分子生物学-mbg-2gene concept基因概念演变与发展

第2章的概念Concept

of

teTrue-False

QuestionAll

gene

products

are

polypeptides.Answer:

False.

Some

genes

produce

functionalRNAsas

the

terminal

genetic

product

(e.g.,

ribosomal

andtransfer

RNA

genes).经典的

概念概念的演变与发展的分子结构概念的多样性1866.

-1926.经典的概念早期的

概念融合遗传理论B.C.460

-

370

Hippocrates

（Blending

inheritance）Ancient

Greece

physician

希波克拉底（古希腊名医）子代具有父，母双亲的性状母本体液父本体液+物种加强和完善对环境的适应逐渐转变为新种获得的性状是由(非遗传物质的改变)新性状一旦获得,便能遗传给后代获得性遗传理论Inheritance

of

acquired

charactersJean-Baptiste

de

Lamarck

1744-1829泛生论假说（Hypothesisof

the

Pangenesis）C.

Darwin

1868Panger种质论

(Weismann

老鼠尾巴切割实验,切割22代,第23代仍有尾巴)（Theory

of

germplasm,Weismann

1883.

）GermplasmRoot,

Stem,

Leaf……→

GermplasmSomatoplasm（体细胞）→

Germplasm

Somatoplasm1834-1914遗传因子假说(Hypothesis

of

the

inherited

factor

G.J.

Mendel

1866.

)生物性状由遗传因子控制亲代传给子代的是遗传因子(A,a….)遗传因子在体细胞内成双(AA,aa)在生殖细胞内为单（A,a）杂合子体细胞内具有成双的遗传因子(Aa)等位的遗传因子独立分离非等位遗传因子间

组合地分配到配子中Theoryofte•是

上的实体象链珠(bead)一样，孤立地呈线状地排列在

上是(Three

in

one)

；功能(functional

unit)突变(mutation

unit)交换(cross-overunit)“三位一体”的最小的不可分割的基本的遗位(1926T.

H.

Morgan)概念的演变与发展分子生物学史的第一个重要发现Onegene

－

OneenzymeThe

one

gene-one

enzyme

hypothesis

is

the

idea

that

genes

actthrough

the

production

of

enzymes,

with

each

gene

responsible

forproducing

a

single

enzyme

that

in

turn

affects

a

single

step

in

ametabolic

pathway.It

is

often

considered

the

significant

result

in

what

came

to

becalled

molecular

biology.

Although

it

has

been

extremely

influential,the

hypothesis

was

recognized

soon

after

its

proposal

to

be

anoversimplification.Even

the

subsequent

reformulation

of

the

"one

gene-onepolypeptide"

hypothesisis

now

considered

too

simple

to

describethe

relationship

between

genes

and

proteins.1941年，GeorgeBeadle和Edward

TatumNeurospora

crassa

（粉色面包霉菌）“one

gene─one

enzyme”的假说（获得1958年Nobel奖）说明了 的生化作用本质是控制酶的生物化学和遗传学之间的联合迈出的第一步，也是分子生物学的第一个重要发现G.

Beadle&E.

Tatum的位置效应PositioneffectＸ－chromosome16ABar

eyePosition

effectDosage

effectDuplicationWild

type780个68个45个Sturtevent385个in

euchromatin常（W>w染色质）Ww whiteeye（W

gene

be

silencedin

heterochromatin异染色质)WWwwWw Red

eyePosition

effectWhy

?Epigenetics

!Epigenetics

表观遗传学Epigenetics

is

the

study

of

heritable

changes

in

phenotype(appearance)

or

gene

expression

caused

by

mechanisms

otherthan

changes

in

the

underlying

DNA

sequence,

hence

the

nameepi-

(Greek:

over,

above)

-genetics.These

changes

may

remain

through

cell

divisions

for

the

remainderof

the

cell's

life

and

may

also

last

for

multiple

generations.

However,there

is

no

change

in

the

underlying

DNA

sequence

of

the

organism;

instead,

non-genetic

factors

cause

the

organism's

genesto

behave

(or

"express

themselves")

differently.拟等位概念的提出（pseudoalleles）Multipleallelesa1Aa2a3Aa1a2a1a1×

a2a2a1a2

(

no

wild

type)野生型

A向不同方向发生突变形成不同的等位

a1,a2,

a3

….又总称为复等位multiple

alleles.But!Ww-wared

eye

(w.t)Xw-Xwa×

Xw-

YXw-

YXw-XwaXw-

Xw-

Xw-

YXw-

Xwa

XwaY?1/1000W.Tred

eyewhiteeye

(mut)amygdaloid

eye

(mut)inDrosophila[ə'migdə.lɔid]杏仁色Pseudo

Alleles紧密连锁（交换率极低）功能相同（表型相似）A1

A2a1

a2W.tMut.A1

a2a1

A2(mut)(mut)When

two

mutations

in

the

same

cistron

give

rise

to

differentphenotypes

in

the

cis

and

trans

conditions

respectively,called—(A)Pseudoalleles (B)

Pseudogene(C)Pseudogamy(D)

None

oftheabove(Answer:

A)拟等位

：紧密连锁，控制同一性状的非等位pseudo

alleles

是!

