protein synthesis
is the process whereby biological cells generate new proteins
Protein synthesis
Protein synthesis involves two types of nucleic acids:
1. DNA (deoxyribonucleic acid)
2. RNA (ribonucleic acid)
The order of bases along the DNA strand codes for the order in which amino acids are chemically joined together to form a polypeptide
DNA (deoxyribonucleic acid)
like DNA, is a polymer formed by a sequence of nucleotides
RNA (ribonucleic acid)
Three Types of RNA:
a. messenger RNA (mRNA)
b. transfer RNA (tRNA)
c. ribosomal RNA (rRNA)
carries the genetic information copied from DNA in the form of a series of three-base code “words,” known as codon, each of which specifies a particular amino acid.
messenger RNA (mRNA)
messenger RNA (mRNA)
carries the genetic information copied from DNA in the form of a series of three-base code “words,” known as _____, each of which specifies a particular amino acid.
codon
Clover-leaf shape
Single stranded molecule with attachment site at one end for an amino acid and Opposite end has three nucleotide bases called the anticodon
is the “truck” delivering the proper amino acid to the ribosomes,
the site of protein synthesis
transfer RNA (tRNA)
transfer RNA (tRNA)
Single stranded molecule with attachment site at one end for an amino acid and Opposite end has three nucleotide bases called the _________
anticodon
is the “construction site” where the proteins are made
o Ribosomal RNA (rRNA) associates with a set of proteins to form ribosomes, the cell organelle for protein synthesis
These complex structures, which physically move along an mRNA molecule, catalyze the assembly of amino acids into protein chains. They also bind tRNAs and various accessory molecules necessary for protein synthesis. Ribosomes are composed of a large and small subunit, each of which contains its own rRNA molecule or molecules.
ribosomal RNA (rRNA)
Differences Between DNA and RNA
DNA
double-stranded
sugar = deoxyribose
bases = A,T,C,G
RNA
single-stranded
sugar = ribose
bases = A,U,C,G
(uracil takes the place of thymine)
Protein Synthesis involves 2 major stages
1. Transcription
2. Translation
the process by which the information in the DNA sequence (gene) is copied into the messenger RNA (mRNA), which leaves the cell nucleus and enters the cytoplasm, where it directs the synthesis of protein in the ribosomes.
➢ It occurs in the Cytoplasm of prokaryotes
➢ It occurs in the Nucleus of eukaryotes
Transcription
Transcription
➢ the process by which the information in the DNA sequence (gene) is copied into the messenger RNA (mRNA), which leaves the cell nucleus and enters the cytoplasm, where it directs the synthesis of protein in the ribosomes.
➢ It occurs in the _______ of prokaryotes
➢ It occurs in the _______ of eukaryotes
-Cytoplasm
-Nucleus
the process of translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis. In the cell cytoplasm, the ribosome reads the sequence of the mRNA in groups of three bases (codon) to assemble the protein.
➢ It occurs in the Cytoplasm of both prokaryotes and eukaryotes
Translation
Translation
➢ the process of translating the sequence of a messenger RNA (mRNA) molecule to a sequence of amino acids during protein synthesis. In the cell cytoplasm, the ribosome reads
the sequence of the mRNA in groups of three bases (codon) to assemble the protein.
➢ It occurs in the Cytoplasm of both _______ and ________
prokaryotes and eukaryotes
Translation
➢ the process of translating the sequence of a messenger RNA (mRNA) molecule to a
sequence of amino acids during protein synthesis. In the cell cytoplasm, the ribosome reads
the sequence of the mRNA in groups of three bases (codon) to assemble the protein.
➢ It occurs in the ________ of both prokaryotes and eukaryotes
Cytoplasm
Transcription
Stage 1: __________
✓ RNA polymerase binds to a region on DNA known as the promoterwhich signals the
start of a gene
✓ Promoters signal the initiation of RNA synthesis. A crucial promoter DNA sequence is
called a TATA box.
✓ Transcription factors help eukaryotic RNA polymerase recognize promoter sequences
✓ Transcription factors assemble at the promoter forming a transcription initiation
complex. The activator proteins help stabilize the complex
✓ ATP is also needed for transcription to begin
✓ Gene expression can be regulated (turned on/off or up/down) by controlling the
amount of each transcription factor
Initiation
Stage 1: Initiation
✓ RNA polymerase binds to a region on DNA known as the _______ which signals the start of a gene
✓ Promoters signal the initiation of RNA synthesis. A crucial promoter DNA sequence is called a _________.
