17 CAMPBLL BIOLOGY TNTH DITION Reece Urry Cain Wasserman Minorsky Jackson Gene to Protein Gene xpression The process in which the information coded in is used to make proteins A gene is the part of the molecule that codes for a specific protein Lecture Presentation by Dr Burns NVC Biol 120 Gene expression, the process by which directs protein synthesis, includes two stages: transcription and translation Copyright 2014 Pearson 2009 ducation, Pearson ducation, Inc. Inc. Figure 17.1 Protein Synthesis Overview Remember back to the lecture on the cell we briefly went through the steps of protein synthesis 1
What structure assembles the polypeptide chains? 1. Nucleus 2. Rough ndoplasmic reticulum 3. Ribosomes 4. Lysosomes Nucleus 25% 25% 25% 25% Rough ndoplasmic... Ribosomes Lysosomes The Nature of Genes The central dogma of molecular biology states that information flows in one direction: RNA protein Transcription is the flow of information from to RNA. Translation is the flow of information from RNA to protein. 1.Transcription: unwinds and nucleotides form base pairs to produce a single strand of 2. leaves nucleus 3. Translation: docks with ribosomes. trna brings amino acids to the ribosome to be assembled into polypeptide RNA During the transcription: part of is copied to make is only a single strand remember that is two strands. RNA has same handrail structure with the phosphates covalently bound to the sugars. The sugars are bound covalently to bases 2
Differences between RNA and 1. RNA is single stranded, is double stranded 2. The sugar is different = ribose 3. RNA has four bases, but one base is different from : CGAU, the U is uracil During transcription uracil is paired with adenine Types of RNA There are different types of RNA: Messenger RNA () single strand, carries information for making a protein from the nucleus to the cytosol Transfer RNA (trna) single strand, folds back on itself. ach trna carries one specific amino acid and brings it to the ribosome Ribosomal RNA (rrna) globular structure, forms the catalytic part of ribosomes. Catalyzes the formation of the peptide bonds between amino acids Types of RNA volution of the Genetic Code There are different types of RNA: small nuclear RNA (snrna) are involved in processing pre-, involved in splicing signal recognition particle (SRP) is composed of protein and RNA and involved in directing ribosome to the RR micro-rna (mirna) are very small and their role is not clear yet, control gene expression, protect cells from viral attack The genetic code is nearly universal, shared by the simplest bacteria to the most complex animals Genes can be transcribed and translated after being transplanted from one species to another Figure 17.6 Figure 17.4 template strand A C C A A A C C G A G T molecule T G G T T T G G C T C A TRANSCRIPTION U G G U U U G G C U C A Codon TRANSLATION Gene 1 Gene 2 (a) Tobacco plant expressing a firefly gene (b) Pig expressing a jellyfish gene Protein Trp Phe Gly Amino acid Ser Gene 3 3
Molecular Components of Transcription Coding strand Transcription RNA synthesis is catalyzed by RNA polymerase, which pries the strands apart and hooks together the RNA nucleotides (complementary copy of template strand) Polypeptide Codon 1 Codon 2 Codon 3 Codon 4 Codon 5 Codon 6 Translation Template strand The RNA is complementary to the template strand RNA synthesis follows the same base-pairing rules as, except that uracil substitutes for thymine Transcription The sequence where RNA polymerase attaches is called the promoter The stretch of that is transcribed is called a transcription unit Transcription RNA polymerase act in a similar manner as polymerase Build the RNA molecule from 5 end of the RNA to the 3 end Nucleotides are added to build the complementary RNA strand, use the hydrolysis of phosphates to provide the energy to build the new strand RNA is antiparallel to Transcription Figure 17.7-1 Promoter Transcription unit Start point RNA polymerase Upstream Template strand: 3 -A-C-C-A-5 Coding strand: 5 -T-G-G-T-3 RNA 5 -U-G-G-U-3 Downstream 4
Figure 17.7-2 Promoter Transcription unit Figure 17.7-3 Promoter Transcription unit Start point RNA polymerase 1 Initiation Start point RNA polymerase 1 Initiation Unwound Coding (Nontemplate) strand of Template strand of RNA transcript Unwound Rewound RNA transcript Coding (Nontemplate) strand of Template strand of RNA transcript 2 longation Figure 17.7-4 Promoter Transcription unit Start point RNA polymerase 1 Initiation Unwound Rewound RNA transcript Nontemplate strand of Template strand of RNA transcript 2 longation 3 Termination Completed RNA transcript Direction of transcription ( downstream ) Which strand is copied to make RNA? 1. Coding 2. Template 50% 50% Animation: Transcription Right-click slide / select Play 1 2 Copyright 2009 Pearson ducation, Inc. 5
