radiobiology II Flashcards
what is the molecular mechanisms of radiation induced injury?
-cell response depends not only on the type and dose of radiation, but also on the type of cell and the place of the cell in its cell cycle
-the worst outcome is cell death
-important to understand the molecular mechanisms in order to devise protection and recovery from the radiation injury, radiotherapy or response to tumors
what is in cells?
what are cell organelles?
carry out multitude functions
what are the macromolecules that these organelles carry?
-whole sequence happens due to oxidation
what is the graph of the cytoskeleton?
-cytoskeleton works in tandem to perform cell function during interphase
-red: active in immune cells
-green: make the cells boundary (also called stress fibers)
what does the cytoskeleton look like during metaphase?
-actin filaments: form stress fibers, focal adhesions, lamelipodia
-microtubules: pull chromosomes from the centromere
-silver=DNA
what is the cell cycle and DNA synthesis?
during interphase:
-a cell frows (G1)
-replicates its chromosomes (S) and
-prepares to divide (G2)
-after leaving the interphase a cell divides (call as mitosis, which is further characterized by four events namely prophase, metaphase, anaphase, telophase) and completes its division
-cellular effects are determined by the present cell phase
-p53: regulators of apoptosis (cell death), it can tell if cell has passes GI phase and S phase
-G2 is when maximum DNA repair occurs so checkpoints correct DNA errors
what’s the proof that DNA damage is important?
-low dose tritiated or halogenated pyrimidines (thymidine and cytosine), confer radiosensitivity (cell killing) due to intra nuclear Beta damage: substituted deoxyuridines induce DNA mutations
-chromosome damage/lethality correlates with the radiation exposure variable (type, dose rate, oxygen level): nucleocytoplasmic protein shutting
-mean viral nucleic acid volume, interphase chromosome volume (nuclear volume to chromosome number) correlate with radiosensitivity/cell lethality
what is the human cell-genome?
-the genome consists of DNA arranged in a network (in the form of chromatin) in the nucleus of each cell of a multi-cellular organism
-chromosomes that carry the hereditary factors (genes)
-genes are made up of DNA
what is DNA folding and packing?
-genomes have complex 3-D architecture and their function drive their structure
-structural chromatin features act as modulators of genome activity
-DNA is wrapped around the nucleosome (octamers of core-histones) forming the chromatin fiber which folds into loops such that regulatory regions of the genes are close to their transcription promoter regions
-the fiber holds into chromatin domains called as TADs (topologically associating domains) which associate with each other to form chromatin compartments which are non-random patterns of chromosomes and genes
-in DNA-free spaces, RNA and proteinaceous aggregates form nuclear bodies
what is chromatin organization?
what is DNA built of?
deoxyribose nucleic acid
what is the structure of DNA?
-the 5’ and 3’ mean “five prime” and “three prime”, which indicate the carbon numbers in the DNA’s sugar backbone
-the 5’ carbon has a phosphate group attached to it and the 3’ carbon a hydroxyl (-OH) group. this asymmetry gives a DNA strand a “direction”
-DNA polymerase works in a 5’->3’ direction, that is, it adds nucleotides to the 3’ end of the molecule
what are base damage sites?
-double bonds, methyl group, amino groups
what is sugar damage and single strand breaks?
what are thymine dimers?
cross-links between bases
what are the types of DNA breaks?
-base damage (BD)
-single strand break (SSB): sugar phosphate backbone clip off
-double strand break (DSB)
-sugar damage (in the sugar phosphate backbone)
-cross-links between bases (dimers)
-adducts
what is clustered DNA damage?
-an electron is initially captured by a base forming core-excited transient anion (TA)
-dissociative electron attachment (DEA) to base can produce base damage (BD)
-if the TA auto-detaches from the base, it can transfer to multiple moieties on same or the opposite strand. Transfer to PO43- group can result in SSB
-if the TA leaves the base detached after transfer, it can lead to multiple BDs
-electron transfer to opposite or same strand PO43- can result in DSB due to break in C-O bond
-electron hopping between bases can result in multiple damage sites farther from the initial capture site
what are cluster lesions?
locally multiply damaged site(s)
-two or more lesions within 20 base pairs in the helix
-characteristic of high energy radiation (HER)
how do we quantify DNA damage?
-pulse-field gel electrophoresis: DNA
-comet assay: cell-based assay
what are cell cycle assays?
what are DNA-protein interactions?
what is DNA damage a function of?
PROBABILITY
what is the cell survival curve?
what is clonogenicity assay?
the loss of cell colony formation from a single/few cells as a function of radiation dose
what are the subtypes of cell death?
-programmed; cell must die after certain amount of time
-accidental: no midpoint, just instant death
what is apoptosis and necrosis graph?
apoptosis=cell suicide
necrosis=dies over time
-sometimes cells just disintegrate
what is apoptosis?
1, 2, 3, 4
-gene regulated (programmed)
-energy dependent (active); cell metabolism intact
-cell shrinkage (actin and tubulin)
-intact plasma membrane (blebbing)
-cell contraction (apoptotic bodies)
-chromatin condensation (pyknosis)
-phagocytosis of surrounding cells (without provoking inflammation)
activation of caspase proteases
-extrinsic (ligand-plasma membrane receptor mediated) apoptosis
-intrinsic (mitochondria) apoptotic pathways
what is necrosis?
1, 7, 8 (sudden death, no blood circulation or trauma)
-result from irreparable cell damage; enzymes and protein regulated
-ATP decreases thus not supporting metabolism
-plasma membrane rupture
-loss of organellar structure
-cell swelling
-without chromatin condensation
-accompanied by inflammation (phlogistic)
what are the types of cell death?
what is the graph of radiation induced apoptosis?
how do we test for radiation induced apoptosis?
how do we quantify apoptosis?
what is autophagy?
-large intracellular vesicles: phagosomes, and later phagolysosomes induce membrane engulfment and catabolic degradation of cytoplasm
-autophagic machinery (autophagy specific genes, ATM)
-mainly survival response to metabolic crises (ATP, nutrient or amino acid deprivation)
-autophagic cell death (failed survival response due to excessive autophagy)
what is the graph of autophagy?
how do we test for autophagy?
what is necroptosis and parthanatos?
regulated
-2 inflammatory proteins assessed by mitochondria
what is pyroptosis and terroptosis?
what is cell cycle and apoptotic fate regulators?
nucleocytoplasmic shuttling of p21Waf1
-oncogenesis=cancerous growth of cells
what are neutrophil extracellular traps (NETs)?
-extracellular DNA fibers comprised of histone and cytoplasmic granule proteins
-not limited to neutrophils: eosinophiles (EETs) and macrophages (METs)
-what is their physiological function: thrombosis, atherosclerosis, autoimmune diseases, sepsis
