1. Translation is the process by which the genetic code stored in mRNA is used to direct the assembly of proteins from amino acids using ribosomes and tRNAs.
2. Initiation involves the assembly of the ribosome and initiation factors at the start codon on the mRNA. Elongation then adds amino acids one by one to the growing polypeptide chain through the actions of elongation factors.
3. Termination occurs when a stop codon is reached, releasing the completed protein and dissociating the ribosome into its subunits. The protein may then undergo further processing to become functional.
Protein synthesis and processing: Ribosome, formation of initiation complex, initiation factors and their regulation, elongation and elongation factors, termination, genetic code, aminoacylation of tRNA, tRNA-identity, aminoacyl tRNA synthetase, and translational proof-reading, translational inhibitors, Post Translational modification of proteins. Protein targeting.
It is the process of synthesis of protein by encoding information on mRNA.
Protein synthesis requires mRNA, tRNA, aminoacids, ribosome and enzyme aminoacyl tRNA synthase
description of translation in both prokaryotes and eukaryotes and the components required for translation and also co translation tranlocation,post translation translocation and also inhibitors of translation in both prokaryotes and eukaryotes
Protein synthesis and processing: Ribosome, formation of initiation complex, initiation factors and their regulation, elongation and elongation factors, termination, genetic code, aminoacylation of tRNA, tRNA-identity, aminoacyl tRNA synthetase, and translational proof-reading, translational inhibitors, Post Translational modification of proteins. Protein targeting.
It is the process of synthesis of protein by encoding information on mRNA.
Protein synthesis requires mRNA, tRNA, aminoacids, ribosome and enzyme aminoacyl tRNA synthase
description of translation in both prokaryotes and eukaryotes and the components required for translation and also co translation tranlocation,post translation translocation and also inhibitors of translation in both prokaryotes and eukaryotes
INTRODUCTION
HISTORY
MECHANISM OF PROTEIN SYNTHESIS
TRANSCRIPTION
TRANSLATION
TRANSCRIPTION
INITIATION
ELONGATION
TERMINATION
TRANSLATION
AMINOACYLATION OF tRNA
INITIATION OF POLYPEPTIDE CHAIN
ELONGATION
TERMINATION
CONCLUSION
REFERENCES
Introduction.
History.
Central dogma.
Mechanism of protein synthesis.
Transcription.
Process of transcription
translation
Step of translation
Activation of amino acid.
Transfer of amino acid to tRNA.
Initiation of polypeptide chain
Elongation of polypeptide chain
Translocation
Termination of polypeptide chain
processing of released polypeptide chain
Main difference between protein synthesis in prokaryotes and eukryotes
Conclusion
Reference
Prokaryotic translation machinery by kk KAUSHAL SAHU
Introduction
Definition
Factors required for Translation
Formation of aminoacyl t-RNA
1)Activation of amino acid
2) Transfer of amino acid to t-RNA
Translation involves following steps:-
1)Initiation
2)Elongation
3)Termination
Conclusion
Reference
Introduction
Definition
Factors required for Translation
Formation of aminoacyl t-RNA
1)Activation of amino acid
2) Transfer of amino acid to t-RNA
Translation involves following steps:-
1)Initiation
2)Elongation
3)Termination
Conclusion
Reference
Translation is the process by which cells make proteins. It involves three key factors: m RNA, t RNA and r RNA.
Elongation factors are required to add amino acids to polypeptide chain.
EF-Tu binds aminoacyl-tRNA to ribosome.
EF-G is required for translocation
Termination occurs at any one of the three special codons, UAA, UAG, and UGA.
Gene expression may be modulated at the level of translation
slide 2 central dogma
slide 3 key molecules used in translation
slide 4,5,6,7 all the key molcules with detail explanation
slide 8 phases of translation
slide 9 initiation and its process
slide 10 explanation initiation
slide 11 elongation and translocation
slide 12 process and steps of elongation and tRNA recharge in detail
slide 13 termination and its stages.
slide 14 diagrammatic representation of all the steps of termination with discrption
slide 15 thank you
Translation is the process of translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis. The genetic code describes the relationship between the sequence of base pairs in a gene and the corresponding amino acid sequence that it encodes.
This presentation includes process of protein synthesis for B.Sc. level. Presentation shows stepwise process for easy understanding.Many steps includes very simple non-grahical figures scanned from the book.
