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Cell Biology
I. Overview
II. Membranes: How Matter Get in and Out of Cells
III. DNA, RNA, and Chromosome Structure
IV. Protein Synthesis
IV. Protein Synthesis
Why is this important?
Well…what do proteins DO?
IV. Protein Synthesis
Why is this important?
Well…what do proteins DO?
Think about it this way:
1) sugars, fats, lipids, nucleic acids and proteins, themselves, are broken down
and built up through chemical reactions catalyzed by enzymes.
2) So everything a cell IS, and everything it DOES, is either done by proteins or is
done by molecules put together by proteins.
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
Genes are read by enzymes and
RNA molecules are produced… (r-RNA)
this is TRANSCRIPTION
UGCUGACUACU
(m-RNA)
(t-RNA)
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
Genes are read by enzymes and
RNA molecules are produced… (r-RNA)
this is TRANSCRIPTION
UGCUGACUACU
(m-RNA)
Eukaryotic RNA and some
prokaryotic RNA have regions
cut out… this is RNA SPLICING
(t-RNA)
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
R-RNA is complexed with
proteins to form ribosomes.
Specific t-RNA’s bind to specific
amino acids.
(r-RNA)
(t-RNA)
Amino acid
(m-RNA)
ribosome
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
The ribosome reads the m-RNA.
Based on the sequence of
(r-RNA)
nitrogenous bases in the m-RNA,
a specific sequence of amino
acids (carried to the ribosome by
t-RNA’s) is linked together to
form a protein. This is
TRANSLATION.
(m-RNA)
ribosome
(t-RNA)
Amino acid
IV. Protein Synthesis
A. Overview
ATGCTGACTACTG
T A C G A CT G A T G A C
UGCUGACUACU
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.
(r-RNA)
Amino acid
(m-RNA)
ribosome
glycoprotein
(t-RNA)
IV. 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 TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
“TAG A CAT” message makes ‘sense’
“ATC T GTA” ‘nonsense’ limited by complementation
IV. 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 TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
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!
IV. 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 antiparallel nature of the double helix, and the chemical limitations of the 'reading'
enzyme, RNA Polymerase.
3’
Promoter
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
exon
Promoters have sequences recognized by the RNA
Polymerase. They bind in particular orientation.
IV. 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 antiparallel nature of the double helix, and the chemical limitations of the 'reading'
enzyme, RNA Polymerase.
3’
Promoter
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
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).
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
nonsense
3’
exon
intron
exon
Terminator sequences destabilize the RNA Polymerase and the
enzyme decouples from the DNA, ending transcription
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
G C A U GUUU G C C A A U AUG A U G A
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
3’
exon
Initial RNA
PRODUCT:
nonsense
intron
exon
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
c. Transcription ends at a sequence called the 'terminator'.
3’
Promoter
Terminator
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
3’
exon
Initial RNA
PRODUCT:
nonsense
intron
exon
G C A U GUUU G C C A A U AUG A U G A
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
exon
Initial RNA
PRODUCT:
intron
exon
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”.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
intron
exon
exon
AUG A
Final RNA
PRODUCT:
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 mRNA and a recipe for a protein.
IV. 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 CAU G U U U G C CAAU U GA
IV. 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 CAU G U U U G C CAAU U GA
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.
IV. 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.
Meth
M-RNA:
G CAU G U U U G C CAAU U GA
IV. 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
Phe
Meth
M-RNA:
G CAU G U U U G C CAAU U GA
IV. 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:
Phe
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
3. Translation
e. polymerization proceeds
Meth
M-RNA:
Ala
Asn
Phe
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
3. Translation
e. polymerization proceeds
Meth
M-RNA:
Asn
Phe
Ala
G CAU G U U U G C CAAU U GA
The amino acids are bound and the ribosome moves 3-bases “downstream”
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
1. Transcription
2. Transcript Processing
3. Translation
e. polymerization proceeds
f. termination of translation
Meth
M-RNA:
Phe
Ala
Asn
G CAU G U U U G C CAAU U GA
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.
IV. 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.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
C. Regulation of Protein Synthesis
1. Regulation of Transcription
- DNA bound to histones can’t 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”.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
C. Regulation of Protein Synthesis
1. Regulation of Transcription
3’
Promoter
5’
sense
A C TATA C G TA C AAA C G G T TATA C TA C T T T
T GATAT G CAT G T T T G C CAATAT GAT GA A A
5’
3’
exon
RNA
POLY
nonsense
intron
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.
IV. Protein Synthesis
A. Overview
B. The Process of Protein Synthesis
C. Regulation of Protein Synthesis
1. Regulation of Transcription
2. Transcript Processing
Initial RNA
PRODUCT:
Cut not made
exon
intron
exon
G C A U GUUU G C C A A U AUG A U G A
UAUA
Mi-RNA’s and si-RNA’s are small RNA molecules that can bind to m-RNA and
disrupt correct spicing, creating non-functional m-RNA’s.
IV. 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
Meth
M-RNA:
Phe
G CAU G U U U U GAAAU U GA
Incorrect splicing can result in a ‘premature’ stop codon, terminating
translation early, resulting in a non-functional protein.
IV. 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
The patterns of cleavage and modification can vary.
Ala
Asn
IV. 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 cells
Affected by
other
genes
Affected by the
environment
Protein ?
Gene activity is responsive to cellular and environmental cues