LEC4 - Cell Organelles

• The basic structural and functional unit of every organism is the cell.
• 4 GENERAL ATTRIBUTES OF A CELL

  1. PLASMA MEMBRANE

  • Phospholipid bilayer – separates the cell from its environment
  • Allows passage of oxygen, nutrients & wastes

  1. CYTOSOL

  • Semifluid substance where the organelles are suspended
  • Cytoplasm – region between the plasma membrane & nucleus

  1. CHROMOSOMES

  • Carry the genes in the form of DNA

  1. RIBOSOMES

  • Tiny organelles that make proteins using the instructions in genes
• PROKARYOTES

  Bacteria, Archaea

  Nucleoid, no membrane-bound nucleus

  Circular strand of DNA

  Few organelles
• EUKARYOTES

  Eukarya (Protists, Fungi, Plant, Animals)

  Nucleus bound by a membrane

  DNA in several linear chromosomes

  Many specialized membrane-bound organelles
• Information Central - nucleus
• NUCLEUS

  • Contains the eukaryotic cell’s genetic library
  • Separated from cytoplasm by a double membrane
  • Nuclear pore allows large macromolecules & particles to pass through
  • Some genes are in MITOCHONDRIA and CHLOROPLASTS
• NUCLEAR LAMINA

  • network of intermediate filaments 
  • maintain the shape of the nucleus
  • mechanically support of the nuclear membrane

  DNA + HISTONES = CHROMATIN

  (appear as diffused mass) 

  • when cell prepares to divide, chromatin fibers coil up, seen as separate structures (CHROMOSOMES)

  NUCLEOLUS

  • site of ribosomal RNA (rRNA) synthesis
  •  rRNA combines with proteins in the cytoplasm to form ribosomal subunits
• RIBOSOMES 

  • Protein Factories

  build a cell’s proteins (Translation) 

  • rRNA + proteins
  • site of protein synthesis
  • cell types that synthesize large quantities of proteins (e.g., pancreas) have large numbers of ribosomes & prominent nucleoli
• FREE ribosomes

  Suspended in cytosol

  Synthesize proteins that function in the cytosol

  
  

  BOUND ribosomes

  Attached to RER, Nuclear envelope

  Synthesize proteins included in the membrane/for export from the cell
• THE ENDOMEMBRANE SYSTEM

  many of the internal membranes in a eukaryotic cell are part of this system
• THE ENDOMEMBRANE SYSTEM

  many of the internal membranes in a eukaryotic cell are part of this system

  • DIRECT CONTACT 
  • INDIRECT CONTACT 
  • (connected via transfer of vesicles, sacs of membrane)
• Plays a key role in the synthesis (& hydrolysis) of macromolecules in the cell

  Various components modify macromolecules for their various functions = endomembrane system
• Nuclear envelope, Endoplasmic reticulum, Golgi apparatus, Lysosomes, Vacuoles/Vesicles, Plasma membrane

  (endomembrane system)
• ENDOPLASMIC RETICULUM 

  • Biosynthetic Factory

  manufactures membranes & performs many other biosynthetic functions

  • membranous TUBULES & fluid-filled sacs CISTERNAE
  • ER membrane is continuous with the nuclear envelope
  • Cisternal lumen is continuous with the space between 2 membranes of nuclear envelope
• Rough ER

  • with ribosomes

  • abundant in cells that

  secrete proteins

  • secretory proteins are packaged into TRANSPORT VESICLES that carry them into the next stage

  • synthesis of membrane

  bound proteins

  • enzymes in RER synthesize phospholipids from precursors in the cytosol
• Smooth ER

  • no ribosomes 

  • synthesis: lipids, oil, phospholipids & steroids 

  • metabolism: carbohydrates 

  • storage: calcium ions

  (muscle cells) 

  • detoxification: drugs, poisons, alcohol (other enzymes in SER of the liver)
• GOLGI APPARATUS 

