C H A P T E R 5 : O V E R V I E W O F C E L L B I O L O G YL A U R A H E R Z , B A , R T ( R )

RADIATION BIOLOGY

THE CELL

• Cell is the fundamental component of structure, development, growth, and life processes in the body• Body is composed of trillions of cells• Some are freely moving, independent units• Some remain in position as part of tissues

• Cells are engaged in an ongoing process of obtaining energy and converting it to support their functions• If exposure to ionizing radiation damages the cell beyond

repair, cells behave abnormally or die

CELL CHEMICAL COMPOSITION

• Cells are made of protoplasm--the chemical building material for all living things• Protoplasm consists of:• Organic compounds• Inorganic compounds• Water

ORGANIC COMPOUNDS

• Compounds that contain carbon• Four major classes:• Proteins• Carbohydrates• Lipids• Nucleic acids

ORGANIC COMPOUNDS

• Proteins• Make up about 15% of cell content• Essential for growth, construction of new body tissue, and

the repair of injured tissue

ORGANIC COMPOUNDS

• Proteins (cont.)• Formed when amino acids are connected by __________

________ into long, chainlike configurations• The order of arrangement of amino acids determines the

precise function of each protein• Structural Proteins: provide the body with shape and form;

source of heat and energy• Enzymatic Proteins: function as catalysts—agents that speed

up reactions to meet the needs of the cell• Repair Enzymes: can mend damaged molecules and are

therefore capable of helping the cell to recover from a small amount of radiation-induced damage

• Hormones: chemical secretions carried by the bloodstream to influence the activities of other parts of the body

• Antibodies: chemically attack any foreign invaders or antigens

ORGANIC COMPOUNDS

• Carbohydrates• Make up about 1% of cell content• Function as energy sources for the body

ORGANIC COMPOUNDS

• Lipids• Also referred to as fats• Make up about 2% of cell content• Functions:• Structural component of cell membranes• Insulate and guard the body against the environment• Support and protect organs

ORGANIC COMPOUNDS

• Nucleic Acids• Comprise about 1% of the cell• Two important types:• Deoxyribonucleic acid (DNA)• Ribonucleic acid (RNA)

ORGANIC COMPOUNDS

• Nucleic Acids (cont.)• DNA• Master chemical because it carries the genetic information

necessary for cell replication and regulates all cellular activity to direct protein synthesis

• Coiled, ladder-like structure• Composed of two long sugar-phosphate chains (sides) linked

by pairs of nitrogenous bases (steps or rungs)• Bases are divided as:

• Purines: • Pyrimidines:

• Purines link with pyrimidines in certain specific combinations• Adenine always bonds with thymine• Cytosine always bonds with guanine

ORGANIC COMPOUNDS

• Nucleic Acids (cont.)• RNA• Helps DNA influence cellular activity that takes place outside

the nucleus• Messenger RNA (mRNA)• Directs the process of making proteins out of amino acids

• Transfer RNA (tRNA)• Receives the genetic code from mRNA in the correct order so

that the necessary proteins are produced

INORGANIC COMPOUNDS

• Compounds that do not contain carbon• Consist of:• Acids• Bases• Salts (Electrolytes)• Maintain proper proportion of water in the cell• Aid in the production of energy• Aid in the conduction of nerve impulses

CELL STRUCTURE

• Cell Membrane• Cytoplasm• Cytoplasmic Organelles• Endoplasmic reticulum• Golgi apparatus or Golgi complex• Mitochondria• Lysosomes• Ribosomes

• Nucleus• Nucleolus

CELL STRUCTURE

• Cell Membrane• Semi-permeable structure encasing the cell• Made up of lipids and proteins• Protects cellular contents from outside environment and

controls the passage of materials into and out of the cell

CELL STRUCTURE

• Cytoplasm• Fluid inside the cell membrane, but outside of the

nucleus• Primarily composed of water and makes up the majority

of the cell• Contains large amounts of cell’s molecular components

except DNA• Where all metabolic functions occur

CELL STRUCTURE

• Endoplasmic Reticulum• Network of tubules and vesicles throughout the

cytoplasm• Enables cell to communicate with outside environment

and transfer food and molecules from one part of the cell to another• “Highway System”

• Two types• Smooth Endoplasmic Reticulum: • Rough Endoplasmic Reticulum:

CELL STRUCTURE

• Golgi apparatus or Golgi complex• Consist of tubes and a tiny sac near the nucleus• Unites large carbohydrate molecules with proteins to

form glycoproteins• Takes enzymes and hormones and concentrates,

packages, and transports them through the cell membrane so they can exit the cell and enter the bloodstream• “Packaging and Shipping Plant”

CELL STRUCTURE

• Mitochondria• Large, oval or bean-shaped structures• Supply energy for cells• “___________________” of the cell

CELL STRUCTURE

• Lysosomes• Small, pea-like sacs that are of great importance for

digestion within the cytoplasm• Break down large, unwanted molecules• Sometimes referred to as “___________ ______”

CELL STRUCTURE

• Ribosomes• Small, spherical organelles that attach to the

Endoplasmic Reticulum• “__________ ______________”

CELL STRUCTURE

• Nucleus• Separated from other parts of the cell by the nuclear

membrane• Controls cell division• Controls chemical reactions that occur in the cell

CELL STRUCTURE

• Nucleolus• Small, rounded body within the nucleus• Manufactures RNA

CELL DIVISION

• Multiplication process whereby one cell divides to form two or more cells• Two types occur in the body• Mitosis (M)• Somatic cells

• Meiosis• Genetic cells

MITOSIS

• Cell divides to form two daughter cells identical to the parent cell• Process results in an approximately equal

distribution of all cellular material between the two daughter cells

MITOSIS

• Interphase• G1

• S• G2

• Mitosis Phase• Prophase• Metaphase• Anaphase• Telephase

MITOSIS

• Interphase• Period of cell growth that occurs before mitosis• Cells are not yet undergoing division• G1: Pre-DNA synthesis

• May take a few minutes to several hours• S: DNA synthesis

• Takes up to 15 hours• G2: Post-DNA synthesis

• Occupies 1 to 5 hours of the whole cycle

MITOSIS• Mitosis Phase• Prophase: Nucleus and chromosomes enlarge, centrioles

migrate to opposite sides of cell• Metaphase: Mitotic spindle forms between centrioles,

chromosomes line up in the center of the cell• Anaphase: Chromatids travel to opposite sides of the cell• Telophase: Chromatids uncoil, nuclear membrane re-

forms, two nuclei appear• After division completes, each daughter cell has a complete

cell membrane and contains 46 chromosomes (exactly the same as the parent cell)

MEIOSIS

• Reduces the number of chromosomes in each daughter cell to half the number of chromosomes in the parent cell• Process of ___________ ___________

MEIOSIS• Interphase• DNA replication• Cells begin meiosis with

twice the genetic material as the parent cell

• Prophase• Metaphase• Anaphase• Telophase• Divides again without DNA

replication