The molecular basis of inheritance. (Chapter 16) презентация

Содержание

Overview: Life’s Operating Instructions In 1953, James Watson and Francis Crick introduced an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA DNA, the substance of inheritance, is the

Слайд 1The Molecular Basis of Inheritance
Chapter 16

Слайд 2Overview: Life’s Operating Instructions
In 1953, James Watson and Francis Crick introduced

an elegant double-helical model for the structure of deoxyribonucleic acid, or DNA
DNA, the substance of inheritance, is the most celebrated molecule of our time
Hereditary information is encoded in DNA and reproduced in all cells of the body
This DNA program directs the development of biochemical, anatomical, physiological, and (to some extent) behavioral traits


Слайд 3Figure 16.1

Слайд 4Concept 16.1: DNA is the genetic material
Early in the 20th century,

the identification of the molecules of inheritance loomed as a major challenge to biologists


Слайд 5The Search for the Genetic Material: Scientific Inquiry
When T. H. Morgan’s

group showed that genes are located on chromosomes, the two components of chromosomes—DNA and protein—became candidates for the genetic material
The key factor in determining the genetic material was choosing appropriate experimental organisms
The role of DNA in heredity was first discovered by studying bacteria and the viruses that infect them


Слайд 6Evidence That DNA Can Transform Bacteria
The discovery of the genetic role

of DNA began with research by Frederick Griffith in 1928
Griffith worked with two strains of a bacterium, one pathogenic and one harmless


Слайд 7
When he mixed heat-killed remains of the pathogenic strain with living

cells of the harmless strain, some living cells became pathogenic
He called this phenomenon transformation, now defined as a change in genotype and phenotype due to assimilation of foreign DNA


Слайд 8Living S cells (control)
Living R cells (control)
Heat-killed S cells (control)
Mixture of heat-killed S cells and living R cells
Mouse

dies

Mouse dies

Mouse healthy

Mouse healthy

Living S cells

EXPERIMENT

RESULTS

Figure 16.2

Слайд 9In 1944, Oswald Avery, Maclyn McCarty, and Colin MacLeod announced that

the transforming substance was DNA
Their conclusion was based on experimental evidence that only DNA worked in transforming harmless bacteria into pathogenic bacteria
Many biologists remained skeptical, mainly because little was known about DNA


Слайд 10Evidence That Viral DNA Can Program Cells
More evidence for DNA as

the genetic material came from studies of viruses that infect bacteria
Such viruses, called bacteriophages (or phages), are widely used in molecular genetics research


Слайд 11
Animation: Phage T2 Reproductive Cycle Right-click slide / select “Play”

Слайд 12Figure 16.3
Phage head
Tail sheath
Tail fiber
DNA
Bacterial cell
100 nm

Слайд 13In 1952, Alfred Hershey and Martha Chase performed experiments showing that

DNA is the genetic material of a phage known as T2
To determine this, they designed an experiment showing that only one of the two components of T2 (DNA or protein) enters an E. coli cell during infection
They concluded that the injected DNA of the phage provides the genetic information



Слайд 14
Animation: Hershey-Chase Experiment
Right-click slide / select “Play”

Слайд 15Figure 16.4-1
Bacterial cell
Phage
Batch 1: Radioactive sulfur (35S)
DNA
Batch 2: Radioactive phosphorus (32P)
Radioactive DNA

EXPERIMENT
Radioactive protein

Слайд 16Figure 16.4-2
Bacterial cell
Phage
Batch 1: Radioactive sulfur (35S)
Radioactive protein
DNA
Batch 2: Radioactive phosphorus (32P)
Radioactive DNA
Empty protein shell
Phage DNA

EXPERIMENT

Слайд 17Figure 16.4-3
Bacterial cell
Phage
Batch 1: Radioactive sulfur (35S)
Radioactive protein
DNA
Batch 2: Radioactive phosphorus (32P)
Radioactive DNA
Empty protein shell
Phage DNA
Centrifuge
Centrifuge
Radioactivity (phage protein) in liquid
Pellet (bacterial cells and contents)
Pellet
Radioactivity (phage DNA) in

pellet


EXPERIMENT

Слайд 18Additional Evidence That DNA Is the Genetic Material
It was known that

DNA is a polymer of nucleotides, each consisting of a nitrogenous base, a sugar, and a phosphate group
In 1950, Erwin Chargaff reported that DNA composition varies from one species to the next
This evidence of diversity made DNA a more credible candidate for the genetic material


