Biochemistry Flashcards

1
Q

what is width of plasma membrane

A

7-10 nm wide

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2
Q

what is the chemical composition of plasma membrane

A

43% lipids
49 % proteins
8 % carbohydrates

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3
Q

what are the types of lipids in cell membrane

A

Phospholipids (Lecithin & Cephalin)
Glycosphingolipids (Cerebrosides & Gangliosides)
Cholesterol

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4
Q

what is significance of lecithin in cell membrane

A

Lecithin is composed of units of choline, phosphoric acid, fatty acids and glycerol. … Without lecithin, the cell membranes would become less fluid, thus less permeable.

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5
Q

what is the significance of cephalin in cell membrane

A

Cephalin plays a role in membrane fusion. Fusion is the process by which two initially distinct lipid bilayers merge their hydrophobic cores, resulting in one interconnected structure.

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6
Q

what is the function of ganliosides in cell membrane

A

Gangliosides is a component of the plasma membrane that modulates cell signal transduction events.
The functions of gangliosides as specific determinants suggest its important role in the growth and differentiation of tissues as well a
s in carcinogenesis.

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7
Q

what is the significance of cholesterol in cell membrane

A

Cholesterol provides stability to the plasma membrane by limiting the movement of the phospholipids.
cholesterol in the cell membrane is to maintain stability, anchor other molecules.
Cholesterol acts as a bidirectional regulator of membrane fluidity because at high temperatures, it stabilizes the membrane and raises its melting point, whereas at low temperatures it intercalates between the phospholipids and prevents them from clustering together and stiffening.

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8
Q

write a short note on the fatty acids in cell membrane

A

They are also major component of cell membrane. 50% of fatty acid groups are saturated. The other half contains unsaturated and polyunsaturated fatty acids.
Oleic acid is the most abundant unsaturated fatty acids in animal membranes.
The degree of unsaturation determines the fluidity of the membranes.

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9
Q

which types of proteins form the cell membrane

A

Integral or intrinsic proteins
Peripheral or extrinsic proteins
Trans-membrane proteins
(span the whole width )

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10
Q

what is integral membrane protein and write about its signifiance

A

An integral membrane protein (IMP) is a type of membrane protein that is permanently attached to the biological membrane.
IMPs include transporters, linkers, channels, receptors, enzymes, structural membrane-anchoring domains, proteins involved in accumulation and transduction of energy, and proteins responsible for cell adhesion. Common examples are Insulin receptors, Glycophorin, Rhodopsins. Band-3 proteins etc

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11
Q

what is peripheral membrane protein and its significance in cell membrane

A

Peripheral membrane proteins are membrane proteins that adhere only temporarily to the biological membrane with which they are associated.
Peripheral enzymes participate in metabolism of different membrane components, such as lipids (phospholipases and cholesterol oxidases).

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12
Q

what is transmembrane protein and write about its significance

A

A trans membrane protein (TP) is a type of integral membrane protein that spans entirely the cell membrane to which it is permanently attached. Many trans membrane proteins function as gateways to permit the transport of specific substances across the membrane.

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13
Q

what are the major functions of membrane proteins

A
Transport
Enzymatic activity
Signal transduction
Cell-cell recognition
Intercellular joining
Attachment to the cytoskeleton and extracellular matrix (ECM)
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14
Q

which carbohydrates are present in cell membrane

A

Glycoproteins

Glycolipids

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15
Q

what is glycosylation

A

The carbohydrate is attached to the protein in a posttranslational modification. This process is known as glycosylation.

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16
Q

what is the significance og glycoprotein and give a detailed example

A

Glycoproteins are also often important integral membrane proteins, where they play a role in cell–cell interactions. One example of glycoproteins found in the body is mucins, which are secreted in the mucus of the respiratory and digestive tracts. The sugars when attached to mucins give them considerable water-holding capacity and also make them resistant to proteolysis by digestive enzymes.

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17
Q

what are glycolipids and write about their significance

A

Glycolipids are lipids with a carbohydrate attached by a glyosidic (covalent) bond. Their role is to maintain the stability of the cell membrane and to facilitate cellular recognition, which is crucial to the immune response and in the connections that allow cells to connect to one another to form tissues. They include glyceroglycolipids and glycosphingolipids.

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18
Q

what is glycocalyx and write about its significance

A

The glycocalyx, is a glycoprotein and glycolipid covering that surrounds the cell membranes. This viscous coating consists of several carbohydrate moieties of membrane glycolipids and glycoproteins, which serve as backbone molecules for support. Generally, the carbohydrate portion of the glycolipids found on the surface of plasma membranes helps these molecules contribute to cell–cell recognition, communication, and intercellular adhesion.

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19
Q

how are caveolae formed

A

The caveolae are formed by the curving inward of the inner leaflet of the plasma membrane an integral protein named caveolin forces the formation of caveolae which are involved in the membrane transport and rigidity

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20
Q

how are rafts formed and write about their structure

A

The rafts are made by the clustering of sphingolipid with cholesterol in the outer monolayer of the plasma membrane. The rafts appear to have receptors and signaling proteins.

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21
Q

write about the clinical significance of cell membrane

A

ALZHEIMER’S DISEASE: Oxidative stress in brain results in alterations in phospholipids that comprise the cell membrane and disrupts the functions of effected brain cells.
CYSTIC FIBROSIS: Defect in calcium ion channels for the unclear reasons in excess production of fluid in lungs

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22
Q

what are ion channels and describe their types

A

Ion channels are transmembrane channels, pore like structures composed of proteins”.

All channels have gates & are controlled by opening
and closing.

TYPES:

Ligand gated channels:
In this a specific molecule binds to a receptor and opens the channel.

Voltage gated channels:
These channels open or close in response to changes in membrane potential.

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23
Q

write a short note on simple or passive diffusion

A

It depends on concentration gradient of a particular substance across the membrane
The solute passes from higher concentration to lower concentration till equilibrium is reached
The process neither requires any carrier protein nor energy

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24
Q

write a short note on facilitated diffuision

A

It is similar to passive diffusion in that the solutes move along the concentration gradient.
But it differs from passive diffusion in that it requires a carrier protein or transport protein.
Energy is not required.

