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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5337_Библиотеки_им_академика_М_И_Перельмана.pdf
19. Endoplasmic reticulum is a term that was coined by
A. Camillo Golgi B. Fleming
C. Robert Brown D. Benda
20. rRNA is synthesised by __________
A. Cytoplasm B. Golgi body
C. Nucleolus D. Nucleus
21. Which of the following statements is/are true
regarding ER?
A. ER provides a structural framework to the cell
B. ER acts as intracellular transporting system
C. SER is involved in the synthesis of lipid
D. All of the above
22. Which of the following inhibitors blocks
translation in eukaryotes?
A. Cyclohexamine B. Tetracycline
C. Puromycin D. Streptomycin
23. The term Golgi apparatus was coined by:
A. Camillo Golgi B. Robert Brown
C. Robert Hook D. Benda
24. The most abundant blood cells in the human body
are:
A. WBCs B. RBCs
C. Platelets D. Plasma cells
25. Conversion of messages carried by mRNA into
amino acid sequences is called___________
A. Replication B. DNA repair
C. Translation D. Transcription
26. The number of iron atoms in one haemoglobin
molecule is:
A. 1 B. 3
C. 4 D. 8
27. Which of the following is not a coenzyme?
A. NAD B. NADP
C. FAD D. Mn
2+
28. What is the type of the prokaryotic ribosome?
A. 80S B. 70S
C. 40S D. 60S
29. Normal blood pH is:
A. 7.3 B. 7.2
C. 7.4 D. 8.4
30. Sodium and potassium pumps are examples of
__________.
A. Passive transport B. Plasmolysis
C. Active transport D. Osmosis
31. Spindle ber shortens during:
A. Prophase B. Telophase
C. Metaphase D. Anaphase
32. Haematocrit value is the ratio of:
A. WBCs to plasma
B. Platelets to plasma
C. RBCs to plasma
D. Total blood cells to plasma
33. Plasma represents _______ percent of total blood
volume.
A. 35 B. 45
C. 55 D. 5
34. Name an organelle that serves as a primary
packaging area for molecules that will be
distributed throughout the cell.
A. Mitochondria B. Plastids
C. Golgi apparatus D. Vacuole
35. A normal amount of plasma protein ranges from:
A. 2.2–4.3 gm% B. 4.4–6.3 gm%
C. 6.4–8.3 gm% D. 8.4–10.2 gm%
36. Cell drinking is ____________
A. Exocytosis B. Endocytosis
C. Pinocytosis D. Phagocytosis
37. The cell wall of a plant is composed of:
A. Cellulose B. Carbohydrates
C. Lipids D. Lipoprotein
38. The location at which crossing over occurs is
known as
A. Centromere B. Kinetochore
C. Chiasmata D. Centriole
39. The outermost thick dead protective layer of plant
and bacterial cells is called:
A. Cell wall B. Cell membrane
C. Cell layer D. None
40. In how many steps protein biosynthesis takes
place?
A. 2 B. 3
C. 4 D. 5
41. The basic protein of the nucleus is:
A. Nucleohistones B. Nucleoprotamines
C. Both A and B D. None of these
42. Plasmodesmata are found in:
A. Cell wall B. Cytoplasm
C. Nucleus D. Cell membrane
43. The sequence in the cell cycle is:
A. S, G1, G2 M B. G1, S G2, M
C. S, M G1, G2, M D. G2, S, M, G1
44. Lysosomes are present in all, except:
A. Muscle cells B. Acinar cells
C. Erythrocytes D. Hepatocytes
45. Who discovered the cell in 1665?
A. Robert Hooke B. Robert Crook
C. David Thomson D. Marie Francois
46. The series of cell division is:
A. Prophase, metaphase, anaphase, telophase
B. Prophase, anaphase, metaphase, telophase
C. Prophase, metaphase, telophase, anaphase
D. Anaphase, metaphase, telophase, prophase
47. All the following have ribosomes, except:
A. Nucleus B. Mitochondrion
C. Chloroplast D. Cytoplasm
Section 3 Biochemistry
369368
48. Which of the following catalyzes ADP-ribosylation
of a diphthamide residue?
