Flashcards in Lab 7 - Chromosomes Deck (38)
Why are histone's positively charged?
Histones have many amino acids that are basic; very positively charged and therefore becomes overall positively charged itself.
What role does the histone being positively charged play in chromosome packing?
Because the histone is positively charged, it strongly attracts the negatively charged DNA molecule and DNA wraps itself tightly around the histone creating a nucleosome; the first level of DNA packing.
What is the purpose of the histone core?
Promotes and guides DNA coiling
What is the purpose of H1?
Act to stabilize the structure
What is a Solenoid?
A cylindrical fibre that is made up of nucleosome units
What are the 5 levels of chromosome packing?
1. Bead-on-string: A double loop of DNA wrapped around a histone core of 8 histones; nucleosome
2. Solenoid: Made up of 6 nucleosomes, H1s, and DNA spacers
3. Chromatin fibre: A cylindrical fibre made up of solenoids
4. Chromatid: coiling of chromatin fibre
5. Chromosome: supercoiling of chromatid
What is Heterochromatin?
Highly condensed portions of the chromatin; DNA in these sections are expressed less or never
What is Euchromatin?
Sections of chromatin that is less condensed than heterochromatin; only condensed during cell division which means it's highly expressed
What is the staining like for heterochromatin vs euchromatin?
Heterochromatin are highly condensed so they hold onto the die more >> darkly stained
Euchromatic are not condensed so they do not hold onto the die as well >> lightly stained
Where is the centromere located on a chromosome that's "Metacentric"?
In the middle
Where is the centromere located on a chromosome known as "submetacentric"?
Somewhere between the middle and the end
Where is the centromere located on a chromosome that is known is "Acrocentric?"
Close to the end
Where is the centromere located on a chromosome that is known as "Telocentric"?
At the end
What is a telomere?
Specialized repeating segment of DNA that stabilizes the end of the chromosome and prevents other chromosome fragments from fusing to it, and protects the chromosome from enzymatic degradation.
What are the 3 main things that happen during prophase of mitosis and prophase II of meiosis?
- Nucleolus and nuclear membrane breakdown
- Chromosomes condense
- Spindle apparatus begins to form
What is the main thing that happens during metaphase during mitosis and metaphase II during meiosis and how does this differ from metaphase I?
Chromosomes line up at the metaplate. This is is different in metaphase I because it's homologous chromosomes that line up rather than sister chromatids as in in metaphase and metaphase II.
What is the key thing that happens during Anaphase in mitosis and Anaphase I? How does Anaphase II differ from those 2 phases?
Sister chromatids are pulled to opposite poles by spindle fibres. The difference with Anaphase I is that it's homologous pairs that split apart, not sister chromatids
What are the 2 key things that happen during Telophase and Cytokinesis?
- Nuclear membrane and nucleolus reforms
- Cleavage furrow forms or cell plate begins to form
What is the purpose of Indole-3-Acetic Acid?
Acts as a growth hormone that encourages cell division in root tips
What is the purpose of adding root tips to HCl and then incubating?
Fixation; kills the tissue without distorting the nuclear material.
Hydrolyzes the root tip; so that it can stain better, and softens the root tip so it can be properly squashed.
What stain is used on the root tip?
What in the stain; aceto-orcein, causes cytoplasm to swell, and combined with the pressure of thumb, cause the chromosome to spread apart?
Do all the cells appear to begin and undergo mitosis at the same time in the root tip?
No, they are in many different phases. This is because the amount of time spent in each phase can vary from cell to cell
What area of the chromosome squash had a higher concentration of mitotic figures?
In the apical meristem, near the bottom of the root, since that's where the most mitotic activity occurs
What are chromosome bands?
Patterns that appear after staining that are specific to each type of chromosome
What is Giemsa?
A stain that is used to reveal chromosome bands; specifically called G-bands
What 3 factors influence banding patterns?
- proteins that are present (interact with dye)
- relative proportions of AT and GC pairs
- repetitiveness of codons in DNA sequence
What is a Karyotype?
The particular array of chromosomes that an individual has
Explain the 7 steps of how a Karyotype is prepared?
1. Add blood to a vial of culture medium w/ stimulator for mitosis
2. Centrifuge and discard supernatant
3. Add saline, fixative and resuspend pellet
4. Prepare and stain cells for microscopy (Geimsa - 짐사)
5. Observe under microscope
6. Photograph and enlarge chromosomes
7. Cutout and arrange