Cell Structures

1. Plasma Membrane (Cell Membrane) 
• Separates internal from external
• allows certain molecules in and out of the cell
1. selective permeability/semipermeability
• is a lipid bilayer
2. Phospholipids
• main type of lipid found in plasma membrane
• made of polar, phosphorus-containing head and two long fatty-acid non polar tails
• makes phospholipid bilayer
3. Membrane proteins
• 2 groups
• Integral membrane proteins
• Permanently embedded within plasma membrane
• channels/transports molecules across the membrane
• Transmembrane proteins span entire plasma membrane
1. found in all types of biological membranes
• Integral monotopic proteins-- permanently attached to membrane from one side. 
4. Cytoplasm
• gel-like material within cell is the cytoplasm
• organelles are suspended and held together by fatty membrane
• cytosol does not contain organelles (80-90% water) 
5. Cytoskeleton
• skeleton that crisscrosses the cytoplasm
• made of long, thin protein fibers
• helps maintain cell shape, holds organelles in place, and enables cell movement. 
• fibers
• Microtubules: hollow cylinders, thickest cytoskeleton structures
1. made of filaments, polymers of alpha and beta tublin
2. tublin forms pairs that twist around each other
3. holds organelles in place, allows them to move, and forms mitotic spindles during cell division
4. makes up parts of cilia and flagella
• Microfilaments
1. made of two thin actin chains that twist around one another
2. mostly concentrated beneath cell membrane
3. actin interacts with myosin to cause contraction in muscle cells
4. numerous in phagocytes
• Intermediate filaments
1. holds organelles and provide strength
2. found in hair, skin, and nail cells
6. Flagella
• long, thin structures that stick out from cell membrane
• helps cells move/swim towards food
• eukaryotic flagella bend and flex like a whip
7. Cilia
• much shorter than flagella
• covers the entire surface of some single-celled organisms
• also used for movement
8. Nucleus
• membrane-enclosed organelle
• contains DNA
• has genes/genetic information
• organized into chromosomes
• maintains integrity of genes and regulates gene expression
9. Nuclear Envelope
• double membrane that encloses genetic material
• made of two lipid bilayers, inside and outside
• outer membrane continuous with rough endoplasmic reticulum
• nuclear pores regulate exchange of materials between nucleus and cytoplasm
10. Nucleolus
• mainly involved in assembly of ribosomes
• exported to cytoplasm
11. Centrioles
• rod-like structures made of short microtubules
• important in cellular division
• arrange mitotic spindles that pull chromosome apart during meiosis
12. Mitochondria
• membrane enclosed organelle
• "power plants" because they make ATP (energy source) 
• mostly made in mitochondria
• has two phospholipid membranes
• smooth outer membrane separates it from cytosol
• inner membrane has many folds, called cristae
• fluid-filled inside (matrix) is where most ATP is made
• have their own DNA
• possibly descended from prokaryotes
• able to reproduce asexually
• endosymbiotic theory
1. once free-living prokaryotes that infected eukaryotic cells
2. protected inside eukaryotic host cell
3. supplied extra ATP to host
13. Endoplasmic Reticulum
• network of phospholipid membranes
• forms hollow tubes, flattened sheets, and round sacs
1. called cisternae
• two functions
1. transport: molecules cam move inside ER, like intracellular highway
2. synthesis: ribosomes make proteins. Lipids also produced in ER
• Rough Endoplasmic Reticulum
• studded with ribosomes, "rough appearance" 
• ribosomes makes proteins, transported by sacs (transport vesicles) 
• works with Golgi apparatus to move new proteins to correct place in cell
• membrane is continuous with outer layer of nuclear envelope
• Smooth Endoplasmic Reticulum
• lipid synthesis, calcium ion storage, and drug detoxification
• made up of tubules and vesicles that branch out to form networks
• interconnected network with rough endoplasmic reticulum
14. Ribosomes
• site of protein synthesis (assembly) 
• made of large and small subunits
• found alone or in groups in cytoplasm
• some attached to ER, and others attached to nuclear envelope
• ribosomes on rough ER usually produce proteins that are destined for cell membrane
15. Golgi Apparatus
• made up of 5-8 cup-shaped, membrane-covered discs called cisternae
• modifies, sorts and packages different substances for cell or non cell use
• close to nucleus of cell
• involved in transport of lipids around the cell
• pieces pinch off to form vesicles to transport molecules
• like a post office
• both in animal and plant cells
• plant cells have more Golgi stacks scattered throughout cytoplasm
• contains enzymes that synthesize cell wall polysaccharides
16. Vesicles
• small compartment that is separated from cytosol by one or more lipid bilayer
• mostly made in Golgi apparatus and ER, or from parts of the cell membrane
• space inside vesicle can be made to be chemically different from the cytosol
• basic tools of cells for organizing metabolism, transport, and storage of molecules
• chemical reaction chambers
• transport vesicles
• move molecules between locations inside the cell
• Lysosomes
• vesicles formed by Golgi apparatus
• contains powerful enzymes that could break down (digest) the cell
• breaks down harmful cell products, waste material, and cellular debris, then force them out of the cell
• digest invading organisms, like bacteria
• also breaks down cells ready to die (autolysis) 
• Peroxisomes
• uses oxygen to break down toxic substances in cell
• self-replicate-- grow bigger then divide
• common in liver and kidney cells
• named for hydrogen peroxide produced when breaking down organic compounds
1. broken down into water and oxygen molecules
17. Vacuoles
• have secretory, excretory, and storage functions
• many used as storage areas
• vesicles smaller than vacuoles

Special Structures in Plant Cells

1. Cell Wall
• rigid layer outside cell membrane and surrounds the cell
• contains cellulose, protein, and other polysaccharides
• provides structural support and protection
• pores in cell wall allow water and nutrients to move in and out
• prevents cell from bursting when water enters cell
• microtubules guide formation of plant cell wall
• cellulose lade down by enzymes forms primary cell wall
• some cells have secondary cell wall
• contains lignin
2. Central Vacuole
• most have one that occupies more than 30% of cell's volume
• can occupy as much as 90% volume
• surrounded by membrane (tonoplast) 
• used to maintain turgor pressure against cell wall
• proteins control flow of water in and out of vacuole
• contains large amount of cell sap
• mixture of water, enzymes, ions, salts, and others
• may also contain toxic byproducts
3. Plastids
• closely related to membrane-bound organelles
• responsible for photosynthesis, storage of starch, synthesis for cellular building blocks molecules
• contains own DNA and ribosomes
• may be descended from photosynthetic bacteria
• chloroplasts
• organelle of photosynthesis
• capture sunlight and use it with water and carbon dioxide to make sugar for plant
• chromoplasts
• make and store pigments that give colors
• leucoplasts
• do not contain pigments
• located in roots and non-photosynthetic tissues of plants 
• mostly do not have a major storage function
• make molecules; fatty acids, and amino acids