Cell Structure & Function Chapter 3 Cell Structure & Function Chapter 3

The Diversity of Cells in the Human Body There are over 200 different kinds of cells in the body Figure 3-1

Anatomy of a representative cell

Parts of a “representative” cell Plasma (Cell) Membrane Lipid barrier between outside environment (extracellular fluid (ECF) and inside environment Cytoplasm Cytosol (intracellular fluid (ICF)) Organelles

Plasma (cell) membrane Phospholipid bilayer acts as a selective physical barrier between extracellular fluid (interstitial fluid) and intracellular fluid (cytosol) Comprised primarily of phospholipids, proteins & carbohydrates

Plasma (cell) membrane Proteins Integral (transmembrane) Peripheral

Plasma (cell) membrane Functions of Membrane Proteins include: Receptors Channels Carriers Enzymes Anchors Identifiers

Plasma (cell) membrane Carbohydrates act as receptors & identity markers

Functions of The Cell Membrane Functions of the plasma membrane include: Physical isolation Regulation of exchange with the environment (“selective permeability”) Sensitivity to surrounding environment Help maintain shape and structural support between cells Cell identification Communication (signaling) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Cytoplasm Cytoplasm All the “stuff” inside a cell The “stuff”: Cytosol (a.k.a. intracellular fluid ICF)) Organelles Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Cytosol Cytosol Intracellular fluid that usually has a “gel-like” consistency Contains dissolved nutrients (including amino acids & lipids), ions, proteins (enzymes), and wastes Functions include: distribution of materials by diffusion, site of some enzymatic reactions Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Fluid compartments of the body Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Intracellular fluid (ICF) – a.k.a. cytosol Extracellular fluid (ECF) interstitial fluid plasma lymph Cell (ICF) Blood vessel (plasma) Lymphatic vessel (lymph) ISF Cell

Two types of processes of transport (movement): Passive – no energy needed Active – energy needed Transport Processes between/within fluid compartments

Passive processes of transport Includes: Diffusion Facilitated diffusion (facilitated transport) Osmosis Filtration Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings - No energy required for movement - Movement occurs with (“down”) the concentration gradient

Diffusion Random movement down a concentration gradient (from higher to lower concentration) Movement continues until “equilibrium” is reached

Diffusion Across Cell Membranes

Facilitated Diffusion (facilitated transport) No ATP required but requires a carrier protein (transporter)

Osmosis Movement of water across a membrane, down a water concentration gradient (from higher H2O concentration to lower) & due to osmotic pressure (from lower to higher osmotic pressure) Osmotic pressure – relates to the concentration of solutes. The higher the concentration of solutes, the higher the osmotic pressure. Water will always move from lower to higher osmotic pressure

Osmosis Figure 3-6

Osmotic Effects of Solutions on cells Isotonic solution- same concentration solutes (equal osmotic pressure) Cells maintain normal size and shape Hypertonic solution- more solutes in solution (higher osmotic pressure) therefore less H2O Cells lose water osmotically and shrink and shrivel Hypotonic solution- less solutes in solution (lower osmotic pressure) therefore more H2O Cells gain water osmotically and swell and may burst. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Osmotic Flow across a RBC Cell Membrane Hemolysis Crenation

Filtration Hydrostatic pressure (blood pressure in the body) pushes on water Water crosses membrane (across capillary endothelium in the body) If membrane is permeable to solutes, solutes follow water movement Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Active processes of transport - Cell must generate energy (ATP – adenosine triphosphate) for movement - Movement can occur against (“up”) the concentration gradient - Larger substances can move in/out of the cell -Includes: Active transport Vesicular transport endocytosis - receptor mediated endocytosis - pinocytosis - phagocytosis exocytosis

Active transport   Carrier-Mediated   Transport Membrane proteins act as carriers   ATP consumed   Independent of concentration gradients   Ion pumps (e.g. Na-K exchange) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Vesicular Transport Membranous vesicles requiring energy for movement Transport in both directions Endocytosis - movement into cell Receptor-mediated endocytosis Pinocytosis Phagocytosis Exocytosis - movement out of cell Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Figure 3-10 EXTRACELLULAR FLUID Ligands binding to receptors Exocytosis Ligand receptors CYTOPLASM Coated vesicle Ligands Endocytosis Lysosome Fused vesicle and lysosome Ligands removed Fusion Detachment Receptor-Mediated Endocytosis Target molecules (ligands) bind to receptors in cell membrane. Areas coated with ligands form deep pockets in membrane surface. Pockets pinch off, forming vesicles. Vesicles fuse with lysosomes. Ligands are removed and absorbed into the cytoplasm. The membrane containing the receptor molecules separates from the lysosome. The vesicle returns to the surface. Receptor-Mediated Endocytosis

Pinocytosis  “Cell drinking”  Cell membrane folds inward “engulfing” ECF  No receptor proteins involved

Figure 3-11 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Cell membrane of phagocytic cell Phagocytosis A phagocytic cell comes in contact with the foreign object and sends pseudopodia (cytoplasmic extensions) around it. Pseudopodia (cytoplasmic extension) EXTRACELLULAR FLUID CYTOPLASM Foreign object Vesicle Lysosomes Exocytosis The pseudopodia approach one another and fuse to trap the material within the vesicle. The vesicle moves into the cytoplasm. Lysosomes fuse with the vesicle. This fusion activates digestive enzymes. The enzymes break down the structure of the phagocytized material. Residue is then ejected from the cell by exocytosis. Phagocytosis