?!内的突变体.Processed

pseudogenes

arise

from

integration

of

reverse

transcribedmRNAs.

When

reverse

transcriptase

is

present

in

a

cell,

mRNA

molecules

can

be

copied

into

dsDNA.

In

rare

instances,

these

DNA

molecules

canintegrate

into

t ome

creating

pseudogenes.

Because

introns

are

rapidlyremoved

from

newly

transcribed

RNAs,

these

pseudogenes

have

thecommon

characteristic

of

lacking

introns.

This

distinguishes

thepseudogenefrom

the

copy

oft e

fromwhichit

wasderived.

Inaddition,pseudogenes

lack

the

appropriate

promoter

sequences

to

direct

theirtranscription

as

these

are

not

part

of

the

mRNA

from

whichthey

are

derived.PseudogenePseudogenes

are

dysfunctionalrelatives

of

known

genes

thathave

lost

their

protein-codingability

or

are

otherwise

nolonger

expressed

in

the

cell.顺反子理论Theory

of

cistron(S.Benzer

1955)对经典的 概念的第一次重要修正与发展1944Oswald

Avery

(Canada)Strptococcum

p

oniceDNA

as

geneticmaterial1941.Beadle

&

TatumNeurospora

crassaOne

gene----one

enzymeJacob

&

Monod1955.

S.BenzerEscherichia

coliLactose

operonE.

coli

T4

phageCistron理论基础Theory

ofcistronMut.T4

rII

:

rII107,

rII105,

rII51,

rII47……(400)PhageE.coli

BE.coli

k12Seymour

Benzer

1955PlaqueW.t

T4Mut.T4rII白,小,边缘模糊白,小,边缘模糊！大,园,边缘清晰Cis:

Latin:

‘on

this

or

the

near

side

of’.Trans:

Latin:

‘across,

beyond,

crossing,

on

the

other

side’.Cistron

and

cis-trans

complementationtestTwo

mutations

in

two

cistrons

and

can

complement

one

another,and

produce

wild-type

phenotype.

A

and

B

represent

two

cistronsor

two

genes./Locked/med

plementation.jpgTwo

mutations

in

the

same

cistron

do

not

complement

oneanother,

and

produce

no

wild-type

phenotype.

A

and

B

representtwo

cistrons

or

two

genes./Locked/med

plementation.jpg顺反子假说（Theoryof

cistron）Cistron

是

的同义词在一个顺反子内，有若干个突变单位,突变子(muton)在一个顺反子内，有若干个交换单位,交换子（recon）是一个具有特定功能的，完整的，不可分割的最小的遗

位

three

inone one

in

one内可以较低频率发生

内的重组，交换pseudo

alleles

是mut1

X

mut2内的突变体W.t

是内发生交换的结果概念的动摇cistron概念的提出是对经典的是对pseudo

alleles概念的修正等位（Allele,Allomorph）概念的发展PseudoalleleAllele

同一座位存在的两个以上不同状态的

,

其总和称之为复等位 （multiple

alleles）（A,

a1,

a2..）全同等位非全同等位(homoallele)(heteroallele)(非全同等位

)Allele

具有相对差异的DNA区域TAAAGTAAT

TAAAGCAATGene

locusMut

a1Mut

a2×W.t

AATTCTGAGCTMut

a1ATTCGGAGCTMut

a2ATTCAGAGCTATTCGGAGCTATTCAGAGCT

(mut2)ATTCAGAGCTATTCGGAGCT

(mut1)全同等位

在同一座位(locus)中，同一突变位点（site）向不同方向发生突变所形成的等位

(

homoallele

)site非全同等位

；在同一

座位（locus）中，不同突变位点（site）发生突变所形成的等位site。(heteroallele)siteGene

locusMut

a1×Mut

a2W.t

AATTCTGAGCTMut

a1TTCGGAGCTMut

a2ATTCTGAGATATTCGGAGCTATTCGGAGAT

(mut)ATTCTGAGATATTCTGAGCT

(W.t)SummaryBenzer关于顺反子理论的提出不仅将

的

“三位一体”的经典概念修正为

的

“一位一体”

