Quick Review of Biochemistry for Undergraduates (Questions and Answers) Krishnananda Prabhu, Jeevan K Shetty
INDEX
Page numbers followed by f refer to figure, t refer to table and b refer to box.
A
Acetyl-CoA 66, 67f, 68
sources 270
Acid-base balance
renal mechanisms 237
Acid-base disorders 234, 239
calcium 239
Acidic pH 159t
Acidosis 162
Acquired immunodeficiency
syndrome 228
Actinomycin D 196t
Active transport 4
primary 5
secondary 5
Acute myocardial infarction 22, 22t, 22f
Acute pancreatitis 23t
Adenosine 175
Albinism 120, 133
Albumin 96, 274
Alcohol de-addiction 24
Alcohol dehydrogenase 9t
Alcohol metabolism 85, 86f
Alcoholic liver disease 23t
Aldolase A 55
Alkaline phosphatase 245
Alkaptonuria 120
Allopurinol 188, 189
α1-antitrypsin 102
α2-macroglobulin 102
α-amanitin 196t
Alpha-helix 91, 91f
Amino acid pool 107
Amino acid
absorption 106, 107f
branched chain 134
classification 90
catabolism 129, 130f
Aminoacyl-tRNA 203
synthetase 200
Ammonia 109
Amyloidosis 103
Anderson's disease (type IV) 47t
Anemia
consequences 291, 291f
Anion gap 234
Anorexia nervosa 173
Anserine 129
Antioxidants
chain-breaking 273
endogenous 273
Antisense therapy 227
Apoenzyme 23
Apolipoproteins 82
Apoptosis 219
Arachidonic acid 63
Arginine 159
compounds 132
Arsenite 55
Ascorbic acid (vitamin C) 157
Asparagine 131, 134
Aspartate 131, 134
Aspirin 63, 262
Atherosclerosis 86, 87f
ATP synthesis 137, 137f
B
Balanced diet 169
Basal metabolic rate (BMR) 166
Base excision repair 209
Base pairing rule 180
Beriberi
dry 149b
infantile 149b
wet (cardiac) 149b
Betaine 84
β-oxidation 66, 67f, 88
Beta-pleated sheet 92
Bile acids 76
functions 76
synthesis 76, 77f
Bile salts 88
enterohepatic circulation 76
Bilirubin 244, 280
conjugated 244, 282
metabolism 280, 281f
total 282
unconjugated 244, 282
Biotin (vitamin B7) 156
Bitot's spots 142
Blood glucose regulation
level 52
Blood pH 234
Blood urea nitrogen (BUN) 248
Blood urea
normal 248
BMR 170
Body mass index (BMI) 172
Bone disease 23t
Brain natriuretic peptide 253
Breast cancer 219, 259
British anti-lewisite (BAL) 140
Brown adipose tissue 85
Buffer systems 233, 233t
Buffers
in body fluids 236
bicarbonate 236
phosphate buffer
system 236
protein buffer system 236
Bulimia nervosa 173
C
Calcitriol 159
Calcium
absorption 159
toxicity 162
Calorific value 166
Cancer 168
Carbamoyl phosphate
synthetase 111, 189
Carbohydrate isomers 26
anomers 27, 28f
optical 27, 28f
stereoisomers 26, 27
structural 26, 27
Carbohydrates
Absorption 33, 33f
digestion 32, 32f
Carbonic anhydrase 9t
Carboxylation 206
Carcinogens 218
Carcinoid syndrome 123t, 152
Cardiac function tests 253t
Carnitine 88
deficiency 69t
Carnosine 129
Catalase 9t
Catecholamines 118
dopamine 117
epinephrine 117
norepinephrine 117
Cell cycle 215
Cell membrane
fluid mosaic model 2, 3f
fluidity 2
proteins 3
Cellular organelles 1
Ceruloplasmin 102
Cervical cancer 259
Chargaff's rule 177, 180
Chemiosmotic hypothesis 137
Chloride 9t
Cholecystokinin 66
Cholesterol 62, 63
ring 63
synthesis 74, 75f
Choline 84
Chromatography 274
column 274
high-performance liquid 274
paper 274
thin layer 274
Chylomicrons 58, 66
metabolism 80, 80f
Chylothorax 87
Chyluria 87
Cistron 214
Clearance 247
Cobalamin 154
Cockcroft and gault formula 248
Codon-anticodon interaction 200f
Coenzymes 9
Cofactors 9, 9t
Collagen 99
formation and maturation
defects 99
Congenital
abetalipoproteinemia 87
Congenital erythropoietic
porphyria 284
Congenital
hyperbilirubinemia 282, 283t
