Cellular Level of Organization

Cells There are approximately 200 different types of cells that make up the basic structures of the human body. Cell division creates new cells. A “parent” cell divides into two new “daughter” cells. Different types of cells carry out different functions in the body.

Parts of a Cell Plasma membrane Cytoplasm Cytosol Organelles Nucleus Chromosomes Genes

3 main parts of a cell Plasma membrane – the cells flexible outer surface. Cytoplasm – all the cellular contents between the plasma membrane and the nucleus. Nucleus – a large organelle that houses most of the cell’s DNA. Chromosomes and genes are contained here.

Typical Structures

Plasma Membrane A flexible, yet sturdy barrier that surrounds and contains the cytoplasm of a cell. Fluid mosaic model. Lipid Bilayer Membrane proteins Membrane Permeability – Selective

Plasma Membrane continued… Gradients Concentration Electrochemical Osmosis Diffusion Active Transport

Lipid Bilayer Phospholipids – 2 layers Amphipathic – polar and nonpolar Hydrophilic Hydrophobic

Membrane Proteins Integral Proteins – extend into or through the lipid bilayer. Transmembrane proteins Peripheral Proteins – attached to either the inside or outside of the membrane.

Functions of Membrane Proteins Ion channel Transporter Receptor Enzyme Cell Identity Marker Linker

Membrane Permeability Selectively Permeable Permeable to nonpolar, uncharged molecules, such as oxygen, carbon dioxide, & steroids. Impermeable to ions and charged or polar molecules, such as glucose. Slightly permeable to water and urea.

Gradients Concentration Gradient – A difference in the concentration of a chemical from one place to another. Electrochemical Gradient – The combination of the effects of the concentration gradient and the membrane potential.

Transport Across the Membrane Passive Transport – does not require cellular energy. Substances move down their concentration or electrochemical gradients using only their own kinetic energy. Active Transport – requires cellular energy in the form of ATP.

3 Types of Passive Transport Diffusion through the lipid bilayer. Diffusion through membrane channels. Facilitated diffusion.

Endocytosis Material enters the cell in vesicles.

Exocytosis Material leaves the cell in vesicles.

Diffusion Materials diffuse from areas of high concentration to areas of low concentration. They move down their concentration gradient. Equilibrium – molecules are mixed uniformly throughout the solution.

Factors Influencing Diffusion Steepness of the concentration gradient. Temperature. Mass of the diffusing substance. Surface Area. Diffusion distance.

Osmosis The net movement of a solvent (water) across a selectively permeable membrane. Water moves from an area of higher water concentration to an area of lower water concentration.

Osmotic Pressure A solution containing solute particles that cannot cross the membrane exerts a force called osmotic pressure. The greater the number of solute particles the greater the pressure.

Tonicity A solution’s tonicity measures the solution’s ability to change the volume of cells by altering their water content. Isotonic – cell maintains shape Hypotonic – cell swells and bursts Hypertonic – cell shrinks - crenation

Cytoplasm 2 components Cytosol – fluid portion that surrounds organelles. 55% of total cell volume Water with dissolved and suspended components Ions, glucose, amino acids, fatty acids, proteins, lipids, ATP, and waste products. Organelles – specialized structures Specific shapes Specific functions

Cytoskeleton Network of protein filaments. Structural framework for the cell. 3 Types of filaments Microvilli – small – increase surface area Intermediate filaments Microtubules – largest – in cilia and flagella – participate in cell division.

Centrosome Located near the nucleus Plays a critical role in cell division

Cilia and Flagella Comprised of microtubules. Cilia – short, hairlike projections that extend from the surface of the cell. Line respiratory tract Movement is paralyzed by nicotine Flagella – longer than cilia Usually move an entire cell Sperm’s tail

Ribosomes Sites of protein synthesis Free Ribosomes – located in cytosol Attached to nuclear membrane and ER In mitochondria

Endoplasmic Reticulum ER Plasmic = cytoplasm; reticulum = network Network of folded membranes Transports substances throughout cell Rough ER – ribosomes attached – synthesizes proteins Smooth ER – synthesizes fatty acids and steroids

Rough ER

Smooth ER

Golgi Complex Consists of 3 – 20 golgi cisternae (membranous sacs) Modifies, sorts, and packages proteins for distribution Proteins leave through secretory vesicles, membrane vesicles, or transport vesicles.

Lysosomes Lyso = dissolving; somes = bodies Contain powerful digestive enzymes and hydrolytic enzymes Lysosomal enzymes can destroy their own cell – autolysis (due to pathology)

Lysosome

Mitochondria Generate ATP – “powerhouses” of the cell

Mitochondrian with Matrix

Mitochondria

Nucleus Spherical or oval shaped Most prominent feature in the cell Most structures have a single nucleus, although mature RBCs have none Contain genes arranged in chromosomes Genome – total genetic information for an organism

Nucleus

Nucleus

Cell Division Somatic Cell Division – replaces dead or injured cells and adds new ones for growth. Mitosis Produces 2 identical daughter cells Reproductive Cell Division – produces gametes – sperm and oocytes. meiosis

Cell Cycle 2 major phases Interphase – the cell is not dividing Mitotic phase – the cell is dividing

Interphase The cell replicates its DNA during this phase. Produces additional organelles and cytosolic components.

Mitotic Phase Nuclear Division – Mitosis Cytoplasmic Division - Cytokinesis

Mitosis Prophase Metaphase Anaphase Telophase Chromatin fibers condense and shorten. Metaphase The microtubules align the centromeres of the chromatid pairs. Anaphase The centromeres split separating the two members of each chromatid pair. Telophase Identical chromosomes uncoil and a nuclear envelope forms around each mass.

Cytokinesis Division of the parent cell’s cytoplasm and organelles into two daughter cells.

Cellular Diversity The body of an average human adult is composed of nearly 100 trillion cells. Approximately 200 different types. The largest cell is the oocyte