INTRODUCTION
HISTORY
MECHANISM OF PROTEIN SYNTHESIS
TRANSCRIPTION
TRANSLATION
TRANSCRIPTION
INITIATION
ELONGATION
TERMINATION
TRANSLATION
AMINOACYLATION OF tRNA
INITIATION OF POLYPEPTIDE CHAIN
ELONGATION
TERMINATION
CONCLUSION
REFERENCES
Introduction.
History.
Central dogma.
Mechanism of protein synthesis.
Transcription.
Process of transcription
translation
Step of translation
Activation of amino acid.
Transfer of amino acid to tRNA.
Initiation of polypeptide chain
Elongation of polypeptide chain
Translocation
Termination of polypeptide chain
processing of released polypeptide chain
Main difference between protein synthesis in prokaryotes and eukryotes
Conclusion
Reference
Prokaryotic translation machinery by kk KAUSHAL SAHU
Introduction
Definition
Factors required for Translation
Formation of aminoacyl t-RNA
1)Activation of amino acid
2) Transfer of amino acid to t-RNA
Translation involves following steps:-
1)Initiation
2)Elongation
3)Termination
Conclusion
Reference
Introduction
Definition
Factors required for Translation
Formation of aminoacyl t-RNA
1)Activation of amino acid
2) Transfer of amino acid to t-RNA
Translation involves following steps:-
1)Initiation
2)Elongation
3)Termination
Conclusion
Reference
Translation is the process by which cells make proteins. It involves three key factors: m RNA, t RNA and r RNA.
Elongation factors are required to add amino acids to polypeptide chain.
EF-Tu binds aminoacyl-tRNA to ribosome.
EF-G is required for translocation
Termination occurs at any one of the three special codons, UAA, UAG, and UGA.
Gene expression may be modulated at the level of translation
slide 2 central dogma
slide 3 key molecules used in translation
slide 4,5,6,7 all the key molcules with detail explanation
slide 8 phases of translation
slide 9 initiation and its process
slide 10 explanation initiation
slide 11 elongation and translocation
slide 12 process and steps of elongation and tRNA recharge in detail
slide 13 termination and its stages.
slide 14 diagrammatic representation of all the steps of termination with discrption
slide 15 thank you
Translation is the process of translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis. The genetic code describes the relationship between the sequence of base pairs in a gene and the corresponding amino acid sequence that it encodes.
This presentation includes process of protein synthesis for B.Sc. level. Presentation shows stepwise process for easy understanding.Many steps includes very simple non-grahical figures scanned from the book.
Professional air quality monitoring systems provide immediate, on-site data for analysis, compliance, and decision-making.
Monitor common gases, weather parameters, particulates.
Seminar of U.V. Spectroscopy by SAMIR PANDASAMIR PANDA
Spectroscopy is a branch of science dealing the study of interaction of electromagnetic radiation with matter.
Ultraviolet-visible spectroscopy refers to absorption spectroscopy or reflect spectroscopy in the UV-VIS spectral region.
Ultraviolet-visible spectroscopy is an analytical method that can measure the amount of light received by the analyte.
A brief information about the SCOP protein database used in bioinformatics.
The Structural Classification of Proteins (SCOP) database is a comprehensive and authoritative resource for the structural and evolutionary relationships of proteins. It provides a detailed and curated classification of protein structures, grouping them into families, superfamilies, and folds based on their structural and sequence similarities.
(May 29th, 2024) Advancements in Intravital Microscopy- Insights for Preclini...Scintica Instrumentation
Intravital microscopy (IVM) is a powerful tool utilized to study cellular behavior over time and space in vivo. Much of our understanding of cell biology has been accomplished using various in vitro and ex vivo methods; however, these studies do not necessarily reflect the natural dynamics of biological processes. Unlike traditional cell culture or fixed tissue imaging, IVM allows for the ultra-fast high-resolution imaging of cellular processes over time and space and were studied in its natural environment. Real-time visualization of biological processes in the context of an intact organism helps maintain physiological relevance and provide insights into the progression of disease, response to treatments or developmental processes.
