Genetics and Cell Cycle: Lecture 8 Flashcards
transcription
process of making mRNA copy of DNA (transcript); exit nucleus through nuclear pore into cytoplasm to ribosomes
RNA polymerase
enzyme builds transcript; binds to gene; brings in complementary nucleotides, linking them together to form mRNA
general stages of transcription and translation
- initiation
- elongation
- termination
initiation (transcription)
beginning; protein transcription factors bind to promoter region near gene on template strand of DNA; RNA polymerase also binds to promoter; DNA unwinds with aid of enzyme helicase
helicase
enzyme that unwinds DNA
elongation (transcription)
RNA polymerase covalently bonds complementary (to DNA template) nucleotides to growing mRNA molecule
termination (transcription)
when last triplet of gene is reached, and the newly formed pre-mRNA molecule is ready for modification
modification (transcription)
RNA processing- introns in pre-mRNA must be removed and exons spliced together
-when complete, mRNA exits nucleus through nuclear pore, enters cytosol, ready for translation into protein
introns/exons
introns: noncoding sections of gene do not specify amino acid sequence
exons: sections that do specify amino acid sequence
translation
occurs at ribosome
-nucleotide sequence of mRNA is translated into amino acid sequence with tRNA
-tRNA is made in nucleus, picks up specific amino acids and transfers to ribosome
anticodons
-sequences of three nucleotides found on tRNA molecules
-pairs with the complementary codon on the mRNA
binding sites for tRNA
A site, P site, E site
A site (aminoacyl)
binds to incoming tRNA carrying amino acid
P site (peptidyl)
amino acid is removed from its tRNA; added to growing peptide chain
E site (exit)
empty tRNA then exits ribosome from site; free to pick up another amino acid
initiation (translation)
initiator tRNA binds to mRNA start codon in ribosome’s P site
elongation (translation)
next tRNA binds to open A site; allows two amino acids to be linked by peptide bond; first tRNA exits from E site; second tRNA moves into P site; A site is open for next tRNA to bind
termination (translation)
end of translation when ribosome reaches stop codon on mRNA and new peptide is released
posttranslational modification
polypeptides folded properly; sometimes combined with other polypeptides to become fully functional
cell cycle main phases
interphase: G1, S, G2
M phase
interphase
period of growth and preparation for cell division
subphases: G1, S, G2
G1
cell performs normal daily metabolic activities (production of new organelles, cytoskeleton, and other proteins), prepares cell for next phase
S phase
synthesis; DNA synthesis (replication); vital for cell to proceed to next phase
G2
cellular growth; proteins required for cell division are rapidly produced and centrioles are duplicated
DNA synthesis or replication
S phase: chromatin unwinds each base pair is duplicated using existing DNA strand as template; helicase unwinds
primase
enzyme builds RNA primer on exposed DNA strands
DNA polymerase
adds nucleotides to RNA primer; can only add to existing chain of nucleotides; proceeds in opposite directions along each strand as helicase separates;
-RNA primer eventually removed and replaced with DNA nucleotides
semiconservative replication
one old strand and one new strand
M phase
overlapping processes of mitosis and cytokinesis
mitosis
newly replicated genetic material is divided between two daughter cells
cytokinesis
cell’s proteins, organelles, and cytosol are divided between two daughter cells
stages of mitosis
prophase
prometaphase
metaphase
anaphase
telophase
prophase
-chromatin becomes compact; each individual chromosome has two sister chromatids joined at centromere
-nucleolus disintegrates, mitotic spindle forms, pairs of centrioles (from newly duplicated centrosomes) migrate to opposite sides of cell; organize spindle fibers
prometaphase
-spindle fibers from each centriole attach to each sister chromatid at centromere
-nuclear envelope begins to break apart
metaphase
-second and longest
-spindle fibers from opposite poles of cell pull sister chromatids into line along middle (equator) of cell
anaphase
-sister chromatids pulled toward opposite poles; individual chromosomes then called daughter chromosomes
-each new daughter cell will have 46 chromosomes (23 pairs)
-cytokinesis may begin at end of this stage
telophase
-fourth and final stage
-as daughter cells separate the nuclear envelope is reassembled, nucleoli reappear, and chromosomes uncoil becoming chromatin
cytokinesis
divides cytosol and organelles equally between two new daughter cells
-cells split apart as actin and myosin proteins tighten around equator creating cleavage furrow
-eventually separates into genetically identical cells
cleavage furrow
equator between cells splitting apart
G0 phase
cells remain in G1 phase and never proceed through rest of cycle; non-dividing state
checkpoints for cell cycle
stop/go signals for cell; most important G1 checkpoint occurs about 3/4 of way through G1
-responds to variety of extracellular signals and may not proceed if conditions are not favorable
extracellular signals for cell division
-enough nutrients in ECF
-growth factors (proteins) must be secreted by other cells to stimulate cell division
-density of cells
-anchored to neighboring cells and surrounding environment
apoptosis
programmed cell death when cell cannot pass through checkpoints and cannot be repaired
tumor
cells may form growth or mass because of loss of cell cycle control and uncontrolled cell division
benign tumor
confined to original location; does not invade surrounding tissues; less likely to cause death
malignant tumor
made up of cancer cells; not inhibited by high cellular density or loss of anchorage to other cells; with enough nutrients, grow and divide indefinitely
metastasis
cells spread into other tissues; can cause widespread tissue destruction; may cause death
