1. multiple choice type questions (select the appropriate ...ggu.ac.in/download/model answer 14/lzc...
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Model AnswerFor Science
B Sc (Zoology Hon’s) Second Semester-2014
Zoology II paper
LZC 202: Biochemistry
SECTION A
1. Multiple choice type questions (Select the appropriate answer) 1 x 10 = 10
1). The protein present in hair is
(a) Elastin (b) Threonine
(c) Keratin (d) Gliadin
2) Neutral amino acid is
(a) Leucine (b) Lysin
(c) Aspartic acid (d) Histidine 3). Cholesterol is transported from liver to extrahepatic tissues by
(a) Chylomicrons (b) VLDL
(c) HDL (d) LDL
4). The major storage form of lipids is
(a) Esterified cholesterol (b) Glycerophospholipids
(c) Triglycerides (d) Sphingolipids
5) Isoelectric pH is that at which protein is electrically
(a) Neutral (b) Anionic
(c) Cationic (d) None of these
6). A Holoenzyme is
(a) Functional unit (b) Apoenzyme
(c) Coenzyme (d) All of these
7). The number of ATP molecules generted for each turn of the citric acid cycles is
(a) 8 (b) 12
(c) 24 (d) 38
8). Oxidation of one molecule of glucose yields
(a) 12 ATP (b) 24 ATP
(c) 36 ATP (d) 38 ATP
9). GAG triplet codon and is a
(a) Glycoseminoglycans (b) Monosaccharide
(c) Proteins (d) Fats
10). During the process of replication Direction of polymerization is
(a) 3′-5′ (b) 4′-5′
(c) 5′-3′ (d) 3′-4′
SECTION B
QII: Descriptive Type question.
Note: Attempt any four questions from this section 20 mark
1). “Water is best biological solvent” Justify the statement. (5)
Ans 2 Water as Biological Solvent
• A water molecule (H2O), is made up of three atoms --- one oxygen and two hydrogen.
• Water is Polar therefore- In each water molecule, the oxygen atom attracts more than its "fair share" of
electrons
• The oxygen end “acts” negative
• The hydrogen end “acts” positive
• Causes the water to be POLAR
• However, Water is neutral (equal number of e- and p+) --- Zer
Hydrogen Bonds Exist Between Water Molecules
Interaction Between Water Molecules- Negative Oxygen end of one water molecule is attracted to the Positive
Hydrogen end of another water molecule to form a HYDROGEN BOND
• At sea level, pure water boils at 100 °C and freezes at 0 °C.
• Other Properties, Cohesion, Adhesion, High Specific Heat, High Heat of Vaporization, Less Dense as a
Solid
• High Heat of Vaporization- Water's heat of vaporization is 540 cal/g.
• Water is Less Dense as a Solid
• One of the most valuable properties of water is its ability to dissolve.
• An individual water molecule has a bent shape with a H-O-H bond angle of approximately 105 degrees.
• Water is polar thus having positive & negative partial charges on its ends.
• The positive ends of a water molecule are attracted to negative cations and the negative ends are
attracted to positive cations in an ionic compound – this is called hydration.
• The ions become hydrated& move around independently.
Covalent Compounds in Water-
• Water also dissolves many nonionic substances such as ethanol (C2H5OH).
Ans 4: Different classes of enzymes and mechanism of action
OXIDOREDUCTASES:
To this class belong all enzymes catalysingoxidoreduction reactions. The substrate that is
oxidized is regarded as hydrogen donor. The systematic name is based
on donor:acceptoroxidoreductase. The common name will be dehydrogenase, wherever this is
possible; as an alternative, reductase can be used. Oxidase is only used in cases where O2 is the
acceptor.
TRANSFERASES:
Transferases are enzymes transferring a group, e.g. a methyl group or a glycosyl group, from one
compound (generally regarded as donor) to another compound (generally regarded as acceptor).
