Cell Division, enzymes

Question 1

Duplication of centrosomes takes place in

Answer 1

G2 phase

Question 2

cell cycle-controlling checkpoints are available at

Answer 2

G1 , G2 and M phases

Question 3

The most cells of the human body are actually in which phase

Answer 3

Go phase. e.g. nerve cells and muscle cells.

Question 4

M phase includes

Answer 4

Mitosis and Cytokinesis

Question 5

Prophase

Answer 5

Chromatin fibers condenses by shortening and thickning forming chromosomes as a result chromosomes get visible under the light microscope.

Nucleolus get dissappeard and chromosomes appear as 2 sister chromatids attached at the centromere. Chomsomal arms of sister chromatids gets attached by special protein known as cohesin.

Formation of mitotic spindle begins which includes aster, centrosome and spindle microtubules. Centrosomes moves towards the opposite poles due to lengthening of microtubules.

Question 6

Spindle includes

Answer 6

Aster, spindle microtubules and centrosome

Question 7

Prometaphase

Answer 7

Nuclear envelpoe fragments. Chromosomes get even more condensed.

A special protein known as kinetochore attaches sister chromatids of each chromosome at centromere. Some of the microtubules attaches kinetochore and moves the chromosome back and forth, microtubules which are not attached to kinetochore interact with those chromosomes from the opppsite pole.

Question 8

Metaphase

Answer 8

Centrosomes reach the opposite pole. Chromosomes have arrived to a place called the metaphase plate which is located in equal distance from each pole. Centromeres of each chromosome are located in the metaphase plate.
At the end of this phase each chromosome of the cell get attached to the kinetochore microtubules and gets arranged at the metaphase plate.

Question 9

Anaphase

Answer 9

Sister chromatids are separated at the centromere. Microtubules attached to kinetochore gets shorten and pulls the sister chromatids towards opposite poles.

Cell elongates due to the lengthening of non kinetochore microtubules.

By the end of anaphase complete and equal set of chromosomes are found at each pole.

Question 10

Telophase

Answer 10

Nuclear envelope reforms at each set of chromosomes found at opposite poles. Nucleolus reappears, spindle microtubules gets depolymerized. Chromosomes unwind and becomes less condensed to form chromatin.

At the the end of telophase two genetically identical daughter nuclei are found within the same cell at 2 opposite poles.

Question 11

In animal cells cytokinesis forms

Answer 11

Clevage furrow

Question 12

In plant cells cytokinesis forms

Answer 12

Cell plate

Question 13

Significances of mitosis

Answer 13

1. Maintains the genetic stability
2. Growth and development
3. Cell repair, replacement and regeneration
4. Asexual reproduction

Question 14

Meiosis gives rise to

Answer 14

Four haploid daughter nuclei from a diploid mother nucleus.

Question 15

Difference between meiosis 1 and meiosis 2

Answer 15

Meiosis 1 is a reduction division while meiosis 2 is similar to mitosis.

Question 16

Homologous chromosomes

Answer 16

Chromosomes having genes controlling the same characteristic.

Question 17

At the end of meiosis 1

Answer 17

2 genetically non-identical haploid daughter nuclei are formed.

Question 18

Meiosis II usually takes place in which direction

Answer 18

Meiosis II usually takes place in the perpendicular direction of Meiosis I. Therefore,
metaphase plate of meiosis II is perpendicular to the metaphase plate of meiosis I

Question 19

Centrosomes or centrioles are not available in

Answer 19

Centrosomes or centrioles are not available in plant cells. However, spindle is formed
during cell division from accumulated microtubule complex

Question 20

Significance of meiosis

Answer 20

• Maintains the constant number of chromosomes through generations in sexually
reproducing species.
• Produces new genetic variations leading to evolution.
• Genetic variation occurs due to crossing over ,recombination and independent assortment.

Question 21

Benign and malignant tumors

Answer 21

• If the abnormal cells remain at the original site, the lump is called benign tumor. Most benign tumors do not cause serious problems and can be completely
removed by a surgery.

• A malignant tumor becomes invasive and attack one or more organs. An individual with a malignant tumor is said to have a cancer.

Question 22

Metastasis

Answer 22

This spread of cancer cells to locations distant from their original site through blood and lymph is called metastasis.

Question 23

The plant cell division is controlled by

Answer 23

maintaining a proper balance between plant growth regulators such as auxins and cytokinins.

Question 24

Galls

Answer 24

are the bumbs and growths that develop on different parts of plants after being invaded by some very unique organisms.

Question 25

Factors affecting the rate of enzymatic reactions

Answer 25

1. Temperature
2. pH
3. Substrate concentration
4. Enzyme concentration
5. Inhibitors

Question 26

enzymes have optimum temperature around

Answer 26

most of the human enzymes have optimum temperature around the body temperature
(35˚C-40˚C). Optimum temperature of bacteria in hot springs is about 70˚C

Question 27

In most enzymes optimum pH range is

Answer 27

6-8,

Question 28

Pepsin works best at pH

Answer 28

2

Question 29

optimum pH for Trypsin

Answer 29

8

Question 30

Enzyme inhibitors

Answer 30

Certain molecules or ions selectively bind permanently or temporarily to the enzyme molecules and prevent them from forming enzyme-substrate complex. These substances are called inhibitors.

Question 31

In many cases, the molecules that naturally regulate enzyme activity in a cell behave like

Answer 31

reversible non-competitive inhibitors

Question 32

cooperativity

Answer 32

Binding of one substrate molecule can stimulate binding or activity at other active site. Thereby increase the catalytic activity.

Question 33

Feedback inhibition

Answer 33

In feedback inhibition, a metabolic pathway is stopped by the inhibitory binding of its end product of a process to an enzyme.

Question 34

Change to ∆G of reaction by enzymes

Answer 34

∆G is unaffected by enzymes

Question 35

Width and length of DNA of a typical human chromosome

Answer 35

2 nm wide
1.8 m long

Question 36

Oncogene

Answer 36

The particular term for a mutated gene that causes cancer is an oncogene

Question 37

Shortest phase of mitosis

Answer 37

The shortest phase of mitosis is anaphase