Cell Theory and Types

• Cells form the basic structural and functional unit of life, a unifying concept in biology.
• All organisms consist of one or more cells.
• Tissues and organs are composed of cells, without which life cannot exist.
• Cell theory: all living organisms consist of cells.
• Cells arise from preexisting cells.
• All cells share common features like having DNA, using the same genetic code, synthesizing proteins, and using ATP in similar ways, implying a common ancestry.

Cell Types

• Prokaryotic cells lack a nucleus and other membrane-bound organelles and are found in Kingdom Archaebacteria and Kingdom Eubacteria.
• Eukaryotic cells have a nucleus and membrane-bound organelles and are found in Kingdom Protista, Kingdom Fungi, Kingdom Plantae, and Kingdom Animalia.
• The plasma membrane surrounds the cell.
• The nucleus is the largest organelle, featuring a double-layered nuclear envelope.
• Cytoplasm is the material between the cell membrane and the nuclear envelope.
• Organelles like mitochondria, Golgi complex, centrioles, and endoplasmic reticulum are in the cytoplasm.
• The plasma membrane consists of two layers of phospholipid molecules with hydrophilic heads facing outward and hydrophobic tails facing inward, making it fluid and flexible.
• The hydrophobic interior of the membrane restricts the passage of polar substances.
• Glycoproteins function in the transport of molecules across the membrane.
• The nuclear envelope contains pores for molecule movement between the nucleus and cytoplasm.
• Chromosomes are located in the nucleus.
• Chromatin is loosely condensed DNA and proteins.
• Nucleoli are chromosome regions with multiple copies of DNA used for ribosomal RNA synthesis.
• Ribosomal RNA joins with protein to form ribosome subunits.
• Ribosomes exit the nucleus through nuclear envelope pores.
• The nuclear envelope connects to the endoplasmic reticulum (ER), a cytoplasmic membranous system.
• Rough endoplasmic reticulum (RER) is covered with ribosomes.
• Smooth endoplasmic reticulum (SER) lacks ribosomes.
• RER ribosomes synthesize proteins that become part of the plasma membrane, are exported from the cell, or are bound for lysosomes.
• Lipids and phospholipids are synthesized in the SER.
• The Golgi complex, a stack of membranous vesicles, stores, modifies, and packages protein products.

Lysosomes and Mitochondria

• Lysosomes contain enzymes that break down foreign material, such as bacteria, or worn-out cellular components.
• Lysosome enzyme release would kill the cell.
• Lysosomes release enzymes into food vacuoles.
• Mitochondria are the powerhouses of cells, producing ATP.
• Mitochondria have a double membrane, with the inner membrane folded into cristae.
• Mitochondria are self-replicating and have their own circular DNA.

Cytoskeleton Components

• Eukaryotic cells possess a cytoskeleton for support, locomotion, and organelle movement.
• The cytoskeleton consists of microfilaments, microtubules, and intermediate filaments.
• Microfilaments are made of actin and myosin, enabling cell contraction, as seen in muscle cells.
• Actin microfilaments move molecules and organelles within the cytoplasm.
• Microtubules are larger tubular structures composed of tubulin.
• Microtubules move chromosomes during cell division.
• Microtubules are part of cilia and flagella structure.
• Microtubules radiate from the centrosome, which is the microtubule organizing center.
• The centrosome is near the nucleus and is not membrane bound.
• Centrioles are in the centrosome.
• Centrioles are made of 9 triplets of microtubules.
• Centrioles replicate before cell division.
• Intermediate fibers are between microfilaments and microtubules in size.
• There are five biochemically distinct types of intermediate fibers.

Cilia, Flagella and Cell Movement

• Cilia and flagella are motile extensions of the cell surface.
• Cilia and flagella provide locomotion for single-celled organisms.
• In multicellular animals, cilia and flagella sweep material past fixed cells.
• Nine pairs of microtubules enclose a central pair in cilia & flagella.
• At the base of cilia & flagella is a basal body that is identical to a centriole.
• Some single-celled organisms, migrating cells in embryos, and white blood cells show ameboid movement.
• Cytoplasmic streaming, via actin microfilaments, extends a pseudopodium outward.
• Specialized pseudopodia with microtubules are assembled and disassembled to allow movement.

Cell Junctions and Microvilli

• Tight junctions are formed when cell membranes of adjacent cells fuse, functioning as seals.
• Adhesion junctions occur under tight junctions, where transmembrane proteins link across a small space and connect to microfilaments.
• Desmosomes act as spot welds, increasing tissue strength.
• Hemidesmosomes are at the base of cells, anchoring them to connective tissue.
• Gap junctions are canals between cells, providing intercellular communication.
• Microvilli are fingerlike projections with bundles of actin microfilaments.
• Microvilli increase the surface area of tissue, such as in the intestine.

