Mitosis involves the replication of DNA and its separation into two new daughter cells. while only four phases of mitosis are often listed. the entire process is actually comprised
of six phases:
• Interphase: Involves extensive preparation for the division process.
• Prophase: The condensation of chromosomes; the nuclear membrane disappears; formation of the spindle apparatus; chromosomes attach to spindle fibers.
• Metaphase: Chromosomes, attached by spindle fibers. align along the mid-line of a cell.
• Anaphase: The centromere splits and chromatin move apart.
• Telophase: The nuclear membrane reforms around newly divided chromosomes.
• Cytokinesis: The division of cytoplasm, cell membranes, and organelles occur. In plants. a new cell wall forms.
Showing posts with label cell structure. Show all posts
Showing posts with label cell structure. Show all posts
How can drug resistance develop in microorganisms?
The use of antibiotics over the last 60 years has led to the development of drug- resistant strains of bacteria.These bacterial strains always existed in the microbial population, but they never needed to use their resistance mechanisms because they were never confronted with the antibiotic. With widespread antibiotic use, the susceptible bacteria died off rapidly, and the surviving bacteria were those with resistance. They
quickly multiplied to form populations of drug- resistant microorganisms. While methicillin- resistant Staphylococcus aureus (MRSA) is a well- known example of a drug- resistant strain, many other organisms are showing alarming rates of drug resistance due to the selective pressures exerted by the increased use of antibiotics.
quickly multiplied to form populations of drug- resistant microorganisms. While methicillin- resistant Staphylococcus aureus (MRSA) is a well- known example of a drug- resistant strain, many other organisms are showing alarming rates of drug resistance due to the selective pressures exerted by the increased use of antibiotics.
Are bacteria able to move, and, if so, how?
Bacteria (and other prokaryotes) have the ability to move by means of flagella. Flagella are composed of the globular protein flagellin. They are extremely long and thin and cannot be seen by the light microscope unless specially stained. They are, however, readily visible under the electron microscope. Bacterial flagella propel the organism by a rotary motion. Each flagellum has three basic parts: the filament, which is the long, outermost region containing the flagellin; the hook, which is composed of a different protein and lies at the proximal end of the filament; and the basal body, which anchors the filament to the cell membrane and cell wall and is composed of a series of rings encircling a central, small rod (Gram- positive bacteria have only an inner pair of rings, while Gram- negative bacteria have both inner and outer pairs of rings).
Down syndrome - what might it be?
Question
In some sufferers of Down syndrome, the somatic cell nuclei do not contain three chromosomes number 21.There is a chromosomal defect relating to chromosome number 21; what might it be?
Answer
A fragment, usually the short arm, of chromosome 21 is translocated onto another chromosome; thus, there are three copies of a fragment of the short arm in any one cell. This is a relatively rare occurrence.
In some sufferers of Down syndrome, the somatic cell nuclei do not contain three chromosomes number 21.There is a chromosomal defect relating to chromosome number 21; what might it be?
Answer
A fragment, usually the short arm, of chromosome 21 is translocated onto another chromosome; thus, there are three copies of a fragment of the short arm in any one cell. This is a relatively rare occurrence.
Mitochondria - what might be the significance of having such a complex membranous structure?
Question
Given that mitochondria do not have the same aggressive autolytic capacity as lysosomes, what might be the significance of having such a complex membranous structure? After all, the endoplasmic reticulum and the plasma membrane could potentially support those enzymes found in mitochondrial membranes.
Answer
In fact, bacteria do not have mitochondria, but some types do have membranous intrusions into the cytoplasm called mesosomes. These are similar in function to the inner membrane of mitochondria .The reason mitochondria are distinct from other membranous structures in higher cells is possibly due to their evolutionary origin as intracellular symbionts and to the fact that the spatial separations of functions lead to more advantageous (in terms of natural selection and selective advantage) control of the various metabolic processes that are now
distributed between distinct compartments.
Given that mitochondria do not have the same aggressive autolytic capacity as lysosomes, what might be the significance of having such a complex membranous structure? After all, the endoplasmic reticulum and the plasma membrane could potentially support those enzymes found in mitochondrial membranes.
Answer
In fact, bacteria do not have mitochondria, but some types do have membranous intrusions into the cytoplasm called mesosomes. These are similar in function to the inner membrane of mitochondria .The reason mitochondria are distinct from other membranous structures in higher cells is possibly due to their evolutionary origin as intracellular symbionts and to the fact that the spatial separations of functions lead to more advantageous (in terms of natural selection and selective advantage) control of the various metabolic processes that are now
distributed between distinct compartments.
what is the primary source of mitochondrial DNA?
