Cell Organelles

• The Cell

General Attributes of the Cell

• The plasma membrane is a phospholipid bilayer which separates the cell from its environment.
• The plasma membrane allows allows passage of oxygen, nutrients, and wastes
• Cytosol is a semifluid substance where organelles are suspended.
• Cytoplasm is the region between the plasma membrane and nucleus.
• Chromosomes contain the genetic material, DNA.
• Ribosomes are organelles that make proteins.

Prokaryotic vs Eukaryotic Cells

• Prokaryotes include bacteria and archaea
• The nucleoid in prokaryotes is not bound by membrane
• Prokaryotes have a circular strand of DNA
• Prokaryotes have fewer organelles than eukaryotes
• Eukaryotes include protists, fungi, plants and animals
• Eukaryotic cells possess a membrane-bound nucleus
• Eukaryotes contain DNA in several linear chromosomes.
• Eukaryotes have specialized membrane-bound organelles

Animal Cell

• Animal cells contain the following components: flagellum, centrosome, chromatin, nucleolus, nuclear envelope, endoplasmic reticulum (ER), ribosomes, Golgi apparatus, plasma membrane, mitochondrion, lysosome, microfilaments, intermediate filaments, microtubules, and cytoskeleton.

Plant Cell

• Plant cells contain the following components: nucleus, chromatin, nucleolus, nuclear envelope, centrosome, rough and smooth endoplasmic reticulum, Golgi apparatus, ribosomes, central vacuole, tonoplast, microfilaments, intermediate filaments, microtubules, cytoskeleton, chloroplast, plasmodesmata, cell wall, plasma membrane, mitochondrion, and peroxisome.

Nucleus: Information Central

• The nucleus contains the eukaryotic cell's genetic library
• It is separated from the cytoplasm by a double membrane.
• Nuclear pores allow macromolecules and particles to pass through.
• Some genes are contained in mitochondria and chloroplasts.

Nuclear Lamina

• The nuclear lamina is a network of intermediate filaments.
• It helps maintain the shape of the nucleus.
• It provides mechanical support for the nuclear membrane. DNA + Histones = Chromatin
• DNA and histones appear as a diffused mass.
• When cells prepares to divide, chromatin fibers coil up, seen as separate structures (chromosomes).

Nucleolus

• Site of ribosomal RNA (rRNA synthesis.
• rRNA combines with proteins in the cytoplasm to form ribosomal subunits.

Protein Factories: Ribosomes

• Ribosomes are built from rRNA and proteins.
• Site of protein synthesis.
• Cell types that synthesize large quantities of proteins have many ribosomes and prominent nucleoli.

Free Ribosomes

• Free ribosomes suspended in cytosol.
• Free ribosomes synthesize proteins that function in the cytosol.

Bound Ribosomes

• Bound ribosomes are attached to the rough endoplasmic reticulum and nuclear envelope.
• Synthesize proteins included in the membrane and for export from the cell.

The Endomembrane System

• Many of the internal membranes in a eukaryotic cell are part of this system.
• Direct contact of membranes or connected via transfer of vesicles or sacs of membrane.

The Endomembrane System components:

• Nuclear envelope
• endoplasmic reticulum
• Golgi apparatus
• lysosomes
• vacuoles/vesicles
• plasma membrane
• Plays a key role in the synthesis and hydrolysis of macromolecules in the cell.
• Components modify macromolecules.

Endoplasmic Reticulum

• The Endoplasmic Reticulum manufactures membranes and performs biosynthetic functions.
• It contains membranous tubules and fluid-filled sacs called cisternae.
• The ER membrane is continuous with the nuclear envelope.
• The cisternal lumen is continuous with the space between the two membranes of the nuclear envelope.

2 ER Regions

• Rough ER has ribosomes
• Abundant in cells that secerete protein.
• Secretory proteins are packaged into transport vesicles
• Synthesis of membrane-bound proteins
• Enzymes in RER synthesize phospholipids from precursors in the cytosol
• Smooth ER has no ribosomes
• Smooth ER facilitates the synthesis of lipids, oil, phospholipids and steroids
• Smooth ER faciliates the metabolism of carbohydrates
• Catalyzes a key step in the mobillization of glucose from stored glycogen in the liver
• Stores calcium ions in muscle cells
• Enzymes in smooth ER of the liver detoxify drugs, poisons and alcohol

Golgi Apparatus: Shipping & Receiving

• The Golgi apparatus finishes, sorts and ships cell products
• Transport vesicles from the ER travel to the Golgi apparatus for modification.
• Abundant in cells specialized for the secretion of glycoproteins.
• Consists of flattened membranous sacs called, cisternae
• Cis side receives by fusing with vesicles
• Trans side buds off vesicles.
• Manufactures polysaccharides such as pectin.

