Giáo trình tiếng anh sinh học english in biology phần 2
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Giáo trình tiếng anh sinh học english in biology phần 2
CHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 he glucose units of these large molecules arc joined by glyeosidic bonds linking carbon 4 (or carbon 6) of one glucose molecule with carbon 1 of the adjacent molecule. These bonds are hydrolyzed by amylases . These enzymes will digest polysaccharides to the disaccharide, maltose, but will not split Giáo trình tiếng anh sinh học english in biology phần 2 the bond between the two glucose units of maltose. The amylases will split tire a-glycosidic bonds present in starch and glycogen but not the IJ-glycoGiáo trình tiếng anh sinh học english in biology phần 2
sidic bonds present in cellulose. Hie garden snail’s digestive juice contains R‘glycosidases that can hydrolyze cellulose, in most vertebrates, amylasCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 ivas containing different amounts of amylase ; thus die time required for the salivary digestion of a given amount of starch will vary. You can test the activity of your own saliva by this simple experiment. An estimate of the amount of starch in solution can be obtained by adding a standard amount Giáo trình tiếng anh sinh học english in biology phần 2 of iodine solution, which yields a bluecoloured complex with starch but not with sugar. Place 10 ml. of a dilute boiled starch solution in a test tubeGiáo trình tiếng anh sinh học english in biology phần 2
and add 1 ml of saliva. Mix thoroughly and at tile end of each minute after the addition of the saliva, remove a drop and add it to a drop of iodine CHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 all the starch has been digested. The red colour results from the reaction of iodine with certain intermediate substances formed in tile breakdown of starch to sugar. All enzymes are proteins and are denatured, i.e., rendered inactive, by heating You can prove that the digestion of starch by saliva Giáo trình tiếng anh sinh học english in biology phần 2 is mediated by enzymes by repeating the test using saliva that has been boiled.285286Unit ElevenDisaccharides are cleaved to monosaccharides by enzymeGiáo trình tiếng anh sinh học english in biology phần 2
s that are specific for the particular disaccharide. Maltose is split by maltases present in saliva and in the intestinal juice secreted by intestinalCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 ich split lactose (milk sugar) to glucose and galactose. The ultimate products of the digestion of carbohydrates -die hexoses, glucose, fructose and galactose - are absorbed into the blood stream through the intestinal wall.There are several kinds of hydrolases dial attack die peptide bonds of prote Giáo trình tiếng anh sinh học english in biology phần 2 ins ; each is specific for peptide bonds in a specific location in a polypeptide chain. Exopeptidases cleave the peptide bond joining the terminal ammGiáo trình tiếng anh sinh học english in biology phần 2
o acids to die peptide chain. Carboxypeptidase splits the peptide bond joining the amino acid with the free terminal carboxyl group to the chain, and CHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 a peptide chain. Pepsin , secreted by die chief cells in die gastric mucosa, and trypsin and chymotrypsin , secreted by the pancreas, are endopeptidases but differ in their requirements for specific amino acids adjacent to the peptide bond to be cleaved. These endopeptidases split peptide chains in Giáo trình tiếng anh sinh học english in biology phần 2 smaller fragments which are then cleaved further by exopeptidases. The combined action of die endopeptidases and exopeptidases results in splitting tGiáo trình tiếng anh sinh học english in biology phần 2
he protein molecules to free amino acids, which are then absorbed through the intestinal wall into die blood stream by active transport.These powerfulCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 ch, but are secreted in the form of inactive precursors - pepsinogen, trypsinogen and chymotrypsinogen. This prevents dieir digesting the proteins of the cells diat produce them. In the gut each is activated by die removal of part of die precursor molecule to yield the active enzyme and an inactive Giáo trình tiếng anh sinh học english in biology phần 2 fragment.The digestion of fats is catalyzed by esterases that split the ester bond between glycerol ami fatty acid. The principal mammalian esterase iGiáo trình tiếng anh sinh học english in biology phần 2