Question:
(a) From what primary source is the DNA in your mitochondria, your mother or your father? (b) Speculate onpossible inheritance patterns if there were a defect in one or the other parent’s mitochondria.
Answer:
(a) Mother.
(b) If a defect exists in a mitochondrial gene, all progeny from that female will carry the defect.
Several well-defined diseases resulting from such a defect have been described.
(a) From what primary source is the DNA in your mitochondria, your mother or your father? (b) Speculate onpossible inheritance patterns if there were a defect in one or the other parent’s mitochondria.
Answer:
(a) Mother.
(b) If a defect exists in a mitochondrial gene, all progeny from that female will carry the defect.
Several well-defined diseases resulting from such a defect have been described.
What might be the consequence and role of compartmentation of enzymes?
Question:
There are two forms of the enzyme carbamyl phosphate synthetase, one in the mitochondrial matrix and the other in the cytoplasm. What might be the consequence and role of this compartmentation of enzymes?
Answer:
It enables separate control over the rates of urea and pyrimidine synthesis
There are two forms of the enzyme carbamyl phosphate synthetase, one in the mitochondrial matrix and the other in the cytoplasm. What might be the consequence and role of this compartmentation of enzymes?
Answer:
It enables separate control over the rates of urea and pyrimidine synthesis
Microsomes - From where do they arise?
Question:
Microsomes are small spherical membranous vesicles with attached ribosomes. They sediment, during differential sedimentation, only in the late stages of a preparation when very high centrifugal velocities are used. They don’t appear in electronmicrographs of a cell. From where do they arise?
Answer:
Fragments of endoplasmic reticulum are transformed from lipid bilayer sheets, with attached ribosomes, into spherical vesicles. This is a result of the homogenization used in preparing the samples and also the tendency of lipid bilayers to spontaneously reseal.
Microsomes are small spherical membranous vesicles with attached ribosomes. They sediment, during differential sedimentation, only in the late stages of a preparation when very high centrifugal velocities are used. They don’t appear in electronmicrographs of a cell. From where do they arise?
Answer:
Fragments of endoplasmic reticulum are transformed from lipid bilayer sheets, with attached ribosomes, into spherical vesicles. This is a result of the homogenization used in preparing the samples and also the tendency of lipid bilayers to spontaneously reseal.
What is the biochemical basis of this test?
Question:
A commonly used test of the viability of cells in tissue culture is whether or not they exclude a supravital dye such as toluidine blue. If the cells exclude the dye, they are considered to be viable. What is the biochemical basis of this test?
Answer:
The membranes of all living cells are selectively permeable to ions and other chemical species. This selectivity is in many cases linked to the supply of ATP, and one feature of cell death is a low concentration of ATP. In this state, the cell no longer excludes foreign compounds, such as toluidine dye.
A commonly used test of the viability of cells in tissue culture is whether or not they exclude a supravital dye such as toluidine blue. If the cells exclude the dye, they are considered to be viable. What is the biochemical basis of this test?
Answer:
The membranes of all living cells are selectively permeable to ions and other chemical species. This selectivity is in many cases linked to the supply of ATP, and one feature of cell death is a low concentration of ATP. In this state, the cell no longer excludes foreign compounds, such as toluidine dye.
PAS staining of microscope sections of red blood cells gives ?
Question:PAS staining of microscope sections of red blood cells gives a pink stain on only one side of the cell membrane. Which side is it, the extracellular or the intracellular side?
Answer:Extracellular. All glycoprotein and glycolipids of the plasma membrane of red and all other cells are on theoutside of the cell. No oligosaccharides are present on the inner face of the cell membrane.
Answer:Extracellular. All glycoprotein and glycolipids of the plasma membrane of red and all other cells are on theoutside of the cell. No oligosaccharides are present on the inner face of the cell membrane.
How many red blood cells are produced in an average 70-kg person every second?
The number is 2.5 million! The average life span of a human red cell is 120 days; therefore the number produced per second is simply given by the 26 trillion (average cells in 70kg person), divided by 120 days and expressed in seconds.
How many red blood cells are there in an average 70-kg person?
There are ∼2.6 × 1013, or 26 trillion. The total blood volume is ∼5.5 L, and ~40% of that is red blood cells;i.e., there are ~2.2 L of red cells. Since each cell has a volume of ∼86 × 10−15 L , the result follows from dividing 2.2 L by this number.
A person’s lysosomes lack the enzyme β-glucosidase ????
Question: There is an inherited disease in which a person’s lysosomes lack the enzyme β-glucosidase What are the clinical and biochemical consequences of this deficiency?
