Structures and Functions ofEukaryotic Cells

Chapter 2.1McGraw-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 membranePeripheral proteins: loosely and temporarily attached to outer

regions of the membrane or to integral proteins

Cell MembraneMembrane proteins help stabilize membranes and link to

cytoskeleton of the cellMembrane proteins also carry out functions:

Transport: proteins allow transport of substances across the membraneReaction catalysis: enzymes in cell membranes carry out chemical reactionsCell 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

NucleusNucleus: 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 ReticulumEndoplasmic 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 apparatusGolgi 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:

1. Rough ER surface’s ribosomes produce polypeptides which are kept in the lumen of ER (rather than cytosol) to go to smooth ER

2. Smooth ER stores and packages proteins in vesicles and sends it to cis face of Golgi apparatus membrane

3. Golgi apparatus membrane merges with vesicle so that it imports protein contents. Proteins are stored and modified to be ready for delivery.

4. 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

VacuoleVacuole: 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

LysosomesLysosomes: 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

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

Mitochondria

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 cellsCiliaConducts wave-like motion for movementCilia are on cells that line respiratory tract to sweep dust

within mucus back to throat

FlagellaTails that whip to propel cells

Homework• Pg 71 #4, 8, 10, 11, 12

Assignment• 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