Bacterial cell - Structure and Functions

                    Bacterial cell 

              Structure and Function:

Bacterial are unicellular prokaryotic organism.

Bacterial cell have simpler internal structure. 

It lacks all membrane bound cell organelles such as mitochondria, lysosome, golgi, endoplasmic reticulum, chloroplast, peroxisome, glyoxysome, and true vacuole.

A typical bacterial cell have following structure.

A. Structure Outside cell wall

1. Capsule
2. Flagella
3. Pili
4. Cell wall
5. Cytoplasmic membrane
6. Nucleoid
7. Mesosomas
8. Ribosome
9. cytoplasm
10. Spore.

1.Capsule:

• Capsule is 0.2µm thick viscus layer outer layer to the cell wall.
• Capsule is 98% water and 2% polysaccharide or glycoprotein/ polypeptide or both.
• There are two types of capsule.
• It helps in attachments as well as it prevent the cell from desiccation and drying.
• Capsule resist phagocytosis by WBCs.

2. Flagella:

• It is 15-20 nm hair like helical structure emerges from cell wall.
• Flagella is not straight but is helical. It is composed of flagellin protein (globular protein) and known as H antigen.
• Flagella has three parts. Basal body, Hook and filament
• It helps motility of the bacteria

3. Pili or fimbriae:

• Pili are hollow filamentous and non-helical structure.
• They are numerous and shorter than flagella
• Pili is the characteristic feature of gram –ve bacteria.
• Pili is composed of pilin protein.
• Bacteria containing pili: Shigella, Proteus, Neisseria gonorrhoae, E. coli
• Attachment: pili helps the bacteria to attach the host cell surface. Most of the human pathogens of respiratory tract, urinary tract are attached with the help of pili.
• Pili (fimbriae) possess antigenic property
• Specialized function: some pili are modified for specialized function. Eg. Sex pilus (F-pili) help in transfer of DNA from donor to recipient cell during conjugation.
• F-pili also act as receptor for bacteriophage.

4. Cell wall:

• It is an important structure of a bacteria.
• It give shape to the organism.
• On the basis of cell wall composition, bacteria are classified into two major group ie. Gram Positive and gram negative.

Gram positive cell wall

Cell wall composition of gram positive bacteria.

1. Peptidoglycan
2. Lipid and Teichoic acid

Gram negative cell wall

Cell wall composition of gram negative bacteria

1. Peptidoglycan
2. Outermembrane:
   • Lipid
   • Protein
   • Lipopopysaccharide (LPS)

• Peptidoglycan layer is present in cell wall of both gram positive as well as gram negative bacteria. However, gram positive have thick layer of peptidoglycan.
• It is the major surface antigen of gram positive bacteria
• It is an additional layer present in gram negative bacteria.
• It is composed of lipid bilayer, protein and lipo-polysaccharide.

 5.Cell membrane:

• Cell membrane is the inner layer that lies inside the cell wall and encloses the cytoplasm.
• It is also known as cytoplasmic membrane or plasma membrane.
• It is about 80nm thick.
• Cell membrane of bacteria is composed of phospholipid and proteins.
• It is selectively permeable as it allows to pass selective substances such as sugar, aminoacids across it.

6. Nucleus:

• Nucleus is the most important part of the cell.
• It controls and directs all the cellular activities and stores hereditary information of cell
• Bacterial nucleus is known as nucleoid; it lacks nuclear membrane, nuceloplasm and nucleolus.
• Bacterial DNA is naked (lacked histone protein)
• It contains and stores hereditary information of the cell.
• It controls all cell activities.

7. Ribosome:

• Bacterial ribosome is of 70s type.
• Ribosomes are rounded granules found freely floating in the cytoplasm
• Ribosomes are known as universal cell organelle because it is found in both bacterial cell and eukaryotic cell.
• Chemically the ribosomes are made up of nucleic acids (particularly RNA and proteins).
• It helps in protein synthesis. 

8. Mesosome:

• Mesosome is a spherical or round sac like structure found commonly in gram positive bacteria.
• Function: It is the site for respiration in bacterial cell

9. Cytoplasm:

• It is colorless, viscus fluid present inside cell membrane.
• All the cell organelles and inclusions are found floating in cytoplasmic fluid.
• It contains proteins, lipid, minerals, nucleic acids, glycogen, water etc.
• It helps to distribute water, oxygen as other substances throughout the cell.
• Literally, all the cellular content including nucleus, and other cell organelle are floating in cytoplasm.

