胆盐的乳化作用属于物理性消化

胆汁的作用主要是由于胆盐或胆酸的作用。胆盐的重要作用之一是作为乳化剂以乳化脂肪,这个作用是属于物理性消化或是化学性消化?在教学实践中常常出现这个问题,往往被少数人理解错。我认为胆盐的乳化作用属于物理性消化。大家知道,食物的消化包括物理性消化和化学性消化,换句话说,食物在消化道中的变化包含着物理性变化和化学性变化。确立这两种变化的基点是食物变化时是否生成了其它物质,如果食物变化时生成了其它物质,为化学性变化,没生成其它物质为物理性变化。我们把通过消化酶对食物的分解作用叫做化学性消化,是因为食物经     

验证胃液消化蛋白质的实验

初中《生物学》教材第 2册在讲述食物的化学性消化这部分内容时 ,由于学生没有学过化学 ,所以对蛋白质的化学性消化学生不易理解。在教学过程中 ,我们采用实验法解释这一过程 ,取得了良好的教学效果。1　制备人造胃液取 10片胃蛋白酶片 ,放入烧杯中 ,用清水溶去药片外面的糖衣 ,然后取出药片 ,放入研钵中研碎 (加少量的水 ) ,加 10 0 m L蒸馏水充分混合 ,并过滤。然后再加 10 0 m L蒸馏水和 2 0 m L3%的盐酸配制成人造胃液备用。2　实验过程　　课前教师取两块形状 ,大小相同的瘦肉条 ,一条浸入盛有清水的大试管甲内 ,另一条浸入盛有人造…     

怎样做好“唾液淀粉酶的消化作用”的实验

“唾液淀粉酶的消化作用”实验是初中生物课的经典实验。做好这个实验,能帮助学生较为深刻地了解消化酶的作用及酶的催化作用受哪些外界因素的影响,从而突破食物的消化这个教学难点。该实验取材方便,操作简单,但要取得理想的实验结果,应注意以下几方面：（1）观察低温对唾液淀粉酶的影响此实验成功的关键是预先对唾液和淀粉液进行冷处理。具体做法是将唾液与淀粉液挪置于冰水（0～3”C）中3min,然后将淀粉液与唾液在冰水中迅速混匀,保温10min后,立即滴加碘液,可观察ffig理想的实验结果。原因分析：酶是生物活细胞产生的具有催化能…     

在“唾液淀粉酶对淀粉的消化作用”实验中值得讨论的几个问题

在中学生理实验中,有一个“唾液淀粉酶对淀粉的消化作用”实验。实验是这样作的:取1、 2两个试管,各注入2毫升浆糊,再向1号管注入2毫升清水,向2号管注入2毫升唾液。把2个试管放在盛着37℃的温水的烧杯里,约过10分钟,取出2个试管,待冷却后,向两个试管各滴2滴碘酒,1号管变成蓝色,2号管蓝色消失,呈无色。此实验想说明2号管内唾液对淀粉的消化作用。对这个实验,我作了一些粗浅的研究,提出几个问题,和大家研究讨论。     

如何利用教材中的著名实验进行教学

高中《生物学》新教材与老教材比较 ,变化较大的就是增加了许多著名的经典的生物学实验。如意大利科学家斯巴兰让尼设计了一个巧妙的实验 ,说明胃具有化学性消化的作用。美国科学家切赫和奥特曼发现少数RNA也具有生物催化作用 ,从而改变了“酶的化学本质是蛋白质”的观点。在“光合作用”一节中 ,新增加了许多著名的实验来说明光合作用是如何发现的 ,等等。这些著名的实验是历史上生物学规律和理论建立的依据 ,是科学家创造性思维活动的典范。在教学中 ,如何利用这些实验教育学生 ,将对学生实验能力的培养和对学生科学素养及思维能力的培…     

试析初中生物的识图教学

识图教学是初中生物教学中的一个重要组成部分,识图教学作用发挥得好,对教师,对学生都非常有利。那么如何充分发挥识图教学在整个初中生物教学中的作用,这就是本文所要探讨的问题。     

