1 DNA DNA is often called the blueprint
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DNA • DNA is often called the blueprint of life. • In simple terms, DNA contains the instructions for making proteins within the cell. 2
Why do we study DNA? DNA We study DNA for many reasons, e. g. , • its central importance to all life on Earth, • medical benefits such as cures for diseases, • better food crops. 3
Chromosomes and DNA • Our genes are on our chromosomes. • Chromosomes are made up of a chemical called DNA. 4
The Shape of the Molecule • DNA is a very long polymer. • The basic shape is like a twisted ladder or zipper. • This is called a double helix. 5
The Double Helix Molecule • The DNA double helix has two strands twisted together. 6
One Strand of DNA • The backbone of the molecule is alternating phosphates and deoxyribose sugar • The teeth are nitrogenous bases. phosphate deoxyribose bases 7
Nucleotides O O -P O O One deoxyribose together with its phosphate and base make a nucleotide. O O -P O O O C C C Phosphate Nitrogenous base C C O Deoxyribose 8
One Strand of DNA • One strand of DNA is a polymer of nucleotides. • One strand of DNA has many millions of nucleotides. nucleotide 9
Four nitrogenous bases DNA has four different bases: C • Thymine T • Adenine A • Guanine G • Cytosine 10
Two Kinds of Bases in DNA • Pyrimidines are single ring bases. • Purines are double ring bases. N N C O C C N N C 11
Thymine and Cytosine are pyrimidines • Thymine and cytosine each have one ring of carbon and nitrogen atoms. N O C C N C thymine N O C C N C cytosine 12
Adenine and Guanine are purines • Adenine and guanine each have two rings of carbon and nitrogen atoms. N C Adenine N C C N O N C N C C C N Guanine C N N C 13
Two Stranded DNA • Remember, DNA has two strands that fit together something like a zipper. • The teeth are the nitrogenous bases but why do they stick together? 14
Hydrogen Bonds N C N N C C N C O N C C C C N • The bases attract each other because of hydrogen bonds. • Hydrogen bonds are weak but there are millions and millions of them in a single molecule of DNA. • The bonds between cytosine and guanine are shown here with dotted lines N O 15
Hydrogen Bonds, cont. • When making hydrogen bonds, cytosine always pairs up with guanine N • Adenine always pairs up with C thymine • Adenine is bonded to thymine here N N O C N C C C O C N N C 16
Chargraff’s Rule: • Adenine and Thymine always join together A T • Cytosine and Guanine always join together C G 17
DNA by the Numbers • Each cell has about 2 m of DNA. • The average human has 75 trillion cells. • The average human has enough DNA to go from the earth to the sun more than 400 times. The earth is 150 billion m • DNA has a diameter of or 93 million miles from the sun. only 0. 00002 m. 18
http: //www. brainpop. com/he alth/geneticsgrowthanddevelo pment/dna/ 19
DNA Replication http: //www. youtube. com/wat ch? v=Kzgnl 5 -8 WAk copyright cmassengale 20
Replication Facts • DNA has to be copied before a cell divides • DNA is copied during the S or synthesis phase of interphase • New cells will need identical DNA strands copyright cmassengale 21
Synthesis Phase (S phase) • S phase during interphase of the cell cycle • Nucleus of eukaryotes S DNA replication takes place in the S phase G 1 interphase G 2 Mitosis copyright cmassengale -prophase -metaphase -anaphase -telophase 22
• Enzyme Helicase unwinds and separates the 2 DNA strands by breaking the weak hydrogen bonds • Single-Strand Binding Proteins attach and keep the 2 DNA strands separated and untwisted copyright cmassengale 23
Semiconservative Model of Replication • The two strands of the parental molecule separate, and each acts as a template for a new complementary strand • New DNA consists of 1 PARENTAL (original) and 1 NEW strand of DNA Template Parental DNA New DNA copyright cmassengale 24
• http: //highered. mcgrawhill. com/olcweb/cgi/pluginpop. cgi? it=s wf: : 535: : /sites/dl/free/007243 7316/120076/micro 04. swf: : DNA%20 Replication%20 Fork 25
6 B Genetic Code • EVERY ORGANISM CONTAINS DNA • The order(sequence) of the nucleotides and the number of chromosomes determines the type of organism • Ex: human has 23 chromosome pairs 26
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