In this webinar we give an overview of advanced applications of the IVM system in preclinical research. IVIM technology is a provider of all-in-one intravital microscopy systems and solutions optimized for in vivo imaging of live animal models at sub-micron resolution. The system’s unique features and user-friendly software enables researchers to probe fast dynamic biological processes such as immune cell tracking, cell-cell interaction as well as vascularization and tumor metastasis with exceptional detail. This webinar will also give an overview of IVM being utilized in drug development, offering a view into the intricate interaction between drugs/nanoparticles and tissues in vivo and allows for the evaluation of therapeutic intervention in a variety of tissues and organs. This interdisciplinary collaboration continues to drive the advancements of novel therapeutic strategies.
Observation of Io’s Resurfacing via Plume Deposition Using Ground-based Adapt...Sérgio Sacani
Since volcanic activity was first discovered on Io from Voyager images in 1979, changes
on Io’s surface have been monitored from both spacecraft and ground-based telescopes.
Here, we present the highest spatial resolution images of Io ever obtained from a groundbased telescope. These images, acquired by the SHARK-VIS instrument on the Large
Binocular Telescope, show evidence of a major resurfacing event on Io’s trailing hemisphere. When compared to the most recent spacecraft images, the SHARK-VIS images
show that a plume deposit from a powerful eruption at Pillan Patera has covered part
of the long-lived Pele plume deposit. Although this type of resurfacing event may be common on Io, few have been detected due to the rarity of spacecraft visits and the previously low spatial resolution available from Earth-based telescopes. The SHARK-VIS instrument ushers in a new era of high resolution imaging of Io’s surface using adaptive
optics at visible wavelengths.
Cancer cell metabolism: special Reference to Lactate PathwayAADYARAJPANDEY1
Normal Cell Metabolism:
Cellular respiration describes the series of steps that cells use to break down sugar and other chemicals to get the energy we need to function.
Energy is stored in the bonds of glucose and when glucose is broken down, much of that energy is released.
Cell utilize energy in the form of ATP.
The first step of respiration is called glycolysis. In a series of steps, glycolysis breaks glucose into two smaller molecules - a chemical called pyruvate. A small amount of ATP is formed during this process.
Most healthy cells continue the breakdown in a second process, called the Kreb's cycle. The Kreb's cycle allows cells to “burn” the pyruvates made in glycolysis to get more ATP.
The last step in the breakdown of glucose is called oxidative phosphorylation (Ox-Phos).
It takes place in specialized cell structures called mitochondria. This process produces a large amount of ATP. Importantly, cells need oxygen to complete oxidative phosphorylation.
If a cell completes only glycolysis, only 2 molecules of ATP are made per glucose. However, if the cell completes the entire respiration process (glycolysis - Kreb's - oxidative phosphorylation), about 36 molecules of ATP are created, giving it much more energy to use.
IN CANCER CELL:
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
Unlike healthy cells that "burn" the entire molecule of sugar to capture a large amount of energy as ATP, cancer cells are wasteful.
Cancer cells only partially break down sugar molecules. They overuse the first step of respiration, glycolysis. They frequently do not complete the second step, oxidative phosphorylation.
This results in only 2 molecules of ATP per each glucose molecule instead of the 36 or so ATPs healthy cells gain. As a result, cancer cells need to use a lot more sugar molecules to get enough energy to survive.
introduction to WARBERG PHENOMENA:
WARBURG EFFECT Usually, cancer cells are highly glycolytic (glucose addiction) and take up more glucose than do normal cells from outside.
Otto Heinrich Warburg (; 8 October 1883 – 1 August 1970) In 1931 was awarded the Nobel Prize in Physiology for his "discovery of the nature and mode of action of the respiratory enzyme.
WARNBURG EFFECT : cancer cells under aerobic (well-oxygenated) conditions to metabolize glucose to lactate (aerobic glycolysis) is known as the Warburg effect. Warburg made the observation that tumor slices consume glucose and secrete lactate at a higher rate than normal tissues.
Richard's entangled aventures in wonderlandRichard Gill
Since the loophole-free Bell experiments of 2020 and the Nobel prizes in physics of 2022, critics of Bell's work have retreated to the fortress of super-determinism. Now, super-determinism is a derogatory word - it just means "determinism". Palmer, Hance and Hossenfelder argue that quantum mechanics and determinism are not incompatible, using a sophisticated mathematical construction based on a subtle thinning of allowed states and measurements in quantum mechanics, such that what is left appears to make Bell's argument fail, without altering the empirical predictions of quantum mechanics. I think however that it is a smoke screen, and the slogan "lost in math" comes to my mind. I will discuss some other recent disproofs of Bell's theorem using the language of causality based on causal graphs. Causal thinking is also central to law and justice. I will mention surprising connections to my work on serial killer nurse cases, in particular the Dutch case of Lucia de Berk and the current UK case of Lucy Letby.
