Chapter 7 – Inside the CellHow does structure correlate with its function?Single-celled organisms and individual cells within multicellularorganisms can vary greatly in appearance as well as in the functions theyperform. Nonetheless, each of these cells is alive and therefore must have some common characteristics: Plasma Membrane, DNA and Ribosomes.I. Bacterial Cell Structures (prokaryotic) and Their Functionsa. Prokaryotic cell structures: a parts listi. The chromosome is organized in a nucleoid; NO nuclear membranes1. Bacterial DNA is inside a chromosome, which contains genes2. In order to fit within the nucleoid, the chromosome is supercoiledii. Bacterial ribosomes are the sites of protein synthesisiii. Many bacterial species have internal photosynthetic membranes that convert solarenergy into chemical energyiv. Bacteria contain protein filaments that make up a simple cytoskeletonv. The plasma membrane separates life from nonlifevi. Some bacteria have flagella that are used to power movementvii. The cell wall (peptidoglycan) protects the bacteria from osmotic stressII. Eukaryotic Cell Structures and Their Functionsa. The benefits of organellesi. Eukaryotic cells are compartmentalized by membrane-bound organelles1. Compartmentalization separates incompatible chemical reactions2. Compartmentalization increases efficiency inside the cell in two ways:a. It allows for the maintenance of high concentrations of reactantsb. It clusters enzymes and reactants together, thus shortening the diffusion distanceii. Prokaryotic versus eukaryotic cells1. Eukaryotic chromosomes are inside a membrane-bound nucleus2. Eukaryotic cells are usually larger than prokaryotic cells3. Eukaryotic cells have extensive amounts of internal membrane4. Eukaryotic cells feature a diverse and dynamic cytoskeletonb. Eukaryotic cell structures: a parts listi. Nucleus1. The nucleus is the largest organelle in the cell2. It is enclosed by a double membrane called the nuclear envelope. It contains the genetic information of the cell, DNA3. It contains the nucleolus, the site or rRNA synthesis and ribosome assembly4. Nuclear pores penetrate the nuclear envelope and connect the cytoplasm to the nucleoplasm (mRNA gets out to cytoplasm through nuclear pores).ii. Rough endoplasmic reticulum1. The rough endoplasmic reticulum (RER) is a network of membrane-bound sacs and tubules2. The RER has ribosomes bound to the cytoplasmic surface on which secreted and endomembrane proteins are made3. It contains enzymes in the lumen that fold and modify proteins after they are synthesized on bound ribosomesiii. Smooth endoplasmic reticulum1. The smooth endoplasmic reticulum is a portion of the ER that does not have ribosomes attached2. It contains enzymes that are involved in the synthesis of lipids, detoxifying harmful substances and storing calcium ions3. The ER (smooth and rough), the Golgi apparatus, and lysosomes make up the endomembrane system, which is the primary center for protein and lipid synthesisiv. Golgi apparatus1. The Golgi apparatus consists of flattened membrane sacs called cisternae2. It has polarity: a cis side that receives proteins from the rough ER and a trans side that ships proteins to their final destination  tagging and sortingv. Ribosomes (an “organelle”)1. Ribosomes are found in the cytosol (or attached to RER during protein synthesis)2. They are composed of two subunits: large and small; No membranes3. They are molecular machines that synthesize proteinsvi. Lysosomes (in animal cells)1. Lysosomes are involved in solid-waste processing and material storage2. They receive material destined for hydrolysis via three mechanisms:a. Phagocytosis: cellular eatingb. Autophagy: the delivery of damaged organelles to lysosomes for recyclingc. Receptor-mediated endocytosis: targeted ingestion of extracellular molecules, some of which are destined for the lysosome3. They contain digestive enzymes, that work best in acidic conditions to hydrolyze macromoleculesNot all endocytic vesicles end up in lysosomes. Pinocytosis (“cellular drinking”)?vii. Vacuoles (in plant cells, similar to lysosomes in animal cells)1. Vacuoles occupy most of the volume of plant cells2. They act as a storage depot for water, ions, pigments and sometimes proteins3. They may contain noxious substances that protect the plant from predatorsviii. Mitochondria1. Mitochondria are the sites of ATP synthesis  power houses of the cell2. They have two membranesa. The outer membrane is smoothb. The inner membrane contains folds called cristae (increased surface)c. The mitochondrial matrix is inside the inner membrane3. Mitochondria contain some of their own circular DNAix. Chloroplasts1. Chloroplasts convert the energy in sunlight into the chemical energy in sugar2. They have two membranesa. The outer membrane is smoothb. The inner membrane is filled with a series of flattened sacs, called thylakoids, that are stacked in granac. Thylakoids are surrounded by stroma, the fluid filling the inner membranex. Cell walls1. Algae, fungi, and plant cells have cell walls2. Cell walls are composed of carbohydrate rods and fibers running through astiff polysaccharide matrixxi. Cytoskeleton1. The cytoskeleton is a system of protein filaments2. It provides structural support to the cell3. It facilitates many types of cellular movementAlso refer to Table 7.2III. Putting the Parts into a WholeStructure and function at the whole-cell leveli. Examples1. Pancreatic cells are specialized for secreting digestive enzymes. They are packed with ER and Golgi apparatus, the organelles that manufacture secreted proteins2. Leaf cells are specialized for absorbing light and manufacturing sugars. They contain a large number of chloroplasts3. Potato tuber cells are specialized for storing sugars. They contain a large storage vacuoleIV. The endomembrane system manufactures and ships proteins:a. Pathway through the endomembrane systemi. Entering the endomembrane system- The signal hypothesis: proteins destined tobe secreted have a signal in the first few amino acids (~20) that function as an address tag directing them to the ER.ii. Signal sequence (SNP) binds to the receptor on ER where the protein synthesis is completed, the signal sequence is removed. Two possibilities for the polypeptide:1. The polypeptide may be transferred to the lumen of the ER so it can be processed and packaged or secreted from the cell2. The polypeptide may be integrated into the rough ER