Cells Prokaryotic Cells Simpler and smaller no nucleus

Cells

Prokaryotic Cells

• Simpler and smaller- no nucleus, no membrane bound organelles. • Domains bacteria and archaebacteria • DNA is in a nucleoid. • Contains: – Nucleoid – Ribosomes – Cell wall – Capsule – Membrane – Flagella – Cytoplasm

Eukaryotic Cells

More complex and larger- nucleus (contains the DNA) and membrane bound organelles. Plant and animal cells Organelles Rough and Smooth ER Nucleus Plasma membrane Ribosomes Mitochondria Chloroplast (P) Central Vacuole (P) Cell Wall (P) Peroxisome Microvilli Microfilaments Cytoskeleton Centrosome (A) Flagellum (A) Golgi Lysosome (A)

Surface Area to Volume Ratio • As a cell increase its size, the volume increases proportionally. • If a cell’s volume is too big compared to its surface area it will not receive enough nutrients to keep the cell alive.

Answer the question Imagine an elongated cell (such as a nerve cell) that measure 125 x 1 arbitrary units. Predict how its surface area-to-volume ratio would compare with those in figure on the previous slide. Then calculate the ratio and check your prediction in appendix A of your book

Nucleus and Ribosomes

Nucleus • Contains the nucleolus and MOST of the cell's DNA. • Enclosed by the nuclear envelope which is a double membrane and contains nuclear pores that allow substances in and out by using the pore complex. • The materials entering and exiting are macromolecules and strands of RNA. • Shape is maintained by the nuclear lamina.

Nucleolus • Contains r. RNA that assembles into ribosomes. • Proteins made in the cytoplasmic ribosomes, enter the nucleus through the pores to assemble ribosomal subunits that then exit the nucleus and assemble into ribosomes. • There can be multiple nucleoli in a single nucleus.

Ribosomes • • • Made up of r. RNA and proteins. Carry out protein synthesis. Lots of protein? Lots of ribosomes? Lots of nucleoli. Proteins are built in 2 different locations: - In the cytosol on the floating ribosomes - Proteins that function within the cytosol - On the attached ribosomes (attached to the RER) - Proteins that function in other organelles

The Endomembrane System

• Includes: - Nuclear envelope - ERs (rough and smooth) - Golgi - Lysosomes - Various vesicles and vacuoles - Plasma membrane • Used for: - Protein synthesis - Transport of proteins - Metabolism and movement of lipids - Detoxification of toxins Transported in tiny vesicles or membrane sacs

The Endoplasmic Reticulums

• Network of tubules and sacs called cisternae. • Continuous with the nuclear envelope. • Smooth ER- no ribosomes. • Rough ER- attached ribosomes.

Smooth ER • Synthesis of lipids - oils, phospholipids, and steroids, sex hormones. - Cells and organs that secret these hormones are rich in SER (testes and ovaries) • Metabolism of carbohydrates • Detoxification of drugs and poisons - The liver. More exposure makes the SER proliferate and that causes an increased tolerance. • Storage of calcium ions

Rough ER • Proteins are made on the attached ribosomes and then move into the RER. • The RER folds the protein into its functional shape. • Most secretory proteins are glycoporteinsproteins with a carbohydrate attached. - The proteins are attached within the ER. • The RER forms a vesicle around the secretory proteins from the transitional ER (side of the RER). • Attaches proteins and phospholipids to its own membrane. WHY? !

Golgi Apparatus

• Transport vesicles from the RER attached to the Golgi. • Mainly used to receiving, sorting, and shipping proteins, but some manufacturing happens. • Many Golgi can be found in cells that specialize in secretion. • Can have hundreds of flattened stackscisternae. • Cis and trans sides: - Cis: receiving side -located near ER becuse it receives vesicles form ER - Trans: shipping side.

• Some macromolecules are manufactured. • Material is moved from the cis side to the trans side modifying as it moves. • Phosphate groups are added and used as molecular tags to aid in sorting and external tags are added that act as docking site for their destinations.