概念,

而且动摇或否定了

“拟等位

”

的概念,

认为拟等位

实际上是内不同位点的突变体,

是复等位

的不同成员.同时将

“在同一

座位(locus)中,

同一突变位点向不同方向发生突变所形成的等位

”

称为全同等位

(homoallele).将“在同一

座位中,

不同突变位点发生突变所形成的等位

”称为非全同等位

(heteroallele).Gene

locusIn

the

diploidcellsof

an

organism,

there

can

be

differentallele(s)

of

a

given

single-copy

nuclear

gene.Only

oneOne

or

twoOne,

two,

three

or

fourManyANSWER:

One

or

twoInapopulation,therecanbe

allele(s)

of

a

given

single-copynuclear

gene.Only

oneOne

or

twoOne,

two,

three

or

fourManyANSWER:

ManyQuestionabcdeThe

diagrams

represent

stages

in

celldivision

bymitosis.

(only

onechromosome

isrepresented).

What

isthe

correct

sequence

of

events?(d)

d

b

a

ce(c)b

a

d

ce(b)

b

a

c

e

d(a)a

b

c

d

eNext

slideeThe

chromosomes

shorten

and

thicken

(b)

after

theyhave

appeared

in

the

nucleus

(b).

Similarly

atofcell

division,

the

chromosomesextend

andless

visible

(d)after

thecell

divides

(e)NoYesThis

isthecorrect

sequenceThe

cell

does

notstart

todivide

(d)

until

thechromatidshave

separated

(c).

Also,

cell

constriction

(e)

precedescell

division

(d)NoNoCell

division

(d)does

not

take

place

until

thechromatidshave

appeared

(b)

and

separated

(c).

Also,

cellconstriction

(e)precedes

cell

division

(d)子理论(Lactose

operon 1961.

Jacob,

Monod)Lac.OperonI

P

O

Z

YAzyaLactose生物体性状的表现往往具有上位性互作的遗传效应某一是若干功能的表现组成的信息表达的整体行为onegene→ one

peptide（缩氨酸）onegene→onefunction(Ribozyme,Abzyme（抗体酶）,rDNA,tDNA..)one

gene

→oneenzymetDNA,

rDNA,

polymertranscribed,

translatable

gene(

Z,Y,A

)transcribed

but

non-translatablegene(

tDNA,

rDNA,

small

RNA…..

)Non-

transcribed,

non-translatable

gene(

promoter,

operator

)的类型★

cis

action

factor

(表达调控因子:顺式作用因子)Affects

the

activity

only

of

DNA

sequenceson

its

own

molecular

of

DNA,

this

propertyusually

implies

that

the

factor

does

not

codefor

protein通过核苷酸自身的特异二级结构控制与它紧密连锁的结构

的表达一般不编码蛋白质(无

产物的DNA功能区)★

trans

action

factor

(表达调控因子：反式作用因子)Affects

the

activity

of

any

gene

located

ongenome

byitstranslated

product.通过扩散自身表达产物（酶，调节蛋白）控制其他

的表达可转录，可翻译调节蛋白的DNA功能区可通过互补测验体系确定其功能区域DNA

is

a

main

genetic

material▲

1928

GriffithRII▲

Hersheylambdar

phage

cycle▲

Watson

&

Crick

DNA

doublehelixDNA1944

Avery

O.TSIIIDNA

是主要的遗传物质DNA编码两类遗传信息phenotype (central

dogma)II类；特定DNA

seq.

+

特定蛋白质

/

核酸结合表达的指令geneon/

offI类；DNA

seq.aaseq.RNA

seq.

(codon)protein内在信息ORFonly

expression

byDNA

RNA内,外(信号分子)结合信息遗传信息存在于模版链的一级结构上三联体简并(degeneration)WobbleIso-acceptor（同功受体）三(IR,

Box,

paracodon…)空间，调控

(key

&

lock)cis

1简并(degeneration)trans1

trans2trans

3cis

1cis

2cis

3I类II类specific

binding结构/DNA序列Helix

,

Ntseq….aa

baseproteinDNA作为遗传物质的优点(自然选择的优势)★

遗传信息量大1kb

DNA序列

41000

种遗传信息★

核糖的2’

