BCHM 4360 ACTUAL EXAM 1 2025 VERIFIED RATIONALES WITH COMPLETE
SOLUTIONS |GRADED A
In eukaryotes, the basic binding proteins are called ________.
histones
How many core histones are there and what are they called?
4, H2A, H2B, H3, H4
Which two amino acids are histones rich in and why?
lysine and arginine due to positive charges
DNA wraps around a histone complex in a ____-handed manner to form a __________.
left, nucleosome
Which two histone dimers associate with DNA first?
H3, H4
Which two histone dimers associate last to form the octamer?
H2A, H2B
,About how many base pairs of DNA wrap around the histone octamer to form the
nucleosome?
146
Removing the histone octamer leaves what kind of supercoiled DNA?
negative
Each core histone has a(n) _-terminal tail that extends outward between the DNA and coils.
N
The histone tails are up to __ amino acids long and have an _________ structure.
25, undefined
Why do the histone tails interact with other nucleosomes?
to help compact DNA further
What are the five mutant variations of histone H2A?
H2A.X, H2A.Z, MacroH2A1, MacroH2A2, H2A-Bbd
,What is the proposed function for H2A.X?
DNA damage signaling
What is the proposed function for H2A.Z?
transcriptional silencing
What is the proposed function for MacroH2A1 and MacroH2A2?
binds inactive X chromosome
What is the variant histone for H2B?
H2B.1
What are the four variant histones for H3?
CENP-A, H3FA3, H3.3B, H3FT
Which variant histone for H3 is the most important and what is its function?
CENP-A, defines centromere chromatin
What are the variant histones for H4?
none
, True or False: nucleosomes prefer some types of DNA sequences over others.
true
DNA is generally ________ bent around histones but has _______ bends in some places.
smoothly, sharper
The sharp bends in DNA usually occurs in which groove and at which sequences?
minor groove, pyrimidine-purine sequences such as TA and CG
The _____ groove needs to narrow during DNA bending, and this is more favorable in which
regions?
AT-rich regions
The first level of chromatin packing is the __nm fiber, which arises from nucleosome
association with DNA, and has what kind of appearance?
10, beads on a string
The 10nm fiber is folded further into the __nm fiber, a regular arrangement that does what?
30, brings nucleosomes together
SOLUTIONS |GRADED A
In eukaryotes, the basic binding proteins are called ________.
histones
How many core histones are there and what are they called?
4, H2A, H2B, H3, H4
Which two amino acids are histones rich in and why?
lysine and arginine due to positive charges
DNA wraps around a histone complex in a ____-handed manner to form a __________.
left, nucleosome
Which two histone dimers associate with DNA first?
H3, H4
Which two histone dimers associate last to form the octamer?
H2A, H2B
,About how many base pairs of DNA wrap around the histone octamer to form the
nucleosome?
146
Removing the histone octamer leaves what kind of supercoiled DNA?
negative
Each core histone has a(n) _-terminal tail that extends outward between the DNA and coils.
N
The histone tails are up to __ amino acids long and have an _________ structure.
25, undefined
Why do the histone tails interact with other nucleosomes?
to help compact DNA further
What are the five mutant variations of histone H2A?
H2A.X, H2A.Z, MacroH2A1, MacroH2A2, H2A-Bbd
,What is the proposed function for H2A.X?
DNA damage signaling
What is the proposed function for H2A.Z?
transcriptional silencing
What is the proposed function for MacroH2A1 and MacroH2A2?
binds inactive X chromosome
What is the variant histone for H2B?
H2B.1
What are the four variant histones for H3?
CENP-A, H3FA3, H3.3B, H3FT
Which variant histone for H3 is the most important and what is its function?
CENP-A, defines centromere chromatin
What are the variant histones for H4?
none
, True or False: nucleosomes prefer some types of DNA sequences over others.
true
DNA is generally ________ bent around histones but has _______ bends in some places.
smoothly, sharper
The sharp bends in DNA usually occurs in which groove and at which sequences?
minor groove, pyrimidine-purine sequences such as TA and CG
The _____ groove needs to narrow during DNA bending, and this is more favorable in which
regions?
AT-rich regions
The first level of chromatin packing is the __nm fiber, which arises from nucleosome
association with DNA, and has what kind of appearance?
10, beads on a string
The 10nm fiber is folded further into the __nm fiber, a regular arrangement that does what?
30, brings nucleosomes together
