General science Biology-1

BIOLOGY

HISTORY OF CELL STUDIES

1. 1665: Robert Hooke discovers cells in cork
2. 1839: Theodor Schwan and Matthias Jakob Schleiden found cell theory
3. 1931: Ernst Ruska builds first Transmission Electron Microscope at the University of Berlin
4. 1953: Watson and Crick discover double helix structure of DNA. They, along with Maurice Wilkins, won the Nobel Prize in Physiology or Medicine in 1962

GENETIC MATERIAL IN A CELL

1. DNA used mainly for storing genetic information
2. RNA used mainly for information transport. Sometimes used for genetic storage in certain viruses
3. Human cell encodes genetic information in DNA
4. Human genetic material found in nuclear genome and mitochondrial genome
5. Nuclear genome divided into 23 pairs of DNA molecules called chromosomes
6. Mitochondrial genome codes for 13 proteins used in mitochondrial energy production

COMPONENTS OF A CELL

1. Cell Membrane
   • Separates interior of a cell from outside environment
   • Semi-permeable
   • Made of proteins and lipids
   • Protein receptors are found on the cell membrane
2. Cytoplasm
   • Part of a cell enclosed withing cell membrane
   • Contains three major elements: cytosol, inclusions, organelles
3. Cytosol
   • Translucent fluid made of water, salts and organic molecules
   • Makes up 70% of cell volume
   • Contains protein filaments (that make up the cytoskeleton) and vault complexes
4. Inclusions
   • Small insoluble particles suspended in cytosol
   • Include energy storage materials such as starch and glycogen
5. Organelles
   • Compartments withing the cell that have specific functions. Eg: mitochondria, golgi apparatus, lysosomes etc
6. Mitochondria and Chloroplasts
   • Both generate energy in the cell
   • Mitochondria uses Oxygen to generate ATP
   • Chloroplasts generate carbohydrates and Oxygen from carbon dioxide and water
   • Mitochondria found in plants and animals. Chloroplasts found only in plants
7. Ribosomes
   • Large complex of RNA and protein molecules
8. Nucleus
   • Contains chromosomes
   • Site of DNA replication and RNA synthesis
     
9. Golgi Apparatus
   • Found in eukaryotes only
   • Process and package proteins and lipids synthesised by a cell
10. Lysosomes and Peroxisomes
    • Lysosomes have digestive enzymes
    • Digest excess or worn-out organelles, food particles, virus/bacteria
    • Peroxisomes have enzymes that rid the cell of toxic peroxides
11. Vacuoles
    • Store food and waste

FUNCTIONS OF A CELL

1. Cell metabolism
   1. Cell metabolism required for cell growth
      
   2. Metabolism is the process by which cells process nutrient molecules
   3. Catabolism: cell produces energy by breaking down complex molecules
      
   4. Anabolism: cell uses energy to construct complex molecules and perform other functions
2. Cell division
   • Required for building tissue and procreation
   • Prokaryotic cells divide by binary fission
   • Eukaryotic cells divide by mitosis or meiosis
   • Mitosis produces two identical daughter cells, meiosis produces two daughter cells each with half the number of chromosomes
   • DNA replication is required every time a cell divides
3. Protein synthesis
   • New proteins formed from amino acids
   • Consists of two steps: transcription and translation

ASK AND TELL…

1. Prokaryotes are
   1. animals without developed nervous systems
   2. organisms lacking nucleus
   3. primitive plants without vascular systems
   4. plants that do not produce flowers and fruits
2. Honey that has high concentration of sugar does not decay because
   1. it contains natural anti oxidants that prevents bacterial attack
   2. bacteria can’t survive in active state in a solution of high osmotic strength as water is drawn out
   3. bacteria can’t survive in active state as it is deprived of oxygen
   4. none of these
3. The number of chromosomes in a bacterium is
   1. 1
   2. 2
   3. 4
   4. varies with species
4. Granum is a component of
   1. chloroplasts
   2. golgi apparatus
   3. ribosomes
   4. starch grains
5. In a plant cell, DNA is found in
   1. chloroplasts
   2. mitochondria
   3. nucleus
   4. all these

      BIOLOGY: NUTRITION
      

      Overview
      
      
   5. Nutrition is the supply to cells and organisms, of the materials necessary to support life
   6. Many common health problems can be prevented by a healthy diet
   7. A poor diet can have injurious impact on health, leading to problems such as scurvy, beriberi and kwashiorkor
   8. A healthy diet can also significantly prevent and mitigate systemic diseases like cardiovascular disease, diabetes and osteoporosis
   9. Eating a wide variety of fresh, unprocessed food has proven favourable compared to monotonous diets of processed food
   10. Consumption of whole plant foods slows digestion, allows better absorption and a more favourable balance of nutrients
       
