biology presentations for a-level, in multimedia james bowles, 2001
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BIOLOGY PRESENTATIONS FOR A-LEVEL, IN MULTIMEDIA JAMES BOWLES, 2001. LEFT CLICK OR PRESS SPACE BAR TO ADVANCE, PRESS P BUTTON TO GO BACK, PRESS ESC BUTTON TO END. ‘A’ Level Biology. DNA Replication. Introduction. Theoretically there are two possible ways in which DNA could replicate. - PowerPoint PPT PresentationTRANSCRIPT
1BIOLOGY PRESENTATIONSFOR A-LEVEL, IN MULTIMEDIA
JAMES BOWLES, 2001
LEFT CLICK OR PRESS SPACEBAR TO ADVANCE, PRESS P BUTTONTO GO BACK, PRESS ESC BUTTON TO END
2
‘A’ Level Biology
DNA Replication
3Introduction
Theoretically there are two Theoretically there are two possible ways in which DNA possible ways in which DNA
could replicatecould replicate
4Introduction
This would be This would be CONSERVATIVE CONSERVATIVE replicationreplication
5IntroductionThis would be This would be SEMI-SEMI-
CONSERVATIVE CONSERVATIVE replicationreplication
6Introduction
Experiments in 1958 by Meselsohn Experiments in 1958 by Meselsohn and Stahl showed that DNA and Stahl showed that DNA
replication is semi-conservativereplication is semi-conservative
7Meselsohn and Stahl
Culture of Culture of E.coliE.coli grown for grown for
many many generations generations with heavy with heavy isotope of isotope of
nitrogen (nitrogen (1515N)N)
8Meselsohn and Stahl
Extracted DNA Extracted DNA was centrifuged was centrifuged and a ‘heavy’ and a ‘heavy’
band was band was establishedestablished
9Meselsohn and Stahl
The The E.coli E.coli were were transferred to a transferred to a
culture culture containing containing 1414N, N,
for one for one generationgeneration
10Meselsohn and Stahl
A lighter band A lighter band for the DNA for the DNA
was established was established when it was when it was centrifugedcentrifuged
11Meselsohn and Stahl
The The E.coliE.coli were were grown for grown for successive successive
generations on generations on the medium the medium
containing the containing the ‘light’ isotope‘light’ isotope
12Meselsohn and Stahl
Two bands now Two bands now appear, one is appear, one is
an intermediate an intermediate and one and one
represents the represents the ‘light’ isotope‘light’ isotope
13DNA Replication
14DNA Replication
DNA strands DNA strands run anti-run anti-
parallel to one parallel to one anotheranother
5’5’ 3’3’
3’3’ 5’5’
15DNA Replication
The enzyme The enzyme Helicase Helicase
unwinds the unwinds the DNA double DNA double
helixhelix
5’5’ 3’3’
3’3’ 5’5’
16DNA Replication
DNA DNA polymerase polymerase
attaches to the attaches to the ‘leading’ ‘leading’
strandstrand
5’5’ 3’3’
3’3’ 5’5’
17DNA ReplicationDNA DNA
polymerase polymerase synthesises a synthesises a
new DNA new DNA strand in the 3’ strand in the 3’ to 5’ directionto 5’ direction
5’5’ 3’3’
3’3’ 5’5’
18DNA ReplicationAnother DNA Another DNA
polymerase polymerase molecule molecule
attaches to the attaches to the ‘lagging’ ‘lagging’
strandstrand
5’5’ 3’3’
3’3’ 5’5’
19DNA Replication
DNA is DNA is synthesised in synthesised in
the 3’ to 5’ the 3’ to 5’ directiondirection
5’5’ 3’3’
3’3’ 5’5’
20DNA Replication
Helicase Helicase continues to continues to unwind the unwind the
DNA double DNA double helixhelix
5’5’ 3’3’
3’3’ 5’5’
21DNA Replication
Continuous Continuous synthesis synthesis
proceeds on proceeds on the ‘leading’ the ‘leading’
strandstrand
5’5’ 3’3’
3’3’ 5’5’
22
5’5’ 3’3’
3’3’ 5’5’
DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
23DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
5’5’ 3’3’
3’3’ 5’5’
24DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
5’5’ 3’3’
3’3’ 5’5’
25DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
5’5’ 3’3’
3’3’ 5’5’
26DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
5’5’ 3’3’
3’3’ 5’5’
27DNA ReplicationDNA DNA
polymerase polymerase detaches from detaches from the ‘lagging’ the ‘lagging’ strand, and strand, and
rejoins further rejoins further downdown
5’5’ 3’3’
3’3’ 5’5’
28DNA Replication
Synthesis of Synthesis of DNA continues DNA continues on the ‘lagging on the ‘lagging
strand’strand’
5’5’ 3’3’
3’3’ 5’5’
29DNA Replication
DNA polymerase DNA polymerase is unable to join is unable to join up the fragments up the fragments on the lagging on the lagging
strandstrand
5’5’ 3’3’
3’3’ 5’5’
30DNA Replication
This is done by This is done by the enzyme the enzyme
LigaseLigase
5’5’ 3’3’
3’3’ 5’5’
31DNA Replication
This is done by This is done by the enzyme the enzyme
LigaseLigase
5’5’ 3’3’
3’3’ 5’5’
32