Flashcards in 8.5.16 Lecture Deck (60)
Where is DNA found?
The nucleus of eukaryotic cells
The levels of ___ organization vary throughout the cell cycle.
Describe the organization of chromosomes during interphase.
During interphase, chromosomes are found in the nucleus, surrounded by a nuclear membrane, and they are somewhat less organized. In other words, the chromatin is in a relatively extended form.
Describe the organization of chromosomes during mitosis.
During mitosis, chromosomes are beginning to condense.
Chromosomes are most condensed during what phase of mitosis?
During interphase, ___ and ___ occur.
DNA replication and gene expression
Three types of DNA sequences are required to produce a eukaryotic chromosome that can be replicated and then segregated in mitosis. What are they?
1. Centromere: used to help pull the daughter chromatids to different daughter cells
2. Origins of replication: start of replication in the S phase
3. Telomere: found at the ends of linear chromosomes, protect DNA from being recognized as broken.
Do bacterial cells have telomeres? If not, why not?
No - they are circular.
Describe the chromosome at metaphase.
The sister chromatids are attached and each contains one of two identical sister DNA molecules generated by DNA replication. It is in its most highly condensed form.
Both centromeres and telomeres are packaged into ___, a very highly compacted form of DNA. Other regions can be in ___ or ___.
Heterochromatin; heterochromatin; euchromatin
Visualizing chromosomes helps achieve two primary goals. What are they?
1. Determine chromosomal abnormalities associated with particular diseases.
2. Determine chromosomal biology - for example, determine that chromosomes localize to subnuclear domains, even in interphase cells.
Giemsa-stained early mitotic chromosomes exhibit what phenomenon?
Characteristic banding pattern that helps distinguish the various chromosomes.
What is a karyotype?
The arrangement of the full chromosome set in numerical order
More recently, each chromosome can be visualized as a different color in ___.
Chromosome painting (spectral karyotyping)
In interphase cells, each of the chromosomes is localized to a different ___.
What is chromatin?
DNA bound to histone proteins and DNA bound to non-histone proteins.
In total, a chromosome is about ___% DNA and ___% protein by mass.
Compare the arrangement of genes in the genome of humans and the genome of yeast S. cerevisiae.
Yeast DNA is primarily made up of genes that code for proteins; there are a few repetitive sequences. Human DNA has a more repeat sequences that do not code for proteins than genes that do code for protein.
One gene may be composed of ___, ___, and ___.
Exons (code for proteins), Introns (do not code for proteins, are spliced out), Regulatory sequences (promoter elements)
A small amount of human DNA actually codes for proteins or functional RNA. Over ___ consist of repetitive sequences. The remainder are introns or regulatory sequences.
About half of human DNA involve ___ sequences. The other half involve ___ sequences.
The unique sequences of the human genome include ___ (introns, protein-coding regions) and non-repetitive DNA that is neither in introns nor codons.
The repeated sequences of the human genome include simple sequence repeats, segmental duplications, and ___. Describe these.
Transposons; remnants of jumping genes, which can move from one location to another within a chromosome via different mechanisms.
____ proteins have a fundamental role in packaging DNA into highly condensed chromosomes.
DNA is more active in its ___ form.
Describe the levels of condensation from naked DNA to the mitotic chromosome.
First level: Beads-on-a-string chromatin (DNA wrapped around core histone proteins)
Second level: Compacted beads-on-a-string into a 30 nm fiber
Third level: 30 nm fibers are looped with proteins attached to the base
Fourth level: Further condensed
Fifth level: Entire mitotic chormosome
Each DNA molecule has been packaged into a mitotic chromosome that is ___-fold shorter than its extended length.
What is a nucleosome?
DNA wrapped around a core of histone proteins.
Nucleosomes are on average ___ nucleotide pairs apart.