Cori cycle 43, 43f
Cori's disease (type III) 47t
Covalent modification 206
C-reactive protein 102
Creatine 114
Creatine phosphokinase 21
Creatinine clearance 247, 248
Creatinine coefficient 248
Cyanide 262
Cyclopentanoperhydrophenan-
threne See
cholesterol ring 63
Cystathioninuria 125
Cysteine 134
metabolism 126
Cystinosis 128t
Cystinuria 8, 106, 128t
Cytidine 175
Cytochrome oxidase 9t
D
Deamination reactions 108
non-oxidative 109
oxidative 108, 109f
Dementia 152t
Deoxyadenosine 175
Deoxyadenosine triphosphate (dATP) 190
Deoxycytidine triphosphate (dCTP) 190
Deoxyguanosine triphosphate (dGTP) 190
Deoxyribonucleic acid (DNA) 174
Deoxyribonucleotides
synthesis 188
Deoxythymidine triphosphate (dTTP) 190
Dephosphorylated state 271
Dermatitis 152t
Desulfhydration 109, 110
Detoxification 260
Dextran 31
Diabetes 168
Diabetic ketoacidosis 73
Diarrhea 152t
Dicarboxylic aciduria 69t, 88
Dietary fibers 167
Digitalis 31
Digoxin 8
Dihydrouracil 180
Disaccharides 25
Disulfide bonds 93
DNA 190
DNA and RNA
differences between 178t
DNA cloning 220
DNA damage 207
DNA helicases 190
DNA libraries 221
DNA polymerase 190, 192, 193
DNA probe 228
DNA repair and mutations 207
DNA replication 190, 193
elongation 192
inhibitors 193, 193t
lagging strand 191
steps 191
DNA sequencing 228
DNA synthesis 191
DNA topoisomerase I 190
DNA topoisomerase II 190
DNA viruses 219
DNA
structure 177f
types 178
Donnan membrane
equilibrium 276
Double-strand break repair 209
E
Ehlers-danlos syndrome 99
Ehrlich's test 244, 244t, 245
Electrolyte concentration 279
Electrolytes 275
Electron transport chain 136, 136f
components 137
inhibitors 139, 140t
uncouplers 139, 140t
Electrophoresis 95, 95f, 273, 274f
Electrostatic (ionic) bonds 92
ELISA
advantages 259
applications 259
procedure 258
Embden-meyerhof pathway 33
Enantiomers 27
Endocytosis 6, 7
Endometrial cancer 219
Endonucleases 228
Energy coupling 135
Enolase 9
Enzyme activity
effect
pH 15, 15f
temperature 15, 15f
Enzyme concentration 14
Enzyme inhibition 17
competitive 17, 24t
non-competitive 18, 24t
suicide 18, 24
Enzymes
active site 12
activity 13
classification 10
inhibition 16
regulation 18
allosteric regulation 18, 19, 19t
covalent modification 18, 20, 20f
specificity 10, 10t
Enzyme-linked immunosorbent
assay (ELISA) 225, 258, 258f
Epimers 26
Escherichia coli 213
Essential fatty acids 59, 63
deficiency 59
Ethanol induces CYP2E1 263
Eukaryotic cell 1, 2
Eukaryotic gene regulation 214
Exocytosis 6, 7
Exonucleases 228
F
Facilitated diffusion 4, 7
Fanconi anemia 194
Fanconi syndrome 146
Farnesylation 206
Fasting state 268, 269t
Fatty acid synthase complex 70, 70f, 270, 271f
Fatty acids 70, 70f, 71f
de novo synthesis 69
disorders associated with oxidation 69
Fatty liver 84
Feed-fast cycle 267
Fibrinogen 102
Flame photometry 279
Fluorescent in situ hybridization
technique 230f
Fluoride 23
Folate antagonists 154, 154t
Folate trap 155
Folic acid 153
Folinic acid 154
Food guide pyramid 170, 171f
Formiminoglutamate (FIGLU)
excretion test 154
Fouchet's test 245
Fractional test meal 251
Fragile x syndrome 211
Free fatty acids 66
Free radicals
effects 272
generation 272
metabolism 271, 273
Fructose 55
G
Gallstones 88
γ-glutamyl transferase 245
Gastric function tests 250
indications 250
Gastric juice
free acidity 251
functions 250
total acidity 251
Gastric lipase 88
Gene therapy 221, 223f
germ cell 221
somatic cell 221
Genetic code 204
Gestational diabetes mellitus (GDM) 56
Globulins 102
Glomerular filtration rate
