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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Bilingual teaching as a reform
Is a stretch of dynamic biochemistry
Focus on the biosynthesis of 3 macromolecules:
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……
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）
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 )
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
Salmonella 0.0143 pg
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
Marked protein by 35S
Marked DNA by 32P
However, 32P was found in the new cells.
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.
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
One gene, one enzyme
One peptide, one gene
Gene——protein——trait： Reverse Biology
Semi-autonomous organelle or plasmid
In most cases DNA works as genetic material
RNA works in some viruses
Transferring and processing genetic information
Focused on protein synthesis
1.Correcting tRNA and the second system of genetic codon
2.Sometimes tRNA will transfer an amino acid in nonsense mutations.
The small double-strand RNA can inhibit gene expression.
C. Elegans or petunias (牵牛花)？
More effective than Antisense RNA
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---
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.
System A: cell-free protein synthesizing systemfrom E. coli
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.
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
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.
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.
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.
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.
Which codon can be recognized by Anticodon IGC？
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