Chapter 15mmsalemscienceteacher.weebly.com/uploads/2/3/3/6/... · 2018. 9. 9. · Exon 1 Intron Exon 2 Branch point A snRNA Exon 1 Exon 2 Lariat 5′ 5′ 3′ 3′ 5′ 5′ 3′

Chapter 15

Genes and How They Work

1

The Nature of Genes

• Early ideas to explain how genes work came

from studying human diseases

• Archibald Garrod – 1902

– Recognized that alkaptonuria is inherited via a

recessive allele

– Proposed that patients with the disease lacked a

particular enzyme

• These ideas connected genes to enzymes

2

3

Beadle and Tatum – 1941

• Deliberately set out to create mutations in

chromosomes and verify that they

behaved in a Mendelian fashion in crosses

• Studied Neurospora crassa

– Used X-rays to damage DNA

– Looked for nutritional mutations• Had to have minimal media supplemented to grow

4

• Beadle and Tatum looked for fungal cells lacking

specific enzymes

– The enzymes were required for the biochemical

pathway producing the amino acid arginine

– They identified mutants deficient in each enzyme of

the pathway

• One-gene/one-enzyme hypothesis has been

modified to one-gene/one-polypeptide

hypothesis

5

Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

Experimental Procedure

Growth on

minimal

medium

plus arginine

Wild-type

Neurospora

crassa

Mutagenize

with X-rays

Grow on

rich medium arg mutants

No growth

on minimal

medium

Results

Mutation

in Enzyme

Plus

Ornithine

Plus

Citruline

Plus

Arginosuccinate

Plus

Arginine

E

F

G

HE F G H

Glutamate Ornithine Citruline Arginosuccinate Arginine

Enzymes

encoded

by arg

genes

arg

genesarg E arg F arg G arg H

Conclusion

Central Dogma

• First described by Francis Crick

• Information only flows from

DNA → RNA → protein

• Transcription = DNA → RNA

• Translation = RNA → protein

• Retroviruses violate this order using reverse

transcriptase to convert their RNA genome into

DNA

6

7


3′3′

5′

5′

Transcription

Protein

Eukaryotes

Prokaryotes

Translation

DNA

template

strand

mRNA

8

• Transcription

– DNA-directed synthesis of RNA

– Only template strand of DNA used

– U (uracil) in DNA replaced by T (thymine) in RNA

– mRNA used to direct synthesis of polypeptides

• Translation

– Synthesis of polypeptides

– Takes place at ribosome

– Requires several kinds of RNA

RNA

• All synthesized from DNA template by

transcription

• Messenger RNA (mRNA)

• Ribosomal RNA (rRNA)

• Transfer RNA (tRNA)

• Small nuclear RNA (snRNA)

• Signal recognition particle RNA (SRP RNA)