10. Spores (endospore):

• Spore is metabolically dormant structure produced during unfavourable condition by the process called sporulation
• Sporulation occur during late log phase or early stationary phase
• Under favourable condition spores germinate to give vegetative cell.

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Vitamins

WHAT ARE VITAMINS? 
  Vitamins are organic substances which are necessary food factors required in small amounts to regulate energy transformation and metabolism.
Vitamins are not energy sources but they protect from diseases and work as food catalysts too.
Vitamins are effective in very small amounts (mg or mg).
Every vitamin has a specific function and deficiency of a vitamin in diet causes a specific disease.
Vitamins are not formed in the body except vitamin D.
Therefore, they must be taken from their sources.

There are two types of vitamins:
1. water soluble vitamins (C, B)
2. fat soluble vitamins (A, D, E, K)
 
VITAMIN A:
The main function of vitamin A is to form VISUAL PIGMENT. It is essential for normal growth, healthy teeth, saves us from infectious diseases, night vision, normal bone and teeth development.
It transports nutrients across the cell membrane.
Vitamin A is an antioxidant.
It increases iron metabolism.
 
FOOD SOURCES:
  Milk, egg yolk , liver fats, cod liver oil, carrot, apricots,Peach, butter, green leafy vegetables, cheese
 
DEFICIENCY
Deficiency of vitamin A causes:
 Night blindness
 Xerophthalmia
 Respiratory infection
 Allergies
 Loss of teeth enamel
 Gum disease
 Decrease in immunity
DOSE
Male : 1.00 mg per day
Female : 0.8 mg per day
 
OVERDOSE
Overdose of Vitamin A may cause:
 Headache
 Fatigue
 Skin problems
 Bone pain
 Dry skin
 Thickening of bone
 Brittle nails
 Constipation
 long term use can cause hair loss
 liver damage
 increase in blood fats/cholesterol.

VITAMIN B1
 
It helps body cells to convert carbohydrates into energy.
Vitamin B1 plays an important role in energy metabolism.
It is essential for growth. Protect us from digestive disturbance.
Healthy heart function. Healthy nerve cells.
Protect us from herpes zoster. Helpful in healthy brain functioning. Useful in anemia.
FOOD SOURCES
sunflower seeds, Liver, kidney, cereal, peanuts, beans, eggs-yolk, legumes, fish, meat, milk, yeast etc.
 
DEFICIENCY
 Deficiency causes beri beri, cardiac failure, Loss of weight, digestive disturbance, weakness , nerve damage, constipation.
 
DAILY DOSE
 Male : 1.4 mg per day
Female : 1.0 mg per day
 
OVERDOSE
 It has very few side effects in case of overdose which includes:
 headache
 itching
 irritability
 flushing

VITAMIN B2

 Vitamin B2 is essential for normal body growth, red cell production, prevents us from rheumatoid arthritis, migraine, skin disorders, Cataract prevention and it is a helper for other B- vitamins.
FOOD SOURCES
 Milk, eggs, liver, fish, yeast, fruits, green leafy vegetables, wheat , pea, soybean.
 
DEFICIENCY
Dry & cracked skin, inflammation on mouth, anemia, eye diseases, slow wound healing ,poor general health, scales on nails, cracks at corners of mouth, sickle cell anemia.
 
DAILY DOSE
Male : 1.6 mg per day
Female : 1.2 mg per day
 
OVERDOSE
  Itching
 Burning sensations
 Numbness


VITAMIN B3
 Vitamin B3 is a metaboliser for amino acids and carbohydrates.
It is required in the synthesis of fats.
Essential for healthy skin.
Cell respiration.
Used to decrease cholesterol and control diabetes.
Proper functioning of nervous system.
Mental alertness
FOOD SOURCES
Red meat, liver, yeast, Milk,peanut, fish, eggs, Legumes,coffee etc.
DEFICIENCY
Deficiency of vitamin B3 includes:
 Mental disturbances
 Diarrhea
 Pellagra
 Skin lesions
 Decreased appetite
DAILY DOSE
 Male : 18 mg per day
Female : 13 mg per day
OVERDOSE
 Liver damage
 Skin flushing
 Itching
 Heartburn
 Peptic ulcer

VITAMIN B5

 VITAMIN B5 is very important in metabolic system and stress resistance.
It is also helpful in the synthesis of antibodies, fats, proteins and hemoglobin.
Vitamin B5 plays very important role in the secretion of hormones.
It slows down aging process.
Prevents from arthritis and helpful against wrinkles.
Vitamin B5 is also known as anti-stress vitamin because it relieves physical and emotional stress.

