Category: Biology Second Paper

Intermediate filaments are intermediate filaments between microtubules and microfilaments in cells. Their diameter is 10 nanometers. It is made of protein. Cells have four types of intermediate filaments. Keratin, vimentin, lamin and neurofilaments.

Function/importance of intermediate filament

Gives shape to cells. Provides cell strength. Helps keep other cell fibers in place.

Microfilaments are fine contractile fibers located in the cytoplasm of cells that aid in movement. They are also called actin filaments. It was first observed by scientist Paleviz in 1974.

Microfilaments are narrow, long, contractile and twisted biaxial. It is located under the cell membrane like a ribbon. Its diameter is 30-60Å. It is composed of actin protein and myosin protein.

Function/importance of microfilaments

1. Microfilaments provide cell shape and mechanical strength.
2. Microfilaments cause cellular movement.
3. Changes the position of the cell organelle.
4. Connects between cell membrane proteins and cytoplasmic proteins.
5. It causes cytokinesis (cell division).
6. Helps in opposite pole movement of chromosomes.
7. It regulates phagocytosis and pinocytosis.

1. Cyclin-Cdk complex: Inside the cell, the cyclin-cdk complex regulates the changes in various stages of the cell cycle.
2. Cyclin-Cdk-MPF complex: MPF binds to the cyclin-cdk complex of the dividing cell to initiate the cell cycle.
3. P⁵³ protein: When DNA is damaged for some reason, P⁵³ protein stops the cell cycle. When DNA is extensively damaged, the P⁵³ protein induces cell death by apoptosis.
4. P²⁷ protein: P²⁷ protein binds to the cyclin-cdk complex and prevents cells from entering the confluent state. High levels of P²⁷ protein in cells cause breast cancer in women.
5. Cyclin: The regulator of cell cycle is cyclin protein. Timothy Hunt (1982) discovered cyclin proteins. For this, Timothy Hunt, Lee Hartwell and Paul Nurse were awarded the Nobel Prize in 2001. There are four types of cyclins in human cells.

(i) Cyclin-D: Cyclin-D transports cells from G1 to S phase and from S phase to G₂ phase.

(ii) Cyclin-E: Cyclin-E prepares the cell for DNA replication in S phase.

(iii) Cyclin-A: Cyclin-A activates and accelerates DNA replication in the S phase of the cell.

(iv) Cyclin-B: Cyclin-B performs spindle fibers and other essential functions for mitosis.

The tiny, granular, self-reproducing and enzyme-rich organelles surrounded by a membrane are called peroxisomes. They are also called microsomes. Its diameter is 0.2-17 millimicrons. It contains enzymes in crystal and granule form. At its center, fine-grained material accumulates to form an opaque core. It is called nucleoid. Its main enzymes are catalase, D-amino acid oxidase and uric acid oxidase. It breaks down fatty acids into acetyl Co by beta-oxidation process. Organelles that carry out beta-oxidation are called glyoxysomes. Belgian psychologist Christian de Duve discovered it in 1967.

Peroxisomes are abundant in photosynthetic cells of plants, such as those in the embryo membrane, liver and kidney cells. Peroxisomes arise from rough endoplasmic reticulum.

 

Function/importance of peroxisomes

1. It breaks down fatty acids into acetyl Co by beta-oxidation process.
2. Enzymes present in it react H2 and O2 to produce toxic H2O2.
3. Catalase enzyme breaks down toxic H2O2 to produce water and oxygen.
4. Catalase enzyme uses H2O2 to oxidize alcohol, phenol, formic acid, formaldehyde etc.
5. It destroys blood toxins in human liver and kidney by causing peroxidation reaction.
6. Plant cells contain a large number of antioxidative enzymes (superoxide dismutase, NADP dehydrogenase) that catalyze important reactions.
7. It regulates the concentration of oxygen in the cells.
8. It helps in the production of NAD, DNA and RNA.
9. It turns love into water.
10. It helps in making glycine and serine in plant cells.
11. It helps carry out photosynthesis in green plants.