   Nutrients
   
   
6. There are six major classes of nutrients: carbohydrates, fats, minerals, proteins, vitamins and water
   
7. These can be classified into
   • Macronutrients: nutrients needed in large quantities. These include carbohydrates, fats, proteins and water. Fibre is another macronutrient whose functions have not been fully understood
   • Micronutrients: nutrients needed in smaller quantities. These include minerals and vitamins. Antioxidants and phytochemicals are micronutrients as well, but their functions are not well understood
     
8. Most foods contain a mixture of nutrients
9. Some nutrients may be stored internally (eg. Fat soluble Vitamins) while others are required more or less continuously

Carbohydrates

• Carbohydrates are sugars, and are classified as monosaccharides, disaccharides or polysaccharides depending on the number of monomer (sugar) units they contain
• Carbohydrates constitute a large part of foods such as rice, noodles, bread and other grain based products
• In general, simple saccharides are easier to digest and absorb than polysaccharides
  
• Since they are absorbed more quickly, simple carbohydrates lead to elevated levels of blood glucose
  

Fibre

• Dietary fibre is a carbohydrate (polysaccharide) that is incompletely absorbed in humans and some animals
  
• Like all carbohydrates, when metabolised it produces energy
• However, it does not contribute much energy due to limitations on its absorbability and digestion
  
• Dietary fibre consists mainly of cellulose, a polysaccharide that is indigestible in humans
• Whole grains, fruits and vegetables are good sources of fibre
• Fibre provides bulk to intestinal contents and stimulates peristalsis – the rhythmic muscular contractions of the intestines that moves digesta along the digestive tract
• For these reasons, fibre is important for digestive health. It helps alleviate constipation and diarrhoea and is said to reduce colon cancer
  

Fats

• Fat consists of fatty acids bonded to glycerol. Fatty acids are carboxylic acids that contain long chains of carbon and hydrogen atoms
• They are typically found as triglycerides
• Fats are classified as
  • Saturated fats: have all the carbon atoms in the fatty acid chains bonded to hydrogen atoms
    
  • Unsaturated fats: have some carbon atoms double bonded to themselves, thereby have fewer hydrogen atoms
    
• Studies have shown that unsaturated fats are preferable to saturated fats in terms of health effects
  
• Saturated fats are usually solids at room temperature (eg butter) while unsaturated fats are liquids at room temperature (eg olive oil)
  
• Trans fats are a type of unsaturated fat with trans-isomer bonds. These are rare in nature and usually created by an industrial process called hydrogenation. Trans fats are harmful to health (coronary heart disease) and their use is to be avoided

Proteins

• Proteins are the basis of many animal body structures and form enzymes that control chemical reactions in the body
• Proteins are composed of amino acids, which contain nitrogen atoms
• The body requires amino acids to produce new proteins and replace damaged proteins
• Since the body cannot store protein, amino acids must be present in the daily diet
  
• Diet with adequate proteins is especially important during early development and maturation, pregnancy, lactation or injury
• A complete protein source is one that contains all essential amino acids
  
• Sources of protein include meat, tofu, soy, eggs, grains, legumes and dairy products
• A few amino acids can be converted into glucose for energy (called gluconeogenesis). This process mainly happens only during starvation

Minerals

• Dietary minerals are the chemical components required by living organisms other than the four elements carbon, oxygen, nitrogen, hydrogen that are present in nearly all organic molecules
• Dietary minerals include some metals as well (sodium, potassium) which are usually found in ionic state
• Minerals are recommended to be supplied in the daily diet
• Most famous dietary mineral is iodine (added to salt) which prevents goitre
  
• Macrominerals (required more than 200 mg/day) include
  
  • Calcium: electrolyte, also needed for structural growth (teeth, bones)
    
  • Chlorine: electrolyte
    
  • Magnesium: required for processing ATP (energy)
    
  • Phosphorous: required component of bones, essential for energy processing
    
  • Potassium: electrolyte (heart and nerve health)
    
  • Sodium: common electrolyte, needed in large quantities. Most common source is common salt. Excess sodium depletes calcium and magnesium leading to high BP an osteoporosis
    
  • Sulphur: essential for certain amino acids and proteins
    
• In addition to the macrominerals, many other minerals are required in trace amounts. These include cobalt, copper, chromium, iodine, iron, manganese, molybdenum, nickel, selenium, vanadium, zinc

Vitamins

• A vitamin is an organic compound required as a nutrient in tiny amounts by an organism
• A compound is called a vitamin when it cannot be synthesised in sufficient amounts by an organism, and must be obtained from the diet
  
