RAD PRO CH 6 & 7: Understanding Cells and Radiation

The Cell

• Exists in various forms and performs diverse bodily functions.
• Can exist as free-moving, independent units, or remain stationary as part of larger organisms' tissues.
• Mature cells are highly specialized with predetermined tasks that support the body.
• Can move, grow, react, protect themselves, repair damage, regulate life processes, and reproduce.

Body Requirements

• Food provides raw materials for energy production.
• Oxygen aids in breaking down food.
• Water is needed to transport inorganic substances into and out of cells
• Proper cell function helps maintain homeostasis, or equilibrium.

Radiation and Cells

• Ionizing radiation can damage components of cells involved in molecular synthesis beyond repair.
• Cells can behave abnormally or die from ionizing radiation.

Cell Chemical Composition

• The three key components are protoplasm, organic compounds, and inorganic compounds.

Protoplasm

• Serves as the chemical building material for all living things.
• It carries out the metabolism, encompassing food and oxygen processing, and waste elimination.
• It consists of organic and inorganic materials, dissolved or suspended in water.
• Primarily composed of carbon, hydrogen, oxygen, and nitrogen.
• Water and mineral salts (electrolytes) are the most important inorganic substances.

Organic Compounds

• Carbon is the basic constituent of all organic matter.
• Combining with hydrogen, nitrogen, and oxygen is essential for life.
• Major classes of organic compounds that compose the cell include proteins, carbohydrates, lipids and nucleic acids.

Proteins

• Consist of the most amount of carbon of all organic compounds.
• Make up about 15% of cell content
• Essential for growth, constructing new body tissue, and repairing injuries.
• Amino acids that combine into long, chain-like molecular complexes form proteins.

Structural and Enzymatic Proteins

• Enzymatic proteins (enzymes) function as organic catalysts.
• Structural proteins provide shape and form for the body.

Hormones and Antibodies

• Antibodies chemically attack foreign invaders or antigens.
• Hormones are chemical secretions from various endocrine glands and carried in the bloodstream, influencing the body.

Carbohydrates (Saccharides)

• Constitute approximately 1% of cell content.
• Carbohydrates include starches and various sugars.
• Carbohydrates’ primary purpose is to provide fuel for cell metabolism.
• Are most abundant in the liver and muscle tissue.
• Serve as structural components of cell walls and intercellular materials.
• All carbohydrates are organic.

Lipids (Fats or Fatlike Substances)

• Account for approximately 2% of cell content.
• Are organic macromolecules
• They form the structural parts of cell membranes.
• Present in all body tissue.

Nucleic Acids

• Comprise about 1% of the cell and are complex macromolecules.
• Made up of nucleotides.
• Deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) are two types found in cells.

DNA: The Master Chemical

• DNA consists of two long sugar-phosphate chains in a double-helix linked by nitrogenous organic bases.
• DNA contains all the information the cell needs to function, and is necessary for cell replication.
• It regulates all cellular activity to direct protein synthesis.
• Determines characteristics by regulating the amino acid sequence in synthesis of protein.
• The nitrogenous base pairs sequence in a DNA molecule constitute the genetic code.
• There are structural differences when compared with RNA.
• Alternating sugar and phosphate molecules form the side rails of the ladder, and the nitrogenous organic bases consisting of adenine (A), thymine (T), guanine (G), and cytosine (C), form the rungs or steps.

Messenger RNA (mRNA)

• DNA regulates cellular activity indirectly, transmitting information outside the cell nucleus via mRNA.
• mRNA leaves the nucleus; in the cytoplasm, mRNA directs the process of making proteins out of amino acids.
• Appears as a single strand of the DNA ladderlike configuration, the ladder being severed in half lengthwise.

Transfer RNA (tRNA)

• tRNA receives the genetic code from mRNA.
• tRNA combines with individual amino acids from different areas of the cell and attaches them to the ribosomes.
• At the ribosomes, amino acids are arranged in specific orders to form chainlike protein molecules.

Ribosomal RNA (rRNA)

• rRNA assists the linking of mRNA to the ribosome to facilitate protein synthesis

Chromosomes and Genes

• Chromosomes' tiny, rod-shaped bodies appear as threadlike structures visible only in dividing cells.
• Chromosomes are composed of protein and DNA.
• Normal human somatic (non-reproductive) cells have 46 chromosomes (23 pairs).
• Reproductive (germ) cells have 23 chromosomes each.
• Genes are segments of DNA serve as the basic units of heredity.
• Each gene contains information responsible for directing cytoplasmic activity, controlling cell growth and development, and transmitting hereditary information.
• Genes control protein formation through genetic coding.

The Human Genome

• The total amount of genetic material (DNA) contained within the chromosomes of a human being.
• Mapping is the process of locating and identifying the genes in the genome.
• There are 2.9 billion base pairs in the human genome.
• Data obtained from the Human Genome Project have allowed us to work on problems in molecular biology.

Inorganic Compounds

• Compounds that do not contain carbon and occur in nature independent of living things.
• Acids, bases, and salts (electrolytes) are examples of inorganic compounds.
• Water and mineral salts are the most important inorganic substances.
• Water comprises approximately 80% to 85% of the body’s weight.
• Maintaining the correct amount of water in a cell is imperative.

