Download 03g - Protein Synth other roles of DNA

Protein Synthesis
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Protein Synthesis

DNA serves as master blueprint for protein synthesis

Genes are segments of DNA carrying instructions for a
polypeptide chain

Triplets of nucleotide bases form the genetic library

Each triplet specifies coding for an amino acid
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
From DNA to Protein
Nuclear
envelope
DNA
Transcription
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Polypeptide
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.33
From DNA to Protein
DNA
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.33
From DNA to Protein
Transcription
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
DNA
Figure 3.33
From DNA to Protein
DNA
Transcription
Pre-mRNA
RNA Processing
mRNA
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.33
From DNA to Protein
Nuclear
envelope
DNA
Transcription
Pre-mRNA
RNA Processing
mRNA
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.33
From DNA to Protein
Nuclear
envelope
DNA
Transcription
Pre-mRNA
RNA Processing
mRNA
Ribosome
Translation
Polypeptide
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.33
Roles of the Three Types of RNA
1.
2.
3.
Messenger RNA (mRNA) – carries the genetic
information from DNA in the nucleus to the
ribosomes in the cytoplasm
Transfer RNAs (tRNAs) – bound to amino
acids base pair with the codons of mRNA at the
ribosome to begin the process of protein
synthesis
Ribosomal RNA (rRNA) – a structural
component of ribosomes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Transcription

Transfer of information from the sense strand of
DNA to RNA

Transcription factor

Loosens histones from DNA in the area to be
transcribed

Binds to promoter, a DNA sequence specifying the
start site of RNA synthesis

Mediates the binding of RNA polymerase to
promoter
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Transcription: RNA Polymerase

An enzyme that oversees the synthesis of RNA

Unwinds the DNA template

Adds complementary ribonucleoside triphosphates
on the DNA template

Joins these RNA nucleotides together

Encodes a termination signal to stop transcription
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
RNA
nucleotides
mRNA
RNA
nucleotides
RNA
polymerase
mRNA synthesis begins
RNA polymerase moves down DNA;
mRNA elongates
mRNA synthesis is terminated
DNA
(a)
mRNA transcript
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
(a)
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
(a)
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
RNA
nucleotides
mRNA synthesis begins
(a)
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
RNA
nucleotides
mRNA synthesis begins
mRNA
(a)
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
RNA
nucleotides
mRNA
RNA
nucleotides
mRNA synthesis begins
RNA polymerase moves down DNA;
mRNA elongates
(a)
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Coding
strand
Termination signal
Promoter
Template
strand
Transcription unit
In a process mediated by a transcription
factor, RNA polymerase binds to
promoter and unwinds 16–18 base
pairs of the DNA template strand
RNA
polymerase
Unwound DNA
RNA polymerase
bound to promoter
RNA
nucleotides
mRNA
RNA
nucleotides
RNA
polymerase
mRNA synthesis begins
RNA polymerase moves down DNA;
mRNA elongates
mRNA synthesis is terminated
DNA
(a)
mRNA transcript
Coding strand
RNA polymerase
Unwinding
of DNA
Rewinding of DNA
Template strand
RNA
nucleotides
mRNA
RNA-DNA
hybrid region
(b)
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.34
Initiation of Translation

