a r X i v :0704.3175v 1 [c o n d -m a t .s o f t ] 24 A p r 2007E?ects of Eye-phase in DNA unzipping
Debaprasad Giri ?and Sanjay Kumar
Department of Physics,Banaras Hindu University,Varanasi 221005,India
Max-Planck Institute for the Physics of Complex Systems,
Noethnitzer,01187Dresden,Germany ?Physics Section,MMV,Banaras Hindu University,Varanasi 221005,India Abstract The onset of an “eye-phase”and its role during the DNA unzipping is studied when a force is applied to the interior of the chain.The directionality of the hydrogen bond introduced here shows oscillations in force-extension curve similar to a ”saw-tooth”kind of oscillations seen in the protein unfolding experiments.The e?ects of intermediates (hairpins)and stacking energies on the melting pro?le have also been discussed.PACS numbers:64.90.+b,36.20.Ey,82.35.Jk,87.14.Gg
Molecular interactions play a key role in living organisms.Recent advances in experimental techniques have allowed nanomanipulation in single biological molecule and made possible to mea-sure these interactions[1].The aim is to exert a force in the pN range by optical tweezers,atomic force microscopy,etc and characterize the molecular,elastic,structural and functional properties of bio-molecules[2,3].In typical experiments of double stranded DNA(dsDNA)unzipping,a force is applied to the ends of the chain(Fig.1a)and one studies the force-extension curve which shows the elastic properties and the gross features that re?ect the local‘G-C’vs‘A-T’content along the sequence[4,5,6,7,8].Moreover,the force-temperature diagram shows,below the melting temperature,that the over-stretching force[8]decreases nearly linearly with temperature.
Theoretically,DNA unzipping may be studied in di?erent ensembles[9]depending on the ex-periments.For example,Atomic force microscopes(AFM)work in constant distance ensemble (CDE)while magnetic bead uses the concept of constant force ensemble(CFE).The prediction of unzipping transition based on interacting Gaussian chains[10]raised a lot interest and now results are available from dynamical approach[11],exact solutions of lattice models[12,13],simple models of quenched-averaged DNA[14,15],numerical simulations and scaling analysis[16,17].Recently for a model of interacting polymers where any monomer of one chain can interact with any monomer of the other chain(we call it model A),the role of an intermediate entropy-stabilized phase was recognized and a force-induced triple point[18]in a force-temperature plane was established.
In most of the models studied for dsDNA[12,13,14,15,16,19],a monomer i of one strand can only interact with the i-th monomer of the other strand,which is similar to the models of DNA(we call it model B)proposed earlier by Poland and Scheraga[20].These models do not take into account the directional nature of the hydrogen bond and underestimate the entropy by restricting the formation of hydrogen bonds.Thus these models may only give a limited picture of the unzipping transition and do not allow to study the e?ect of intermediate states[21].
So far,most of the theories of DNA unzipping have focused on the thermodynamic limit,and therefore,consist of a few parameters typically in the form of an e?ective base-pair interaction in a simpli?ed way.In all the single molecule experiments,a?nite size chain is used and hence no“true phase transition”can in principle be observed.Still,the“phase transition”observed in such experiments may be considered as real if the length of the chain exceeds the characteristic correlation lengths.It is now becoming possible to go to the other limit of studying shorter segments(～10base pair)at coarse grained level[22,23].The purpose of this letter is to provide exact results of a semi-microscopic model of short chains by incorporating the directional nature of hydrogen bonds and then propose a method to study the e?ect of molecular interactions right at the individual base pair level and their role on melting pro?le.
In the following,we adopt a more realistic model of DNA,which may be de?ned in any dimension
(a)
(c)(d)(e)
FIG.1:The schematic representation of DNA unzipping by force(g)applied at(a)one end of the two strands;(b)at the interior of the strands.Figs.(c-e)represent the possible conformations of model C.Here (c)represents the completely zipped state,(d)a non pairing con?guration and(e)a partial bound state with hairpin loop.
[24](herein after we call it model C).A similar model has been used in Ref.24in the context of relative stabilities of DNA hairpin structures.The model takes care of important shortcomings of model B and also incorporates some additional features like existence of intermediate states, e?ects of stacking energy,excluded volume properties of nucleotides and the directional nature of hydrogen bonds.
Although the importance of bubble formation during thermal melting has been recognized,no attempt has been made so far to experimentally explore the phase diagram when a force is applied to the interior of the chain as shown in Fig1b.Such situations occur in many biological processes, for example,during gene-expression,RNA forms bubbles or“eye-type”conformations on DNA. Therefore,we consider two cases:(i)force has been applied at the end of the chain(Fig.1a,‘END’case or Y case),and(ii)at the middle of the chain(Fig.1b,‘MID’case).The contribution to energy by this force,g,is?2gx,where2x is the absolute distance in the x-direction between the two strands at the point of application of the force.
We model the two strands(e.g.A-T)of a homopolymer DNA by two mutually-attracting-self-avoiding walks(MASA Ws)on a square lattice as shown in Figs.1(c-e).The bases are associated with the link between two monomers of a chain as depicted in Fig.1.In one strand the bases point towards the right while on the other they are on the left,as one traverses the chains sequentially.We associate a contact energy??(e?ective base pair interaction)with each pairing between complementary strands only if the bases are nearest neighbors(short range nature of the hydrogen bond)and approach each other directly without the strands coming in between[Fig.1c]. Fig.1e shows the possibility of formation of hairpin(which is not possible in model B)in a single strand of DNA.However,in this case,non-native contribution has been taken into account but no
FIG.2:Variation of critical force()for model B and C.
apparent weight has been assigned to stem as it is made up of same nucleotides.
