce the cell's emergent properties Manufacturing Breakdown Energy processing Support, movement, and communication between cells