✓ _____________ help eukaryotic RNA polymerase recognize promoter sequences
✓ Transcription factors assemble at the promoter forming a ___________. The activator proteins help stabilize the complex
✓ ____ is also needed for transcription to begin
✓ _________ can be regulated (turned on/off or up/down) by controlling the amount of each transcription factor
-promoter
-TATA box
-Transcription factors
-transcription initiation complex
-ATP
-Gene expression
Transcription
Stage 2: _________
✓ RNA polymerase unwinds the DNA and breaks the H-bonds between the bases of the two strands, separating them from one another
✓ The RNA polymerase uses only one of the strands of DNA as a template for mRNA synthesis. This is called the template strand or sense strand. The coding strandor anti-sense strand contains the complementary nucleotide sequence to the sense strand.
✓ RNA polymerases can add nucleotides only to the 3’ end of a DNA sequence. Thus, an RNA molecule elongates in the 5’ to 3’ direction.
✓ As RNA polymerase moves along the DNA it continues to untwist the double helix, exposing about 10 to 20 DNA bases at a time for pairing with RNA nucleotides
✓ Base pairing occurs between incoming RNA nucleotides and the DNA nucleotides of the gene (template)
• recall RNA uses uracil instead of thymine
✓ RNA polymerase catalyzes bond to form between ribose of 3’ nucleotide of RNA and phosphate of incoming RNA nucleotide
✓ The gene occurs on only one of the DNA strands; each strand possesses a separate set of genes
Elongation
Transcription
Stage 2: Elongation
✓ __________ unwinds the DNA and breaks the H-bonds between the bases of the two strands, separating them from one another
✓ The RNA polymerase uses only one of the strands of DNA as a template for mRNA
synthesis. This is called the ________ or ________. The _______or ________ contains the complementary nucleotide sequence to the sense strand.
✓ RNA polymerases can add nucleotides only to the 3’ end of a DNA sequence. Thus, an ______________________________.
✓ As RNA polymerase moves along the DNA it continues to untwist the double helix, exposing about 10 to 20 DNA bases at a time for pairing with RNA nucleotides
✓ Base pairing occurs between incoming RNA nucleotides and the DNA nucleotides of the
gene (template)
• recall RNA uses uracil instead of thymine
✓ RNA polymerase catalyzes bond to form between ribose of 3’ nucleotide of RNA and phosphate of incoming RNA nucleotide
✓ The gene occurs on only one of the DNA strands; each strand possesses a separate set of genes
-RNA polymerase
-template strand or sense strand
coding strand or anti-sense strand
-RNA molecule elongates in the 5’ to 3’ direction
Transcription
Stage 3: ________
✓ A region on DNA known as the terminator signals the stop of a gene
✓ When one of these is encountered by the polymerase, the RNA transcript is released from the DNA and the double helix can zip up again.
✓ RNA polymerase disengages the mRNA and the DNA
Termination
Transcription
Stage 3: Termination
✓ A region on DNA known as the ______ signals the stop of a gene
✓ When one of these is encountered by the polymerase, the RNA transcript is released
from the DNA and the double helix can zip up again.