Membrane Transport

• Membranes surround the outside of the cell and the organelles inside it.
• The plasma membrane acts as a selective gatekeeper.
• Substances cross the plasma membrane by diffusion, a mediated transport system, or endocytosis.
• Diffusion is the movement of molecules from high to low concentration areas, equalizing concentration.
• Movement occurs down the concentration gradient.
• Solutes are molecules, such as salt, in a solution.
• Cell membranes are selectively permeable.
• Water can pass through, but not most solutes.
• Gases (oxygen and carbon dioxide), urea, and lipid-soluble solutes can cross the membrane.
• Osmosis occurs when water flows toward the side with less water/more solute across a membrane until concentrations are equal.
• Animals use osmosis to control internal fluid and solute levels.
• Marine fishes' blood has 1/3 the salt content of seawater.
• Marine fish are hypoosmotic to seawater.
• Freshwater fishes have blood that is saltier than the water.
• Freshwater fish are hyperosmotic to the water.
• If solute concentrations are the same, the two solutions are isoosmotic.
• Charged substances cannot diffuse across, but instead pass through channels created by transmembrane proteins.
• Some channels are always open, while others are gated.
• Gated channels require a signal to open or close.
• Chemically-gated channels open or close when a signaling molecule binds to the transmembrane protein.
• Voltage-gated channels open or close when the ionic charge across the membrane changes.
• Sugars and amino acids enter cells, and waste products exit, via transporter proteins.
• Transporter proteins are specific.
• Facilitated diffusion uses transporter proteins to bind substrate molecules on one side of the membrane, change shape, and release them on the other side in the direction of the concentration gradient.
• Active transport requires energy (ATP) to transport molecules against the concentration gradient.
• Endocytosis is the ingestion of material by cells.
• Phagocytosis is "cell eating" and a method of feeding by single-celled organisms.
• Pinocytosis involves small molecules or ions enclosed in vesicles called caveolae.
• Receptor-mediated endocytosis brings large molecules into a cell with clathrin.
• Exocytosis occurs when vesicle membranes fuse with the plasma membrane to discharge contents outside the cell.
• Transcytosis is where a substance is picked up on one side of the cell, transported across, and discharged on the other side.

Mitosis and Cell Division

• Mitosis is nuclear cell division in nonreproductive, or somatic, cells.
• A fertilized egg, or zygote, divides by mitosis to produce a multicellular organism.
• Damaged cells are replaced by mitosis.
• In cells that are not dividing, DNA is loosely organized as chromatin.
• Before division, chromatin becomes compact, and chromosomes can be recognized.
• All nonreproductive cells in a species have the same number of chromosomes; 46 in humans.
• Half of the chromosomes come from each parent, resulting in two sets of chromosomes or a diploid state.
• Chromosome 1 from Mom and chromosome 1 from Dad are homologous chromosomes.
• Cells come from preexisting cells through cell division.
• Cell division, including mitosis and cytokinesis, occupies a small portion of the cell cycle.
• Interphase includes G1, where RNA and functional proteins are synthesized, S, where DNA replicates, and G2, where structural proteins are made.
• Cell division includes mitosis and cytokinesis.
• During S phase, each of the 2 homologues replicates, resulting in identical copies called sister chromatids.
• Chromatids remain connected at the centromere.
• Cell division has two phases: mitosis for nuclear cell division and cytokinesis for division of the cytoplasm.
• Mitosis consists of prophase, metaphase, anaphase, and telophase.
• Multiple nuclear divisions without cytokinesis result in a multinucleate cell.
• During prophase, chromosomes condense and become visible with a light microscope.
• The spindle forms between the 2 centrioles.
• Spindle fibers attach to kinetochores.
• During metaphase, chromosomes align along the center of cell or metaphase plate.
• Fibers attach to kinetochores on both sides of each chromosome.
• During anaphase, sister chromatids separate.
• The centromere splits apart, and sister chromatids move to opposite poles.
• Disassembly of tubulin subunits shortens microtubules.
• During telophase, nuclei re-form once chromosomes are at opposite poles.
• Chromosomes unwind.
• Cytokinesis is the division of the cytoplasm.
• The result is two complete, diploid cells identical to the original cell.
• During cytokinesis in animal cells, the cell pinches in two.
• A cleavage furrow, produced by microfilaments, deepens until the cell splits.