应改为"淀粉遇碘变蓝"

《生物学通报》2 0 0 0年第 5期“‘唾液淀粉酶对淀粉的消化作用’一节探索课的尝试”一文中写道 :“如在设计‘唾液淀粉酶对淀粉的消化作用’实验中 ,启发学生思考实验的原理 ,即淀粉遇碘酒变蓝。唾液中有唾液淀粉酶 ,它能消化淀粉为麦芽糖 ,而麦芽糖遇碘酒不变色。”文中出现“淀粉遇碘酒变蓝”、“麦芽糖遇碘酒不变色”的说法值得商确。“碘酒 ,碘汀俗称 ,是碘和碘化钾的稀酒精溶液 ,在溶液中 I- I2 I-3 。在溶液中极微量的碘与淀粉相遇立即形成深蓝色的加合物 ,这是定性检验碘的灵敏方法。淀粉是由许多葡萄糖分子缩合而成的多糖 ,分子…     

大熊猫胃肠道中消化酶活力的分析

为了研究大熊猫对食物的化学性消化特点和机制,测定了9只大熊猫唾液和3只大熊猫胃肠道中主要消化酶的活力,并与其他动物进行了比较.结果显示,大熊猫唾液呈碱性,蛋白酶和淀粉酶等消化酶活力低;肠道中淀粉酶活力高,而脂肪酶活力明显低于棕熊.大熊猫小肠粘膜中存在显著量的蔗糖酶、乳糖酶和麦芽糖酶活力.另外,在1只大熊猫胃和直肠液中检测到了少量纤维素酶活力.研究结果提示,大熊猫唾液直接参与食物消化的作用可能很弱;大熊猫对淀粉类食物有很好的消化能力,但对脂肪类食物消化能力相对不高.大熊猫胃肠道消化酶的活力特点适应其消化天然食物中的营养物质.     

对“观察唾液淀粉酶对淀粉的消化作用”实验的改进

在指导学生进行该实验时,发现教材对以下问题处理不妥：（1）无量简（材料用具）,如何量取2ml的溶液？（2）要求向试管内滴入清水或唾液2ml,但材料用具中没有滴管,并且满多少滴,大滴还是小滴,学生不易把握。（3）取唾液的方法不卫生,不雅观。（4）淀粉的特性可以让学生去检验,不必平铺直叙。针对以上问题,我对该实验作了一些改动,下面就是改进后的实验。目的要求（略）材料用具大烧杯、试管、滴管、量简、吸管、酒精灯、温度计、碘液、干淀粉、清水、三脚架方法步骤互制备淀粉浆糊（略,课前制好）2检验淀担的特性取一试管,注入…     

“观察唾液淀粉酶对淀粉的消化作用”实验的改进

“观察唾液淀粉酶对淀粉的消化作用”实验的改进按实验要求，取１ｇ干淀粉放在烧杯里，加清水煮沸，作成浆糊备用。这种当堂配制的方法太费时，影响后面的实验。此外，这种浆糊还有两个明显的缺点：一是浆糊遇碘显紫红色。学生从小学以来一直接受淀粉遇碘变蓝的认识，这显...     

In vitro digestion and fermentation characteristics of canola co-products simulate their digestion in the pig intestine

