Biochemistry L07 Online - Mitosis and Meiosis Flashcards Preview

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Flashcards in Biochemistry L07 Online - Mitosis and Meiosis Deck (21):

What is a centrosome?

Main place where microtubules get organized, regulates cell division cycle. It’s a pair of centrioles at right angles to each other. Only have one per cell until cell prepares to divide.


What are centrioles?

Small set of microtubules arranged in a specific way. Two at right angles are a centrosome.


What is a centromere?

Middle bit that links sister chromatids. Kinetochore is a part of the centromere where spindles attach during mitosis.


Which protein keeps sister chromatids together until division?



What is a kinetochore?

Part of centromere where spindles attach


What is a telomere and what is its function?

The ends of chromosomes containing repeated DNA sequences. Each chromosome has 2, one at each end. Protects from deterioration or fusion.


What is a chromosome made out of?

1 unit of DNA + Histone H1 + 8 Histones.

H1 holds 8 Histones and DNA together.

Nucleosome = 1 unit of DNA + 8 Histones


What is chromatin?

Chromatin is the resulting DNA-protein complex thread (not condensed)


What is a chromatid?

When a chromosome duplicates itself and has two parts, then each copy is called a chromatid but together are still a chromosome. When cell divides, they will go their separate ways and will each be a chromosome.


What is the difference between Heterochromatin and Euchromatin?

Heterochromatin is tightly packed DNA which is inaccessible and therefore not transcribed.

Euchromatin is more of an open configuration where DNA is more accessible and is hence more actively transcribed.


What does chiasma mean?

This is where two homologs connect during meiosis for genetic cross-over.


What are the subunits that make up spindle microtubules?



What is Synapsis?

Synapsis (also called syndesis) is the pairing of two homologous chromosomes that occurs during meiosis. It allows matching-up of homologous pairs prior to their segregation, and possible chromosomal crossover between them. Synapsis takes place during prophase I of meiosis.


What is a tetrad?

Tetrads, present only in Meiosis, is a composition of Four chromatids that are formed after the S1 block during prophase 1. Each tetrads holds two chromosomes, with two chromtaids on each chromosome. during Metaphase 1 the tetrads line up the middle of the cell and servce as a place for crossing over to occur.


What are the phases in Mitosis?

1. Inerphase
- G0 - cell exits cell cycle and enters non-dividing state where
- G1 - First Gap Phase
- S - Synthesis Phase
- G2 - Second Gap Phase

2. Mitotic Phase
- Prophase
- Prometaphase
- Metaphase
- Anaphase
- Telophase

3. Cytokinesis - cytoplasmic division


What are the key characteristics of a cell in interphase during mitosis?

- nuclear envelope present
- individual chromosomes cannot be distinguished
- DNA in decondensed state – chromatin


What are the key characteristics of a cell in mitotic phase during mitosis?

- nuclear envelope absent
- Individual replicated chromosomes are highly condensed


What are the main differences between mitosis daughter cells and meiosis daughter cells?

Mitosis daughter cells are diploid (2n) and daughter cells have the same genotype, whereas meiosis daughter cells (gametes) are haploid (n) and have half the chromosomes of their parent cell.


What is Meiosis I and what are the phases?

Meiosis I is reduction division - centromere number is reduced by half - 2n – n. Similar to mitosis except instead of separating sister chromotids, homologous pairs couple and cross over, and whole chromosomes are divided but remain with their sister chromatids (which are separated in Meiosis II).

1. Middle Prophase I
2. Late Prophase I
3. Metaphase I
4. Anaphase I
5. Telophase I


What is Meiosis II and what are the phases?

Meiosis II is equational division - centromere number remains equal – n-n. More like mitosis with separation of sister chromatids.

1. Prophase II
2. Metaphase II
3. Anaphase II
4. Telophase II


What is the result of crossing over?

Results in exchange of genetic material between members of each homologous pair of chromosomes. Allows new combination of genetic material. Occurs at the tetrad state. Leads to genetic variation (Meiosis I only, not Meiosis II).