Transcription http://vcell.ndsu.nodak.edu/animations/tran scription/index.htm Transcription RNA polymerase binds to a promoter region of the = initiation stage The RNA polymerase acts to bind nucleotides bound together to form the complementary RNA strand = elongation stage The RNA polymerase continues to add nucleotides until it comes to a stop signal, a set of three nucleotides on the that signals the end = termination stage Copyright 2009 Pearson ducation, Inc. RNA Polymerase Binding and Initiation of Transcription Promoters signal the transcriptional start point and usually extend several dozen nucleotide pairs upstream of the start point Transcription factors mediate the binding of RNA polymerase and the initiation of transcription The completed assembly of transcription factors and RNA polymerase II bound to a promoter is called a transcription initiation complex A promoter called a TATA box is crucial in forming the initiation complex in eukaryotes Figure 17.8 TA A T TATA box Transcription factors RNA polymerase II T A A A A A T T T T Promoter 1 A eukaryotic promoter Start point Nontemplate strand 2 Several transcription factors bind to 3 Transcription initiation complex forms Template strand Transcription factors RNA transcript Transcription initiation complex longation of the RNA Strand Figure 17.9 Nontemplate strand of RNA nucleotides As RNA polymerase moves along the, it untwists the double helix, 10 to 20 bases at a time RNA polymerase C A T C C A A end Transcription progresses at a rate of 40 nucleotides per second in eukaryotes C A U C C A T A G G T T Nucleotides are added to the end of the growing RNA molecule Direction of transcription Template strand of Newly made RNA 6
If the sequence was 3 -ATCG-5 then the complementary sequence would be: 1. 3 -TAGC-5 2. 5 -TACG-3 3. 3 -UAGC-5 4. 5 -UAGC-3 25% 25% 25% 25% Termination of Transcription The mechanisms of termination are different in bacteria and eukaryotes In bacteria, the polymerase stops transcription at the end of the terminator and the can be translated without further modification 1 2 3 4 In eukaryotes, RNA polymerase II transcribes the polyadenylation signal sequence; the RNA transcript is released 10 35 nucleotides past this polyadenylation sequence Figure 17.10 Protein synthesis in Prokaryotes In bacteria the transcription and translation steps are coupled G P P P Cap UTR Protein-coding segment Start codon codon Polyadenylation signal AAUAAA UTR AAA AAA Poly-A tail Remember that there is no nucleus so the does not leave the nucleus to go to the cytosol to bind with the ribosomes The bacterial is not modified after it is transcribed, it is used immediately after transcription Figure 17.3 ukaryotic cells modify RNA after transcription TRANSCRIPTION TRANSLATION (a) Bacterial cell Polypeptide Ribosome TRANSCRIPTION RNA PROCSSING TRANSLATION (b) ukaryotic cell Pre- Ribosome Polypeptide Nuclear envelope nzymes in the eukaryotic nucleus modify pre (RNA processing) before the genetic messages are dispatched to the cytoplasm During RNA processing, both ends of the primary transcript are usually altered Also, usually some interior parts of the molecule are cut out, and the other parts spliced together 7
Post transcriptional modifications of ach end of a pre- molecule is modified in a particular way The end receives a modified nucleotide cap The end gets a poly-a tail These modifications share several functions They seem to facilitate the export of to the cytoplasm They protect from hydrolytic enzymes They help ribosomes attach to the end Figure 17.10 Post transcriptional modification - RNA Splicing G P P P Cap UTR Protein-coding segment Start codon codon Polyadenylation signal AAUAAA UTR AAA AAA Poly-A tail The contains regions that do not code for amino acids that are found between coding regions Areas of the gene that are noncoding = introns Coding areas of the gene = exons RNA splicing removes introns and joins exons, creating an molecule with a continuous coding sequence Figure 17.11 Pre- Codon numbers xon Intron xon Cap 1 30 31 104 Intron Introns cut out and exons spliced together xon Poly-A tail 10 146 Cap UTR 1 146 Coding segment Poly-A tail UTR 8