Слайд 19
Animation: DNA and RNA Structure Right-click slide / select “Play”

Слайд 20Two findings became known as Chargaff’s rules
The base composition of DNA

varies between species
In any species the number of A and T bases are equal and the number of G and C bases are equal
The basis for these rules was not understood until the discovery of the double helix


Слайд 21Figure 16.5
Sugar–phosphate backbone
Nitrogenous bases
Thymine (T)
Adenine (A)
Cytosine (C)
Guanine (G)
Nitrogenous base
Phosphate
DNA nucleotide
Sugar (deoxyribose)
3′ end
5′ end

Слайд 22Building a Structural Model of DNA: Scientific Inquiry
After DNA was accepted

as the genetic material, the challenge was to determine how its structure accounts for its role in heredity
Maurice Wilkins and Rosalind Franklin were using a technique called X-ray crystallography to study molecular structure
Franklin produced a picture of the DNA molecule using this technique


Слайд 23Figure 16.6
(a) Rosalind Franklin

Слайд 24Figure 16.6a
(a) Rosalind Franklin

Слайд 25Figure 16.6b

Слайд 26Franklin’s X-ray crystallographic images of DNA enabled Watson to deduce that

DNA was helical
The X-ray images also enabled Watson to deduce the width of the helix and the spacing of the nitrogenous bases
The pattern in the photo suggested that the DNA molecule was made up of two strands, forming a double helix


Слайд 27
Animation: DNA Double Helix Right-click slide / select “Play”

Слайд 28Figure 16.7
3.4 nm
1 nm
0.34 nm
Hydrogen bond
(b) Partial chemical structure
3′ end
5′ end
3′

end

5′ end

T

T

A

A

G

G

C

C

C

C

C

C

C

C

C

C

C

G

G

G

G

G

G

G

G

G

T

T

T

T

T

T

A

A

A

A

A

A

Слайд 293.4 nm
1 nm
0.34 nm
Hydrogen bond
(b) Partial chemical structure
3′ end
5′ end
3′ end
5′

end

T

T

A

A

G

G

C

C

C

C

C

C

C

C

C

C

C

G

G

G

G

G

G

G

G

G

T

T

T

T

T

T

A

A

A

A

A

A

Figure 16.7a

Слайд 30Figure 16.7b
(c) Space-filling model

Слайд 31Watson and Crick built models of a double helix to conform

to the X-rays and chemistry of DNA
Franklin had concluded that there were two outer sugar-phosphate backbones, with the nitrogenous bases paired in the molecule’s interior
Watson built a model in which the backbones were antiparallel (their subunits run in opposite directions)


Слайд 32At first, Watson and Crick thought the bases paired like with

like (A with A, and so on), but such pairings did not result in a uniform width
Instead, pairing a purine with a pyrimidine resulted in a uniform width consistent with the X-ray data


Слайд 33Figure 16.UN01
Purine + purine: too wide
Pyrimidine + pyrimidine: too narrow
Purine +

pyrimidine: width consistent with X-ray data

Слайд 34Watson and Crick reasoned that the pairing was more specific, dictated

by the base structures
They determined that adenine (A) paired only with thymine (T), and guanine (G) paired only with cytosine (C)
The Watson-Crick model explains Chargaff’s rules: in any organism the amount of A = T, and the amount of G = C


Слайд 35Figure 16.8
Sugar
Sugar
Sugar
Sugar
Adenine (A)
Thymine (T)
Guanine (G)
Cytosine (C)

Слайд 36Concept 16.2: Many proteins work together in DNA replication and repair
The

relationship between structure and function is manifest in the double helix
Watson and Crick noted that the specific base pairing suggested a possible copying mechanism for genetic material


Слайд 37The Basic Principle: Base Pairing to a Template Strand
Since the two

strands of DNA are complementary, each strand acts as a template for building a new strand in replication
In DNA replication, the parent molecule unwinds, and two new daughter strands are built based on base-pairing rules