normal 248
Glucagon 53, 53f
Glucagon action
steps 266
Glucocorticoids 266
Gluconeogenesis 41, 42f, 66
key enzymes 43
non-carbohydrate
substrates 44, 44t
regulation 43
Gluconeogenic enzymes 266
Glucose-6-phosphate
dehydrogenase (G6PD)
deficiency 50, 56
Glutamate
metabolic functions 132
synthesis 131
Glutathione 115
Glutathione 262, 263f
Glycated Hb (HbA1c) 56
Glycemic index 168
Glycerophosphate shuttle 138, 139f
Glycine
degradation 114
metabolic disorders 114
specialized products 114
Glycinuria 106t
Glycogen 30
Glycogen phosphorylase 206
Glycogenesis reactions 46, 48f
Glycogenolysis 44, 44f, 45f
Glycolipids 58, 61
Glycolysis 33, 34, 35f, 66
Glycolysis
anaerobic 34
energetics 36
inhibitors 37, 37t
metabolic disorders associated 37
regulation 36
Glycoproteins 30
Glycoside 29, 29t
Glycosylation 206
Goiter 165
Gout 184, 189
primary 184
secondary 185
Group I hormones general mechanism 265
Guanosine 175
H
Half-life 254
radioactive compound 255
Hand in glove model of daniel E
koshland 13f
Haptoglobin 102
Hartnup disease 8, 106, 123t, 133, 152
Hay's sulfur test 245
Hb electrophoresis 290
HDL 63, 81
Heme degradation 280f
Heme synthesis 115
regulation 283
steps 284
Hemochromatosis 164
Hemoglobin 99, 288
functions 100
oxygen transport 100
structure 99, 100f
types 99
Hemoglobinopathies 101, 101t
Henderson-Hasselbalch
equation 233
Hepatitis 23t
Hereditary fructose intolerance (HFI) 56
Hereditary rickets 146
Hers' disease (type VI) 47t
Heteropolysaccharides 26
High-density lipoprotein (HDL) 81t
High-energy compounds 136, 136t
Hippuric acid 244
Hippuric acid test 244
intravenous 245
oral 245
Histamine 129
Histidine catabolism 128, 128f
Histidine
metabolic disorders 129
specialized products 129
Histones 197
HMG-CoA reductase 75
HMP shunt/direct oxidative
pathway See pentose phosphate pathway 48
Hodgkin disease 259
Holoenzyme 23
Homocysteinemia 155t
Homocystinuria 126f
Homopolysaccharides 26
Hormones 264
amino acid derivatives 264
group I 264, 265f
group II 264
protein 264
steroid 264
Human genome project (HGP) 232
Huntington's disease 193, 211
Hyaluronic acid 30
Hybridoma technology 226
steps 227
Hydrogen bonds 92
Hydrolases 11
Hydrophobic bonds 93
Hydroxylation 206
Hypercalcemia 160
Hyperglycemia 53, 54
Hyperkalemia 161
Hyperlipidemia 82
primary 83
secondary 83
Hypermethioninemia 125t
Hypernatremia 160
Hyperphosphatemia 160
Hyperuricemia 186
Hypoalbuminemia 96
Hypocalcemia 160
Hypoglycemia 53, 69t
Hypokalemia 161
Hyponatremia 160
Hypophosphatemia 160
Hypothyroidism
congenital 165
Hypoxanthine 180
I
Immunoglobulins 97, 97t
functions 98, 98t
general structure 98, 98f
Impaired fasting glycemia (IFG) 56
Impaired glucose tolerance (IGT) 56
Indole 262
Induced fit model 13, 13f
Initiation codon AUG 201
Initiation complex
30S 201, 201f
48S 203
70S 201, 201f
80S 203
Insulin 53, 53f, 96
function 97
structure 97, 97f
Interphase 215
G1 phase 215
G2 phase 215, 216
S phase 215
Introns 198
Inulin 30
Iodine number 60, 63
Ion channels 7
Iron 9t
absorption 163, 163f
deficiency 164
overload 164
Isoelectric pH 93
Isoenzymes 21
Isomerases 11
Isoniazid 262
Isotopes 254, 254t
J
Jamaican vomiting
sickness 69t, 88
Jaundice 245, 281, 282
biochemical investigations 281
hemolytic 245, 282
hepatic 245, 282
neonatal 287
obstructive 23t, 245
posthepatic 282
K
Kashin-beck disease 165
Keratan 31
Keratomalacia 142
Keshan disease 165
Ketogenesis 71, 72f, 73
Ketolysis 73, 73f
Ketone bodies 71, 73
Ketosis 71, 73, 74f
Kidney functions 245
