Lesson 5 Flashcards
Chromosomes
What microscope is used to visualize detailed structure of a chromosome
Electron microscope
When a cell is dividing, chromosomes get _____ and can be seen in what microscope?
shorter and fatter, light microscope
packaged form of DNA
Chromosomes
In the cell nucleus, DNA exists in what form
non-condensed
When does DNA condense into chromosomes
During cell replication
Carries a code that instructs the cell about which kind of proteins it should make
DNA molecule
What do you call the end points of each chromosome?
Telomeres
The upper arm of a chromosome
p arm
The lower arm of a chromosome
q arm
The region where two chromatids meets in a chromosome
Centromere
Half a duplicated chromosome
Chromatid
Responsible for a particular characteristic is always on the same relative position on the chromosome
Gene
May be in different form of the gene on each chromosome when they are in pairs
Alleles
In the 46 chromosomes, how many pairs are autosomal?
22 pairs
In the 46 chromosomes, how many pairs are sex chromosomes?
1 (the 23rd)
It is the pair that determines whether a fetus becomes male or female
Sex chromosomes
Chromosomes where the genes on both pairs are capable of being fully expressed
Nonsex/ autosomal
The absence of one X chromosome
Turner’s syndrome
One of the two X chromosomes are turned off
X inactivation
Abnormal or Normal: triple X syndrome
Often normal
Abnormal or Normal: XYY syndrome
abnormal
Tiny structures inside cell that synthesize molecules used for energy
Mitochondria
Each mitochondrion contains its own ______
Circular chromosome
Mitochondrial chromosomes also contain
DNA
Mitochondrial DNA usually comes from
Mother
The three minimal requirements for proper maintenance of chromosomes in cells
- centromere
- telomere
- origin of replication
Basis for segregation and the region of the chromosome where kinetochore attaches
Centromere function
Protein machine that mediates the alignment of duplicated chromosomes, then splitting into copies.
Kinetochore
Cells with the wrong number of chromosomes are termed
Aneuploid
Centromere position
center or towards the end
Centromere structure
condensed heterochromatin structure
Helps mediate attachment of the kinetochore to centromeres
histone H3 variant CENP-A
Telomeres short repeated sequence
TTAGGG
Adds new DNA to the 3’ end of a DNA chain using an intrinsic RNA component of the enzyme to act as the template strand
Telomerase
Discovered by Griffith and de Lange in 1999 that essentially hides the chromosome end, and means the ends of the chromosome is resistant to degradation or “repair
Tloop
Cells that have limited proliferative capacity
Cells with short telomeres
Cells that have much greater proliferative capacity
Long telomeres
A significant component of aging
Cellular senescence
The linear length of the human genome is about _____
two meters
The basic unit of eukaryotic chromatin structure
Nucleosome
A nucleosome consists of
Core octamer: (two copies each)
- H2A
- H2B
- H3
- H4
All histones are compact globular proteins with an extended tail rich in basic amino acids that are what charge?
positive charges
The positive charge of the histone interacts with what?
The negative charge of the DNA phosphate backbone
Each nucleosome consists how many histone proteins
8
How many times does DNA wrap in each nucleosome
2 times
Varies from gene to gene over the life of the cell
Higher order organization
Mediates the packing of adjacent nucleosomes
histone H1 (linker histone)
Popular model of DNA packaging
solenoid and zigzag
Loosely packed and transcriptionally active, allowing genes to be expressed.
Euchromatin
Highly condensed structure found in areas of the chromosome that aren’t transcriptionally active
Heterochromatin (silent regions)
The ability to adjust nucleosome positioning in chromatin is termed
Chromatin remodeling
Important in assembly of nucleosomes de novo in recently replicated DNA
Remodeling complexes
Remodeling complexes typically use energy from _____ to perform remodeling
ATP hydrolysis
Modifications that alter, remodel, loosening association of DNA with nucleosomes in a chromatin state
Covalent modifications of histone
What do covalent modifications do?
neutralize positive charges in histone tails so that the negatively charged DNA backbone no linger sticks to nucleosomes quite tightly
Histone modifying enzymes
- histone acetylases and deacetylases
- histone methylases
- histone kinases
The beads on a string; made up of DNA wrapped around histone proteins
Chromatin
Critical events both for assembly of new nucleosomes after DNA replication
Acetylation and methylation
Important for chromosome condensation prior to cell division
Phosphorylation
Nucleosome regions where normal H2A is substituted with the H2A variant H2AZ
Stably heterochromatic
What mediates the formation of the loop, and protection of the branch point?
TRF-2 protein (Telomere Repeat binding Factor -2)