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25
write a short note on active transport
It occurs against a concentration gradient Energy is required 40% of the total energy requirement in a cell is utilized for active transport system Carrier or transport proteins are needed
26
write a short note on uniport
This system involves the movement of certain substance across the plasma membrane singly and independently of any other substance The transporter involved is called uniporter
27
write a short note on symport
This system involves the movement of two substances across the membrane together & in the same direction The transporter involved is called symporter
28
write a short note on antiport an give an example
Also called counter transport This system involves the movement of two different substances simultaneously, but in two different directions Example: Efflux of 3 Na + ions to cell exterior & a simultaneous influx of 2 K+ ions
29
what are the mechanisms for transport of macromolecules
``` The mechanism of transport of macromolecules such as proteins, hormones, immunoglobulins, LDL, and even viruses takes place across the membrane by two independent mechanisms Exocytosis Endocytosis Phagocytosis = “cellular eating” Pinocytosis = “cellular drinking ```
30
what is exocytosis
In exocytosis, transport vesicles migrate to the membrane, fuse with it, and release their contents. Many secretory cells use exocytosis to export their products.
31
what is endocytosis
In endocytosis, the cell takes in macromolecules by forming vesicles from the plasma membrane. Endocytosis is a reversal of exocytosis, involving different proteins
32
describe the types of endocytosis
Phagocytosis (cellular eating): Cell engulfs particle in a vacuole Pinocytosis (cellular drinking): Cell creates vesicle around fluid Receptor-mediated endocytosis: Binding of ligands to receptors triggers vesicle formation
33
describe the activity of sodium potassium pump and its significance
Transports sodium from inside to outside the cell and at the same time pumps K+ from outside to inside the cell. Maintain sodium and potassium concentrations Establishing a negative electrical voltage inside the cells Complex of two separate globular proteins  subunit, with a molecular weight of about 100,000. β subunit, with a molecular weight of about 55,000. It has three receptor sites for binding sodium ions on the portion of the protein that protrudes to the inside of the cell. It has two receptor sites for potassium ions on the outside. The inside portion of this protein near the sodium binding sites has ATPase activity
34
write about the primary active transport of calcium
Calcium is actively transported from inside to outside the cell by calcium pump. Energy is obtained from ATP by the catalytic activity of ATPase. Present in the sarcoplasmic reticulum of muscle cells and the mitochondria of all the cells.
35
write about the primary active transport of hydrogen ions
In the gastric glands of the stomach Involved in the formation of hydrochloric acid In the late distal tubules and cortical collecting ducts of the kidneys Hydrogen ions are secreted from the blood into the urine
36
what is the biochemical importance of carbohydrates
Glucose is major metabolic fuel for mammals & is precursor for synthesis of all other carbohydrates in the body Glycogen for storage Ribose & deoxyribose in nucleic acids Galactose in the lactose of milk (milk sugar) Carbohydrates occurs in cell membranes as glycoproteins & glycolipids Present in lipoproteins Diseases related to CHO metabolism include galactosemia, lactose intolerance, glycogen storage diseases, diabetes mellitus
37
what are carbohydrates
Poly hydroxy aldehydes or Poly hydroxy ketones
38
describe classification of carbohydrates
``` Monosaccharides Disaccharides Oligosaccharides Polysaccharides Derived carbohydrates ```
39
write a short note on monosaccharides
Monosaccharides are simple sugars Can not be further hydrolyzed A carbonyl group (aldehyde or ketone) & several hydroxyl groups Eg. Glucose, fructose, galactose General formula (CH2O)n ( n= 3 or some larger number
40
write a short note on disaccharides
Those sugars which yield two molecules of the same or different monosaccharides on hydrolysis The two monosaccharides are linked by a glycosidic bond Eg. lactose, sucrose, maltose, isomaltose, trehalose General formula Cn(H2O)n-1
41
what are glucose dimers
Maltose α 1-4 linkage…..isomaltose α 1-6 linkage…..trehalose α 1-1 linkage…..all are glucose dimers
42
write a short note on oligosaccharides
Those sugars which yield 3 to 10 monosaccharides on hydrolysis Monosaccharides are joined to each other covalently through O- glycosidic bonds or linkages E.g α dextrins ( polymer of eight glucose molecules)
43
write a short note on polysaccharides
``` Those sugars which yield more than 10 molecules of monosaccharides on hydrolysis General formula (C6H10O5)n Further divided into Homopolysaccharides (homoglycans) Heteropolysaccharides (heteroglycans) ```
44
what are homopolysaccharides
Polymer of same monosaccharide units | Eg . Starch, glycogen, dextrin, dextran, cellulose
45
what are heteropolysaccharides
Polymer of different monosaccharide units Eg. Mucopolysaccharides ( GAGs) Glycoconjugates, Mucilages
46
write a short note on complex/derived carbohydrates and their examples
Derived from carbohydrates by various reactions Eg. Oxidation products, reduction products, amino sugars, deoxy sugar Oxidation… gluconic acid glucaric acid ascorbic acid……. Reduction… polyhydroxy alcohols-glycerol….. Amino sugar ….glucosamine….. Deoxysugar… deoxyribose
47
monosaccharides can be classified into
aldoses | ketoses
48
aldoses can be classified into -------- according to number of carbon atoms
``` triose (3 C atoms) (glyceraldehyde) tetrose (4 C atoms) (erythrose) pentose (5 C atoms) (ribose) hexose (6 C atoms) (glucose, galactose, mannose) heptose (glucoheptose) ```
49
ketoses can be classified into --------- according to number of carbon atoms
``` tritulose (dihydroxy acetone) tetrulose (4 C atoms) (erthrulose pentulose (5 C atoms) (ribulose) hexulose (6 C atoms) (fructose) heptulose (sedoheptulose) ```
50
what are disaccharides and give some examples
A disaccharide consists of two monosaccharides. Glucose + Glucose Maltose + H2O Glucose + Galactose Lactose + H2o Glucose + Fructose Sucrose + H2o
51
what is fisher projection
straight chain representation | 3D structure of stereoisomers can easily be drawn and represented in 2D
52
what is harworth projection
simple ring in perspective
53
what are conformational representation
chair and boat configuration
54
what are hemiacetal and hemiketal
aldehyde and alcohol from hemiacetal ketone and alcohol form hemiketal
55
write a short note on D-glucose
Found in fruits, corn syrup, and honey. An aldohexose with the formula C6H12O6. Known as blood sugar in the body. The monosaccharide in polymers of starch, cellulose, and glycogen.
56
write a short note D-fructose