• Thus, the term “vitamin” is conditional both on the circumstance and the organism. For instance ascorbic acid is termed Vitamin C for some organisms but not for others, and Vitamins D and K are required in the human diet only under certain circumstances
• Vitamins must be supplied in the diet (except Vitamin D, which can be synthesised by the skin in the presence of UV radiation)
  
• Fresh fruits and vegetables are good sources of vitamins
• Vitamin deficiencies may results in diseases like goitre, scurvy, osteoporosis, impaired immune system etc
• Excess of some vitamins can also be dangerous: excess Vitamin A can cause jaundice, nausea, blurry vision, vomiting, muscle pain etc

Water

• About 70% of non-fat mass of the body is water
  
• To function properly, the body requires between one and seven litres of water every day
• It is recommended that daily water intake for an adult male be 3.7 l and for females be 2.7. However, these requirements vary with climate, activity level and other factor
• Too little water can lead to dehydration
• Too much water can lead to water intoxication, a potentially fatal disturbance to the brain. However, this is very rare in normal humans and usually only occurs during water drinking contests or intense bouts of exercises when electrolytes are not replenished
  

Malnutrition

Nutrients	Deficiency	Excess
Carbohydrates	Low energy	Diabetes, obesity
Fats	None	Cardiovascular disease, obesity
Cholesterol	none	Cardiovascular disease
Protein	Kwashiorkor (edema, anorexia, inadequate growth)	Rabbit starvation (diarrhoea, headache, low BP, low heart rate Discomfort/hunger that can only be satisfied by eating fats and carbohydrates
Sodium	Hyponatremia (electrolyte imbalance)	Hypernatremia, hypertension
Iron	Anaemia	Cirrhosis (chronic liver disease), heart disease
Iodine	Goitre, hypothyroidism	Iodine toxicity
Vitamin A	Night blindness, xeropthalmia (dry eyes)	Hypervitaminosis A (birth defects, liver problems, osteoporosis)
Vitamin B1	Beri-beri
Vitamin B2	Cracking of skin
Vitamin B12	Pernicious anaemia
Niacin (Vitamin B3)	Pellagra (diarrhoea, dermatitis, dementia, death)	Dyspepsia (indigestion), cardiac arrhythmias
Vitamin C	Scurvy	Diarrhoea
Vitamin D	Rickets	Hypervitaminosis D (dehydration, vomiting, constipation)
Vitamin E	Nervous disorders	Hypervitaminosis E (anticoagulant)
Vitamin K	Haemorrhage
Calcium	Osteoporosis	Fatigue, vomiting, depression, cardiac arrhythmias
Magnesium	Hypertension	Weakness, nausea, vomiting
Potassium	Hypokalaemia, cardiac arrhythmias	Hyperkalaemia, palpitations

1. BIOLOGY: VACCINES
   

   Overview
   
   
2. A vaccine is a biological preparation that improves immunity to a particular disease
3. Vaccines were first used by Edward Jenner (England) in the 1770s to inoculate against small pox using the cow pox microbe
4. Vaccines have resulted in the eradication of small pox, one of the most contagious and deadly diseases known to man
5. Other diseases like polio, measles, mumps, typhoid etc are have been significantly reduced. Currently, polio is prevalent in only four countries: Afghanistan, Pakistan, Nigeria and India
   Mechanism of action
   
6. A vaccine is usually made from a weakened or dead form of the microbe that it is intended to fight
   
7. It stimulates the body’s immune system to recognise the microbe as foreign, and destroy it and remember it
8. When the same microbe re-appears later, the immune system easily recognises and destroys it
9. When the body recognises the virulent microbe attack, it
   • Neutralises the target microbe before it can enter body cells
   • Destroys infected cells before the microbe can spread to other cells and multiply

Types of vaccines

• Killed vaccines: these are vaccines that contain micro-organisms that have been killed using chemicals or heat. Eg: influenza, cholera, bubonic plague, polio, hepatitis A
  
• Attenuated vaccines: these contain live attenuated (numerous) micro-organisms. These are usually live viruses that have been cultivated under conditions which disable their virulent properties, or use closely-related by less dangerous micro-organisms. These vaccines provide more durable immune response and are preferred type for healthy adults. Eg: yellow fever, measles, rubella, mumps, typhoid
  
• Toxoid vaccines: inactivated toxic compounds that cause illness. Eg: tetanus, diphtheria
  
• Subunit vaccines: these use protein subunits instead of the entire micro-organism as a vaccine. Eg: Hepatitis B vaccine (which uses only surface proteins), Human Papilloma Virus (HPV) vaccine (which uses subunits of influenza virus)
  

Effectiveness of vaccines

• Vaccines do not guarantee complete protection from a disease
• This could be due to
  • Host’s immune system may not respond adequately
  • Host may have lowered immunity (such as due to diabetes, HIV, steroid use etc)
  • Host may not have a B cell capable of producing antibodies to that particular antigen
• The efficacy of a vaccine depends on a number of factors
  • The disease itself
  • The strain of vaccine
  • Following the schedule of vaccinations
  • Individual host factors
  • Genetic and ethnic predisposition
• Most vaccines use adjuvants to boost immune system response. Adjuvants are compounds added to the vaccine that increase the immune response, without having any specific antigenic effect by themselves.
  