–

OH

脱氧

在水中的稳定性高于RNA★

可以突变方便修复以求不断进化以求稳定遗传★

A

/

T,

C

/

G

互补

双螺旋结构,转录遗传稳定DNA中U潜在的遗传?G/C

G/UG/C错配修复系统倾向除U插CC

U

突变★

DNA中有T无U无后顾之忧DNA扩增进化★DNA中有T无U是进化的结果错配修复系统不能识别两种U，难以对突变进行修复的分子结构Nucleic

Acid

(NA)Polynucleotide

chain

(poly

Nt)Nucleotide

(Nt)

basic

unitMono-phosphate

(Mp)Nucleoside

(Ns)Deoxy-ribose脱氧核糖(

Ribose

)BasePurine

(pu)Adenine

(A)Guanine

(G)Pyrimidine

(py)Thymine

(T)Uracil

(U)Cytosine

(C)是DNA分子的片段DNA1.

Double

helixBases(碱基):DNA,adenine(A),guanine(G)

are

purines;cytosine(C),thymine(T)

arepyrimidinesRNA,

…… uracil

(U)…Nucleosides:

base

+

sugar

=

nucleosideNucleotides:

base

+

sugar

+

phosphate

=

nucleotides(

核苷酸

)

The

nucleoside

5’-triphosphates

(NTPs

or

dNTPs)

arerespectively

the

building

blocks

of

polymeric

RNA

and

DNAPhosphodiester

bonds:

covalent

linkage

of

a

phosphate

group

between

the(磷酸二脂键)

5’-hydroxyl

ofariboseand

the

3’-hydroxylof

thenext.

At

neutral

pH,

each

phosphate

group

has

a

single

negative

charge.Nucleic

acids

are

thus

highly

charged

polymers.(核苷)RNA:

ribonucleosides

or

just

nucleosides;DNA:

2’-deoxyribonucleosidesorjustdeoxynucleosidesDNA/RNA

sequence:

The

nucleic

acid

sequence

is

the

sequence

ofbasesA,

C,

G,

T/U

in

the

DNA/RNA

chain.

The

sequence

isconventionally

written

from

the

free

5’-

to

the

free

3’-

endofthemolecule,5’-

ATTAGCTC-

3’(DNA)

, 5’-

AUAGCUUGA-3’

(RNA)DNA

double

helixDNA是右手螺旋(right-handed

double

helix)。双螺旋包括两条多核苷酸链.磷酸-核糖骨架(back-bone)在外侧，含氮碱基层状排列在双螺旋

。两条多核苷酸链的碱基通过氢键(hydrogen

bonding)互作。双螺旋每一圈有10个碱基对(basepairs)，长度为34

Angstroms，螺旋的直径20

Angstroms

。双螺旋的两条链是反向平行互补的

(anti-parallel

and

complementary)。双螺旋有两种不同的沟:major

grooves

and

minor

grooves。Major

grooves:

the

place

for

gene

expression

regulation.Nucleotide

(Nt)

basic

unitA

portion

of

a

DNApolynucleotide

chain,showing

the

3'

→

5'phosphodiester

linkagesthat

connect

thenucleotides.

Phosphategroups

connect

the

3'carbon

of

one

nucleotidewith

the

5'

carbon

of

thenext.The

nucleotidesof

DNA.

Thestructures

of

thedifferentcomponents

ofeach

of

the

fournucleotides

areshown.A

portion

of

apolyribonucleotide(RNA)

chain.Elements

in

redare

distinct

fromDNA.Distinctions

between

the

nucleotides

of

RNA

and

DNA.

A

nucleotide

of

DNAis

shown

next

to

a

nucleotide

of

RNA.

All

RNA

nucleotides

have

the

sugarribose

(instead

of

deoxyribose

for

DNA),

which

has

a

hydroxyl

group

oncarbon

2

(shown

in

red).

In

addition,

RNA

has

the

pyrimidine

base

uracilinstead

of

thymine.

The

three

other

bases

that

occur

in

DNA

and

RNA

areidentical.Which

of

the

following

is

a

true

statement

regardingmessenger

RNA

(mRNA)?

mRNA

is

single

stranded

while

DNA

is

doublestranded.

mRNA

uses

a

uracil

nucleotide

instead

ofthyminebut

all

other

nucleotides

are

used

by

both

nucleicacid

species.

RNA

nucleotides

use

a

ribose

sugar

while

DNAnucleotides

use

a

deoxyribosesugar.all

of

the

aboveAnswer:

D核苷的构象(conformationof

nucleoside)χ =

C4-N9---C1’-O4’0opurinepyrimidineχ =

C2-N1---C1’-O4’0oDNA

双螺旋结构模型(DNA

Double

Helix

Model)1938.