Слайд 38
Animation: DNA Replication Overview
Right-click slide / select “Play”

Слайд 39Figure 16.9-1
(a) Parent molecule
A
A
A
T
T
T
C
C
G
G

Слайд 40Figure 16.9-2
(a) Parent molecule
A
A
A
A
A
A
T
T
T
T
T
T
C
C
C
C
G
G
G
G

Слайд 41Figure 16.9-3
(a) Parent molecule
A
A
A
A
A
A
A
A
A
A
A
A
T
T
T
T
T
T
T
T
T
T
T
T
C
C
C
C
C
C
C
C
G
G
G
G
G
G
G
G

Слайд 42Watson and Crick’s semiconservative model of replication predicts that when a

double helix replicates, each daughter molecule will have one old strand (derived or “conserved” from the parent molecule) and one newly made strand
Competing models were the conservative model (the two parent strands rejoin) and the dispersive model (each strand is a mix of old and new)


Слайд 43Figure 16.10
(c) Dispersive model
Parent cell
First replication
Second replication

Слайд 44Experiments by Matthew Meselson and Franklin Stahl supported the semiconservative model


They labeled the nucleotides of the old strands with a heavy isotope of nitrogen, while any new nucleotides were labeled with a lighter isotope


Слайд 45The first replication produced a band of hybrid DNA, eliminating the

conservative model
A second replication produced both light and hybrid DNA, eliminating the dispersive model and supporting the semiconservative model


Слайд 46Figure 16.11
Bacteria cultured in medium with 15N (heavy isotope)
Bacteria transferred to medium with 14N (lighter isotope)
DNA sample centrifuged after first replication
DNA sample centrifuged after

second replication

Less dense

More dense

Predictions:

First replication

Second replication

Conservative model

Semiconservative model

Dispersive model

EXPERIMENT

RESULTS

CONCLUSION

Слайд 47Figure 16.11a
Bacteria cultured in medium with 15N (heavy isotope)
Bacteria transferred to medium with 14N (lighter isotope)
DNA sample centrifuged after first replication
DNA sample centrifuged after

second replication

Less dense

More dense

EXPERIMENT

RESULTS

Слайд 48Figure 16.11b
Predictions:
First replication
Second replication
Conservative model
Semiconservative model
Dispersive model
CONCLUSION

Слайд 49DNA Replication: A Closer Look
The copying of DNA is remarkable in

its speed and accuracy
More than a dozen enzymes and other proteins participate in DNA replication


Слайд 50Getting Started
Replication begins at particular sites called origins of replication, where

the two DNA strands are separated, opening up a replication “bubble”
A eukaryotic chromosome may have hundreds or even thousands of origins of replication
Replication proceeds in both directions from each origin, until the entire molecule is copied


Слайд 51
Animation: Origins of Replication
Right-click slide / select “Play”

Слайд 52Figure 16.12
(a) Origin of replication in an E. coli cell
(b) Origins

of replication in a eukaryotic cell

Origin of replication

Parental (template) strand

Double- stranded DNA molecule

Daughter (new) strand

Replication fork

Replication bubble

Two daughter DNA molecules

Origin of replication

Double-stranded DNA molecule

Parental (template) strand

Daughter (new) strand

Bubble

Replication fork

Two daughter DNA molecules

0.5 μm

0.25 μm




Слайд 53Figure 16.12a
(a) Origin of replication in an E. coli cell
Origin of replication
Parental

(template) strand

Double- stranded DNA molecule

Daughter (new) strand

Replication fork

Replication bubble

Two daughter DNA molecules

0.5 μm


Слайд 54Figure 16.12b
(b) Origins of replication in a eukaryotic cell
Origin of replication
Double-stranded DNA

molecule

Parental (template) strand

Daughter (new) strand

Bubble

Replication fork

Two daughter DNA molecules

0.25 μm



Слайд 55Figure 16.12c
0.5 μm

Слайд 56Figure 16.12d
0.25 μm

Слайд 57At the end of each replication bubble is a replication fork,

a Y-shaped region where new DNA strands are elongating
Helicases are enzymes that untwist the double helix at the replication forks
Single-strand binding proteins bind to and stabilize single-stranded DNA
Topoisomerase corrects “overwinding” ahead of replication forks by breaking, swiveling, and rejoining DNA strands


