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Essentials of

Biology

Sylvia S. Mader

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

Chapter 11

Lecture Outline

Transcription & Translation

DNA RNA Protein

• Transcription: DNA

copied into mRNA

molecule

• Translation:

ribosomes translate

mRNA into protein—

a chain of amino

acids

• Proteins control

phenotype. How?

The Flow of Genetic Information: DNA to RNA to Protein Phenotype

A few of the many roles played by proteins:

1. Enzymes: catalysts for nearly all chemical reactions in cells;

Determine what cells can make and digest

2. Structural components: muscles (actin and myosin), connective

tissue (collagen, elastin)

3. Receptors on cell surface for growth factors, hormones, etc.

4. Hormones: e.g. insulin, growth hormone, prolactin

5. Transport: e.g. hemoglobin, spindle fibers

6. Immune system: antibodies

The function of a gene is to dictate the production of a one ore more proteins. Why are proteins so important?

C C G G G

U A A A

C C G G G

U A A A

C C C G G

U U U A

C C C G G

T T T A

Gly Arg Thr

anticodon

codon

C

G G G

T A

A A

C C C

G C

G

T

T

T

A DNA

double helix

Cytoplasm

Nucleus

Polypeptide

DNA

mRNA

Transcription

mRNA

Translation

tRNA

5 3

5 3

Figure 11.9

Flow of genetic information

• Transcription

DNA serves as template to

make mRNA.

• Translation

mRNA directs sequence of

amino acids in a protein.

rRNA and tRNA assist

The order of Bases in a gene determines the order of amino acids in the protein it codes for

Why is the

order of

amino acids

in a protein

important?

Figure 11.8 Structure of RNA

One RNA nucleotide

Ribonucleic acid (RNA) • Contains sugar ribose

• Uses uracil, not thymine

Uses A, C, and G like DNA

• Single-stranded

• 3 majors types

Messenger RNA (mRNA)

Transfer RNA (tRNA)

Ribosomal RNA (rRNA)

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(a) Parent DNA

RNA Polymerase separates strands

(b) Transcription begins

RNA polymerase

Complementary base pairing

Transcription: copying DNA into RNA ( 1 of 2)

(c) Transcription continues (d) Products of transcription

Non-coding strand

Template Strand (coding strand)

Nucleotide joining

New RNA strand (actually several hundred base pairs long)

Parent DNA totally conserved

Transcription: copying DNA into RNA ( 2 of 2)

Transcription (Campbell)

Transcription (Freeman)

RNA

polymerase

This mRNA transcript is

Almost ready to be processed.

template

DNA

strand

to processing

mRNA 5

3

G

C

G

C G

G

C G

C G

G

C

T

C

G

A

Figure 11.11 Transcription to form mRNA

During transcription,

complementary RNA is made from

a DNA template.

Portion of DNA unwinds and

unzips at the point of attachment of

RNA polymerase.

Bases join in the order dictated by

the sequence of bases in the

template DNA strand.

Figure 11.12 mRNA processing

• Capping & poly-A tail

provide stability

• Introns (non-coding)

removed

• Exons remain (coding)

• Alternative splicing

produces different

mRNA molecules

leading to different

proteins.

• Mature mRNA leaves

nucleus and associates

with ribosome in

cytoplasm.

Fig. 7.07

(a) Gene

(b) Primary transcript Transcription

RNA splicing: Differential splicing can result in different mRNA molecules and, therefore, different proteins

RNA Processing

Translation

(c) Spliced RNA

(d) Mature RNA

(d) protein

Exon 1 Exon 2

Intron 1

Exon 3

Intron 2

Exon 4

Intron 3

Exon 5

Intron 4

Exon 6

Intron 5

Transcription in Eukaryotic Cells:

Differential RNA splicing can result in one gene producing more than one protein Processing of Eukaryotic RNA

RNA Processing includes • Adding a cap and tail

• Removing introns

• Splicing exons together

– Differential splicing produces

different mRNA molecules

Gene (DNA)

RNA transcript with cap and tail

mRNA

Exon Intron Exon Intron Exon

Cap

Introns removed Tail

Exons spliced together

Coding sequence

Nucleus

Cytoplasm

Transcription + the Addition of cap and tail

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Comparing DNA and RNA

DNA RNA

Number of

Strands

Sugars

Bases

DNA & RNA Structure

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Translation

• Ribosomes read

mRNA to

produce a

protein

• tRNA brings in

amino acids

• Resulting protein

contains the

sequence of

amino acids

originally

specified in the

DNA.