Interphase stage and division stage of the cell are together called cell cycle. The cycle through which cells form, grow and divide is called the cell cycle. According to scientist Lewin, the period between two periodic cell divisions is called cell cycle. According to scientist Karp, the periodic stages between the formation of two cells from one cell through cell division are called cell cycles. Growth factors (growth hormones) bind to receptor proteins on the surface of target cells (cells that will divide) to initiate the cell cycle. In 1953 scientists Howard & Pelc introduced the cell cycle. In 2001, American scientist Leland H. Hartwell discovered the master regulator of the cell cycle.

 

Cell cycle characteristics

1. It takes a certain amount of time for the cell cycle to complete. The period of the cell cycle is called the natal period.
2. The cell cycle is controlled by a genetic program.
3. The cyclin-cdk complex provides intrinsic stimulation of the cell cycle.
4. Hormones and growth factors provide extrinsic stimulation of the cell cycle.
5. When cut in any part of the body, the growth factor is produced. Stimulation of this growth factor causes the surrounding cells to divide and repair the wound.
6. White blood cells make growth factors for the body’s immune system.
7. Erythropoietin is produced in the kidneys. Erythropoietin helps the bone marrow produce red blood cells.
8. The P⁵³ protein stops the cell cycle when the cell’s DNA is severely damaged.
9. P⁵³ protein causes cell death by apoptosis process when cell DNA is severely damaged.
10. Abnormal or uncontrolled cell cycle disrupts the growth and development of the organism. Can even cause cancer.

 

Cell cycle time

It takes 10 minutes to 24 hours for the cell cycle to complete. The cell cycle of the human body is completed in 20-24 hours. In yeast cells it takes 90 minutes. Broad bean takes 18-19 hours.

 Steps of cell cycle

The cell cycle is completed in two stages. Interphase state and division state.

Interphase state

The period between two consecutive cell divisions is called interphase. This state is called rest state. The nucleus in this state is called the metabolic nucleus.

Characterization of the interphase state

(i) CDK (Cyclin Dependent Kinase) compounds provide external stimulation in interphase state.

(ii) Various hormones and growth factors provide internal stimulation during interphase.

(iii) Various metabolic activities continue in the cell during this stage. As the nucleus increases in size and many reactions take place, it is called metabolic nucleus.

(iv) DNA, RNA and protein synthesis takes place in this stage. Hence it is called synthesis stage.

(v) Chromosomes are arranged as chromatin.

(vi) In this state, the cells have the necessary energy reserves.

(vii) Increase in cell volume is greatest in this condition.

(viii) Duplication of the DNA of the cell takes place, i.e. the monad turns into a dyad.

(ix) Centrosomes of animal cells divide.

(x) This phase takes 90-95% time.

 

3 subphases of interphase

1. G₁ Phase: Metabolically active cell growth phase is called pause-1 phase. This state is called antiphase. A cell that will no longer divide remains locked in the G₁ subphase for a week or a year or forever. The characteristics of Birama-1 dasha are-

(i) Cell cycle starts in this state.

(ii) Whether a cell will participate in division depends on this stage.

(iii) Cyclin proteins, gabular proteins, fibrous proteins and RNA are produced in this subphase.

(iv) Cyclin protein binds to CDK and accelerates and regulates the process. CDK regulates the phosphorylation process.

(v) Enzymes are produced to make DNA and proteins.

(vi) Cytoplasm and nucleus of the cell increases in size.

(vii) Synthesis of various nucleotides and amino acids takes place.

(viii) In this state, the cells double in number.

(ix) Sub-phase takes 30-40% time.

 

2. Synthesis phase: The next phase after break-1 is called Synthesis phase or S phase or Synthesis phase. It is also called DNA replication. The characteristics of synthesis state are-

(i) Histone proteins and DNA are synthesized in subphase A.

(ii) The amount of DNA increases and doubles.

(iii) Physical elongation of chromosomes occurs and each chromosome divides to form two chromatids.

(iv) Subunits of kinetochore are formed at this stage.

(v) Division of centrosome occurs in animal cells.

