1 Nucleic acids Nucleic acids Nucleic acids: –Maintain genetic information –Determine Protein...
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Transcript of 1 Nucleic acids Nucleic acids Nucleic acids: –Maintain genetic information –Determine Protein...
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Nucleic acidsNucleic acids
Nucleic acidsNucleic acids: – Maintain genetic informationMaintain genetic information– Determine Protein SynthesisDetermine Protein Synthesis
DNADNA = deoxydeoxyribonucleic acid– “Master Copy” for most cell information.– Template for RNA
RNA =RNA = ribonucleic acid– Transfers information from DNA– Template for Proteins
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Nucleic AcidsNucleic AcidsChromosomes
(in nucleus)
Have genesgenes
1 gene
1 enzyme or protein
EnzymesEnzymes determine determine
external & internal characteristicsexternal & internal characteristics
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NUCLEIC ACIDSNUCLEIC ACIDS
Long chains (polymers) of repeating nucleotides.nucleotides.– Each nucleotide has 3 parts:3 parts:
A A phosphate unitphosphate unit H H
OO
H
H
OH
H
H
HO
A sugarsugar
A heterocyclic heterocyclic Amine BaseAmine BaseN
H
P OH
O
OH
HO
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NucleoNucleottide ide = phosphate + sugar + base= phosphate + sugar + baseNucleoNucleottide ide = phosphate + sugar + base= phosphate + sugar + base
P
O
O
ON
H H
OH
OH
H
H
O
-N-glycosidiclinkage
-N-glycosidiclinkage
BaseBase
SugarSugar
PhosphatePhosphate
Nucleoside = Nucleoside = sugar + basesugar + baseNucleoside = Nucleoside = sugar + basesugar + base
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Nucleic AcidsNucleic Acids
Nucleic AcidsNucleic Acids = polymerspolymers of Nucleotides.Nucleotides.
phosphate sugar
base
SS SS SSSSSSSS
BB BB BBBBBBBB
PPPP PP PPPPPP
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THE SUGAR PARTTHE SUGAR PART• The major difference between RNA and DNA is
the different form of sugar used.
OHOCH2
H HHH
OH OHOH
OHOHOCH2
H HHH
OH HH
OH
Ribose C5H10O5
in RNADeoxyDeoxyRibose C5H10O4
in DNA
The difference is at carbon #2carbon #2.
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The Nitrogenous BasesThe Nitrogenous Bases
5 bases5 bases used fall in two classestwo classes
Purines Purines & & PyrimidinesPyrimidines
N
N
N
NH
A double ringdouble ring (6 & 5 members)
A single ringsingle ring(6 membered)
N
N
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Pyrimidines:Pyrimidines:
The Nitrogenous BasesThe Nitrogenous Bases
Purines:Purines:N
N
N
N
NH2
H
N
N
N
NH
H2N
O
H
N
N
O
O
CH3
H
HN
N
O
O
H
H N
NO
H
H
NH2
Adenine (A)Adenine (A)Adenine (A)Adenine (A) Guanine (G)Guanine (G)Guanine (G)Guanine (G)
Thiamine (T)Thiamine (T)In In DNADNA only onlyThiamine (T)Thiamine (T)In In DNADNA only only
Uracil (U)Uracil (U)In In RNARNA only only
Uracil (U)Uracil (U)In In RNARNA only only
Cytosine (C)Cytosine (C)Cytosine (C)Cytosine (C)
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H
N
N
N
N
NH2
P
O
O
H H
OH
OH
H
O
OH
1'
2'3'
4'
5'
H
HN
N
N
NP
O
O
H H
OH
OH
H
O
OH
O
H2N
1'
2'3'
4'
5'
1'
2'3'
4'
5'
H
N
P
O
O
H H
OH
OH
H
O
OH
N
O
O
CH3
Primary structurePrimary structure
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H
N
N
N
N
NH2
P
O
O
H H
OH H
O
OH
H
HN
N
N
NP
O
O
H H
OH H
O
O
O
H2N
H
N
P
O
O
H H
OH
OH
H
O
N
O
O
CH3
O
1'
2'3'
4'
5'
1'
2'3'
4'
5'
1'
2'3'
4'
5'
Primary structurePrimary structure
Phosphate bondsPhosphate bondslink DNA or RNAlink DNA or RNAnucleotides togethernucleotides togetherin a linear sequence.
Similar to proteinswith their peptide
bonds and sidegroups.
5’
3’
Adenine (A)
Guanine (G)
Thymine (T)
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Structure of DNAStructure of DNA
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In 1938 William Thomas Astbury took the first fiber diffraction pictures of DNA, correctly predicting, in an article in the journal Nature, the overall dimensions of the molecule and that the nucleotide bases were stacked at intervals of 3.3Å perpendicular to its long axis. It was left, however, to Watson and Crick after the Second World War to elucidate the detailed double helical structure of DNA.