The partitions function(Z N)of the system under consideration can be written as a sum over
all possible con?gurations of MASA W s i.e.
m,x
C(m,x)exp(βm?)exp(βgx),whereβ=1/k B T
is the inverse temperature,k B being the Boltzmann constant.C(m,x)is the number of distinct conformations walks of length2N having m number of intact base pairs whose end(or mid)points are at a distance x apart.We have obtained C(m,x)for N≤16and analyzed the partition function using exact enumeration and series analysis technique[25,26].We prefer this technique because it can predict various phases of the system[27]quite e?ectively and the scaling corrections can be correctly taken into account by a suitable extrapolation methods[25,26].To achieve the same accuracy in Monte Carlo,a chain of two orders of magnitude larger than in the exact enumeration method is required[28].We set?/k B=1and calculate the reduced free energy per base pair from the relation G(T,g)=lim N→∞1
?(1/T)2
.
A force-temperature(g?T)phase diagram of model
B and
C for end and mid case is shown in Fig. 2.The qualitative features of the phase diagram obtained here may be compared with experiments[8].The phase boundary separates the zipped and the unzipped state.At T=0,the critical force can be found from a simple analytic calculation and is equal to0.5[18]that is in agreement with the one from Fig.2.
Experimentally,the melting pro?les are obtained by monitoring the change in the UV ab-sorbence with temperature which provides the information about the fraction of open base pairs and the melting temperature is de?ned when half of the total base pairs get open[29].Another quantity of experimental interest is to monitor and measure the end separation by varying the force.
We calculate these quantities from the expressions
N
and
N and plot their variations with temperature and
force in Figs.3and4,respectively.It is evident from Fig.3that,with increasing temperature
FIG.3:Variation
(MID);(b)with
dot and
FIG.4:Plot of
constant g=0.25
(or force),the
state to the
Remarkably,
double the force
with the exact
double the force
Another interesting observation is the variation of average elongation with force which shows a monotonically increasing trend(Fig.4a)at constant temperature and approaches unity.Meanwhile the variation of extension at constant force shows a sharp rise with temperature(Fig.4b)and then a slight decline to approach a value below unity.At constant temperature,there is a transition from the zipped to the unzipped(“rod-like”)state.Keeping force constant,when temperature is varied,there is a transition and the chain acquires conformations close to the rod-like states. As this temperature is still low,with further increase in temperature,the entropy of the system increases and the chain acquires coil-like state at higher temperature and thus average distance decreases.
We also study the probability distribution curves P(x)with x and P(m)with m for
model B and C de?ned by P(x)=
m
C N(m,x)exp(βm?)exp(βgx)/Z N and P(m)=
x C N(m,x)exp(βm?)exp(βgx)/Z N respectively.In Figs.5(a-f)we have shown P(x)and P(m)
FIG.5:Figs.(a-f)
at constant T=0.3.Fig.5e
the mid case in model C but absent in model B.
for di?erent values of force and a?xed temperature T=0.3.The x-component of the distribution function gives information about the states of dsDNA.The maxima of P(x)at x≈0correspond to the zipped state for a given set with g=0.1and T=0.3.For small forces,thermal?uctuations are too weak to unzip the strand and the DNA remains in the zipped state.This is being re?ected in the structure-less distribution function with a well de?ned peak at the most likely value of the extension(Figs.5a and5d).For both the models at higher force and at the same temperature (g=0.6for end and0.95for mid respectively at T=0.3),thermal?uctuations have been sup-pressed by a strong force and strands are found in the segregated“rod-like”state with more or less an identical distribution peaked at maximum extension.However,striking di?erences are observed in the probability distribution curves for model B and C at intermediate forces below transition line(g?T plane)when the force is applied in the middle.No such di?erences are observed for the end case.For the mid case,the probability distribution curve of model C shows strong oscil-lations,whereas for model B no such oscillations are observed.This indicates that the model B may be described by two state models.However,model C shows that certain intermediates states (“eye-shape”of even width)are more favorable than others.
It is interesting to note that the g?T phase diagram of model B and C are almost identical without any re-entrance at low temperature.This may be because of the fact that the energy of the ground state and the unbound state for both models are the same.At the center point of the‘Y’(end case),the phase boundary is determined by a balance of the net force-2gx and the
(a)(b)(c)
FIG.6:Schematic diagrams showing the di?erent conformations keeping2x(≤Nν)distance constant.For model B,(b)and(c)has same weight while for model C,(c)has more weight than(b).
unzipping potential??m with associated entropy.In the thermodynamic limit,directionality of the hydrogen bonds,which appear in the form of entropy of the partial bound states does not play a crucial role in this balance.The absence of re-entrance is understood with the zero entropy of the ground state for both models.As shown recently by Kapri et al.[13]for mid case,in the CDE there is a possibility of a coexistence region that is better thought of as an“eye-phase”≡two‘Y’joined together.In this case,the separation at the point of application of force is smaller than the fully open case and thus such conformations statistically have more weight than the other conformations.