A. Chloramphenicol B. Cycloheximide
C. Diphtheria toxin D. Ricin
49. Outermost thin living protective layer of animal
cell is __________.
A. Cell membrane/plasma membrane
B. Cell wall
C. Cell barrier
D. Cell Layer
50. Who explained the wobble hypothesis?
A. Darwin B. Watson and Crick
C. Samuel B. Weiss D. Nirenberg
51. In 70S ribosome ‘S’ stands for:
A. SI unit B. Solubility factor
C. Svedberg unit D. None of these
52. In the word Lysosoma, ‘lyso’ means splitting and
‘soma’ means:
A. Cell B. Body
C. Tissue D. Organic
53. The subunits of 70S ribosomes include:
A. 40S and 50S B. 30S and 40S
C. 30S and 50S D. 20S and 50S
54. Microlaments are composed of a protein called
A. Tubulin B. Actin
C. Myosin D. Chitin
55. Ribosomes are made-up of:
A. RNA only
B. RNA and proteins
C. RNA, DNA and proteins
D. Nucleic acids, proteins and lipids
56. Phagocytosed food is digested with help of
enzymes that are present in
A. Ribosome B. Lysosomes
C. Mitochondria D. Golgi complex
57. The rough ER is very well formed, in cells that are
actively involved in a process:
A. Protein synthesis
B. DNA synthesis
C. Lipid synthesis
D. Fat molecules synthesis
58. Which of the following is a correct order of phases
in prophase I ?
A. Leptotene, diakinesis, pachytene, diplotene,
zygotene
B. Leptotene, zygotene, pachytene, diplotene,
diakinesis
C. Diakinesis, diplotene, pachytene, zygotene,
leptotene
D. Laptotene, pachytene, zygotene, diplotene,
dikinesis
Section 3 Biochemistry
59. With how many cells reproduction starts ?
A. Two cells B. Single cell
C. Many cells D. Somatic cell
60. A common chemical of secondary walls of xylem
cells is:
A. Amino acids B. Peptidoglycan
C. Chitin D. Lignin
61. The nucleus contains:
A. Mitochondria B. Chromosomes
C. Lysosomes D. Golgi apparatus
62. The nuclear membrane disintegrates and the
spindle appears at:
A. Prometaphase B. Early prophase
C. Late telophase D. Late prophase
63. Lysosomes are known as “suicidal bags” because
of:
A. Parasitic activity
B. The presence of food vacuole
C. Hydrolytic activity
D. Catalytic activity
64. An organism whose cell wall is not made-up of
cellulose is:
A. Fungi B. Algae
C. Volvox D. Mosses
65. Plasma membrane is:
A. Permeable
B. Selectively permeable
C. Impermeable D. Semipermeable
66. Golgi apparatus is found virtually in all cells
which are __________ in nature
A. Prokaryotic B. Eukaryotic
C. Protozoans D. Protoctista
67. A denite shape to cell is given by
A. Cell membrane B. Ribosome
C. Cell wall D. Nucleus
68. Holoenzyme is made of:
A. Apoenzyme and zymogen
B. Apoenzyme and coenzyme
C. Coenzyme and prosthetic group
D. Prosthetic group and cofactor
69. At which of the following stages of cell cycle
proteins and microtubules, required for mitosis,
are synthesised:
A. G2 phase B. G1 phase
C. Interphase D. M phase
70. Important structures of cells other than organelles
are:
A. Cell wall
B. Cell membrane
C. Cytoplasm and cytoskeleton
D. All of the above
71. Which of the following organelles is called
‘suicidal bag’?
A. Mitochondria
B. Endoplasmic reticulum
C. Lysosome
D. Ribosome
72. Ribosomes are synthesised in part of a cell called:
A. Golgi complex B. Mitochondria
C. Nucleolus D. Nucleus
73. Postmitotic gap phase and synthesis phase of cell
cycle are also, respectively referred to as:
A. G2 and S B. G1 and S
C. G1 and G2 D. S and G2
74. Which of the following is responsible for the
beginning of the life of organisms?