The Functional and volutionary Importance of Introns Fig. 16.17 Some introns contain sequences that may regulate gene expression Some genes can encode more than one kind of polypeptide, depending on which segments are treated as exons during splicing This is called alternative RNA splicing Consequently, the number of different proteins an organism can produce is much greater than its number of genes RNA splicing In some cases, RNA splicing is carried out by spliceosomes Spliceosomes consist of a variety of proteins and small nuclear RNA (snrna) 9
Ribozymes Ribozymes are catalytic RNA molecules that function as enzymes and can splice RNA The discovery of ribozymes rendered obsolete the belief that all biological catalysts were proteins modifications http://vcell.ndsu.nodak.edu/animations/mrn aprocessing/index.htm Translation is the RNA-directed synthesis of a polypeptide: a closer look Genetic information flows from to protein through the process of translation Copyright 2009 Pearson ducation, Inc. Translation Codons http://vcell.ndsu.nodak.edu/animations/tran slation/index.htm Three bases code for one amino acid The three bases together are called a codon So when CCU are next to each other as a codon then that will be read as proline 10
First base ( end of codon) Third base ( end of codon) Figure 17.5 Second base U C A G UUU UCU UAU UGU U Phe Tyr Cys UUC U UCC Ser UAC UGC C UUA UCA Leu UAA UGA A UUG UCG UAG UGG Trp G CUU CUC C CUA CUG CCU CCC Leu CCA CCG CAU CAC Pro CAA CAG CGU His CGC CGA Gln CGG U C Arg A G AUU ACU AAU AGU Asn AUC A Ile ACC AAC Thr AGC AUA ACA AAA AGA Lys AUG Met or start ACG AAG AGG U Ser C A Arg G GUU GUC G GUA GUG Val GCU GCC GCA GCG GAU GAC Ala GAA GAG GGU Asp GGC GGA Glu GGG U C Gly A G Molecular Components of Translation A cell translates an message into protein with the help of transfer RNA (trna) trnas transfer amino acids to the growing polypeptide in a ribosome trna codes for which amino acids go in what order, also copied to make trna trna (transfer RNA) brings the amino acids to the ribosomes One side of trna attaches to an amino acid, the other side will attach to the trna Figure 17.14 ach trna is covalently bound to an amino acid trna molecules have an anticodon region = complementary to the region Polypeptide Ribosome Amino acids trna with amino acid attached trna C G Anticodon U G G U U U G G C Codons 11
The Structure and Function of Transfer RNA Molecules of trna are not identical ach carries a specific amino acid on one end ach has an anticodon on the other end; the anticodon base-pairs with a complementary codon on BioFlix: Protein Synthesis The Structure and Function of Transfer RNA A trna molecule consists of a single RNA strand that is only about 80 nucleotides long Figure 17.15 Amino acid attachment site Amino acid attachment site Hydrogen bonds Hydrogen bonds Anticodon (a) Two-dimensional structure Anticodon (b) Three-dimensional structure A A G Anticodon (c) Symbol used in this book The Structure and Function of Transfer RNA Because of hydrogen bonds, trna actually twists and folds into a three-dimensional molecule trna is roughly L-shaped Translation Accurate translation requires two steps First: a correct match between a trna and an amino acid, done by the enzyme aminoacyltrna synthetase Second: a correct match between the trna anticodon and an codon 12
Translation Figure 17.16-1 Aminoacyl-tRNA synthetase (enzyme) Amino acid Flexible pairing at the third base of a codon is called wobble and allows some trnas to bind to more than one codon P P P Adenosine ATP Figure 17.16-2 Aminoacyl-tRNA synthetase (enzyme) Figure 17.16-3 Aminoacyl-tRNA synthetase (enzyme) Amino acid Amino acid P Adenosine P Adenosine P P P Adenosine ATP P P i P i P i P P P Adenosine ATP P P i P i P i trna Aminoacyl-tRNA synthetase trna Amino acid P Adenosine AMP Computer model Figure 17.16-4 Aminoacyl-tRNA synthetase (enzyme) Ribosomes Amino acid P P P Adenosine ATP P Adenosine P P i P i P i trna Aminoacyl-tRNA synthetase Ribosomes facilitate specific coupling of trna anticodons with codons in protein synthesis trna P Adenosine Amino acid The two ribosomal subunits (large and small) are made of proteins and ribosomal RNA (rrna) AMP Computer model Aminoacyl trna ( charged trna ) 13