Is a ketohexose C6H12O6. Is the sweetest carbohydrate. Is found in fruit juices and honey. Converts into glucose in the body.
57
write a short note on D - galactose
``` An aldohexose C6H12O6 Not found free in nature. Obtained from lactose, a disaccharide A similar structure to glucose except for the –OH on C4. ```
58
how are glyosidic bonds formed
Glycosidic bonds are formed by the enzymes glycosyl transferases that use nucleotide sugars as substrate
59
write a short note on maltose
Maltose, a cleavage product of starch (e.g., amylose), is a disaccharide with an a(1® 4) glycosidic link between C1 - C4 OH of 2 glucoses. It is the a anomer (C1 O points down).
60
write a short note on sucrose
common table sugar, has a glycosidic bond linking the anomeric hydroxyl of glucose & fructose, the linkage is α (12)
61
write a short note on lactose
milk sugar, is composed of galactose & glucose, with β (14) linkage from the anomeric OH of galactose
62
what is inversion phenomenon
In free form fructose occurs in pyranose form which is strong levorotatory Rotation is reversed & process is called inversion phenomenon Product of sucrose hydrolysis ( fructose) is called invert sugar
63
write a short note on reducing and non-reducing sugars
Sugars having atleast one free aldehyde or keto group in their structure are Reducing sugars Those which do not have any free active group (aldehyde or keto) are known as Non-reducing Sugars All monosaccharides & disaccharides are reducing except sucrose A non-reducing sugar can be hydrolyzed using dilute hydrochloric acid. After hydrolysis and neutralization of the acid, the product may be a reducing sugar
64
what are structural and storage polysaccharides
Storage polysaccharides contain only α-glucose units. Important ones are starch & glycogen Structural polysaccharides contain only -glucose units. Important ones are cellulose and chitin. Chitin contains a modified -glucose unit
65
write a short note on starch
Starch is a storage compound in plants, and made of αD-glucose units It is a homo-polymer of glucose made up of two components: amylose and amylopectin. Starch is 15-20% amylose and 80-85% amylopectin It is also non-reducing (because no potential aldehyde group
66
describe amylose
Amylose – a straight chain structure formed by α 1→4 glycosidic bonds between α-D-glucose molecules. The amylose chain forms a helix or coiled structure
67
describe amylopectin structure
Amylopectin-a glucose polymer with mainly α -(14) linkages, but it also has branches formed by α -(16) linkages
68
what is the action of enzymes on starch
Salivary & pancreatic amylases (α-amylases) hydrolyze starch into Maltose Maltotriose α- dextrins
69
write a short note on starch
Structural polysaccharide It is an unbranched polymer of -D-glucose mainly present in plant kingdom Consists of large number of glucose residues joined to each other through (1→4) linkages Cellulose is made up of repeating disaccharide units called cellubiose Cellubiose has same structure as maltose, but unlike maltose it has (1→4) glycosidic linkage
70
write about significance of cellulose
Cellulose is important in our diet because it Provides fiber & bulk to the food Serves to satisfy appetite & Assists with digestive movements in the small and large intestine Humans can not digest cellulose because they lack the enzyme cellulase to hydrolyze the (1→4) glycosidic bond
71
write a short note on glycogen
Homo-polymer of α D-glucose Storage polysaccharide also known as animal starch Present in liver & muscles Resembles amylopectin but it is more compact A glucose polymer with mainly α -(14) linkages, but also has branches formed by α -(16) linkages Glycogenesis Glycogenolysis
72
what are dextrins
Intermediate products in the hydrolysis of starch by acids or enzyme amylase Each dextrin molecule consists of 8 α D-glucose residues showing mostly α -(14) linkages in addition to α -(16) linkage at each of branching site Sweet in taste
73
what are dextrans
Dextrans homo-polymer of α D-glucose residues Showing mostly α -(16) linkages in addition to (12), (13) & (14) linkages Used in medicine as plasma substitute or plasma extender in the treatment of hypovolemic shock
74
what are lipids
Heterogeneous group of organic compounds” | Soluble in organic solvents but in soluble in water
75
what is the biomedical importance of lipids
``` High energy dietary constituent Lipoprotein (lipid transporter) Structural components (plasma membrane) Protective covering to internal organs Production of hormones Fat soluble vitamins ```
76
lipids are classified into
simple lipids compound lipids derived lipids
77
simple lipids are derived into
fats | waxes
78
simple fats are
neutral fats/ triglycerides | esters of fatty acids with glycerol
79
what are waxes and their types
``` Esters of fatty acids with long chain alcohols 1. True Waxes Bees Wax, Lanolin, Spermaceti 2. Others Waxes Cholesterol Esters, Vitamins A & D Lipase can not hydrolyze waxes ```
80
compound lipids include
``` phospholipids sulfolipids gangliosides glycolipids lipopolysaccharides lipoproteins ```
81
phospholipids include
glycerophospholipids (lecithin, cephalin, plasmalogens) sphingophospholipids (sphingomyelins)
82
derived lipids include
``` diglyceride fatty acids alcohols cholesterol fat soluble vitamins ```
83
what are fatty acids and their characteristics
“Aliphatic Mono-carboxylic Acids” Double bonds are always spaced at 3-Carbon intervals from each other ``` Numbered from carboxyl end CH3-R-COOH Even number of carbon atoms Unbranched Saturated or unsaturated Cis or Trans ```
84
what are the properties of enzymes
``` Protein catalysts ( except Ribozymes) ``` Increases the velocity of chemical reactions Not consumed during reactions they catalyze
85
what are catalysts
Speeds up chemical reactions in living organisms by decreasing the energy needed to start the reaction (activation energy)
86
describe the location of enzymes
Enzymes are localized in specific organelles within the cell | This isolation separates reaction substrates or products from other competing reactions
87
what are characteristic of enzymes
Enzymes are highly specific, interacting with one or few substrates & catalyzing only one type of chemical reaction Enzyme catalyzed reactions are faster than un catalyzed reactions Each enzyme molecule is capable of transforming 100-1000 substrate molecules into product each second.
88
what is turnover number
The number of molecules of substrate converted to product per enzyme molecule per second is called the turnover number
89
what are the mechanisms of enzyme catalysis
Lock & key model | Induced fit model
90
what is lock and key hypothesis
Enzyme and substrate both are rigid structures | Both fit in each other just like a specific key fix in a lock
91
what is induced fit model
Enzyme will induce change in its shape when substrate comes close to fit in it
92
what are the classifications of enzymes
site of action (intracellular/extracellular) source of enzymes (plants, animals) chemical composition (simple/conjugated) type of reaction (hydrolase, oxidase, dehydrogenase) type of substrate(proteinn, carb, lipids)