FOOD SOURCES
Yeast, chicken, fish, Kidneys, beef, liver ,Peanuts, mushrooms, soybean , eggs , sunflower seeds , lentils,cashews ,fresh vegetables,wheat.
 
DEFICIENCY
Deficiency symptoms of vitamin B5 include:
 Frequent infection
 Cardiovascular disorders
 Digestive disorders
 neurological disorders
 Low blood cholesterol level
 Decrease in serum potassium
 General weakness
 
DAILY DOSE
 No recommended dosage however 10mg to 100 mg per day is necessary.
 
OVERDOSE
 Not toxic in high dosage (less than 10 grams per day).
Sensitive to teeth if taken 1.5 grams per day for a long period regularly.

VITAMIN B6

 Vitamin B6 is involved in the following functions:
 Protein and fatty acid metabolizer
 Red cells production.
 Healthy brain function.
 Helps to synthesize antibodies.
FOOD SOURCES
 Milk, liver, yeast, green leafy vegetables , cereals, kidney, fish, chicken, eggs, nuts, banana etc.

DEFICIENCY
  Skin disorders
  Anemia
 Seizures in infant
 Memory problem
 Low absorption of fats, proteins and sugar
 Water retention in body

DAILY DOSE

1.3 mg to 2.00 mg per day

 OVERDOSE
 Large dosages may cause neurological disorders.
It is sensitive to sun light and heat.
Vitamin B2 and zinc are necessary to absorb Vitamin B6.

VITAMIN B12

 Vitamin B12 is necessary in the formation of red blood cell and for normal growth.
Prevents us from anemia, allergies, asthma and skin disorders.
FOOD SOURCES
 Liver , fish , Meat, Eggs, yeast , Kidney , Milk , Dairy products
 
DEFICIENCY
 Deficiency of Vitamin B12 may include:
 Anemia
 Fatigue
 Memory loss
 Depression
 Confusion
 
DAILY DOSE
 2.4 micro gram per day
 
OVERDOSE
Not known


VITAMIN C
 Vitamin C is essential for:
 In the synthesis of collagen in connective tissue.
 Healing of wounds & fractures
 Facilitates absorption of iron.
 Helps in haemoglobin formation.
 Formation of steroid hormones
 Reduces the chances of infections
 prevents from scurvy
 Antioxidant
 For healthy gums
FOOD SOURCES
 All citrus fruits such as orange, lemon, guava , strawberries, Pineapple,grape fruit, tomato, cabbage, cauliflower 
DEFICIENCY
 Decrease in body resistance to infection
 Bleeding of teeth.
 Scurry
 Anaemia
 poor wound healing
 painful joint
DAILY DOSE
60 mg per day

OVERDOSE
  Diarrhea
 Painful urination
 Flatulence
 Skin rash

VITAMIN D

 Vitamin D controls the absorption of calcium & Phosphorus in our body to develop healthy bones & teeth. It is very very necessary for the development of bones and teeth. You should not avoid the importance of vitamin D because it helps in the absorption of calcium which in turn forms strong bones.
People deficient in vitamin D suffer a great deal in old age, Therefore you must care about it.
SOURCES
 Fish oil, liver, egg yellow, milk etc.
It is also produce on skin by sun light
DEFICIENCY
  Softness of bones
 Tooth decay
 Rickets
DAILY DOSE
 400 international units per day
 
OVERDOSE
 Extra heavy doses of vitamin D are harmful and cause loss of appetite , thickening of bones , Softness of tissues and calcification of joints.