The systematic names are formed according to the scheme donor:acceptorgrouptransferase. The
common names are normally formed according to acceptor grouptransferase or donor
grouptransferase. In many cases, the donor is a cofactor (coenzyme) charged with the group to
be transferred. A special case is that of the transaminases
HYDROLASE:
These enzymes catalyse the hydrolytic cleavage of C-O, C-N, C-C and some other bonds,
including phosphoric anhydride bonds. Although the systematic name always
includes hydrolase, the common name is, in many cases, formed by the name of the substrate
with the suffix -ase. It is understood that the name of the substrate with this suffix means a
hydrolytic enzyme.
LYASES:
Lyases are enzymes cleaving C-C, C-O, C-N, and other bonds by elimination, leaving double
bonds or rings, or conversely adding groups to double bonds. The systematic name is formed
according to the pattern substrate group-lyase. The hyphen is an important part of the name, and
to avoid confusion should not be omitted, e.g. hydro-lyase not 'hydrolyase'. In the common
names, expressions likedecarboxylase, aldolase, dehydratase (in case of elimination of CO2,
aldehyde, or water) are used. In cases where the reverse reaction is much more important, or the
only one demonstrated, synthase (not synthetase) may be used in the name. Various subclasses of
the lyases include pyridoxal-phosphate enzymes that catalyse the elimination of a β- or γ-
substituent from an α-amino acid followed by a replacement of this substituent by some other
group.
ISOMERASES:
These enzymes catalyse geometric or structural changes within one molecule. According to the
type of isomerism, they may be called racemases, epimerases, cis-trans-isomerases, isomerases,
tautomerases, mutases or cycloisomerases.
LIGASES:
Ligases are enzymes catalysing the joining together of two molecules coupled with the
hydrolysis of a diphosphate bond in ATP or a similar triphosphate. The systematic names are
formed on the system X:Y ligase (ADP-forming). In earlier editions of the list the
term synthetase has been used for the common names. Many authors have been confused by the
use of the terms synthetase (used only for Group 6) and synthase (used throughout the list when
it is desired to emphasis the synthetic nature of the reaction). Consequently NC-IUB decided in
1983 to abandon the use of synthetase for common names, and to replace them with names of the
type X-Y ligase. In a few cases in Group 6, where the reaction is more complex or there is a
common name for the product, a synthase name is used (e.g. EC 6.3.2.11 and EC 6.3.5.1).
Mechanism of enzyme action.
The biological processes that occur within all living organisms are chemical reactions,
and most are regulated by enzymes. Without enzymes, many of these reactions would not take
place at a perceptible rate. Enzymes catalyze all aspects of cell metabolism. This includes the
digestion of food, in which large nutrient molecules (such as proteins, carbohydrates, and fats)
are broken down into smaller molecules; the conservation and transformation of chemical
energy; and the construction of cellular macromolecules from smaller precursors. Many inherited
human diseases, such as albinism, result from a deficiency of a particular enzyme. There are
several theories has been put forwarded by different biochemists to explain the mechanism of the
enzyme action.
(i) Lock and key thoery:
According to Emil Fisher only a specific substrate can combine with the active site of a
particular enzyme as a specific key fits to open a specific lock. In this enzyme molecule posses
an active site to fit correctly with the substrate forming ES complex. When reaction completed
ES complex breaks into products and enzymes. Enzymes remain intact.
(II) Inducted fit Theory:
According to Koshland, when a suitable substrate approaches the active site of an enzyme, the
substrate inducts some conformational changes in the enzyme as a result the attractive groups
and buttressing groups form a complementary structure so that the catalytic group of the active
site is in proximity of the bonds to be broken.
After the suitable enzyme substrate complex has been formed, the subtract molecule is held by
hydrogen bonds while a strain nucleophilic attack of the charged catalytic groups of the active
site. The strain weaker the bond which is ultimately broken and the products are formed.
4). Discuss stepwise Embden-Meyerhof pathway showing degradation of glucose to pyruvic
acid.
Answer 5: Glycolysis : Glycolysis (from glycose, an older term for glucose + -lysisdegradation) is
the metabolic pathway that converts glucoseC6H12O6, into pyruvate, The free energyreleased in this
process is used to form the high-energy compounds ATP (adenosine triphosphate) and
NADH (reduced nicotinamide adenine dinucleotide). Glycolysis is a determined sequence of
ten enzyme-catalyzed reactions. The intermediates provide entry points to glycolysis. For
example, most monosaccharides, such as fructose andgalactose, can be converted to one of these
intermediates. The intermediates may also be directly useful. For example, the
intermediate dihydroxyacetone phosphate (DHAP) is a source of the glycerol that combines with
fatty acids to form fats.