A leader sequence on mRNA attaches to the small
subunit of the ribosome

Methionine-charged initiator tRNA binds to the
small subunit

The large ribosomal unit now binds to this
complex forming a functional ribosome
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Amino acids
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
tRNA
Aminoacyl-tRNA
synthetase
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
Direction of
ribosome advance
Portion of mRNA
already translated
tRNA “head”
bearing
anticodon
Large
ribosomal
subunit
2
4
Once its amino acid is
released, tRNA is
ratcheted to the E site
and then released to
reenter the cytoplasmic
pool, ready to be
recharged with a new
amino acid.
3
As the ribosome
moves along the
mRNA, a new amino
acid is added to the
growing protein chain
and the tRNA in the A
site is translocated
to the P site.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Incoming aminoacyltRNA hydrogen bonds
via its anticodon to
complementary mRNA
sequence (codon) at
the A site on the
ribosome.
Energized by ATP,
the correct amino
acid is attached to
each species of tRNA
by aminoacyl-tRNA
synthetase enzyme.
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Released mRNA
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
Direction of
ribosome advance
Portion of mRNA
already translated
Large
ribosomal
subunit
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Amino acids
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
Aminoacyl-tRNA
synthetase
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
tRNA
Direction of
ribosome advance
Portion of mRNA
already translated
Large
ribosomal
subunit
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Energized by ATP,
the correct amino
acid is attached to
each species of tRNA
by aminoacyl-tRNA
synthetase enzyme.
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Amino acids
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
tRNA
Aminoacyl-tRNA
synthetase
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
Direction of
ribosome advance
Portion of mRNA
already translated
tRNA “head”
bearing
anticodon
Large
ribosomal
subunit
2
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Incoming aminoacyltRNA hydrogen bonds
via its anticodon to
complementary mRNA
sequence (codon) at
the A site on the
ribosome.
Energized by ATP,
the correct amino
acid is attached to
each species of tRNA
by aminoacyl-tRNA
synthetase enzyme.
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Amino acids
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
tRNA
Aminoacyl-tRNA
synthetase
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
Direction of
ribosome advance
Portion of mRNA
already translated
tRNA “head”
bearing
anticodon
Large
ribosomal
subunit
2
3
As the ribosome
moves along the
mRNA, a new amino
acid is added to the
growing protein chain
and the tRNA in the A
site is translocated
to the P site.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Incoming aminoacyltRNA hydrogen bonds
via its anticodon to
complementary mRNA
sequence (codon) at
the A site on the
ribosome.
Energized by ATP,
the correct amino
acid is attached to
each species of tRNA
by aminoacyl-tRNA
synthetase enzyme.
Figure 3.36
Nucleus
Nuclear membrane
RNA polymerase
Nuclear pore
mRNA
Template strand
of DNA
Amino acids
Released mRNA
1
After mRNA processing, mRNA
leaves nucleus and attaches to
ribosome, and translation begins.
tRNA
Aminoacyl-tRNA
synthetase
Small ribosomal
subunit
Codon 15 Codon 16 Codon 17
Direction of
ribosome advance
Portion of mRNA
already translated
tRNA “head”
bearing
anticodon
Large
ribosomal
subunit
2
4
Once its amino acid is
released, tRNA is
ratcheted to the E site
and then released to
reenter the cytoplasmic
pool, ready to be
recharged with a new
amino acid.
3
As the ribosome
moves along the
mRNA, a new amino
acid is added to the
growing protein chain
and the tRNA in the A
site is translocated
to the P site.
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Incoming aminoacyltRNA hydrogen bonds
via its anticodon to
complementary mRNA
sequence (codon) at
the A site on the
ribosome.
Energized by ATP,
the correct amino
acid is attached to
each species of tRNA
by aminoacyl-tRNA
synthetase enzyme.
Figure 3.36
Genetic Code

RNA codons code
for amino acids
according to a
genetic code
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.35
Information Transfer from DNA to RNA

DNA triplets are transcribed into mRNA codons
by RNA polymerase

Codons base pair with tRNA anticodons at the
ribosomes

Amino acids are peptide bonded at the ribosomes
to form polypeptide chains

Start and stop codons are used in initiating and
ending translation
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Information Transfer from DNA to RNA
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Figure 3.38
Other Roles of RNA



Antisense RNA – prevents protein-coding RNA
from being translated
MicroRNA – small RNAs that interfere with
mRNAs made by certain exons
Riboswitches – mRNAs that act as switches
regulating protein synthesis in response to
environmental conditions
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Cytosolic Protein Degradation

Nonfunctional organelle proteins are degraded by
lysosomes

Ubiquitin attaches to soluble proteins and they are
degraded in proteasomes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Extracellular Materials

Body fluids and cellular secretions

Extracellular matrix
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Developmental Aspects of Cells

All cells of the body contain the same DNA but
develop into all the specialized cells of the body

Cells in various parts of the embryo are exposed to
different chemical signals that channel them into
specific developmental pathways
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Developmental Aspects of Cells

Genes of specific cells are turned on or off (i.e., by
methylation of their DNA)

Cell specialization is determined by the kind of
proteins that are made in that cell
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings
Developmental Aspects of Cells

Development of specific and distinctive features in
cells is called cell differentiation

Cell aging

Wear and tear theory attributes aging to little
chemical insults and formation of free radicals that
have cumulative effects throughout life

Genetic theory attributes aging to cessation of
mitosis that is programmed into our genes
Copyright © 2006 Pearson Education, Inc., publishing as Benjamin Cummings