Introduction:
RNA interference (RNAi) or Post-Transcriptional Gene Silencing (PTGS) is an important biological process for modulating eukaryotic gene expression.
It is highly conserved process of posttranscriptional gene silencing by which double stranded RNA (dsRNA) causes sequence-specific degradation of mRNA sequences.
dsRNA-induced gene silencing (RNAi) is reported in a wide range of eukaryotes ranging from worms, insects, mammals and plants.
This process mediates resistance to both endogenous parasitic and exogenous pathogenic nucleic acids, and regulates the expression of protein-coding genes.
What are small ncRNAs?
micro RNA (miRNA)
short interfering RNA (siRNA)
Properties of small non-coding RNA:
Involved in silencing mRNA transcripts.
Called “small” because they are usually only about 21-24 nucleotides long.
Synthesized by first cutting up longer precursor sequences (like the 61nt one that Lee discovered).
Silence an mRNA by base pairing with some sequence on the mRNA.
Discovery of siRNA?
The first small RNA:
In 1993 Rosalind Lee (Victor Ambros lab) was studying a non- coding gene in C. elegans, lin-4, that was involved in silencing of another gene, lin-14, at the appropriate time in the
development of the worm C. elegans.
Two small transcripts of lin-4 (22nt and 61nt) were found to be complementary to a sequence in the 3' UTR of lin-14.
Because lin-4 encoded no protein, she deduced that it must be these transcripts that are causing the silencing by RNA-RNA interactions.
Types of RNAi ( non coding RNA)
MiRNA
Length (23-25 nt)
Trans acting
Binds with target MRNA in mismatch
Translation inhibition
Si RNA
Length 21 nt.
Cis acting
Bind with target Mrna in perfect complementary sequence
Piwi-RNA
Length ; 25 to 36 nt.
Expressed in Germ Cells
Regulates trnasposomes activity
MECHANISM OF RNAI:
First the double-stranded RNA teams up with a protein complex named Dicer, which cuts the long RNA into short pieces.
Then another protein complex called RISC (RNA-induced silencing complex) discards one of the two RNA strands.
The RISC-docked, single-stranded RNA then pairs with the homologous mRNA and destroys it.
THE RISC COMPLEX:
RISC is large(>500kD) RNA multi- protein Binding complex which triggers MRNA degradation in response to MRNA
Unwinding of double stranded Si RNA by ATP independent Helicase
Active component of RISC is Ago proteins( ENDONUCLEASE) which cleave target MRNA.
DICER: endonuclease (RNase Family III)
Argonaute: Central Component of the RNA-Induced Silencing Complex (RISC)
One strand of the dsRNA produced by Dicer is retained in the RISC complex in association with Argonaute
ARGONAUTE PROTEIN :
1.PAZ(PIWI/Argonaute/ Zwille)- Recognition of target MRNA
2.PIWI (p-element induced wimpy Testis)- breaks Phosphodiester bond of mRNA.)RNAse H activity.
MiRNA:
The Double-stranded RNAs are naturally produced in eukaryotic cells during development, and they have a key role in regulating gene expression .