Glycolysis occurs, with variations, in nearly all organisms, bothaerobic and anaerobic.
The wide occurrence of glycolysis indicates that it is one of the most ancient known metabolic
pathways It occurs in the cytosol of the cell.
5). Answer 6: Triglycerides and functional significance
A. Simple lipids or Homolipids. These are esters of- fatty acid with farious alcohols.
1. Fats and oils (triglycerides, triacylglycerols).
These are esters of fatty acids with a trihydroxy alcohol, glycerol. A fat is solid at ordinary room
temperature wheras an oil is liquid.
2. Waxes. These are esters of fatty acids with high molecular weight monohydroxy alcohols.
B. Compound lipids or Heterolipids. These are - esters of fatty acids with alcohol and possess
additional group(s) also.
1. Phospholipids (phosphatids), These are compounds containing, in addition to fatty acids and
glycerol, a phosphoric acid, nitrogen bases and other Substituents.
2. Glycolipids (cerebrosides). These are the compounds of fatty acids with carbohydrates and
contain
nitrogen but no phosphoric acid. The glycolipids also include certain structurally-related compounds
comprising the groups, gangliosides, sulfolipids and sulfatids.
C. Derived lipids. These are the substances derived -from simple and compound lipids by hydrolysis.
These include fatty acids, alcohols, mono- and diglycerides, steroids, terpenes and carotenoids.
Glycerides and cholesterol esters, because of their uncharged nature, are also called neutral lipids
Triglycerides (TAG) - Simple lipids/ Homolipids
constitute about 98% of total dietary lipids ; the remaining 2% consists of phospholipids and cholesterol
and its esters. They are the major components of storage or depot fats in plant and animal cells but are
not normally found in membranes. They are nonpolar, hydrophobic molecules since they contain no
electrically charged or highly polar functional groups. In animals, the fat cells or adipocytes contain
very large quantities of triglycerides in the form of fat droplets, which fill almost the entire cell
volume . Adipocytes are abundantly found under the skin, in the abdominal cavity and in the
mammary glands. Triglycerides can be stored in quantities, sufficient to supply the energy needs of the
body for many months, as in the case of obese persons. Triglycerides are much better adapted than
glycogen to serve as storage form of energy. They are not only stored in large amounts but also yield
over twice as much energy as carbohydrates. Since fats tend to remain in the stomach longer than
carbohydrates and are digested more slowly, they also have greater satiety value than carbohydrates.
The arctic and antarctic animals (Fig. 13-2) such as whales, seals, walruses and penguins are amply
padded with triglycerides to serve both as energy storage depots and as an insulation against very low
temperatures. Most fats and oils, upon hydrolysis, yield several fatty acids as well as glycerol.
However, the milk of spiny anteater is an exception in that it comprises almost pure triolein. Human
body contains enough fat to make 7 bars of soap. TAG is found in all organs of the human body,
particularly in adipose tissue, in which droplets of triacylglycerols may represent more than 90% of the
cytoplasm of the cells. Body lipid is a reservoir of potential chemical energy. About 100 times more
energy is stored asmobilizable lipid than as mobilizablecarbohyldrate in the normal human being.
TAG is stored in a relatively water-free state in the tissue, in comparison to carbohydrate, which is
heavily hydrated.Chemically, triglycerides are esters of glycerol with 3 fatty acid molecules.
Optically active forms of triglycerides - When the groups attached to carbon 1 and 3 differ, a centre of
asymmetry is created at C 2. The 2 optical isomers may, thus, be represented- The naturally-occurring
fats are of L-type.
Simple triglycerides- A fat molecule contains 3 moles of fatty acids which may be similar or dissimilar.