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Maurice Wilkins with one of the cameras he developed specially for X-ray diffraction studies
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Work on x-ray diffraction patterns by Maurice Wilkins and Rosalind Franklin in 1953, revealed that the molecule had a "helical shape“.
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Rosalind Franklin is most associated with the discovery of the structure of DNA. At 26, after she had her PhD, Franklin began working in x-ray diffraction - using x-rays to create images of crystallized solids. She pioneered the use of this method in analyzing complex, unorganized matter such as large biological molecules, and not just single crystals.Franklin made marked advances in x-ray diffraction techniques with DNA. She adjusted her equipment to produce an extremely fine beam of x-rays. She extracted finer DNA fibers than ever before and arranged them in parallel bundles. And she studied the fibers' reactions to humid conditions. All of these allowed her to discover crucial keys to DNA's structure. Maurice Wilkins, her laboratory's second-in-command, shared her data, without her knowledge, with James Watson and Francis Crick, at Cambridge University, and they pulled ahead in the race, ultimately publishing the proposed structure of DNA in March, 1953.It is clear that without an unauthorized peek at Franklin's unpublished data, Watson and Crick probably would neither have published their famous paper on the structure of DNA in 1953, nor won their Nobel Prizes in 1962. Franklin did not share the Nobel Prize; she died in 1958 at the age of 37.
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1953, James Watson & Francis Crick and their scale model for DNA
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DNA secondary and tertiary structureDNA secondary and tertiary structure
Sugar-phosphate backboneSugar-phosphate backboneCauses each DNA chain to coilcoil around the outsideoutside of the attached basesof the attached bases like a spiral stair case.
Base PairingBase PairingHydrogen bonding occurs between purines and purines and pyrimidinespyrimidines. This causes two DNA strands to bond together.
adenine - thymineadenine - thymine guanine - cytosineguanine - cytosineAlways pair together!Always pair together!
Results in a double helix structure.
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Base pairing and hydrogen bondingBase pairing and hydrogen bonding
N
N
O| |
- H
N - H
N
NN
N
O| |
H - N
N
N O| |
O| |
H3C
- H
guanine cytosine
thymine adenineN
N N
N|
HH
N
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Hydrogen bondingHydrogen bonding
Each base wants toform either two or three hydrogen bonds.
That’s why only certain bases will form pairs.
G
T
C
A
C G
A
C
T
G
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Sugar-Sugar-phosphate phosphate backbonebackboneDNA coilscoils around outsideoutside of of attached attached basesbases like a spiral stair case.
Results in a double helix structure.
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• Crick and Watson (1962 Nobel Prize)
– Proposed the basic structure of DNA
– 2 strands wrap around each other
– Strands are connected by H-bonds between the amines.
• Like steps of a spiral staircase
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ChromosomesChromosomes
The normal number of chromosome pairs varies among the species.
AnimalAnimal Pairs Pairs PlantPlant PairsPairsMan 23 Onion 8Cat 30 Rice 14Mouse 20 Rye 7Rabbit 22 Tomato 12Honeybee, White pine 12
male 8 Adder’s 1262female 16 tongue fern
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Role of RNA and DNA in Heredity
RNA and DNA are involved in three major processes in a cell related to heredity as shown below:
1. Replication (DNA copies itself)
2. Transcription (The genetic code in DNA is rewritten into RNA and carried to the ribosomes by mRNA
3. Translation (tRNA carries amino acids to the ribosomes as part of protein synthesis
Replication is an important process during mitosis
Transcription and translation are two steps in the biosynthesis of a protein
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TTCC
AA
SS SSSS SSSSSS
GG TT CCAA
PPPP PP PPPPPP
CC GG
GG
DNA: Self - ReplicationDNA: Self - Replication
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GGGGAA
SS SSSS SSSSSS
GG TT CCAA
PPPP PP PPPPPP
CC GG
DNA: Self - ReplicationDNA: Self - Replication
TT CCCC
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Replication of DNAReplication of DNA
ReplicationReplication occurs on both halvesboth halvesin opposite directions.opposite directions.
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DNA DNA ReplicationReplication
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RNA synthesisRNA synthesis
In the first step, RNA polymeraseRNA polymerase bindsto a promotorpromotor sequenceon the DNA chain.
This insuresinsures that transcription occurs in the correct directioncorrect direction.
The initial reaction is toseparate the twoseparate the twoDNA strandsDNA strands.