✓ ____________ disengages the mRNA and the DNA
-terminator
-RNA polymerase
Transcription
Stage 4: ________________________________ (___________)
✓ After the DNA is transcribed into RNA in eukaryotic cell, editing must be done to the nucleotide chain (pre-mRNA) to make it functional by the following processes:
1. RNA splicing removes introns and joins exons
-Introns(non-functional segments of DNA) are snipped out or cut out of the chainby Ribozymes or Spliceosomes
-Exons (segments of DNA that code for proteins) are then rejoined by the enzyme ligase
2. A modified nucleotide cap (guanine triphosphate cap)is added to the 5” end of the newly copied mRNA
3. A poly A tail is added to the 3’ end of the RNA
The newly processed mRNA can then leave from the nucleus to the cytoplasm for protein translation
Post-transcriptional Modification(eukaryotes only)
Transcription
Stage 4: Post-transcriptional Modification(eukaryotes only)
✓ After the DNA is transcribed into RNA in eukaryotic cell, editing must be done to the nucleotide chain (______) to make it functional by the following processes:
1. __________ removes introns and joins exons
- ______ (non-functional segments of DNA) are snipped out or cut out of the chainby _________ or _________
- ________(segments of DNA that code for proteins) are then rejoined by the enzyme _______
2. A _____________ (___________)is added to the 5” end of the newly copied mRNA
3. A _________ is added to the 3’ end of the RNA
The newly processed _______ can then leave from the nucleus to the cytoplasm for protein translation
-(pre-mRNA)
-RNA splicing
-Introns Ribozymes or Spliceosomes
-Exons ligase
-modified nucleotide cap (guanine triphosphate cap)
-poly A tail
-mRNA
Translation
➢ After transcription mRNA exits the nucleus via nuclear pores and ribosomes bind to mRNA
➢ Ribosomes synthesize different proteins by reading the coding sequence on mRNA
➢ The mRNA is read in triplets of nucleotides each of which encodes an amino acid
-Every three mRNA nucleotides (_____) specify an amino acid
➢ The correct amino acids must be delivered to the polypeptide building site by _____
-tRNA has an ______ region that specifically binds to its codon
-Each tRNA carries a specific amino acid
➢ _______________ attaches amino acids to their specific tRNA
➢ Each active ribosome has 3 different binding sites for tRNA molecules: the __(____)____, which holds one aa-tRNA and the growing chain of amino acids; the ___ (_____)____, which holds the tRNA bringing the next amino acid to be added to the chain; and the ___ (____)____, which releases the tRNA molecules back into the cytoplasm.
-(codon)
-tRNA
-anti-codon
-AminoacyltRNAsynthetase
-P (peptide) site
-A (acceptor) site
-E (exit) site
Name the amino acid?
UUG?
GCA?
Ans. Leucine
Ans. Alanine
Translation
Stage 1: Initiation
✓ mRNA binds to a ribosome, and the transfer RNA corresponding to the START codon (____) binds to this complex. Ribosomes are composed of 2 subunits (large and small), which come together when the messenger RNA attaches during the initiation processThe initiation stage
of translation brings together mRNA, tRNA bearing the first amino acid of the polypeptide, and two subunits of a ribosome
✓ Start codon (AUG) signals where the gene begins (at 5’ end of mRNA)
✓ ________________ (____________) upstream from the start codon binds to small ribosomal subunit
• then this complex recruits the large ribosomal subunit
✓ The ribosome moves in __________ “reading” the mRNA and assembling amino acids into the correct protein
-(AUG)
-Ribosome binding site(Shine Dalgarno sequence)
-5’ to 3’ direction
Translation
Stage 2: ________
✓ In the elongation stage, amino acids are added one by one to the preceding amino acid
✓ As ribosome moves, two tRNA with their amino acids move into site A and P of the ribosome
✓ Peptide bonds join the amino acids
Elongation
Translation
Stage 3: Termination
✓ Ribosome disengages from the mRNA when it encounters a stop codon (___,____,____)
-When the ribosome reaches a STOP codon(UAA, UAG, UGA), there is no corresponding transfer RNA.
-Instead, a small protein called a “_______” attaches to the stop codon.
-The release factor causes the whole complex to fall apart: messenger RNA, the two ribosome subunits, the new polypeptide.
➢ The messenger RNA can be translated many times, to produce many protein copies
➢ Multiple RNA polymerases can engage a gene at one time
➢ Multiple ribosomes (___________) can engage a single mRNA at one time
➢ Polyribosomes enable a cell to make many copies of a polypeptide very quickly
-(UAA, UAG, UGA)
-“release factor”
- (Polyribosomes)
Comparing Gene Expression In Prokaryotes And Eukaryotes
• In a eukaryotic cell:
• The nuclear envelope separates transcription from translation; hence transcription occurs in the ______ and translation occurs in the ________
• Extensive RNA processing occurs in the nucleus
• Prokaryotic cells lack a ____________, allowing translation to begin while transcription progresses; hence, transcription and translation occurs _______________________
-nucleus
-cytoplasm
-nuclear envelope
-simultaneously in the cytoplasm