Please note that due to differing

operating systems, some animations

will not appear until the presentation is

viewed in Presentation Mode (Slide

Show view). You may see blank slides

in the “Normal” or “Slide Sorter” views.

All animations will appear after viewing

in Presentation Mode and playing each

animation. Most animations will require

the latest version of the Flash Player,

which is available at

http://get.adobe.com/flashplayer.

Figure 11.13 Transfer RNA: tRNA

tRNA

1. Acts as a molecular

interpreter

2. Each tRNA carries a

specific amino acid

3. Matches amino acids

with codons in mRNA

using anticodons

Figure 11.13 tRNA structure

Amino acid

Codon on mRNA

mRNA

A portion of an mRNA molecule attached to a tRNA

Each Codon codes

Specifies a specific

tRNA—amino acid

complex

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Protein under construction

Large subunit

Small subunit

A ribosome translating mRNA into protein

mRNA

Ribosomes

• Organelle that makes

protein

• Reads mRNA 5’ 3’

• Made of rRNA and

protein

• Consist of 2 subunits

1. Initiation of Translation

Anticodon

tRNA Ribosome

mRNA

Codon

Amino acid

2. Elongation

Peptide bond forms

2. Elongation continues: Translocation of Ribosome

tRNA ejected

Ribosome moves

3. Termination of Translation

tRNA ejected

Ribosome moves

Termination factor binds

Peptide bond forms

3. Termination continued: Disassembly of Ribosome

Polypeptide chain

tRNA

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• Polyribosome – several ribosomes attach to and

translate the same piece of mRNA.

Figure 11.14 Polyribosome structure and function

mRNA codon

a.

b. 400,000

5

3

Cystic Fibrosis: autosomal recessive

Most common lethal genetic disease

– 1 in 2000 children is born with CF in U.S.

– Untreated children die by age 5

– Ave. life expectancy: ~27 yrs

– Special diet + daily dose of antibiotic prevent infection

Carriers of CF gene:

– Hispanics: 1 in 46

– African Americans: 1 in 63

– Asian Americans: 1 in 150

– Caucasian of European descent: 1 in 25

• CF allele protects against the plague and many viruses

Cystic Fibrosis phenotype

Our Goal…

To determine the

connection between

DNA and the

symptoms

associated with

cystic fibrosis

Cystic Fibrosis A single faulty protein is connected to the symptoms In 1989 the gene was mapped to chromosome #7

Transcription & Translation of the CRTR Gene in Healthy People

Part of a normal CFTR gene:

5’...ATCATCTTTGGTGTT...3’ non-coding strand

3’...TAGTAGAAACCACAA...5’ coding strand

1. Transcribe this portion of the gene.

The whole gene codes for 1480 amino acids in CFTR protein!

What is the order of bases in the resulting mRNA molecule?

2. Translate this portion of the gene.

– What is the order of amino acids in the resulting protein?

phenylalanine (Phe)

leucine (Leu)

leucine (Leu)

Fir

st

base

Th

ird b

ase

Second base

valine (Val)

methionine (Met) (start)

isoleucine (Ile)

serine (Ser)

proline (Pro)

threonine (Thr)

alanine (Ala)

tyrosine (Tyr)

stop

stop

cysteine (Cys)

tryptophan (Trp)

arginine (Arg)

glycine (Gly)

serine (Ser)

arginine (Arg)

histidine (His)

glutamine (Gln)

asparagine (Asn)

lysine (Lys)

aspartic acid (Asp)

glutamic acid (Glu)

UUU

UUC

UUA UUG

CUU

CUC

CUA

CUG

AUU

AUC

AUA

AUG

GUU

GUC

GUA GUG

G

A

C

U

UCU

UCC

UCA

UCG

CCU

CCC

CCA

CCG

ACU

ACC

ACA

ACG

GCU

GCC

GCA GCG

UAU

UAC

U C A G

U

C

A

G

U

C

A

G

U

C

A

G

U

C

A

G

UAA

CAU

CAC

CAA

CAG

AAU

AAC

AAA

AAG

GAU

GAC

GAA GAG

UAG

UGA

UGU

UGC

UGG

CGU

CGC

CGA

CGG

AGU

AGC

AGA AGG

GGU

GGC

GGA GGG

stop

Figure 11.10 Messenger RNA codons—“genetic code”