Слайд 58Figure 16.13
Topoisomerase
Primase
RNA primer
Helicase
Single-strand binding proteins
5′
3′
5′
5′
3′
3′

Слайд 59DNA polymerases cannot initiate synthesis of a polynucleotide; they can only

add nucleotides to the 3′ end
The initial nucleotide strand is a short RNA primer


Слайд 60An enzyme called primase can start an RNA chain from scratch

and adds RNA nucleotides one at a time using the parental DNA as a template
The primer is short (5–10 nucleotides long), and the 3′ end serves as the starting point for the new DNA strand


Слайд 61Synthesizing a New DNA Strand
Enzymes called DNA polymerases catalyze the elongation

of new DNA at a replication fork
Most DNA polymerases require a primer and a DNA template strand
The rate of elongation is about 500 nucleotides per second in bacteria and 50 per second in human cells


Слайд 62Each nucleotide that is added to a growing DNA strand is

a nucleoside triphosphate
dATP supplies adenine to DNA and is similar to the ATP of energy metabolism
The difference is in their sugars: dATP has deoxyribose while ATP has ribose
As each monomer of dATP joins the DNA strand, it loses two phosphate groups as a molecule of pyrophosphate


Слайд 63Figure 16.14
New strand
Template strand
Sugar
Phosphate
Base
Nucleoside triphosphate
DNA polymerase
Pyrophosphate
5′
5′
5′
5′
3′
3′
3′
3′
OH
OH
OH
P
P i
2 P i

P
P
P
A
A
A
A
T
T
T
T
C
C
C
C
C
C
G
G
G
G

Слайд 64Antiparallel Elongation
The antiparallel structure of the double helix affects replication
DNA polymerases

add nucleotides only to the free 3′ end of a growing strand; therefore, a new DNA strand can elongate only in the 5′ to 3′ direction


Слайд 65Along one template strand of DNA, the DNA polymerase synthesizes a

leading strand continuously, moving toward the replication fork


Слайд 66
Animation: Leading Strand Right-click slide / select “Play”

Слайд 67Figure 16.15
Leading strand
Lagging strand
Overview
Origin of replication
Lagging strand
Leading strand
Primer
Overall directions of replication
Origin of replication
RNA primer
Sliding clamp
DNA pol

III

Parental DNA

3′

5′

5′

3′

3′

5′

3′

5′

3′

5′

3′

5′

Слайд 68Figure 16.15a
Leading strand
Lagging strand
Overview
Origin of replication
Lagging strand
Leading strand
Primer
Overall directions of replication

Слайд 69Origin of replication
RNA primer
Sliding clamp
DNA pol III
Parental DNA
3′
5′
5′
3′
3′
5′
3′
5′
3′
5′
3′
5′
Figure 16.15b

Слайд 70To elongate the other new strand, called the lagging strand, DNA

polymerase must work in the direction away from the replication fork
The lagging strand is synthesized as a series of segments called Okazaki fragments, which are joined together by DNA ligase


Слайд 71
Animation: Lagging Strand Right-click slide / select “Play”

Слайд 72Origin of replication
Overview
Leading strand
Leading strand
Lagging strand
Lagging strand
Overall directions of replication
Template strand
RNA primer for fragment 1
Okazaki fragment 1
RNA primer for

fragment 2

Okazaki fragment 2

Overall direction of replication

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

2

2

2

1

1

1

1

1

2



1

Figure 16.16

Слайд 73Figure 16.16a
Origin of replication
Overview
Leading strand
Leading strand
Lagging strand
Lagging strand
Overall directions of replication
1
2

Слайд 74Figure 16.16b-1
Template strand
3′
3′
5′
5′

Слайд 75Figure 16.16b-2
Template strand
RNA primer for fragment 1
3′
3′
3′
3′
5′
5′
5′
5′

1

Слайд 76Figure 16.16b-3
Template strand
RNA primer for fragment 1
Okazaki fragment 1
3′
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
5′
1