• Aluminum salts like aluminium phosphate and aluminium hydroxide are the most common adjuvants used
  
  

List of important vaccines

Vaccine	Disease	Type	Notes
Anthrax vaccine	Anthrax	Protein subunit
Bacillus Calmette-Guerin (BCG)	Tuberculosis	Live bacteria
DTP	Diphtheria Pertussis (whoopoing cough) Tetanus
Gardasil (Human Papilloma Virus (HPV))	Cervical cancer	Protein subunit
Polio vaccine	Polio	Killed/inactivated	Polio is prevalent only in humans Currently polio has been eradicated from all countries except Afghanistan, Pakistan, Nigeria and India
MMR	Measles Mumps Rubella
Meningococcal vaccine	Meningococcus
Rabies vaccine	Rabies	Attenuated
Yellow fever vaccine	Yellow fever	Attenuated

BIOLOGY: STEM CELLS

Overview

• Stem cells are cells that can renew themselves.
  
• Stem cells renew themselves through mitotic cell division and can differentiate into a diverse range of specialised cell types
  
• Stem cells are found in most multi-cellular organisms
  
• There are two types of stem cells in mammals
  
  • Embryonic stem cells
    
  • Adult stem cells
    
• Stem cells are mainly found in blood from the umbilical cord and the bone marrow
  
• Due to their self-renewing nature, stem cells are very important for treatment of diseases
  

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Importance of stem cells

• For a cell to be characterised as a stem cell, it must exhibit the following properties
  
  • Self renewal: the ability to go through numerous cycles of cell division while maintaining the undifferentiated state
    
  • Potency: the capacity to differentiate into specialised cell types
    
• In developing embryos, stem cells can differentiate into all of the specialised embryonic tissues
  
• In adult organisms, stem cells act as a repair system for the body, replenishing specialised cells
  
• Stem cells also maintain the normal turnover of regenerative organs such as blood, skin or tissues
• Stem cells can be grown and transformed into specialised cells of various tissues such as muscles and nerves using cell culture
• Stem cell treatment holds the potential of transforming human medicine, wherein stem cells introduce new cells into damaged tissue in order to treat a disease or injury
• The ability of stem cells to self renew and differentiate offers the potential to replace diseased and damaged tissue without the risk of rejection or side effects
  

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Current stem cell treatments

• Currently, stem cell treatment is available to treat the side effects of chemotherapy on cancer patients, such as leukaemia or lymphoma
  
• During chemotherapy most growing cells are killed by cytotoxic agents
• These agents kill not only the leukaemia cells but also healthy haematopoietic stem cells in adjacent bone marrows.
• Using stem cell therapy, healthy bone marrow stem cells are used to reintroduce healthy stem cells to replace those lost in the treatment

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Potential stem cell treatments

• Stem cells can be potentially used to treat a number of serious diseases. These include
  • Brain diseases such as Parkinson’s and Alzheimer’s
  • Cancers
  • Spinal cord injury
  • Heart damage
  • Haematopoiesis (blood cell formation)
  • Baldness, missing teeth
  • Blindness, deafness
  • Diabetes
  • Neural damage
• Almost all these treatments are still in the research stage
• In Jan 2009, the US Food and Drug Administration (FDA) gave clearance to Geron Corporation for the first clinical trials of an embryonic stem cell therapy on humans. The trial will evaluate the efficacy of the drug GRNOPC1 on patients with spinal cord injury
  

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Important milestones in stem cell research

• 1963: Ernest McCullogh (Canada) and James Till (Canada) illustrate the presence of self renewing cells in the bone marrow
• 1968: Bone marrow transplant between two siblings successfully treats Severe Combined Immunodeficiency (SCID)
• 1978: haematopoietic stem cells discovered in human blood
• 1998: James Thomson (USA) derives the first human embryonic stem cell line
  
• 2001: Scientists at Advanced Cell Technology (USA) clone first early human embryos for the purpose of generating embryonic stem cells
• 2006: Scientists at Newcastle University (England) create first every artificial liver cells using umbilical cord blood cells
• 2008: Robert Lanza and colleagues at ACT create first human embryonic stem cells without destruction of the embryo