Since the bottom end is kept?xed,the top side of the strand may open due to thermal?uc-tuations(Fig.6b)and form a partial bound state as shown in Fig.6c which is more stable than Fig.6b.Therefore,in model C,the half of the chain undergoes an unzipping transition while other half due to the non-native contacts,shows the combined e?ects of unzipping and slippage (shearing)transition.Thus in the model C,the transition appears more smoother than the model B which can be seen in Fig.3b.The consecutive peaks in P(x)vs x curve(Fig.5e)represent the“eye-phase”of even widths which contribute most to the partition function.Because of native contacts,the contribution of the“eye-shape”conformation is signi?cantly less and small thermal ?uctuations are su?cient to unzip the chain in model B.
We substantiate our arguments by extending calculation in CDE also.The partition function
in CDE may be de?ned as Z N(x,T)=
m
exp(βm?).The two ensemble are related by Z N(T,g)=
x
Z N(x,T)exp(βgx)[13,14].The free energy is given by the relation F N(x,T)=?T ln Z N(x,T). In CFE the average separation
FIG.7:
To see this,we associate an
possible in model C)and
shift in the transition
becomes sti?er.However,it
distribution curves for the‘MID’case.
The exact results on short chains of a new semi-microscopic dsDNA that incorporates the directional nature of hydrogen bond show unequivocal signature of an“eye phase”,without going to the long chain limit.This happens for the case with a force acting in the middle of the dsDNA. The variation of elongation due to the force in di?erent ensembles has di?erent behaviour both qualitatively and quantitatively.We anticipate that re?nements in high precision single molecule experiments will be able to verify these predictions.
We thank Y.Singh,S.M.Bhattacharjee and Je?Chen for many fruitful discussions on the subject and University Grants Commission,India for the?nancial assistance.One of us(SK) would like to acknowledge?nancial support from MPIPKS,Dresden,Germany.
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比较级与最高级 1.as...as 与(not) as(so)...as as...as...句型中，as的词性 第一个as是副词，用在形容词和副词的原级前，常译为“同样地”。第二个as是连词，连接与前面句子结构相同的一个句子(相同部分常省略)，可译为“同..... He is as tall as his brother is (tall) . (后面的as 为连词) 只有在否定句中，第一个as才可换为so 改错: He is so tall as his brother.（X） 2.在比较状语从句中，主句和从句的句式结构一般是相同的 与as...as 句式中第二个as一样，than 也是连词。as和than这两个连词后面的从句的结构与前面的句子大部分情况下结构是相同的，相同部分可以省略。 He picked more apples than she did. 完整的表达为: He picked more apples than she picked apples. 后而的picked apples和前面相同，用did 替代。 He walked as slowly as she did.完整表达为: He walked as slowly as she walked slowly. she后面walked slowly与前面相同，用did替代。
3.谓语的替代 在as和than 引导的比较状语从句中，由于句式同前面 主句相同，为避免重复，常把主句中出现而从句中又出现的动词用do的适当形式来代替。 John speaks German as fluently as Mary does. 4.前后的比较对象应一致 不管后面连词是than 还是as,前后的比较对象应一致。The weather of Beijing is colder than Guangzhou. x than前面比较对象是“天气”，than 后面比较对象是“广州”，不能相比较。应改为: The weather of Bejing is colder than that of Guangzhou. 再如: His handwriting is as good as me. 应改为: His handwriting is as good as mine. 5.可以修饰比较级的词 常用来修饰比较级的词或短语有: Much,even,far,a little,a lot,a bit,by far,rather,any,still,a great deal等。 by far的用法: 用于强调，意为“...得多”“最最...”“显然”等，可修饰形容词或副词的比较级和最高级，通常置于其后，但是若比较级或最高级前有冠词，则可置于其前或其后。
