Structures and Functions of Eukaryotic Cells Chapter 2.1 McGraw-Hill Ryerson Biology 12 (2011)

Cell Membrane Cell membrane made out of a phospholipid bilayer Semi-fluidity of phospholipids in this arrangement allows flexibility of the membrane Also allows membrane to be embedded with proteins and carbohydrates “Fluid Mosaic Model”

Cell Membrane Phospholipid bilayer Lipids are held together by weak intermolecular forces Thus molecules in membrane are able to move freely The phospholipids are aligned like this due to the hydrophillic head and hydrophobic tails

Cell Membrane Phospholipid bilayer fluidity If the bilayer is too fluid, too many molecules diffuse in and out of the cell If the bilayer is too rigid, not enough molecules diffuse in and out of cell

Cell Membrane Phospholipid bilayer fluidity Factors affect fluidity: Temperature (higher temperature = more fluidity) Presence of double bonds in fatty acids of phopholipid tail (more d-bonds= more fluidity) Fatty acid length (shorter = less intermolecular attraction between nonpolar tails = more fluidity) Presence of cholesterol in membrane but depends on temperature - presence of cholesterol increases intermolecular forces in membrane to hold tightly together at high temperatures = less fluidity - presence of cholesterol break up packing that occurs as phospholipid solidify into a gel at low temperatures = more fluidity

Cell Membrane Proteins are embedded in cell membranes Integral proteins: embedded in the membrane Peripheral proteins: loosely and temporarily attached to outer regions of the membrane or to integral proteins

Cell Membrane Membrane proteins help stabilize membranes and link to cytoskeleton of the cell Membrane proteins also carry out functions: Transport: proteins allow transport of substances across the membrane Reaction catalysis: enzymes in cell membranes carry out chemical reactions Cell recognition: proteins on membrane act as “identity tags” Signal reception and transduction: Receptor proteins bind to signal molecules, and react in accordance to the signal

Nucleus Nucleus: Labeled 2 on Diagram Contains DNA Surrounded by nuclear envelope Has double membrane of two phospholipid bilayers Membrane separates nucleus from rest of cell – why is this needed? Nuclear pores present to permit passage of RNA Contains Nucleolus (1 on diagram) Contains RNA, protein, chromatin

Endoplasmic Reticulum Endoplasmic Reticulum (ER) Rough ER (Labeled 5 on diagram) Studded with ribosomes Synthesizes proteins that are part of membranes or intened for export from the cell Smooth ER (Labeled 8 on diagram) Synthesizes lipids and lipid-containing molecules (e.g. phospholipids)

Golgi apparatus Golgi apparatus: labeled 6 Packages, processes, sorts, and distributes proteins, lipids, and other substances within the cell Acts like a “post office” Packaged into membrane-bound sacs called vesicles Vesicles are labeled 4 on diagram

Endomembrane system System acts as the transportation and product-processing section Consists of: nuclear envelope endoplasmic reticulum Golgi apparatus Vesicles

Endomembrane system Steps: Rough ER surface’s ribosomes produce polypeptides which are kept in the lumen of ER (rather than cytosol) to go to smooth ER Smooth ER stores and packages proteins in vesicles and sends it to cis face of Golgi apparatus membrane Golgi apparatus membrane merges with vesicle so that it imports protein contents. Proteins are stored and modified to be ready for delivery. When ready for delivery, proteins pinch off from trans face of golgi apparatus membrane to form vesicles. These vesicles transport the proteins to various destinations

Vacuole Vacuole: labeled 10 Typical animal cells contains many small vesicles Plant cells contain a large central vesicle called vacuole Stores water, ions, sugars, amino acids, and macromolecules Also contains enzymes to break down materials Water that fills it up, allows it to engorge and push up against the cell giving it rigidity Vacuoles determine Turgor pressure Unwatered plants wilt because not enough turgor pressure

Lysosomes Lysosomes: labeled 12 Membrane-enclosed sacs with digestive enzymes (more than 40) Enzymes’ optimal pH is ~5 Cytosol pH is ~7.2 Breaks down parts that are not needed Also break down foreign particles E.g. white blood cells’s lysosomes destroys bacteria

Mitochondria Chloroplast Mitochondria: labeled 9 Break down high-energy-yielding organic molecules to convert stored energy into usable energy (we will see this in Unit 2) Chloroplast: Only photosynthetic organisms Contains chlorophyll Uses light energy to convert CO2 and H2O, through redox reactions, into energy-rich organic molecules Chloroplast

Cytoskeleton Internal network of protein fibres Provides structure and anchoring cell membrane and organelles in place Can act like tracts for vesicles to move

Cilia and Flagella Located on the outside of some cells Cilia Flagella Conducts wave-like motion for movement Cilia are on cells that line respiratory tract to sweep dust within mucus back to throat Flagella Tails that whip to propel cells

Homework Assignment Pg 71 #4, 8, 10, 11, 12 Draw out an animal cell and draw in the organelles and components Draw out a plant cell and draw in the organelles and components Make a table to correspond with your drawings and list all the organelles that you’ve learned with information and facts to help you remember what they do Due: Saturday, May 18, 2013