1

Слайд 77Figure 16.16b-4
Template strand
RNA primer for fragment 1
Okazaki fragment 1
RNA primer for fragment 2
Okazaki fragment 2
3′
3′
3′
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
5′
5′
5′
2
1
1


1

Слайд 78Figure 16.16b-5
Template strand
RNA primer for fragment 1
Okazaki fragment 1
RNA primer for fragment 2
Okazaki fragment 2
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
3′
5′
5′
5′
5′
5′
5′
5′
5′
5′
5′
5′
2
2
1
1
1


1

Слайд 79Figure 16.16b-6
Template strand
RNA primer for fragment 1
Okazaki fragment 1
RNA primer for fragment 2
Okazaki fragment 2
Overall direction

of replication

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

3′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

5′

2

2

2

1

1

1

1



1

Слайд 80Figure 16.17
Overview
Leading strand
Origin of replication
Lagging strand
Leading strand
Lagging strand
Overall directions of replication
Leading strand
DNA pol III
DNA pol III
Lagging

strand

DNA pol I

DNA ligase

Primer

Primase

Parental DNA

5′

5′

5′

5′

5′

3′

3′

3′

3′

3′

3

2

1

4

Слайд 81Figure 16.17a
Overview
Leading strand
Origin of replication
Lagging strand
Leading strand
Lagging strand
Overall directions of replication
Leading strand
DNA pol III
Primer
Primase
Parental DNA
5′
5′
3′
3′
3′

Слайд 82Overview
Leading strand
Origin of replication
Lagging strand
Leading strand
Lagging strand
Overall directions of replication
Leading strand
Primer
DNA pol III
DNA pol I
Lagging strand
DNA

ligase

5′

5′

5′

3′

3′

3′

3

4

2

1

Figure 16.17b

Слайд 83The DNA Replication Complex
The proteins that participate in DNA replication form

a large complex, a “DNA replication machine”
The DNA replication machine may be stationary during the replication process
Recent studies support a model in which DNA polymerase molecules “reel in” parental DNA and “extrude” newly made daughter DNA molecules


Слайд 84
Animation: DNA Replication Review
Right-click slide / select “Play”

Слайд 85Figure 16.18
Parental DNA
DNA pol III
Leading strand
Connecting protein
Helicase
Lagging strand
DNA pol III
Lagging strand template
5′
5′
5′
5′
5′
5′
3′
3′
3′
3′
3′
3′

Слайд 86Proofreading and Repairing DNA
DNA polymerases proofread newly made DNA, replacing any

incorrect nucleotides
In mismatch repair of DNA, repair enzymes correct errors in base pairing
DNA can be damaged by exposure to harmful chemical or physical agents such as cigarette smoke and X-rays; it can also undergo spontaneous changes
In nucleotide excision repair, a nuclease cuts out and replaces damaged stretches of DNA


Слайд 87Figure 16.19
Nuclease
DNA polymerase
DNA ligase
5′
5′
5′
5′
5′
5′
5′
5′
3′
3′
3′
3′
3′
3′
3′
3′

Слайд 88Evolutionary Significance of Altered DNA Nucleotides
Error rate after proofreading repair is

low but not zero
Sequence changes may become permanent and can be passed on to the next generation
These changes (mutations) are the source of the genetic variation upon which natural selection operates


Слайд 89Replicating the Ends of DNA Molecules
Limitations of DNA polymerase create problems

for the linear DNA of eukaryotic chromosomes
The usual replication machinery provides no way to complete the 5′ ends, so repeated rounds of replication produce shorter DNA molecules with uneven ends
This is not a problem for prokaryotes, most of which have circular chromosomes


Слайд 90Figure 16.20
Ends of parental DNA strands
Leading strand
Lagging strand
Last fragment
Next-to-last fragment
Lagging strand
RNA primer
Parental

strand

Removal of primers and replacement with DNA where a 3′ end is available

Second round of replication

Further rounds of replication

New leading strand

New lagging strand

Shorter and shorter daughter molecules

3′

3′

3′

3′

3′

5′

5′

5′

5′

5′



Слайд 91Figure 16.20a
Ends of parental DNA strands
Leading strand
Lagging strand
Last fragment
Next-to-last fragment
Lagging strand
RNA primer
Parental

strand

Removal of primers and replacement with DNA where a 3′ end is available

3′

3′

3′

5′

5′

5′



Слайд 92Figure 16.20b
Second round of replication
Further rounds of replication
New leading strand
New lagging strand
Shorter and

shorter daughter molecules

3′

3′

3′

5′

5′

5′

Слайд 93Eukaryotic chromosomal DNA molecules have special nucleotide sequences at their ends

called telomeres
Telomeres do not prevent the shortening of DNA molecules, but they do postpone the erosion of genes near the ends of DNA molecules
It has been proposed that the shortening of telomeres is connected to aging


