biology outline chapter 12: 10th edition molecular biology ...€¦ · 19 replication of dna!dna...
TRANSCRIPT
Sylvia S. Mader
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or displayPowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
BIOLOGY10th Edition
Molecular Biology of the Gene
Chapter 12: pp. 211 - 232
1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b.
3.4 nm
2 nm
0.34 nm
GC
A
T
TA
P
P
P
P
CG
G
CComplementary
base pairing
Sugar hydrogen bonds
sugar-phosphatebackbone
2
Outline! Genetic Material
! Transformation
! DNA Structure! Watson and Crick
! DNA Replication! Prokaryotic versus Eukaryotic
! Replication Errors
! Transcription
! Translation
! Structure of Eukaryotic Chromosome
3
Genetic Material
!Frederick Griffith investigated virulence of Streptococcus pneumoniae !Concluded that virulence passed from the dead
strain to the living strain!Transformation
!Further research by Avery et al.!Discovered that DNA is the transforming substance!DNA from dead cells was being incorporated into
genome of living cells
4
Griffith’s Transformation Experiment
!Mice were injected with two strains of pneumococcus: an encapsulated (S) strain and a non-encapsulated (R) strain.!The S strain is virulent (the mice died); it has a
mucous capsule and forms “shiny” colonies.!The R strain is not virulent (the mice lived); it has
no capsule and forms “dull” colonies.
5
Griffith’s Transformation Experiment
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
capsule
Injected live S strain hascapsule and causes mice
to die.
a. b.
Injected live R strain hasno capsule
and mice do not die.
c.
Injected heat-killed S strain
does not causemice to die.
d.
Injected heat-killed S strain plus liveR strain causes
mice to die.Live S strain iswithdrawn from
dead mice.
Animation
6
7
Transformation of Organisms Today
!Result the so-called genetically modified organisms (GMOs) ! Invaluable tool in modern biotechnology today!Commercial products that are currently much used !Green fluorescent protein (GFP) used as a marker
! A jellyfish gene codes for GFP! The jellyfish gene is isolated and then transferred to a bacterium,
or the embryo of a plant, pig, or mouse. ! When this gene is transferred to another organism, the organism
glows in the dark
8
Transformation of Organisms
A normal canola plant (left) and a transgenic canolaplant expressing GFP (right) under a fluorescent light.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
(Bacteria): © Martin Shields/Photo Researchers, Inc.; (Jellyfish): © R. Jackman/OSF/Animals Animals/Earth Scenes; (Pigs): Courtesy Norrie Russell, The Roslin Institute; (Mouse): © Eye of Science/Photo Researchers, Inc.; (Plant): © Dr. Neal Stewart
9
Structure of DNA
!DNA contains:!Two Nucleotides with purine bases
!Adenine (A)!Guanine (G)
!Two Nucleotides with pyrimidine bases!Thymine (T)!Cytosine (C)
11
Chargaff’s Rules
!The amounts of A, T, G, and C in DNA:! Identical in identical twins!Varies between individuals of a species!Varies more from species to species
! In each species, there are equal amounts of:!A & T!G & C
!All this suggests DNA uses complementary base pairing to store genetic info
!Human chromosome estimated to contain, on average, 140 million base pairs
!Number of possible nucleotide sequences, 4,140,000,000
12
Nucleotide Composition of DNACopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
O
N
N
CH
CH
C
C
NH 2
cytosine(C)
3 C C2
C1
OHO P O
O
H
HHHH
OH
CH 3
O
HN
N
C
CH
C
C
OHO P OO
H
HHHH
OHHN
N
N
CCH
O
C
CC
NH2N
C2
C2
C1
C1
OHO P O
O
guanine(G)
phosphate
H
HHHH
OH
N
N
N
HCCH
NH 2
C
CC
N
4
3 C2
C1
5 OO
O
O
O
O
H
HHHH
OH
c. Chargaff’s data
DNA Composition in Various Species (%)
Species
Homo sapiens (human)Drosophila melanogaster (fruit fly)Zea mays (corn)Neurospora crassa (fungus)Escherichia coli (bacterium)Bacillus subtilis (bacterium)
31.027.325.623.024.628.4
31.527.625.323.324.329.0
19.122.524.527.125.521.0
18.422.524.626.625.621.6
A T G C
a. Purine nucleotides b. Pyrimidine nucleotides
nitrogen-containingbase
sugar = deoxyribose
thymine(T)
adenine(A)
HO P O CH 2
5CH 2
5CH 2
5CH 2
C
4 C
4 C
4 C
C
3 C
3 C
15
Watson and Crick Model
!Watson and Crick, 1953
!Constructed a model of DNA
!Double-helix model is similar to a twisted ladder
!Sugar-phosphate backbones make up the sides
!Hydrogen-bonded bases make up the rungs
!Received a Nobel Prize in 1962
16
Watson/Crick Model of DNACopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a: © Kenneth Eward/Photo Researchers, Inc.; d: © A. Barrington Brown/Photo Researchers, Inc.
