Transcript Genetics Class- Ch. 10 Notes

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Powerpoint Lecture Outline
Human Genetics
Concepts and Applications
Eighth Edition
Ricki Lewis
Prepared by
Dubear Kroening
University of
Wisconsin-Fox Valley
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Chapter 10
Gene Action: From DNA to Protein
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Gene Expression
• Production of protein from the instructions on
the DNA
• Proteins have diverse functions in the body
examples are listed in Table 10.1
• Protein synthesis requires several steps
including:
 Transcription - production of mRNA
 RNA processing
 Translation - production of protein using
mRNA, tRNA, and rRNA
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Central Dogma
Figure 10.1
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Two Types of Nucleic Acids
Table 10.2
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Major Types of RNA
Table 10.3
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mRNA
• Carries information from DNA to
ribosome
• Produced in the nucleus
• Transported to the ribosome
• A three nucleotide codon specifies a
particular amino acid
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rRNA
• With associated
proteins make up
ribosome
• Two subunits that join
during protein synthesis
• Provides structural
support and some are a
catalyst (ribozymes)
Figure 10.4
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tRNA
• Cloverleaf shape
• Anticodon of tRNA
forms hydrogen
bonds with the
mRNA codon and
has a specific
amino acid at the
Figure 10.5
other end
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Figure 10.6
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Protein Synthesis
• Transcription
– production of mRNA in the nucleus
• mRNA processing
– an mRNA exits the nucleus
• Translation
– Production of amino acid chain within
ribosome
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Transcription
• RNA is the bridge from DNA to protein
• mRNA is synthesized from the template
strand of DNA
• The complementary strand is the
coding strand of DNA
• Requires enzyme RNA polymerase and
transcription factors
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Transcription Factors
• In bacteria, operons control gene expression
• In more complex organisms transcription
factors control gene expression and link
genome to environment
• Over 2,000
• Mutations in transcription factors may cause a
wide range of effects
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Figure 10.2
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Base Pairing
Template DNA strand
C
G
C
G
T
A
A
U
G
C
C
G
T
A
A
U
C
G
T
C
G
A
T
G
mRNA strand
G
G
A
Coding DNA strand
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Steps in Transcription
Figure 10.7
• Proteins and RNA polymerase bind to
promoter region
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Transcription Initiation
Figure 10.8
RNA polymerase reads the nucleotides on the
template strand from 3’ to 5’ and creates an RNA
molecule that looks like the coding strand
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Transcription
Occurs in three steps:
• Initiation  promoter
• Elongation  RNA polymerase adds
nucleotides to growing RNA
• Termination  Sequences in the DNA prompt
the RNA polymerase to fall off, ending the
transcript
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RNA Processing
• mRNA transcripts are modified before use as a
template for translation:
• Addition of capping nucleotide at the 5’ end
• Addition of polyA tail to 3’ end
• Important for moving transcript out of nucleus
and for regulating when translation occurs
• Splicing occurs, removing internal sequences
Introns are sequences removed
Exons are sequences remaining
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RNA Processing
Figure 10.10
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Translation
• The process of
reading the RNA
sequence of an
mRNA and
creating the amino
acid sequence of a
protein
Figure 10.11
• Occurs within the
ribosome
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The Genetic Code
• Codons are the triplet code groups of three RNA
nucleotides used to encode one amino acid
• The genetic code refers to which codons encode which
amino acids, one start codon, and three stop codons
• Non overlapping
• Genetic code is universal  evidence of a common
ancestor
• The genetic code is degenerate  some codons encode
the same amino acid
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mRNA Nucleotides and the Amino
Acids in a Protein
• Proteins are formed from 20 amino acids in humans
Codons of three nucleotides:
AAA AGA ACA AUA AAG AGG ACG AUG
AAC AGC ACC AUC AAU AGU ACU AUU
GAA GGA GCA GUA GAG GGG GCG GUG
GAC GGC GCC GUC GAU GGU GCU GUU
CAA CGA CCA CUA CAG CGG CCG CUG
CAC CGC CCC CUC CAU CGU CCU CUU
UAA UGA UCA UUA UAG UGG UCG UUG
UAC UGC UCC UUC UAU UGU UCU UUU
Allows for 64 potential codons => sufficient!
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The Genetic Code
Table 10.5
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Translation
Composed of three steps
• Initiation
– Translation begins at start codon
(AUG = methionine)
• Elongation
– The ribosome uses the tRNA anticodon to
match codons to amino acids and adds those
amino acids to the growing peptide chain
• Termination
– Translation ends at the stop codon
– UAA, UAG or UGA
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Translation Initiation
Figure 10.13
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Translation Elongation
Figure 10.14a
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Elongation
Figure 10.14b
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Elongation
Figure 10.14c
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Termination
Figure 10.15
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Translation:
Multiple Copies of a Protein Are
Made Simultaneously
Figure 10.16
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Protein Folding
• After synthesis, proteins must be folded
into three-dimensional shape
• Enzymes and chaperone proteins assist
• Misfolded proteins are tagged and
dismantled
• Proteins can fold in more than one way
• Misfolded proteins can cause disease
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Levels of Protein Structure
Figure 10.17
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Misfolded Proteins Are Destroyed
•Ubiquitin tags misfolded proteins
•Transports it to a proteasome
Figure 10.19
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Misfolding of Protein
Impairs Function
• Misfolded prion protein disrupts functions of other
normally folded prion proteins
• Aberrant conformation can be passed on, propagating like
an “infectious” agent
Table 10.6
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Study guide- DNA- Ch. 9; RNA &
protein synthesis- Ch. 10.1-10.2
• History of DNA knowledge:
– Discoveries
– Who isMiescher
Garrod
Frederick Griffith
Avery, Macleod, McCarty
Chargaff
Hershey & Chase
Levene
Wilkins & Franklin
Watson & Crick
Meselson & Stahl
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Prions
• Protein folding disorder  Infectious prions cause
scrapie (sheep), bovine spongiform encephalopathy
(cows), and a variant Creutzfeldt-Jakob disease
(humans)
Figure 10.20
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• Experiments of transforming factor– Griffith experiment
– Hershey & Chase bacteriophage experiment
• DNA structure–
–
–
–
–
Components of nucleotide
Directionality
5’, 3’
Arrangement of components
Bonding
• DNA replication
–
–
–
–
Model- semiconservative
ProcessEnzymes- helicase, DNA polymerase- function
Complementary base pairing rules
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• What are chromosomes?
• Central Dogma of Biology
• RNA components
– 3 Types of RNA
– Complementary base rules
• Protein Synthesis– Transcription- process , where it occurs
– Translation- process, where it occurs
– Enzymes involved- RNA polymerase and transcription
factors.
• Triplet code, codon, anticodon, amino acid,
proteins.
• Folding of proteins
• Mutations
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