Слайд 94Figure 16.21
1 μm

Слайд 95If chromosomes of germ cells became shorter in every cell cycle,

essential genes would eventually be missing from the gametes they produce
An enzyme called telomerase catalyzes the lengthening of telomeres in germ cells


Слайд 96The shortening of telomeres might protect cells from cancerous growth by

limiting the number of cell divisions
There is evidence of telomerase activity in cancer cells, which may allow cancer cells to persist


Слайд 97Concept 16.3 A chromosome consists of a DNA molecule packed together

with proteins

The bacterial chromosome is a double-stranded, circular DNA molecule associated with a small amount of protein
Eukaryotic chromosomes have linear DNA molecules associated with a large amount of protein
In a bacterium, the DNA is “supercoiled” and found in a region of the cell called the nucleoid


Слайд 98Chromatin, a complex of DNA and protein, is found in the

nucleus of eukaryotic cells
Chromosomes fit into the nucleus through an elaborate, multilevel system of packing


Слайд 99
Animation: DNA Packing Right-click slide / select “Play”

Слайд 100Figure 16.22a
DNA double helix (2 nm in diameter)
DNA, the double helix
Nucleosome (10 nm

in diameter)

Histones

Histones

Histone tail

H1

Nucleosomes, or “beads on a string” (10-nm fiber)

Слайд 101Figure 16.22b
30-nm fiber
30-nm fiber
Loops
Scaffold
300-nm fiber
Chromatid (700 nm)
Replicated chromosome (1,400 nm)
Looped domains (300-nm fiber)
Metaphase chromosome

Слайд 102Figure 16.22c
DNA double helix (2 nm in diameter)

Слайд 103Figure 16.22d
Nucleosome (10 nm in diameter)

Слайд 104Figure 16.22e
30-nm fiber

Слайд 105Figure 16.22f
Loops
Scaffold

Слайд 106Figure 16.22g
Chromatid (700 nm)

Слайд 107Chromatin undergoes changes in packing during the cell cycle
At interphase, some

chromatin is organized into a 10-nm fiber, but much is compacted into a 30-nm fiber, through folding and looping
Though interphase chromosomes are not highly condensed, they still occupy specific restricted regions in the nucleus


Слайд 108Figure 16.23
5 μm

Слайд 109Figure 16.23a

Слайд 110Figure 16.23b

Слайд 111Figure 16.23c
5 μm

Слайд 112Most chromatin is loosely packed in the nucleus during interphase and

condenses prior to mitosis
Loosely packed chromatin is called euchromatin
During interphase a few regions of chromatin (centromeres and telomeres) are highly condensed into heterochromatin
Dense packing of the heterochromatin makes it difficult for the cell to express genetic information coded in these regions


Слайд 113Histones can undergo chemical modifications that result in changes in chromatin

organization


Слайд 114Figure 16.UN02
Sugar-phosphate backbone
Nitrogenous bases
Hydrogen bond
G
G
G
G
C
C
C
C
A
A
A
A
T
T
T
T

Слайд 115Figure 16.UN03
DNA pol III synthesizes leading strand continuously
Parental DNA
DNA pol III starts DNA synthesis

at 3′ end of primer, continues in 5′ → 3′ direction

Origin of replication

Helicase

Primase synthesizes a short RNA primer

DNA pol I replaces the RNA primer with DNA nucleotides

3′

3′

3′

5′

5′

5′

5′

Lagging strand synthesized in short Okazaki fragments, later joined by DNA ligase

Слайд 116Figure 16.UN04

Слайд 117Figure 16.UN05

Слайд 118Figure 16.UN06

Слайд 119Figure 16.UN07

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