A. Tissue B. Zygote
C. Cell D. Embryonic layer
75. Cellulose, pectin, and hemicelluloses together
make up to form a:
A. Primary wall B. Secondary wall
C. Middle wall D. Tertiary wall
76. Who proposed the cell theory?
A. Singer and Nicholsen
B. Schwann and Schleiden
C. Hooke and Brown
D. Robertson
77. The distribution of intrinsic proteins in the plasma
membrane is:
A. Random B. Symmetrical
C. Asymmetrical D. None of these
78. Match the following:
Coulmn-I Coulmn-II
(a) Prophase (i) Reorganization of
nuclear membrane and
other orgenelles
(b) Metaphase (ii) Chromatid arrangement
on the poles
(c) Anaphase (iii) Formation of
cytoplasmic fibres of
proteins
(d) Telophase (iv) Arranged on equatorial
plane
(e) Cytokinesis (v) The formation of
syncytium
A. (a - i) (b - ii) (c - iii) (d - iv) (e - v)
B. (a - iii) (b - iv) (c - ii) (d - i) (e - v)
C. (a - v) (b - iv) (c - iii) (d - ii) (e - i)
D. (a - ii) (b - iii) (c - iv) (d - v) (e - i)
79. Who proposed that new cells arise through cell
division of pre-existing cells.
A. Robert Hook B. Rudolf Virchow
C. Robert Brown D. Singer
80. Thylakoid stack present in plastids, is known as:
A. Glycogen B. Granum
C. Nucleolus D. Ribosomes
81. The smallest cell is:
A. Bacteria B. Mycoplasm
C. Yeast D. Blue-green algae
82. Prokaryotic cells have which architectural regions?
A. Cell B. Appendages
C. Nucleus D. All of these
83. The association of more than one ribosome with
a single molecule of mRNA complex is called:
A. Polypeptide B. Polysome
C. Polymer D. Polysaccharide
84. Colour of chlorophyll is:
A. Green B. Yellow
C. Brown D. Red
85. Which structure possesses agellin protein?
A. Muscle fibres B. Flagellum
C. Pilli D. All of these
86. The cells involved in a large amount of lipid
synthesis, do not possess this organelle on
endoplasmic reticulum:
A. Mitochondrion B. Ribosomes
C. Golgi apparatus D. Lysosome
87. Which cell organelle is involved in apoptosis?
A. Lysosome B. ER
C. Golgi D. Mitochondria
88. In mitochondria, it contains F-particles:
A. Matrix B. Cristae
C. Outer layer D. All of these
89. The materials essential for the dark reaction, are
located in:
A. Circular-DNA B. Thylakoids
C. Stroma D. Ribosomes
90. Select unicellular organisms which possess cilia.
A. Amoeba B. Paramoecium
C. Yeast D. Opalina
91. In meiosis, the daughter cells are not similar to
that of a parent because of:
A. Crossing over B. Synapsis
C. Both (A) and (B) D. None of these
92. Which organelle(s) is/are found only in animal
cell?
A. Centriole B. Mitochondria
C. Golgi apparatus D. Chloroplast
93. Ribosomes are composed of:
A. rPNA B. rENA
C. rRNA D. rDNA
94. Which is the biggest animal cell?
A. Ostrich’s egg B. Hen’s egg
C. PPLO D. Mycoplasma
95. Flattened sacs that are present in the cell were
discovered by:
A. Ernst Haeckel B. David Baltimore
C. Camillo Golgi D. Rachel Carson
96. What is the function of SER?
A. Synthesis of steroid hormone
B. Synthesis of protein
C. Synthesis of enzyme
D. All of the above
97. A cell without a cell wall is termed:
A. Tonoplast B. Protoplast
C. Symplast D. Apoplast
98. How many units occur in each stack pile of Golgi
apparatus?
