Cell Division, enzymes Flashcards
Duplication of centrosomes takes place in
G2 phase
cell cycle-controlling checkpoints are available at
G1 , G2 and M phases
The most cells of the human body are actually in which phase
Go phase. e.g. nerve cells and muscle cells.
M phase includes
Mitosis and Cytokinesis
Prophase
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.
Spindle includes
Aster, spindle microtubules and centrosome
Prometaphase
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.
Metaphase
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.
Anaphase
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.
Telophase
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.
In animal cells cytokinesis forms
Clevage furrow
In plant cells cytokinesis forms
Cell plate
Significances of mitosis
- Maintains the genetic stability
- Growth and development
- Cell repair, replacement and regeneration
- Asexual reproduction
Meiosis gives rise to
Four haploid daughter nuclei from a diploid mother nucleus.
Difference between meiosis 1 and meiosis 2
Meiosis 1 is a reduction division while meiosis 2 is similar to mitosis.
Homologous chromosomes
Chromosomes having genes controlling the same characteristic.
At the end of meiosis 1
2 genetically non-identical haploid daughter nuclei are formed.
Meiosis II usually takes place in which direction
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
Centrosomes or centrioles are not available in
Centrosomes or centrioles are not available in plant cells. However, spindle is formed
during cell division from accumulated microtubule complex
Significance of meiosis
• 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.
Benign and malignant tumors
• 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.
Metastasis
This spread of cancer cells to locations distant from their original site through blood and lymph is called metastasis.
The plant cell division is controlled by
maintaining a proper balance between plant growth regulators such as auxins and cytokinins.
Galls
are the bumbs and growths that develop on different parts of plants after being invaded by some very unique organisms.
Factors affecting the rate of enzymatic reactions
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
- Inhibitors
enzymes have optimum temperature around
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
In most enzymes optimum pH range is
6-8,
Pepsin works best at pH
2
optimum pH for Trypsin
8
Enzyme inhibitors
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.
In many cases, the molecules that naturally regulate enzyme activity in a cell behave like
reversible non-competitive inhibitors
cooperativity
Binding of one substrate molecule can stimulate binding or activity at other active site. Thereby increase the catalytic activity.
Feedback inhibition
In feedback inhibition, a metabolic pathway is stopped by the inhibitory binding of its end product of a process to an enzyme.
Change to ∆G of reaction by enzymes
∆G is unaffected by enzymes
Width and length of DNA of a typical human chromosome
2 nm wide
1.8 m long
Oncogene
The particular term for a mutated gene that causes cancer is an oncogene
Shortest phase of mitosis
The shortest phase of mitosis is anaphase