• Micro-RNA (miRNA)9

Genetic Code

• Francis Crick and Sydney Brenner

determined how the order of nucleotides in

DNA encoded amino acid order

• Codon – block of 3 DNA nucleotides

corresponding to an amino acid

• Introduced single nulcleotide insertions or

deletions and looked for mutations

– Frameshift mutations

• Indicates importance of reading frame10

11

One Bases Deleted

Met Pro Thr His Arg Asp Ala Ser

Met Pro HisAla

Met Pro Thr His Arg Asp Ala Ser

Met Pro His Arg Asp Ala Ser

Ser Thr Thr

Delete one bases

AUGCCUACGCACCGCGACGCAUCA

AUGCCUAGCACCGCGACGCAUCA

AUGCCUACGCACCGCGACGCAUCA

AUGCCUCACCGCGACGCAUCA

Amino acids do not

change after third deletion

All amino acids changed

after deletion

Amino acids

Amino acids

Delete three bases

Three Bases Deleted


Spaced or unspaced codons

• Spaced

– Codon sequence in a gene punctuated

• Unspaced

– codons adjacent to each other

12

13

SCIENTIFIC THINKING

Delete one letter

Only one word changed

WHY DID THE RED BAT EAT THE FAT RAT

WHY DID HE RED BAT EAT THE FAT RAT

Delete one letter

All words after deletion changed

WHYDIDTHEREDBATEATTHEFATRAT

WHYDIDHEREDBATEATTHEFATRAT

Sentence with Spaces

Sentence with No Spaces


14

• Marshall Nirenberg identified the codons that

specify each amino acid

• Stop codons

– 3 codons (UUA, UGA, UAG) used to terminate

translation

• Start codon

– Codon (AUG) used to signify the start of translation

• Code is degenerate, meaning that some amino

acids are specified by more than one codon

15

Code practically universal

• Strongest evidence

that all living things

share common

ancestry

• Advances in genetic

engineering

• Mitochondria and

chloroplasts have

some differences in

“stop” signals

16

17

Prokaryotic transcription

• Single RNA polymerase

• Initiation of mRNA synthesis does not

require a primer

• Requires

– Promoter

– Start site Transcription unit

– Termination site

18

• Promoter

– Forms a recognition and binding site for the

RNA polymerase

– Found upstream of the start site

– Not transcribed

– Asymmetrical – indicate site of initiation and

direction of transcription

19


Holoenzyme

׳

a.

Prokaryotic RNA polymerase

Core

enzyme

20


Upstream

Downstream

5′

b.

Coding

strand

Template

strand

Start site (+1)

TATAAT– Promoter (–10 sequence)

TTGACA–Promoter

(–35 sequence)

Holoenzyme

׳

a.


Core

enzyme

3′

5′

3′

TATAAT

TTGACA

21


Upstream

Downstream

5′

binds to DNA

b.

Helix opens at

–10 sequence

Coding

strand

Template

strand

Start site (+1)


TTGACA–Promoter

(–35 sequence)

Holoenzyme

׳

a.


Core

enzyme

3′

5′

3′

5′ 3′

5′

3′

TATAAT

TTGACA

22


binds to DNA

dissociates

Start site RNA

synthesis begins

Transcription

bubble

RNA polymerase bound

to unwound DNA

Helix opens at

–10 sequence

ATP

5′ 3′

5′

3′


Upstream

Downstream

5′

b.

Coding

strand

Template

strand

Start site (+1)


TTGACA–Promoter

(–35 sequence)

Holoenzyme

׳

a.


Core

enzyme

3′

5′

3′

TATAAT

TTGACA

• Elongation

– Grows in the 5′-to-3′ direction as

ribonucleotides are added

– Transcription bubble – contains RNA

polymerase, DNA template, and growing RNA

transcript

– After the transcription bubble passes, the

now-transcribed DNA is rewound as it leaves

the bubble

23

24


RNA

polymerase

Start site

3'

5′

Codingstrand Unwinding

Template strand

Transcription bubble

Upstream

mRNA

Rewinding

5′

3'

3'

5′

DNA

Downstream

25

• Termination

– Marked by sequence that signals “stop” to

polymerase

• Causes the formation of phosphodiester bonds to

cease

• RNA–DNA hybrid within the transcription bubble

dissociates

• RNA polymerase releases the DNA

• DNA rewinds

– Hairpin


DNA and RNA

Polymerase dissociates

mRNA

dissociates

from DNA

Cytosine

Guanine

Adenine

Uracil

mRNA hairpin

causes RNA

polymerase to pause

RNA polymerase

DNA

3'

5′

3'

5′

Four or more U

ribonucleotides

5′26

• Prokaryotic transcription is coupled to

translation

– mRNA begins to be translated before

transcription is finished

– Operon

• Grouping of functionally related genes

• Multiple enzymes for a pathway

• Can be regulated together

27

28


0.25 µm

RNA polymerase DNA

mRNA

Ribosomes

Polyribosome

Polypeptide

chains

© Dr. Oscar Miller

29

Eukaryotic Transcription

• 3 different RNA polymerases

– RNA polymerase I transcribes rRNA

– RNA polymerase II transcribes mRNA and

some snRNA

– RNA polymerase III transcribes tRNA and

some other small RNAs

• Each RNA polymerase recognizes its own

promoter

30

• Initiation of transcription

– Requires a series of transcription factors

• Necessary to get the RNA polymerase II enzyme

to a promoter and to initiate gene expression

• Interact with RNA polymerase to form initiation

complex at promoter

• Termination

– Termination sites not as well defined

31


TATA box

Transcription

factor

Eukaryotic

DNA

Other transcription factors

1. A transcription factor recognizes and binds to the TATA box sequence, which is part of

the core promoter.

32


Other transcription factors RNA polymerase II

TATA box

Transcription

factor

Eukaryotic

DN A

1. A transcription factor recognizes and

binds to the TATA box sequence, which

is part of the core promoter.

