NOTES: 7.2 – CELL STRUCTURES & FUNCTIONS

Comparing the cell to a factory: ● each cell part (“organelle”) can be compared to a specialized machine in a factory; ● each part performs a specific “job” or function towards the functioning of the cell as a whole…

Cell Organization: ● each eukaryotic cell can be divided into 2 major parts: 1) Cytoplasm 2) Nucleus

CYTOPLASM: ● CYTOPLASM: the portion of the cell outside the nucleus; mostly water; all other organelles suspended in cytoplasm

NUCLEUS: ● NUCLEUS: contains nearly all of the cell’s DNA (the coded instructions for making all of the cell’s proteins); ● considered the “control center” of the cell; ● nucleus is surrounded by a nuclear envelope

NUCLEAR ENVELOPE ● double membrane which encloses the nucleus; ● includes many nuclear pores (holes) which allow material to move in and out of the nucleus

CHROMATIN ● threadlike complex of DNA bound to proteins; it makes up chromosomes in eukaryotic cells

CHROMOSOMES ● compacted, coiled up chromatin; ● human cells have 46 chromosomes (23 pairs)

NUCLEOLUS ● dense, spherical region in the nucleus -ribosome assembly begins here

Organelles that Store, Clean Up, and Support: ● vacuoles & vesicles ● lysosomes ● cytoskeleton

VACUOLE: ● used for storage (of water, salts, proteins, carbs); ● in animal cells, vacuoles are smaller than in plant cells

PLANT VACUOLES… ● may contain soluble pigments in some cells (red and blue pigments in flowers);

PLANT VACUOLES… ● help protect from predators by storing waste products that may also be poisonous compounds ● contractile vacuole: specialized vacuole that pumps excess water out of cell.

VESICLES: ● VESICLES: small, membrane-enclosed structures that store and move materials between cell organelles, or to and from cell surface

LYSOSOMES: ● the cell’s “clean-up crew”! ● contain digestive enzymes that break down macromolecules into smaller subunits; ● recycle the cell’s own organic material; ● can destroy cells by breaking open all at once and digesting the cell from within

CYTOSKELETON: ● CYTOSKELETON: provides shape & internal organization; also involved in transport of materials within the cell, as well as whole-cell movement ● includes protein filaments: -microfilaments -microtubules

Cytoskeleton

MICROTUBULES & MICROFILAMENTS ● make up the cytoskeleton ● structural support to cell; maintain shape ● involved in cell movement

Microfilaments: ● threadlike structures; ● made up of protein: ACTIN ● stabilize cell shape ● microfilament assembly & disassembly allow amoebas & other cells to “crawl” along surfaces Yellow: nucleus Green: microfilaments throughout cytoplasm

Microtubules: ● thin, hollow cylinders made of protein: TUBULIN ● maintain cell shape; ● can serve as “tracks” to guide organelle movement; ● involved in separation of chromosomes in cell division; make up SPINDLE FIBERS / CENTRIOLES (in animal cells)

Microtubules (cont.)… ● responsible for movement of flagella & cilia

FLAGELLA and CILIA: ● FLAGELLA: longer usually single extensions; used to propel a cell ● CILIA: shorter and more numerous than flagella; wavelike motion used to sweep extracellular material over/away from cell

Organelles that Build, Modify, and Transport Proteins: ● ribosomes ● endoplasmic reticulum ● Golgi Apparatus

RIBOSOMES: ● site of protein synthesis -small particles of RNA & protein -follow coded instructions from DNA -made in the nucleolus -cells especially active in protein synthesis often contain large #s of ribosomes -may be free (in cytoplasm) or attached to the ER

ENDOPLASMIC RETICULUM (ER): ● extensive network of internal membranes ● used to transport and/or modify proteins; ● can be ROUGH (ribosomes) or SMOOTH (no ribosomes)

Rough ER: ● rough appearance due to ribosomes on outer surface; ● newly made proteins leave the ribosomes and are “dropped off” into the rough ER; ● modifies and transports proteins;

Smooth ER: ● synthesizes lipids, phospholipids, steroids ● detoxifies drugs and poisons

GOLGI APPARATUS: ● stacked, flattened membranes ● finishes, sorts, packages and ships many cell products (a.k.a. the “post office” of the cell)

Organelles that Capture and Release Energy: ● chloroplasts ● mitochondria

CHLOROPLASTS: (“the organelles that feed the world”) ● contain chlorophyll; ● site of photosynthesis (convert light energy into “food”, or chemical energy)

MITOCHONDRIA: ● sites of cellular respiration ● convert the chemical energy stored in food into usable energy packets for the cell ● the # in cells varies and is related to the cell’s metabolic activity (i.e. if a cell uses more energy, it will have more mitochondria!)

Cellular Boundaries: ● cell wall ● cell membrane

Cellular Boundaries: ● CELL WALL: - semi-rigid structure outside of cell membrane of PLANT CELLS & most prokaryotes; - in plants, consists of CELLULOSE fibers; provides support, limits cell’s volume, and protects against fungi and/or microorganism infection; most cell walls are porous enough to allow water, oxygen, carbon dioxide, etc. to pass through.

CELL WALL:

CELL MEMBRANE:

What must a membrane do? ● let some things leave / enter cell ● keep stuff inside or outside of cell ● be flexible as cell changes shape

● cell membranes form a LIPID BILAYER that is flexible & can regulate what enters & exits the cell; ● The cell membrane is composed of molecules called PHOSPHOLIPIDS.

PHOSPHOLIPIDS: -one end is strongly nonpolar (hydrophobic); -one end is extremely polar (hydrophilic)

● the nonpolar lipid “tails” are repelled by polar water molecules; the polar “heads” of the molecules form hydrogen bonds with water molecules.

● So, every phospholipid molecule orients so that its polar “head” faces water and its nonpolar “tails” face away... two layers are formed with the tails facing each other...the result is called a LIPID BILAYER.

Lipid bilayer membranes are: ● PERMEABLE to: lipids nonpolar molecules: O2, CO2 small polar molecules: H2O ● IMPERMEABLE to: ions (Na+, K+, Cl-) large polar molecules: sugars, proteins

3 Main Types of Cell Membrane PROTEINS… 1) Channels 2) Receptor proteins 3) Cell surface markers

1. CHANNELS: ● a channel will transport only certain kinds of molecules...which gives the cell membrane its selectively permeable nature                       

2. RECEPTOR PROTEINS: ● collect & transmit information from the cell’s environment

3. CELL SURFACE MARKERS: ● identify your body‘s cells as belonging to you (useful in cell-cell recognition)