Week 3 Flashcards
(43 cards)
types of rna
mRNA—code for proteins
rRNA—Core of ribosome
in vitro
in glass, in test tube
in vivo
in life, without disrupting organism
Nirenberg experiments
make a cell free extract from E. coli
added different parts at different times (similar to electrophoresis)
use 14C as a tracer to label proteins (allows to track very small amounts)
show protein synthesis in vitro (add amount of soluble RNA, show that more proteins occur, add ribosomal rna—necessary)
mRNA—needed for protein production in a dose dependent manner
mRNA—needed for protein synthesis once endogenous rna removed by DNAse (can stimulate, once DNA destroyed)
x-ase
short way to say an enzyme that destroys x
penicillinase—enzyme that destroys penicillin, etc.
DNase—enzyme that destroys dna, etc.
how did scientists find genetic code?
idea: take simple synthetic rna (UUU poly-U), then see what this codes for
poly U results in poly phenylalanine peptide
very simplified system
make poly C, poly A, etc, in each case only single amino acid made
can’t make poly G, since makes secondary and tertiary structures—not really translatable
UC… gives 2 amino acids, so triplicate code, etc.
UA… gives 4 amino acids
Khorana
did experiments on genetic code, chemically synthesized nucleotides
wobble base
third base in nucleotide sequence, changes
UC together, AG together for wobbling
directionality of mRNA synthesis
5’ terminus of mRNA first, then 3’ terminus last
during protein synthesis, same direction
but reading of dna is 3’ to 5’
correspondence between tRNA and codon
not a clean (one to one) correspondence, always
UAA, UAG, UGA
stop codons—mean stop, terminator, nonsense
if mutation changes base of codon
1) no change—e.g wobble base, synonymous mutation
2) change one amino acid to another—nonsynonymous mutation
3) changes amino acid to stop—nonsense mutation, or stop gain
dna structure
dna is wrapped around histones in large coils in the cell
- special enzymes needed to uncool and recoil dna
- dna is very long molecule that is highly condensed
chromosome
highly packed structure of dna
each species has a characteristic number of chromosomes (46 for humans)
-22 autosome pairs, 2 sex chromosomes x and y
when cell divides, chromosomes are visible
nondividing cell—tangled mess
two parts—chromatid and centromere
chromatin
when eukaryotic cell is not dividing, dna is tangled mass of thin threads
material from which chromosomes of eukaryotes are composed
consists of protein, rna, dna
the cell cycle
organization of how dna and life of cell is organized
most of cell happens during interphase (dna replication as chromosomes duplicate, protein production, etc.)
then growth phase, and prepares to divide (mitosis, cytokinesis—movement into 2 cells)
orderly sequence of events that occurs in time
stages: G1 (cell increases in size), S (copies it’s dna), G2 (prepares to divide), and M (divides)
- interphase —G1, S, G2
mitotic phase
where cell division occurs
four phases: prophase, metaphase, anaphase, telephase
interphase
majority of time for cell
late interphase—when chromosomes begin to compact
end of interphase—two copies, so four copies of each gene (one on each chromosome)
G1, S, G2
no observable changes under the microscope
early and late prophase
early prophase—nuclear membrane becomes in distinct, chromatin fibers more packed and condensed
late prophase—nuclear membrane and nucleosus vanish completely
metaphase
short moment during which chromosomes look like we see (in well known shape)
chromosomes become attached to spindle fibers
then anaphase, then telophase
karyotype
number of chromosomes
species specific
chromosomes can be very small of very late, different shapes
species differing by chromosome number cannot interbreed
diploid number
number of chromosomes found in somatic (non sex) cells
haploid number
one chromosome of each kind
autosome
non-sex chromosome
22 autosome pairs (not sex chromosomes)
receive one of each autosome from father, one of each from mother, X chromosome from m, etc.