2. From RNA to protein: translation
The genetic code
Three possible “reading frames”
THE ABC FOR THE DNA
THE AXB CFO RTH EDN A
THE ACF ORT HED NA
Insertion (X)
or
Deletion (B)
3. 3
Messenger RNA (mRNA)
methionine glycine serine isoleucine glycine alanine stop
codon
protein
A U G G G C U C C A U C G G C G C A U A A
mRNA
start
codon
Primary structure of a protein
aa1 aa2 aa3 aa4 aa5 aa6
peptide bonds
codon 2 codon 3 codon 4 codon 5 codon 6 codon 7
codon 1
copyright cmassengale
5. Ribosomes
• Ribosomes facilitate specific coupling of
tRNA anticodons with mRNA codons in
protein synthesis
• The two ribosomal subunits (large and
small) are made of proteins and
ribosomal RNA (rRNA)
• Bacterial and eukaryotic ribosomes are
somewhat similar but have significant
differences: some antibiotic drugs
specifically target bacterial ribosomes
without harming eukaryotic ribosomes
8. • A ribosome has three binding sites for tRNA
– The P site holds the tRNA that carries the
growing polypeptide chain
– The A site holds the tRNA that carries the next
amino acid to be added to the chain
– The E site is the exit site, where discharged
tRNAs leave the ribosome
9. Exit tunnel
A site (Aminoacyl-
tRNA binding site)
Small
subunit
Large
subunit
P A
P site (Peptidyl-tRNA
binding site)
mRNA
binding site
(b) Schematic model showing binding sites
E site
(Exit site)
E
10. Amino end
mRNA
E
(c) Schematic model with mRNA and tRNA
5 Codons
3
tRNA
Growing polypeptide
Next amino
acid to be
added to
polypeptide
chain
11. Factors Translation steps Functions
IF-1 Initiation Helps to stabilize 30S ribosomal subunit
IF-2 Initiation
Binds fmet-tRNA with 30S subunit
mRNA complex; bind GTP and
hydrolyse
IF-3 Initiation Binds 30S subunit with mRNA
EF-TU Elongation
Binds GTP; bring Aminoacyl-tRNA to A-
site of ribosome
EF-TS Elongation Generates EF-TU
EF-G Elongation Helps in translocation of ribosome
RF-1 Termination
Helps to dissociates polypeptide from
tRNA ribosome complex; specific for
UAA and UAG
RF-2 Termination
Helps to dissociates polypeptide;
specific for UGA and UAA
RF-3 Termination Stimulates RF-1 and RF-2
13. Chemistry of tRNA Charging with Amino Acid
1. Activation of aminoacids
14. Aminoacyl-tRNA
synthetase (enzyme)
Amino acid
P P P Adenosine
ATP
P
P
P
P
P
i
i
i
Adenosine
tRNA
Adenosine
P
tRNA
AMP
Computer model
Amino
acid
Aminoacyl-tRNA
synthetase
Aminoacyl tRNA
(“charged tRNA”)
Figure 17.16-4
15. 1. Activation of aminoacids
• The activation of aminoacids take place in cytosol.
• The activation of aminoacids is catalyzed by their aminoacyl tRNA
synthetases.
• All the 20 aminoacids are activated and bound to 3’ end of their
specific tRNA in the presence of ATP and Mg++.
• The N-formylated methionine is chain initiating aminoacid in bacteria
whereas methionine is chain initiating aminoacid in eukaryotes.
• Methionine is activated by methionyl-tRNA synthetase. For N-
formylmethionine two types of tRNA are used ie. tRNAmet and
tRNAfmet.
• Similarly, all 2o aminoacids are activated (amino acyl-AMP enzyme
complex) and then bound to their specific tRNA forming Aminoacyl
tRNA.
17. Translation Initiation Complex in Prokaryotes
Initiation factors deliver initiator fMet-tRNA to
mRNA initiation codon positioned at the “P” site
of the 30S ribosomal subunit.
Initiation codon is AUG preceded by “Shine-Delgarno
sequence that is recognized by the 16S rRNA in
the 30S ribosomal subunit.
18.
19.
20. 2. Initiation:
• In the first step, initiation factor-3 (IF-3) binds to 30S ribosomal unit.
• Then mRNA binds to 30S ribosomal subunit in such a way that AUG
codon lie on the peptidyl (P) site and the second codon lies on
aminoacyl (A) site.
• The tRNA carrying formylated methionine ie. FMet–tRNAFMet is
palced at P-site. This specificity is induced by IF-2 with utilization of
GTP. The IF-1 prevent binding of FMet–tRNAFMet is in A-site.
• Shinedalgrno sequence in the mRNA guide correct positioning of
AUG codon at P-site of 30S ribosome.
• After binding of FMet–tRNAFMet on P-site, IF-3, IF-2 and IF-1 are
released so that 50S ribosomal unit bind with 30S forming 70S
sibosome. The exit site is located in 50S.
22. • i. Binding of AA-tRNA at A-site:
• The 2nd tRNA carrying next aminoacid comes into A-site and recognizes the codon
on mRNA. This binding is facilitated by EF-TU and utilizes GTP.
