RADIATION BIOLOGY

Radiobiology – the study of the effects of ionizing radiation on living organisms

• Radiation that makes changes – ionizing radiation (ejection of electrons)
• Plant cells and animal cells are effected

Protoplasm - The complex, semifluid, translucent substance that constitutes the living matter of plant and animal cells and manifests the essential life functions of a cell. Composed of proteins, fats, and other molecules suspended in water(solvent), it includes the nucleus and cytoplasm.

Cell – smallest unit of protoplasm capable of sustaining life

Tissue - A group of cells to each other, along with their associated intercellular substances, which perform the same function within a multicellular organism. Major tissue types include epithelial, connective, skeletal, muscular, glandular, and nervous tissues.

Organ - A group of tissues which work together as a single unit to perform a particular function within a multicellular organism.

System -  a group of organs (ex. Circulatory system, nervous system etc.)

Chemical Composition of Cells:

Protoplasm:

    Water: makes up 70 - 85% of the weight of a average active cell

• stabilizes the temperature of the cell
• excellent conductor
• molecules slow cohesion (resists rupturing when put under tension)
• excellent solvent
• aids in diffusion
• hydrophobic and hydrophilic substances interact with water in ways that influence the shape and structure of membranes and other cell components

Inorganic compounds :

• salt
• potassium
• vitamins
• minerals

Organic Compounds:

Carbohydrates: 1%

• provide necessary energy

Lipids: 2%

• store energy
• key component to the cell membrane
• protective barrier
• can be reaaranged into other steriods

Proteins: 15%

• basic building blocks of cells and tissues
• components of enzymes (catalysts) - necessary to initiate reactions

 

Neuclotides: 1% (DNA and RNA)

• DNA, RNA - storage, translation and transmission of genetic information
  • DNA (deoxyribonucleic acid) - passes genetic information from one generation to the next and directs cellular activity
  • RNA (ribonucleic acid) - formation of proteins

Cell Structure: (somatic cells)

Cell membrane -  The semipermeable membrane that encloses the cytoplasm of a cell.   Has 3 layers :  Protein, Lipid, Protein

• offers protection from the outside world (lipid layer)
• selective permeability (protein layer)
• transport materials into and out of the cell (protein layer)

Cellular Organelles:

centrosome: a dense area of cytoplasm, generally spherical in shape and located near the nucleus

centrioles: within the centrosome is a pair of cylindrical structures which is composed of nine triplet cluster of microtubules arranged in a circular pattern

Centrosomes and centrioles both play a role in cell reproduction by serving as centers about which chromosome movement is organized

• If cell is not reproducing they are hard to identify

nucleus:

• is a generally a spherical or oval shaped organelle and is the largest structure in the cell
• contains the hereditary factors of the cell, called genes
• controls and directs all cellular activity
• seperated from the cytoplasm by a nuclear membrane (double membrane), which has minute pores to allow the nuclues to communicate with the cytoplasm
• DNA, RNA, chromatin, nucleolus
• DNA only in the nucleus / cannot leave
• RNA can be anywhere in the cell

nucleoplasm - gelllike fluid that fills the nucleus

nucleolus - (plural is nucleoli) one or more of these structures MAY be present and are composed of protein, DNA, and RNA (site of ribisomal RNA synthesis)

chromatin - when the cell is not reproducing the genetic material appears as a threadlike mass in the nucleoplasm (prior to  cell reproduction the chromatin shortens and coils into rod-like shaped bodies called chromosomes)

nuclear membrane - seperated the nucleus from the cytoplasm and has minute pores to allow the nucleus to communicate with the cytoplasm (double membrane)

mitochondria:

• appear throughout the cytoplasm and because their function in generating energy, they are referred to as the "power house" of the cell.  Within the mitochondria, energy is transferred from carbon compunds, such as glucose, to ATP ® ADP + phosphate + energy (which is a catabolic reaction)
• ADP – adenosine diphosphate / has a double bond between 2 phosphate groups
• ATP – adenosinetriphosphate / has a triple bond between 2 phosphate groups (stores energy for use by the cell)
• Catabolic reaction – breakdown reacton (ATP to ADP)
• Anabolic reaction – buildup reaction (ADP to ATP)
• active cells such as heart muscle and liver cells have a large number of mitochondria because of their high energy expenditure
• mitochondria are self-replicating for they can divide to form new ones.  The replication process is controlled by the DNA that is incorporated into the structure

ribosomes:

• tiny granules. 25nm at their largest, that are composed of ribosomal RNA (rRNA) and a number of specific ribosomal proteins.  The rRNA is manufactured by the DNA in the nucleolus
• sites of protein synthesis (recieve genetic instruction and use them to produce proteins)
• ribosomes are either "free ribosomes" or part of the Endoplasmic Rectilium (ER)

Free Ribosomes:

• free ribosomes are scattered in the cytoplasm (they have no attachements to other parts of the cell)
• primarily concerned with sythesizing protein for use inside the cell

Ribosomes attrached to granular(rough) ER:

• concerned with the sythesis of proteins for export from the cell

Endoplasmic Rectilium: within the cytoplasm is a system of double membrane channels of varying shapes. The channels are continous with the nuclear membrane.  On the basis of its association with ribosomal RNA, the ER is divided into 2 types:

Agranular (smooth) endoplasmic rectilium : is free of ribosomes

Granular (rough) endoplasmic rectilium : studded with ribosomes

Functions of ER:

• mechanical export and distrubution of cytoplasm
• intracellular exchange of materials with the cytoplam
• with the Golgi Complex the ER assumes a role in synthesis and packaging of molecules
• ribosomes associated with granular ER synthesize proteins

Golgi Complex:

• generally near the nucleus and in cells with high secretion activity the golgi complex is extensive
• consists of 4 to 8 flattened sacs, stacked upon each other like a pile of dishes with expanded areas at their ends
• function is to process, sort, package, and deliver proteins to various parts of the cell

Lysosomes:

• membrane enclosed spheres
• have powerful digestive enzymes (lytic acids) which are capable of breaking down many kinds of molecules in the process of phagocytosis
• these digestive enzymes aid in the digestion of nutrients and rids the body of bacteria

Vacoule :

• A small cavity in the cytoplasm of a cell, bound by a single membrane and containing water, food, or metabolic waste
• Contains lytic acids that causes cell death / releases it when it is time for it to die

Homeostasis - The ability of an organism to maintain a constant internal environment (i.e. body temperature, fluid content, etc.) though regulatory mechanisms that compensate for a changing external environment.