Mutations and Cancer. Flashcards
mutations can occur at which level?
at the chromosomal level or the nucleotide level.
a mutation in a germ cell is serious . why?
germ cells give rise to many cells ! can be very serious for offspring as well.
mutations can be spontaneous and …
induced! - caused by mutagens.
what is a point mutation?
if a mutation changes a single base pair of nucleotides
base pair substitution mutation?
when one base pair is replaced by another!
transition mutation
sub a purine for a purine
transversion mutation
sub a purine for a pyrimidine
what is a missense mutation?
base pair mutation that occurs in the aa coding seq of a gene. a missense mutation may or may not alter the aa sequence of a protein , and an alteration of a single aa may or may not have serious effects on the function of the protein.
neutral mutation
if there is no change in protein function
silent mutation
if the aa is not changed.
frameshift mutation
can be caused by an insertion or deletion of a base pair
normally if they occur in multiples other then 3
- frameshift mutations often result in a completely non functional protein, whereas nonframeshift mutations may still result in a partially or even completely active protein.
nonsense mutation
if a base pair substitution or an insertion or deletion mutation creates a stop codon.
these are very serious bc they prevent translation of a functional protein
chromosomal mutations
structural changes may occur to a chromosome in the form of deletions, duplications, translocations and inversions
what are transposons and transposable elements?
DNA segments called transposable elements or transposons can excise themselves from a chromosome and reinsert themselves at another location.
forward mutation or a backward mutation
term refers to an already mutated organism that is mutated again.
backward is reverting the organism back to its original state.
Cancer
unrestrained and uncontrolled growth of cells.
cancer cells continue to grow and divide indefinitely.
what are oncogenes?
genes that cause cancer by mutagens such as UV radiation, chemicals or simply random mutations. mutagens that can cause cancer are called carcinogens.
Chromosomes
DNA that are not in use are wrapped tightly around globular proteins called histones. (eight ) 8 histones wrapped in DNA form a nucleosome. nucleosomes will then wrap into coils called solenoids, which wrap into supercoils. the entire DNA/protein complex is called chromatin.
what is chromatin?
chromatin is about one third DNA , two thirds protein and a small amount of RNA.
what is heterochromatin?
chromatin condensed as described earlier is called heterochromatin. when transcribed, chromatin has to be uncoiled. - when uncoiled and transcribed it is called euchromatin.
how many homologous pairs of chromosomes do humans have?
23!
diploid ?
any cell that contains homolog pairs is said to be diploid
diploid means that the cell has homologous pairs.
haploid?
any cell that does not contain homologous is said to be haploid.
every cell has a lifecycle. The lifecycle of a typical somatic cell of a multicellular organism is divided into 4 stages
1) growth phase (G1)
2) synthesis (S)
3) The second growth phase (G2)
4) Mitosis or Meiosis (M) and cytokinesis (C)
G1, S, G2 are collectively called interphase.
what happens in the growth phase 1 (G1)?
cell grows in size, makes new organelles and proteins. RNA synthesis and protein synthesis is very active. the cell growth is assessed at the G1 checkpoint near end of G1 . if favourable for division, it enters the S phase. otherwise it enters G0. the main factor in triggering the beg of S is cell size based upon ratio of cytoplasm to DNA. G1 is normally but not always the longest phase.
G0 is what?
NON growing phase and is distinct from interphase.
What happens in the S phase?
cell devotes most of its energy to replicating DNA. each chromosome is exactly duplicated . each chromosome is made of two identical sister chromatids.
what happens in G2?
cell prepares to divide. cellular organelles continue to duplicate. end of G2 is the G2 checkpoint. it checks for mitosis promoting factor, when MPF level is high enough, mitosis is triggered.
