Ch 4 Tour of the Cell

Microscopic Worlds Microscopes led to the discovery of the cell – Light microscopes – Cell membrane - yes – Large macromolecules - no – Microtubules - no – Mitochondria - maybe just barely – Many bacteria - yes

Microscopic Worlds Electron scanning microscope Scanning electron microscope Transmission electron microscope

Cell Size House DNA, protein molecules and internal structures Obtain nutrients and diffuse nutrients and O 2 Smaller cells have a greater surface area to volume ratio than do larger cells – Surface area is significant for diffusion and osmosis

Surface area : Volume Volume= 30 um *30 um* 30 um=27000um SA (large)= 6*(30um*30um)=5,400 um SA (small)=(6*(10um*10um))*27=16,200 um 30  m 10  m 30  m 10  m Surface area of one large cube  5,400  m 2 Total surface area of 27 small cubes  16,200  m 2

Domains of Life The 3 domains of life – Bacteria (prokaryotic cells) – Archaea (prokaryotic cells) – Eukarya (all other life forms)

Cells Prokaryotic – Bacteria & Archaea Eukaryotic – Protists, fungi, plants, animals Prokaryotic cells are simpler & usually smaller than Eukaryotic cells Prokaryotic cell Nucleoid region Nucleus Eukar yotic cell Organelles Colorized TEM 15,000 

In Common Bounded by plasma membrane Ribosomes Cytoplasm DNA as genetic material

Prokaryote Do not have membrane bound nucleus Have a cell wall outside their plasma membrane Circular DNA strands No membrane bound organelles Prokar yotic flagella Ribosomes Capsule Cell wall Plasma membrane Nucleoid region (DNA) Pili

Eukaryote Membrane bound nucleus Linear DNA Membrane bound organelles Nucleus Smooth endoplasmic reticulum Rough endoplasmic reticulum Ribosomes Golgi apparatus Plasma membrane Mitochondrion Flagellum Not in most plant cells Lysosome Centriole Microtubule Cytoskeleton Intermediate filament Microfilament Peroxisome

Size of cellSmallerLarger NucleusNo nuclear membraneTrue nucleus, consisting of nuclear membrane & nucleoli Membrane-enclosed organelles AbsentPresent Cell wallUsually present; chemically complex When present, chemically simple Plasma membranePresent CytoplasmPresent RibosomesPresent Chromosome (DNA) arrangement Single circular chromosome; lacks histones Multiple linear chromosomes with histones Sexual reproductionNo meiosis; transfer of DNA fragments through cell-to-cell contact Involves meiosis

Eukaryotic Cells A typical animal cell: Contains a variety of membranous organelles (underlined) Nucleus Smooth endoplasmic reticulum Rough endoplasmic reticulum Ribosomes Golgi apparatus Plasma membrane Mitochondrion Flagellum Not in most plant cells Lysosome Centriole Microtubule Cytoskeleton Intermediate filament Microfilament Peroxisome Figure 4.4A

Categories of Organelles Manufacturing – Nucleus, ribosomes, endoplasmic reticulum, Golgi apparatus Hydrolysis – Lysosomes (animals), vacuoles (plants), peroxisomes Energy processing – Mitochondria (animal), chloroplasts (plants) Structural support, movement, communication – Cytoskeleton, plasma membrane, cell wall (plants)

Plasma Membrane Forms boundary around cell Controls and regulates material transport Phospholipid bilayer

Nucleus Contains most of the cells DNA Nucleus enclosed by nuclear envelope rRNA synthesized in the nucleolus Nucleus Chromatin Nucleolus Pore Ribosomes Rough endoplasmic reticulum Two membranes of nuclear envelope

Ribosomes Synthesize proteins Free and bound ribosomes Composed of 2 subunits

Endoplasmic Reticulum Smooth lacks attached ribosomes – Synthesis of lipids, oils, phospholipids, and steroids – Processes toxins and drugs in liver cells – Stores and releases calcium ions in muscle cells Smooth ER Rough ER Nuclear envelope Rough ER Ribosomes Smooth ER TEM 45,000  Figure 4.7

ER Makes more membrane & proteins Rough ER has attached ribosome – Produce proteins that are secreted, inserted into membranes, or transport ed in vesicles to other organelles

Fig. 4-9b Transport vesicle buds off Secretory protein inside trans- port vesicle Glycoprotein Polypeptide Ribosome Sugar chain Rough ER

Golgi Apparatus Finishes, sorts, and ships cell products – Stacks of membranous sacs receive and modify ER products then ship them to other organelles or the cell surface Figure 4.9 Golgi apparatus TEM 130,000  Transport vesicle from the Golgi “Shipping” side of Golgi apparatus Golgi apparatus “Receiving” side of Golgi apparatus Transport vesicle from ER New vesicle forming

Lysosomes Digestive functions in many single celled organisms In white blood cells, they destroy ingested bacteria Also recycle damaged organelles

Lysosomes Figure 4.10A Golgi apparatus Plasma membrane “Food” Food vacuole Lysosomes 2 Lysosome engulfing damaged organelle 5 Digestion 4 3 Engulfment of particle Transport vesicle (containing inactive hydrolytic enzymes) 1 Rough ER

Vacuoles Function in the general maintenance of the cell – Plant cells contain a large central vacuole, which has lysosomal and storage functions Chloroplast Central vacuole Nucleus Colorized TEM 8,700  Figure 4.12A

Endomembrane System Interconnected structurally and functionally Nucleus Smooth ER Nuclear envelope Golgi apparatus Lysosome Vacuole Plasma membrane Rough ER Transport vesicle from ER to Golgi Transport vesicle from Golgi to plasma membrane

Mitochondria Cellular respiration – Converts chemical energy to ATP – Phospholipid bilayer membrane – Has own DNA and ribosomes Mitochondrion Outer membrane Intermembrane space Matrix Inner membrane Cristae TEM 44,880 

Chloroplasts Convert solar energy to chemical energy (photosynthesis) Stroma – Contains DNA, ribosomes and enzymes Thylakoids – Interconnected sacs that form stacks called granum

Endosymbosis Hypothesis of endosymbosis – Mitochondria and chloroplasts were once small prokaryotes living independently – At some point, began living within larger cells

The Cytoskeleton and Related Structures The cell’s internal skeleton helps organize its structure and activities – A network of protein fibers make up the cytoskeleton Actin subunit Microfilament 7 nm Fibrous subunits 10 nm Intermediate filamentMicrotubule 25 nm Tubulin subunit

– Microfilaments (actin filiments) Enable cells to change shape and move – Intermediate filaments Reinforce the cell and anchor cer tain organelles – Microtubules give the cell rigidity And provide anchors for organelles and act as tracks for organelle movement Actin subunit Microfilament 7 nm Fibrous subunits 10 nm Intermediate filamentMicrotubule 25 nm Tubulin subunit

Movement Cilia and flagella move when microtubules bend – Eukaryotic cilia and flagella are locomotor appendages that protrude from cer tain cells LM 600  Colorized SEM 4,100  Figure 4.17AFigure 4.17B

Cell Junctions Tight junctions can bind cells together into leakproof sheets Anchoring junctions link animal cells into strong tissues Gap junctions allow substances to flow from cell to cell Anchoring junction Tight junctions Gap junctions Extracellular matrix Space between cells Plasma membranes of adjacent cells Figure 4.18B

Plants and Cell Walls Supported by rigid cell walls made largely of cellulose Connect by plasmodesmata Connecting channels Plasma membrane Cytoplasm Plasmodesmata Vacuole Layers of one plant cell wall Walls of two adjacent plant cells Figure 4.18A

Fig. 4-23