Functions of the Cell Basic unit of life Protection and support Movement Communication Cell metabolism and energy release Inheritance

Cell Characteristics Plasma Membrane Outer cell boundary Substances inside the cell membrane are intracellular Substances outside the cell are extracellular. Encloses an supports the cell contents.

Plasma Membrane It attaches cells to the extracellular environment or to other cells. The ability of cells to recognize and communicate with each other take place through the plasma membrane It determines what moves into and out of cells.

Plasma Membrane Ion movement by cells results in a charge difference across the plasma membrane called the MEMBRANE POTENTIAL The outside of the plasma membrane is positively charged compared to the inside because there are more positively charged ions immediately on the outside of the plasma membrane and more negatively charged ions inside.

Plasma Membrane The membrane potential allows cells to function like tiny batteries with a positive and negative pole. It is an important feature of a living cell’s normal function.

Plasma Membrane Consists of: 45% -50% lipids 45% - 50% proteins 4% - 8% carbohydrates The carbohydrates combine with lipids to form glycolipids The proteins combine with lipids to form glycoproteins.

Membrane Lipids 1st: Phosoplipids Form lipid bilayer Double layer of lipid molecules They have a polar head (exposed to water inside and outside the cells) and a non polar tail (face one another in the interior of the plasma membrane.

Membrane Lipids 2nd: Cholesterol Interspersed among the phospholipids and accounts for about 1/3 of the total lipids in the plasma membrane. The amount of cholesterol in a given membrane is a major factor in determining the fluid nature of the membrane. Which is critical to its function.

Membrane Lipids Phospholipids form a lipid bilayer Hydrophilic (water-loving) polar heads Hydrophobic (water-fearing) nonpolar heads Cholesterol: Determines fluid nature of membrane

Membrane Proteins Many functions of the plasma membrane are determined by its proteins. FLUID-MOSAIC MODEL: The plasma membrane is neither rigid nor static in structure. It is highly flexible and can change its shape and composition through time.

Movement through the Plasma Membrane Diffusion Osmosis Filtration Mediated transport mechanisms Facilitated diffusion Active transport Secondary active transport

Osmosis Diffusion of water (solvent) across a selectively permeable membrane Important because large volume changes caused by water movement disrupt normal cell function Cell shrinkage or swelling Isotonic: cell neither shrinks nor swells Hypertonic: cell shrinks (crenation) Hypotonic: cell swells (lysis)

Filtration Works like a sieve Depends on pressure difference on either side of partition Moves from side of greater pressure to lower Example: In kidneys in urine formation

Endocytosis Internalization of substances by formation of a vesicle Types Phagocytosis Pinocytosis Receptor-mediated endocytosis

Pinocytosis

Exocytosis Accumulated vesicle secretions expelled from cell Examples Secretion of digestive enzymes by pancreas Secretion of mucus by salivary glands Secretion of mild by mammary glands

Cell Characteristics Cytoplasm Cytosol Cytoskeleton Cytoplasmic inclusions

Cytoplasm Cellular material outside nucleus but inside plasma membrane Cytosol: Fluid portion Cytoskeleton: Supports the cell Microtubules Microfilaments Intermediate filaments Cytoplasmic inclusions

Organelles Small specialized structures for particular functions Most have membranes that separates interior of organelles from cytoplasm Related to specific structure and function of the cell

Centrioles In specialized zone near nucleus: Centrosome Each unit consists of microtubules Before cell division, centrioles divide, move to ends of cell and become spindle fibers

Cilia Appendages projecting from cell surfaces Capable of movement Moves materials over the cell surface

Flagella Similar to cilia but longer Usually only one exists per cell Move the cell itself in wavelike fashion Example: Sperm cell

Microvilli Extension of plasma membrane Increase the cell surface Normally many on each cell One tenth to one twentieth size of cilia Do not move

Ribosomes Sites of protein synthesis Composed of a large and small subunit Types Free Attached to endoplasmic reticulum

Endoplasmic Reticulum Types Rough Attached ribosomes Proteins produced and modified Smooth Not attached ribosomes Manufacture lipids Cisternae: Interior spaces isolated from rest of cytoplasm

Golgi Apparatus Modification, packaging, distribution of proteins and lipids for secretion or internal use Flattened membrane sacs stacked on each other

Mitochondria Provide energy for cell Major site of ATP synthesis Membranes Cristae: Infoldings of inner membrane Matrix: Substance located in space formed by inner membrane Mitochondria

Nucleus DNA dispersed throughout Consists of : Nuclear envelope: Separates nucleus from cytoplasm and regulates movement of materials in and out Chromatin: Condenses to form chromosomes during cell division Nucleolus: Assembly site of large and small ribosomal units

Chromosome Structure

Overview of Cell Metabolism

Overview of Protein Synthesis

Overview of Protein Synthesis Transcription Copies DNA to form mRNA tRNA carries amino acids to ribosome Translation Synthesis of a protein at ribosome

Translation

Cell Life Cycle Interphase Phase between cell divisions Mitosis Prophase Metaphase Anaphase Telophase Cytokinesis Division of cell cytoplasm

Mitosis

Mitosis

Meiosis

Cellular Aspects of Aging Cellular clock Death genes DNA damage Free radicals Mitochondrial damage