93
what is composition classification of enzyme
simple enzymes (composed completlyof protein) complex enzymes (composed of protein plus non-protein part) holoenzymes are complex enzymes protein component is called apoenzyme
94
what is holoenzyme
active enzyme with its non-protein component
95
what is co-factor
non protein part | usually metal ion of iron and zinc
96
what is co enzyme and its types
Non-protein part is a small organic molecule Coenzyme A & NAD+ Transiently associated coenzyme = Co-Substrate Permanently associated coenzyme= Prosthetic Group
97
what are the factors that affect enzyme activity
``` Enzyme concentration Substrate concentration Temperature pH Product concentration Presence of cofactors, coenzymes & prosthetic group Inhibitors ```
98
what is the effect of enzyme concetration on rate of reaction
directly proportional
99
what is the effect of substrate concetration on rate of reaction
Enzyme reaction is directly proportional to the substrate concentration Substrate concentration α velocity of reaction When the maximum velocity is achieved the increasing concentration of substrate does not further increase the reaction rate
100
what is the effect of temperature on rate of reaction
Optimum temperature Humans … 35 C- 40 C The reaction velocity increases with temperature until a peak velocity is reached Further elevation of the temperature results in a decrease in reaction velocity (denaturation of the enzyme)
101
what is the effect of ph on rate of reaction
Enzymatic activity is maximum at optimum pH Optimum pH is different for different enzymes e.g Pepsin ---pH 2 Extreme changes in pH may denature enzyme The reaction rate is decreased
102
what is the effect of product conc on rate of reaction
Excess of products may lower the enzymatic reaction by occupying the active site of the enzyme Reaction slows down or stops
103
what is the effect of inhibitors on rate of reaction
Enzymes are proteins which can be inactivated by the agents known inhibitors & this process is known as enzyme inhibition Inhibitors of enzymes generally resemble particular enzymes substrate(s) Many therapeutic drugs are some type of enzyme inhibitor
104
what is optimum ph for enzymes in humans
Optimum pH of most enzymes is 4-9 Exceptions: Digestive enzymes in stomach (pH 2) Digestive enzymes intestine (pH 8)
105
what are inhibitor and their types
Enzyme inhibitors inhibits the enzyme activity ``` Two types Reversible inhibition (noncovalent bonds) Competitive Noncompetitive (mixed) Uncompetitive Irreversible inhibition (covalent bonds) ```
106
what are reversible competitive inhibitors
These are chemicals that resemble an enzyme’s normal substrate and compete with it for the active site Increasing the conc. of substrate can reverse this type of inhibition
107
what are reversible non-competitive inhibitors
Do not enter the active site, but binds to another part of the enzyme change its shape & alters the active site Increasing the conc. of substrate cannot reverse this type of inhibition
108
what is non-competitive inhibition
An uncompetitive inhibitor binds to the enzyme substrate complex but not to free enzyme The effect of an uncompetitive inhibitor can not be overcome by high concentrations of the substrate Result in the destruction or modification of an essential amino acid required for enzyme activity Suicide inhibitors
109
what are allosteric enzymes
Allosteric means “occupy different sites” In addition to active sites these enzymes possess other sites where certain reagents called effectors ( modifiers & modulators) can bound Non-covalent linkages e.g cAMP, cGMP Allosteric enzyme + effector = change in 3 dimensional structure of enzyme Inhibition or activation of enzyme activity
110
what are nucleic acids
These are non protein nitrogenous substances made up of a monomeric unit called a nucleotide.
111
what are nucleic acids and its types
These are non protein nitrogenous substances made up of a monomeric unit called a nucleotide. DNA and RNA
112
what are nucleic acids types
DNA and RNA
113
what are the bases and nucleosides
``` adenine (adenosine) guanine (guanosine) cytosine (cytidine) uracil (uridine) thymine (thymidine) ```
114
what is nucleoside
base plus sugar
115
what the nucleosides in DNA
ATGC
116
what are the nucleosides in RNA
AUGC
117
what are purines and examples
two rings structure | AG
118
what are pyrimidine
one ring structure | TCU
119
what is the significance of phosphate group
Used to form phosphodiester linkage between 5’ and 3’ carbons of adjacent nucleotides in order to form polynucleotide chains.
120
number of hydrogen bonds between two nucleotides
AT 2 AU 2 GC 3
121
structure of DNA is
double stranded helix
122
describe detailed structure of DNA
In crystalline DNA the bases are separated by 0.34nm and each base is rotated 36 in relation to the previous base . The helical structure repeats at interval of 3.4nm . Therefore there are 10 base pairs in each completed helix . The helix is 2nm in diameter . The molecule shows a minor groove and a major groove . These grooves wind along the molecule parallel to the phosphodiester linkage . These grooves serves to accommodate proteins which binds with specific nucleotide sequences without disturbing the base pairing of double helical DNA molecule
123
what are the types of DNA replication
conservative | semi-conservative
124
write a short note on DNA replication
DNA in the chromosomes replicates itself every cell division . Maintains correct genetic information . Two strands of DNA unwind . Each strand acts like a template . New bases pair with their complementary base. Two double helixes are formed that are copies of original DNA .
125
why is DNA called genetic material
Present in all cells and virtually restricted to the nucleus . The amount of DNA in somatic cells (body cells) of any given species is constant (like the number of chromosomes) . The DNA content of gametes (sex cells) is half that of somatic cells. In cases of polyploidy (multiple sets of chromosomes) the DNA content increases by a proportional factor . The mutagenic effect of UV light peaks at 253.7nm. The peak for the absorption of UV light by DNA .
126
why do we need both DNA and RNA
DNA holds all the genetic information/instructions for the proteins produced in a cell so why do we need RNA. It is bcause DNA holds all the genetic information, this means it is Extremely important. If DNA is damaged in any way, the coding sequence can change and a mutationwill arise that will potentially influence the particular protein and perhaps the whole cell or organism. If DNA ventured into the cytoplasm to give instructions for protein synthesis it would be vulnerable to damage from chemicals, UV radiation and other mutagens. RNA acts as a massenger. Damage to mRNA will not permanently affect function of the cell as the DNA template is undamaged.
127
what are the steps involved in DNA replication
Identification of site of origin of replication Unwinding the DNA molecule Formation of replication fork Initiation and elongation Formation of replication bubble and ligation
