Mitotic Chromosome Structure Flashcards
Where is hereditary information found in eukaryotic cells? What form does hereditary information take?
hereditary information in the form of genes is found along many linear DNA molecules
What is a chromosome?
an individual DNA molecule + associated histone + non-histone proteins
What allows a chromosome to have 2 arms?
a centromere
What is a centromere?
a point on a chromosome where the spindle fibers attach during mitosis and meiosis
What is chromatin?
the complex of DNA and histone proteins that make up a chromosome
T or F: the appearance and arrangement of the chromatin in the nucleus is the same at all stages of the cell cycle
FALSE! it differs at different stages of the cycle
What is the most dominant component of an interphase nucleus?
chromatin - it makes up 80-90% of the nuclear mass
How does the chromatin appear in the interphase nucleus?
fine, intertwined fibers or threads
What are the two classifications of interphase nuclear chromatin?
euchromatin
heterochromatin
How is the interphase nuclear chromatin divided into the two classifications?
based on its appearance and possible activity level
Describe the structure of euchromatin
the interphase nuclear chromatin that appears as loosely packed threads
How does euchromatin appear under an electron microscope?
it is less densely stained and appears as if the threads are dispersed
What is the transcription activity level of euchromatin?
transcriptionally active
Describe the structure of heterochromatin
densely packed mass around the periphery of the nucleus
How does heterochromatin appear under an electron microscope?
densely stained
What is the transcription activity level of heterochromatin?
inactive
When are chromosomes at their most condensed and compact state?
during metaphase of mitosis or meiosis
When can chromosomes be visualized with a light microscope?
during metaphase
What are the stages of the cell cycle
G1 S G2 Mitosis or meiosis C
What occurs during the G1 phase of the cell cycle?
gap phase
growth or regular cell function - anything that isn’t cell division
What occurs during the S phase of the cell cycle?
DNA synthesis
duplication of DNA
Describe the structure of chromosomes at metaphase of mitosis
two identical sister chromatids attached at their centromeres
How do the centromeres appear at metaphase of mitosis?
narrowed or constricted areas along the length of the chromosome
What is another term for centromeres?
primary constriction
How do researchers see and count the number of chromosomes in a single cell?
by preparing a slide with cells held at metaphase and exposing them to a hypotonic solution to burst the cells and release the chromosomes
What is karyotyping?
determining the chromosomal complement of cells by staining and taking a picture of released chromosomes from a cell and pairing them with their homologue and arranging them according to size and structure
How are the characteristic morphology of metaphase chromosomes determined?
by their size and location of centromere
What are the 4 classifications of chromosomes?
metacentric
submetacentric
acrocentric
telocentric
Describe metacentric chromosomes
chromosomes with a centromere that is equidistant between the 2 arms and the 2 arms are of equal length
Describe submetacentric chromosomes
chromosomes with an off centered centromere (slightly different arm lengths)
Describe acrocentric chromosomes
chromosomes with a centromere that is closer to one end than to the other (very different arm lengths)
Describe telocentric chromosomes
chromosomes with the centromere AT the end of the chromosome
Which 2 types of chromosomes have 2 arms of unequal lengths?
submetacentric
acrocentric
How are two unequal arms of submetacentric or acrocentric chromosomes classified?
the shorter arm = the p arm
the longer arm = the q arm
Which arm is the p arm?
the shorter arm
can remember as p for ‘petite’ arm
Which arm is the q arm?
the longer arm
can remember that p = petite and q comes after p
the movement of sister chromatids of each chromosome pair toward the poles of cell depends on what?
the development of a kinetochore on each centromere
Where are kinetochores located?
on centromeres of chromosomes
Where do sister chromatids separate from?
their centromeres
Describe a kinetochore
a large multiprotein complex that appears in the EM as a plate-like trilaminar structure
How does a kinetochore appear in an EM?
as a plate-like trilaminar structure
How many centromeres are there in a chromosome consisting of 2 sister chromatids?
2
How many kinetochores are there in a chromosome consisting of 2 sister chromatids?
2
Where do microtubule spindle fibers attach on a sister chromatid? What stages of mitosis does this occur?
to its kinetochore on its centromere during prophase and metaphase
What does the kinetochore do during anaphase?
it climbs the microtubule while digesting it along the way and this pulls the sister chromatid along with it
T or F: the kinetochore is providing the force that pulls sister chromatids apart and towards the poles, NOT the spindle fiber microtubules
true
What is another term for the secondary constriction?
Nuclear Organizer Region (NOR)
Describe the NOR/secondary constriction
a large cluster of repeating rRNA genes that marks the site of nucleolar formation during interphase
What does secondary constriction/NOR do to the appearance of a metaphase chromosome?
the NOR can be so narrow that it makes the distal portion of an arm appear to be completely detached from the rest of the chromosome
What is a satellite?
the distal portion of a metaphase chromosome that appears to be separated from the chromosome because of the NOR/secondary constriction
T or F: every species has the same number of NORs/secondary constrictions on their chromosomes
false! it varies from species to species
How many NORs do human chromosomes have?
5 pairs
Which human chromosomes have NORs?
13, 14, 15, 21, 22
What are telomeres?
the ends of linear chromosomes
What are telomeres made of?
long stretches of repetitive nucleotide sequences covered with protein complexes
What are the 3 major function of telomeres?
- to protect the chromosome from fusing with other chromosomes
- to protect transcriptionally valuable DNA from being lost
- preventing uncontrolled cell division (cancer) due to telomere loss initiating apoptosis
What happens to telomeres with every round of cell division?
they shorten by a few hundred base pairs
How is the total number of cell division limited? Why?
by the length of telomeres because they shorten with every round of cell division
How do telomeres prevent uncontrolled cell division?
the loss of telomeres (after rounds of cell division) initiates apoptosis
