1|Page
BCHM 4360 EXAM 1 NEWEST 2025/2026 ACTUAL EXAM WITH
COMPLETE QUESTIONS AND CORRECT DETAILED ANSWERS (100%
VERIFIED ANSWERS) |ALREADY GRADED A+| ||PROFESSOR
VERIFIED||
What is the method that DNA methyltransferases use to access
cytosines and what are the three steps? - ANSWER-base-flipping
1) A cytosine is flipped out of the DNA double helix
2) An amino acid is temporarily inserted to stack in the double
helix
3) The cytosine is methylated and reinserted into the double helix
Explain how DNA methylation distinguishes newly synthesized
DNA in repair processes in bacteria. - ANSWER-Just after
replication, only the parental strand of DNA is methylated (called
hemi-methylated). When mismatch repair enzymes detect a
mismatch, the methylation status is read, allowing the repair
machinery to identify the parental strand and correclty repair the
mismatch
Explain how DNA methylation allows bacteria to distinguish
genomic DNA from invading bacteriophage DNA. - ANSWER-
,2|Page
Restriction enzymes cut DNA at specific recognition sites so
bacteria defend their own DNA from being cut by methylating the
recognition sites. The bacteriophage DNA is not methylated and
will therefore be cut by the restriction enzymes and destroyed.
True or False: Methylation in eukaryotes is only used to silence
transcription, not activate it. - ANSWER-False
Eukaryotic methylation is usually at which two sites? - ANSWER-
CpG or CpXpG
Up to __% of human CpGs are methylated, and methylation state
can be _________. - ANSWER-inherited
What is an example of epigenetic silencing in mammals and how
does it work? - ANSWER-X-chromosome inactivation, one X
chromosome in each cell is inactivated in females so they have
the same amount of gene product as in males
,3|Page
Some gene activity is affected by __________, which is thought
to control expression of genes from mother and father in the
embryo. - ANSWER-imprinting
True or false: If one copy of a gene is silenced and the other is
absent, there is still some gene expression due to recombination.
- ANSWER-False, there will be no gene expression and no
recombination
Explain how fruit flies occasionally have white eyes. - ANSWER-
Fruit fly eyes are normally red, from expression of white+.
Occasionally, white eyes are seen as a result of white+ moving
near to heterochromatic regions and being silenced
How do boundary elements work to silence some genes? -
ANSWER-They slide down the chromosome, shutting down
genes due to the heterochromatin being able to spread
True or false: Boundary elements can both allow and prevent
heterochromatin spreading. - ANSWER-True
, 4|Page
Give an example of how boundary elements prevent
heterochromatin spreading. - ANSWER-In S. pombe, two
boundary elements flank a region of silent heterochromatin
around the centromere. H3 histones between the boundary
elements are highly methylated at lysine 9 and are silenced. H3
histones outside the boundary elements are highly methylated at
lysine 4 and are active. Removal of the boundary elements will
allow spreading of lysine 9 methylation and will cause silencing
Boundary elements are like _____ that prevent the rapid
spreading of silencing and activation sites. - ANSWER-walls
Boundary elements are _______ _________ that physically block
histones from sharing their messages. - ANSWER-protein
complexes
What could be an effect of a transposable element inserting
where boundary elements are? - ANSWER-Preventing proper
function, allowing for heterochromatin spreading
BCHM 4360 EXAM 1 NEWEST 2025/2026 ACTUAL EXAM WITH
COMPLETE QUESTIONS AND CORRECT DETAILED ANSWERS (100%
VERIFIED ANSWERS) |ALREADY GRADED A+| ||PROFESSOR
VERIFIED||
What is the method that DNA methyltransferases use to access
cytosines and what are the three steps? - ANSWER-base-flipping
1) A cytosine is flipped out of the DNA double helix
2) An amino acid is temporarily inserted to stack in the double
helix
3) The cytosine is methylated and reinserted into the double helix
Explain how DNA methylation distinguishes newly synthesized
DNA in repair processes in bacteria. - ANSWER-Just after
replication, only the parental strand of DNA is methylated (called
hemi-methylated). When mismatch repair enzymes detect a
mismatch, the methylation status is read, allowing the repair
machinery to identify the parental strand and correclty repair the
mismatch
Explain how DNA methylation allows bacteria to distinguish
genomic DNA from invading bacteriophage DNA. - ANSWER-
,2|Page
Restriction enzymes cut DNA at specific recognition sites so
bacteria defend their own DNA from being cut by methylating the
recognition sites. The bacteriophage DNA is not methylated and
will therefore be cut by the restriction enzymes and destroyed.
True or False: Methylation in eukaryotes is only used to silence
transcription, not activate it. - ANSWER-False
Eukaryotic methylation is usually at which two sites? - ANSWER-
CpG or CpXpG
Up to __% of human CpGs are methylated, and methylation state
can be _________. - ANSWER-inherited
What is an example of epigenetic silencing in mammals and how
does it work? - ANSWER-X-chromosome inactivation, one X
chromosome in each cell is inactivated in females so they have
the same amount of gene product as in males
,3|Page
Some gene activity is affected by __________, which is thought
to control expression of genes from mother and father in the
embryo. - ANSWER-imprinting
True or false: If one copy of a gene is silenced and the other is
absent, there is still some gene expression due to recombination.
- ANSWER-False, there will be no gene expression and no
recombination
Explain how fruit flies occasionally have white eyes. - ANSWER-
Fruit fly eyes are normally red, from expression of white+.
Occasionally, white eyes are seen as a result of white+ moving
near to heterochromatic regions and being silenced
How do boundary elements work to silence some genes? -
ANSWER-They slide down the chromosome, shutting down
genes due to the heterochromatin being able to spread
True or false: Boundary elements can both allow and prevent
heterochromatin spreading. - ANSWER-True
, 4|Page
Give an example of how boundary elements prevent
heterochromatin spreading. - ANSWER-In S. pombe, two
boundary elements flank a region of silent heterochromatin
around the centromere. H3 histones between the boundary
elements are highly methylated at lysine 9 and are silenced. H3
histones outside the boundary elements are highly methylated at
lysine 4 and are active. Removal of the boundary elements will
allow spreading of lysine 9 methylation and will cause silencing
Boundary elements are like _____ that prevent the rapid
spreading of silencing and activation sites. - ANSWER-walls
Boundary elements are _______ _________ that physically block
histones from sharing their messages. - ANSWER-protein
complexes
What could be an effect of a transposable element inserting
where boundary elements are? - ANSWER-Preventing proper
function, allowing for heterochromatin spreading
