Cell Biology

1
Cell Biology I. Overview II. Membranes How
Matter Get in and Out of Cells III. Cellular
Respiration IV. Photosynthesis V. DNA, RNA, and
Chromosome Structure VI. Protein Synthesis
2
VI. Protein Synthesis Why is this
important? Wellwhat do proteins DO?
3
VI. Protein Synthesis Why is this
important? Wellwhat do proteins DO?

• Think about it this way
• sugars, fats, lipids, nucleic acids and proteins,
  themselves, are broken down and built up through
  chemical reactions catalyzed by enzymes.
• So everything a cell IS, and everything it DOES,
  is either done by proteins or is done by
  molecules put together by proteins.

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VI. Protein Synthesis A. Overview
A T G C T G A C T A C T G
T A C G A CT G A T G A C
Genes are read by enzymes and RNA molecules are
produced this is TRANSCRIPTION
(t-RNA)
(r-RNA)
U G C U G A C U A C U
(m-RNA)
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VI. Protein Synthesis A. Overview
A T G C T G A C T A C T G
T A C G A CT G A T G A C
Genes are read by enzymes and RNA molecules are
produced this is TRANSCRIPTION
(t-RNA)
(r-RNA)
U G C U G A C U A C U
(m-RNA)
Eukaryotic RNA and some prokaryotic RNA have
regions cut out this is RNA SPLICING
6
VI. Protein Synthesis A. Overview
A T G C T G A C T A C T G
T A C G A CT G A T G A C
R-RNA is complexed with proteins to form
ribosomes. Specific t-RNAs bind to specific
amino acids.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
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VI. Protein Synthesis A. Overview
A T G C T G A C T A C T G
T A C G A CT G A T G A C
The ribosome reads the m-RNA. Based on the
sequence of nitrogenous bases in the m-RNA, a
specific sequence of amino acids (carried to the
ribosome by t-RNAs) is linked together to form a
protein. This is TRANSLATION.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
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VI. Protein Synthesis A. Overview
A T G C T G A C T A C T G
T A C G A CT G A T G A C
The protein product may be modified (have a
sugar, lipid, nucleic acid, or another protein
added) and/or spliced to become a functional
protein. This is POST-TRANSLATIONAL
MODIFICATION.
(t-RNA)
(r-RNA)
U G C U G A C U A C U
Amino acid
(m-RNA)
ribosome
glycoprotein
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription a. The
message is on one strand of the double helix -
the sense strand
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
TAG A CAT message makes sense ATC T
GTA nonsense limited by complementation
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription a. The
message is on one strand of the double helix -
the sense strand
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon
In all eukaryotic genes and in some prokaryotic
sequences, there are introns and exons. There
may be multiple introns of varying length in a
gene. Genes may be several thousand base-pairs
long. This is a simplified example!
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription b.
The cell 'reads' the correct strand based on the
location of the promoter, the anti-parallel
nature of the double helix, and the chemical
limitations of the 'reading' enzyme, RNA
Polymerase.
Promoter
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon
Promoters have sequences recognized by the RNA
Polymerase. They bind in particular orientation.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription b.
The cell 'reads' the correct strand based on the
location of the promoter, the anti-parallel
nature of the double helix, and the chemical
limitations of the 'reading' enzyme, RNA
Polymerase.
Promoter
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
G C A U GUUU G C C A A U AUG A U G A
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon

1. Strand separate
2. RNA Polymerase can only synthesize RNA in a 5?3
   direction, so they only read the anti-parallel,
   3?5 strand (sense strand).

