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Section A: DNA as the Genetic MaterialSection A: DNA as the Genetic Material
CHAPTER 16 THE MOLECULE BASIS OF
INHERITANCE
Watson and Crick discovered the double helix by building models to conform to X-ray data
In April 1953, James Watson and Francis Crick shook the scientific world with an elegant double-helical model المزدوج ذالنمو الحلزونى ج for the structure of deoxyribonucleic acid or DNA.
Watson and Crick began to work on a model of DNA with two strands, the double helix المزدوج .الحلزونى
• The amino acid sequence of a polypeptide is
programmed by a gene.
• A gene is a small region in the DNA.
• Nucleic acids store and transmit hereditary
information الوراثية .المعلومات
• There are two types of nucleic acids: ribonucleic
acid (RNA) and deoxyribonucleic acid (DNA).
• Organisms inherit تتوارث DNA from their parents.– When a cell divides تنقسم, its DNA is copied and
passed to the next generation of cells.
DNA : Introduction
Structures of nucleic acids (DNA & RNA)
o
H
HH
HH
CH2
o
P oo
oBase
o
P oo
o
o
H
HH
HH
CH2
Base
DNA nucleotide
Bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
Purine
Pyrimidine
Deoxyribose
Phosphate group
1
23
4
5
3
5
35
3
Fig. 16.3, Page 290
• The PO4 group of one
nucleotide is attached
to the sugar of the
next nucleotide in line
مستقيم صف .فى
Nitrogenous bases النيتروجينية القواعد
Sugar-phosphate backbones
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
PurinePyrimidines
Hydrogen bonds
Nit
rog
eno
us
bas
es
5
35
3
Uracil (U)
• Adenine (A) would form 2 hydrogen bonds only with thymine (T)
• Guanine (G) would form 3 hydrogen bonds only with cytosine (C).
Fig. 16.6, Page 292
DNA
DNA & RNA
o
H
HH
HH
CH2
Deoxyribose sugar (O on C2 is missed)
o
OH
HH
HH
CH2
Ribose sugar (no missed O)
Ribo-Nucleic-AcidDeoxiribo-Nucleic-Acid
Single stranded nucleic acidDouble stranded nucleic acid
Bases: A, G, C, T Bases: A, G, C, U
• Nucleic acids consist of من .nucleotides تتكون
• Each nucleotide consists of three parts اجزاء a nitrogen base :ثالثنتروجينية خماسي a pentose sugar ,قاعدة and a phosphate ,سكر
group.
• The nitrogen bases come in two types: Purines and Pyrimidines.
• The pentose sugar joined to بـ the nitrogen base is ribose المرتبطin nucleotides of RNA and deoxyribose in DNA.
• The only difference بين of نقص between the sugars is the lackالفرقan oxygen atom ذرة on carbon 2 in deoxyribose.
Nucleic acids االحماض النووية
• Sugars of one nucleotide join ترتبط the phosphate of the next with a phosphodiester bond.
• Genes are normally hundreds to thousands of nucleotides long.
• The linear order التتابعى of bases in الترتيبa gene specifies ُي2حدد the order of amino acids األمينية األحماض the monomers of a) ترتيب
protein).
• The flow of genetic information is from DNA mRNA protein.
– Protein synthesis occurs in Ribosomes.
Fig. 5.28
• An RNA molecule is single polynucleotide chain (single strand).• DNA molecules have two polynucleotide strands (double strand)
that spiral around حلزونيا مزدوج to form a double helix تدور .حلزون
Inheritance is based on replication of the DNA double helix
Fig. 16.5, Page 291
– Adenine (A) always pairs with thymine (T) and guanine (G) with cytosine (C).
• If we know the sequence of bases تتابع we know ,الخيط on one strand القواعدthe sequence on the opposite المقابل strand.
• The two strands are complementary لبعضهما .مكملين
Repeated Sugar - PhosphateRepeated Sugar - Phosphate
Sugar–Phosphate-BaseSugar–Phosphate-Base
PolynucleotidePolynucleotide
DNA backboneDNA backbone
One nucleotideOne nucleotide
DNA MoleculeDNA Molecule
DNA Double strandedDNA Double stranded
RNA single strandedRNA single stranded
T C G A T A G
A G TC T A C
UUmRNA
DNA
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