A. 4–8 B. 2–6
C. 4–6 D. 2–8
Section 3 Biochemistry
371370
ANSWER KEY
1. D 2. A 3. B 4. A 5. B 6. D 7. B 8. C 9. C 10. C 11. D 12. B 13. C 14. C
15. B 16. C 17. A 18. C 19. B 20. C 21. D 22. A 23. A 24. B 25. C 26. C 27. D 28. B
29. C 30. C 31. D 32. C 33. C 34. C 35. A 36. C 37. A 38. C 39. A 40. D 41. D 42. D
43. B 44. C 45. A 46. A 47. A 48. C 49. A 50. B 51. C 52. B 53. C 54. B 55. B 56. B
57. A 58. B 59. B 60. D 61. B 62. D 63. C 64. A 65. B 66. B 67. C 68. B 69. A 70. D
71. C 72. C 73. B 74. B 75. A 76. B 77. C 78. B 79. B 80. B 81. B 82. B 83. B 84. A
85. B 86. B 87. D 88. B 89. B 90. B 91. A 92. A 93. C 94. A 95. C 96. A 97. B 98. A
2. Carbohydrates
INTRODUCTION
Carbohydrates are food molecules.
An important source of energy for our cells to perform
their work.
After digestion carbohydrates are converted into glucose
molecules.
Extra glucose molecules are stored in liver and muscle
cells.
Carbohydrates can be simple or complex depending on
their chemical structure.
The name carbohydrate literally means ‘hydrates of
carbon’. Some of the carbohydrates possess the empirical
formula (C.H
Carbohydrates are polyhydroxyaldehydes, ketones, or
substances that generate them when they are hydrolyzed.
Important source of energy for our cells to perform
their work. After digestion carbohydrate converted into
glucose molecules.
z
Simple carbohydrates mean sugars occur naturally in
foods, fruits, vegetables, milk, etc.
z
Complex carbohydrates mean whole-grain bread,
cereals and legumes. They are a good source of fibres.
Classication: Carbohydrates are divided into four groups:
1. Monosaccharide: Grapes sugar
2. Disaccharide: Cane sugar, milk sugar
3. Oligosaccharide
4. Polysaccharide
No. of carbon Class of monosaccharide
3 Triose
4 Tetrose
5 Pentose
6 Hexose
Structure
Carbohydrate (CH2O)n.
Section 3 Biochemistry
Functions of carbohydrates
Source of energy
Help in regulating the protein metabolism
O)n.
2
Elimination of toxins
As a precursor
Help in maintaining overall positive health
Monosaccharides
[C(H2O)]n, where n is ≥3, e.g. glucose, fructose,
glyceraldehyde.
Some monosaccharides do not have this formula like
uronic acid and fucose.
Some substances also have this formula but they are
not considered to be monosaccharides, e.g. inositol and
formaldehyde.
Three-dimensional structure of monosaccharides—
cyclic form (represented by its Haworth projection).
Disaccharides
Disaccharide is formed when the alcohol component of
a glycoside is given by a hydroxyl function on another
monosaccharide, e.g. cellobiose.
Maltose—malt sugar comes from the hydrolysis of starch.
It is one-third sweet as natural sugar. It can be digestible
by humans and fermented with the help of yeast.
Cellobiose is obtained by hydrolysis of cellulose, has
no taste, cannot be digestible by humans and is not
fermented by yeast. One of the two components of
cellobiose should be glucose generally.
Milk sugar (reducing sugar)—galactose, in which glucose
compound joins and make beta-glycoside.
Sucrose—cane sugar. It is a common sweetening agent.
It is a non-reducing disaccharide (glucose and fructose)
they joined together at the position of anomeric carbon
of each by a bond (glycoside bond).
Polysaccharides
Polysaccharides are glycosidic bond-bound chains of
monosaccharides or its variants. Monosaccharide is a
kind of sugar (e.g. starch, glycogen, cellulose, inulin).
Heteropolysaccharides (e.g. mucopolysaccharides) are a
mixture of a few monosaccharides or their derivatives,
e.g. biological polymers.
Starch is an example of storage polysaccharide stored
in plants.
Some examples of structural polysaccharides are
cellulose, pectin, chitin.
Cellulose is found in the cell walls of plants and other
organism, it is most abundant organic molecule present
on earth.
Chitin has a structure like cellulose also has nitrogen
in their side branches which increases their strength.
