F Genetic control
Ⅰ Syllabus Contentsbbc learning english
托业1 Structure and replication of DNA
Structure: double helix
The basic unit is nucleotide. A nucleotide is made of a 5-carbon sugar(deoxyribo), a phophate and a nitrogen ba. Four nitrogen bas in DNA are: A(adenine), C(cytosine), G(guanine) and T(thymine).
A = T(2 hydrogen bonds)
CG(3 hydrogen bonds)
Semi-conrvative replication: the DNA double helix unzips, and each strand rves as a template for the formation of a new strand. The new molecules each consist of one old strand and one new strand.
Direction: from 5' to 3' end.
2 Role of DNA in protein synthesis
Ⅱ Samples of A-LEVEL biology examination for analyzing
1 describe the structure of RNA and DNA and explain the importance of ba pairing and the different hydrogen bonding between bas;
the structure of DNA and RNA
| DNA | RNA |
Stand | Double strands | Single strand | foundation是什么意思
Unit | Nucleotide | Nucleotide |
Pento sugar | Deoxyribo | Ribo |
Phosphate group | Yes | Yes |
Nitrogen-containing ba | A,T,C,G | A,U,C,G |
Ba pairing | A = T(2 hydrogen bonds) CG(3 hydrogen bonds) | A = U(2 hydrogen bonds) CG(3 hydrogen bonds) |
| | |
Complementary pairing
Ba complementary pairing is very important for DNA replication and transcription. It ensures the accuracy of genetic information transmission. The number of four kinds of different bas and their quence in a DNA molecule reprent some genetic information. During DNA mi-conrve replication or transcription, one old DNA strand act as a template, four kinds of bas are pairing by A pair with T in DNA replication or A pair with U in transcription and C pair with G. There are little error occurred during ba pairing.
Sample:
1.(9700_w11_qp_11,21) What makes the exact copying of DNA molecules possible?训练大脑的方法
A ba pairing
B hydrogen bonding between nucleotides
judgementC sugar-phosphate backbone
D the double helix shape
Key: A
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Interpretion: Ba complementary pairing is very important for DNA replication. It ensures the accuracy of genetic information transmission. The number of four kinds of different bas and their quence in a DNA molecule reprent some genetic information. During DNA mi-conrve replication, one old DNA strand act as a template, four kinds of bas are pairing by A pair with T in DNA replication and C pair with G. There are little error occurred during ba pairing.
2 putinto>for lifeexplain how DNA replicates mi-conrvatively during interpha;
DNA molecules replicate during interpha. The hydrogen bonds between the bas break, allowing free nucleotides to fall into position opposite their complementary ones on each strand of the original DNA molecule. Adjacent nucleotides are then linked, through t
heir phosphates and sugars, to form new strands. Two complete new molecules are thus formed from one old one, each new molecule containing one old strand and one new.
Sample:
1.(9700_w11_qp_11,23) Bacteria were grown in a medium containing 15N. After veral generations, all of the DNA contained 15N. Some of the bacteria were transferred to a medium containing the common isotope of nitrogen, 14N. The bacteria were allowed to divide once. The DNA of some of the bacteria was extracted and analyd. This DNA was all hybrid DNA containing equal amounts of 14N and 15N.
The remaining bacteria were left in the medium with 14N and allowed to divide one more time.旋律的英文
The DNA of some of the bacteria was extracted and analyd.
What is the composition of this DNA?
A 25 % hybrid DNA
B 影视制作培训学校 50 % hybrid DNA
C 75 % hybrid DNA
D 100 % hybrid DNA
Key: B
Interpretion:
In the first DNA replication, one old DNA strand contains 15N act as template and replicates a new DNA strand contain 14N, so does the other old one. As a result, one DNA molecule contain 15N is divided into two DNA molecules contain both 15N and 14N, namely hybrid DNA.
In the cond DNA replication, one old DNA strand contains 15N act as template and replicates a new DNA strand contain 14N, formed a hybrid DNA. However, the other old DNA strand contains 14N and replicates a new DNA strand also contain 14N, formed a non-hybrid DNA.
In other words, only 50% DNA produced in the cond DNA replication are hybrid DNA.
3 state that a gene is a quence of nucleotides as part of a DNA molecule, which codes for a polypeptide and state that a mutation is a change in the quence that may result in an altered polypeptide;
The quence of bas on a DNA molecules codes for the quence of amino acid in a p
rotein or polypeptide. Each amino acid is coded for by three bas. A length of DNA coding for one complete protein or polypeptide is a gene.
Mutation can be defined as an unpredictable change in the ba quence in a DNA molecule(gene mutation) or in the structure or number of chromosomes (chromosome mutation). New alleles ari by gene mutation. Gene mutation include ba substitution, deletions or additions.