VITAMIN E

 Vitamin E an antioxidant and it slows down the aging process. It is helpful in skin treatment. If you want to be young,healthy,energetic and good skin texture with no wrinkles you must add vitamin E in your diet. Maintenance of cell membrane,normal function of muscular and vascular system are also due to vitamin E.
FOOD SOURCES
fish, meat, eggs,Green leafy vegetables, oil, wheat, milk.
DEFICIENCY
 Deficiency of vitamin E may causes:
 premature aging
 Fragility of red blood cells.
 skin problems
 Respiratory problems.
DAILY DOSE
 Male :10 mg per day
Female : 8 mg per day

VITAMIN K
 Vitamin K is used to control blood clotting mechanism.
FOOD SOURCES
 Green leafy vegetables, vegetable oils, meat, liver, milk, bran, broccoli.
Vitamin K is also produced by intestinal bacteria.
DEFICIENCY
 Failure of blood clotting mechanism
DOSE
 Male : 80 mg per day
Female : 70 mg per day
 
OVERDOSE
  Jaundice
 Anemia

Carbohydrates

Carbohydrates:

Introduction of carbohydrates
Carbohydrates are the organic molecules that are composed of elements carbon, hydrogen and oxygen.

Classification of carbohydrate

Carbohydrates are classified into three groups based on the number of sugar units and upon their behaviour towards hydrolysis. They are
>Monosaccharides
>Oligosaccharides and
>Polysaccharides

Monosaccharides:

These are simplest group of carbohydrates and are referred as simple sugars as they are sweet in taste. 
They cannot be further hydrolyzed to simpler compounds.
They have the general formula C_n(H₂O)_n

Examples: Glucose and fructose

Oligosaccharides:

These carbohydrates liberate two to ten monosaccharide molecules on hydrolysis.

 They are further classified as disaccharides, trisaccharides, tetrasaccharides, etc. based on the number of monosaccharide units. 

For e.g., disaccharides like sucrose produce two molecules of monosaccharides on hydrolysis. 

Polysaccharides:

These carbohydrates liberate a large number of monosaccharide molecules on hydrolysis. They are usually amorphous, insoluble in water and tasteless and are called non-sugars. 

They are again sub-divided into two types. They are homopolysaccharides and heteropolysaccharides

Open and ring structure of Sucrose:

Sucrose is made up of a-D-Glucose and b-D-fructose held together by a glycosidic bond, between C₁ of a-glucose and C₂ of b-fructose. The reducing groups of glucose and fructose are involved in glycosidic bond, so it is a non-reducing sugar.

Ring structures:

Maltose:

Maltose is made up of two a-D-glucose (in pyranose form) units held together by a(1-->4) glycosidic bond. As there is a free aldehyde group at C-1 position of the second glucose molecule, maltose is known as reducing sugar. Maltose forms osazones. The enzyme that hydrolyses maltose is maltase.

lactose:

Lactose is made up of b-D-galactose and b-D-glucose held together by b(1-->4) glycosidic bond. As the aldehyde group at C-1 position of glucose is free, lactose is known as reducing sugar. Lactose forms osazones.

Partial representation  of structure  of  starch:

Starch is a white amorphous powder, insoluble in cold water. 

It solution in water gives a blue color with iodine solution. 

The blue color disappears on heating and reappears on cooling. 

Partial Representation of structure of 

cellulose:

It is a colourless amorphous solid which decomposes on heating. 

It is largely linear and its individual strands align with each other through multiple hydrogen bonds.

Glycogen:

The structure of glycogen consists of long polymer chains of glucose units connected by an alpha acetal linkage. 

The graphic on the left shows a very small portion of a glycogen chain. 

All of the monomer units are alpha-D-glucose, and all the alpha acetal links connect C # 1 of one glucose to C # 4 of the next glucose.

Carbohydrates are source of energy /functions:

1)Carbohydrates are most abundant dietary source of energy for all organisms.

2)They supply energy and serve as storage form of energy.

3)Carbohydrates such as glucose, fructose, starch, glycogen, etc. provide energy for functioning of living organisms.

4)Carbohydrates are utilizes as raw materials for several industries. For e.g., paper, plastics, textiles etc.

5)Polysaccharides like cellulose act as chief structural material for cell walls in plants.

