Fifth Lecture

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Fifth Lecture
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DNA
Protein
Oxidative damage by free radicals
Lipids
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And so on
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Effects of ionizing radiation on DNA RNA

• DNA is the most important material making up the
  chromosomes.
• It determines what types of RNA are produced
  which, in turn, determine the types of protein
  that are produced.
• The DNA molecule takes the form of a twisted
  ladder or double helix.
• The sides of the ladder are strands of
  alternating sugar and phosphate groups. Branching
  off from each sugar group is one of four
  nitrogenous bases cytosine, thymine, adenine and
  guanine.

I I S-AT-S I I P P I
I S-CG-S I I P P I
I S-GC-S I I P P I
I S-TA-S I I
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Effects of ionizing radiation on DNA RNA

• DNA is the primary target for cell damage from
  ionizing radiation.
• Toxic effects at low to moderate doses (cell
  killing, mutagenesis, and malignant
  transformation) appear to result from damage to
  cellular DNA.
• Thus, ionizing radiation is a classical genotoxic
  agent.

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Effects of ionizing radiation on DNA RNA

• Radiation can induce a variety of DNA lesions
  including-
• specific base damage,
• Single strand breaks,
• double strand breaks
• and cross-linkage formation.

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Effects of ionizing radiation on DNA RNA

• Active enzymatic repair processes exist for the
  repair of both DNA base damage and strand breaks.
  
• In many cases breaks in the double-strand DNA can
  be repaired by the enzymes, DNA polymerase, and
  DNA ligase.
• The repair of double strand breaks involves
  recombinational events, depending upon the nature
  of the initial break.

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Radiation Induced Chromosome Damage

• Chromosomes are composed of DNA, a macromolecule
  containing genetic information.
• This large, tightly coiled, double stranded
  molecule is sensitive to radiation damage.
• Radiation effects range from complete breaks of
  the nucleotide chains of DNA, to point mutations
  which are essentially radiation-induced chemical
  changes in the nucleotides.

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Radiation effects on Chromosomes

• After irradiation, chromosomes may appear to be
  "sticky" with formation of temporary or permanent
  interchromosomal bridges preventing normal
  chromosome separation during mitosis and
  transcription of genetic information.
• In addition, radiation can cause structural
  aberrations with pieces of the chromosomes break
  and form aberrant shapes.
• Unequal division of nuclear chromatin material
  between daughter cells may result in production
  of nonviable, abnormal nuclei.