Exam 2: Other Things Flashcards
when exactly does an inversion loop form?
prophase of meiosis I during bivalent formation
what is a pachytene cross
a structure that forms from 2 homologous pairs of chromosomes during bivalent formation in meiosis if there is a balanced reciprocal translocation
all 4 chromosomes come together in a cross
what is the ori
single origin of replication site in the circular chromosome of a bacterium like E. coli
what does primase do, during what process
makes an RNA primer on ssDNA during replication
example of post-translational processing
removing initial methionine
modifying aa side chains
guided protein folding
why is colinearity not true in most eukaryote genes?
b/c coding sequences in transcription units are likely to be interrupted by introns
also exons with coding sequences btwn introns may not be included in mRNA
what is colinearity
when aa sequences in the formed protein correspond to the order of codons on mRNA
what feature of DNA is found at the beginning of a transcription unit?
promotor region
what does lac operon do, and why
single transcription unit that codes for 3 proteins used in the processing and breaking down of lactose
what is a sigma factor
transcription factors in bacteria that participate in the transcription complex
each sigma factor enables specific groups (modules) of operons to be turned on simultaneously in bacteria
half a dozen or more different ones depending on species
when lac repressor binds to allolactose why can’t it bind to the promotor?
repressor undergoes a conformational change when found to allolactose
how can you change a weak promotor to a strong one?
change base sequence to increase its affinity to the transcription complex
what is a nick and what fixes it
broken covalent bond on a single strand of dsDNA between the sugar’s 3’ carbon and adjacent phosphate
no material is missing
ligase fixes
difference between 3’ and 5’ ends of an Okazaki fragment
5’ end has original RNA primer and the rest of the fragment out to the 3’ end is made of DNA
5’ end has attached phosphate
how could a mutation outside a transcription unit affect the expression of a gene
change a cis regulatory site so a TF that binds to the site doesn’t bind as strongly or binds too strongly
why do eukaryote genes need to have many different ways of being turned on?
single genes need to be turned on and off in different places in the body, or at different times, or under different conditions
for each new case, a separate CRM may be needed
what is combinatorial control in gene regulation
when a CRM can only be activated by a specific combination of TFs at the right time and sequence
difference between trisomy and triploidy
trisomy is 3 copies of an individual chromosome
triploidy is 3 copies of every chromosome at the same time
what causes triploidy?
dispermy-fertilization of one egg with two sperms
how to diagnose Klinefelter in a male
if he has a Barr body
XXY
phenotype of a person with a ring chromosome
retarded growth and short
in a G2 chromosome how many generations of DNA are represented
3
how can a eukaryote replicate its DNA in a short time when movement of replication forks is faster in bacteria?
eukaryotes have thousands of replicon origins
how are separate Okazaki fragments joined
3’ (DNA) end meets 5’ (RNA) end and DNA polymerase I rips out RNA nucleotides 1 at a time and replaces with DNA nucleotides 1 at a time
nick migrates forward 1 nt until only nick is left and is fixed by ligase
why are telomeres needed
protect ends of chromosomes from fusing to other chromosomes
b/c chromosomes get shorter with every replication
found at ends of linear chromosomes made of many copies of the same short non-coding repeat sequence
why do chromosomes get shorter after every replication?
3’ end of ssDNA can’t be copied to the very end
how does telomere system work
allows some of the repeat units to be lost every replication without the loss of essential genetic info
whats the trend in introns as you go from simple to complex organisms
introns per gene increases
where is start codon located, what does it start
mRNA 1st codon of ORF at 5’ end
starts process of translation, coding for 1st aa methionine
how many protein coding genes in human genome
20,000-25,000
during transcription does RNA polymerase use coding or antisense strand as a template?
anti-sense