128
describe the process of unwinding in DNA molecule
Replication of DNA begins at a sequence of nucleotides called the origin of replication. An enzyme called helicase unwinds the dsDNA helix and single-stranded binding proteins (SSBP) react with the ssDNA and stabilize it. At the same time, DNA gyrase relieves the strain that unwinding causes on the molecule by cutting, winding and rejoining DNA strands. Under an electron microscope the unwound section looks like a “bubble” and thus is known as the replication bubble.
129
describe step of the formation of new stands in DNA replication
DNA polymerase III is the major enzyme involved in DNA replication. It adds nucleotides to the 3’ end of a pre-existing chain of nucleotides thus generating a new complementary strand of DNA, but it cannot initiate a nucleotide chain. An RNA polymerase called primase is needed to start a new nucleotide chain. Primase constructs an RNA primer (sequence of about 10 nucleotides complementary to the parent strand) which DNA polymerase III can then add nucleotides to. The unwound DNA exposes two parental strands of DNA which are antiparallel. This means they are orientated in different directions and must be replicated by different mechanisms. The leading strand elongates towards the replication fork (in the direction of unwinding) by the simple addition of nucleotides to is 3’ end by DNA polymerase III. The lagging strand must elongate away from the replication fork. It is synthesized discontinuously as a series of short segments called Okazaki fragments. When DNA polymerase III reaches the RNA primer on the lagging strand, it is replaced by DNA polymerase I, which removes the RNA primer and replaces it with DNA. DNA ligase then attaches and forms phosphodiester bonds. Since each new strand is complementary to its old template strand, two identical new copies of the DNA double helix are produced during replication. In each new helix, one strand is the old template and the other is new synthesised, therefore replication is said to be semi-conservative. The two DNA molecules rewind into the double-helices, then each double-helix is coiled around histone proteins and further wrapped up to form separate chromatids (still joined by a common centromere). The two chromatids will become separated in the cell division process to form two separate chromosomes
130
what is transcription
Process of RNA synthesis from DNA template is called transcription.
131
write a detailed note on transcription of DNA
Process of transcription begins when a section of DNA (a gene) unwinds and the bases separate exposing two single strands of DNA with unpaired bases. One of these strands act as a template for the formation of an mRNA molecule (it is transcribed). Individual nucleotides of RNA align with the exposed bases on the DNA template according to base pairing rules. And nucleotides are added to 3’ end of growing RNA molecule. The formation of the mRNA molecule is catalysed by the enzyme RNA polymerase. This molecule is actually referred to as pre-mRNA. It is complementary to the template strand but requires some post-transcriptional modification. Post-transcriptional modification of pre-mRNA or nuclear mRNA involves the removal of introns (non-coding regions within genes) and stitching together of exons (coding regions of genes). This process is known as RNA splicing. Following RNA splicing a chemical cap is added to the 5’ end of the molecule and a poly-A tail (string of A nucleotides) to the 3’ end. The 5’ cap enables efficient protein synthesis as it is part of the structure recognized by the small ribosomal subunit. The poly-A tail is also important for initiating translation. It also has a role in regulating the degradation of mRNA molecules in the cytoplasm.
132
what is translation
It is the process by which RNA synthesizes proteins.
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write a detailed note on transcription of mRNA
mRNA exits the nucleus through nuclear pores and binds to ribosomes within the cytoplasm. Translation of mRNA begins with the sequence AUG (start codon). Transfer RNAs (tRNA) bring specific amino acids to the ribosome and these are added to the growing polypeptide chain by condensation polymerisation. New amino acids are added to the carboxyl (COOH) end of the polypeptide. The tRNA drops away from the mRNA and acquires another specific amino acid from the pool in the cytoplasm. Each tRNA can only carry one type of amino acid. Translation ends when the ribosome reaches a stop codon – the tRNA molecules corresponding to the stop codons UAG, UGA and UAA don’t carry a amino acid. The mRNA is then released from the ribosome .
134
what are interons
sequences in the DNA that are not used to make mRNA or to make proteins they are not transcribed
135
what are exons
sequences in the DNA that are expressed or used to make mRNA and ultimately are used to make proteins
136
what is codon
Codon is the message on mRNA for specific aminoacid required for the protein, which is to b synthesized. Each codon consists of 3 consecutive nitrogenous bases ,e.g for phenylalanine there are two codons i.e UUU and UUC .
137
what is anticodon
Every codon has its specific anti codon . Anti codon has a sequence of 3 nitrogenous bases, which give the tRNA the specific property to recognize the site of codon present on mRNA. Nitrogenous bases of anti codon are complementary to the nitrogenous bases of the codons.
138
what is post translational modification
It is the modification of proteins after they have been synthesized . Proteins may b modified by phosphorylation, glycosylation ,hydroxylation and addition of other groups .
139
describe the four types of RNA
``` Messenger RNA (mRNA) Copied portion of coding DNA Carries genetic information from the DNA out of the nucleus into the cytoplasm ``` ``` Transfer RNA (tRNA) Transports amino acids to the ribosome during protein synthesis ``` ``` Ribosomal RNA (rRNA) Structural component of ribosomes ``` snRNA (snRNA) Involved in splicing of pre-mRNA message in the nucleus to remove introns
140
describe the structure of tRNA
Also called soluble RNA Largely in cytoplasm Small and single stranded At least 20 different tRNA molecules Consists of 75 nucleotides Their basis include A , G , C , U , pseudouridine , uracil 5 ribofuranoside and thymine in one loop A clover leaf structure H- bonds between bases All tRNA molecules contains 4 arms r loops Once a tRNA gene is transcribed, the RNA that is produced folds to form the shape of a three-leafed clover. This is a functional tRNA molecule. This tRNA is charged with the amino acid lysine at the amino acid attachment site. The anticodon UUU will bind to the complementary AAA sequence in the mRNA
141
what are the sources of calcium
``` • Sources in the diet • Milk • Yogurt • Cheese • Dark green vegetables • Fortified sources • Cereals • Bread • Orange Juice broccli figs spinach sesame seeds cabbage ```
142