2. Other transcription factors are

recruited, and the initiation complex

begins to build.

33


Other transcription factors RNA polymerase II

TATA box

Transcription

factor

Eukaryotic

DNA

Initiation

complex

1. A transcription factor recognizes and

binds to the TATA box sequence, which

is part of the core promoter.

2. Other transcription factors are

recruited, and the initiation complex

begins to build.

3. Ultimately, RNA polymerase II associates with the

transcription factors and the DNA, forming the

initiation complex, and transcription begins.

34

• In eukaryotes, the primary transcript must

be modified to become mature mRNA

– Addition of a 5′ cap

• Protects from degradation; involved in translation

initiation

– Addition of a 3′ poly-A tail

• Created by poly-A polymerase; protection from

degradation

– Removal of non-coding sequences (introns)

• Pre-mRNA splicing done by spliceosome

mRNA modifications

35


Methyl group

5′ cap

CH2

HO OH

PP

P mRNA

PP

P

+N+

CH35′

3′

CH3

Eukaryotic pre-mRNA splicing

• Introns – non-coding sequences

• Exons – sequences that will be translated

• Small ribonucleoprotein particles

(snRNPs) recognize the intron–exon

boundaries

• snRNPs cluster with other proteins to form

spliceosome

– Responsible for removing introns

36

37


E1 I1 E2 I2 E3 I3 E4 I4

Transcription

Introns are removed

a.

Exons

Introns

Mature mRNA

׳33 poly-A tail5׳ cap

׳5 cap ׳3 poly-A tail

Primary RNA transcript

DNA template

38


b: Courtesy of Dr. Bert O’Malley, Baylor College of Medicine

E1 I1 E2 I2 E3 I3 E4 I4

Intron

Exon

DNA

1

2 34

5 6

7

a.

b. c.

Exons

Introns

mRNA

Mature mRNA

3' poly-A tail5' cap

5' cap 3' poly-A tail


DNA template

Introns are removed

Transcription

39

snRNPs

Exon 2Exon 1 Intron

Branch point A

snRNA

5′ 3′

1. snRNA forms base-pairs with 5′end of intron, and at branch site.

A


40


snRNPs

Exon 2Exon 1 Intron

Branch point A

snRNA

5′

5′

3′

3′

2. snRNPs associate with other factors to form spliceosome.


Spliceosome

A

A

41


snRNPs

Exon 2Exon 1 Intron

Branch point A

snRNA

Lariat

5′

5′

3′

3′

5′ 3′



3. 5′end of intron is removed and forms bond at branch site,

forming a lariat. The 3′end of the intron is then cut.

Spliceosome

A

A

A

42


snRNPs

Exon 2Exon 1 Intron

Branch point A

snRNA

Exon 1 Exon 2

Lariat

5′

5′

3′

3′

5′

5′

3′

3′


4. Exons are joined; spliceosome disassembles.


3. 5′end of intron is removed and forms bond at branch site,

forming a lariat. The 3′end of the intron is then cut.

Mature mRNA

Excised

intron

Spliceosome

A

A

A

Alternative splicing

• Single primary transcript can be spliced into

different mRNAs by the inclusion of different sets

of exons

• 15% of known human genetic disorders are due

to altered splicing

• 35 to 59% of human genes exhibit some form of

alternative splicing

• Explains how 25,000 genes of the human

genome can encode the more than 80,000

different mRNAs43

tRNA and Ribosomes

• tRNA molecules carry amino acids to the

ribosome for incorporation into a

polypeptide

– Aminoacyl-tRNA synthetases add amino

acids to the acceptor stem of tRNA

– Anticodon loop contains 3 nucleotides

complementary to mRNA codons

44

4545


c: Created by John Beaver using ProteinWorkshop, a product of the RCSB PDB, and built using the Molecular Biology Toolkit developed by

John Moreland and Apostol Gramada (mbt.sdsc.edu). The MBT is financed by grant GM63208

2D “Cloverleaf” Model

Acceptor end

Anticodon

loop

׳3׳5

3D Ribbon-like Model Acceptor end

Anticodon loop

3D Space-filled Model

Anticodon loop

Acceptor end

Icon

Anticodon end

Acceptor end

tRNA charging reaction

• Each aminoacyl-tRNA synthetase

recognizes only 1 amino acid but several

tRNAs

• Charged tRNA – has an amino acid added

using the energy from ATP

– Can undergo peptide bond formation without

additional energy

• Ribosomes do not verify amino acid

attached to tRNA46

47

tRNA

PiPi

NH3+

O–

C O

OH

Amino

group

Carboxyl

group

Trp

ATP

Amino

acid site

Accepting

site

Anticodon

specific to tryptophan

Aminoacyl-tRNA

synthetase

tRNA

site

1. In the first step of the reaction, the amino acid is activated.

The amino acid reacts with ATP to produce an intermediate

with the carboxyl end of the amino acid attached to AMP.

