Ch17 Flashcards
Interphase
Occupies most of the cell cycle and no division takes place
Cell increases in size & carries normal cellular function like protein synthesis and DNA replication
Interphase stages
G1 = cell makes enzymes & protein required for growth
S = DNA in nucleus replicates —> each chromosomes of 2 sister chromatids
G2 = cell continues to grow and new DNA is checked so errors are repaired
Production of tubulin proteins to make microtubules for spindles
Importance of mitosis
Growth of multicellular organisms
Replacement of cells And repair of tissues
Asexual reproduction
Prophase
Chromosomes condense and become visible
2 identical sister chromatids held by centromere
2 centrosomes move towards opposite poles
Spindle fibers emerge from centrosomes
Nuclear envelope disintegrates & nucleolus disappears
Metaphase
Centrosomes reach opposite poles
Spindlefibers continue to extended from centrosomes
Chromosomes line up at equator
Spindle fibers reach chromosomes and attach to centromere
Each sister chromatid attached to spindle fiber
Anaphase
Sister chromatids separate at centromere
Spindle fibers shorten
Chromosomes pulled to opposite poles
Telophase
Chromosomes arrive at opposite poles
Nuclear envelope reforms around each set of chromosome
Spindle fibers break down
Centrosomes will replicate later
how do prokaryotic cells divide
binary fission
circular DNA molecule must be replicated
stages of binary fission
chromosomes replicate
one copy of origin moves rapidly towards the other end of the cell and reaches as replication continues
plasma grows inwards and new cell wall deposited
parent cell divides and cytoplasm halved between two daughter cells
conjugation
DNA transferred from one cell to another
one cell produces a thin projection that meets another cell and forms a thin conjugation tube between them
donor cell replicates one of its plasmids
plasmid broken to be linear before it passes along tube into other cell
Brief contact lets only a small portion of donor DNA to be transferred
new characteristics obtained by recipient cell
horizontal and vertical gene transmisson
in H DNA in form of genes passed down from one species to another
in V DNA in form of genes passes down from one generation of same species to another
mutation
change to quantity or structure of the DNA of an organism
occuring in body cells not passed on
occuring during formation of gametes can be passed on
gene mutation
change in base sequence in DNA
3 types of substitution
type of gene mutation where nucleotide in DNA replaced by another nucleotide with different base
1.nonsense
2.missense
3.silent
nonsense mutation
base change results in formation of stop codon (UAG)
production of polypeptide stopped and final protein different so cannot perform
missense mutation
results in different amino acid being coded for
polypepitde produced will differ in single amino acid
silent mutation
base substituted still codes for same amino acid as genetic code is degenerate
no change in polypeptide produced
deletion of bases
nucleotide lost from the normal DNA sequence causes frameshift so gene now read in wrong three base groups
causes of mutation
arise spontaneously during DNA replication
mutagenic factors ;
high energy radiation
chemicals that alter the DNA structure or interfere with transcription
genes that control cell divison
protooncogenes : stimulate cell divison
tumor supressor genes : slow cell divison
proto oncogenes
stimulate cell division by growth factors which attach to receptor proteins on CSB and relay proteins switch on genes necessary for DNA replication
how gene mutations can affect protooncogenes
can muatate into oncogenes
causes receptor on cell surface membrane to be perm activated = rapid divison
may code for growth factor that is produced in excess
benign and malignant tumors
benign do not spread
malignant can invade nearby tissue and spread to other parts and grow
tumour supressor genes
inhibit cell division
if becomes mutated then it is inactiavted so increases cell division