  • Shipping & Receiving

  Center finishes, sorts, & ships cell products

  • Transport vesicles from ER travel to Golgi apparatus for modification
  • Abundant in cells specialized for secretion of glycoproteins
  • Flattened membranous sacs – CISTERNAE
  • CIS SIDE – receives by fusing with vesicles
  • TRANS SIDE – buds off vesicles
  • Manufactures polysaccharides such as pectin
• LYSOSOMES 

  • Digestive Compartments
  • Membranous sac of hydrolytic enzymes
  • Digests macromolecules (proteins, fats, polysaccharides, & nucleic acids) • Enzymes work best at pH 5
  • Massive leakage from lysosomes can destroy an entire cell by autodigestion
  • Creates a space where the cell can digest macromolecules safely Lysosomal enzymes & membrane
• Lysosomal enzymes & membrane are synthesized through RER then to Golgi

  Arise from budding from Golgi
• Lysosomes can fuse with

  • food vacuoles, formed when a food item is brought into cell by phagocytosis
  •  other organelles or parts of the cytosol 
  • Recycling process of autophagy renews the cell
• VACUOLES 

  • Diverse Maintenance Compartments
  • VESICLES & VACUOLES – membrane bound sacs with varied functions

  Food vacuoles 

  • From phagocytosis, fuse with lysosomes

  Contractile vacuoles

  • In freshwater protists, pump excess water out of the cell

  Central vacuoles 

  • Found in many mature plant cells
• • Tonoplast membrane surrounding the central vacuole
  • selective in its transport of solutes into the central vacuole
  • contains glycolipids (instead of phospholipids)
• Functions of the central vacuole

  • Stockpiling proteins or inorganic ions (K, Cl)
  • Depositing metabolic by products
  • Storing pigments
  • Storing defensive compounds against herbivores
• Major role in growth of plant cells

  • Cells enlarge as their vacuoles absorb water, with minimal investment in new cytoplasm
• MITOCHONDRIA & CHLOROPLASTS:

  Main Energy Transformers of Cells

  Convert energy to forms that cells can use for work 
• Mitochondria

  • site of cellular respiration

  • generates ATP from catabolism of sugars, fats & other fuels in the presence of oxygen
• Chloroplast

  • in plants & eukaryotic algae

  • site of photosynthesis

  • convert solar energy to chemical energy & synthesize new organic compounds from CO2 & H2O
• • not part of the endomembrane system
  • proteins come from free ribosomes in the cytosol & a few from their own ribosomes
  • have small quantities of DNA that direct synthesis of the polypeptides in these internal ribosomes
  • grow & reproduce as autonomous organelles (mitochondria & chloroplast)
• MITOCHONDRIA 

  • Chemical Energy Conversion
  • smooth outer membrane & highly folded inner membrane – CRISTAE 
  • fluid filled space (intermembrane space) in between outer & inner membrane
  • Cristae present ample surface area for enzymes that synthesize ATP
  • Inner membrane encloses the mitochondrial matrix, a fluid filled space with DNA, ribosomes & enzymes
• Chloroplast is a member of a class of plant structures called plastids
• Chloroplasts produce sugar via photosynthesis
• Chloroplasts are found in leaves and other green structures
• Chloroplasts reproduce by pinching into 2
• Mitochondria and Chloroplasts are mobile and move around the cell along tracks in the cytoskeleton
• Processes in chloroplasts are separated from cytosol by 2 membranes
• Inside the innermost membrane of chloroplasts is a fluid-filled space called stroma, which contains DNA, ribosomes, and enzymes
• Thylakoids are flattened sacs inside chloroplasts, stacked into grana, and are critical for converting light to chemical energy
• Other plastids include:

  • Amyloplasts: store starch
  • Chromoplasts: store pigments such as carotene
• CHLOROPLAST 

  • Capture of Light Energy

  One of the several members of a generalized class of plant structures called PLASTIDS
• Stroma – contains DNA, ribosomes, enzymes 

  Thylakoids – flattened sacs, stacked into grana, and are critical for converting light to chemical energy