3-1 Functions of the Cell Basic unit of life Protection and support Movement Communication Cell metabolism and energy release Inheritance

3-2 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.

3-3 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.

3-4 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.

3-5 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.

3-6 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.

3-7 Membrane Lipids 1 st : 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.

3-8 Membrane Lipids 2 nd : 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.

3-9 Membrane Lipids Phospholipids form a lipid bilayer –Hydrophilic (water-loving) polar heads –Hydrophobic (water-fearing) nonpolar heads Cholesterol: Determines fluid nature of membrane

3-10 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.

3-11 Membrane Proteins Integral or intrinsic –Extend from one surface to the other Peripheral or extrinsic –Attached to either the inner or outer surfaces of the lipid bilayer

3-12 Marker Molecules Allow cells to identify one another or other molecules

3-13 Channel Proteins Nongated ion channels –Always open Ligand gated ion channel –Open in response to small molecules that bind to proteins or glycoproteins Voltage-gated ion channel –Open when there is a change in charge across the plasma membrane

3-14 Movement through the Plasma Membrane Diffusion Osmosis Filtration Mediated transport mechanisms –Facilitated diffusion –Active transport –Secondary active transport

3-15 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)

3-16 Osmosis

3-17 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

3-18 Mediated Transport Mechanisms Many essential molecules, such as amino acids and glucose, cannot enter the cell by simple diffusion. Many products such as proteins cannot exit the cell by diffusion. Mediated transport mechanisms involve carrier proteins within the plasma membrane that move large, water-soluble molecules across the membrane.

3-19 Mediated Transport Mechanisms Involve carrier proteins Characteristics –Specificity To a single type of molecule –Competition –Saturation Rate of transport limited to number of available carrier proteins

3-20 Mediated Transport Mechanisms Facilitated diffusion –Higher to lower concentration without metabolic energy Active transport –Requires ATP Secondary active transport –Ions or molecules move in same (symport) or different direction (antiport)

3-21 Endocytosis Internalization of substances by formation of a vesicle Types –Phagocytosis –Pinocytosis –Receptor-mediated endocytosis

3-22 Pinocytosis

3-23 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

3-24 Cell Characteristics Cytoplasm –Cytosol –Cytoskeleton –Cytoplasmic inclusions

3-25 Cytoplasm Cellular material outside nucleus but inside plasma membrane Cytosol: Fluid portion Cytoskeleton: Supports the cell –Microtubules –Microfilaments –Intermediate filaments Cytoplasmic inclusions

3-26 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

3-27 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

3-28 Cilia Appendages projecting from cell surfaces Capable of movement Moves materials over the cell surface

3-29 Flagella Similar to cilia but longer Usually only one exists per cell Move the cell itself in wavelike fashion Example: Sperm cell

3-30 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

3-31 Ribosomes Sites of protein synthesis Composed of a large and small subunit Types –Free –Attached to endoplasmic reticulum

3-32 Endoplasmic Reticulum Types –Rough Attached ribosomes Proteins produced and modified –Smooth Not attached ribosomes Manufacture lipids Cisternae: Interior spaces isolated from rest of cytoplasm

3-33 Golgi Apparatus Modification, packaging, distribution of proteins and lipids for secretion or internal use Flattened membrane sacs stacked on each other

3-34 Peroxisomes and Proteasomes Peroxisomes –Smaller than lysosomes –Contain enzymes to break down fatty and amino acids –Hydrogen peroxide is a by-product of breakdown Proteasomes –Consist of large protein complexes –Include several enzymes that break down and recycle proteins in cell

3-35 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

3-36 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

3-37 Chromosome Structure

3-38 Overview of Cell Metabolism

3-39 Overview of Protein Synthesis

3-40 Overview of Protein Synthesis Transcription –Copies DNA to form mRNA –tRNA carries amino acids to ribosome Translation –Synthesis of a protein at ribosome

3-41 Translation

3-42 Cell Life Cycle Interphase –Phase between cell divisions Mitosis –Prophase –Metaphase –Anaphase –Telophase Cytokinesis –Division of cell cytoplasm

3-43 Mitosis

3-44 Mitosis

3-45 Meiosis

3-46 Cellular Aspects of Aging Cellular clock Death genes DNA damage Free radicals Mitochondrial damage