Cell structures and functions

Centrosome and Microtubules

Centrosomes -Structure: Microtubules grow out from these. Contains a pair of centrioles, each composed of nine sets of triplet microtubules in a ring. -Both microtubules and centrosome are in cytoskeleton. -Function: compression-resisting girders of the cytoskeleton. Help organize microtubule assembly in animal cells. Microtubules -Structure: Largest cytoskeletal filaments. Hollow rods constructed from subunits called tubulin. Includes "plus" and "minus" ends. Found in eukaryotic cells. -Part of a variety of cell movements and cell division. -Function: Shape and support the cell. Guide organelle movement. Involved in the separation of chromosomes in cell division. Position of tubulin dimers determine the growing and shrinking in cellular activities.

Plasma Membrane

-found in both prokaryotic and eukaryotic cells -surrounds the entire cell -consists of a double layer of phospholipids *hydrophobic parts of phospholipids and proteins are on the inside *hydrophilic on both sides -various proteins embedded within -may have carb side chains attached to proteins or lipids on the outer surface -function: regulates concentrations of certain substances in and out of a cell -maintains shape of cell

Cell junctions

Structure and Functions: -Gap Junctions *Allow movement of ions, proteins, amino acids between cells (Allows heart to contract in unison) -Plasmodesmata *Connects internal chemical environments of adjacent cells *Similar to gap junctions -Tight Junctions *Prevent leakage of extracellular fluid (Skin is watertight) -Desmosomes *Fasten cells together like anchors (Muscle cells attach with these)

Golgi Apparatus

Structure: -"cisternae" -cis/trans faces -10-20 ㎛ diameter -present in EUKARYOTES containing protein filled vesicles from ER Function: -Receives vesicles, sorts them, repackages them, and reforming them to be sent to different locations -Vesicles that are not matured enough can be sent back to be used for other functions in the GA

Intermediate Filaments

Structure: -10 nanometers across, subdomains in rod domain called helices, fibrous proteins coiled into cables. Only found in some animals, including vertebrates (Eukaryotes) Function: Provides plasma membrane support, anchorage of nucleus and certain other organelles, formation of nuclear lamina -Especially sturdy structure (reinforcing the shape of a cell and fixing the position of certain organelles).

Cell Wall

Structure: -Plant cell wall is composed of cellulose *It is a structural carbohydrate and complex structure -Bacteria cell wall is composed of peptidoglycan *composed of alternating N- acetylglucosamine (NAG) and N- acetylmuramic acid (NAM) cross-linked by short peptides -Protozoa, Algae, and Fungi have cell wall made of Chitin -Composed of three different layers: Middle Lamella, Primary Cell Wall, Plasma Membrane -The cell wall contains many distinct holes, in plants they are called plasmodesmata Function: -Complex cellulose, peptidoglycan or chitin structure allows for protection and structure of cell -Limited flexibility: keeps plants shape and prevents hydrolysis from too much water -Plasmodesmata/pores: Used as filter to take in nutrients and release waste, allows water loss

Nucleus

structure: surrounded by nuclear envelope perforated by nuclear pores; nuclear envelope continuous with ER Function: houses chromosomes, which are made of chromatin; contains nucleoli, where ribosomal subunits are made; pores regulate entry and exit of material

Endocytic and Exocytic Vesicles

Structure: Vesicles are made up of plasma membrane that can take material into, within or out of a cell. Because they are made of the membrane, they are able to pinch off or fuse to the outside of a cell and do their job of moving particles. Function: -Endocytic and exocytic vesicles are two different types of vesicles that are part of the endomembrane system. These vesicles are found in eukaryotes and vary in diameter. -Endocytic vesicles form when cells take in a particle. The particle on the outside of the plasma membrane is covered by that membrane. The plasma membrane then "pinches" inward to form a bubble, which is a vesicle. If a cell ingests a large particle, a larger vesicle called phagosomes form, which are about 250nm in diameter. Smaller vesicles, pinocytic vesicles, form when ingesting tinier particles and are about 100nm in diameter. -Exocytic vesicles form when cells secret particles. A vesicle, varying in size again from 100-250nm in diameter carry particles from inside the cell and fuse to the plasma membrane. The vesicle becomes part of this membrane and releases the particle it contained to the outside.

