Download Genes 基因

Genes Code for Proteins
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Ex Biochem c2-gene code
2.1 Introduction
Figure 2.1
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Ex Biochem c2-gene code
Genes and locus
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Genes 基因: units of inheritance that are passed
down to the next generation
Arranged as DNA segments in a chromosome
Locus 基因座: specific positions of every gene
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Ex Biochem c2-gene code
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Allele「對偶基因」或「等位基因」
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The genes found at the same locus on different
homologous chromosomes
Genes that are alleles of one another always
control the same characteristic
2 alleles result in different expression of the same
character: heterozygote (same: homozygote)
Ex Biochem c2-gene code
Allele
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一位於染色體上單一位置的特定基因，其
所有的不同形式中之任一形式即謂之
allele (顯性/隱性; 血型A/B/O)
同一位置的基因控制同一性狀
某個基因的基因型是由該基因所擁有的一
對等位基因所決定(顯性/隱性)
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2.2 A Gene Codes for
a Single Polypeptide
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The one gene : one
enzyme hypothesis
summarizes the basis of
modern genetics:
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Figure 2.2
Ex Biochem c2-gene code
A gene is a stretch of DNA
coding for a single
polypeptide chain
Sometimes may not be true
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Ex Biochem c2-gene code
2.3 Mutations in the Same Gene
Cannot Complement
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A mutation in a gene affects only the protein
coded by the mutant copy of the gene.
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It does not affect the protein coded by any other
allele.
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Ex Biochem c2-gene code
2.4 Mutations May Cause Lossof-Function or Gain-of-Function
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Recessive mutations are
due to loss-of-function by
the protein product.
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Dominant mutations
result from a gain-offunction.
Figure 2.4
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Ex Biochem c2-gene code
2.8 The Genetic Code Is Triplet
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The genetic code is read in triplet nucleotides called
codons.
The triplets are nonoverlapping and are read from a
fixed starting point
Mutations that insert or delete individual bases
cause a shift in the triplet sets after the site of
mutation.
Combinations of mutations that together insert or
delete three bases (or multiples of three) insert or
delete amino acids;
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But they do not change the reading of the triplets beyond
the last site of mutation
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Ex Biochem c2-gene code
Figure 2.9
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Ex Biochem c2-gene code
2.9 Every Sequence Has 3
Possible Reading Frames
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Usually only one reading frame is translated and
the other two are blocked by frequent
termination signals.
Figure 2.10
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Ex Biochem c2-gene code
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2.11 Several Processes Required to
Express Protein Product of a Gene
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A prokaryotic gene is expressed by transcription into
mRNA and then by translation of the mRNA into
protein.
Figure 2.14
Ex Biochem c2-gene code
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In eukaryotes, a gene may
contain internal regions that
are not represented in protein.
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Exon, intron
Internal regions are removed
from the RNA transcript by
RNA splicing
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This gives an mRNA that is
colinear with the protein product
Figure 2.15
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Ex Biochem c2-gene code
RNA structure
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Each mRNA consists of:
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a nontranslated 5′ leader
a coding region
a nontranslated 3′ trailer (poly A tail)
Figure 2.13
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Ex Biochem c2-gene code
RNA extraction
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More water soluble than DNA
Purification of total RNA
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Tissue/cell homogenate/lysis in phenol and guanidine
thiocyanate: inhibition of RNase
addition of bromochloropropane or chloroform:
separation into aqueous and organic phases. RNA to
aqueous phase, DNA to interphase, and proteins to
organic phase
RNA precipitated from the aqueous phase with
isopropanol.
Purification of mRNA
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Oligo-dT column, bind poly A tail of mRNA
Elute with NaCl
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