Transcript Protein Synthesis

Protein Synthesis & Gene Expression
• DNA provides the instructions for how to build proteins
• Each gene dictates how to build a single protein in prokaryotes
• The sequence of nucleotides (AGCT) in DNA dictates the
order of amino acids that make up a protein
nucleotide sequence of His protein Amino acid sequence of His protein
Protein Synthesis & Gene Expression
Protein Synthesis & Gene Expression
• Protein Synthesis = Gene Expression
 The process in which the instructions encoded by a gene are used to
build a protein
Gene
mRNA
polypeptide
transcription
translation
DNA in the made in nucleus, built out of
nucleus
exits out of a
amino acids by a
pore in the
ribosome in the
nuclear envelope cytoplasm using
and finds a
instructions from
ribosome in the
an mRNA
cytoplasm
protein
Final resulting
molecule after
polypeptide is
modified and
folded into final
shape in the
rough ER
Packaged into
a vesicle in the
golgi and
shipped out to
where it is
needed
Protein Synthesis & Gene Expression
• Transcription
 RNA polymerase makes an
mRNA (messenger RNA)
copy of a gene
 occurs in cytoplasm of
prokaryotes, nucleus
of eukaryotes
 Enables cell to make many
copies of a gene so that a lot
of protein can be made at one
time
 Enables eukaryotic cells to
keep DNA protected in the
nucleus, only mRNA copies
of genes leave the nucleus
Protein Synthesis & Gene Expression
• Transcription
Initiation
1) INITIATION
 RNA polymerase binds to a
region on DNA known as the
promoter, which signals the
start of a gene
 Promoters are specific to genes
 RNA polymerase does not need
a primer
 Transcription factors assemble
at the promoter forming a
transcription initiation complex
– activator proteins help stabilize
the complex
(eukaryotes)
 Gene expression can be regulated (turned
on/off or up/down) by controlling the amount
of each transcription factor
HONORS
Protein Synthesis & Gene Expression
• Transcription
Elongation
1) INITIATION
 RNA polymerase unwinds
the DNA and breaks the
H-bonds between the bases
of the two strands, separating
them from one another
 Base pairing occurs between
incoming RNA nucleotides
and the DNA nucleotides of
the gene (template)
• recall RNA uses uracil
instead of thymine
AGTCAT
UCAGUA
HONORS
Protein Synthesis & Gene Expression
• Transcription
Elongation
The gene occurs on only one of the DNA
strands; each strand possesses a separate
set of genes
RNA polymerase slides down the template
strand connecting together RNA nucleotides
Protein Synthesis & Gene Expression
• Transcription
Termination
 A region on DNA known as
the terminator signals the
stop of a gene
 RNA polymerase separates
from the mRNA and the DNA
HONORS
1) INITIATION
Protein Synthesis & Gene Expression
• Alternative Splicing (eukaryotes only)
 Exons are
“coding” regions
provide instructions
for one or more
proteins)
 Introns are removed
 different combinations
of exons form
different mRNA
resulting in multiple
proteins from the
same gene
 Humans have 30,000
genes but are capable
of producing 100,000
proteins
HONORS
Web Resources
Transcription
• http://www.biostudio.com/d_%20Transcription.htm
• http://www.youtube.com/watch?v=WsofH466lqk
• http://www.dnalc.org/resources/3d/TranscriptionBasic_withFX.html
Alternative Splicing
• http://www.youtube.com/watch?v=FVuAwBGw_pQ&feature=related
Protein Synthesis & Gene Expression
• Translation
 mRNA is used by ribosome to build
polypeptides (Ribosomes attach to
the mRNA and use its sequence of
nucleotides to determine the order
of amino acids in the polypeptide)
 occurs in cytoplasm of prokaryotes
and eukaryotes
Transcription
tRNA
synthesis
mRNA
 some polypeptides feed directly
into rough ER in eukaryotes where
they are modified and folded into
the final protein
Translation
Protein Synthesis
mRNA
• Translation
Initiation
 Start codon signals where the
gene begins (at 5’ end of mRNA)
Translation
5’
3’
AUGGACAUUGAACCG…
start codon
Protein Synthesis & Gene Expression
• Translation
Initiation
 Start codon signals where the gene
begins (at 5’ end of mRNA)
 Ribosome binding site on the mRNA
binds to a small ribosomal subunit
 Then this complex binds to a large
ribosomal subunit forming the complete
ribosome
Protein Synthesis & Gene Expression
• Translation
Scanning
 The ribosome moves in 5’ to 3’ direction “reading” the mRNA and
assembling amino acids into the correct polypeptide
Protein Synthesis & Gene Expression
• Translation
Scanning
Transcription
tRNA
synthesis
 Every three mRNA nucleotides (codon) specify an amino acid
mRNA
Translation
Protein Synthesis & Gene Expression
• Translation
Scanning
 Each tRNA carries a specific amino acid
 tRNA have an anticodon region that specifically binds to its codon
anticodon
Protein Synthesis
• Translation
Termination
 Ribosome disengages from the mRNA
when it encounters a stop codon
Web Resources
Translation
• Eukaryotic: http://www.youtube.com/watch?v=5bLEDd-PSTQ&feature=related
• Prokaryotic: http://www.biostudio.com/d_%20Protein%20Synthesis%20Prokaryotic.htm
• http://www.biostudio.com/d_%20Peptide%20Bond%20Formation.htm
• http://www.johnkyrk.com/DNAtranslation.html
• http://www.dnalc.org/resources/3d/TranslationBasic_withFX0.html
• http://www.dnalc.org/resources/3d/TranslationAdvanced.html
Protein Synthesis & Gene Expression
• Post-Translational Modifications
 Polypeptide is modified in the rough ER – this might include cutting out
sections and/or cut a section from one part of the polypeptide and moving
it to another part
 Chaperone proteins help to fold the polypeptide into its final tertiary shape.