Ribosomes Bacterial and eukaryotic ribosomes are somewhat similar but have significant differences Some antibiotic drugs specifically target bacterial ribosomes without harming eukaryotic ribosomes Figure 17.17a trna molecules Growing polypeptide P A xit tunnel Large subunit Small subunit (a) Computer model of functioning ribosome Figure 17.17b Figure 17.17c P site (Peptidyl-tRNA binding site) site (xit site) xit tunnel A site (AminoacyltRNA binding site) Amino end Growing polypeptide Next amino acid to be added to polypeptide chain P A Large subunit trna binding site Small subunit Codons (b) Schematic model showing binding sites (c) Schematic model with and trna Ribosomes Building a Polypeptide 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 site is the exit site, where discharged trnas leave the ribosome The three stages of translation Initiation longation Termination All three stages require protein factors that aid in the translation process 14
Ribosome Association and Initiation of Translation The initiation stage of translation brings together, a trna with the first amino acid, and the two ribosomal subunits Ribosome Association and Initiation of Translation First, a small ribosomal subunit binds with and a special initiator trna (carrying the amino acid methionine) Then the small subunit moves along the until it reaches the start codon (AUG) Proteins called initiation factors bring in the large subunit that completes the translation initiation complex Figure 17.18 longation of the Polypeptide Chain Initiator trna Start codon binding site U A C A U G GTP Small ribosomal subunit P i GDP P site A Large ribosomal subunit Translation initiation complex During the elongation stage, amino acids are added one by one to the preceding amino acid at the C-terminus of the growing chain ach addition involves proteins called elongation factors and occurs in three steps: codon recognition, peptide bond formation, and translocation Translation proceeds along the in a 5 to 3 direction Figure 17.19-1 Amino end of polypeptide Figure 17.19-2 Amino end of polypeptide P site A site P site A site GTP GDP P i P A 15
Figure 17.19-3 Amino end of polypeptide Figure 17.19-4 Amino end of polypeptide P site A site GTP Ribosome ready for next aminoacyl trna P site A site GTP GDP P i GDP P i P A P A P A GDP P i GTP P A P A Protein Synthesis Fig. 15.18 Protein synthesis proceeds from the N- terminus to the C-terminus of the protein. The ribosomes "read" the in the 5' to 3' direction. https://www.rpi.edu/dept/bcbp/molbiochem /MBWeb/mb2/part1/translate.htm http://cen.acs.org/articles/85/i8/protein- Factory-Reveals-Secrets.html Created by Dr. Joachim Frank 16
Termination of Translation Termination occurs when a stop codon in the 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 Animation: Translation Right-click slide / select Play Figure 17.20-1 Figure 17.20-2 Release factor Release factor Free polypeptide 2 GTP codon (UAG, UAA, or UGA) codon (UAG, UAA, or UGA) 2 GDP 2 P i Figure 17.20-3 Initiation Release factor codon (UAG, UAA, or UGA) Free polypeptide 2 GTP 2 GDP 2 P i 1. The binds with the small subunit of the ribosome 2. The beginning of the coding region of is AUG 3. The trna with the anticodon UAC has methionine attached to it. 4. The trna with met attached binds to the P site of the ribosomes. 5. This requires energy in the form of GTP 6. Large subunit joins the small subunit 17
longation This is the stage where amino acids are added to the growing polypeptide chain 7. A trna with the next amino acid comes into the A site, requires GTP for energy 8. The amino acids are bound by a peptide bond 9. The bond is between the carboxyl end of the P site amino acid and the amino side of the A amino acid longation 10. The now ribosome moves so the free trna is at the site and the trna with the polypeptide chain moves is at the P site = translocation 11. This requires GTP 12. The free trna exits the ribosome Termination 13. The end of the coding region will have a stop codon that signals the end of the polypeptide chain 14. No trna binds to this codon, instead a release factor binds, requires GTP for energy What molecules are produced in transcription? 1. Amino acids 2. Proteins 3. RNA 4. 25% 25% 25% 25% 15. The polypeptide chain is released Amino acids Proteins RNA Polyribosomes Figure 17.21 Growing polypeptides Completed polypeptide A number of ribosomes can translate a single simultaneously, forming a polyribosome (or polysome) Incoming ribosomal subunits (a) Start of ( end) nd of ( end) Polyribosomes enable a cell to make many copies of a polypeptide very quickly Ribosomes (b) 0.1 m 18