The two terminal phosphates (pyrophosphates) are cleaved

from ATP in this reaction.


48


PiPi

Amino

group

Carboxyl

group

Trp

ATP

Amino

acid site

Aminoacyl-tRNA

synthetase

tRNA

site

NH3+ C

O–

O

49


tRNA

PiPi

NH3+

O–

C O

OH

Amino

group

Carboxyl

group

Trp

ATP

Amino

acid site

Accepting

site

Anticodon


Aminoacyl-tRNA

synthetase

tRNA

site

50


tRNA

PiPi

NH3+

O–

C OC O

OH

O

Charged tRNA travels to ribosomeAmino

group

Carboxyl

group

TrpNH3

+

ATP

Amino

acid site

Accepting

site

Anticodon


Aminoacyl-tRNA

synthetase

tRNA

site

Charged

tRNA

dissociates

Trp

1. In the first step of the reaction, the amino acid is activated.

The amino acid reacts with ATP to produce an intermediate

with the carboxyl end of the amino acid attached to AMP.

The two terminal phosphates (pyrophosphates) are cleaved

from ATP in this reaction.

2. The amino acid-AMP

complex remains bound

to the enzyme. The tRNA

next binds to the enzyme.

3. The second step of there action transfers

the amino acid from AMP to the tRNA,

Producing a charged tRNA and AMP. The

charged tRNA consists of a specific amino acid

attached to the 3′ accept or stem of it sRNA.

51

• The ribosome has multiple tRNA binding

sites

– P site – binds the tRNA attached to the

growing peptide chain

– A site – binds the tRNA carrying the

next amino acid

– E site – binds the tRNA that carried the

last amino acid

52


mRNA

90°

0°

3′

5′

Large

subunit

Small

subunit

Large

subunit

Small

subunit

Large

subunit

Small

subunit

53

• The ribosome has two primary functions

– Decode the mRNA

– Form peptide bonds

• Peptidyl transferase

– Enzymatic component of the ribosome

– Forms peptide bonds between amino acids

54

Translation

• In prokaryotes, initiation complex includes

– Initiator tRNA charged with N-formylmethionine

– Small ribosomal subunit

– mRNA strand

• Ribosome binding sequence (RBS) of mRNA positions small subunit correctly

• Large subunit now added

• Initiator tRNA bound to P site with A site empty

55


3′

5′

AUG

U CA

GTP GDP

+

Pi

Small

subunit

Initiation

factor

Initiation

factor

fMet 3′

5′

mRNA


U CA

A GU

GTP GDP

+

E site

Initiation complex Complete ribosome

Pi

tRNA in

P site

A site

Large

subunit

5′ 5´

3′

3′

• Initiations in eukaryotes similar except

– Initiating amino acid is methionine

– More complicated initiation complex

– Lack of an RBS – small subunit binds to 5′

cap of mRNA

56

57

• Elongation adds amino acids

– 2nd charged tRNA can bind to empty A site

– Requires elongation factor called EF-Tu to bind to tRNA and GTP

– Peptide bond can then form

– Addition of successive amino acids occurs as a cycle

58


NH3+

3′

5′

OHO

O

N

O

NH3+

Amino

acid 1

Amino

acid 2

Peptide

bond

formation

Polypeptide

chain

“Empty”

tRNA

Amino

group

Amino

acid 1

Peptide

bond

Amino

acid 2

Amino end

(N terminus)

Amino

acid 1

Amino

acid 2

Amino

acid 3

Amino

acid 4

Amino

acid 5

Amino

acid 6

Amino

acid 7

Carboxyl end

(C terminus)

