Biochemistry L07 Online - Mitosis and Meiosis

Question 1

What is a centrosome?

Answer 1

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.

Question 2

What are centrioles?

Answer 2

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

Question 3

What is a centromere?

Answer 3

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

Question 4

Which protein keeps sister chromatids together until division?

Answer 4

Cohesin

Question 5

What is a kinetochore?

Answer 5

Part of centromere where spindles attach

Question 6

What is a telomere and what is its function?

Answer 6

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

Question 7

What is a chromosome made out of?

Answer 7

1 unit of DNA + Histone H1 + 8 Histones.

H1 holds 8 Histones and DNA together.

Nucleosome = 1 unit of DNA + 8 Histones

Question 8

What is chromatin?

Answer 8

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

Question 9

What is a chromatid?

Answer 9

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.

Question 10

What is the difference between Heterochromatin and Euchromatin?

Answer 10

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.

Question 11

What does chiasma mean?

Answer 11

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

Question 12

What are the subunits that make up spindle microtubules?

Answer 12

Tubulin

Question 13

What is Synapsis?

Answer 13

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.

Question 14

What is a tetrad?

Answer 14

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.

Question 15

What are the phases in Mitosis?

Answer 15

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

Question 16

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

Answer 16

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

Question 17

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

Answer 17

• nuclear envelope absent

- Individual replicated chromosomes are highly condensed

Question 18

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

Answer 18

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.

Question 19

What is Meiosis I and what are the phases?

Answer 19

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

Question 20

What is Meiosis II and what are the phases?

Answer 20

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

Question 21

What is the result of crossing over?

Answer 21

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).