Lysosomes – Digestive Compartments

• Lysosomes are membranous sacs of hydrolytic enzymes.
• Digests macromolecules.
• Enzymes work at pH 5.
• Leaks from lysosomes can destroy entire cells by autodigestion.
• Creates a space where the cell can digest macromolecules safely.
• Lysosomal enzymes and the membrane are synthesized through the rough ER, then to Golgi.
• Arise from budding from the Golgi.

Lysosomes Can Fuse With

• Food vacuoles, formed when food is brought into the cell by phagocytosis.
• Other organelles or parts of cytosol.
• Recycling processes of autophagy renew the cell.

Vacuoles: Diverse Maintenance Compartments

• Vesicles & vacuoles are membrane bound sacs that have varied functions.
• Food vacuoles are from phagocytosis and fuse with lysosomes.
• Contractile vacuoles are in freshwater protists and pump excess water out of the cell.
• Central vacuoles are found in many mature plant cells.

Tonoplast

• Tonoplast: membrane surrounding the central vacuole
• Selective in the transport of solutes into the central vacuole- contains glycolipids instead of phospholipids.
• Functions of the central vacuole include; Stockpiling proteins or inorganic ions (K, Cl), Depositing metabolic by products, storing pigments and storing defensive compounds against herbivores
• Major role in the growth of plant cells due to cells enlarging from vacuoles absorbing water.

Mitochondria: Chemical Energy Conversion

• Smooth outer membrane and highly folded inner membrane
• Cristae are an ample surface area for enzymes that synthesis ATP
• The inner membrane encloses the mitochrondrial matrix which is a fluid filled space with DNA, ribosomes and enzymes

Chloroplast: Capture of Light Energy

• Plant structures called plastids
• AmylOPLASTS - store starch
• CHROMOPLASTS - store pigments such as carotene
• Produces sugar via photosynthesis
• Found in leaves and other green structures
• Reproduce themselves by pinching into two.
• Mitochondria and Chloroplasts are mobile & move around the cell along tracks in the cytoskeleton

Peroxisomes

• Oxidation
• Generates & degrade hydrogen peroxide in performing various metabolic functions
• Bound by a single membrane
• Formed by incorporation of proteins and lipids in the cytosol
• Splits into 2 upon reaching a certain size
• Contain enzymes that transfer H from various substrates to O₂ (oxidation reactions)
• Intermediate product is H₂O₂ but converted into H₂O by catalase
• Some break fatty acids to smaller molecules that are transported to mitochondria for fuel
• Some detoxify alcohol and other harmful compounds

Cytoskeleton

• Network of fibers that organizes structures and actvities in the cell
• Made up of microtubules, microfilaments and intermediate filaments

Roles of the Cytoskeleton

• Mechanical support & cell shape maintenance
• Anchorage for organelles & cytosolic enzymes
• Dynamic, dismantling in one part and reassembling in another to change cell shape

Cytoskeleton: Role in Cell Motility

• Cilia & flagella, motor proteins pull components of cytoskeleton past each other.
• Interactions of motor proteins and the cytoskeleton circulates materials within a cell via streaming.
• Also in muscle cells

Microtubules

• alpha & beta tubulin dimers
• move chormosomes during cell division
• grow out from a centrosome near the nucleus
• animal cells, the centrosome has a pair of centrioles, each with nine triplets of microtubules arranged in a cell
• During cell division, the centrioles replicate.
• Central structural support in cilia & flagella
• Same ultrastructure - a core of microtubules sheathed by the plasma membrane
• Nine doublets of microtubules are arranged around one pair at the center (9 + 2 pattern)

Microfilaments

• Thinnest among the 3
• Solid rods of the globular protein actin
• Resist tension
• Form a 3D network with other proteins just inside the plasma membrane to support cell shape

Cell Wall

• Found in prokaryotes, fungi, some protists and plants.
• Protection, maintain shape, & prevent excessive uptake of H₂O
• Thickness & chemical composition differ from species to species & among cell types
• Basic Design- microfibrils of cellulose embedded in a matrix of proteins & other polysaccharides
• Primary cell wall(cellulose), middle lmella with sticky polysachharides (pectin) that holds the cell together and layers of a secondary wall

Intracellular Junctions

• Neighboring cells in tissues adhere, interact and communicate through direct physical contact.
• Perforated with Plasmodesmata that allows cytosol to pass between cells.

Extracellular Matrix (ECM)

• Animal cells functions include support, adhesion, movement and regulation.
• Made up of glycoproteins that are embedded in a network of proteoglycans
• Interconnections from ECM to the cytoskeleton via the fibrenotin integriin link permit the interaction of changes inside and outside of te call

Animal Intercellular Links

• Tight Junctions- fuse adjacent cells and prevents leakage of extracellular fluid
• Desmososmes- (anchoring junctions) fasten cells totgether into strong sheets
• Gap Junctions- (or communicating junctions) provide cytoplasmic channnels
• small molcules pass
• facilitate chemical communication during devlopment

Plant Crystals

• Waste or exretory products of the protoplasts
• Calcium carbonate
• Calcium oxalate