Water Function

• Within cells, it is the medium in which the chemical reactions that are the basis of metabolic activities occur.
• Acts as a solvent, keeping compounds dissolved so that they can more easily interact, and their concentration may be regulated.
• Water functions as a transport vehicle for materials the cell uses or eliminates outside cells.
• It maintains a constant body core temperature of 98.6° F (37° C).
• It lubricates both the digestive system and skeletal articulations.
• Water protects organs such as the brain and lungs.

Mineral Salts Functions

• Mineral salts keep the correct water proportion to maintain osmotic pressure.
• They're also necessary for proper cell performance, energy creation, and conduction of impulses along nerves.
• Ions, constituents of salt, via chemical reaction cause materials to be altered, broken down, and recombined to form new substances.

Cell Structure

• The normal human cell includes the cell membrane, cytoplasm, cytoplasmic organelles, and nucleus.
• Cytoplasmic organelles include the endoplasmic reticulum, Golgi apparatus/complex, mitochondria, lysosomes, ribosomes, and centrosomes.

Cell Division

• Mitosis is a cell division in which the nucleus divides first, followed by the cytoplasm’s division.
• Mitosis occurs when all somatic cells divide.
• Meiosis is a process of reduction cell division.
• Meiosis occurs when genetic cells divide.

Radiation Biology

• Branch of biology concerned with the effects of ionizing radiation on living systems.
• It includes the sequence of events occurring after the absorption of energy from ionizing radiation.
• The actions of living systems to make up for this energy assimilation.
• The injury to living systems that may be produced.

Ionizing Radiation

• Ionizing radiation can damage living systems by ionizing the composing atoms’ molecular structure.
• Biologic damage begins with ionization produced by various radiation types.
• Examples of radiation include X-rays, gamma rays, alpha/beta particles, and protons.
• Ionized atoms will not bond properly in molecules.

Radiation Energy Transfer Determinants

• Charge, mass, and energy vary among the different types of radiation.
• These attributes determine the extent to which different radiation modalities transfer energy into biologic tissue.
• Three important radiation concepts are linear energy transfer, relative biologic effectiveness, and oxygen enhancement ratio.

Linear Energy Transfer (LET)

• It is the average energy deposited per unit length of track by ionizing radiation as it passes through and interacts with a medium along its path.
• The radiation can cause more biologic effects as LET increases.
• Radiation categories are determined according to LET.
• Radiation categories include low-linear energy transfer and high-linear energy transfer.

Relative Biologic Effectiveness (RBE)

• RBE describes radiation's capabilities with differing LETs to produce a particular biologic reaction.

Oxygen Enhancement Ratio (OER)

• OER measures the radiation dose needed to cause a particular biologic response of cells/organisms in an oxygen-deprived environment vs. normal conditions.
• Oxygen enhances the effects of ionizing radiation on biologic tissue by increasing tissue radiosensitivity.

Molecular Effects of Irradiation

• Biologic damage from ionizing radiation is seen on three levels,
• Molecular, cellular, and organic systems.
• Visible radiation-induced injuries initially start damaging at the molecular level.
• Molecular damage can impair cellular function
• Molecules that are structurally changed are due to molecular damage.

Irradiation Effects on Somatic and Genetic Cells

• Radiation may disturb the cell's chemical balance, affecting its operation.
• The cell can no longer perform its purpose.
• Sufficient damage to somatic cells may disrupt entire body processes.
• Radiation damage to germ cells can pass down to future generations as genetic mutations.

Ionizing Radiation Interaction

• Two classifications of ionizing radiation interaction on a cell:
  • Direct action (e.g., in DNA)
  • Indirect action (e.g., in H2O)
• The human body is mostly water (80%) with minor amounts of DNA (less than 1%).
• It results in the low-LET irradiation in a living cell leading effects in indirect action.

Radiolysis of Water

• Radiolysis involves ionization of water molecules.
• It leads to the production of free radicals, and undesirable chemical reactions, and biologic damage.
• Eventually, it causes cell-damaging substances.

Ionizing Radiation

• Interactions of ionizing radiation with DNA molecules can cause the loss of/change in a nitrogenous base in the DNA chain,
• Which alters the base sequence, resulting in a mutation.
• This is not reversible and may cause acute consequences for the cell
• If the cell remains viable and then divides, it passes any incorrect genetic information onto new cells.

Target Theory

• A master or key molecule is is necessary for the cell's survival.
• Used to explain cell death and injury from cell exposure from radiation.

Irradiation of the Entire Cell

• Types of damage cells suffer.
  • Instant death
  • Reproductive death
  • Apoptosis, or programmed cell death (interphase death)
  • Mitotic, or genetic, death
  • Mitotic delay
  • Interference with function

Cell Radiosensitivity

• Cell maturity and specialization
• Radiosensitivity relies on maturity and specialization of different types of cells and tissues in the human body.

Bergoiné and Tribondeau Law

• Observed ionizing radiation's effects on testicular germ cells after exposing rabbits to x-rays.
• Radiosensitivity was a function of the metabolic state of cell when exposed to X-Rays.
• The law states that radiosensitivity of cells is directly proportional to their reproductive activity.
• Radiosensitivity is inversely proportional to their degree of differentiation