P
P
P
P
c.
b.
complementarybase
sugar-phosphatebackbone
3.4 nm
2 nm
0.34 nm
P
P
SS
4
5 end 3 end
11
23
2 35
4
5
CG
G
C
C
G
T
T
A
A
C
G
a.
d.d.
5 end
sugar
hydrogen bonds
17
X-Ray Diffraction of DNA
!Rosalind Franklin studied the structure of DNA using X-rays.
!She found that if a concentrated, viscous solution of DNA is made, it can be separated into fibers.
!Under the right conditions, the fibers can produce X-ray diffraction pattern!She produced X-ray diffraction photographs.!This provided evidence that DNA had the following
features:! DNA is a helix.! Some portion of the helix is repeated.
18
X-Ray Diffraction of DNA
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
© Photo Researchers, Inc.; c: © Science Source/Photo Researchers, Inc.
X-ray beam
b.c.
Rosalind Franklin
diffraction pattern
CrystallineDNA
diffractedX-rays
a.
Dark Lady of DNA
16
19
Replication of DNA
!DNA replication is the process of copying a DNA molecule.
!Replication is semiconservative, with each strand of the original double helix (parental molecule) serving as a template (mold or model) for a new strand in a daughter molecule.
Animation
18
23
Replication: Eukaryotic
!DNA replication begins at numerous points along linear chromosome
!DNA unwinds and unzips into two strands
!Each old strand of DNA serves as a template for a new strand
!Complementary base-pairing forms new strand on each old strand!Requires enzyme DNA polymerase
26
Replication: Eukaryotic
!Replication bubbles spread bi-directionally until they meet
!The complementary nucleotides join to form new strands. Each daughter DNA molecule contains an old strand and a new strand.
!Replication is semiconservative:!One original strand is conserved in each daughter
molecule i.e. each daughter double helix has one parental strand and one new strand.
Animation
21 28
Semiconservative Replication of DNACopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
region of parentalDNA double helix
GG
GT
AAC
C
3'5'
AT
C G
A TA
GGC
C G
A
region ofreplication:new nucleotidesare pairingwith those ofparental strands
region ofcompletedreplication
daughter DNA double helix
oldstrand
newstrand
daughter DNA double helix
oldstrand
newstrand
C CA
AT
T
GG
TA
TA
CG
AT
AT
A
C GATA
TA
TA
CG
CG
A
G
T
A
C
G
C
G
A
Animation
23 31
Science Focus: Aspects of DNA Replication
GC
AT
T
GC
G C
AP
P
P
P
P
P
P
P
P
P
P
P is attached hereOH
CH2
C
C C
CH H
H
H H
OH
OHO
base is attached here
5! end
3! end 5! endtemplate strand
Direction of replicationnew strand
Deoxyribose molecule
RNA primer
3!
3!
5!
3!
5!
5!parental DN A helix
helicase at replication fork
leading new strand
template strand
template strand
lagging strand
DNA polymerase
DNA polymeraseDNA ligase
Okazaki fragment
Replication fork introduces complications
5
7
6
4
3
2
1
DNA polymeraseattaches a newnucleotide to the 3carbon of theprevious nucleotide.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
5!
4!
3! 2!
1!
3! end
3!