大学生毕业晚会主持词 A：青春是一曲荡气回肠的歌，三年前我们怀着彩色梦想走进了鄂大，三年中我们有过欢笑，流过泪水，经历磨炼，得到成长 B：三年后的今天，我们在这里重温青春过往，因为明天就将各奔天涯。也正因为此，今夜，我们承载了太多的祝福与惦念，寄托了太多的关怀与企盼。 C：今晚，让我们再一次重温，那些感动过我们的人和事：灯火通明的教学楼里用功的身影，篮球场上捍卫集体尊严的男儿霸气，满是欢声笑语的宿舍边不着边际的闲谈…… D：又一个三年轮回之后，在同样微凉的夏夜，你是否会记起校园里的梧桐树，你是否会记起日记本里的书签，那些五彩缤纷的日子？ A：无数个三年之后，你们的思念是否会有增无减？在你成长的岁月里，在你闯荡社会的每一天，是否会有那么几个瞬间让你渴望回到过去 B：让我们静静享受一下挑战，在日复一日与时间的赛跑中，你会变得更加坚强，更加神采奕奕！又一个青春之旅从今晚启航，又一个光阴的故事在今晚讲述 C：亲爱的同窗，不要带着离别的愁绪，因为明天又是一个新的起点，因为我们相信再次相逢，我们还是一首动人的歌！D：很高兴今天能有这个机会同大家相聚一堂，共叙离别。就让今天铭刻在我们心间，让母校留住我们的风采！ A：今天，我们也非常荣幸的请到了…… B：下面让我们用热烈的掌声有请……上台讲话 结束语A：欢快的舞蹈表达不尽我们对母校的敬意 B：热情的赞歌唱不尽我们对母校的一腔深情
C：流火的六月，我们将带着恩师的叮咛，怀着必胜的信心，走向新的征程 D：绚烂的七月，我们将载着母校的祝愿，带着亲人的希望，向着新的征程扬帆起航A：老师们，同学们，欢送10级毕业生联欢晚会合：到此结束 A李：毕业，是一个沉重的动词； 刘：毕业，是一个让人一生难忘的名词； 李：毕业，是感动时流泪的形容词； 刘：毕业，是当我们以后孤寂时候，带着微笑和遗憾去回想时的副词； 李：毕业，是我们夜半梦醒，触碰不到而无限感伤的虚词。 刘：若干年后，假如我们还能够想起那段时光，也许这不属于难忘，也不属于永远，而仅仅是一段记录了成长经历的回忆。 李：尊敬的各位领导老师 刘：亲爱的各位同学们 合：大家晚上好！ 李：很荣幸和大家相聚在这激情如火的六月，在这充满忧伤的六月！ 刘：很高兴和大家相聚在“放心去飞，20年后再相聚—毕业晚会”现场！ 李：我是李扬 刘：我是刘伟清 李：今天晚会现场非常荣幸的邀请到院系的各位领导和老师们。 刘：让我们首先欢迎…… 李：灿烂的星空曾经铭刻你我的笑容
人教版（新目标）初中英语形容词与副词的比较级与最高级 （一）规则变化： 1．绝大多数的单音节和少数双音节词，加词尾-er ，-est tall—taller—tallest 2．以不发音的e结尾的单音节词和少数以-le结尾的双音节词只加-r，-st nice—nicer—nicest , able—abler—ablest 3．以一个辅音字母结尾的重读闭音节词或少数双音节词，双写结尾的辅音字母，再加-er，-est big—bigger—biggest 4．以辅音字母加y结尾的双音节词，改y为i再加-er，-est easy—easier—easiest 5．少数以-er，-ow结尾的双音节词末尾加-er，-est clever—cleverer—cleverest, narrow—narrower—narrowest 6．其他双音节词和多音节词，在前面加more，most来构成比较级和最高级 easily—more easily—most easily （二）不规则变化 常见的有： good / well—better—best ; bad (ly)/ ill—worse—worst ; old—older/elder—oldest/eldest many / much—more—most ; little—less—least ; far—farther/further—farthest/furthest
用法： 1．原级比较：as + adj./adv. +as（否定为not so/as + adj./adv. +as）当as… as中间有名字时，采用as + adj. + a + n.或as + many / much + n. This is as good an example as the other is . I can carry as much paper as you can. 表示倍数的词或其他程度副词做修饰语时放在as的前面 This room is twice as big as that one. 倍数+as+adj.+as = 倍数+the +n.+of Your room is twice as larger as mine. = Your room is twice the size of mine. 2．比较级+ than 比较级前可加程度状语much, still, even, far, a lot, a little, three years. five times,20%等 He is three years older than I (am). 表示“（两个中）较……的那个”时，比较级前常加the（后面有名字时前面才能加冠词） He is the taller of the two brothers. / He is taller than his two brothers. Which is larger, Canada or Australia? / Which is the larger country, Canada or Australia? 可用比较级形式表示最高级概念，关键是要用或或否定词等把一事物（或人）与其他同类事物（或人）相分离 He is taller than any other boy / anybody else.
大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和 -est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音字母然后再加 -er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不 形容词比较级的用法: 形容词的比较级用于两个人或事物的比较,其结构形式如下: 主语+谓语(系动词)+ 形容词比较级+than+ 对比成分。也就是, 含有形容词比较级的主句+than+从句。注意从句常常省去意义上和主句相同的部分, 而只剩下对比的成分。
英语比较级和最高级的用法归纳 在学习英语过程中，会遇到很多的语法问题，比如比较级和最高级的用法，对于 这些语法你能够掌握吗？下面是小编整理的英语比较级和最高级的用法，欢迎阅读！ 英语比较级和最高级的用法 一、形容词、副词的比较级和最高级的构成规则 1.一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级 在后面加-est; (1)单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest (2)双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2.以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st; 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3.在重读闭音节(即：辅音+元音+辅音)中，先双写末尾的辅音字母，比较级加-er，最高级加-est; 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4.以“辅音字母+y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est; 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5.其他双音节词和多音节词，比较级在前面加more，最高级在前面加most; 如：bea utiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily 注意：(1)形容词最高级前通常必须用定冠词 the，副词最高级前可不用。 例句： The Sahara is the biggest desert in the world. (2) 形容词most前面没有the，不表示最高级的含义，只表示"非常"。 It is a most important problem. =It is a very important problem.