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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
G C A U GUUU G C C A A U AUG A U G A
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon
Terminator sequences destabilize the RNA
Polymerase and the enzyme decouples from the DNA,
ending transcription
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
G C A U GUUU G C C A A U AUG A U G A
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon
Initial RNA PRODUCT
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription c.
Transcription ends at a sequence called the
'terminator'.
Promoter
Terminator
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing
G C A U GUUU G C C A A U
AUG A
U G A
Introns are spliced out, and exons are spliced
together. Sometimes these reactions are
catalyzed by the intron, itself, or other
catalytic RNA molecules called ribozymes.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing
AUG A
G C A U GUUU G C C A A U
U G A
This final RNA may be complexed with proteins to
form a ribosome (if it is r-RNA), or it may bind
amino acids (if it is t-RNA), or it may be read
by a ribosome, if it is m-RNA and a recipe for a
protein.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation a.
m-RNA attaches to the ribosome at the 5' end.
M-RNA
G C A U G U U U G C C A A U
U G A
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation a.
m-RNA attaches to the ribosome at the 5' end.
M-RNA
G C A U G U U U G C C A A U
U G A
It then reads down the m-RNA, one base at a time,
until an AUG sequence (start codon) is
positioned in the first reactive site.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation a.
m-RNA attaches to the ribosome at the 5' end.
b. a specific t-RNA molecule, with a
complementary UAC anti-codon sequence, binds to
the m-RNA/ribosome complex.
M-RNA
G C A U G U U U G C C A A U
U G A
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation a.
m-RNA attaches to the ribosome at the 5' end.
b. a specific t-RNA molecule, with a
complementary UAC anti-codon sequence, binds to
the m-RNA/ribosome complex. c. A second
t-RNA-AA binds to the second site
M-RNA
G C A U G U U U G C C A A U
U G A
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation a.
m-RNA attaches to the ribosome at the 5' end.
b. a specific t-RNA molecule, with a
complementary UAC anti-codon sequence, binds to
the m-RNA/ribosome complex. c. A second
t-RNA-AA binds to the second site d.
Translocation reactions occur
Meth
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds
Meth
Phe
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds
Meth
Phe
Ala
M-RNA
G C A U G U U U G C C A A U
U G A
The amino acids are bound and the ribosome moves
3-bases downstream
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation e.
polymerization proceeds f. termination of
translation
M-RNA
G C A U G U U U G C C A A U
U G A
Some 3-base codon have no corresponding t-RNA.
These are stop codons, because translocation does
not add an amino acid rather, it ends the chain.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis 1. Transcription 2.
Transcript Processing 3. Translation 4.
Post-Translational Modifications
Meth
Phe
Ala
Asn
Most initial proteins need to be modified to be
functional. Most need to have the methionine
cleaved off others have sugar, lipids, nucleic
acids, or other proteins are added.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription -
DNA bound to histones cant be accessed by RNA
Polymerase - but the location of histones
changes, making genes accessible (or
inaccessible)
Initially, the orange gene is off, and the
green gene is on
Now the orange gene is on and the green gene is
off.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription
Promoter
3
5
sense
A C T A T A C G T A C A A A C G G T T A T A C T A
C T T T
T G A T A T G C A T G T T T G C C A A T A T G A T
G A A A
nonsense
3
5
intron
exon
exon
Transcription factors can inhibit or encourage
the binding of the RNA Polymerase. And, through
signal transduction, environmental factors can
influence the activity of these transcription
factors. So cells can respond genetically to
changes in their environment.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription 2.
Transcript Processing
Cut not made
U G A
U A U A
Mi-RNAs and si-RNAs are small RNA molecules
that can bind to m-RNA and disrupt correct
spicing, creating non-functional m-RNAs.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription 2.
Transcript Processing 3. Regulating Translation
M-RNA
G C A U G U U U U G A A A U
U G A
Incorrect splicing can result in a premature
stop codon, terminating translation early,
resulting in a non-functional protein.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription 2.
Transcript Processing 3. Regulating
Translation 4. Regulating Post-Translational
Modification
Meth
Phe
Ala
Asn
The patterns of cleavage and modification can
vary.
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VI. Protein Synthesis A. Overview B. The Process
of Protein Synthesis C. Regulation of Protein
Synthesis 1. Regulation of Transcription 2.
Transcript Processing 3. Regulating
Translation 4. Regulating Post-Translational
Modification
Affected by other genes
Affected by other cells
Affected by the environment
Protein ?
Gene activity is responsive to cellular and
environmental cues