Chitin is generally found in orthopod’s exoskeleton and
in Fungi’s. Monosaccharides joined together and formed
polysaccharides.
Pectin is a complex polysaccharide made-up of 1,4-linked
alpha-D-galactosyluronic acid residues.
Glucose is the most important energy source of
carbohydrates to the mammals (except ruminants).
The majority of carbohydrates (starch) is metabolised
and absorbed into the body as glucose, e.g. in medical
practice, dextrose (glucose in solution in dextrorotatory
form) is frequently used.
Fructose is prevalent in the sperm, and it is used for
power by the sperm. Carbohydrates are linked to a
number of disorders, notably diabetes, glycogen storage
diseases, and galactosemia.
Sorbitol and dulcitol aggregation in the tissues can
lead to pathological diseases including cataracts and
nephropathy.
In human, the non-digestible carbohydrate cellulose
plays an significant role. These include limiting glucose
and cholesterol retention in the intestine and increasing
the bulk of stools to prevent constipation.
Hyaluronic acid is a mucopolysaccharide that acts as a
lubricant and shock absorbent in joints.
The enzyme hyaluronidase of semen degrades the gel
(contains hyaluronic acid) around the ovum. This allows
effective penetration of sperm into the ovum.
The mucopolysaccharide heparin is an anticoagulant
(prevents blood clotting). The survival of Antarctic fish
below –2ºC is attributed to the antifreeze glycoproteins.
Streptomycin is a glycoside employed in the treatment
of tuberculosis.
Storage polysaccharide
Starch and glycogen are the carbohydrate reserves of plants
and animals, respectively. Cellulose, exclusively found in
plants, is the structural constituent. Inulin is utilised to
possess kidney function by measuring glomerular filtration
rate (GFR).
Glycogen is an analogue of starch polymer of alpha
(1- 4) glycosidic bonds linked with alpha (1-6) ceiling
branches.
Glycogen store energy especially in muscles, liver, red
blood cells. The amount of stored energy is dependent
upon physical activity, basal metabolic rate and eating
habits.
Glycogen is made-up of a branched chain of glucose
residues.
It shows insolubility in water.
When it mixed with iodine it turns into red.
Starch is a glucose polymer made-up of amylose and
amylopectin. It can be digested through hydrolysis and
catalysed with amylases enzyme in humans and other
animals have amylases so they can digest starch it is
exclusively formed in plants not in animals.
Mucopolysaccharides (glycosaminoglycan) are the
essential components of tissue structure. They provide
the matrix or ground substance extracellular tissue
spaces in which collagen and elastin fibers are embedded.
Hyaluronic acid, chondroitin 4-sulphate, heparin, are
among the important glycosaminoglycan.
Glycoproteins are a group of biochemically important
compounds with a variable composition of carbohydrate
(1–90%), covalently bound to protein. Several enzymes,
hormones, structural proteins and cellular receptors are
in fact glycoproteins.
The metabolism of carbohydrates, lipids and proteins
is integrated to meet the energy and metabolic demands
of the organism.
Major Pathway of Carbohydrate Metabolism
The most important glucose metabolic routes are given
below:
1. Glycolysis (Embden-Meyerhof pathway) is the process
of converting glucose to pyruvate and lactate.
2. The oxidation of acetyl-CoA to CO2 is known as the
citric acid cycle (Krebs cycle or tricarboxylic acid cycle).
Through acetyl-CoA, the Krebs cycle is the final common
oxidative path for carbohydrates, lipids, and amino
acids.
3. Gluconeogenesis is the process of producing glucose
from non-carbohydrate sources (e.g. amino acids,
glycerol, etc.).
4. Glycogenesis is the method of producing glycogen from
glucose.
5. Glycogenolysis is the process of breaking down
glycogen into glucose.
6. Hexose monophosphate shunt (pentose phosphate route
or direct oxidative pathway): This process for glucose
oxidation offers an alternative to glycolysis and the TCA
cycle (directly to carbon dioxide and water).
7. The uronic acid pathway converts glucose to glucuronic
acid, pentose, and ascorbic acid in some organisms.
8. Galactose metabolism: The processes involved in
converting galactose to glucose and lactose production.
