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Section 3: Molecular Biology. Bilingual teaching as a reform Is a stretch of dynamic biochemistry Focus on the biosynthesis of 3 macromolecules: DNA: replication RNA: transcription Protein: translation. Chapter 29 An Overview of Genetic Information.

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slide1

Section 3:

Molecular Biology

Bilingual teaching as a reform

Is a stretch of dynamic biochemistry

Focus on the biosynthesis of 3 macromolecules:

DNA: replication

RNA: transcription

Protein: translation

slide2

Chapter 29 An Overview of Genetic Information

Life is produced by the metabolism of macromolecules

Which are macromolecules?

The function of life is executed by proteins, which encoded by nucleic acid

The second genetic codon

The second genetic codon……

slide3

生物进化的C值矛盾 (C value paradox of nucleotide)

最大C值 (Maximum C value)

The total amount of DNA in the genome of haploid

is a characteristic of each living species known as its Maximum C value(单倍体基因组总DNA 的含量)

最小C值 (Minimum c value)

The total amount of DNA for encoding the genes

information is termed its Minimum c value (编码基因信息的总DNA含量)

slide4

显花植物

鸟类

哺乳类

爬行类

两栖类

硬骨鱼类

软骨鱼类

赖皮类

甲壳类

昆虫类

软体动物

蠕虫类

霉菌

藻类

真菌

G+细菌

G-细菌

枝原体

C value paradox of nucleotide

A Is not linearly correlative with evolution extent

B The standard deviation varies in the same genus

C C value is far from c value.

(Euk. 人体 c = C/10)

( Prok. Φx174 c >C )

slide5

Eukaryote DNA chromosomes

(2C) (2N)

两栖鲵 168.0 pg(10-12g) 24

肺鱼 100 38

蝾螈 85.3 24

警蛙 28.2 24

牛 6.4 60

人 6.4 46

绵羊 5.7 54

果蝇 0.2 8

贝母 196.7 24

豌豆 28 12

玉米 11 20

Prokaryote DNA

(C)

Salmonella 0.0143 pg

E.coli 0.0040

T2 0.00022

λ 0.0000055

ΦΧ174 0.000005

Repeat sequence

slide6

DNA的复杂度:单倍体细胞基因组中非重复序列的碱基对数DNA的复杂度:单倍体细胞基因组中非重复序列的碱基对数

单一序列长度愈小(重复度愈大)

kinetic complexity(K.C.)愈小

Cot(1/2)值小(复性愈快)

poly(A ) K.C. = 1

Cot(1/2) = 2 × 10-6

T4 DNA K.C. = 1.7 × 106

Cot(1/2) = 0.3

E.coli DNA K.C. = 4.2×106 bp

Cot(1/2) = 9

slide8

Experiment 2:

Marked protein by 35S

Marked DNA by 32P

slide9

35S can not enter the new cells.

However, 32P was found in the new cells.

slide10

Experiment 3:

German Fraenkel

Extract the RNA and protein of the virus individually.

Put them into the surface of the healthy leaves.

RNA caused the disease.

While protein can not.

Conclusion: Genetic material is RNA not protein.

slide13

Founder of modern genetics: Thomas Hunt Morgan

Tied genetic factor (gene) with chromosomes.

Sexual linkage by drosophila is regarded as the third discover in genetics because it brings together a specific gene and chromosomes.

If 2 genes are near in the same chromosome, maybe linked heredity.

If far, maybe exchanged-heredity.

Opportunity for exchange can be viewed as the distance of 2 genes

slide14

Essence of the genes

One gene, one enzyme

One peptide, one gene

Trait——protein——gene:Forward Biology

Gene——protein——trait: Reverse Biology

slide15

Mostly in chromosome

Semi-autonomous organelle or plasmid

Nucleus

Cytoplast

Heredity

DNA

slide16

Category of genetic materials

In most cases DNA works as genetic material

RNA works in some viruses

Protein?

slide17

Functional diversity of RNA

Transferring and processing genetic information

Focused on protein synthesis

Messenger RNA

Transfer RNA

Ribosome RNA

slide18

RNA processing genetic information

Cut

Trimming

Adding

General process

Modification

Isomerization

Splicing

Editing

Recoding sequence

Recoding

Alternative transcript

slide19

Recoding

1.Correcting tRNA and the second system of genetic codon

赭石突变(UAA)

琥珀突变(UAG)

乳白突变(UGA)

nonsense mutations

2.Sometimes tRNA will transfer an amino acid in nonsense mutations.

slide20

RNA interfering干涉(干扰,RNAi)

The small double-strand RNA can inhibit gene expression.