6)Carbohydrates participate in cellular functions such as cell growth, adhesion and fertilization

Chemical Bonding

Chemical bond:-  

Chemical bond is the attractive force which holds together the constituents atoms or ions  or molecules present in a substance.

There are three types of chemical bonds: 

Ionic Bond or electrovalent bond

Covalent Bond

Co-ordinate Bond.



Octet Rule: 


Atoms form chemical bonds in order to complete their octet i.e. eight electrons in their valence shell.




Ionic bond or electrovalent bond:

"Ionic bond is formed by the complete transfer of one or more electrons from the outermost energy shell of one atom to the outermost energy shell of another atom". 

Ex:-

When sodium (Na) and chlorine (Cl) are combined, the sodium atoms each lose an electron, forming cations (Na+), and the chlorine atoms each gain an electron to form anions (Cl−). These ions are then attracted to each other in a 1:1 ratio to form sodium chloride (NaCl).






Factors  favouring of Ionic bond:

1)low ionisation energy of the metal atoms.

2)Higher electron affinity of non-metal atoms.

3)Higher value of lattice energy of the resulting Ionic crystals.

4)Large radius of cations and small radius of anions.

5)Large differences of eletronegativity between the combining atoms.




Co-valent Bond:

A covalent bond is a force which binds atoms of same or different elements by mutual sharing of electrons.

Ex:-1:



 2:-







Factors favouring covalent bonds:



1)The combining atoms should have small difference in electronegativity.

2)The combining atoms should obtain octate structure by sharing one or more electrons.

3)High electron affinity.

4)Small atomic size.

5)High ionisation energy.





Bond Length:



"The distance between the nuclei of two atoms bonded together is called bond length".







The lengths of double bonds are less than the lengths of single bonds between the same two  atoms, and triple bonds are even shorter than double bonds.
Single bond > Double bond > Triple bond (decreasing bond length)




HYBRIDIZATION:


The mixing or merging of dissimilar orbitals of similar energies to form new orbitals is known as hybridisation.
               There are many different types of hybridization depending upon the type of orbitals involved in mixing such as sp3, sp2 , sp. sp3d. sp3d2 , etc.


Formation of methane (CH4):
    In methane carbon atom acquires sp3 hybrid states as described below: 
Here, one orbital of 2s-sub-shell and three orbitals of  2p-sub-shell of excited carbon atom undergo hybridization to  form four sp3 hybrid orbitals. 
  The process involving promotion of 2s-electron followed by hybridization.






 
As pointed out earlier the sp3 hybrid orbitals of carbon atom are directed towards the comers of regular tetrahedron.
Each of the sp3 hybrid orbitals overlaps axially with half filled Is-orbital of hydrogen atom constituting a sigma bond.


Because of sp3 hybridization of carbon atom, CH4 molecule has tetrahedral shape.. 


Formation of ethane:


In ethane both the carbon atoms assume sp3 hybrid state. 
One of the hybrid orbitals of carbon atom overlaps axially with similar orbital of the other carbon atoms to form sp3-sp3 sigma bond.
 The other three hybrid orbitals of each carbon atom are used informing sp3-s sigma bonds with hydrogen atoms. 






Each C-H bond in ethane is sp3-s sigma bond with bond length 109 pm. The C-C bond is sp3-sr sigma bond with bond length 154 pm.

Formation of ammonia (NH)3 molecule;


In NH3 molecule the nitrogen atom adopts sp3-hybrid state.
Three of sp3-hybrid orbitals of the N atom are used for forming sp3 (sigma) bonds with H atoms.
The fourth sp3-hybrid orbital carry lone pair of electrons.
The relatively larger lone pair bond pair interactions cause HNH angle to decrease from 109°.281 to 107°. 
The ground state, hybrid state of N atom and orbital overlap in are shown in Fig.










Formation of water (H2O) molecule.


In H2O molecule, oxygen atom adopts sp3 hybrid state.
Two of the sp3-hybrid-orbitals of oxygen contains lone pairs of electrons whereas the other two hybrid orbitals constitutesp3-scr (sigma) bonds with H atoms. 
The lone pair orbitals exert relatively greater repulsive interactions on bond pair-orbitals causing HOH angle to decrease from 109°.28′ to 104.5°. 
The hybridization Of O atom along with orbital overlap in  molecule are shown in Fig.