Cell Structure and Function

• The cell is the basic unit of all living matter
• It is essential for life
• Cells are the fundamental components of structure, development, growth, and life processes in the human body
• Cells exist in different forms and perform many diverse functions
  • Nerve impulse conduction
  • Muscle contraction
  • Support of organs
  • Transportation of body fluids
• Some cells, such as leukocytes, move freely
• Other cells, such as bone marrow cells, remain in one position
• Cells can move, grow, react, protect themselves, repair damage, regulate life processes, and reproduce
• The body requires food for energy, oxygen, and water
• Proper cell function enables the body to maintain homeostasis or equilibrium
• Ionizing radiation can damage components of the cell involved in molecular synthesis
  • Damage beyond repair can cause cells to behave abnormally or die
• Cells are made of protoplasm
• Protoplasm is the chemical building material for all living things
• Protoplasm carries out metabolism, receives and processes food and oxygen, and eliminates waste products
• Protoplasm consists of organic and inorganic materials, either dissolved or suspended in water
• The 4 primary elements are carbon, hydrogen, oxygen, and nitrogen
• Water and mineral salts (electrolytes) are vital inorganic substances for nerve pulse conduction

Organic Compounds

• The major ones are proteins, carbohydrates, lipids (fats), and nucleic acids (DNA and RNA)
• Carbon is the basic constituent of all organic matter
• Carbon combines with hydrogen, nitrogen, and oxygen to make life possible

Proteins

• Proteins contain the most carbon of all organic compounds
• Proteins constitute approximately 15% of a cell's content
• They are essential for growth, the construction of new body tissue, and the repair of injured or debilitated tissue
• Proteins are formed when amino acids combine into long, chainlike molecular complexes
• There are 22 different amino acids involved
• The order of arrangement of these amino acids determines the precise function of each protein molecule
• The macromolecule in a given cell determines the characteristics of that cell

Structural and Enzymatic Proteins

• Enzymatic proteins (enzymes) function as organic catalysts to speed up reactions
• Structural proteins provide the body with its shape and form
• Structural proteins also provide source of heat and energy
• Enzymes control the cell’s various physiologic activities
• Enzymes cause biochemical reactions to occur more rapidly to meet the needs of the cell
• Repair enzymes help the cell recover from small radiation-induced damage and are vital to cell survival

Hormones and Antibodies

• Antibodies are produced by specialized cells in bone marrow called B lymphocytes
• Antibodies chemically attack foreign invaders or antigens
• Hormones are manufactured by endocrine glands
• Hormones are carried in the bloodstream to influence the activities of other parts of the body
• Hormones regulate body functions like growth and development

Carbohydrates

• Carbohydrates make up approximately 1% of cell content
• They include starches and various sugars
• Carbohydrates range from simple to complex and are needed for energy
• They function as short-term energy warehouses for the body
• The primary purpose of carbohydrates is to provide fuel for cell metabolism
• Carbohydrates are most abundant in the liver and muscle tissue
• They are important structural parts of cell walls and intercellular materials

Lipids

• Lipids constitute approximately 2% of cell content
• They are made up of a molecule of glycerin and three molecules of fatty acid
• Lipids are organic macromolecules
• They are the structural parts of cell membranes
• Lipids are present in all body tissue
• Lipids perform various body functions

Nucleic Acids

• Nucleic acids comprise approximately 1% of cells
• Nucleic acids are very large, complex macromolecules
• They are made up of nucleotides
• Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are the two types of nucleic acid cells contain

DNA, the Master Chemical

• DNA is composed of 2 long sugar-phosphate chains
• The chains twist around each other in a double-helix configuration
• The chains are linked by pairs of nitrogenous organic bases at the sugar molecule
• Hydrogen bonds attach the bases to each other
• DNA contains all the information the cell needs to function
• DNA carries the genetic information necessary for cell replication
• DNA regulates cellular activity to direct protein synthesis
• DNA determines characteristics by regulating the sequence of amino acids in proteins
• The sequence of nitrogenous base pairs in a DNA molecule constitutes the genetic code
• The 4 nitrogenous organic bases in DNA are adenine (A), cytosine (C), guanine (G), and thymine (T)
• DNA has a double-strand macromolecular structure
• DNA contains deoxyribose
• DNA carries genetic information
• RNA has a single-strand macromolecular structure
• RNA contains ribose
• RNA performs different biologic functions
• DNA contains the 4 nitrogenous bases
  • adenine
  • cytosine
  • guanine
  • thymine
• RNA contains the 4 nitrogenous bases
  • adenine
  • cytosine
  • guanine
  • uracil