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 Protein Folding and Post-Translational Modifications During and after synthesis, a polypeptide chain spontaneously coils and folds into its threedimensional shape Proteins may also require post-translational modifications before doing their job Some polypeptides are activated by enzymes that cleave them Other polypeptides come together to form the subunits of a protein Post-translational Modifications Folding, either spontaneously or with the aid of chaperone proteins Proteolysis some polypeptide chains are cut into smaller chains Glycosylation sugars are added to some proteins, some of these sugar chains are important to address the protein Phosphorylation Protein Kinases phosphorylate proteins to activate them Methionine is often removed Targeting Polypeptides to Specific Locations Two populations of ribosomes are evident in cells: free ribsomes (in the cytosol) and bound ribosomes (attached to the R) 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 Targeting Polypeptides to Specific Locations Polypeptide synthesis always begins in the cytosol Synthesis finishes in the cytosol unless the polypeptide signals the ribosome to attach to the R Polypeptides destined for the R or for secretion are marked by a signal peptide Targeting Polypeptide Chains Polypeptide chains that need to be brought into the RR will start (after MT) with a short sequence of amino acids = signal sequence signal recognition particles (SRPs), in the cytoplasm recognize this sequence during translation and bind to the amino acid sequence. 19
Targeting Polypeptides to Specific Locations A signal-recognition particle (SRP) binds to the signal peptide The SRP brings the signal peptide and its ribosome to the R Signal recognition particle (SRP) is composed of protein and RNA Targeting Polypeptide Chains The signal sequence and SRP complex binds to a receptor on the RR membrane The complex docks with the RR As the polypeptide chain is built, the chain is brought into the RR Once inside the RR the polypeptide chain can be folded, modified Then the protein is transported via a vesicle to the Golgi Figure 17.22 Mutations of one or a few nucleotides can affect protein structure and function 1 SRP R LUMN Ribosome Signal peptide 2 SRP receptor protein Translocation complex 3 4 Signal peptide removed 5 R membrane Protein 6 CYTOSOL Mutations are changes in the genetic material of a cell or virus Point mutations are chemical changes in just one base pair of a gene The change of a single nucleotide in a template strand can lead to the production of an abnormal protein Figure 17.23 Types of Small-Scale Mutations Wild-type hemoglobin Wild-type hemoglobin C T T G A A G A A Sickle-cell hemoglobin Mutant hemoglobin C A T G T A G U A Point mutations within a gene can be divided into two general categories Nucleotide-pair substitutions One or more nucleotide-pair insertions or deletions Normal hemoglobin Glu Sickle-cell hemoglobin Val 20
Substitutions A nucleotide-pair substitution replaces one nucleotide and its partner with another pair of nucleotides Silent mutations have no effect on the amino acid produced by a codon because of redundancy in the genetic code Missense mutations still code for an amino acid, but not the correct amino acid Nonsense mutations change an amino acid codon into a stop codon, nearly always leading to a nonfunctional protein Figure 17.24 Wild type template strand T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A A U G A A G U U U G G C U A A Protein Met Lys Phe Gly Amino end Carboxyl end (a) Nucleotide-pair substitution (b) Nucleotide-pair insertion or deletion A instead of G xtra A T A C T T C A A A C C A A T T T A C A T T C A A A C C G A T T A T G A A G T T T G G T T A A A T G T A A G T T T G G C T A A U instead of C xtra U A U G A A G U U U G G U U A A A U G U A A G U U U G G C U A A Met Lys Phe Gly Met Silent (no effect on amino acid sequence) Frameshift causing immediate nonsense (1 nucleotide-pair insertion) T instead of C A missing T A C T T C A A A T C G A T T T A C T T C A A C C G A T T T A T G A A G T T T A G C T A A A T G A A G T T G G C T A A A A instead of G U missing A U G A A G U U U A G C U A A A U G A A G U U G G C U A A Met Lys Phe Ser Met Lys Leu Ala Missense Frameshift causing extensive missense (1 nucleotide-pair deletion) A instead of T T T C missing T A C A T C A A A C C G A T T T A C A A A C C G A T T A T G T A G T T T G G C T A A A T G T T T G G C T A A U instead of A A A G missing A U G U A G U U U G G C U A A A U G U U U G G C U A A U A A Met Met Phe Gly Nonsense No frameshift, but one amino acid missing (3 nucleotide-pair deletion) Figure 17.24a Figure 17.24b Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly (a) Nucleotide-pair substitution: silent Met Lys Phe Gly A instead of G T A C T T C A A A C C A A T T A T G A A G T T T G