C. Elegans or petunias (牵牛花)?

More effective than Antisense RNA

Models

slide21

Genetic codon

  • Nature
  • Deciphering
  • Feature
  • Effect of mutation
  • Universality
  • ORFs
  • Overlapping genes
slide22

Nature

1.Genetic codeis a triplet code

(three nucleotide encode one amino acid)

The way in which the nucleotide sequence in nucleic acids specifies the amino acid sequence in proteins.

The triplet codons arenonoverlappingandcomma-less.

---UCU UCC CGU GGU GAA---

slide23

2. Genetic code is degenerate :

Only 20 amino acids are encoded by 4 nucleotides in triplet codons (43 =64 of amino acids could potentially be encoded). Therefore, more than one triplet are used to specify a amino acids, and the genetic code is said to be degenerate, or to have redundancy.

slide24

Deciphering

System A: cell-free protein synthesizing systemfrom E. coli

  • cell lysate treated by DNase to prevent new transcription
  • Add homopolymeric synthetic mRNAs [poly(A)] + 19 cold (non-labeled) and one labeled aminoacids
  • In vitro translation
  • Analyze the translated polypeptides
slide25

poly(U) ---UUU--- polyphenylalanine

poly(C) ---CCC--- polyproline

poly(A) ---AAA--- polylysine

poly(G) --- did not work because of the complex secondary structure

Random co-polymers (e.g. U and G in the same RNA) were used as mRNAs in the cell-free system to determine the codon for many amino acids.

slide28

Features

Synonymous codons:

18 out of 20 amino acids have more than one codon to specify them, causing the redundancy of the genetic code.

the third position:

pyrimidine ----synonymous (all cases)

purine ----synonymous (most cases)

the second position:

pyrimidine ----hydrophobic amino acids

purine -----polar amino acids

slide29

Effect of Mutation

1. Transition: the most common mutation in nature

changes from purine to purine, or pymidine to pymidine

At third position: no effect except for

Met  Ile; Trp  stop

second position: results in similar chemical type of amino acids.

slide30

2. Transversions:

purine  pymidine

At third position: over half have no effect and result in a similar type of amino acid. (Example: Asp  Glu)

At second position: change the type of amino acid.

slide31

In the first position, mutation (both transition and transvertion) specify a similar type of amino acid, and in a few cases it is the same amino acid.

Thus, natural triplet codons are arranged in a way to minimize the harmful effect of an mutation to an organism.

slide32

Summary

  • 简并性:64种密码子决定20种氨基酸,重复,同义密码子
  • 摆动性(变偶性):反密码子的3个碱基与密码子反向互补,前两个碱基严格互补,第三个可以摆动
  • 普遍性:生物体普遍适用
  • 偏爱性:不同生物体(线粒体)使用何种同义密码子有偏爱
slide33

Universality

  • The standard codons are true for most organisms, but not for all.
slide34

ORFs

Open reading frames (ORFs) are suspected coding regions starting with ATG and end with TGA,TAA or TAG identified by computer.

When the ORF is known to encode a certain protein, it is usually referred as a coding region.

slide35

I coupled with U,A and C

Which codon can be recognized by Anticodon IGC?

slide36

m7G加在5,端:

免受酶切

促进启始蛋白质合成

Processing of RNA

Only the mature RNA could be translated.

The precursor of mRNA is called heterogeneous nuclear RNA, (hnRNA), which needs be processed.

Processing:Capping in 5,end

Poly A in 3,end

Cutting intron

Linked exon