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 Figure 3-2

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

Structure of the cell membrane Plasma membrane comprised primarily of phospholipids, proteins & carbohydrates Phospholipid bilayer acts as a selective physical barrier

Structure of the cell membrane Proteins Integral (transmembrane) Peripheral

Structure of the cell membrane Functions of Membrane Proteins include: Receptors Channels Carriers Enzymes Anchors Identifiers

Structure of the 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 Shape and structural support Cell identification & communication (signaling) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

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

The Cytosol The 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 ICF not the only place we have fluids in body Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Fluid compartments of the body Intracellular fluid (ICF) – a.k.a. cytosol Extracellular fluid (ECF) interstitial fluid plasma lymph ISF Blood vessel (plasma) One of the things the cell membrane is important for is separating fluids of the body. Fluids separated into compartments” (ICF/ECF). These fluids are mainly H2O with different concentrations of solutes dissolved within each. We will look at how these fluids & solutes can move between these fluid compartments in the lab next week. Cell (ICF) Cell ISF Lymphatic vessel (lymph) Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The Organelles Membranous organelles Nonmembranous organelles - Isolated compartments Nucleus Mitochondria Endoplasmic reticulum (smooth & rough ER) Golgi apparatus Lysosomes Peroxisomes Membranous organelles have membrane that is similar structure to plasma membrane (phospholipids & proteins) Nonmembranous organelles - In direct contact with cytosol Cytoskeleton (including microvilli, centrioles, cilia, flagella) Ribosomes Proteasomes

The Nucleus The Nucleus Figure 3-16 Largest organelle in the cell; most cells have single nucleus, some (skel. musc.) are multinucleate, some (RBCs) are anucleate. Often described as “control center” of a cell but what is it controlling & how? Surrounded by a nuclear membrane (nuclear envelope) that contains nuclear pores. The envelope separates the nucleoplasm from the cytosol, & the pores allow for some chemical communication between. Nucleoplasm contains DNA, RNA, & one or more Nucleoli (a/w/a proteins, ions, enzymes, etc) Figure 3-16

DNA/Chromosomes/Chromatin/Genes Structure of DNA molecule is a double helix shaped pair of DNA strands comprised of nucleotide units (made of a sugar (deoxyribose), a phosphate group & a nitrogenous base (A, G, C, T)). A gene is a segment of the DNA strand that codes for a particular protein. DNA molecules coil up around histone proteins to form loosely arranged chromatin or tightly coiled chromosomes (depending on whether cell dividing or not). Human body cells have 23 pair (46) of chromosomes/cell. Gametes have 23 single (unpaired) chromosomes. Adenine Guanine Cytosine Uracil (RNA only) Thymine Figure 3-17

The Nucleus “The Big Picture” The nucleus contains DNA, the genetic code, within chromosomes. Genes, segments of chromosomes, contain the “blueprint” for the production of specific proteins. The proteins synthesized not only determine cell structure and function, but the organism’s structure (anatomy) & function (physiology). Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

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

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 Codon 1 RNA nucleotide KEY Adenine Guanine Cytosine Uracil (RNA) Thymine mRNA strand 2 3 Codon 4 (stop signal) Promoter Triplet 1 Triplet 2 Triplet 3 Triplet 4 Complementary triplets polymerase

Protein Synthesis Translation—the assembling of a protein on ribosomes Adenine Guanine Cytosine Uracil (RNA) Thymine KEY NUCLEUS mRNA Amino acid tRNA Anticodon tRNA binding sites Small ribosomal subunit mRNA strand Start 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 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 Completed polypeptide Translation—the assembling of a protein on ribosomes Transfer RNAs (tRNA) bring specific amino acids based on transcribed “message” of mRNA Occurs in cytoplasm

Protein Synthesis http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/transcription.swf http://www.stolaf.edu/people/giannini/flashanimat/molgenetics/translation.swf

The Endoplasmic Reticulum Network of intracellular membranes primarily for molecular synthesis, storage & intracellular tranport Rough ER (RER) Contains ribosomes Stores, modifies & transports newly made proteins Smooth ER (SER) Lacks ribosomes Synthesizes, stores & transports lipids & carbohydrates Figure 3-13

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

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

Lysosomes, Peroxisomes, Proteasomes 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 production Double layered membrane with inner folds (cristae) enclosing metabolic enzymes for cellular (aerobic) respiration Figure 3-15

Mitochondria “The Big Picture” Mitochondria provide most of the energy needed to keep your cells (and you) alive. They consume oxygen and organic substrates, and they generate carbon dioxide and ATP. Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

The Cytoskeleton Internal protein framework to provide strength & structural support, movement of cellular structures & materials Comprised mainly of: Microfilaments (actin) Intermediate filaments (varies) Microtubules (tubulin) Figure 3-12

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

The Cytoskeleton 2. Microtubules a. centrioles - move chromosomes during mitosis b. cilia - move substances across cell surface c. flagella - moves cell through fluid (sperm) 3. Intermediate filaments – provide structural support

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 - The nuclear (chromosomal) division of somatic cells (after chromosomal replication has occurred). Cytokinesis - The division of cytoplasmic contents Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Nucleus Spindle fibers Mitosis begins Chromosome with two Interphase Early prophase Late prophase Nucleus Spindle fibers Mitosis begins Chromosome with two sister chromatids Centrioles (two pairs) Centromeres Metaphase Anaphase Telophase Separation Daughter chromosomes Cytokinesis Metaphase plate Cleavage furrow Daughter cells Figure 3-22 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

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 Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Processes of Transport Lab

Two types of processes of transport (movement): Passive – no energy needed Active – energy needed

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

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

Diffusion Across Cell Membranes Figure 3-5

Passive Membrane Transport Facilitated diffusion no ATP required but requires a carrier protein

Osmosis 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 Cell Membrane Fig. 3-7 Figure 3-7

RBCs in hypertonic solution (crenation) 9% NaCl RBCs in isotonic solution 0.9% NaCl RBCs in hypotonic solution (hemolysis) Distilled H20

Passive Membrane Transport 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 Dialysis – using a semi-permeable membrane to “filter” blood of wastes if kidneys are unable Copyright © 2007 Pearson Education, Inc., publishing as Benjamin Cummings

Active processes of transport - Cell must generate energy (ATP) 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 - phagocytosis - pinocytosis 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

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

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

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

Phagocytosis animation & video http://www.stolaf.edu/people/giannini/flashanimat/cellstructures/phagocitosis.swf http://www.youtube.com/watch?v=W6rnhiMxtKU

Exocytosis Exocytosis