5/29/2012 4 Protein under construction Large subunit Small subunit A ribosome translating mRNA into...
Transcript of 5/29/2012 4 Protein under construction Large subunit Small subunit A ribosome translating mRNA into...
5/29/2012
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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