Functional Human Physiologyfor the Exercise and Sport Sciences

The Cell: Structure and Function

Jennifer L. Doherty, MS, ATCDepartment of Health, Physical Education, and RecreationFlorida 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

1) 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

2) Oxygen3) Carbon Dioxide4) Inorganic Salts/Electrolytes

Organic Substances

Carbon Major classes of organic substances

Carbohydrates (CHO)1) Example

Glucose C6H12O6

2) 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

1) 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, cortisol4) Eicosanoids

Function in intercellular communication Prostaglandins, thromboxanes, and leukotrines

Proteins

Contain carbon, hydrogen, oxygen, nitrogen, and sometimes sulfur

Amino acids1) Building blocks of proteins2) Joined by peptide bonds in condensation reactions

(release water) Peptides

1) Dipeptide2) Polypeptide3) Protein

Protein Structure Proteins exhibit four levels of structural

organization1) Primary

Amino acid sequence2) Secondary

Folding or twisting Alpha (α) helix structure (twisted) Beta (β) pleated-sheet (folded)

3) Tertiary Bonding of folded or twisted segments

4) 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:

1) A phosphate group2) A 5-carbon sugar (ribose or deoxyribose)3) Nitrogen containing bases

Pyrimidines – contain a single ring Cytosine (C) Thymine (T) Uracil (U)

Purines – contain two rings Adenine (A) Guanine (G)

Examples1) Adenosine Triphosphate (ATP)2) Nicotinamide adenine dinucleotide (NAD)3) Cyclic AMP

Nucleic Acids Deoxyribonucleic Acid (DNA) Ribonucleic Acid (RNA) Law of complementary base pairing

1) The RNA nitrogenous bases are paired with the nitrogenous bases on DNA to produce new RNA.

2) 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 Membrane1) Membrane structure is a phospholipid bilayer

Water soluble, or hydrophilic, phosphate heads form the outer surfaces of the membrane

2) 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.3) Fluid mosaic model

Molecules move and change with many different components associated with it.

Membrane Proteins1) Function as receptors, transporters, and enzymes. 2) 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.

3) Transmembrane proteins Channels, carriers, and pores

Water soluble (or lipid insoluble) materials pass in and out of the cell.

1) 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 Carbohydrates1) 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