s lipase , secreted by die pancreas. Like other proteins, lipase is water-soluble, but its substrates are not. Tims the enzyme can attack only tliose CHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 f fat into very fine ones ; diis greatly increases the surface area of fat exposed to die action of lipase and increases die rate of digestion of lipids. Conditions in the intestine are usually not optimal for the complete hydrolysis of lipids to glycerol and fatty acids. The products of digestion i Giáo trình tiếng anh sinh học english in biology phần 2 nclude glycerol and free fatty acids plus monoacylglycerols, diacylglycerols and some triacylglycerols, undigested fats.The pancreas also secretes ribGiáo trình tiếng anh sinh học english in biology phần 2
onuclease, an esterase which splits the phosphate ester bonds linking adjacent nucleotides in ribonucleic acids, and deoxyribonuclease, which splits tCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 he intestinal mucosa. Phosphodiesterase removes nucleotides one at a time from the end of a polynucleotide chain. The nucleotides in turn are attacked by phosphatases which remove the phosphate group and leave the nucleosides, which are absorbed.It should be noted that these hydrolytic enzymes do no Giáo trình tiếng anh sinh học english in biology phần 2 t usually serve for the formation of the bonds they normally split. Starches are not synthesized by amylases, proteins are not synthesized by pepsin oGiáo trình tiếng anh sinh học english in biology phần 2
r trypsin, and fats are not usually synthesized by lipase. TheEnglish in Biology287synthesis of 4 polysaccharide chain does not involve the removal ofCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 hesized in the cell by enzyme systems that differ, at least in certain key enzymes, from those that take the compound apart.II.BIOLOGICAL TERMS (CÁC THUẬT NGỬ SINH HOC)1.>4n7R/a.se(amilazu): Enzyme which hydrolyses the internal 1,4-glycosidic bonds of starch.2.Chymotrypsin (kimotlipxin) : A peptidas Giáo trình tiếng anh sinh học english in biology phần 2 e of the mammalian digestive system which is specific for peptide ponds adjacent to amio acids with aromatic or bulky hydrophobic side chains.3.DenatuGiáo trình tiếng anh sinh học english in biology phần 2
ration (sự biến tính) : The destruction of the native conformation or state of a biological molecule by heat, extremes of pH, heavy metal ions, chaotrCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 uclure, a process which can I’M' reserved by renaturation or annealing.4.Endopeptidase (endopeptidaza) : An enzyme which cuts a polypeptide chain internally, not just removing terminal peptides.5.Exopeptidases (ekzopeptidaza) : Peptidases which attack terminal peptide linkages, thus spitting off ami Giáo trình tiếng anh sinh học english in biology phần 2 no acids.6.Esterase (esteraza); An enzyme which catalyses the hydrolysis of ester bonds.7.Fatty acids (axit béo) : A term for the whole group of saturGiáo trình tiếng anh sinh học english in biology phần 2
ated and unsaturated monobasic aliphatic carboxylic acids. The lower members of the series are liquids of pungent odour and corrosive action, soluble CHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 lids, insoluble in water, but soluble in ethanol and in ethoxyethane.Medically, saturated fatty acids with no double bonds are linked with the development of atheroma. In contrast the polyunsaturated fatty acids, linoleic, linolenic and arachidonic are termed essential fatty acids as they must be in Giáo trình tiếng anh sinh học english in biology phần 2 cluded in the diet and may have a preventative role against atheroma and are required for the synthesis of prostaglandins (biologically active lipidsGiáo trình tiếng anh sinh học english in biology phần 2
produced during anaphylactic reactions, some of which have antagonistic actions on platelet activation and vascular permeability).8.Glycogen (glicogenCHEMICAL ASPECTS OF DIGESTIONI.TEXTPolysaccharides such as starch and glycogen form an important part of the food ingested by man and most animals. Th Giáo trình tiếng anh sinh học english in biology phần 2 lasm of cuinycete fungi and animals but not in plants or algae.9.Mucosa (Mucous membrane, màng nhãy) : A tissue layer found lining various tubular cavities of the body (as the gut, uterus, trachea etc.). It is composed of a layer of epithelium containing numerous unicellular mucous glands and an und Giáo trình tiếng anh sinh học english in biology phần 2 erlying layer of areolar and lymphoid tissue, separated by a basement membrane.10.Pancreas (tụy) : A moderately compact structure found in VertebratesGiáo trình tiếng anh sinh học english in biology phần 2
, the larger part of which consists of exocrine glandular tissue with one or more ducts opening to the small intestine , and also containing scatteredGọi ngay
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