1. The genetic code is the same for almost all organisms!!

2. In which base do the codons for the same amino acid differ?

3. What is the function of the start and stop codons?

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Part of CFTR gene associated with Cystic Fibrosis:

5’...ATCATTGGTGTT...3’ non-coding strand

3’...TAGTAACCACAA...5’ template strand

1. Transcribe this portion of the gene.

What is the order of bases in the resulting mRNA molecule?

2. Translate this portion of the gene.

– What is the order of amino acids in the resulting protein?

3. What is different about the gene and the protein in people

with cystic fibrosis?

Transcription & Translation of the CRTR Gene in People with CF CFTR Protein: The cystic fibrosis transmembrane regulator protein

Carbohydrate

Chloride ions

Water

CFTR Protein

Cell membrane

Cytoplasm of cell lining duct or lungs

Water

Inside of duct or

Air sac in lungs

CFTR Protein

• Pumps

chloride ions

(salt) into cells

lining ducts or

the lungs

• What are the

consequences

when CFTR

doesn’t work?

• How does a

gene control

the production

of a protein?

Explaining the symptoms of CF

Chloride ions

in cell

Chloride ions

outside of cell CFTR Protein: Pumps

Chloride ions into cell

• In CF, the faulty CFTR protein never makes it to cell membrane

1. What builds up outside of cells? Why?

2. Why salty sweat?

3. Why does mucus collect in lungs?

4. Why respiratory infections?

5. Why problems with digestion?

6. Why male sterility?

Understanding Cystic Fibrosis at the Cellular Level

How does CFTR protein get from where it’s produced to its home

in the cell membrane?

1. Where is the CFTR protein produced?

2. CFTR is a glycoprotein—where does it go for modification?

How does it get there?

3. How does the modified CFTR protein get to the plasma membrane?

4. The defective CFTR protein is recognized at the ER as defective

Where is the defective CFTR protein sent?

CF symptoms may be mild or severe

Several hundred different mutations are associated with CF

CFTR

Gene

What’s a Gene Mutation?

• Any change in the nucleotide sequence of DNA

• Types of Mutations

– Base pair Substitution, insertion or deletion

– Occur during DNA replication

• Mutations may Result from:

1. Errors in DNA replication (Why uncommon?)

2. Transposons

• “Jumping genes” – pieces of DNA that move within and between chromosomes

3. Some Viruses

4. Mutagens

• physical or chemical agents that cause errors during DNA replication

chemicals in cigarette smoke

Radiation (e.g. U.V. light, X-rays)

• Do gene mutations always affect the protein a gene codes for?

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Mutations responsible for Sickle Cell Anemia

Normal hemoglobin Sickle-cell hemoglobin

Glu Val

Normal hemoglobin DNA Mutant hemoglobin DNA

mRNA mRNA

• Only one amino acid in 146 is incorrect in sickle-cell

hemoglobin!

Types of Gene Mutations: Base Pair Substitutions, Insertions or deletions

• Base pair

substitutions

– May result in

changes in the

amino acid

sequence in a

protein, or

– May be silent

(have no effect)

mRNA

Protein Met Lys Phe Gly Ala

(a) Base substitution

Met Lys Phe Ser Ala

Types of Mutations: Base Insertions and deletions

• Can have

disastrous

effects

– Change the

reading frame

of the genetic

message

Met Lys Leu Ala His

(b) Nucleotide deletion

mRNA

Protein Met Lys Phe Gly Ala

Although

mutations

are often

harmful…

– mutations are

the source of

the rich

diversity of

genes in the

living world

– mutations

contribute to

the process of

evolution by

natural

selection

DNA and RNA: Polymers of Nucleotides

SUMMARY OF KEY CONCEPTS

DNA

Polynucleotide

Nitrogenous base

Phosphate group

Nucleotide

Sugar

Figure 11.17 Summary of gene expression in eukaryotes