Eukaryotic Cells: An Overview

Exploring Eukaryotic Cellular Structure Substructures of Animal & Plant cells Figure 1-12  Major components of Eukaryotic Cells Plasma Membrane 700µm2 Internal Membranes & Organelles 7,000µm2 Cytoskeleton 94,000µm2 ...

Exploring Eukaryotic Cellular Structure Substructures of Animal & Plant cells Figure 1-12  Major components of Eukaryotic Cells Plasma Membrane 700µm2 Internal Membranes & Organelles 7,000µm2 Cytoskeleton 94,000µm2  Organelles Double Membrane Bound Single-Membrane Bound Nucleus Smooth Endoplasmic Reticulum Mitochondrion Rough Endoplasmic Chloroplast Reticulum Lysosome Non-Membrane Bound Golgi Apparatus Ribosomes Peroxisome Proteasomes Vacuoles & Vesicles Cytoskeleton elements Cilia & Flagella Centrioles – Centrosomes – Basal Bodies  Nucleus Typically largest organelle (in animal cells) “Control center of the cell” – contains most of cell’s DNA Double-membrane structure: – outer nuclear membrane – inter-membrane space – inner nuclear membrane Inner material: nucleoplasm Nucleolus: rRNA synthesis Nuclear lamina: Inner membrane’s inner surface – Lamin proteins Nuclear Pore Complex (NPC)  Endoplasmic Reticulum (ER) Single-membrane bound organelle – Extensive network of closed, flattened membrane-bound sacs ER membrane continuous with outer nuclear membrane ER lumen is continuous with inter-membrane space of the nucleus Divided into two parts: – Rough ER – Smooth ER  Smooth ER Continuous with rough ER Lacks bound ribosomes Four main functions: 1. Ca+2 storage 2. Glycogen metabolism 3. Lipid synthesis 4. Detoxification or modification of certain chemicals Rough ER Immediately adjacent to nucleus Studded with ribosomes on its cytosolic surface which synthesize proteins Site of initial processing of the following proteins: – exported from the cell – embedded in plasma membrane – found in ER, Golgi apparatus & lysosomes Nascent polypeptides associate w/ Rough Endoplasmic Reticulum membrane or enter ER lumen – chaperones will assist in folding – enzyme modifications take place  Ribosomes Sites of protein synthesis (translation) Consist of rRNA and proteins Ribosomes may be either: – free in the cytosol – bound to the cytosolic surface of the rough ER Functional ribosome consists of 2 subunits: 40S – large and small – designated by S values 60S Eukaryotic ribosome (80S)  Fates of Proteins Synthesized on Bound or Free Ribosomes Although the structures of free and bound ribosomes are identical, the fates of their synthesized proteins differ. Proteins made on bound ribosomes are meant for: – export from the cell – embedding in the plasma membrane – the ER, the Golgi or lysosomes Proteins made on free ribosomes are meant for use in: – cytosol, nucleus, mitochondria, chloroplasts, peroxisomes  Golgi Apparatus Series of flattened membrane-bound sacs (cisternae) Cell’s “post office” – Newly made proteins arrive from rough ER within transport vesicles Exhibits polarity: cis and trans faces – Divided into the cis-Golgi, medial-Golgi and trans-Golgi – Different luminal enzymes present that modify proteins Golgi Apparatus  Secretory Pathway Movement of proteins from: – bound ribosomes – through rough ER – transport vesicles – cis-Golgi – medial-Golgi – trans-Golgi – transport vesicles – plasma membrane or lysosomes  Lysosome Animal cell’s “digestive system” & “garbage disposal system” – hydrolytic enzymes (acid hydrolases) degrade polymers into monomeric subunits – low pH (lysosomal lumen = ~4.8) V-class proton pumps bring in H+ Cl- channels present to bring in Cl- Functions: – digest materials taken up by cell – digest damaged or aged organelles (autophagy = eating oneself) – involved in apoptosis Several human diseases are caused by defects in specific lysosomal enzymes (substrates accumulate inside lysosome) – Tay-Sachs disease: defective enzyme for breakdown of gangliosides, glycolipids accumulate, nerve cells enlarged with lipid-filled lysosomes Cellular structures that deliver materials to lysosomes  Peroxisomes Degrade fatty acids & toxic compounds Contain oxidases: hydrolytic enzymes that use O2 to oxidize organic substances – by-product of oxidase action is production of toxic H2O2 Contains catalase: breaks down H2O2 2H2O2  2H2O + O2 Peroxisomes are self-assembling – their "life-span" is only a day – process of reproduction is called peroxisomal biogenesis  Endomembrane System It is a group of membranes and organelles in eukaryotic cells that works together to modify, package, and transport lipids and proteins. Consists of: – Nuclear envelope – Membranes of endoplasmic reticulum – Golgi apparatus – Vesicles – Lysosomes Endomembrane System: A Visual Summary  Mitochondrion Double-membrane bound organelle Basic structure: – outer membrane – intermembrane space – inner membrane with infoldings (cristae) – lumen termed matrix Contains circular mtDNA, granules, and mitoribosomes Site of aerobic cellular respiration “Powerhouse of the cell”  Vesicles & Vacuoles General term for a variety of single-membrane bound sacs that serve a number of roles including storage, transport, endocytosis, exocytosis….. Vacuoles (plant cells): storage site for ions and nutrients, uptake of water by osmosis creates pressure to push membrane up against cell wall  Cytoskeleton Elements Responsible for: – maintaining and changing cell shape – internal transport – anchoring of internal & external components – movement of the cell – movement of chromosomes during cell division – scaffolding of the cell Types of Cytoskeleton Elements: – Microtubules: Polymers of α and β tubulin – Microfilaments: Polymers of actin – Intermediate filaments: Various proteins  Functions of Microtubules Move chromosomes during cell division Component of centrioles, basal bodies and centrosomes Serve as tracks for the movement of vesicles and vacuoles Internal scaffolding of eukaryotic cilia and flagella  Cilia & Flagella Locomotor structures that are cytoplasmic extensions Cilia and flagella differ in length – Cilia: shorter, move in an oar-like motion – Flagella: longer, move in a whip-like motion Cilia and flagella are structurally similar – share 9+2 microtubule arrangement  Functions of Microfilaments Cell contraction – e.g. cleavage furrow formation during cytokinesis Anchor for extra-cellular elements Cytoplasmic streaming  Functions of Intermediate Filaments Scaffold for the cell Internal lining of the inner nuclear membrane  Different Types of Microscopes Basic microscope is a bright-field microscope Phase contrast and differential interference contrast microscopy used to view details of live cells and to monitor cell movement Bright-field DIC Phase-contrast  Different Types of Microscopes Proteins can be tagged w/ florescent proteins and seen w/ flourescence microscopy Confocal microscopy allows for sharper images of a specimen  Preparing Tissues for Microscopy Tissues are fixed, embedded and cut into sections Deconvolution fluorescence microscopy: reduced blurring & sharper images Differential Centrifugation  Cell Fractionation and Differential Centrifugation Grind cells Then Then centrifuge centrifuge Centrifuge longer even longer @ 600 g @ 15,000 g @ 100,000 g Sediment Sediment Sediment Soluble contains contains contains portion of nuclei mitochondria, ribosomes, cytoplasm. lysosomes ER No sediment 36 Equilibrium Density-Gradient Centrifugation Organelle pellet (from last slide) can be further separated using sucrose banding