A Tour of the Cell Chapter 3

Answer the Following: What functions must a cell perform in order to maintain life? What cellular structures perform each of these properties.

A Typical Cell 3 main structural components Plasma or Cell Membrane – surrounds the cell Cytoplasm – gel like substance, holds organelles Nucleus – surrounded by a membrane

Cell Membrane Fluid Mosaic Model – Membrane molecules can float around the membrane Double layer of phospholipid molecules Hydrophilic phosphate heads Hydrophobic fatty acid tails In aqueous solutions these phospholipids form a sheet with fatty acid tails away from water and phosphate heads toward the water

Cell Membrane Different molecules are embedded in the membrane Cholesterol – keeps the membrane from becoming brittle Forms rafts for proteins to move on

Membrane proteins: Protein Channels = Transport Proteins Enzymes = Enzymatic activity Receptor Proteins = Signal transduction Glycoproteins = Cell-cell recognition Proteins for Intercellular joining

Transport Enzymatic activity Signal transduction Signal Enzymes LE 7-9a Signal Enzymes Receptor ATP Transport Enzymatic activity Signal transduction

Cell-cell recognition Intercellular joining Attachment to the LE 7-9b Glyco- protein Cell-cell recognition Intercellular joining Attachment to the cytoskeleton and extra- cellular matrix (ECM)

The endomembrane system regulates protein traffic and performs metabolic functions in the cell Parts of the endomembrane system: Nuclear envelope Endoplasmic reticulum Golgi apparatus Lysosomes Vacuoles Plasma membrane These are either continuous or connected by vesicles moving from part to part Copyright © 2008 Pearson Education, Inc., publishing as Pearson Benjamin Cummings

Endomembrane Animation http://users.uma.maine.edu/SBaker/nucleus_endo.html

Endoplasmic Reticulum 2 Types Rough ER – with ribosomes Smooth ER – without ribosomes Structure – Broad, flattened sacs Extend outward from the nucleus

Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Fig. 6-12 Smooth ER Nuclear envelope Rough ER ER lumen Cisternae Transitional ER Ribosomes Transport vesicle 200 nm Smooth ER Rough ER Figure 6.12 Endoplasmic reticulum (ER)

Functions of ER The smooth ER (no Ribosomes) Makes lipids for making membranes throughout the cell Removes Calcium ions from the cytoplasm and stores them Detoxifies poison The rough ER (Has Ribosomes) Has bound ribosomes Ribosomes produce polypeptide strands that enter the ER and are folded or joined with other proteins Proteins may be embedded in the ER membrane or move to the Golgi Apparatus in transport vesicles

Ribosomes Made of RNA 2 sub units, not membrane bound May be free or attached to the endoplasmic reticulum Site of protein synthesis Translation of mRNA into polypeptide chain

The Golgi Apparatus Functions of the Golgi apparatus include Receives many of the transport vesicles produced in the rough ER Consists of flattened membranous sacs Functions of the Golgi apparatus include To sort and modify of the products of the rough ER Packages these into vesicles to be transported Produces lysosomes

Golgi Animation http://bcs.whfreeman.com/thelifewire/content/chp04/0402002.html

(a) Phagocytosis: lysosome digesting food Lysosomes carry out intracellular digestion by Phagocytosis Break down proteins that are not needed The monomers can be reused Peroxisomes contain peroxidase to break down hydrogen peroxide (a) Phagocytosis: lysosome digesting food 1 µm Lysosome contains active hydrolytic enzymes Food vacuole fuses with lysosome Hydrolytic enzymes digest food particles Digestion Food vacuole Plasma membrane Lysosome Digestive Nucleus

Lysosome Animation http://highered.mcgraw-hill.com/sites/0072507470/student_view0/chapter3/animation__lysosomes.html

Mitochondria Found in nearly all eukaryotic cells Mitochondria are enclosed by two membranes A smooth outer membrane An inner folded membrane This increases the surface area for reactions to occur Mitochondrion Intermembrane space Outer membrane Free ribosomes in the mitochondrial matrix Mitochondrial DNA Inner Cristae Matrix 100 µm Figure 6.17

Mitochondria change energy from one form to another Are the sites of cellular respiration Breaks down large molecules to produce ATP Much of this process takes place in the inner membrane

Eukaryotes: The Nucleus DNA is located in the nucleus and does not leave Transcription of DNA into mRNA occurs Pre-mRNA is edited before leaving the nucleus Nuclear envelope has nuclear pores Is double sided Nucleolus – ribosomes are produced

The cytoskeleton Is a network of fibers extending throughout the cytoplasm Microtubule 0.25 µm Microfilaments Figure 6.20 Figure 6.20

There are three main types of fibers that make up the cytoskeleton

Microtubules Microtubules Shape the cell Guide movement of organelles Help separate the chromosome copies in dividing cells

Microfilaments (Actin Filaments) Are built from molecules of the protein actin

Microfilaments that function in cellular motility Contain the protein myosin in addition to actin Actin filament Myosin filament Myosin motors in muscle cell contraction. (a) Muscle cell Myosin arm Figure 6.27 A

Centrosomes and Centrioles The centrosome Is considered to be a “microtubule-organizing center” Plants and yeast cells lack centrosomes

Molecular Motors http://www.youtube.com/watch?feature=player_detailpage&v=kOeJwQ0OXc4

Cell Extensions Microvilli Found on cells where absorption is important Functions Increase surface area Allow for quick absorption

Cell Extensions Cilia and flagella Contain specialized arrangements of microtubules Are locomotor appendages of some cells

Cilia versus Flagellum

Cell Connections In animals, there are three types of intercellular junctions Desmosomes – like spot welds, hold cells together like velcro Example – Skin Cells

Cell Connections Gap junctions – Tight Junctions – When membranes of adjacent cells stick together Form tunnels that join cytoplasm Fuse the two membranes into one Tight Junctions – Membrane proteins from different cells fuse Like soft drink cans held by plastic

Cell Animation http://aimediaserver4.com/studiodaily/videoplayer/?src=ai4/harvard/harvard.swf&width=640&height=520

Variety of Cell Types

Plasma Membrane Structure: – Lipid bi-layer: 2 layers of phospholipids clustered back to back with polar heads and non-polar tails Proteins: are embedded in the lipid bi-layer or on the surface

Cell Membrane Function: Regulates what enters and leaves the cell. Cell membranes are selectively permeable. Also provides protection and support 2 ways in which molecules can be transported into a cell: Passive transport Active transport

Passive Transport = Diffusion Osmosis – diffusion of water through a selectively permeable membrane Facilitated diffusion - the use of membrane proteins to aid diffusion of a substance through a membrane

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_osmosis_works.html

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_facilitated_diffusion_works.html

Types of Solutions Hypertonic – contains higher concentration of solute Hypotonic – contains lower concentration of solute Isotonic – Contains an equal concentration of solute.

http://www.youtube.com/watch?v=7-QJ-UUX0iY

Active Transport Energy must be used to transport molecules into the cell. Molecular Transport - Using membrane proteins: ATP (energy) is required

http://highered. mcgraw-hill http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_the_sodium_potassium_pump_works.html

Review of Diffusion http://www.youtube.com/watch?v=2UPqLm-uDnI

Active Transport Other types of active transport: Endocytosis –Taking particles into the cell Phagocytosis – endocytosis of solids Pinocytosis – endocytosis of liquids Exocytosis – Secreting particles from the cell