Exam 2: Other Things

Question 1

when exactly does an inversion loop form?

Answer 1

prophase of meiosis I during bivalent formation

Question 2

what is a pachytene cross

Answer 2

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

Question 3

what is the ori

Answer 3

single origin of replication site in the circular chromosome of a bacterium like E. coli

Question 4

what does primase do, during what process

Answer 4

makes an RNA primer on ssDNA during replication

Question 5

example of post-translational processing

Answer 5

removing initial methionine

modifying aa side chains

guided protein folding

Question 6

why is colinearity not true in most eukaryote genes?

Answer 6

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

Question 7

what is colinearity

Answer 7

when aa sequences in the formed protein correspond to the order of codons on mRNA

Question 8

what feature of DNA is found at the beginning of a transcription unit?

Answer 8

promotor region

Question 9

what does lac operon do, and why

Answer 9

single transcription unit that codes for 3 proteins used in the processing and breaking down of lactose

Question 10

what is a sigma factor

Answer 10

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

Question 11

when lac repressor binds to allolactose why can’t it bind to the promotor?

Answer 11

repressor undergoes a conformational change when found to allolactose

Question 12

how can you change a weak promotor to a strong one?

Answer 12

change base sequence to increase its affinity to the transcription complex

Question 13

what is a nick and what fixes it

Answer 13

broken covalent bond on a single strand of dsDNA between the sugar’s 3’ carbon and adjacent phosphate

no material is missing

ligase fixes

Question 14

difference between 3’ and 5’ ends of an Okazaki fragment

Answer 14

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

Question 15

how could a mutation outside a transcription unit affect the expression of a gene

Answer 15

change a cis regulatory site so a TF that binds to the site doesn’t bind as strongly or binds too strongly

Question 16

why do eukaryote genes need to have many different ways of being turned on?

Answer 16

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

Question 17

what is combinatorial control in gene regulation

Answer 17

when a CRM can only be activated by a specific combination of TFs at the right time and sequence

Question 18

difference between trisomy and triploidy

Answer 18

trisomy is 3 copies of an individual chromosome

triploidy is 3 copies of every chromosome at the same time

Question 19

what causes triploidy?

Answer 19

dispermy-fertilization of one egg with two sperms

Question 20

how to diagnose Klinefelter in a male

Answer 20

if he has a Barr body

XXY

Question 21

phenotype of a person with a ring chromosome

Answer 21

retarded growth and short

Question 22

in a G2 chromosome how many generations of DNA are represented

Answer 22

3

Question 23

how can a eukaryote replicate its DNA in a short time when movement of replication forks is faster in bacteria?

Answer 23

eukaryotes have thousands of replicon origins

Question 24

how are separate Okazaki fragments joined

Answer 24

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

Question 25

why are telomeres needed

Answer 25

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

Question 26

why do chromosomes get shorter after every replication?

Answer 26

3’ end of ssDNA can’t be copied to the very end

Question 27

how does telomere system work

Answer 27

allows some of the repeat units to be lost every replication without the loss of essential genetic info

Question 28

whats the trend in introns as you go from simple to complex organisms

Answer 28

introns per gene increases

Question 29

where is start codon located, what does it start

Answer 29

mRNA 1st codon of ORF at 5’ end

starts process of translation, coding for 1st aa methionine

Question 30

how many protein coding genes in human genome

Answer 30

20,000-25,000

Question 31

during transcription does RNA polymerase use coding or antisense strand as a template?

Answer 31

anti-sense