W.

T.

AstburyX~

ray

photograph

of

DNA1950.

Erwin

ChargaffA

+G

/

T

+C

=

1A+T

= G+CRich

AT

form

&

rich

GC

form1952. Alexander

Todd3’,

5’

phosphodiester

bondNt~~Nt~~Nt~~Nt~~Nt1953. Watson

&

CrickRight

handed

B-form

DNADouble

helix

Model碱基的重叠与堆积G-C

pair,

held

together

by

three

hydrogen

bondsA-T

pair

,held

together

by

two

hydrogen

bonds162342The

hydrogen-bondedbase

pairs

of

DNA.The

figure

shows

theposition

and

length

ofthe

hydrogen

bondsbetween

the

base

pairs.The

covalent

bondsbetween

the

atomswithin

each

base

areshown,

but

double

andsingle

bonds

are

notdistinguished.QuestionIn

a

DNA

molecule,

whichof

the

molecules

listedbelo irs

with

adenine?thymineguaninevalinecytosineNext

slidethymineYesadenineNoguaninecytosineGuanine

pairs

with

cytosineNoValine

is

an

amino

acid

and

not

an

organicbaseNocytosineguanineCytosine

pairs

with

guaninel

碱基顶部基团 露在DNA

大沟内l

蛋白质因子与DNA

的特异结合依赖于氨基酸与DNA

间的氢键的形成l

蛋白质因子沿大沟与DNA形成专一性结合的机率与多样性高于沿小沟的结合l

大沟的空间更有利于与蛋白质的结合DNA双螺旋的结构特点The

helical

structure

of

DNA.

(a)

Schematic

model

of

the

double

helix.

One

turn

ofthe

helix

(3.4

nm)

spans

approxima y

10.5

base

pairs,

(b)

Space-filling

model

ofthe

double

helix.

The

sugar

and

phosphate

residues

in

each

strand

form

thebackbone,

which

are

traced

by

the

yellow,

gray,

and

red

circles,

showing

the

helicaltwist

of

the

overall

molecule.

The

bases

project

inward

but

are

accessible

throughmajor

and

minor

grooves.Formation

of

nucleotide

by

removal

of

water.

The

numbers

of

thecarbon

atoms

in

2'-deoxyribose

are

labeled

inred.Right

handed

B-form

DNADouble

helix

Model每一单链具有5‘

3’

极性两条单链间以氢键连接两条单链，极性相反，反向平行以中心为轴，向右盘旋(B-form)双螺旋中存在大沟(2.

2nm)小沟(1.

2nm)影响双螺旋结构稳定性的因素碱基堆积的棒状实体氢键

(Hydrogen

bond 4~6

kc

/mol)弱键,可加热解链氢键堆积,有序排列(线性,方向)磷酸酯键(phosphodiester

bond

80~90kc/mol)强键,需酶促解链0.2

mol/L

Na+生理盐条件消除DNA单链上磷酸基团间的静电斥力l

碱基堆积力(非特异性结合力)3.4A°(0.34

nm/碱基对间距)(1

kc/mol—0.6kc/mol)×n(热运动消耗)☆磷酸骨架,氨基,酮基周围水分子间的有序排列☆

Van

de

waals

force

(1.7A°/嘌呤环与嘧啶环作用半径)☆疏水作用力(Hydrophobic

interaction)不溶于水的非极性分子在水中相互联合,成串结合的疏水作用力，即为熵Entropy

（ΔS）DNA分子中非极性碱基的

, ,产生疏水作用力成为碱基间的部分堆积力磷酸基团间的静电斥力碱基间的挤压、抵御使其内能增加,碱基间有序排列的状态破坏（氢键作用力被减弱）影响双螺旋结构稳定性的因素氢键

(Hydrogen

bond 4~6

kc

/mol)磷酸酯键

(phosphodiester

bond 80~90

kc

/mol)0.2mol/L Na+生理盐条件碱基堆积力(非特异性结合力)磷酸基团间的静电斥力碱基间的挤压、抵御使其内能增加,碱基间有序排列的状态破坏（氢键作用力被减弱）DNA分子变性(DNA

denaturation)D.S.

DNA(加温,S.S.

DNApH,尿素,酰胺)变性过程的表现☆S.S.

DNA粘度降低D.S

DNAS.S

DNA粘度降低？溶液粘度取决于分子流动过程中的内摩擦和阻力高分子溶液

>普通溶液线状分子>

不规则线团

>

球形分子D.S.DNA

钢性较强，结构较为舒展的Double

helixS.S.DNA

没有