what is daily requirement of calcium
Daily Recommended Intakes • 9-18 years = 1300 mg • 19-50 years = 1000 mg • 51 years and older =1200 mg
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what are he functions of calcium
``` Major component of bones and teeth •A small amount of calcium circulates in the blood •Essential for clotting of the blood •Aids in the normal functioning of the nerves, muscles, and heart ``` • Ca salts in bone provide structural integrity of the skeleton. • Ca is the most abundant mineral in the body. • The amount of Ca is balance among intake, storage, and excretion. • This balance is controlled by transfer of Ca among 3 organs: intestine, bone, kidneys. • Ca ions in extracellular and cellular fluids is essential to normal function of a host of biochemical processes • Neuoromuscular excitability and signal transduction • Blood coagulation • Hormonal secretion • Enzymatic regulation • Neuron excitation
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who is at risk of calcium deficiency
* Children and youth * Post-menopausal women * Elderly * People with poor diets, lacking in dairy food
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how to reduce risk of osteoporosis
Calcium in the diet • habitual exercise • avoidance of smoking and alcohol intake • avoid drinking carbonated soft drinks
146
describe the formation and resorption of bone with respect to age and gender
The total bone mass of humans peaks at 25-35 years of age. •Men have more bone mass than women. •A gradual decline occurs in both genders with aging, but women undergo an accelerated loss of bone due to increased resorption during perimenopause. •Bone resorption exceeds formation.
147
what is the relationship of calcium with blood
Ca2+ normally ranges from 8.5-10 mg/dL in the plasma. •The active free ionized Ca2+ is only about 48% 46% is bound to protein in a non-diffusible state while 6% is complexed to salt. •Only free, ionized Ca2+ is biologically active.
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what is the relationship of calcium with bone
• 99% of Ca is found in the bone. Most is found in hydroxyapatite crystals. Very little Ca2+ can be released from the bone– though it is the major reservoir of Ca2+ in the body.
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describe the intake of calcium
•About 1000 mg of Ca is ingested per day. •About 200 mg of this is absorbed into the body. •Absorption occurs in the small intestine, two mechanisms ve been proposed for absorption of calcium by gut mucosa 1/ simple diffusion and 2/ active transport .
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describe the storage of calcium
•The primary site of storage is our bones (about 1000 grams). • Some calcium is stored within cells (endoplasmic reticulum and mitochondria). •Bone is produced by osteoblast cells which produce collagen, which is then mineralized by calcium and phosphate (hydroxyapatite). •Bone is remineralized (broken down) by osteoclasts, which secrete acid, causing the release of calcium and phosphate into the bloodstream. •There is constant exchange of calcium between bone and blood
151
describe the excretion of calcium
The major site of Ca excretion in the body is the kidneys. •The rate of Ca loss and reabsorption at the kidney can be regulated. •Regulation of absorption, storage, and excretion of Ca results in maintenance of calcium homeostasis
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describe the characteristics of plasma calcium and its subfractions
•Occurs in two forms. Non- diffusible; This fraction cannot be dialyzed out bcoz it is in firm combination with negatively charged plasma proteins specially albumin and immunoglobulin. Its level is 3.4 to 4.4mg/dl Diffusible; It can b dialyzed out. It occurs in two subfractions. • Ionized calcium • Complexed calcium •Ionized calcium 50% • Protein-bound calcium 40% • 90% bound to albumin •Remainder bound to globulins •Calcium complexed to serum constituents 10% •Citrate and phosphate •The normal level of plasma calcium is 9-10 mg / dl •About 0.5 – 1 % of bone calcium is freely exchangeable i.e in chemical equilibrium with calcium in ECF •The exchange process is regulated primarily by the PTH, Active Vitamin D & Calcitonin
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what are the factors affecting calcium level in plasma
* Intestinal absorption * Excretion in urine * Amount of Ca absorbed from GIT * Parathyroid hormone * Inverse relation between plasma Ca and P levels * Plasma protein level * Renal excretion * calcitonin
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what are the actions of parathyroid hormone on bone
PTH acts to increase degradation of bone (release of calcium). - causes osteoblasts to release cytokines, which stimulate osteoclast activity - stimulates bone stem cells to develop into osteoclasts - net result: increased release of calcium from bone - effects on bone are dependent upon presence of vitamin D
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describe PTH general characteristics
PTH is synthesized and secreted by the parathyroid gland which lie posterior to the thyroid glands. •The blood supply to the parathyroid glands is from the thyroid arteries. •The Chief Cells in the parathyroid gland are the principal site of PTH synthesis. •It is THE MAJOR of Ca homeostasis in humans.
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how is PTH regulated
The dominant regulator of PTH is plasma Ca2+ . • Secretion of PTH is inversely related to [Ca2+]. •Maximum secretion of PTH occurs at plasma Ca2+ below 3.5 mg/dL. •At Ca2+ above 5.5 mg/dL, PTH secretion is maximally inhibited.
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describe the action of PTH
•The overall action of PTH is to increase plasma Ca2+ levels and decrease plasma phosphate levels. • PTH acts directly on the bones to stimulate Ca2+ resorption and kidney to stimulate Ca2+ reabsorption in the distal tubule of the kidney and to inhibit reabosorptioin of phosphate (thereby stimulating its excretion). • PTH also acts indirectly on intestine by stimulating 1,25-(OH)2 -D synthesis.
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what is the relationship between calcium and phosphate
Ca is tightly regulated with P in the body. • P is an essential mineral necessary for ATP, cAMP 2nd messenger systems, and other roles
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describe calcitonin with respect to calcium regulation