湘艺版五年级音乐《长白山下的歌谣》 教学设计 《长白山下的歌谣》教学设计 教材版本：湘艺版音乐教材 教学对象：五年级上期 一、教学案例： （一）题：《长白山下的歌谣》音乐综合 （二）教材版本：湘版新标实验教材 （三）年级：五年级 （四）教具准备：钢琴、AI、打击乐器、朝鲜族服饰、长鼓、金达莱花。 （五）教学目标： ①、认知目标：认真听赏朝鲜民歌《道拉基》，学习三拍子节奏特点。 ②、能力目标：通过小组合作学习（设计身势节奏、用长鼓为歌曲伴奏、即兴歌舞等形式）培养学生的创新能力、合作能力，体验朝鲜族民歌的韵律。 ③、情感目标：通过感受性学习歌曲《金达莱花开朵朵红》，了解朝鲜族人民勤劳淳朴、团结互助、热情好客、能歌善舞的优良传统与民族风情。 （六）设计思路： 五十六个民族五十六枝花，生活在吉林省长白山脚下的
朝鲜族，其歌舞有着独特的节奏韵律。湘版新标实验教材五年级上册第八单元题为：《长白山下的歌谣》，它引起了我的研究兴趣。本单元的教育主题为：用民族音乐激发学生的爱国情感，实现多元文化的交流。即：通过音乐去感受民族文化，进而去了解民族文化；反之，通过文化，我们才可以去体验民族音乐，整体地去认识民族音乐。本时选用听赏《桔梗谣》和演唱歌曲《金达莱花开朵朵红》这两部分内容，教学设计的基本思路是：使学生通过多种形式听、唱“长白山下的歌谣”，深刻体验民族音乐“原生态”的美，以及其歌舞文化、思想内涵；在师生平等互动的学习氛围里，通过实践创作、对歌曲的再表现等形式，激发学生热爱民族音乐、热爱我们伟大祖国的情感。 堂教学中我以“新程”为指导思想，对教学设计进行了一些新的尝试。以下结合自己教学实践中的堂教学个案，和大家共同评析与探讨。 （七）教学过程 ᠄ 导入新过程：即“看风景”。 、AI播放《大长今》影片，背景音乐:《大长今》的主题曲《希望》。 （学生起立，跟随老师自由律动。） 师：刚才同学们听到的旋律出自？
More than的用法 A. “More than+名词”表示“不仅仅是” 1)Modern science is more than a large amount of information. 2)Jason is more than a lecturer; he is a writer, too. 3) We need more than material wealth to build our country.建设我们国家，不仅仅需要物质财富. B. “More than+数词”含“以上”或“不止”之意，如： 4)I have known David for more than 20 years. 5)Let's carry out the test with more than the sample copy. 6) More than one person has made this suggestion. 不止一人提过这个建议. C. “More than+形容词”等于“很”或“非常”的意思，如： 7)In doing scientific experiments, one must be more than careful with the instruments. 8)I assure you I am more than glad to help you. D. more than + (that)从句，其基本意义是“超过（=over）”，但可译成“简直不”“远非”.难以，完全不能（其后通常连用情态动词can） 9) That is more than I can understand . 那非我所能懂的. 10) That is more than I can tell. 那事我实在不明白。 11) The heat there was more than he could stand. 那儿的炎热程度是他所不能忍受的 此外，“more than”也在一些惯用语中出现，如： more...than 的用法 1. 比……多，比……更 He has more books than me. 他的书比我多。 He is more careful than the others. 他比其他人更仔细。 2. 与其……不如 He is more lucky than clever. 与其说他聪明，不如说他幸运。 He is more （a）scholar than （a）teacher. 与其说他是位教师，不如说他是位学者。 注：该句型主要用于同一个人或物在两个不同性质或特征等方面的比较，其中的比较级必须用加more 的形式，不能用加词尾-er 的形式。 No more than/not more than 1. no more than 的意思是“仅仅”“只有”“最多不超过”，强调少。如： --This test takes no more than thirty minutes. 这个测验只要30分钟。 --The pub was no more than half full. 该酒吧的上座率最多不超过五成。-For thirty years，he had done no more than he （had）needed to. 30年来，他只干了他需要干的工作。 2. not more than 为more than （多于）的否定式，其意为“不多于”“不超过”。如：Not more than 10 guests came to her birthday party. 来参加她的生日宴会的客人不超过十人。 比较： She has no more than three hats. 她只有3顶帽子。（太少了） She has not more than three hats. 她至多有3顶帽子。（也许不到3顶帽子） I have no more than five yuan in my pocket. 我口袋里的钱最多不过5元。（言其少） I have not more than five yuan in my pocket. 我口袋里的钱不多于5元。（也许不到5元） more than, less than 的用法 1. （指数量）不到，不足 It’s less than half an hour’s drive from here. 开车到那里不到半个钟头。 In less than an hour he finished the work. 没要上一个小时，他就完成了工作。 2. 比……（小）少 She eats less than she should. 她吃得比她应该吃的少。 Half the group felt they spent less than average. 半数人觉得他们的花费低于平均水平。 more…than,/no more than/not more than (1)Mr．Li is ________ a professor; he is also a famous scientist． (2)As I had ________ five dollars with me, I couldn’t afford the new jacket then． (3)He had to work at the age of ________ twelve． (4)There were ________ ten chairs in the room．