Kinase 9t
Korsakoff's psychosis 149t
Krebs cycle 38
Kwashiorkor 168, 171
L
Lac A 213
Lac operon 213
Lac operon model 212
Lac Y 213
Lac Z 213
Lactate dehydrogenase 21
Lactose 30
Lactulose 173
LDH flip 253
LDL 63
Leber hereditary optic
neuropathy (LHON) 140
Lesch-nyhan syndrome 183, 184, 188
Leukotrienes 63
Ligases 11
Lipases 87
Lipid peroxidation 272
steps 272
initiation 272
propagation 273
termination 273
Lipid profile 82, 253
Lipids
absorption 64, 65f
classification 57, 57t
digestion 64, 65f
functions 58
Lipogenesis 55
Lipoprotein (HDL) 58
Lipoproteins 77, 78f
classification 78, 78t
functions 78
Lipotropic factors 83
Liver diseases 103
Liver function tests 242, 243t
uses 242
Liver functions 242
Lock and key model 12
Low-density lipoproteins (LDL) 79
Lyases 11
Lymphoma 259
Lysine 159t
M
Macrominerals 158
Magnesium 9t
toxicity 162
Malate-aspartate shuttle 138, 138f
Malignant melanoma 259
Malonyl-CoA 88
Manganese 9t
Mannitol 31
Maple syrup urine disease (MSUD) 129
Marasmus 168, 171
Maturity onset diabetes of young (MODY) 55
Mcardle's disease (type V) 47t
Megaloblastic anemia 155
Melanin 118
Melatonin 121, 122
Menkes disease 165
Metabolic acidosis 234, 239
Metabolic alkalosis 239
Metabolic syndrome (syndrome X) 173
Metabolism glycine 113
Methanol poisoning 23
Methemoglobin 288
Methemoglobinemia
causes 289
clinical features 289
Methionine 123, 134
metabolism 125, 125t
Methotrexate 188
Methylmalonic acidemia 155t
Michaelis-Menten equation 16
Microalbuminuria 103, 248
Microarray technique 230, 231f
Microcytic anemia 153
Microminerals 162, 162t
Mitosis phase 216
Modified sugars 28, 28t
Molecular chaperones 228
Molybdenum 9t
Monosaccharides 25
Mucosal block theory 164
Multienzyme complexes 270
Multiple myeloma 103
Muscle disease 23t
Mushroom poisoning 199
Mutarotation 29
Mutations
chromosomal 210
frameshift 210, 211
gene 210
missense 210, 211t
nonsense 211
point 210
silent 210
Myasthenia gravis 8
Myocardial infarction 23t
Myoglobin 253
Myotonic dystrophy 211
N
N-acetyl-p-benzoquinoneimine (NAPQI) 263
NADPH 74, 76, 88
Neotame 56
Neural tube defect 154t
Neuroblastoma 259
Niacin 151
Nicotinamide 122
Nicotinamide adenine
dinucleotide (NAD) 121
Night blindness 142
Nitric oxide 133
Nitrogen balance 168
Non-protein nitrogen (NPN) 248
Northern blotting
applications 225
Nucleic acids 176
Nucleoside 180
Nucleoside analogues 180
Nucleosides 175, 175t, 175f
Nucleotide 180
structure 175, 176f
Nucleotide excision
repair (NER) 208
O
Obesity 171
Okazaki fragments 193
Olestra 31
Oligosaccharides 25
Omega-3 fatty acids 63
Omega-6 fatty acids 63
Omeprazole 8
Oncogenes 216, 216t
Oral cancer 259
Organophosphorus
compounds 23
Orlistat 88
Orotic acid 186
Orotic aciduria 186, 189
Osmotic concentration 279
Osteoblastoma 256, 259
Osteogenesis imperfecta 99
Osteomalacia 145t
Oxidative phosphorylation 138
Oxidoreductases 10
P
Paget's disease 160t
Palmitic acid 63
Pancreatic function tests 252
indications 252
Pantothenic acid (vitamin B5) 156
Paracetamol 262
Parathyroid hormone (PTH) 159
Parkinson's disease 133
Pellagra (4D) 152t
Pentose phosphate
pathway 48
metabolic defects 50
Pepsinogen 206
Peptide bond 93
Peptide bond formation 202
Peptides 93, 94t
Peroxidase 9t
Phagocytosis
carrier 7
channel-forming 7
Phenobarbital 262
Phenylalanine
metabolism 116, 116f
Phenylketonuria 119, 119f
Pheochromocytoma 133
Phospholipids 58, 60
classification 60
glycerophospholipids 60, 60t
sphingophospholipids 61
functions 61
Phosphorylation 36, 37t, 206