• After binding, GTP is hydrolysed and EF-TU-GDP is releasd
• EF=TU-GDP then and enter into EF-TS cycle.
• ii. Peptide bond formation:
• The aminoacid present in t-RNA of P-site ie Fmet is transferred to t-RNA of A-site
forming peptide bond. This reaction is catalyzed by peptidyltransferase.
• Now, the t-RNA at P-site become uncharged
• iii. Ribosome translocation:
• After peptide bond formation ribosome moves one codon ahead along 5’-3’
direction on mRNA, so that dipeptide-tRNA appear on P-site and next codon
appear on A-site.
• The uncharged tRNA exit from ribosome and enter to cytosol.
• The ribosomal translocation requires EF-G-GTP (translocase enzyme) which
change the 3D structure of ribosome and catalyze 5’-3’ movement.
• The codon on A-site is now recognized by other aminoacyl-tRNA as in previous.
• The dipeptide on P-site is transferred to A-site forming tripeptide.
• This process continues giving long polypeptide chain of aminoacids.
3. Elongation:
24. 4. Termination:
• The peptide bond formation and elongation of
polypeptide continues until stop codon appear on A-site.
• If stop codon appear on A-site it is not recognized by t-
RNA carrying aminoacids because stop codon donot
have anticodon on mRNA.
• The stop codon are recognized by next protein called
release factor (Rf-1, RF-2 and RF-3) which hydrolyses
and cause release of all component ie 30s, 50S, mRNA
and polypeptide separates.
• RF-1 recognisaes UAA and UAg while RF-2 recognises
UAA and UGA while RF-3 dissociate 30S and 50S
subunits.
• In case of eukaryotes only one release actor eRF causes
dissociation.
26. Translation of the genetic code:
two adaptors that act one after another
27. mRNA translation mechanism
Step1: An aminoacyl-tRNA molecule binds to the A-site
on the ribosome
Step2: A new peptide bond is formed
Step3: The small subunit moves a distance of three
nucleotides along the mRNA chain ejecting the
spent tRNA molecule
Step4: The next aminoacyl-tRNA molecule binds to the A-site
on the ribosome
Step5: . . .
28. The initiation phase of protein synthesis in eukaryotes
1. Initiation complex (small ribosomal subunit + initiation factors)
binds DNA and searches for start codon
2. Large ribosomal subunit adds to the complex
3. Translation starts
4. . . .
29. The final phase of protein synthesis
binding of release factor to a stop codon terminates translation
the completed polypeptide is released
the ribosome dissociates into its two separate subunits
30. Ribosome Association and
Initiation of Translation
• The initiation stage of translation brings
together mRNA, a tRNA with the first amino
acid, and the two ribosomal subunits
• First, a small ribosomal subunit binds with
mRNA and a special initiator tRNA
• Then the small subunit moves along the
mRNA until it reaches the start codon (AUG)
• Proteins called initiation factors bring in the
large subunit that completes the translation
initiation complex
32. Elongation of the Polypeptide Chain
• During the elongation stage, amino acids
are added one by one to the preceding
amino acid at the C-terminus of the
growing chain
• Each addition involves proteins called
elongation factors and occurs in three
steps: codon recognition, peptide bond
formation, and translocation
• Translation proceeds along the mRNA in a
5′ to 3′ direction
42. Termination of Translation
• Termination occurs when a stop codon in
the mRNA reaches the A site of the
ribosome
• The A site accepts a protein called a
release factor
• The release factor causes the addition of a
water molecule instead of an amino acid
• This reaction releases the polypeptide,
and the translation assembly then comes
apart
48. Polyribosomes
• A number of ribosomes can translate a
single mRNA simultaneously, forming a
polyribosome (or polysome)
• Polyribosomes enable a cell to make many
copies of a polypeptide very quickly
53. Completing and Targeting the
Functional Protein
• Often translation is not sufficient to make a
functional protein
• Polypeptide chains are modified after
translation or targeted to specific sites in the
cell
54. Targeting Polypeptides to Specific
Locations
• Two populations of ribosomes are evident in
cells: free ribsomes (in the cytosol) and
bound ribosomes (attached to the ER)
• Free ribosomes mostly synthesize proteins
that function in the cytosol
• Bound ribosomes make proteins of the
endomembrane system and proteins that
are secreted from the cell
• Ribosomes are identical and can switch
from free to bound