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RNA synthesisRNA synthesis
initiationsequence
terminationsequence
‘Special’ baseSpecial’ basesequencessequences in theDNA indicatewhere RNARNAsynthesis startssynthesis startsand stops.and stops.
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RNA synthesisRNA synthesis
Once the terminationsequence isreached, thenew RNA moleculenew RNA moleculeand the RNA synthaseare released.released.
The DNA recoils.The DNA recoils.
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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.
rRNA
rRNA
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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.
rRNA
rRNA
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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.
rRNA
rRNA
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• The messenger RNAmessenger RNA (mRNA) move outside the nucleus to the cytoplasmto the cytoplasm where RibosomesRibosomes are anxiously awaiting their arrival.
rRNA
rRNA
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rRNA
rRNA
Ribosomal RNA – rRNARibosomal RNA – rRNA: Platform for protein synthesis. Holds mRNA in place and helps assemble proteins.
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AUG GCU AUG UUG
5’
3’
rRNArRNA
•The RibosomesRibosomes are like train stationslike train stations
–The mRNA is the trainmRNA is the train slowly moving through the station.
rRNArRNA
Codons
mRNAmRNA
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Transfer RNA Transfer RNA - tRNA- tRNA =• relatively small small compared to other RNA’s
(70-90 bases.)70-90 bases.)• transports amino acidstransports amino acids to site of protein synthesis.
A
C
C
A
C
C
U
C
G
U
CU
U
C
G
G
G
G
G
CC GGG
CC GG
A CGG
CC GGU
C
C
C
C
U
C
A
U
G
G
A
G
G
G
G
GU
U
CC G
U
C GC
AU
G
G
C
U
AG U
A GU
G
GC
HO-A
C
C
A
C
C
U
C
G
U
CU
U
C
G
G
G
G
G
CC GGG
CC GG
A CGG
CC GGU
C
C
C
C
U
C
A
U
G
G
A
G
G
G
G
GU
U
CC G
U
C GC
AU
G
G
C
U
AG U
A GU
G
GC
HO-
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Anticodons on t-RNAAnticodons on t-RNA
A
C
C
A
C
C
U
C
G
U
CU
U
C
G
G
G
G
G
CC GGG
CC GG
A CGG
CC GGU
C
C
C
C
U
C
A
U
G
G
A
G
G
G
G
GU
U
CC G
U
C GC
AU
G
G
C
U
AG U
A GU
G
GC
HO-
Site of aminoacid attachment
Site of aminoacid attachment
Three base anticodon site
Three base anticodon site
Point ofattachmentto mRNA
Point ofattachmentto mRNA
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UUU or UUC is the codon for Phe. UUG is the codon for Leu. AUG is the codon for Met.
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CodonsCodons
There are two additional types of codons:
Initiation Initiation AUGAUG(same as methionine)
TerminationTermination UAG, UAA, UGAUAG, UAA, UGA
A total of 64 condons are used for all aminoacids and for starting and stopping. All proteinsynthesis starts with methionine. After the poly-peptide has been made, an enzyme removes thisamino acid.
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Protein SynthesisProtein Synthesis1: Activation1: Activation
Each AA is activated by reacting with an ATP
The activated AA is then attached to particular tRNAtRNA... (with the correct anticodon)
C G A
MET
anticodon
activated AA
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TranslationTranslation
AUG GCU AUG UUG mRNA
5’
3’
Initiationfactors
ribosome unit
U A C
MET
PPsitesite AA site site
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U A C
MET
TranslationTranslation
ribosome unit
AUG GCU AUG UUG mRNA
5’
3’
PPsitesite AA site site
C G A
Ala
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ribosome unit
AUG GCU AUG UUG mRNA
5’
3’
TranslationTranslation
U A C
MET
C G A
Ala
peptide bondforms
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ribosome unit
GCU UUC UUGmRNA
5’
3’
TranslationTranslation
C G A
Ala
peptide bond
Met
A A G
Phe
AU G
U A C
U A C
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ribosome unit
GCU UUC UUGmRNA
5’
3’
TranslationTranslation
C G A
Ala
peptide bondforms
Met
A A G
Phe
AU G
U A C
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TerminationTermination
After the last translocation (the last codon is a STOP), no more AA are added.
“Releasing factors” cleave the last AA from the tRNA
The polypeptide is complete
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Recombinant DNARecombinant DNA
Circular DNA found in bacteriaE.Coli plasmid bodiesRestriction endonucleases cleave DNA at
specific genesResult is a “sticky end”Addition of a gene from a second
organismSpliced DNA is replaced and organism
synthesizes the new protein
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Recombinant DNARecombinant DNA
Bacterium
Remove gene segment
DNAPlasmid sticky ends
Cut genefor insulin
Replace inbacterium