purine ribonucleoside 184
Phrynoderma 59
Ping-pong model 4
Pinocytosis 7
Plasma proteins
relative percentage 96
separation methods 95
Poly-A tail 198
Polyamines 125
Polymerase chain reaction (PCR) 225, 226f
applications 226
steps 226
Polysaccharides 25, 26t
Polyunsaturated fatty acids 173
Pompe's disease (type II) 47t
Porphobilinogen 286, 286f
Porphyria 284
classification 285, 285t
clinical features 286
intermittent 286
Post-transcriptional
modification 198
Post-translational
modification 205
Potassium 277
Potassium imbalance 277
Preinitiation complex 195
Prion diseases 103
Procarcinogen 219
Proinsulin 206
Prokaryotic cell 1
Promoters
eukaryotic 194
prokaryotic 194, 194f
Propionic acid 59
Propionyl-CoA 68
Prostaglandins 62
Prostate cancer 23t
Prosthetic group 23
Protein energy malnutrition 171, 171t
Protein farnesyltransferase
inhibitors 206
Protein targeting 206, 228
Proteins
absorption 104
acute phase 102
complete 95
denaturation 93
denaturing agents 93
digestion 104, 105f
functions 94, 94t
mutual supplementation 173
nutritional value 169, 169t
structures 90
synthesis 199f
Proteinuria 248
Proto-oncogenes 216, 216t
Pseudouridine 180
Purine analogues 180
Purine ring 115f, 181
inhibitors 183, 183t
regulators 183, 183t
sources 181
synthesis 182f
Purines 174, 174t, 174f, 178
Pyridoxine 152
Pyrimidine analogues 180
Pyrimidine ring 131, 186
Pyrimidines 174, 174t, 174f, 178
synthesis 187f
Pyruvate dehydrogenase
complex 270
R
Radiation 255
alpha (a) decay 255
beta (b) radiation 255
forms 255
gamma (g) radiation and
X-rays 256
Radiation hazard 259
Radioactive decay 254
Radioactivity 254
Radioimmunoassay (RIA) 256, 257f
advantages 257
disadvantages 257
interpretation 257
principle 256
procedure 257
Radioisotopes 254
applications 256
Radiosensitivity 259
Radiotherapy 256
Rancidity 59, 63
types 60
Rapoport-luebering shunt See
BPG shunt 37
Recombinant DNA technique
steps 220, 222f
Red blood cell (RBC) life 256
Redox potential 140
Refsum's disease 88
Renal clearance 247
creatinine 247t, 248
inulin clearance 247t
urea clearance 247t
Renal diseases 103
Renal function tests 245
uses 246, 246t
Replication fork 191, 192f
Respiratory acidosis 235, 239
Respiratory alkalosis 235, 235t, 239
Respiratory quotient 166, 166t
Restriction endonucleases 220
Restriction fragment length
polymorphism (RFLP) 224
sickle cell anemia 225
Retinoblastoma (RB) gene 219
Reverse transcriptase 197, 197f, 199
RHO-dependent termination 196
RHO-independent termination 196
Riboflavin (vitamin B2) 150
Ribonucleic acid (RNA) 174
Ribosomes 200
Rickets 145t
Rifampicin 196t
RNA interference 227
RNA polymerases 194, 195, 196t, 199
RNA primer 191, 192, 193
RNA viruses 219
RNAs 178
messenger 178
ribosomal 180
transfer 179, 179f
Rothera's test 88, 130
S
Salivary amylase 9t
Saponification number 60, 63
Schilling test 155, 251
Scurvy 99, 157
Secondary diabetes 56
Selenocysteine 206
Serotonin 121, 122f
Serum amylase 252
Serum bicarbonate 234
Serum calcium 159
Serum cholesterol 79
Serum creatinine 248
Serum lipase 252
Serum potassium 239
Severe combined
immunodeficiency (SCID) 186, 189
Shine-dalgarno sequence 201
Sickle cell anemia
treatment 290
Sickle cell disease
classification 289
complications 290
Sickle cell trait 291
Simple diffusion 6
Single-stranded DNA-binding
proteins (SSB proteins) 191
Sodium 277
Sodium imbalance 277
Sodium-glucose cotransport 6, 6f
Sorbitol 31
Southern blotting 223
applications 223
steps 224, 224f