However, the number of the children is twelve． (5)If you tel l your father what you’ve done, he’ll be ________ angry． (6)－What did you think of this novel? －I was disappointed to find it ________ interesting ________ that one． 倍数表达法 1. “倍数+形容词（或副词）的比较级+than+从句”表示“A比B大（长、高、宽等）多少倍” This rope is twice longer than that one.这根绳是那根绳的三倍（比那根绳长两倍）。The car runs twice faster than that truck.这辆小车的速度比那辆卡车快两倍（是那辆卡车的三倍）。 2. “倍数+as+形容词或副词的原级+as+从句”表示“A正好是B的多少倍”。
大学毕业晚会主持词四人 四个主持人主持的大学毕业晚会应该怎么说主持词呢下面小编跟大家分享几篇大学毕业晚会主持词，以供参考! 大学毕业晚会主持词一 1.节奏引领时尚，余音环绕广场，新鲜的韵律，高难度的声响，一样为您缔造不一样的完美想象，下面请欣赏来自07音乐班的xxx为您带来的《》相信会给您带来意外的惊喜。 2.铃声清脆鼓铿锵，天山铃舞尽展情，来自天山的自然是蝶飞花影动，美丽各不同，那就让我们停下脚步，一饱眼福，欣赏由xxx为我们带来的舞蹈《天山铃舞》 3. 军中有歌，歌才动情，军旅里飞来一只熟悉的百灵，不错下面就由请xxx为大家献上一首耳熟能详的老歌，《军中飞来一只百灵》 4.炫酷才叫时尚，八零后心之向往，相信大家都一样，需要个性张扬。今天我们特意请来了城市建设学院的武状元优秀团队，为大家献上一段充满活力的XXX，感谢他们的到来，大家掌声欢迎! 5.相信大家都看过一部曾经风靡一时的电影，那是周杰伦曾经推出的一部年度巨献《不能说的秘密》.里面的四手联弹一定给大家留下了不可磨灭的深刻印象，旋律依旧在脑中回响。不过经典一样可以复制，精彩一样能够粘贴，下面给大家带来的这个惊喜，可谓是非常具有特色，一样是所见
不多，机会难得。下面请欣赏xxxx为大家带来的，钢琴四手连弹《军队进行曲》 6.幽幽云水意.漫漫古典情. 诗情画境的晕染为我们带来流动的娴静。请大家随着动人的舞蹈穿越书法的妙境，伴随优雅的琴韵体会超越喧嚣的古韵墨香。下面请欣赏xxx为您带来的xxxx 7.四年的岁月流光见证了你我在辽东学院的欢欣成长，相信由很多即将走出校园的同学都想倾诉衷肠，下面我们就请出来自05对外汉语的毕业生代表xxx听听她如何表达。 8.当你离开的时候，我送走你的只有沉默。当你离开我的时候，我绝不会把泪滴落。这是金达莱花的歌词大意，相信朝鲜族金达莱花的舞姿会像歌词一样优美，让人回味。下面请欣赏xxxx金达莱花。 9.是谁带来远古的呼唤，是谁留下千年的期盼，这首歌自打年初就开始被人重新无数次的翻唱，不过下面的歌曲，同样青藏高原的演唱，绝对会给您用实力带来不一样。由请xxxx 10.因为有爱，我们才牵手，因为有爱，我们才会风雨同舟。与身边爱自己的人共同牵手，一同遨游，幸福生活才能没有尽头。下面欣赏牵手。 11. 我对你的敬仰之情,如滔滔江水,连绵不绝;又如黄河之水,一发不可收拾;相信大家对电影《月光宝盒》中这一
初中英语比较级和最高级讲解与练习 形容词比较级和最高级 一．绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 1. 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。例如: poor tall great glad bad 2. 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基 础上变化的。分为规则变化和不规则变化。 二．形容词比较级和最高级规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加-er 和-est 构成。 great (原级) greater(比较级) greatest(最高级) 2) 以-e 结尾的单音节形容词的比较级和最高级是在词尾加-r 和-st 构成。 wide (原级) wider (比较级) widest (最高级) 3) 少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加 -er 和-est构成。 clever(原级) cleverer(比较级) cleverest(最高级)， slow(原级) slower(比较级) slowest (最高级) 4) 以-y 结尾,但-y 前是辅音字母的形容词的比较级和最高级是把-y 去掉,加上-ier 和-est 构成. happy (原形) happier (比较级) happiest (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该 辅音字母然后再加-er和-est。 原形比较级最高级原形比较级最高级 big bigger biggest hot hotter hottest red redder reddest thin thinner thinnest 6) 双音节和多音节形容词的比较级和最高级需用more 和most 加在形容词前面来构 成。 原形比较级最高级 careful careful more careful most careful difficult more difficult most difficult delicious more delicious most delicious 7)常用的不规则变化的形容词的比较级和最高级: 原级比较级最高级 good better best 好的 well better best 身体好的 bad worse worst 坏的 ill worse worst 病的 many more most 许多 much more most 许多 few less least 少数几个 little less least 少数一点儿 （little littler littlest 小的） far further furthest 远（指更进一步，深度。亦可指更远） far farther farthest 远（指更远，路程）