32
Replication: Prokaryotic
!Prokaryotic Replication
!Bacteria have a single circular loop
!Replication moves around the circular DNA molecule in both directions
!Produces two identical circles
!Cell divides between circles, as fast as every 20 minutes
33
Replication: Prokaryotic vs. EukaryoticCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
origin
replication isoccurring in
two directions
replication iscomplete
replication fork replication bubblea. Replication in prokaryotes
parental strand
daughter strand
new DNAduplexes
b. Replication in eukaryotes
34
Replication Errors
!Genetic variations are the raw material for evolutionary change
!Mutation:!A permanent (but unplanned) change in base-pair
sequence!Some due to errors in DNA replication
!Others are due to to DNA damage
!DNA repair enzymes are usually available to reverse most errors
Animation
28
35
Function of Genes
!Genes Specify Enzymes!Beadle and Tatum:
!Experiments on fungus Neurospora crassa!Proposed that each gene specifies the synthesis of one enzyme
!One-gene-one-enzyme hypothesis!Genes Specify a Polypeptide
!A gene is a segment of DNA that specifies the sequence of amino acids in a polypeptide
!Suggests that genetic mutations cause changes in the primary structure of a protein
36
Protein Synthesis: From DNA to RNA to Protein!The mechanism of gene expression
!DNA in genes specify information, but information is not structure and function
!Genetic info is expressed into structure & function through protein synthesis
!The expression of genetic info into structure & function:!DNA in gene controls the sequence of nucleotides
in an RNA molecule!RNA controls the primary structure of a protein
38
The Central Dogma of Molecular Biology
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
nontemplate strand
3'5'
A G G G A C C C C
T C G C T G G G G
5'3'
template strandtranscriptionin nucleus
3'5'
mRN
DNA
A G G G A C C C C
codon 1 codon 2 codon 3
polypeptide
translationat ribosome
N N NC C C C C C
R1 R2 R3
Serine Aspartate Proline
O O O
39
Types of RNA
!RNA is a polymer of RNA nucleotides!RNA Nucleotides are of four types: Uracil,
Adenine, Cytosine, and Guanine!Uracil (U) replaces thymine (T) of DNA!Types of RNA
!Messenger (mRNA) - Takes genetic message from DNA in nucleus to ribosomes in cytoplasm
!Ribosomal (rRNA) - Makes up ribosomes which read the message in mRNA
!Transfer (tRNA) - Transfers appropriate amino acid to ribosome when “instructed”
40
Structure of RNA
G
U
A
C
S
S
S
S
P
P
P
P
ribose
G
U base isuracil insteadof thymine
A
C
one nucleotide
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
41
RNA vs. DNA structure
42
The Genetic Code
!Properties of the genetic code:!Universal
! With few exceptions, all organisms use the code the same way! Encode the same 20 amino acids with the same 64 triplets
!Degenerate (redundant)! There are 64 codons available for 20 amino acids! Most amino acids encoded by two or more codons
!Unambiguous (codons are exclusive)! None of the codons code for two or more amino acids! Each codon specifies only one of the 20 amino acids
!Contains start and stop signals! Punctuation codons! Like the capital letter we use to signify the beginning of a sentence,
and the period to signify the end
43
The Genetic Code
!The unit of a code consists of codons, each of which is a unique arrangement of symbols
!Each of the 20 amino acids found in proteins is uniquely specified by one or more codons ! The symbols used by the genetic code are the mRNA bases
! Function as “letters” of the genetic alphabet! Genetic alphabet has only four “letters” (U, A, C, G)
! Codons in the genetic code are all three bases (symbols) long! Function as “words” of genetic information! Permutations:
! There are 64 possible arrangements of four symbols taken three at a time
! Often referred to as triplets! Genetic language only has 64 “words”
44
Messenger RNA CodonsCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Second Base ThirdBase
FirstBase
U C GA
U
C
A
G
UUUphenylalanine
UCUserine
UAUtyrosine
UGUcysteine
UUCphenylalanine
UCCserine
UACtyrosine
UGUcysteine
UCAserine
UUAleucine
UCGserine
UUGleucine
UGGtryptophan
UGAstop
UAAstop
UAGstop
U
C
A
G
CUUleucine
CUCleucine
CUAleucine
CUGleucine
CCUproline
CCCproline
CCAproline
CCGproline
CAChistidine
CAAglutamine
CAGglutamine
CAUhistidine
CGAarginine
CGGarginine
CGUarginine
CGCarginine
U
C
A
G
AUG (start)methionine
AUUisoleucine
AUCisoleucine
AUAisoleucine
ACUthreonine
ACCthreonine
ACAthreonine
ACGthreonine
AAUasparagine
AACasparagine
AAAlysine
AAGlysine
AGUserine
AGCserine
AGAarginine
AGGarginine
U
C
A
G
GUUvaline
GUCvaline
GUAvaline
GUGvaline
GCUalanine
GCCalanine
GCAalanine
GCGalanine
GAUaspartate
GACaspartate
GAAglutamate
GAGglutamate
GGUglycine
GGCglycine
GGAglycine