Specific dynamic action (SDA) 167, 167t
Sphingolipidoses 84, 85t
Spliceosome 199
Steatorrhea 87
Steroids 63
Stroke-like episode (melas) 140
Substrate 23
Substrate concentration 13
Succinate dehydrogenase 56
Succinate thiokinase 56
Sucrose and trehalose 30
T
TCA cycle
amphibolic role 40, 41t
anaplerotic reactions 41
energetics 39, 39t
inhibitors 40, 40t
regulation 40, 40t
TCA, tricarboxylic acid 73f, 269
Telomerase 194
inhibitors 194
Telomeres 194
Tetany 162
Thalassemias
α-thalassemia 287, 288, 288t
β-thalassemia 287, 288, 288t
Thiamine 149
Thiamine deficiency (beriberi) 51
Thiophorase 88
Thymidine 175, 180
Thyroid function tests 248, 249t
Thyroid hormones 118, 118f
Thyroid scan 256
Total parenteral nutrition (TPN) 172
Trans fatty acids 63
Transaminases 107
Transcription 194, 195
inhibitors 196t
steps 195
Trans-fatty acids 173
Transferases 11
Transferrin 102
Translation 199
eukaryotes 203
prokaryotes 201
inhibitors 205, 205t
Translocation 202, 202f
Transmethylation reactions 124
Tricarboxylic acid (TCA) cycle 68
Trypsinogen 206
Tryptophan 134
catabolism 121
metabolism disorders 122
specialized products 121
Tuberculosis 153
Tumor markers 217
types 218, 218t
Tyrosine
metabolism 116, 117f
Tyrosinemia 120, 120t
U
Urea cycle 110, 111f
defects 112
treatment 112
disorder 188
regulation 110
Uric acid formation 184
Uric acid level 189
Uric acid synthesis 185f
Uridine 175
Urine
abnormal constituents 248
normal specific gravity 248
Uronic acid pathway metabolic disorder associated 52
V
Van den bergh reaction 243, 244t, 281
Vectors 228
Very low density lipoprotein (VLDL) 58, 79
Visual cycle 142, 143f
Vitamin
A 142
B1 see thiamine 149
B12 see cobalamin 154
B3 see niacin 151
B6 see pyridoxine 152
B9 see folic acid 153
D 144
transporter 146
K 147
toxic manifestations 148
von gierke (type I) 47t
W
Warfarin 263
Water and electrolyte balance 277
Watson-crick model of DNA 176
Well-fed state 267, 268f
Wernicke-korsakoff syndrome 51
Wernicke's encephalopathy 149t
Western blotting 225
Wilson's disease 165
Wobble hypothesis 204, 205
X
Xanthine oxidase 9t
Xenobiotic 260
Xenobiotic metabolism
sites 260
Xenobiotics detoxification 260
acetylation 261
conjugation 261
conjugation with glycine 261
glucuronidation 261
hydrolysis 261
methylation 261
oxidation 260
phase 1 260
phase 2 261
reduction 261
sulfation 261
Xeroderma pigmentosum 190, 193, 194, 207, 208
Xerophthalmia 142
X-inactive specific transcript (XIST) RNA 228
Z
Zellweger's syndrome 69t, 88
Zinc 9t
×
Chapter Notes

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Cell and Plasma Membrane1

  1. Name all cellular organelles with one function for each.
    The function of different cellular organelles is given in Table 1.1.
    Table 1.1   Different cellular organelles and their functions
    Organelle
    Functions
    Plasma membrane
    Protection, selective barrier and maintains shape of the cell
    Endoplasmic reticulum
    Translation and folding of new proteins (rough endoplasmic reticulum), synthesis of lipids (smooth endoplasmic reticulum) and metabolism of drugs
    Golgi apparatus
    Sorting and modification of proteins
    Mitochondria
    Energy production—ATP—from the oxidation of food substances
    Nucleus
    Maintenance of genetic material, deoxyribonucleic acid (DNA); controls all activities of the cell, ribonucleic acid (RNA) transcription
    Nucleolus
    Ribosome production
    Lysosome
    Breakdown of large molecules—carbohydrates, lipids, proteins, etc.