Exocytosis Exocytosis

The Organelles Membranous organelles - Isolated compartments Nucleus Mitochondria Endoplasmic reticulum (smooth & rough ER) Golgi apparatus Lysosomes Peroxisomes Nonmembranous organelles - In direct contact with cytosol  Cytoskeleton (including microvilli, centrioles, cilia, flagella)  Ribosomes  Proteasomes

The Nucleus Figure 3-16

DNA/Chromosomes/Chromatin/Genes Gene Adenine Guanine Cytosine Uracil (RNA only) Thymine DNA = deoxyribonucleic acid

Nucleoli   Nucleoli are non membranous organelles within the nucleus   Synthesize ribosomal RNA (rRNA) – building block that creates ribosomes RNA = ribonucleic acid

Ribosomes   Made of ribsosomal RNA & protein subunits   Found free in cytoplasm (free ribosomes) or attached to rough endoplasmic reticulum (ER) (fixed ribosomes)   Site of protein synthesis

Protein Synthesis Two step process:   Transcription – occurs in the nucleus   Translation – occurs on ribosomes in the cytoplasm

Protein Synthesis Transcription — the production of RNA from a single strand of DNA Occurs in nucleus with production of messenger RNA (mRNA) mRNA exits through nuclear pore to go to ribosome DNA Gene RNA nucleotide KEY Adenine Guanine Cytosine Uracil (RNA) Thymine mRNA strand 4 Complementary triplets RNA polymerase

Adenine Guanine Cytosine Uracil (RNA) Thymine KEY NUCLEUS mRNA Amino acid tRNA Anticodon tRNA binding sites Small ribosomal subunit mRNA strandStart codon The mRNA strand binds to the small ribosomal subunit and is joined at the start codon by the first tRNA, which carries the amino acid methionine. Binding occurs between comple- mentary base pairs of the codon and anticodon. The small and large ribosomal subunits interlock around the mRNA strand. Large ribosomal subunit A second tRNA arrives at the adjacent binding site of the ribosome. The anticodon of the second tRNA binds to the next mRNA codon. Stop codon Peptide bond The first amino acid is detached from its tRNA and is joined to the second amino acid by a peptide bond. The ribosome moves one codon farther along the mRNA strand; the first tRNA detaches as another tRNA arrives. The chain elongates until the stop codon is reached; the components then separate. Small ribosomal subunit Large ribosomal subunit Completed polypeptide Translation — the assembling of a polypeptide (“potential” protein) on ribosomes Transfer RNAs (tRNA) bring specific amino acids based on transcribed “message” of mRNA Occurs within cytoplasm Protein Synthesis

The Endoplasmic Reticulum Rough ER (RER)   Contains ribosomes on surface of membrane   Stores, modifies (folds) & transports newly made proteins Network of intracellular membranes primarily for molecular synthesis, storage & intracellular transport Smooth ER (SER)  Lacks ribosomes  Synthesizes, stores & transports lipids & carbohydrates

Golgi apparatus Receives new proteins from RER & lipids from SER Modifies proteins by adding carbohydrates and lipids Packages proteins & lipids in vesicles Secretory vesicles (for exocytosis) Membrane renewal vesicle Synthesizes Lysosomes

Figure 3-14 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings Endoplasmic reticulum Transport vesicle Golgi apparatus (a) Membrane renewal vesicles Secretory vesicles Lysosomes CYTOSOL EXTRACELLULAR FLUID Cell membrane Vesicle Incorporation in cell membrane (b)Exocytosis Golgi apparatus

Lysosomes, Peroxisomes, Proteasomes Lysosomes: Produced by golgi apparatus Vesicles containing digestive enzymes Clean-up cellular debris & recycle worn out organelles Defend against bacteria Peroxisomes: contain digestive enzymes to break down fatty acids & other organic compounds Proteasomes: contain digestive enzymes (proteases) to break down proteins

Mitochondria   Site of ATP (adenosine triphosphate) production   Double layered membrane with inner folds (cristae) enclosing metabolic enzymes for cellular (aerobic) respiration Figure 3-15

The Cytoskeleton Internal protein framework to provide strength & structural support, movement of cellular structures & materials Includes: Microfilaments (actin) Microtubules (tubulin)

The Cytoskeleton Microfilaments myofilaments of muscle cells – muscle contraction microvilli – increase cell surface area

The Cytoskeleton Microtubules   centrioles - move chromosomes during mitosis   cilia - move substances across cell surface   flagella - moves cell through fluid (sperm)

Cell division Somatic Cell division - The reproduction of body cells; necessary for growth & repair. Results in the formation of 2 genetically identical “daughter” cells   Mitosis - nuclear (chromosomal) division of somatic cells (after chromosomal replication has occurred).   Cytokinesis - division of cytoplasmic contents Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Nucleus Mitosis begins Centrioles (two pairs) Spindle fibers Centromeres Chromosome with two sister chromatids Cytokinesis Daughter cells Cleavage furrow Daughter chromosomes Metaphase plate Early prophaseLate prophase MetaphaseAnaphaseSeparationTelophase Interphase Figure 3-22

Cell Diversity and Differentiation Somatic (Body) Cells All have same genes Some genes inactivate during development Cells thus become functionally specialized. This specialization is known as “differentiation” of cells Specialized (differentiated) cells form distinct tissues in the body