Answer:The disease is called Gaucher disease, and it is the most common of the sphingolipidoses; its incidence in the general population is ∼1:2500. This class of disease results from defective hydrolysis of membranecomponents, sphingolipids , that are normally turned over in the cell by hydrolytic breakdown inthe lysosomes. The sphingolipids are lipid molecules with attached carbohydrate groups. A failure to beable to remove glucose from these molecules results in their accumulation in the lysosomes. In fact, over a few years, the cells which have rapid membrane turnover, such as the liver and spleen, become engorgedwith this lipid breakdown product. Clinically the patients have a large liver and spleen and may show signs of mental deterioration if much of the lipid accumulates in the brain as well.
Answer:The disease is called Gaucher disease, and it is the most common of the sphingolipidoses; its incidence in the general population is ∼1:2500. This class of disease results from defective hydrolysis of membranecomponents, sphingolipids , that are normally turned over in the cell by hydrolytic breakdown inthe lysosomes. The sphingolipids are lipid molecules with attached carbohydrate groups. A failure to beable to remove glucose from these molecules results in their accumulation in the lysosomes. In fact, over a few years, the cells which have rapid membrane turnover, such as the liver and spleen, become engorgedwith this lipid breakdown product. Clinically the patients have a large liver and spleen and may show signs of mental deterioration if much of the lipid accumulates in the brain as well.
How may cells be disrupted in order to obtain subcellular organelles by centrifugal fractionation?
There are several ways of disrupting cells:
1. Osmotic lysis. The plasma membranes of cells are water-permeable but are impermeable to large molecules and some ions. Thus if cells are placed into water or dilute buffer, they swell due to the osmotically driven influx of water. Since the plasma membrane is not able to stretch very much (the red cell membrane can only stretch by up to 15% of its normal area before disruption), the cell bursts. The method is effective for isolated cells but is not so effective for tissues.
2. Homogenizers.
3. Sonication. This involves the generation of shear forces in a cell sample in the vicinity of a titanium probe (0.5 mm in diameter and 10 cm long) that vibrates at ∼20,000 Hz. The device contains a crystal of lead zirconate titanate that is piezoelectric; i.e., it expands and contracts when an oscillatory electric field is applied to it from an electronic oscillator. The ultrasonic pressure waves cause microcavitation in the sample, and this disrupts the cell membranes, usually in a few seconds.
1. Osmotic lysis. The plasma membranes of cells are water-permeable but are impermeable to large molecules and some ions. Thus if cells are placed into water or dilute buffer, they swell due to the osmotically driven influx of water. Since the plasma membrane is not able to stretch very much (the red cell membrane can only stretch by up to 15% of its normal area before disruption), the cell bursts. The method is effective for isolated cells but is not so effective for tissues.
2. Homogenizers.
3. Sonication. This involves the generation of shear forces in a cell sample in the vicinity of a titanium probe (0.5 mm in diameter and 10 cm long) that vibrates at ∼20,000 Hz. The device contains a crystal of lead zirconate titanate that is piezoelectric; i.e., it expands and contracts when an oscillatory electric field is applied to it from an electronic oscillator. The ultrasonic pressure waves cause microcavitation in the sample, and this disrupts the cell membranes, usually in a few seconds.
Methods of studying the structure and function of cells ? Q&A - 1
Question:Acidic dyes such as eosin and acid fuchsin have a net negative charge at the pH of usual staining solutions. Therefore they bind to many cellular proteins that have a net positive charge. Give some regions of a liver cell that might be acidophilic.?
Answer: The cytoplasm, mitochondrial matrix, and inside the smooth endoplasmic reticulum; all regions have a high protein content.
Answer: The cytoplasm, mitochondrial matrix, and inside the smooth endoplasmic reticulum; all regions have a high protein content.
Methods of studying the structure and function of cells ? Q&A - 2
Question:Basic dyes such as methylene blue or toluidine blue are positively charged at the pH of most staining solutions used in histology. Thus the dyes bind to acidic (negatively charged) substances in the cell. These acidic molecules are therefore referred to as basophilic substances in cells. Give some examples of basophilic substances?
Answer:Examples of basophilic components are DNA and RNA; the latter includes messenger RNA and ribosomes.The youngest red blood cells in the blood circulation contain a basophilic reticulum (network) in their cytoplasm; this is composed of messenger and ribosomal RNA. The network is slowly dissolved over the first 24h of the cell’s life in the circulation. This readily identifiable red cell type is called the reticulocyte.