    Peroxisome
    Breakdown of peroxides
    Ribosome
    Translation of RNA into proteins
  2. Compare and contrast prokaryotic cell with eukaryotic cell.
    The comparison between prokaryotic cell and eukaryotic cell is given in Table 1.2.
    Table 1.2   Comparison of prokaryotic and eukaryotic cells
    Property
    Prokaryotic cell
    Eukaryotic cell
    Size
    Small
    Large
    Cell membrane
    Rigid
    Flexible
    Nucleus
    Not well-defined
    Well-defined with nucleolus
    Subcellular organelles
    Absent
    Present
    Cytoplasm
    Organelles and cytoskeleton absent
    Organelles and cytoskeleton present
    Cell division
    Binary fission
    Mitosis and meiosis
    Transport system
    Absent
    Present
    2
  3. Draw a neat and labeled diagram of eukaryotic cell.
    The structure of eukaryotic cell is shown in Figure 1.1.
    zoom view
    Fig. 1.1: Eukaryotic cell
  4. Write short notes on fluid mosaic model of membrane.
    As proposed by Singer and Nicolson in 1972, membrane is made up of lipid bilayer with embedded proteins (enzymes, transporters and receptors). Membrane lipids are amphipathic in nature, so they spontaneously form a bilayer in aqueous medium, by arranging their hydrophilic ends exposed to water and hydrophobic tails away from water (Fig. 1.2). Membrane lipids are mainly phospholipids, glycolipids and cholesterol.
    • Phospholipids: Glycerophospholipids and sphingomyelin
    • Glycolipids: Cerebrosides and gangliosides, present on the outer surface of the membrane
    • Cholesterol: Provides fluidity to membrane.
    Membrane lipids show lateral movements and flip-flop movements. Hence, membrane is fluid in nature. Hydrophobic interaction between the hydrocarbon tails in the phospholipids keeps the bilayer intact.
 
 
Factors Affecting Membrane Fluidity
  • Amount of unsaturated fatty acids: More the unsaturated fatty acids, more will be the fluidity
  • Saturated fatty acids: Decreases the membrane fluidity
  • Cholesterol: Increases the membrane fluidity at low temperatures.
3
zoom view
Fig. 1.2: Fluid mosaic model of membrane structure
 
Membrane Proteins
Peripheral membrane proteins: Are attached loosely to the surface of membrane bilayer.
Integral membrane proteins: Are deeply embedded in bilayer structure (proteins that extend all along the membrane bilayer are called transmembrane proteins).
 
Functions of Membrane Proteins
  • Transport of molecules across the membrane
  • Act as receptors
  • Function as enzymes
  • Components of respiratory chain.
 
Asymmetry in Membranes
The protein to lipid ratio varies in different membranes to suit their functions. For example, inner mitochondrial membrane, which has electron transport chain, is rich in proteins with protein and lipid ratio of 3.2, whereas in myelin sheath, which is designed to insulate the nerve fibers, this ratio is 0.23. Also, there is asymmetry with respect to distribution of phospholipids. For example, phosphatidylcholine, sphingomyelin are predominantly on the outer leaflet and phosphatidylserine, phosphatidylinositol, phosphatidylethanolamine are predominantly on the inner leaflet.
  1. Write the functions of plasma membrane.
    Plasma membrane is a barrier with selective permeability. It is made up of lipids and proteins. It separates the cell from external environment and divides the interior of cell into different compartments. Fluid outside the membrane is called extracellular fluid and inside the cell is intracellular fluid.
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Functions of Plasma Membrane
  • Protects cytoplasm and organelles
  • Maintains shape and size of the cell
  • Selective barrier—permits transport of required substances in either direction
  • Cell-cell interaction
  • Signal transmission.
  1. Describe the characteristics of facilitated diffusion. Mention two examples of transport by facilitated diffusion.
    Definition: Movement of particles along the concentration gradient with the help of transport proteins. Facilitated diffusion does not require energy, e.g. transport of glucose, galactose, leucine and other amino acids.
 
Mechanism: Ping-pong Model
Carrier protein has two conformations—ping and pong conformation: Pong conformation of the carrier protein exposes it to higher concentration of molecules (solute) to be transported. Binding of molecules induces conformational change in the carrier protein to ping state, which exposes it to lower concentration of the molecules resulting in their release. Once the molecules are released, the conformation of the carrier protein reverts back to pong form (Fig. 1.3).
