Ch. 3a Cells

50 to 100 trillion cells in the Human Body Generalized Cell 50 to 100 trillion cells in the Human Body Each one is composed mainly of 4 elements Carbon, Hydrogen, Oxygen, Nitrogen Cells have three basic parts: Plasma membrane—outer boundary regulating movement of material in and out of cell Cytoplasm—gel-like fluid in cell; contains organelles Nucleus—contains DNA

Chromatin Nuclear envelope Nucleolus Nucleus Smooth endoplasmic reticulum Plasma membrane Mitochondrion Cytosol Lysosome Centrioles Centrosome matrix Rough endoplasmic reticulum Ribosomes Golgi apparatus Secretion being released from cell by exocytosis Cytoskeletal elements • Microtubule • Intermediate filaments Peroxisome Figure 3.2

Plasma Membrane The plasma membrane separates the intracellular fluid (ICF) from extracellular fluid (ECF) The plasma membrane is semi-permeable which means that some things can cross the membrane and some things cannot

Extracellular fluid Intracellular fluid Figure 3.3

Types of Membrane Transport A concentration gradient is: Passive Transport No cellular energy (ATP) required Substance moves down its concentration gradient Active Transport Energy (ATP) required Substances are moved or“pumped” against their gradient

Passive Transport What determines whether or not a substance can passively cross the plasma membrane? Is the substance a lipid (Lipid solubility of substance) Size of substance passing

Three Types of Passive Transport Across Cellular membranes Simple diffusion Facilitated diffusion Osmosis

Passive Transport: Simple Diffusion What types of substances use simple diffusion to cross the plasma membrane? Small, nonpolar, hydrophobic substances diffuse directly through phospholipid bilayer (O2, CO2)

Extracellular fluid Lipid- soluble solutes Cytoplasm Figure 3.7a

Passive Transport: Facilitated Diffusion What types of substances use facilitated diffusion to cross the plasma membrane? Larger, hydrophilic molecules (glucose, amino acids) Can pass through carriers or channels

Hydrophilic molecules A Carrier Protein Figure 3.7b

Passive Transport: Osmosis Movement of solvent (water) across a selectively permeable membrane from where it is most concentrated to where it is less concentrated Water diffuses through plasma membranes: mainly through channels

Water molecules A Channel Protein Lipid billayer Aquaporin Figure 3.7d

(a) Membrane permeable to both solutes and water Solute and water molecules move down their concentration gradients in opposite directions. Both solutions have the same osmolarity: volume unchanged H2O Solute Solute (sugar) Membrane Figure 3.8a

Both solutions have identical osmolarity, increases on the right (b) Membrane permeable to water, impermeable to solutes Solute molecules are prevented from moving but water moves by osmosis. Volume increases in the compartment with the higher osmolarity. Both solutions have identical osmolarity, increases on the right because only water is free to move Left compartment Right compartment H2O Solute (sugar) Membrane Figure 3.8b

Importance of Osmosis When osmosis occurs, water enters or leaves a cell A change in cell volume disrupts cell function

Tonicity Defined as: The ability of a solution to cause a cell to shrink or swell Isotonic: A solution that does not cause a change in cell volume Hypertonic: A solution that causes a cell to shrink Hypotonic: A solution that causes a cell to swell.

Figure 3.9 (a) Isotonic solutions (b) Hypertonic solutions (c) Hypotonic solutions Figure 3.9

Active Transport Defined as: The Sodium-potassium pump (Na+-K+ ATPase) is a specific example of active transport Located in all plasma membranes Maintains electrochemical gradients essential for muscle and nerve functions

Other Cellular Organelles Membranous structures Nucleus with chromatin- Mitochondria – Endoplasmic Reticulum (ER) (rough and smooth) – Golgi Apparatus- Lysosomes-

Nucleus Nuclear envelope Smooth ER Rough ER Vesicle Golgi apparatus Plasma membrane Transport vesicle Lysosome Figure 3.22

Smooth ER Nuclear envelope Rough ER Ribosomes Figure 3.18a

Rough ER ER membrane Phagosome Plasma mem- brane Vesicle becomes lysosome Secretory vesicle Golgi apparatus Secretion by exocytosis Extracellular fluid Figure 3.20

Mitochondria Organelle with shelflike folds called cristae Provide most of cell’s ATP (enzymes for this process are located on cristae)

Other Organelles Non-Membranous structures Centrioles- involved in cell division Cytoskeleton- protein filaments that help maintain cell shape, cell movement and in cell division (microtubules)

Centrosome matrix Centrioles (a) Microtubules Figure 3.25a

Extensions of the plasma membrane Cilia are: short, hairlike structures; move substances across cell surfaces Flagella are: Whiplike, tails that move the entire cell Microvilli are: fingerlike extensions found on absorptive cells

Microvillus Actin filaments Terminal web Figure 3.28

The Cell Cycle Includes: Interphase Period from cell formation to cell division Three sub phases of Interphase: G1 (gap 1)—growth and metabolism S (synthetic)—DNA replication G2 (gap 2)—preparation for division Cell division (mitotic phase or mitosis) Consists of four sub phases of mitosis (PMAT) and cytokinesis

Mitosis (Cell Division) Purpose: Does not occur in:

S Growth and DNA synthesis Growth and final preparations for division G1 Growth M Figure 3.31

During the S-phase of Interphase DNA is Replicated Helicase untwists the double helix and exposes complementary chains Each nucleotide strand serves as a template for building a new complementary strand DNA polymerase forms new DNA strand

DNA Replication End result: two DNA molecules formed from the original This process is called semiconservative replication After DNA has been replicated the cell progresses into mitosis and cytokinesis

Template for synthesis of new strand Free nucleotides DNA polymerase Chromosome Leading strand Lleading and lagging strands are synthesized in opposite directions Lagging strand Old DNA Helicase unwinds the double helix and Exposes bases Replication fork Adenine Thymine Cytosine DNA polymerase Old (template) strand Guanine Figure 3.32

Mitosis and Cytokinesis Mitosis—four stages of nuclear division: Prophase- Metaphase- Anaphase- Telophase- Cytokinesis—division of cytoplasm by cleavage furrow

S Growth and DNA synthesis M Figure 3.31

Early mitotic Early Prophase spindle Aster Chromosome Centromere consisting of two sister chromatids Centromere Early Prophase Figure 3.33

Microtubule Late Prophase Fragments of nuclear envelope Microtubule Figure 3.33

Metaphase Spindle Metaphase plate Metaphase Figure 3.33

Anaphase Daughter chromosomes Anaphase Figure 3.33

Cytokinesis Begins during late anaphase Ring of actin microfilaments contracts to form a cleavage furrow Two daughter cells are pinched apart, each containing a nucleus identical to the original

Telophase and Cytokinesis Nuclear envelope forming Nucleolus forming Contractile ring at cleavage furrow Telophase and Cytokinesis Telophase Figure 3.33