Canola co-products are sources of amino acid and energy in pig feeds, but their fermentation characteristics in the pig intestine are unknown. Thus, we determined the in vitro fermentation characteristics of the canola co-products Brassica juncea solvent-extracted canola meal (JSECM), Brassica napus solvent-extracted canola meal (NSECM), B. napus expeller-pressed canola meal (NEPCM) and B. napus cold-pressed canola cake (NCPCC) in comparison with soybean meal (SBM). Samples were hydrolysed in two steps using pepsin and pancreatin. Subsequently, residues were incubated in a buffer solution with fresh pig faeces as inocula for 72 h to measure gas production. Concentration of volatile fatty acids (VFA) per gram of dry matter (DM) of feedstuff was measured in fermented solutions. Apparent ileal digestibility (AID) and apparent hindgut fermentation (AHF) of gross energy (GE) for feedstuffs were obtained from pigs fed the same feedstuffs. On DM basis, SBM, JSECM, NSECM, NEPCM and NCPCC contained 15, 19, 22, 117 and 231 g/kg ether extract; and 85, 223, 306, 208 and 176 g/kg NDF, respectively. In vitro digestibility of DM (IVDDM) of SBM (82.3%) was greater (P<0.05) than that of JSECM (68.5%), NSECM (63.4%), NEPCM (67.5%) or NCPCC (69.8%). The JSECM had greater (P<0.05) IVDDM than NSECM. The IVDDM for NSECM was lower (P<0.05) than that for NEPCM, which was lower (P<0.05) than that for NCPCC. Similarly, AID of GE was greatest for SBM followed by NCPCC, JSECM, NEPCM and then NSECM. Total VFA production for SBM (0.73 mmol/g) was lower (P<0.05) than that of JSECM (1.38 mmol/g) or NSECM (1.05 mmol/g), but not different from that of NEPCM (0.80 mmol/g) and NCPCC (0.62 mmol/g). Total VFA production of JSECM was greater (P<0.05) than that of NSECM. Total VFA production of NSECM was greater (P<0.05) than that of NEPCM or NCPCC, which differed (P<0.05). The ranking of feedstuffs for total VFA production was similar to AHF of GE. In conclusion, in vitro fermentation characteristics of canola co-products and SBM simulated their fermentation in the small and large intestine of pigs, respectively. The 30% greater VFA production for JSECM than NSECM due to lower lignified fibre of JSECM indicates that fermentation characteristics differ between canola species. The NSECM had the highest fermentability followed by NEPCM and then NCPCC, indicating that fat in canola co-products can limit their fermentability in the hindgut.     

Carboxypeptidase digestion in the presence of detergents

The detergents, sodium dodecyl sulfate (SDS), lauryl glutamate (LG), and octyl-(polydisperse)oligooxyethylene (Octyl-POE), were tested as to their effects on the activities of carboxypeptidases A, B, and P. In general, Octyl-POE showed little inhibition and SDS showed the strongest inhibition. Carboxypeptidase B was only slightly inhibited by SDS. The inhibitory effect of SDS on these enzyme activities depended not on its concentration but on its absolute amount. For a constant amount of SDS, the activities of carboxypeptidases A and B remained almost constant with increasing reaction volume. Commercial carboxypeptidase B is usually contaminated by carboxypeptidase A. With the addition of SDS, almost only carboxypeptidase B activity was detected.     

Cellulose digestion by the firebrat Thermobia domestica

• 1.1. A highly efficient cellulose digestion could be demonstrated in a primitive insect species, Thermobia domestica (Thysanura:Lepismatidae), by the application of a uniformly ¹⁴C-labelled substrate.
• 2.2. Gut extracts exhibit distinct hydrolytic activities toward different cellulosic substrates (cellobiose, sodium carboxymethylcellulose and microcrystalline cellulose). Therefore, the complete cellular complex must be present.
• 3.3. Besides cellulases, several other carbohydrates occur in the digestive juice, thus reflecting the omnivorous feeding habits of the insect.
• 4.4. The crop was found to be the main site of carbohydrate digestiopn, also including cellulolysis.
• 5.5. It is very likely that the cellulolytic enzymes derive from the gut tissues of the firebrat.

     

Betaine improved restriction digestion

Here we report that supplementation of a common compound betaine (1-carboxy-N,N,N-trimethylmethanaminium inner salt) enhances restriction digestion of DNA molecules being resistant to digestion despite the existence of recognition sites. A previous study reported total isostabilization of DNA was achieved in the presence of 5.2M of betaine, however, we have observed the enhancement of restriction kinetics at 0.3M of betaine, therefore, it likely provided some catalytic proficiency to restriction enzymes rather than the induction of DNA conformational changes. Betaine also enhances catalytic efficiency of PCR, and our result of restriction digestion, taken together, suggests potential application of betaine in other enzymatic reactions in an aqueous solution.