Those containinga single kind of fatty acid in all 3 positions (α, β, α′) are called simple (or
symmetrical) triglycerides ;they are named after the fatty acids they contain . Ex. tripalmitin,
tristeariand triolein. They occur in natural fats. Such simple triglycerides have, however, been
synthesized in the laboratory e.g., tristearin and triolein
Mixed triglycerides- Most of the triglycerides of nature are mixed (or asymmetrical) triglycerides, i.e.,
they contain 2 or 3 different fatty acid units in the molecule. Representatives of such mixed
triglycerides are oleodipalmitin and oleopalmitostearin
6). Write an account on Watson – Crick DNA double helix structure with diagrammatic illustration. (5)
7) Answer the following (any two): 2.5 x 2 = 5
Initiation of Replication
For a cell to divide, it must first replicate its DNA. This process is initiated at particular
points in the DNA, known as "origins", which are targeted by initiator proteins.In E. coli this
protein is DnaA; in yeast, this is the origin recognition complex. Sequences used by initiator
proteins tend to be "AT-rich" (rich in adenine and thymine bases), because A-T base pairs have
two hydrogen bonds (rather than the three formed in a C-G pair) which are easier to unzip. Once
the origin has been located, these initiators recruit other proteins and form the pre-replication
complex, which unzips the double-stranded DNA.
2. Prostaglandin
The prostaglandins are a group of lipid compounds that are derived enzymatically from fatty acids and have
important functions in the animal body. Every prostaglandin contains 20 carbon atoms, including a 5-carbon
ring.They are mediators and have a variety of strong physiological effects, such as regulating the contraction and
relaxation of smooth muscle tissue. Prostaglandins are not endocrine hormones, but autocrine or paracrine, which
are locally acting messenger molecules. They differ from hormones in that they are not produced at a discrete site
but in many places throughout the human body. Also, their target cells are present in the immediate vicinity of the
site of their secretion (of which there are many).The prostaglandins, together with
the thromboxanes and prostacyclins, form the prostanoid class of fatty acid derivatives, a subclass of eicosanoids.
The abbreviation for "prostaglandin" is PG; specific prostaglandins are named with a letter (which indicates the type
of ring structure) followed by a number (which indicates the number of double bonds in the hydrocarbon structure).
For example, prostaglandin E1 is abbreviated PGE1 or PGE1, and prostaglandin I2 is abbreviated PGI2 or PGI2. The
number is traditionally subscripted when the context allows, but as with many similar subscript-containing
nomenclatures, the subscript is simply forgone in many database fields that can store only plain text (such
as PubMed bibliographic fields), and readers are used to seeing and writing it without subscript.
Function
There are currently ten known prostaglandin receptors on various cell types. Prostaglandins ligate a sub-
family of cell surface seven-transmembrane receptors, G-protein-coupled receptors. These receptors are
termed DP1-2, EP1-4, FP, IP1-2, and TP, corresponding to the receptor that ligates the corresponding
prostaglandin (e.g., DP1-2 receptors bind to PGD2).
The diversity of receptors means that prostaglandins act on an array of cells and have a wide variety of
effects such as:
cause constriction or dilation in vascular smooth muscle cells
cause aggregation or disaggregation of platelets
sensitize spinal neurons to pain
induce labor
decrease intraocular pressure
regulate inflammatory mediation
regulate calcium movement
control hormone regulation
control cell growth
acts on thermoregulatory center of hypothalamus to produce fever
acts on mesangial cells in the glomerulus of the kidney to increase glomerular filtration rate
acts on parietal cells in the stomach wall to inhibit acid secretion
brain masculinization (in rats)
Prostaglandins are potent but have a short half-life before being inactivated and excreted. Therefore, they
send only paracrine (locally active) or autocrine (acting on the same cell from which it is synthesized)
signals.
3. Enzyme distribution on mitochondrial membrane
4. 30S initiation complex
30S INITIATION COMPLEX
• Formation of Initiation complex involves protein initiation factors
• IF-3 keeps ribosome subunits apart
• IF-2 identifies and binds initiator tRNA. IF-2 must bind GTP to bind tRNA.
• IF-1, IF-2, and IF-3 bind to 30S subunit to form initiation complex
• Once 50S subunit binds initiation complex, GTP is hydrolyzed, initiator tRNA enters P-
site and IFs disassociate