Cellular Anatomy Ch 2

• There are trillions of cells in the body.
• Cells are the structural building blocks of all plants and animals.
• Cells are produced by the division of preexisting cells.
• Cells form all the structures in the body.
• Cells perform all vital functions of the body.
• There are two types of cells in the body: sex cells and somatic cells.
• Sex cells are also called germ cells.
• Sperm are sex cells in males.
• Oocytes are sex cells in females.
• Somatic cells are all the other cells in the body that are not sex cells.

Cellular Anatomy

• The cell consists of cytoplasm, organelles, and a plasma membrane.
• Cytoplasm include the cytosol and organelles
• Cytosol is the intracellular fluid of the cell.
• Organelles are intracellular structures within the cell.
• Some organelles have membranes, and some do not.
• The plasma membrane is the cell membrane.
• The cell membrane consists of individual molecules.

The Plasma Membrane

• Four major functions include: providing a physical barrier, regulating the exchange of material with the environment, exhibiting sensitivity to respond to changes in the extracellular fluid, provides cell-to-cell communication, adhesion, and structural support.
• The cell membrane is composed of phospholipids, proteins, glycolipids, and sterols.
• Phospholipids are arranged in a phospholipid bilayer, composed of two layers of phospholipid.
• Hydrophilic heads are at the surfaces (inside and outside lining), and hydrophobic fatty acids (tails) face toward each other.
• The outer layer contains glycolipids and glycoproteins, forming a glycocalyx coating.
• The inner layer does not contain glycolipids or glycoproteins.
• Peripheral proteins are attached to either the inner layer or the outer layer of the membrane.
• Integral proteins are embedded in the membrane.
• Some integral proteins form channels through the membrane, which are called gated channels.
• Glycolipids are associated only with the outer layer of the membrane.
• Glycolipids have carbohydrates attached to the glycerol molecule.
• Many will serve as receptors for the cell.
• Sterols stabilize the cell membrane structure.
• Cholesterol is an example of a cell membrane sterol.

Membrane Permeability

• Permeability can be impermeable, freely permeable, or selectively permeable.
• An impermeable membrane means that nothing crosses the membrane.
• Freely permeable means that material crosses the membrane without difficulty.
• Selectively permeable means the membrane allows some material to pass through while inhibiting other material from crossing.
• Passive processes are diffusion, osmosis and facilitated diffusion.
• Active processes are active transport, endocytosis including pinocytosis and phagocytosis, and exocytosis.
• Diffusion is any molecule moving from an area of high concentration to an area of low concentration, down a concentration gradient.
• Osmosis is water molecules moving from an area of high concentration to an area of low concentration across a biological membrane.
• Facilitated diffusion involves solutes being passively transported by a carrier protein.
• Concentration gradient, size and charge of the solute, temperature, and number of carrier proteins affect the rate of movement, and glucose and amino acids are involved
• Active transport, solutes are actively transported by a carrier protein regardless of the concentration gradient.
• Some carrier proteins are called exchange pumps.
• ATP, number of carrier proteins, and availability of substrate affect the rate of movement, and sodium, potassium, calcium, and magnesium ions are involved
• Pinocytosis is vesicles bringing smaller molecules into the cell and extracellular fluid.
• Phagocytosis is vesicles that bring solid particles into the cell, with the presence of extracellular pathogens affecting the rate of movement.
• Bacteria, viruses, foreign matter, and cell debris are involved
• Receptor-mediated endocytosis is molecules binding to specific receptors on the cell membrane.
• Exocytosis is the release of intracellular material to the extracellular area.
• Requires ATP and calcium ions for movement and fluid and cellular waste and secretory products are involved.
• Microvilli are fingerlike projections of the plasma membrane.
• Microvilli absorb material from the ECF.
• Microvilli increase the surface area of the plasma membrane.
• Microvilli can bend back and forth in a waving manner.
• This movement helps circulate extracellular fluid and absorb nutrients.

The Cytoplasm

• The cytoplasm is all of the intracellular material, including cytosol and organelles
• Cytosol consists of the ICF (intracellular fluid), nutrients, protein, and waste products.
• Organelles are intracellular structures that perform specific functions.
• The cytosol contains a higher concentration of potassium ions and a lower concentration of sodium ions compared to the ECF.
• The cytosol consists of a net negative charge (intracellular is negative, extracellular is positive).
• The cytosol contains a high concentration of protein.
• The cytosol contains a small quantity of carbohydrates, and a large reserve of amino acids and lipids.
• The cytosol contains masses of insoluble substances called inclusions.
• Nonmembranous organelles are cytoskeleton, centrioles, cilia, flagella, ribosomes.
• Membranous organelles are mitochondria, nucleus, endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes.