GGGglycine
U
C
A
G
45
Steps in Gene Expression: Transcription
!Transcription!Gene unzips and exposes unpaired bases!Serves as template for mRNA formation!Loose RNA nucleotides bind to exposed DNA
bases using the C=G & A=U rule!When entire gene is transcribed into mRNA, result
is a pre-mRNA transcript of the gene!The base sequence in the pre-mRNA is
complementary to the base sequence in DNA
47
Transcription of mRNA! A single chromosomes consists of one very long molecule encoding
hundreds or thousands of genes! The genetic information in a gene describes the amino acid sequence of
a protein! The information is in the base sequence of one side (the “sense” strand) of the
DNA molecule! The gene is the functional equivalent of a “sentence”
! The segment of DNA corresponding to a gene is unzipped to expose the bases of the sense strand! The genetic information in the gene is transcribed (rewritten) into an mRNA
molecule! The exposed bases in the DNA determine the sequence in which the RNA bases
will be connected together! RNA polymerase connects the loose RNA nucleotides together
! The completed transcript contains the information from the gene, but in a mirror image, or complementary form
49
TranscriptionCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
nontemplatestrand
templatestrand
5'
C
C G
T A
A T
G
C
A
A
C
G
T
C
T
C
U
G
G
A
C
C
A
C
A
T
G
G
C
RNApolymerase
DNAtemplatestrand
mRNAtranscript
C
G
C
A T
C G
T A
to RNA processing
3'
3'
5'
Animation
41 52
RNA Polymerase
© Oscar L. Miller/Photo Researchers, Inc.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. 200m
b.
spliceosome
DNA
RNApolymerase
RNAtranscripts
53
Processing Messenger RNA
!Pre-mRNA, is modified before leaving the eukaryotic nucleus. !Modifications to ends of primary transcript:
!Cap of modified guanine on 5! end! The cap is a modified guanine (G) nucleotide! Helps a ribosome where to attach when translation begins
!Poly-A tail of 150+ adenines on 3! end!Facilitates the transport of mRNA out of the nucleus!Inhibits degradation of mRNA by hydrolytic enzymes.
54
Processing Messenger RNA!Pre-mRNA, is composed of exons and introns.
!The exons will be expressed, !The introns, occur in between the exons.
! Allows a cell to pick and choose which exons will go into a particular mRNA
!RNA splicing:! Primary transcript consists of:
! Some segments that will not be expressed (introns)! Segments that will be expressed (exons)
! Performed by spliceosome complexes in nucleoplasm! Introns are excised! Remaining exons are spliced back together
!Result is mature mRNA transcript
55
RNA Splicing
!In prokaryotes, introns are removed by “self-splicing”—that is, the intron itself has the capability of enzymatically splicing itself out of a pre-mRNA
57
Messenger RNA ProcessingCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
exon
intron intron
exon exonDNA
transcription
exon
intron intron
exon exon
5' 3'pre-mRNA
exon exon exon
intron introncap poly-A tail5' 3'
exon exon exon
spliceosome
cap poly-A tail
pre-mRNAsplicing
intron RNA
5' 3'
cap poly-A tail
mRNA
nuclear porein nuclear envelope
nucleus
cytoplasm
5' 3'
59
Functions of Introns
!As organismal complexity increases;!Number of protein-coding genes does not keep pace!But the proportion of the genome that is introns increases!Humans:
! Genome has only about 25,000 coding genes! Up to 95% of this DNA genes is introns
!Possible functions of introns:!More bang for buck
! Exons might combine in various combinations! Would allow different mRNAs to result from one segment of DNA
! Introns might regulate gene expression!Exciting new picture of the genome is emerging
Animation
48
60
Steps in Gene Expression: Translation
! tRNA molecules have two binding sites! One associates with the mRNA transcript! The other associates with a specific amino acid! Each of the 20 amino acids in proteins associates with one or more of
64 species of tRNA
! Translation! An mRNA transcript migrates to rough endoplasmic reticulum! Associates with the rRNA of a ribosome! The ribosome “reads” the information in the transcript! Ribosome directs various species of tRNA to bring in their specific
amino acid “fares”! tRNA specified is determined by the code being translated in the
mRNA transcript
61
tRNA
!tRNA molecules come in 64 different kinds!All very similar except that
!One end bears a specific triplet (of the 64 possible) called the anticodon
!Other end binds with a specific amino acid type! tRNA synthetases attach correct amino acid to the
correct tRNA molecule!All tRNA molecules with a specific anticodon will
always bind with the same amino acid
63
Structure of tRNACopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
aminoacid
leucine
3
5
Hydrogenbonding
anticodon
mRNA
5'
codon
3'
b.