(vi) At this stage inactive proteins are synthesized.

(vii) This sub-phase takes 30-50% time. Mammals take 7 hours in this state.

 

3. G₂ Phase: The stage after synthesis phase is called phase-2. The features of phase-2 are-

(i) Cell metabolism increases in this condition.

(ii) Histone proteins, non-histone proteins, tRNA, mRNA, rRNA etc. are synthesized.

(iii) Nucleus increases in volume as various elements are prepared.

(iv) In this phase the damaged DNA molecule is repaired.

(v) Two centrosomes arise from one centrosome. Centrosomes form microtubules. Microtubules form spindle fibers.

(vi) Cells enter mitosis from G₂ phase with the help of maturation promoting factor (MPF).

(vii) Volume of nucleus and cytoplasm increases.

(viii) This sub-phase takes 10-20% time.

 

Importance of interphase state

(i) At this stage it is determined whether the cell will participate in the next division.

(ii) Energy required for cell division (ATP) is produced.

(iii) DNA replication takes place.

(iv) RNA synthesis and histone protein content increase.

(v) At this stage microtubules are formed which form centrosomes.

(vi) Centrioles are formed in animal cells in this state.

(vii) Cell division will not take place if there is no interphase state. A living organism will not form a body. As a result, new organisms will not be created.

The organelles that carry out the beta-oxidation process are called glyoxysomes. It was discovered and named by scientist R. W. Briedenback in 1967.

Glyoxysomes are found in fungi, yeast, Neurospora and oilseed cells. It is present in the lipid storage cells of the seed.

Glyoxysomes are spherical or oval or polygonal. It is a unicellular organelle. Its diameter is 0.5-1.5 µm. Their matrix is ​​granular and the core part is visible in the center. It contains various enzymes of β-oxidation and glyoxalate cycle. It contains isocitrate ligase, malate synthetase, glycolate oxidase and catalase enzymes.

Function/importance of glyoxysome

1. Glyoxysomes mainly regulate the metabolism of fats or lipids or fatty acids.
2. Seedling growth continues during seed germination.
3. It oxidizes ionic substances through the glyoxalate cycle.
4. It participates in the metabolic metabolism of amino acids.

The period between two consecutive cell divisions is called interphase. This state is called rest state. The nucleus in this state is called the metabolic nucleus.
Characterization of the interphase state
(i) CDK (Cyclin Dependent Kinase) compounds provide external stimulation in interphase state.
(ii) Various hormones and growth factors provide internal stimulation during interphase.
(iii) Various metabolic activities continue in the cell during this stage. As the nucleus increases in size and many reactions take place, it is called metabolic nucleus.
(iv) DNA, RNA and protein synthesis takes place in this stage. Hence it is called synthesis stage.
(v) Chromosomes are arranged as chromatin.
(vi) In this state, the cells have the necessary energy reserves.
(vii) Increase in cell volume is greatest in this condition.
(viii) Duplication of the DNA of the cell takes place, i.e. the monad turns into a dyad.
(ix) Centrosomes of animal cells divide.
(x) This phase takes 90-95% time.

3 subphases of interphase dasha
1. G1 Phase: Metabolically active cell growth phase is called pause-1 phase. This state is called antiphase. A cell that will no longer divide remains locked in the G1 subphase for a week or a year or forever. The characteristics of Birama-1 dasha are-
(i) Cell cycle starts in this state.
(ii) Whether a cell will participate in division depends on this stage.
(iii) Cyclin proteins, gabular proteins, fibrous proteins and RNA are produced in this subphase.
(iv) Cyclin protein binds to CDK and accelerates and regulates the process. CDK regulates the phosphorylation process.
(v) Enzymes are produced to make DNA and proteins.
(vi) Cytoplasm and nucleus of the cell increases in size.
(vii) Synthesis of various nucleotides and amino acids takes place.
(viii) In this state, the cells double in number.
(ix) Sub-phase takes 30-40% time.