形容词比较级和最高级的形式 一、形容词比较级和最高级的构成 形容词的比较级和最高级变化形式规则如下 构成法原级比较级最高级 ①一般单音节词末尾加 er 和 est strong stronger strongest ②单音节词如果以 e结尾，只加 r 和 st strange stranger strangest ③闭音节单音节词如末尾只有一个辅音字母， 须先双写这个辅音字母，再加 er和 est sad big hot sadder bigger hotter saddest biggest hottest ④少数以 y, er(或 ure), ow, ble结尾的双音节词， 末尾加 er和 est(以 y结尾的词，如 y前是辅音字母， 把y变成i，再加 er和 est，以 e结尾的词仍 只加 r和 st) angry Clever Narrow Noble angrier Cleverer narrower nobler angriest cleverest narrowest noblest ⑤其他双音节和多音节词都在前面加单词more和most different more different most different 1) The most high 〔A〕mountain in 〔B〕the world is Mount Everest，which is situated 〔C〕in Nepal and is twenty nine thousand one hundred and fourty one feet high 〔D〕 . 2) This house is spaciouser 〔A〕than that 〔B〕white 〔C〕one I bought in Rapid City，South Dakota 〔D〕last year. 3) Research in the social 〔A〕sciences often proves difficulter 〔B〕than similar 〔C〕work in the physical 〔D〕sciences. 二、形容词比较级或最高级的特殊形式：
比较级和最高级 1.在形容词词尾加上―er‖ ―est‖ 构成比较级、最高级： bright（明亮的）—brighter—brightest broad（广阔的）—broader—broadest cheap（便宜的）—cheaper—cheapest clean（干净的）—cleaner—cleanest clever（聪明的）—cleverer—cleverest cold（寒冷的）—colder—coldest cool（凉的）—cooler—coolest dark（黑暗的）—darker—darkest dear（贵的）—dearer—dearest deep（深的）—deeper—deepest fast（迅速的）—faster—fastest few（少的）—fewer—fewest great（伟大的）—greater—greatest hard（困难的,硬的）—harder—hardest high（高的）—higher—highest kind（善良的）—kinder—kindest light（轻的）—lighter—lightest long（长的）—longer—longest loud（响亮的）—louder—loudest low（低的）—lower—lowest near（近的）—nearer—nearest new（新的）—newer—newest poor（穷的）—poorer—poorest quick（快的）—quicker—quickest quiet（安静的）—quieter—quietest rich（富裕的）—richer—richest short（短的）—shorter—shortest slow（慢的）—slower—slowest small（小的）—smaller—smallest smart（聪明的）—smarter—smartest soft（柔软的）—softer—softest strong（强壮的）—stronger—strongest sweet（甜的）—sweeter—sweetest tall（高的）-taller-tallest thick（厚的）—thicker—thickest warm（温暖的）—warmer—warmest weak（弱的）—weaker—weakest young（年轻的）—younger—youngest 2.双写最后一个字母,再加上―er‖ ―est‖构成比较级、最高级： big（大的）—bigger—biggest fat（胖的）—fatter—fattest hot（热的）—hotter—hottest red（红的）—redder—reddest sad（伤心的）—sadder—saddest thin（瘦的）—thinner—thinnest wet（湿的）—wetter—wettest mad（疯的）—madder—maddest 3.以不发音的字母e结尾的形容词,加上―r‖ ―st‖ 构成比较级、最高级：able（能干的）—abler—ablest brave（勇敢的）—braver—bravest close（接近的）—closer—closest fine（好的,完美的）—finer—finest large（巨大的）—larger—largest late（迟的）—later—latest nice（好的）—nicer—nicest ripe（成熟的）—riper—ripest
精彩的大学毕业晚会主持词示范文格式本推荐 Ａ：青春是一曲荡气回肠的歌，三年前我们怀着彩色梦想走进了鄂大，三年中我们有过欢笑，流过泪水，经历磨炼，得到成长Ｂ：三年后的今天，我们在这里重温青春过往，因为明天就将各奔天涯。也正因为此，今夜，我们承载了太多的祝福与惦念，寄托了太多的关心与企盼。 Ｃ：今晚，让我们再一次重温，那些感动过我们的人和事：灯火通明的教学楼里用功的身影，篮球场上保卫集体尊严的男儿霸气，满是欢声笑语的宿舍边不着边际的闲谈…… Ｄ：又一个三年轮回之后，在同样微凉的夏夜，你是否会记起校园里的梧桐树，你是否会记起日记本里的书签，那些五彩缤纷的日子? Ａ：无数个三年之后，你们的思念是否会有增无减?在你成长的岁月里，在你闯荡社会的每一天，是否会有那么几个霎时让你渴望回到过去 Ｂ：让我们静静享受一下挑战，在日复一日与时间的赛跑中，你会变得更加坚强，更加神采奕奕!又一个青春之旅从今晚启航，又一个光阴的故事在今晚讲述 Ｃ：亲爱的同窗，不要带着离别的愁绪，因为明天又是一个新的起点，因为我们相信再次相逢，我们还是一首动人的歌!Ｄ：很快乐今天能有这个时机同大家相聚一堂，共叙离别。就让今天铭刻在我们心间，让母校留住我们的风采!
Ａ：今天，我们也非常荣幸的请到了…… Ｂ：下面让我们用热烈的掌声有请……上台讲话 结束语Ａ：愉快的舞蹈表达不尽我们对母校的敬意 Ｂ：热情的赞歌唱不尽我们对母校的一腔深情 Ｃ：流火的六月，我们将带着恩师的叮咛，怀着必胜的信心，走向新的征程 Ｄ：绚烂的七月，我们将载着母校的祝愿，带着亲人的希望，向着新的征程扬帆起航 Ａ：教师们，同学们，欢送10级毕业生联欢晚会合：到此结束Ａ李：毕业，是一个沉重的动词; 刘：毕业，是一个让人一生难忘的名词; 李：毕业，是感动时流泪的形容词; 刘：毕业，是当我们以后孤寂时候，带着浅笑和遗憾去回想时的副词; 李：毕业，是我们夜半梦醒，触碰不到而无限感伤的虚词。 刘：若干年后，假设我们还能够想起那段时光，也许这不属于难忘，也不属于永远，而仅仅是一段记录了成长经历的回忆。 李：尊敬的各位领导教师 刘：亲爱的各位同学们 合：大家晚上好! 李：很荣幸和大家相聚在这激情如火的六月，在这充满忧伤的六月!