Now it is called a protein.
Protein Synthesis & Gene Expression
Rough Endoplasmic Reticulum (ER)
• Folded membrane that forms compartments
where newly synthesized proteins are processed
(cut, joined, folded into their final shape)
• Ribosomes bind to rough ER when they start to
synthesize proteins that are intended to be
exported from the cell – the proteins enter the ER
directly from the ribosome
Protein Synthesis & Gene Expression
Golgi Apparatus
• Folded membranes form compartments that each contain different
enzymes which selectively modify the contents depending on where they
are destined to end up
• Processes and packages
macromolecules produced
by the cell (e.g. proteins
and lipids) – sent out as
excretory vesicles “labeled”
for their destination
Protein Synthesis & Gene Expression
• Multiple RNA polymerases can
engage a gene at one time
• Multiple ribosomes can engage
a single mRNA at one time
Transcription
DNA
mRNAs
Translation
Protein Synthesis & Gene Expression
• Eukaryotes:
transcription occurs
in the nucleus and
translation occurs in
the cytoplasm
• Prokaryotes:
Transcription and
translation occur
simultaneously in
the cytoplasm
Protein Synthesis & Gene Expression
•
There are three main types of RNA:
1. mRNA (messenger RNA)
- RNA copy of a gene used as a template for protein synthesis
2. rRNA (ribosomal RNA)
- part of structure of ribosomes
3. tRNA (transfer RNA)
- amino acid carrier that matches to mRNA codon
Practice Question
Translate the following mRNA sequence
AGCUACCAUACGCACCCGAGUUCUUCAAGC
Practice Question
Translate the following mRNA sequence
AGCUACCAUACGCACCCGAGUUCUUCAAGC
Serine – Tyrosine – Histidine – Threonine – Histidine – Proline – Serine – Serine – Serine - Serine
Practice Question
Translate the following mRNA sequence
AGCUACCAUACGCACCCGAGUUCUUCAAGC
Serine – Tyrosine – Histidine – Threonine – Histidine – Proline – Serine – Serine – Serine - Serine
Ser – Tyr – His – Thr – His – Pro – Ser – Ser – Ser - Ser
Practice Question
Translate the following mRNA sequence
AGCUACCAUACGCACCCGAGUUCUUCAAGC
Serine – Tyrosine – Histidine – Threonine – Histidine – Proline – Serine – Serine – Serine - Serine
Ser – Tyr – His – Thr – His – Pro – Ser – Ser – Ser - Ser
S – Y –H– T – H – P – S – S – S - S
Protein Synthesis & Gene Expression
• Protein Synthesis = Gene Expression
 Process in which a gene is used to build a protein resulting in the
presence of a particular phenotype (physical characteristic)
 Phenotypic variation among organisms is due to genotypic variation
(differences in the sequence of their DNA bases)
 Differences exist between species and within a species
• Different genes (genomes)  different proteins (proteomes)
• Different versions of the same gene = alleles
• Differences in gene expression = epigenetics
Web Resources
Insulin Example of Protein Synthesis
http://www.biotopics.co.uk/as/insulinproteinstructure.html
Hemoglobin Example of Protein Synthesis
http://www.biotopics.co.uk/as/insulinproteinstructure.html
Collagen Example of Protein Synthesis
http://www.biotopics.co.uk/JmolApplet/collagen.html