•Calcitonin acts to decrease plasma Ca2+ levels. •While PTH and vitamin D act to increase plasma Ca2+ -- only calcitonin causes a decrease in plasma Ca2+ . •Calcitonin is synthesized and secreted by the parafollicular cells of the thyroid gland. •They are distinct from thyroid follicular cells by their large size, pale cytoplasm, and small secretory granules. •Role of calcitonin in normal Ca2+ control is not understood—may be more important in control of bone remodeling. •Used clinically in treatment of hypercalcemia and in certain bone diseases in which sustained reduction of osteoclastic resorption is therapeutically advantageous. •Chronic excess of calcitonin does not produce hypocalcemia and removal of parafollicular cells does not cause hypercalcemia. PTH and Vitamin D3 regulation dominate. •May be more important in regulating bone remodeling than in Ca2+ homeostasis. The major stimulus of calcitonin secretion is a rise in plasma Ca2+ levels •Calcitonin is a physiological antagonist to PTH with regard to Ca2+ homeostasis The target cell for calcitonin is the osteoclast. •Calcitonin acts via increased cAMP concentrations to inhibit osteoclast motility and cell shape and inactivates them. •The major effect of calcitonin administration is a rapid fall in Ca2+ caused by inhibition of bone resorption.
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what are the actions of calcitonin
•The major action of calcitonin is on bone metabolism. •Calcitonin inhibits activity of osteoclasts, resulting in decreased bone resorption (and decreased plasma Ca levels).
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how does vitamin D facilitate calcium absorption
It facilitates intestinal absorption of calcium, as well as stimulates absorption of phosphate and magnesium ions. In the absence of vitamin D, dietary calcium is not absorbed at all efficiently. Vitamin D stimulates the expression of a number of proteins involved in transporting calcium from the lumen of the intestine, across the epithelial cells and into blood. The vitamin D form, 1,25-dihydroxcholecalciferol [1,25(OH)2D3], •stimulates the synthesis of the epithelial calcium channels in the plasma membrane calcium pumps , and • induces the formation of the calbindins. Once joined with ingested vitamin D, facilitate increased serum calcium levels Shows Expressed Calbindins and How this facilitate transport of Calcium through the Membranes •Calcium absorption is transport across the epithelial cell, which is greatly enhanced by the carrier protein calbindin, the synthesis of which is totally dependent on vitamin D
162
describe excretion of calcium
Reabsorption occurs in proximal convoluted tubules, thick ascending loop of Henle and in distal convoluted tubules amounting to 65%, 20%, and 10% respectively. 1… is coupled to Na+ reabsorption and takes place paracellularly. 2… is helped by protein paracellin & also paracellularly. 3… is occuring transcellularly. Ca enters the luminal surface of the cell through apical Ca channels followed by its entry into cell interior with calcium binding proteins Calbindin- D 28 K.
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what are the factor affecting absorption of calcium
``` Ph of intestinal milieu •Composition of the diet a) high protein diet b) fatty acids c) minerals d) sugars and organic acids • State of the health of the individual and old age •Hormonal a) PTH b) calcitonin c) glucocorticoids ```
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what is hypo and hyper calcium with their causes
Hypercalcemia Serum calcium level exceeds 11.0 mg/dl * Hyperparathyroidism * Malignancy * Over dosage of vitamins * Drug induced hypercalcemia * Acute renal failure Hypocalcemia When serum calcium less than 8.5mg/dl * Hypoparathyroidism * Renal disease * Hypoalbuminaemia * Neonatal hypocalcemia
165
what are macrominerals
required in amounts greater than 100mg/dl
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what are microminerals
required in amount less than 100mg/dl
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name the macrominerals
``` calcium MG K S Cl P Na ```
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what is the requirement of phosphorus
WBC contain 47mg P /dl as inorganic phosphate RBC contain more P than plasma Plasma contain more phosphorus than plasma it plasma level is 3-4.5 mg/dl in adults plasma level in children is 4-7 mg/dl (due to growth hormone) dietary requirement is 1.5g
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sources of P are
cheese milk nuts egg
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sources of iron are
Animal sources are the best and include liver, meat & egg yolk. • Plant sources include spinach and green leafy vegetables. • Milk is very low in iron. • Cooking in iron utensils increases iron content of food
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what is the function of iron
``` Helps in the formation of very important structures and compounds of the body e.g • Hemoglobin • Myoglobin • Cytochromes • Catalase ```
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describe absorption of iron
Only 10% of ingested iron is absorbed. • Absorption takes place at mid jejunum. • Iron is first converted to ferrous form. • It enters the intestinal mucosal cells by an energy dependant transport mechanism. • From the mucosal cells iron enters the plasma
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factors that increase iron absorption are
Increased erythropoieses e.g. At high altitude ,blood loss. • Decreased iron stores e.g. In iron deficiency anemia and also after multiple pregnancies. • Increased iron absorption e.g. in case of taking vitamin C with iron. • Inorganic form e.g. In iron supplements is absorbed very quickl
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factors that decrease iron absorption are
• Malabsorption as in steatorrhea, celiac disease. • Diarrhoea because there is less time for iron to stay in intestine. • Excess of phosphates and oxalates because these make insoluble complexes with iron preventing its absorption. • Antacid therapy.
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describe loss of iron from the body
* Males ....0.5 -1 mg of iron /day * Females....35-70 ml of blood/day * Women lose iron during and after pregnancy
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describe iron deficiency
• Iron deficiency leads to Hypochromic- microcytic anaemia
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what are the causes of iron deficiency
Nutritional deficiency of iron • Lack of absorption: Subtotal gastrectomy and hypochlorhydria • Hookworm infection: One hookworm will cause the loss of about 0.3 mL of blood per day.
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what is the required daily intake of iron
Adult - 20 mg of iron • • Children between 13–15 years need 20–30 mg/day. • Pregnant women need 40 mg/da
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sources of copper and its content in body
The body contains about 100mg coThe body contains about 100mg copper distributed in different organs. • Liver is the richest source • Copper distributed in different organs.
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describe absorption and secretion of cooper from the body
Only 5-10% of the ingested Cu is absorbed mainly in duodenum and the remaining passes out in feces. • Metallothionein is a transport protein that facilitates copper absorption. • Zinc and Molybedenum decrease copper uptake