Nonmembranous Organelles

• The Cytoskeleton consists of microfilaments, intermediate filaments, thick filaments, and microtubules.
• Microfilaments consist of actin protein.
• Microfilaments anchor the membrane to integral proteins, stabilize membrane proteins, anchor cell membrane to the cytoplasm.
• Microfilaments produce movement or a change in the cell's shape.
• Actin interacts with myosin which allows movement of the cell or change the cell's shape
• Intermediate Filaments provide strength and stabilized organelle position.
• Neurofilaments support the axons of nerves, and transports material within the cytosol
• Thick Filaments are composed of myosin protein and abundant in muscle cells, involved in muscle contraction
• Microtubules are composed of tubulin protein.
• They change shape of the cell, move organelles, form centrioles to be used during cell reproduction and forms cilia and flagella
• Located in the centrosome, produce microtubules that move chromosomes during cell reproduction
• Cilia is located at the cell surface, anchored by the basal body just under the cell surface beat rhythmically to move fluid or secretions across its surface
• Flagella are located at the cell surface and propel sperm through fluid
• Ribosomes float in cytoplasm or attached to the endoplasmic reticulum.
• Both of these are involved in producing protein.

Membranous Organelles

• Membranous Organelles are double-layered or single-layered
• Double-layered membraned organelles include the mitochondria and nucleus.
• Mitochondria produce ATP
• The Nucleus contains chromosomes, and is the control center for the cell
• Single-layered membrane organelles include Endoplasmic reticulum, Golgi apparatus, Lysosomes, Peroxisomes
• Endoplasmic reticulum is a network of hollow tubes
• The Golgi apparatus modifies protein, and Lysosomes contain cellular digestive enzymes and Peroxisomes contain catalase to break down hydrogen peroxide
• In nucleus the Nuclear envelope consists of perinuclear space and nuclear pores.
• Nucleoplasm consists of filaments making the nuclear matrix
• Nucleus consists of one to four nucleoli and of chromatin material including chromosomes of DNA (deoxyribonucleic acid)
• DNA wraps around histones and the complex of DNA and histones is a nucleosome
• The Endoplasmic Reticulum (ER) has two types made of cisternae: rough and smooth
• Rough endoplasmic reticulum(RER) consists of attached ribosomes
• After the proteins processed by ribosomes enter, they are transported to the cell membrane or the Golgi apparatus via transport vesicles
• Smooth endoplasmic reticulum (SER) synthesizes lipids, steroids, and carbohydrates, provides for storage of calcium ions and is involved in detoxification of toxins
• The Golgi Apparatus synthesizes and packages of secretions, packages enzymes (modifies protein), and provides renewal and modification of the cell membrane
• Lysosomes defends against disease, removes bacteria, removes organic debris, consists of enzymes to break down contents.
• Lysosomes break down contents with primary enzymes (inactive enzymes) and secondary enzymes (activated enzymes) and recycles amino acids and sugars.
• Lysosomes are involved in autolysis
• Peroxisomes consists of catalase (enzyme) Abundant in liver cells, converts hydrogen peroxide to water and oxidants

Membrane Flow

• Membrane flow involves continuous movement and recycling of the cell membrane:
• Transport vesicles connect the endoplasmic reticulum with the Golgi apparatus
• Secretory vesicles connect the Golgi apparatus with the plasma membrane, and Vesicles remove and recycle segments of the plasma membrane.

Intercellular Attachment

• Many cells form permanent or temporary attachment to other cells, attach via cell adhesion molecules (CAMs) or via cellular cement proteoglycan (hyaluronan).
• Examples of cell junctions include: Gap junctions, and tight junctions such as desmosomes (spot desmosome, and hemidesmosome)

Cell Life Cycle

• Cell reproduction consists of special events including interphase, mitosis, and cytokinesis.
• Mitosis is one part of the entire process of cell reproduction.
• Mitosis has prophase, metaphase, anaphase, and telophase
• Cytokinesis overlaps with anaphase and telophase.
• Interphase consists of G0, G1, S, and G₂ phases
• Go phase: the cell is "just living" and not preparing for reproduction while carrying on daily functions.
• G₁ phase: duplication of organelles and protein synthesis.
• S phase: Chromosome replication and DNA synthesis and histone synthesis.
• G₂ phase: protein synthesis.
• In DNA replication, weak bonds of the nitrogenous bases break and the double strands unwind, forming two segments.
• DNA polymerase binds to nitrogenous bases and Ligases is what allows the linking of complementary nucleotide chains to each other.
• This results in a duplicated DNA molecule where after, the cell enters G2 phase of interphase and shortly after that, cellular mitosis

Mitosis

• Frequency at which cell reproduction occurs, called the mitotic rate
• Stem cells: Somatic cells that undergo cell reproduction
• The first phase of mitosis: Prophase
• Metaphase: Paired chromatids line up in the middle of the nuclear region
• Anaphase: Paired chromatids separate to opposite poles of the cell
• Telophase: Two new nuclear membranes begin to form