2. Synthesis phase: The next phase after break-1 is called Synthesis phase or S phase or Synthesis phase. It is also called DNA replication. The characteristics of synthesis state are-
(i) Histone proteins and DNA are synthesized in subphase A.
(ii) The amount of DNA increases and doubles.
(iii) Physical elongation of chromosomes occurs and each chromosome divides to form two chromatids.
(iv) Subunits of kinetochore are formed at this stage.
(v) Division of centrosome occurs in animal cells.
(vi) At this stage inactive proteins are synthesized.
(vii) This sub-phase takes 30-50% time. Mammals take 7 hours in this state.

3. G2 Phase: The stage after synthesis phase is called pause-2. The features of Biram-2 are-
(i) Cell metabolism increases in this condition.
(ii) Histone proteins, non-histone proteins, tRNA, mRNA, rRNA etc. are synthesized.
(iii) Nucleus increases in volume as various elements are prepared.
(iv) In this phase the damaged DNA molecule is repaired.
(v) Two centrosomes arise from one centrosome. Centrosomes form microtubules. Microtubules form spindle fibers.
(vi) Cells enter mitosis from G2 phase with the help of maturation promoting factor (MPF).
(vii) Volume of nucleus and cytoplasm increases.
(viii) This sub-phase takes 10-20% time.

Importance of interphase state
(i) At this stage it is determined whether the cell will participate in the next division.
(ii) Energy required for cell division (ATP) is produced.
(iii) DNA replication takes place.
(iv) RNA synthesis and histone protein content increase.
(v) At this stage microtubules are formed which form centrosomes.
(vi) Centrioles are formed in animal cells in this state.
(vii) Cell division will not take place if there is no interphase state. A living organism will not form a body. As a result, new organisms will not be created.

The empty space in the cytoplasm of the cell is called vacuole. The membrane of the cell cavity is called tonoplast. Tonoplast is a rubbery material. In plant cells, several small cavities combine to form larger cavities. It has no specific shape or size. It is filled with tissue. Cells contain water, inorganic salts, organic acids, meat, sugars, fats, various types of dyes, etc.

Function of Cell Vacuole

1. It contains sarsa.
2. It contains waste material.
3. Protects water pressure.
4. It regulates the pH of cells.
5. Separates substances that are harmful or threatening to cells.
6. Helps in retention of leaves and flowers of plants.
7. It contains proteins in the seed cells.
8. It contains numerous tiny cells.

(i) At this stage it is determined whether the cell will participate in the next division.
(ii) Energy required for cell division (ATP) is produced.
(iii) DNA replication takes place.
(iv) RNA synthesis and histone protein content increase.
(v) At this stage microtubules are formed which form centrosomes.
(vi) Centrioles are formed in animal cells in this state.
(vii) Cell division will not take place if there is no interphase state. A living organism will not form a body. As a result, new organisms will not be created.

The stage after synthesis phase is called pause-2. The features of Biram-2 are-
(i) Cell metabolism increases in this condition.
(ii) Histone proteins, non-histone proteins, tRNA, mRNA, rRNA etc. are synthesized.
(iii) Nucleus increases in volume as various elements are prepared.
(iv) In this phase the damaged DNA molecule is repaired.
(v) Two centrosomes arise from one centrosome. Centrosomes form microtubules. Microtubules form spindle fibers.
(vi) Cells enter mitosis from G2 phase with the help of maturation promoting factor (MPF).
(vii) Volume of nucleus and cytoplasm increases.
(viii) This sub-phase takes 10-20% time.

The next phase after break-1 is called Synthesis phase or S phase or Synthesis phase. It is also called DNA replication. The characteristics of synthesis state are-
(i) Histone proteins and DNA are synthesized in subphase A.
(ii) The amount of DNA increases and doubles.
(iii) Physical elongation of chromosomes occurs and each chromosome divides to form two chromatids.
(iv) Subunits of kinetochore are formed at this stage.
(v) Division of centrosome occurs in animal cells.
(vi) At this stage inactive proteins are synthesized.
(vii) This sub-phase takes 30-50% time. Mammals take 7 hours in this state.