G T T A A U instead of C A U G A A G U U U G G U U A A Carboxyl end Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly (a) Nucleotide-pair substitution: missense T instead of C T A C T T C A A A T C G A T T A T G A A G T T T A G C T A A A instead of G A U G A A G U U U A G C U A A Met Lys Phe Ser Carboxyl end Figure 17.24c Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly (a) Nucleotide-pair substitution: nonsense A instead of T T A C A T C A A A C C G A T T A T G T A G T T T G G C T A A U instead of A A U G U A G U U U G G C U A A Met T instead of C Carboxyl end Insertions and Deletions Insertions and deletions are additions or losses of nucleotide pairs in a gene These mutations have a disastrous effect on the resulting protein more often than substitutions do Insertion or deletion of nucleotides may alter the reading frame, producing a frameshift mutation 21
Figure 17.24d Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly (b) Nucleotide-pair insertion or deletion: frameshift causing immediate nonsense xtra A T A C A T T C A A A C G G A T T A T G T A A G T T T G G C T A A xtra U A U G U A A G U U U G G C U A A Met 1 nucleotide-pair insertion Carboxyl end Figure 17.24e Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly (b) Nucleotide-pair insertion or deletion: frameshift causing extensive missense A missing T A C T T C A A C C G A T T A T G A A G T T G G C T A A U missing A U G A A G U U G G C U A A Met Lys Leu Ala 1 nucleotide-pair deletion Carboxyl end Figure 17.24f Wild type template strand A Protein Amino end T A C T T C A A A C C G A T T A T G A A G T T T G G C T A A U G A A G U U U G G C U A A Met Lys Phe Gly Carboxyl end (b) Nucleotide-pair insertion or deletion: no frameshift, but one amino acid missing T T C missing T A C A A A C C G A T T A T G T T T G G C T A A A A A G missing U G U U U G G C U A A Met Phe Gly 3 nucleotide-pair deletion Mutagens Spontaneous mutations can occur during replication, recombination, or repair Mutagens are physical or chemical agents that can cause mutations to the While gene expression differs among the domains of life, the concept of a gene is universal Archaea are prokaryotes, but share many features of gene expression with eukaryotes Comparing Gene xpression in Bacteria, Archaea, and ukarya Bacteria and eukarya differ in their RNA polymerases, termination of transcription, and ribosomes; archaea tend to resemble eukarya in these respects Bacteria and archaea can simultaneously transcribe and translate the same gene In eukarya, transcription and translation are separated by the nuclear envelope 22
Figure 17.25 RNA polymerase Polyribosome Polypeptide (amino end) RNA polymerase Polyribosome Direction of transcription Ribosome ( end) 0.25 m If the sequence is: AUGCCCAAGUAA then the amino acid sequence would be: 1. Start-Pro-Lys 2. Met-Pro-Lys 3. Met-Pro-Lys- 4. Start-Pro-Lys- Start-Pro-Lys 25% 25% 25% 25% Met-Pro-Lys Met-Pro-Lys- Start-Pro-Lys- Which of the following processes occur in the nucleus? 1. replication transcription, and translation 2. replication and transcription 3. replication only 4. Transcription only replication trans... 25% 25% 25% 25% replication and t... replication only Transcription only Which molecule is produced during translation? 1. Amino acids 2. Proteins 3. RNA 4. 25% 25% 25% 25% 1 2 3 4 Copyright 2009 Pearson ducation, Inc. Important concepts Know the vocabulary for this lecture Know what monomers are bound together to make a protein and what kind of bonds hold them together Differences between and RNA Know the types of RNA, their role and where they work in the cell Be able to determine the complementary sequence from a sequence. Important concepts Steps of transcription and translation, know which direction is built and which direction it is read Be able to read the to make a protein, given the table of codons. Know how the peptide bond is formed Know the role of RNA polymerase Know the three stages of transcription (initiation, elongation, and termination stage Know the structure of ribosomes what it is made of, how many subunits, what are the binding sites, which part of the ribosome is the catalytic region 23
Important concepts Know the steps of translation, what powers translation (know which steps need the energy) Know how the processes are different in prokaryotes Know the post-transcriptional and posttranslational modifications to eukaryotic and proteins Know how polypeptide chains are brought into the RR Know the types of mutations discussed in lecture, be able to recognize examples of each 24