9. Fructose metabolism: The oxidation of fructose to
pyruvate and the relation between fructose and glucose
metabolism.
10. The synthesis of amino sugars and other sugars for the
production of mucopolysaccharides and glycoproteins
is known as amino sugar and mucopolysaccharide
metabolism.
Types of metabolic pathways are:
Linear pathway– Glycolysis
Cyclic pathway– Citric acid cycle
Spiral pathway– Biosynthesis of fatty acids
Digestion of carbohydrate
In mouth: Salivary amylase also known as ptyalin starts
the digestion.
Section 3 Biochemistry
373372
In stomach: Here, food mixed with the gastric juice,
the action of amylase stops due to high acidic nature of
stomach.
In small intestine:
The pancreatic amylase converts starch and glycogen
into a mixture of maltose and isomaltose:
Then maltose and isomaltose along with sucrose, lactose
present in the diet are digested as depicted below:
Cellulose is not digested in humans.
Types of metabolic pathways
Linear pathway: Glycolysis
Cyclic pathway: Citric acid cycle
Spiral pathway: Biosynthesis of fatty acids.
respiration. This conversion may occur aerobically or
anaerobically (which depends on oxygen availability).
Glycolysis—first step of glucose metabolism.
Oxidation of glucose under aerobic conditions produces
1 mole of glucose— 32 moles of ATP
Oxidation of glucose under anaerobic conditions
produces
1 mole of glucose— 2 moles of ATP
Anaerobic glycolysis occurs in muscle cells in those
situations where oxygen becomes depleted like in the
case of exercise resulting in the formation of lactic acid.
Aerobic glycolysis end-products— carbon dioxide and
water.
Three fates of glucose molecule in body:
1. Glucose—produceds pyruvate through oxidation by
glycolysis.
2. Glucose—produces ribose-5-phosphate through
oxidation by pentose phosphate pathway.
3. Glucose—can be stored as glycogen, starch or sucrose.
Glycolysis meaning “sweet“, “splitting” also known as
Embden-Meyerhof Pathway (EMP).
A glucose molecule (6 carbon molecules) undergoes a
cascade of reactions and each reaction is catalysed by an
enzyme, ATP generated in this whole process.
Glycolysis— an exergonic reaction:
Glucose transporter
Transporter Function
GLUT1— found most of
Glucose uptake in the cell
the body cells
GLUT2— found on
Glucose regulation
enterocyte, hepatocyte and
pancreas cells
GLUT3— found on
Glucose uptake in neurons
neuronal cells
GLUT4— found on
myocyte, adipocytes, heart
Its activity enhanced by
insulin hormone
cells
GLUT5— found on
Fructose transport
Intestine, testis, kidney and
on sperm
GLUT6–GLUT12 Under study
Glycolysis
All cells of the body need ATP to function properly.
Human cells can generate ATP from energy-rich
molecules like glucose, by the method of cellular
Ten steps of glycolysis can be divided into two main
phases in phase one reaction, one glucose molecule
get phosphorylated and changed to fructose. Again,
this fructose gets phosphorylated and splitted into
glyceraldehyde-3-phosphate (2 molecules). This phase
required the investment of 2 molecules of ATP. In phase
two glyceraldehyde-3-phosphate (2 molecule) changed into
pyruvate along with the production of four ATP molecules
and two molecules of NADH. So, as a resultant, there is
a gain of two ATP molecules from one glucose molecule
in glycolysis.
Section 3 Biochemistry
Glycolysis (Embden-Meyerhof Pathway)
Energetics of Glycolysis Pathway
ATP FORMED:
1. Gly-3-PO4 1,3-bisphosphoglycerate (6 ATP molecules
are produced)
2. 1,3-bisphosphoglycerate-3-phosphoglycerate (2 ATP
molecules are produced)
3. Phosphoenolpyruvate enol pyruvate (produced 2 ATP
molecules)
ATP CONSUMED
4. Glucose-6-PO4 (produced 1 ATP molecule)
5. Fru-6-PO4, Fru-1,6-bisphosphate (produced 1ATP
molecule)
Net ATP synthesised = 10 – 2 = 8 ATP
Initiators of EMP pathway: Insulin, glucagon
Inhibitors of EMP: Iodoacetate, arsenate, fluoride
Glycolysis can produce spontaneously ATP molecules
without any oxygen molecule, with the help of glucose
and glycogen (stored in muscle and hepatic cells).