Answer:Examples of basophilic components are DNA and RNA; the latter includes messenger RNA and ribosomes.The youngest red blood cells in the blood circulation contain a basophilic reticulum (network) in their cytoplasm; this is composed of messenger and ribosomal RNA. The network is slowly dissolved over the first 24h of the cell’s life in the circulation. This readily identifiable red cell type is called the reticulocyte.
MCQ in biological science: Answer
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Your Answer: Adenosine triphosphate
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Your Answer: yes Yes they can be hungry. If you want to know how this has been discovered give me a sign. (But I hope you don't want to know it because it's quite complex and difficult to explain)
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Your Answer: Insects The Malpighian tubules are fine, thin-walled excretory tubules, leading into posterior part of gut in insects.
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Your Answer: Papaveraceae
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Your Answer: Left ventricle
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Your Answer: 4000 x mass of the earth Incredible but true. One of the stages of bacterial growth is characterized by exponential growth. This means 1 becomes 2 becomes 4 - 8 - 16 - 32 - 64 - 128 - 256 - 512 - 1024 - 2048 - 4096 ...
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Your Answer: Atrium The atrium is a part of the heart
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Your Answer: True Flies and Mosquitoes belong to the Diptera, and they only have 2 wings. The second pair is reduced to small halteres.
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Your Answer: Glycogen Glycogen acts as a storage substance in vertebrate liver and muscle.
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Your Answer: Apis mellifera
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Multiple choice questions answers in Biology
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Your Answer: Small Intestine In human beings, most digestion takes place in the small intestines. |
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Your Answer: Medulla Oblongata The medulla oblongata is the part of the brain which controls breathing and circulation. |
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Your Answer: Alcohol Alcohol is one of a very few substances very quickly absorbed after being ingested. |
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Your Answer: Cardiovascular Stress Cigarette smoking is generally associated with cardiovascular stress. The other conditions are produced by specific viruses. |
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Your Answer: Sperm Cell The sperm cell contains the particular chromosome which determines the sex of a human embryo. |
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Your Answer: Jellyfish A jellyfish is the only one of the possible choices which is an invertebrate. |
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Your Answer: 50 Percent Since each sperm can carry the X or Y chromosome with equal probability, sex determination for each birth is the same, 50 percent for a boy, and 50 percent for a girl. |
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Your Answer: Wind The most common form of pollination of grasses is caused by the wind. |
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Your Answer: Iodine Iodine is an antiseptic, an item used to clean wounds. |
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Your Answer: Reflex A reflex is an immediate response to a stimulus which takes place without thought or intent. |
Test your Biology - MCQ in life science Answer
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Your Answer: They change the activation energy. Enzymes decrease the activation energy (the energy which is needed to start off the reaction), and also increase the speed of the reaction.
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Your Answer: Its temperature varies much less than air temperature The other three points are true of water but they do not take a part in providing a stable environment for aquatic animals.
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Your Answer: An alkanoic (fatty) acid Tricarboxylic acids and amino acids share the same carboxyl group but have different functional groups joined to them. An example of a monosaccharide is glucose (C6H12O6).
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Your Answer: Tumour Formation
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Your Answer: A virus
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Your Answer: Protein Enzymes in plant and animal cells are made from proteins.
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Your Answer: Half An example of a haploid cell is an egg cell (gamete) which only contains half the genetic material of the mother's cells. A diploid cell is just a regular cell.
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Your Answer: Codominance If a person has an Ai gene and a Bi gene, their blood type will be AB. This shows codominance. Codominance is where two differeent alleles both show themselves in the phenotype of a person. Another example would be in the gene for type of hair. There are two alleles: one for curly hair, and one for straight hair. Someone who is heterozygous for these alleles would have wavy hair.
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Your Answer: Modification of proteins for secretion
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Your Answer: She is a carrier of Haemophilia She is a carrier because haemophilia is a recessive trait and she only has one of the recessive alleles. However, in the case of males, one of the recessive alleles would make them a sufferer because it is carried on the X chromosome and males only have one X chromosome.
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MCQ in life science - Answer
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Your Answer: Nitrogen They are the only main food component that contains an extra element.
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Your Answer: Sheep Sheep are ruminants and do not need incisors.
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Your Answer: Indicator
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Your Answer: phloem Xylem carries water from the roots to all parts of the plant. Phloem carries food from the leaves to places that can't make food for itself.
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Your Answer: Glucose
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Your Answer: food
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Your Answer: small intestine It is called the small intestine because it is thinner of the two.
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Your Answer: ligament Tendons attach muscles to bones, cartilage acts as a shock absorber and allows smooth movement and synovial fluid acts as a lubricant.
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Your Answer: cornea Each eye sees a different picture and the brain puts the two images together.
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Your Answer: lactose This is converted into lactic acid by fermentation.
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