anticodon end
amino acid end
64
Ribosomes
!Ribosomal RNA (rRNA):!Produced from a DNA template in the nucleolus!Combined with proteins into large and small ribosomal
subunits
!A completed ribosome has three binding sites to facilitate pairing between tRNA and mRNA!The E (for exit) site!The P (for peptide) site, and!The A (for amino acid) site
65
Ribosomal Structure and Function
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Courtesy Alexander Rich
large subunit
small subunit
a. Structure of a ribosome
tRNA bindingsites
outgoingtRNA
35
mRNA
b. Binding sites of ribosome
polypeptideincomingtRNA
incomingtRNA
c. Function of ribosomes d. Polyribosome
66
Steps in Translation: Initiation
!Components necessary for initiation are:!Small ribosomal subunit!mRNA transcript! Initiator tRNA, and!Large ribosomal subunit! Initiation factors (special proteins that bring the above
together)! Initiator tRNA:
!Always has the UAC anticodon!Always carries the amino acid methionine!Capable of binding to the P site
67
Steps in Translation: Initiation
!Small ribosomal subunit attaches to mRNA transcript
!Beginning of transcript always has the START codon (AUG)
!Initiator tRNA (UAC) attaches to P site
!Large ribosomal subunit joins the small subunit
69
Steps in Translation: Initiation
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A small ribosomal subunitbinds to mRNA; an initiatortRNA pairs with the mRNAstart codon AUG. The large ribosomal subunit
completes the ribosome.Initiator tRNA occupies theP site. The A site is readyfor the next tRNA.
Initiation
Met
amino acid methionine
initiator tRNA
U A CA U G
mRNA
small ribosomal subunit
3'
5'
P site A siteE site
Met
large ribosomal subunitU A CA U G
start codon5' 3'
70
Steps in Translation: Elongation
!“Elongation” refers to the growth in length of the polypeptide
!RNA molecules bring their amino acid fares to the ribosome!Ribosome reads a codon in the mRNA
!Allows only one type of tRNA to bring its amino acid!Must have the anticodon complementary to the mRNA codon being read
!Joins the ribosome at it’s A site!Methionine of initiator is connected to amino acid
of 2nd tRNA by peptide bond
71
Steps in Translation: Elongation
!Second tRNA moves to P site (translocation)
!Spent initiator moves to E site and exits
!Ribosome reads the next codon in the mRNA!Allows only one type of tRNA to bring its amino acid
! Must have the anticodon complementary to the mRNA codon being read
! Joins the ribosome at it’s A site
!Dipeptide on 2nd amino acid is connected to amino acid of 3nd tRNA by peptide bond
73
Steps in Translation: ElongationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
A tRNA–amino acidapproaches theribosome and bindsat the A site.
Two tRNAs can be at aribosome at one time;the anticodons arepaired to the codons.
Peptide bond formationattaches the peptidechain to the newlyarrived amino acid.
The ribosome moves forward; the“empty” tRNA exits from the E site;the next amino acid–tRNA complexis approaching the ribosome.