Glycogenolysis—breakdown of glycogen into glucose,
occurs in muscle and liver cells it happens when glucose
is required to body quickly.
Two glycosidic linkages are found in glycogen: 1. Linear
linkages as α-(1→4); 2. branching linkages as α–(1→6).
Branching present at after every 8–10 residues.
Section 3 Biochemistry
375374
Step I: Phosphorylation occur with the help of glycogen
phosphorylase, pyridoxal phosphate acts as a coenzyme,
product by this step is glucose-1-phosphate.
Step II: Branching removal is done by debranching enzymeglycosyl 4:4 transferase and amylo-1,4 glucosidase.
Step III: Formation of free glucose and glucose-6-phosphate,
an enzyme for this step is phosphoglucomutase.
Insulin Hormone: Inhibits Glycogenolysis
Regulation of glycogenolysis occurs with the help of
enzyme glycogen phosphorylase by three mechanisms:
Allosteric regulation
Hormonal regulation
Influence of calcium
Glycogenesis: Production of glycogen from glucose, occurs
in liver and muscle cells, it takes place when glucose and
ATP are already present in excess in the body.
METABOLIC PATHWAYS: GLYCOGENESIS AND
GLYCOLYSIS
Gluconeogenesis
The production of glucose from non-carbohydrate
substances.
The major precursors for gluconeogenesis: Lactate,
pyruvate, glucogenic amino acids, propionate and
glycerol.
The liver is the main site for gluconeogenesis and to some
extent renal cortex.
This occurs partly in mitochondria and partly in
cytoplasm.
In starvation, condition gluconeogenesis regulates and
balances glucose level in blood.
If a starvation condition exists for a long-time, the
gluconeogenesis is speeded up and then catabolism of
protein starts for the production of glucose.
In glycolysis, three irreversible steps occur, those steps
are catalysed by three different enzymes:
z
Hexokinase
z
PFK
z
Pyruvate kinase.
Net reaction: 2 Pyruvate + 4 ATP + 2 GTP + 2 NADH + 2
H+ + 6 H2O → Glucose + 4 ADP + 2 GDP+ 2 NAD+ + 6 Pi
Pathways involved in gluconeogenesis:
z
Reverse glycolysis
z
TCA cycle
z
Some special reactions— Cori cycle, glucose alanine
cycle.
Cori cycle is a pathway of gluconeogenesis from lactate
that occurs in liver cells.
Gluconeogenesis regulation is done by following
hormones:
z
Glucagon
z
Insulin.
Disorders of glucose metabolism
Pyruvate kinase deficiency
Pyruvate dehydrogenase deficiency
Muscle phosphofructokinase deficiency
Galactosemia
Glucose-6-phosphate dehydrogenase deficiency
Essential pentosuria
Hypoglycaemia
Glycogen storage diseases
Glycosuria
Diabetes
Section 3 Biochemistry
Other Important Pathways
Gluconeogenesis pathway
HMP shunt pathway
Section 3 Biochemistry
377376
Shikimic Acid Pathway
MULTIPLE CHOICE QUESTIONS
1. Salivary amylase acts which on starch leads to the
formation of:
A. Maltose B. Maltotriose
C. Both A and B D. None of these
2. In the structure of amylopectin, the space between
glucose units (in each branch) is:
A. 45–60 B. 24–30
Section 3 Biochemistry
3. Bulk transport across cell membrane occurs
C. 12–25 D. 46–50
through:
A. Phagocytosis B. Pinocytosis
C. Extrusion D. All of these
4. Citrate is converted to isocitrate by aconitase which
contains:
A. Ca2+ B. Fe
C. Zn2+ D. Na
2+
2+
5. A lipid bilayer (phospholipid membrane) is
permeable to:
A. Urea B. Fructose
C. Nitrogen D. Potassium