Transcript ppt - Science with Ms. Wood!

Protein Synthesis
Biology 11 preAP
Overview and
Application
Try This!
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1) One strand of DNA has the following
sequence: T A C C G A C G G
What is the corresponding sequence of RNA?
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2) If this new RNA is transported out of the
nucleus directly to a ribosome, which of the
three types of RNA is it?
Overview
Molecular Biology’s central dogma: replication, transcription, translation,
assembly: Howard Hugh’s Medical
http://www.youtube.com/watch?v=D3fOXt4MrOM
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It is expected that you will know:
The key terms gene expression, transcription,
and translation.
How to explain the process of transcription
How eukaryotic cells modify RNA after
transcription
The steps to translation
How point mutations can change the amino
acid sequence
Overview
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What are the stages of Protein Synthesis?
1)
Transcription
2)
mRNA Processing and Modification
3)
Translation
Transcription
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DNA is used as a
template to form a
molecule of singlestranded mRNA
(messenger RNA)
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http://vcell.ndsu.nodak.edu/animatio
ns/transcription/movie.htm
Transcription
Three steps:
1) DNA unzips
2) Complimentary base pairing of
ribonucleotides
3) Termination
Transcription – 1) Unzip
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One section of DNA is unzipped (H-bond
between nitrogen bases are broken) when
RNA polymerase attaches to the promotor
region of the DNA with the assistance of
transcription factors.
–
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Transcription Initation Complex
The DNA continues to be unzipped by RNA
polymerase
Transcription – 2) Complimentary
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RNA polymerase attatches free-floating
ribonucleotides in the 5’-3’ direction
–
–
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temporarily hydrogen bond with their complimentary
nucleotides on the DNA transcription unit
Covalent bond to the 3’ end of the previous
ribonucleotide
Only one of the DNA strands is used as the
template.
Ex: DNA – A T C G
RNA –
Transcription - Termination
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RNA polymerase reaches terminator sequence
RNA polymerase detaches from DNA,
releasing single-stranded RNA strand
DNA rewinds into its double helix
mRNA Processing
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http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm
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Addition of 5’ cap
Addition of poly-A tail
RNA splicing
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Introns are removes, exons are spliced together by
an enzyme called spliceosome
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This enzyme has small nuclear RNA (snRNA) to help it
work and is therefore referred to as a riboenzyme
Modified mRNA is transported out of the
nucleus
Significance of mRNA splicing…
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We have fewer than 25000 genes to make
~100000 proteins!
–
One gene can make different proteins due to
alternative mRNA splicing.
Translation
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mRNA goes to the
ribosome and is
used as a template
to synthesize a
protein molecule.
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http://vcell.ndsu.nodak.edu/animatio
ns/translation/movie.htm
Translation
Three Steps:
1) Initiation
2) Elongation
3) Termination
Translation – 1) Initiation
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need start codon
AUG
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The first tRNA, with
anticodon UAC and
amino acid
methionine
temporarily binds to
the first site
Translation – 2) Elongation
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The second tRNA
molecule attaches
to the second site
of translation.
Translation – 2) Elongation
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The amino
acid from the
first tRNA is
transferred to
the amino
acid on the
second tRNA.
Translation – 2) Elongation
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The first tRNA
exits, the
ribosome
moves, a new
tRNA enters,
and the
process is
repeated.
Translation – 2) Elongation
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The process is
repeated many
times, and a
peptide, or
strand of
amino acids,
is formed.
Translation – 3) Termination
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The release
factor enters.
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Translation, or
protein
synthesis,
ends.
Translation – 3) Termination
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The
completed
polypeptide
is released.
Translation - Application
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What does this
diagram represent?
- Translation
- ELONGATION
Polyribosomes
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Many ribosomes
transcribing the
same mRNA
Very efficient!
Destination of Proteins
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How does a protein “know” whether it to be
used for a function in the cell, or bound for
secretion?
–
Signal peptide: the first ~20 amino acids directs the
final destination
Application
– table of mRNA codons (p 511)
Application
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Consider the following DNA base sequence
read from left to right:
TACGCAAAATGG
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Determine the amino acid sequence that
results from this DNA strand.
Application
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DNA sequence:
TACGCAAAATGG
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mRNA sequence:
AUGCGUUUUACC
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Animo acid sequence:
methionine – arginine – phenylalanine – threonine
Application
Which of the following is an anticodon of a
molecule of tRNA carrying glycine?
A. G G A
B. C C U
C. C C T
D. C G C
Application
Which of the following is an anticodon of a
molecule of tRNA carrying glycine?
Amino acid: glycine
mRNA codon: GGU/GGC/GGA/GGG
tRNA anticodon: CCA/CCG/CCU/CCC
Application
Which of the following is an anticodon of a
molecule of tRNA carrying glycine?
A. G G A
B. C C U < ANSWER!
C. C C T
D. C G C
Mutation Definitions
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point mutation:
A change in the sequence of a base pair within a
gene
1) Base-pair substitution
–
A.
B.
2)
Missense mutation – still amino acid
Nonsense Mutation – code for stop
Insertion and deletion – can cause frameshift
mutation!
Definitions – Gene Mutations
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frameshift mutations
THE CAT ATE THE RAT – what if the “C” was
deleted?
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The original DNA coded for which amino acids?
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DNA: TAC GGT TAG
mRNA: AUG CCA AUC
amino acids: methionine – proline - isoleucine
The mutated DNA now codes for which amino acids?
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DNA: TAC CGG TTA G
mRNA: AUG GCC AAU C
animo acids: methionine – alanine - asparagine
Definitions - Gene Mutation
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What effect does
changing the amino
acids have on the
protein product?
–
Changes the shape.
Since shape
determines function, it
alters how the protein
will function.
Proteins:
Shape determines Function!
Definitions - Gene Mutation
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Which has the potential for the most damage,
deletions or subsitituations?
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Deletions! Frameshift
Definitions
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Mutagens
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Environmental influences that cause mutations
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Examples:
Radiaton: radioactive elements, ultraviolet (UV) light, X rays
Organic chemicals: cigarette smoke, pesticides
Any
Questions?
Closing
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http://vcell.ndsu.nodak.edu/animations/transcription/movie.htm
http://vcell.ndsu.nodak.edu/animations/translation/movie.htm
http://vcell.ndsu.nodak.edu/animations/mrnaprocessing/movie-flash.htm
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Molecular Biology’s central dogma: replication, transcription, translation,
assembly: Howard Hugh’s Medical
http://www.youtube.com/watch?v=D3fOXt4MrOM
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Epic:
http://www.youtube.com/watch?v=u9dhO0iCLww