COO–

P site

A site

NH3+

NH3+

59


3′

3′

3′3′

3′

5′

5′

5′

5′

“Ejected” tRNA

E P A

E P A

E P AE P A

E P A

Sectioned ribosome

Pi

GTP

GTP

GDP +

Next round

Elongation

factor

Elongation

factor

+ Pi

Elongation

factor

Elongation

factorGrowing

polypeptide GDP

GTP

5′

60

• There are fewer tRNAs than codons

• Wobble pairing allows less stringent

pairing between the 3′ base of the codon

and the 5′ base of the anticodon

• This allows fewer tRNAs to accommodate

all codons

61

• Termination

– Elongation continues until the ribosome

encounters a stop codon

– Stop codons are recognized by release

factors which release the polypeptide from the

ribosome

62


3′

5′

3′

5′

EP

A

Dissociation

Sectioned

ribosome

Release

factor

Polypeptide

chain releases

63

Protein targeting

• In eukaryotes, translation may occur in the

cytoplasm or the rough endoplasmic reticulum

(RER)

• Signal sequences at the beginning of the

polypeptide sequence bind to the signal

recognition particle (SRP)

• The signal sequence and SRP are recognized

by RER receptor proteins

• Docking holds ribosome to RER

• Beginning of the protein-trafficking pathway

64


Signal recognition

particle (SRP)

Signal

Ribosome

synthesizing

peptide

Exit tunnel

Docking

Polypeptide

elongation

continues

Rough endoplasmic

reticulum (RER)Cytoplasm Lumen of the RER

SRP binds to signal

peptide, arresting

elongation

Protein channel

NH2

65


1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.


RNA polymerase IIRNA polymerase II

Primary RNA transcript5´

3´

5´

3´

66



Poly-A tail

Mature mRNACut intron

5´ cap

1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.

2. The primary transcript

is processed by

addition of a 5′

methyl-G cap,

cleavage and

polyadenylation of the

3′end, and removal of

introns. The mature

mRNA is then

exported through

nuclear pores to the

cytoplasm.


RNA polymerase II


Poly-A tail


5´ cap

RNA polymerase II


3´

5´

3´

67



Poly-A tail


5´ cap

1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.


is processed by

addition of a 5´methyl-G cap,

cleavage and


3´ end, and removal of

introns. The mature

mRNA is then

exported through


cytoplasm.

3. The 5′cap of the

mRNA

associates with

the small subunit

of the ribosome.

The initiator

tRNA and large

subunit are

added to form

an initiation

complex.


RNA polymerase II


Poly-A tail


5´ cap

Large

subunit

mRNA 5´ cap

Small

subunit Cytoplasm

RNA polymerase II


3´

5´

3´

68


1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.


is processed by

addition of a 5′

methyl-G cap,

cleavage and



introns. The mature

mRNA is then

exported through


cytoplasm.


mRNA

associates with

the small subunit

of the ribosome.

The initiator

tRNA and large

subunit are

added to form

an initiation

complex.

4. The ribosome cycle begins with the

growing peptide attached to the tRNA

in the P site. The next charged tRNA

binds to the A site with its anticodon

complementary to the codon in the

mRNA in this site.

mRNA

Small

subunitCytoplasm

tRNA arrivesin A site Amino acids

mRNA

A siteP site

E site

Cytoplasm

3´

5′

3′


Cut intron

Large

subunit

5′cap

RNA polymerase II


Poly-A tail


5′cap


5´

69


1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.


is processed by

addition of a 5′

methyl-G cap,

cleavage and



introns. The mature

mRNA is then

exported through


cytoplasm.


mRNA

associates with

the small subunit

of the ribosome.

The initiator

tRNA and large

subunit are

added to form

an initiation

complex.






mRNA in this site.

5. Peptide bonds form between the

amino terminus of the next amino

acid and the carboxyl terminus of

the growing peptide. This transfers

the growing peptide to the tRNA in

the A site, leaving the tRNA in the

P site empty.

mRNA

Small

subunitCytoplasm


mRNA

A siteP site

E site

Lengthening

polypeptide chain

Emptyt

RNA

Cytoplasm

3´

5′

3′

5′

3′


Cut intron

Large

subunit

5′cap

RNA polymerase II


Poly-A tail


5′cap


5´

70


1. RNA polymerase

II in the nucleus

copies one

strand

of the DNA to

produce the

primary

transcript.


is processed by

addition of a 5′

methyl-G cap,

cleavage and



introns. The mature

mRNA is then

exported through


cytoplasm.


mRNA

associates with

the small subunit

of the ribosome.

