Functional Human Physiologyfor the Exercise and Sport Sciences The Cell: Structure and Function Jennifer L. Doherty, MS, ATC Department of Health, Physical Education, and Recreation Florida International University
Introduction to The Cell • The cell is the basic structural and functional unit of the body. • It is an independent unit. • It is able to carry on all of the functions necessary to keep it alive and to reproduce itself. • No other unit of the body, short of the total organism, is capable of this.
Biomolecules • Major Chemical Constituents of Body Cells • Inorganic Substances • Water • Contributes to body functions in the following ways: • As a solvent and chemical reactant • As a medium • As a lubricant • Hydraulic shock absorber • Chemical reactant • Absorbs and releases heat • Oxygen • Carbon Dioxide • Inorganic Salts/Electrolytes
Organic Substances • Carbon • Major classes of organic substances • Carbohydrates (CHO) • Example • Glucose C6H12O6 • Classified according to size, complexity, and solubility in water. • Monosaccharides • Glucose, Fructose, Galactose • Disaccharides • Sucrose • Lactose • Polysaccharides • Glycogen • Starch • Cellulose
Lipids • Non-polar • Not water soluble • Four main classes of lipids • Triglycerides or Neutral Fats • Contain one glycerol ”backbone” and three fatty acid “chains” • Saturated fatty acids • Carbons linked with single bonds • Hydrogen atoms on every carbon • Cause heart disease and stroke • Unsaturated fatty acids • Carbons linked with double bonds • Fewer hydrogen atoms • Polyunsaturated • More than one double bond
2) Phospholipids • Phosphate base • Hydrophilic • Fatty acid tail • Hydrophobic • Form a lipid bilayer in water 3) Steroids • Most common is cholesterol • Sex hormones • Testosterone, estradiol, cortisol 4) Eicosanoids • Function in intercellular communication • Prostaglandins, thromboxanes, and leukotrines
Proteins • Contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur • Amino acids • Building blocks of proteins • Joined by peptide bonds in condensation reactions (release water) • Peptides • Dipeptide • Polypeptide • Protein
Protein Structure • Proteins exhibit four levels of structural organization • Primary • Amino acid sequence • Secondary • Folding or twisting • Alpha (α) helix structure (twisted) • Beta (β) pleated-sheet (folded) • Tertiary • Bonding of folded or twisted segments • Quaternary • Three-dimensional shape
Fibrous or Structural proteins • Collagen • Tropomyosin • Myoglobin • Globular or Functional proteins • Chemical messengers • Receptors • Carriers • Enzymes
Nucleotides and Nucleic Acids • Nucleotides • Consist of: • A phosphate group • A 5-carbon sugar (ribose or deoxyribose) • Nitrogen containing bases • Pyrimidines – contain a single ring • Cytosine (C) • Thymine (T) • Uracil (U) • Purines – contain two rings • Adenine (A) • Guanine (G) • Examples • Adenosine Triphosphate (ATP) • Nicotinamide adenine dinucleotide (NAD) • Cyclic AMP
Nucleic Acids • Deoxyribonucleic Acid (DNA) • Ribonucleic Acid (RNA) • Law of complementary base pairing • The RNA nitrogenous bases are paired with the nitrogenous bases on DNA to produce new RNA. • RNA is the genetic messenger necessary for protein synthesis • Transcription • Translation
Cell Structure • The major components of the cell are… • The cytosol or cytoplasm, • The cell or plasma membrane, and • The organelles.
Plasma Membrane • Structure of the Plasma Membrane • Membrane structure is a phospholipid bilayer • Water soluble, or hydrophilic, phosphate heads form the outer surfaces of the membrane • The water insoluble, or hydrophobic, tails form the interior • Prevents water soluble molecules from passing directly through the membrane. • Water and dissolved substances move though easily because of small molecular size. • Fluid mosaic model • Molecules move and change with many different components associated with it.
Membrane Proteins • Function as receptors, transporters, and enzymes. • Integral or intrinsic proteins • Firmly inserted or embedded in the lipid bilayer. • Most pass completely through the bilayer and have surfaces extending through to both sides of the membrane. • Membrane Receptors • Extend outward from the surface while communicating with the cell’s interior. • Specialized to combine with specific molecules such as hormones. • Transmembrane proteins • Channels, carriers, and pores • Water soluble (or lipid insoluble) materials pass in and out of the cell.
Peripheral or extrinsic proteins • Not embedded but are attached to the membrane surface. • Globular proteins that function as enzymes • Promote specific chemical reactions within the cell • Cholesterol inserted in the phospholipid bilayer serves to stabilize the membrane and help make it less permeable to water soluble molecules. • Membrane Carbohydrates • Bound to the plasma membrane in the form of glycolipids or glycoproteins • Glycocalyx • Found on the outer surface of the plasma membrane • Acts as a protective layer • Holds cells together • Functions in cell recognition by labeling the cell so it can be recognized as part of the body or as a foreign particle. This is important in immunity.
Cytosol • Fluid that bathes the organelles • Site of chemical reactions • Storage site for molecules • Structures with the cytosol are called inclusions • Function to store energy in the form of glycogen or triglycerides
Membranous Organelles • Endoplasmic Reticulum • Rough • Smooth • Golgi Apparatus • Mitochondria • Lysosomes • Peroxisomes
Nonmembranous Organelles • Ribosomes • Vaults • Centrioles • Cytoskeleton • Microfilaments • Intermediate filaments • Microtubules