Chapter 12: DNA Organization in Chromosomes Flashcards
This is the decondensed nucleoprotein structure eukaryotic chromosomes are in during interphase.
chromatin
Why do eukaryotes organize their DNA into chromatin?
The genome is huge, and this is an efficient way of packing it.
Chromatin’s structure resembles ______.
beads on a string
The “beads” in chromatin are called _____.
nucleosomes
Nucleosomes are made of _____.
histone proteins
Histone proteins are _____ charged.
positively
How many histone molecules are there per histone?
Eight.
True or false: histone proteins are highly conserved.
True.
Why does DNA stick to the histone particles?
They are positively charged, and DNA is negatively charged due to the phosphates, so they form tight ionic bonds.
How many types of histones are there?
Four.
What are the four types of histones?
H2A, H2B, H3, and H4
H2A and H2B histones are ______ rich.
slightly lysine
H3 histones are _____ rich.
arginine
H4 histones are _____ rich.
arginine
This type of histone is not part of the core particle, but is made of linker DNA and wraps around the core.
H1 protein
The nucleosome core particle is comprised of _____ base pairs.
147
This particle is made up of two tetramers and is a form of linker DNA.
Nucleosome core particle
What must the packing ratio be in order for DNA to fit in the nucleus?
500 to 1.
How many levels/orders of condensation are there in chromatin condensation?
Four.
In this level of condensation, chromatin is reduced to 1/3 of original length.
Level 1
What happens in level 1 of chromatin condensation?
The 147 base pairs wrap around the histone.
The histone with the 147 base pairs wrapped around it is called a _____.
Nucleosome
In this level of condensation, chromatin is reduced by an additional 6-fold, resulting in the chromatin being 18-fold smaller than its initial size.
Level 2
The structure formed by nucleosomes coiling and stacking in level 2 of chromatin condensation is called the _____.
solenoid
This protein is necessary for compaction into the solenoid.
H1 linkers
What shape is the solenoid?
Tubular, like a cylinder.
At this level of condensation, chromatin is at 180-fold compaction.
Level 3
At this level of compaction, the solenoids are folded into looped domains to make a chromatin fiber.
Level 3
What are chromatin fibers made of?
Looped domains of solenoids.
At this level of compaction, the chromatin fibers are packed into the metaphase chromosomes at the 500-fold level.
Level 4
When does the DNA compact into level four chromosomes?
Only when preparing for mitosis or meiosis.
Changes in gene expression or phenotype not attributable to changes in the DNA sequence is called _____.
epigenetics
These have no secondary structure and protrude through the minor groove channels, actually touching the DNA.
Histone tails
What is the purpose of histone tails?
They provide targets for chemical modifications such as acetylation and methylation, which in turn loosens DNA’s bond with the histone and allows proteins to come in and work on the DNA.
How do proteins and enzymes get in the tightly packed DNA for protein remodeling and changes in gene expression?
Histone tails act as targets for methyl or acetyl groups. These remove the positive charge from the histones, loosening the ionic bond between them and the negatively charged DNA.
This neutralizes positive histone charges so that the DNA is only loosely associated with them.
Acetylation
This histone modification is characteristic of gene expression.
Acetylation
This recruits repressor proteins by acting like a little flag telling the proteins to come stick to the histones.
Methylation
This histone modification is characteristic of gene repression.
Methylation
This form of chromatin is uncoiled and active.
euchromatin
This form of chromatin is condensed and inactive.
heterochromatin
What are the two types of heterochromatin?
facultative and constitutive
This type of heterochromatin can switch to euchromatin when it becomes less tightly bound.
Facultative
This type of heterochromatin never becomes active/expressed and has tandem repeats.
Constitutive
What is the function of constitutive heterochromatin?
Structural and functional support
What are the two different types of human repetitive sequences?
Tandem repeats and interspersed repeats
This type of repetitive sequence is when the same sequence is repeated over and over again.
tandem repeats
This type of repetitive sequence is when the same sequence pops up here and there.
interspersed repeats
True or false: Over half of the DNA in the human body never gets expressed.
True
True or false: methylation is always good in DNA.
False
The position of a gene or group of genes relative to all other genetic material being affect their expression is called a _____.
position affect
Staining patterns where only the centromeric region takes up stain is called _____.
C-banding
Staining patterns where different regions along the length of the chromosome take up stain is called _____.
G-banding
This region of the centromere supports the function of chromosomal segregation.
CEN region
Telomeric DNA sequences protect the stability and integrity of the chromosome because of _____.
tandem repeats
This component of the telomere contributes to its heterochromatic nature by facilitating methylation of the histone H3K9.
TERRA
This type of repetitive DNA can potentially move to different parts of the genome.
Transposable sequences
These are short transposable sequences.
Short interspersed elements (SINEs)
These are longer transposable sequences.
Long interspersed elements (LINEs)
Genes that may resemble the original gene but are not transcribed due to significant mutational alteration are called _____.
pseudogenes