Chromosomes and Genes

• Chromosomes are composed of protein and DNA
• Normal humans have 46 different chromosomes (23 pairs) in each somatic (nonreproductive) cell
• Reproductive cells (germ cells) have only 23 chromosomes each
• Genes are segments of DNA that serve as the basic units of heredity
• They control the formation of proteins in every cell through genetic coding

Inorganic Compounds

• Inorganic compounds do not contain carbon
• They occur in nature independent of living things
• They are acids, bases, and salts (electrolytes)
• Water and mineral salts are the most important inorganic substances
• Water comprises approximately 80% to 85% of the body’s weight
• Important electrolytes in the body include:
  • Sodium (Na+)
  • Chloride (Cl−)
  • Potassium (K+)
  • Bicarbonate (HCO3−)
  • Calcium (Ca++)
  • Phosphate (HPO4−)
  • Magnesium (Mg++)
  • Sulfate (SO4−2)

Water

• Water is the medium in which the chemical reactions occur for metabolic activities
• Water acts as a solvent, keeping compounds dissolved so that they can easily interact and their concentration can be regulated
• Outside the cell, water functions to transport materials the cell uses or eliminates
• Water maintains a constant body core temperature of 98.6° F (37° C)
• Water lubricates both the digestive system and skeletal articulations and protects organs

Mineral Salts

• Mineral salts keep correct proportion of water in the cell to maintain osmotic pressure
• This is necessary for:
  • Proper cell performance
  • Creation of energy
  • Conduction of impulses along nerves
• Ions react to alter, break down, and recombine materials

Cell Structure Components

• Cell membrane
• Cytoplasm
• Cytoplasmic organelles:
  • Endoplasmic reticulum
  • Golgi apparatus or complex
  • Mitochondria
  • Lysosomes
  • Ribosomes
  • Centrosomes
• Nucleus

Organelles and their Activities

• Cell membrane acts as a plastic storage bag, protecting contents and controlling passage of materials
• Endoplasmic reticulum acts as a highway to communicate and transfer food
• Golgi apparatus acts as a freight hauler uniting carbohydrate molecules with proteins to form glycoproteins
• Mitochondria are power-generating stations, producing energy
• Lysosomes are garbage bags with poison pills that dispose of large particles
• Ribosomes are manufacturing facilities that manufacture proteins
• Centrosomes are spindle weavers, organizing the mitotic spindle
• The Nucleus is information-processing and administrative center, contains the genetic material
• DNA is the blueprints containing the genetic material, controlling cell division
• The Nucleolus is a RNA copy center that synthesizes Ribosomes

Cell Division

• Cell division is the multiplication process where one cell divides to form two or more cells
• The cell divides into somatic cells via mitosis
• Cells divide to form reduction cells via meiosis

Mitosis

• A parent cell divides into two daughter cells, identical to the parent cell
• Results in an equal distribution of cellular material to the daughter cells
• The 4 distinct phases of the cellular life cycle:
  • G1 pre-DNA synthesis
  • S synthesis (actual DNA synthesis period)
  • G2 post-DNA synthesis
  • M mitosis
• G1, S and G2 constitute interphase
• The 4 subphases of mitosis are: prophase, metaphase, anaphase, and telophase
• Chromosome damage from radiation can be evaluated in metaphase

Meiosis

• It is division for genetic cells (germ cells)
• It reduces the number of chromosomes in each daughter cell to half the number in the parent cell
• For sexually mature individuals, male (sperm) and female (ova) cells begin meiosis with 46 chromosomes
• Before male and female germ cells unite to create a new organism, each germ cell must reduce its number of chromosomes to 23
• Ensures their daughter cells have the standard number of 46 chromosomes

Multiple Births

• Monozygotic twins come from one zygote, fertilized by one sperm: identical twins
• Split after fertilization to produce two separate offspring
• Dizygotic twins are fraternal twins: separate egg cells are fertilized by separate spermatozoa
• Polyzygotic siblings are twins or triplets that come from more than two such twins