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what are copper containing substances in the body
``` Ceruloplasmin • Erythrocuprin • Cerebrocuperin • Copper containing enzymes: • Cytochrome oxidase • Catalase • Tyrosinase • Monoamine oxidase ```
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what are the functions of copper
Copper is an essential constituent of several enzymes: • Cytochrome oxidase • Catalase • Tyrosinase • Monoamine oxidase • Hemoglobin synthesis • Lysyl oxidase (Cu containing enzyme): • It is required for the conversion of certain lysine residues of collegen and elastin to allysine which are necessary for cross-linking these structural proteins. • Ceruloplasmin serves as ferroxidase and is involved in the conversion of iron from Fe⁺⁺ to Fe⁺⁺⁺ ,a form in which iron is transported in plasm Copper is necessary for the synthesis of melanin and phospholipids. • Development of bone and nervous system require Cu. • Hemocyanin, a copper protein complex in invertebrates, functions like hemoglobin for O₂ transpor
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what is RDA of copper
Adults __ 2-3 mg/day | • Infants and children__ 0.5-2 mg/day
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what are the clinical disorder associated with copper
* Wilson’s disease | * Menke’s disease
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describe wilsons disease
Hepatolenticular degeneration) • In liver, lenticular nucleus of brain and the descements membrane of the cornea. • Diagnostic feature is the presence of Kaeyser Fleischer ring in the cornea
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describe menke's disease
Genetic disorder of poor Cu++ absorption. • Failure to grow • Mental deterioration • Degenerative changes in the metaphysis and in the elastin of aorta
187
what are sources of zinc
shellfish poultry meat mushrooms legumes whole grains
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what is the RDA of zinc
• Men: 11 mg/day • Women: 8 mg/day • The total content of zinc in an adult body is about 2 g. • Erythrocytes contain higher content of Zn (1.5 mg/dl) which is found in association with the enzyme carbonic anhydrase
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what are the functions of zinc
It is an essential component of several enzymes e.g Carbonic anhydrase, Alkaline phosphatase etc • It may be regarded as an antioxidant since the enzyme superoxide dismutase protects the body against free radical damage. • The storage and secretion of insulin from β-cells of pancreas require Zn. • It is required for wound healing • Gusten, a zinc containing protein of the saliva, is important for taste
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describe zinc deficiency
• Zinc deficiency is associated with growth retardation, poor wound healing, anaemia, loss of appetite, loss of taste sensation, impaired spermatogenesis . • Deficiency of Zn may result in depression, dementia and other psychiatric disorders. • Acrodermatitis Enteropathica: Rare inherited metabolic disease of zinc deficiency caused by defect in Zn absorption from intestine.
191
describe zinc toxicity
Is often observed in welders due to inhalation of zinc oxide fumes. • Manifested by nausea , gastric ulcer , pancreatitis and excessive salivation
192
what are the sources of sulfur
``` meat fish eggs cheese tea cocoa dried apricots ```
193
what are the functions of sulfur
Sulfur containing amino acids are important constituents of body proteins. • The disulfide bridges keep polypeptide units together, e.g. insulin, immunoglobulins. • Chondroitin sulfates are seen in cartilage and bone. • Keratin is rich in sulfur, and is present in hair and nail • Co-enzymes derived from thiamine, biotin, pantothenic acid and lipoic acid also contain sulfur. • Sulfates are also important in detoxification mechanisms, e.g. production of indoxyl sulfate
194
describe content, absorption, excretion of iodine
• The total body contains about 20 mg iodine, most of it (80%) being present in the thyroid gland. • It is mainly absorbed from the small intestine. • Iodine absorption also occurs through skin and lungs. • Its excretion mostly occurs through kidney & also through saliva, bile, skin and milk (in lactating women)
195
what is the RDA of iodine
ADULTS ➔ 100-150 µg/day | • PREGNANT WOMEN ➔ 200 µg/day
195
what are the sources of iodine
``` Sea foods • Drinking water • Vegetables • Fruits • Iodized salt ```
196
describe deficiency of iodine
* Simple Goitre: * Thyroxin function is low * Weight gain * Thick skin * Sleepiness * Coarse voice * Constipation.
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describe toxic goiter
``` Hyper functioning of the thyroid gland • Weight loss • Anxiety • Lack of sleep, • Fine tremors of fingers • Bulging eyes (Exophthalmos) • Diarrhoea ```
198
describe cretinism
Deficiency of Iodine in newborns may lead to hypothyroidism which may cause problems with brain growth.
199
what is RDA of selenium
• Upper level for adults: 400 g/day
200
what are the sources of selenium
Seafood, meat • Whole grains • Vegetables
201
what are the functions of selenium
Acts as co-factor of glutathione (an antioxidant tripeptide). • Defends against oxidation (antioxidant role). • Regulates thyroid hormone
202
describe role of selenium as antioxidant
Helps in lowering oxidative stress in the body, which reduces inflammation and enhances immunity
203
describe deficiency of selenium
• Predisposition to heart disease characterized by cardiac tissue becoming fibrous.
204
describe toxicity of selenium
Loss and brittleness of hair and nails • Skin rash, fatigue, irritability, and nervous system disorders • Garlic breath odor
205
what is the RDA of fluoride
Men: 3.8 mg/day. • Women: 3.1 mg/day. • Upper level for adults: 10 mg/day
206
what are chief functions of fluoride
* Involved in the formation of bones and teeth. | * Helps to make teeth resistant to decay
207
sources of flouride
* Drinking water (if fluoride containing or fluoridated). | * Tea, seafoo
208
describe deficiency of fluoride
• Susceptibility to tooth decay.
209
what are symptoms of fluoride toxicity
Fluorosis (pitting and discoloration of teeth).
210
what is RDA manganese
* Men: 2.3 mg/day * Women: 1.8 mg/day * Upper level for adults: 11 mg/day
211
what are the sources of manganese
Nuts • Whole grains • Leafy vegetables
212
what are the functions of manganese
: cofactor for many enzymes that metabolize carbohydates, | lipids and amino acids
213
what is the RDA of chromium
Men: 35 g/day. | • Women: 25 g/day.
214
what is the function of chromium
• Enhances insulin action.
215
what are sources of chromium
Meats (especially liver). | • Whole grains, brewer’s yeast
216
what are symptoms of chromium deficiency
Diabetes-like condition
217
what is RDA of molybdenum
for adults: 45 g/day. | • Upper level for adults: 2 mg/day.
218
what are sources of molybdenum
* Legumes, cereals. * Organ meats. * Reproductive effects in animals
219
what is the function of molybdenum
• Cofactor for several enzymes e.g. xanthine oxidase