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Fig. 1.3: Facilitated diffusion
  1. Explain active transport with suitable examples.
    Definition: Carrier-mediated transfer of molecules against the concentration gradient (from lower concentration to higher concentration) with the help of energy [adenosine triphosphate (ATP)]. Substances that are actively transported through cell membranes include Na+, K+, Ca2+, Fe2+, H+, Cl, I. Active transport is susceptible to inhibition and this property is used for designing of drugs in some diseases.
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Classification
  1. Primary active transport: Transport of substrate against its concentration gradient with utilization of energy directly. For example, Na+-K+ ATPase, Ca2+-pump, H+-pump.
  2. Secondary active transport: ATP is used indirectly for transport.
    For example,
    Symport: Glucose-sodium cotransport, amino acid-sodium cotransport; two different substances are carried across the membrane in the same direction.
    Antiport: Sodium-calcium cotransport, sodium-hydrogen pump; two different substances are carried across the membrane in the opposite direction.
 
Primary Active Transport
Na+-K+ ATPase: It pumps 3 Na+ from inside to outside of the cell and brings in 2 K+ from outside to inside of the cell against their concentration gradient, using energy provided by hydrolysis of one ATP molecule (Fig. 1.4).
Inhibitor of Na+-K+ ATPase and its significance:
Digoxin: Used in the treatment of congestive cardiac failure (CCF).
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Fig. 1.4: Na+-K+ antiport (ECF, extracellular fluid; Na+, sodium ion; K+, potassium ion; ADP, adenosine diphosphate; ICF, intracellular fluid)
 
Secondary Active Transport
For example, Na+-glucose cotransport (Fig. 1.5). The Na+- K+ ATPase in the basolateral membrane of the cell transports Na+ out of the cell with the help of energy (ATP hydrolysis) creating a Na+ gradient. This Na+ gradient is used by sodium-glucose cotransporter—sodium moves 6along its concentration gradient into the cell pulling glucose along with it against its gradient. Hence, energy is utilized indirectly.
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Fig. 1.5: Sodium-glucose cotransport
  1. Describe transport processes across the membrane.
    Membrane is a selectively permeable barrier. Non-polar substances gain easy access because of solubility in lipid bilayer, but polar substances cross the membrane selectively.
    Selectivity of membrane transport depends upon:
    1. Size of molecules: Small solutes pass through easily than larger ones.
    2. Charge of the molecule: Molecules with less charge pass through the membrane easily than one with more charges.
    3. Transport proteins: Specific proteins transport specific molecules.
    4. Type of molecules: Water readily traverses through the membrane.
    Classification of transport mechanisms across the membrane:
    1. Passive transport.
    2. Active transport.
    3. Endocytosis/exocytosis.
    4. Ionophores.
      Passive transport: Simple diffusion, facilitated diffusion and transport through ion channels.
      Simple diffusion
      Definition: Movement of the particles across the membrane, along the concentration gradient, without any involvement of carrier proteins. Energy is not required for simple diffusion.
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For example, small and lipophilic molecules like O2, CO2, N2 and H2O are transported by this process.
Facilitated diffusion (Refer question number 6)
Definition: Movement of the particles with the help of transport proteins along the concentration gradient. Facilitated diffusion does not require energy and is carried out by Ping-Pong mechanism (refer Fig. 1.3), e.g. glucose, galactose, leucine and other amino acids.
Ion channels
Ions pass through the ion channels, which open or close in response to a signal. Ion channels are:
  1. Voltage gated: Open due to changes in membrane potential, e.g. Ca2+, Na+ and K+ channels.
  2. Ligand gated: Binding of ligand to receptor site results in opening and closing of the channel, e.g. acetylcholine receptor.
Active transport (Refer question number 7)
Endocytosis and exocytosis
Endocytosis
Uptake of macromolecules into the cells. For example, uptake of low-density lipoproteins (LDL), polysaccharides, proteins and polynucleotides.
Two types:
  1. Pinocytosis: Uptake of fluid and fluid contents by cell (cellular drinking).
  2. Phagocytosis: Ingestion of larger particles like bacterial cells and tissue debris by macrophages, which are further hydrolyzed by lysosome.
Exocytosis
Release of macromolecules from the cell to outside. For example, calcium-dependent secretion from vesicles (secretion of hormones).
Ionophores
Ionophores are the molecules that facilitate transport of ions across membranes.
Two types:
  1. Carrier ionophores: They increase permeability for a particular ion, e.g. valinomycin transports K+ and inhibits oxidative phosphorylation.
  2. Channel-forming ionophores: They facilitate passage of ions by forming channels, e.g. gramicidin A inhibits oxidative phosphorylation by facilitating movement of Na+ and K+ across the membrane.
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