1 2 3 4
Elongation
peptidebond
Met
Ala
Trp
Ser
Val
UA
C AUG G A C
33
C G
anticodon
tRNA
asp
U
Met
AlaTrp
Ser
Val
UA
C AUG G A C
C U G
Asp
6
UA
C AUG G A C
C U G
Met
Val
Asp
Ala
Trp
Ser
peptidebond
6 3
UC A
G A CC U G
AUG
U G G
A C C
Met
Val
Asp
Ala
Trp
Ser Thr
6 3
74
Steps in Translation: Termination
!Previous tRNA moves to P site!Spent tRNA moves to E site and exits!Ribosome reads the STOP codon at the end of the
mRNA!UAA, UAG, or UGA!Does not code for an amino acid
!Polypeptide is released from last tRNA by release factor
!Ribosome releases mRNA and dissociates into subunits
!mRNA read by another ribosome
76
Steps in Translation: TerminationCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Termination
The release factor hydrolyzes the bondbetween the last tRNA at the P site andthe polypeptide, releasing them. Theribosomal subunits dissociate.
3
5
AG AU G A
The ribosome comes to a stopcodon on the mRNA. A releasefactor binds to the site.
UA
UA U G A
stop codon5' 3'
Asp
Ala
TrpVal
Glu
release factor
Ala
Trp
Val
Asp
Glu
UC U
Animation
62
78
Summary of Gene Expression (Eukaryotes)
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
TRANSCRIPTION1. DNA in nucleus serves as a template for mRNA.
2. mRNA is processed before leaving the nucleus.
mRNA
pre-mRNA
DNA
introns
3. mRNA moves into cytoplasm and becomes associated with ribosomes.
TRANSLATION
mRNAlarge and smallribosomal subunits
5
3'
nuclear pore4. tRNAs with anticodons carry amino acids to mRNA.
5
peptide
codon
ribosome
3UA
AU
CG
5 C CGG
GCG
CG
C
CCC
GUA
UA
UA
UUA A
6. During elongation, polypeptide synthesis takes place one amino acid at a time.
7. Ribosome attaches to rough ER. Polypeptide enters lumen, where it folds and is modified.
8. During termination, a ribosome reaches a stop codon; mRNA and ribosomal subunits disband.
5. During initiation, anticodon-codon complementary base pairing begins as the ribosomal subunits come together at a start codon.
aminoacids
anticodon
tRNA
CU A
3'
Animation
64
80
Structure of Eukaryotic Chromosome
!Contains a single linear DNA molecule, but is composed of more than 50% protein.
!Some of these proteins are concerned with DNA and RNA synthesis,
!Histones, play primarily a structural role! Five primary types of histone molecules! Responsible for packaging the DNA
!DNA double helix is wound at intervals around a core of eight histone molecules (called nucleosome)
!Nucleosomes are joined by “linker” DNA.
81
Structure of Eukaryotic ChromosomeCopyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
a. Nucleosomes (“beads on a string”)
b. 30-nm fiber
c. Radial loop domains
d. Heterochromatin
e. Metaphase chromosome
1. Wrapping of DNA around histone proteins.
4. Tight compaction of radial loops to form heterochromatin.
3. Loose coiling into radial loops.
2. Formation of a three-dimensional zigzag structure via histone H1 and other DNA-binding proteins.
5. Metaphase chromosome forms with the help of a protein scaffold.
2 nm
1 nm
300 nm
1,400 nm
700 nm
30 nm
DNAdouble helix
histones
histone H1
nucleosome
euchromatin
83
Review! Genetic Material
! Transformation
! DNA Structure! Watson and Crick
! DNA Replication! Prokaryotic versus Eukaryotic
! Replication Errors
! Transcription
! Translation
! Structure of Eukaryotic Chromosome
Sylvia S. Mader
Copyright © The McGraw Hill Companies Inc. Permission required for reproduction or displayPowerPoint® Lecture Slides are prepared by Dr. Isaac Barjis, Biology Instructor
BIOLOGY10th Edition
Molecular Biology of the Gene
Chapter 12: pp. 211 - 232
1
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
b.
3.4 nm
2 nm
0.34 nm
GC
A
T
TA
P
P
P
P
CG
G
CComplementary
base pairing
Sugar hydrogen bonds
sugar-phosphatebackbone