Lysosomes and Vacuoles

• Contain hydrolytic enzymes that animal cells use to digest macromolecules. • Lysosomes have an acidic internal environment so if they bust inside the cell, no damage is done because the cytosol has a neutral p. H. However, if many leaks happen, the cell will destroy itself by selfdigestion. • They also digest damaged organelles. Breaks it down to its organic compounds and then releases them for reuse.

Phagocytosis • “Cell eating” • Large food molecules are engulfed and packed into a vacuole. The vacuole then fuses with a lysosome for digestion. • The food is broken down to simple sugars, amino acids, and other monomers pass into the cytosol to be used as nutrients. • Macrophages (white blood cells) perform phagocytosis. They engulf and destroy bacteria

Vacuoles • Food vacuoles • Contractile vacuoles: Fresh water protistspump out excess water to maintain the proper ion concentration within the cell. • Central vacuole: storage of inorganic ions. Plays a role in the growth of plants by absorbing water

Answer the question Imagine a protein that functions in the ER but requires modification in the Golgi before it can achieve that function. Describe the protein’s path through the cells, starting with the m. RNA (RNA made from the ribosome) that specific the protein.

Mitochondria and Chloroplast

Mitochondria • • Site of cellular respiration to generate ATP. Inside is made of a folded membrane, cristae. Found in all eukaryotic cells. The number of mitochondria correlates with the amount of metabolic activity– muscle cells use a lot of energy therefore they have a lot of mitochondria.

Chloroplast • Site of photosynthesis. • Stacks of thylakoid disks called granum. • Found in plant cells

Mitochondria and Chloroplast • Endosymbiotic Theory: both organelles were prokaryotic cells. They were engulfed by a larger eukaryote. They formed a relationship and evolved together. • Both have 2 membranes (inner and outer) and both contain their own DNA and ribosomes. • Both can move throughout the cell, changed shape, and even split to form more of themselves.

Peroxisome

• Metabolic compartment. • Enzymes remove hydrogen from molecules and transfer them to oxygen to produce hydrogen peroxide. • In the liver: detoxify alcohol by transferring hydrogen from poisons to oxygen • Hydrogen peroxide is toxic, so it also contains enzymes that convert it to water.

Answer the question A classmate proposes that mitochondria and chloroplast should be classified in the endomembrane system. Argue against that proposal.

Cytoskeleton

Components • Three main types of fibers make up the cytoskeleton • Microtubules are thickest of the three components of the cytoskeleton • Microfilaments, also called actin filaments, are thinnest components • Intermediate filaments are fibers with diameters in a middle range

Microtubules • Hollow rods constructed from globular protein dimers called tubulin • Functions: – Shape and support the cell – Guide movement of organelles – Separate chromosomes during cell division

Centrosomes and Centrioles • In animal cells, microtubules grow out from a centrosome near the nucleus. • The centrosome is a “microtubule organizing center” • The centrosome has a pair of centrioles, each with 9 triplets of microtubules arranged in a ring

Cilia and Flagella • Microtubules control the beating of cilia and flagella, microtubule containing extensions projecting from some cells. • Flagella are limited to one or a few per cell, while cilia occur in large numbers on cell surfaces. • Cilia and flagella also differ in their beating patterns

Answer the question Males afflicted with Kartagener’s syndrome are sterile because of immotile sperm, and they tend to suffer from lung infections. This disorder has a genetic basis. Suggest what the underlying defect might be.

Extracellular Components

Cell Wall of Plant Cells • • Protects Maintains shape of the plant cell Prevents excessive uptake of water Also located in prokaryotes, fungi and some portists • Made up of cellulose • Plasmodesmata are channels through cell walls that connect the cytoplasm of adjacent plant cells

ECM of Animal Cells • Made up of glycoporteins: collagen, proteoglycans, and fibronectin. • ECM proteins bind to receptor proteins in the plasma membrane called integrins

Cell Junctions • Neighboring cells in an animal or plant often adhere, interact, and communicate through direct physical contact. – Plasmodesmata – Tight junctions – Desmosomes Animal cells, particularly skin – Gap junctions cells

Answer the question If the plant cell wall or the animal extracellular matrix (ECM) were impermeable, what affect would this have on a cell function?