英语语法---比较级和最高级的用法 在英语中通常用下列方式表示的词:在形容词或副词前加more(如 more natural,more clearly )或加后缀 -er(newer,sooner )。典型的是指形容词或副词所表示的质、量或关系的增加。英语句子中，将比较两个主体的方法叫做“比较句型”。其中，像“A比B更……”的表达方式称为比较级；而“A最……”的表达方式则称为最高级。组成句子的方式是将形容词或副词变化成比较级或最高级的形态。 一、形容词、副词的比较级和最高级的构成规则 1．一般单音节词和少数以-er，-ow结尾的双音节词，比较级在后面加-er，最高级在后面加-est； （1）单音节词 如：small→smaller→smallest short→shorter→shortest tall→taller→tallest great→greater→greatest （2）双音节词 如：clever→cleverer→cleverest narrow→narrower→narrowest 2．以不发音e结尾的单音节词，比较在原级后加-r，最高级在原级后加-st； 如：large→larger→largest nice→nicer→nicest able→abler→ablest 3．在重读闭音节（即：辅音＋元音＋辅音）中，先双写末尾的辅音字母，比较级加-er，最高级加-est； 如：big→bigger→biggest hot→hotter→hottest fat→fatter→fattest 4．以“辅音字母＋y”结尾的双音节词，把y改为i，比较级加-er，最高级加-est； 如：easy→easier→easiest heavy→heavier→heaviest busy→busier→busiest happy→happier→happiest 5．其他双音节词和多音节词，比较级在前面加more，最高级在前面加most； 如：beautiful→more beautiful→most beautiful different→more different→most different easily→more easily→most easily
初中英语形容词比较级和最高级讲解与练习 形容词比较级和最高级 绝大多数形容词有三种形式,原级,比较级和最高级, 以表示形容词说明的性质在程度上的不同。 形容词的原级: 形容词的原级形式就是词典中出现的形容词的原形。 例如: poor tall great glad bad 形容词的比较级和最高级: 形容词的比较级和最高级形式是在形容词的原级形式的基础上变化的。分为规则变化和不规则变化。 规则变化如下: 1) 单音节形容词的比较级和最高级形式是在词尾加 -er 和 -est 构成。 great (原级) (比较级) (最高级) 2) 以 -e 结尾的单音节形容词的比较级和最高级是在词尾加 -r 和 -st 构成。 wide (原级) (比较级) (最高级) 3)少数以-y, -er, -ow, -ble结尾的双音节形容词的比较级和最高级是在词尾加-er 和-est 构成。 clever(原级) (比较级) (最高级) 4) 以 -y 结尾,但 -y 前是辅音字母的形容词的比较级和最高级是把 -y 去掉,加上 -ier 和-est 构成. happy (原形) (比较级) (最高级) 5) 以一个辅音字母结尾其前面的元音字母发短元音的形容词的比较级和最高级是双写该辅音 字母然后再加-er和-est。 big (原级) (比较级) (最高级) 6) 双音节和多音节形容词的比较级和最高级需用more 和 most 加在形容词前面来构成。 beautiful (原级) (比较级) (比较级) difficult (原级) (最高级) (最高级) 常用的不规则变化的形容词的比较级和最高级: 原级------比较级------最高级 good------better------best many------more------most much------more------most bad------worse------worst far------farther, further------farthest, furthest 形容词前如加 less 和 least 则表示"较不"和"最不"
na bu gei ma ya kiu 那不给妈呀久儿我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有大 na bu gei ma ya kiu 那不给妈呀久儿我 ga xi yi dai gei no 噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 na dou na han bu ka qi 那都那汗不卡气 yi jian gu dai a ni ji 一见古带啊你几 ku dai pa la bu miao 苦带怕拉不秒 ca la wu dai ka 擦拉屋带卡 ku niao ti yi ka niao ji 苦鸟提一卡鸟几 ca la gu a gu mi no mu kou 擦拉古啊古米闹木口 cu wu xi wu s ka wo so 粗屋西屋丝卡我收 ku dai han bu ka gei 苦带汗不卡给 yi lu jiur gei you 一路酒给又 nei you mu nu lo 内有木奴咯 yi lu jiu gei you 一路就给又 na bu gei ma ya kiu 那不给妈呀久我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有里大yang gou li ya sang jin dang nei gu wu 羊够里呀桑金当内古 a long da ma de xi gei lei gu li you li da 啊龙大吗的西给类古里有里大ka xi le gong long no yin ku kou qiu 卡西了工龙木因哭口求 na bu li qiu liu ma pu ma xi you so sou 那不里求留吗扑吗西有否搜 na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 nei ga dou na ba leng dei you 内噶都那吧冷给又 ku dai lu man du la wu 苦带路满度啦舞 ku dan ku miao sa la han gei ji 苦但苦秒撒拉汗给几 na bu gei ma ya kiu 那不给妈呀久我 ga xi yi dai gei no 噶西带给路 ma lou xi bu yi mu lei du gei you li da 吗楼西不一木类度给有里大 yang gou li ya sang jin dang nei gu wu 羊够里呀桑金当内古 a long da ma de xi gei lei gu li you li da 啊龙大吗的西给类古里有里大ka xi le gong long no yin ku kou qiu 卡西了工龙木因哭口求 na bu li qiu liu ma pu ma xi you so sou 那不里求留吗扑吗西有否搜na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那 na bu gei ga ya piao ka xi dei you nu 那不给妈呀久我噶西带给路 qiu kou lo a ni nu mu nu li you li na 求口咯啊你奴木奴里又里那