Lysosomes

Structure: membranous sac of hydrolytic enzymes (in animal cells) Function: breakdown of ingested substances, cell macromolecules, and damaged organelles for recycling

Central Vacuole

Structure: -large vesicle with a selective membrane for transporting solutes, only found in eukaryotes (specifically only in plant cells) Function: Part of the endomembrane system > aids in the maintaining of water balance > stores waste > isolates hazardous material > contains enzymes for digestion > plant cell growth > contains inorganic ions- cell sap > contain pigments to attract pollinating insects > contains poisonous compound to defend against herbivores

Smooth ER

Structure: -A long network of folded tube like structures; lacks ribosomes. -Makes up 10% of a cell -Subdomain: Autocrine Motility Factor Receptor (AMF-R) -Smooth on the outside with an interior called the lumen enclosed by a phospholipid membrane -Only found in Eukaryotes Function: -Synthesizes lipids -Produce hormones -Metabolizes carbohydrates -Detoxifies drugs and poisons -Stores calcium Ions -Part of endocrine system

Rough ER

Structure: -Network of membranous sacs and tubes *Called cisterna (latin-"reservoir for a liquid") -Rough ER (ribosome-studded) which allows for protein synthesis -Lumen- where polypeptides fold into functional shape -The ER accounts for more than ½ the total membrane in eukaryotic cells Function: -Assembly of proteins *mRNA moves from nucleus to a ribosome *ribosome builds amino acid chain -"Membrane factory for the cell" - it grows in place by adding membrane proteins and phospholipids to its own membrane -Membrane synthesis

Microfilaments

Structure: 7 nanometers, thin solid rods built from actin (globular protein). Can form structural networks when certain proteins bind along the side of such a filament and allow a new filament to extend as a branch. Seem to be present in all eukaryotic cells. Function: As well, cortical microfilaments help support the cell's shape. This network of cortical microfilaments gives the outer cytoplasmic layer of a cell, called the cortex, the semisolid consistency of a gel, in contrast with the more fluid state of the interior cytoplasm. Microfilaments are well known for their role in cell motility. As well contributes to the division of animal cells. Thousands of actin filaments and thicker filaments made of a protein called myosin interact to cause contraction of muscle cells.

Mitochondria

Structure: Bounded by double membrane, inner membrane has infoldings Function: cellular respiration

Cytoplasm

Structure: The cytoplasm of a cell contains both the jelly-like substance inside a cell, called cytosol, and the sub-structures of the cell itself, called organelles. Also, has some small inclusions they are non-living elements. It is found in both animal and plant cells. It fills the cell and is 80% water. Function: The cytoplasm is responsible for cell shape, material transport like genetic material and products for cellular respiration, and storage. Cell growth and expansion, facilitates movement, acts as a buffer and protects genetic material and organelles. Link: Cytoplasmic organelles are specialized structures that haves its own functions like cellular respiration, protein synthesis etc. The inclusions are non-soluble molecules, they are seen floating in the cytoplasm, they act as stored fats and sugars that are ready for cellular respiration. The jelly like structure disallows grouping and other parts running into each other. The cytoskeleton of the cytoplasm provides shape to the cell and it also facilitates movement. Cytosol makes up about 70% of the volume of the cell.

Chloroplast

Structure: Typically two membranes around fluid stroma, which contains thylakoids stacked into granum Function: photosynthesis

Peroxisome

Structure: specialized metabolic compartment bounded by a single membrane Function: contains enzymes that transfer hydrogen atoms from substrates to oxygen, producing hydrogen peroxide as a by-product; H2O2 is converted to water by another enzyme

Ribosomes

Structure: two subunits made of ribosomal RNA and proteins; can be free in cytosol or bound to ER Function: protein synthesis