The initiator

tRNA and large

subunit are

added to form

an initiation

complex.






mRNA in this site.

5. Peptide bonds form between the

amino terminus of the next amino

acid and the carboxyl terminus of

the growing peptide. This transfers

the growing peptide to the tRNA in

the A site, leaving the tRNA in the

P site empty.

mRNA

Small

subunitCytoplasm


mRNA

A siteP site

E site

Lengthening

polypeptide chain

Emptyt

RNA

3´

5′

3′

5′

3′


Cut intron

Large

subunit

5′cap

RNA polymerase II


Poly-A tail


5′cap


5´

6. Ribosome translocation moves the

ribosome relative to the mRNA and

its bound tRNAs. This moves the

growing chain into the P site, leaving

the empty tRNA in the E site and the

A site ready to bind the next

charged tRNA.

Empty tRNA moves into

E site and is ejected

5′

3′

Cytoplasm

71

72

Mutation: Altered Genes

• Point mutations alter a single base

• Base substitution – substitute one base for

another

– Silent mutation – same amino acid inserted

– Missense mutation – changes amino acid

inserted

• Transitions

• Transversions

– Nonsense mutations – changed to stop codon

73

74

Stop

mRNA

Protein

Coding

CG

AT

AT

Template

Pro Thr ArgMet

a.

5′–ATGCCTTATCGCTGA–3′

3′–TACGGAATAGCGACT–5′

5′–AUGCCUUAUCGCUGA–3′

Stop

mRNA

Protein

Coding

CG

Template

Pro Thr ArgMet

b.

Silent Mutation

5′–ATGCCCTATCGCTGA–3′

3′–TACGGGATAGCGACT–5′

5′–AUGCCCUAUCGCUGA–3′


75

Stop

mRNA

Protein

Coding

AT

Template

Pro Thr HisMet

c.

Missense Mutation

5′–ATGCCCTATCACTGA–3′

3′–TACGGGATAGTGACT–5′

5′–AUGCCCUAUCACUGA–3′


Stop

mRNA

Protein

Coding

AT

Template

ProMet

d.

Nonsense Mutation

5′–ATGCCCTAACGCTGA–3′

3′–TACGGGATTGCGACT–5′

5′–AUGCCCUAACGCUGA–3′

76


Polar

Normal HBB Sequence

Abormal HBB Sequence

Nonpolar (hydrophobic)

Amino acids

Nucleotides

Amino acids

Nucleotides

Leu

C C C CGT T TA GG A GAA

Thr Pro Glu Glu

CT TGAA

Lys Ser

Leu

C C C CGT T TA GG GAG

Thr Pro val Glu

CTT TGAA

Lys Ser

1

1

Normal

Deoxygenated

Tetramer

Abnormal

Deoxygenated

Tetramer

Tetramers form long chains

when deoxygenated. This

distorts the normal red blood

cell shape into a sickle shape.

Hemoglobin

tetramer

"Sticky" non-

polar sites

2

2

1

1

2

2

77

• Frameshift mutations

– Addition or deletion of a single base

– Much more profound consequences

– Alter reading frame downstream

– Triplet repeat expansion mutation

• Huntington disease

• Repeat unit is expanded in the disease allele

relative to the normal

78

Chromosomal mutations

• Change the structure of a chromosome

– Deletions – part of chromosome is lost

– Duplication – part of chromosome is copied

– Inversion – part of chromosome in reverse order

– Translocation – part of chromosome is moved to a new location

79

A B C D E F G H A E F G HI IJ J

B C D E F G H I J A B C D B C D E F G H I J

Duplication

Deletion

Deleted

Duplicated

a.

A

b.


80

A B C D E F G H I J

A B C D E F G H I J

K L M N O P Q R

K L M D E F G H I J

A B C N O P Q R

A D C B E F G H I J

Inversion

Inverted

c.

d.

Reciprocal Translocation


81

• Mutations are the starting point for

evolution

• Too much change, however, is harmful to

the individual with a greatly altered

genome

• Balance must exist between amount of

new variation and health of species

Documents

Chapter 15mmsalemscienceteacher.weebly.com/uploads/2/3/3/6/... · 2018. 9. 9. · Exon 1 Intron Exon 2 Branch point A snRNA Exon 1 Exon 2 Lariat 5′ 5′ 3′ 3′ 5′ 5′ 3′