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43 Cards in this Set
- Front
- Back
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Protein synthesis in Eukaryotes |
Eukaryotes: -Transcription and translation are NOT coupled (do not occur simultaneously) -Transcription occurs in the Nucleus -Translation occurs in the cytoplasm -RNA is modified -Uses RNA pol II (main) for transcription |
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Protein synthesis in Prokaryotes |
Prokaryotes: -Transcription and translation are coupled (occur simultaneously) -Occurs in the cytoplasm -RNA is NOT modified -Uses RNA polymerase for transcription |
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RNA Polymerase |
1) Synthesizes 5' to 3' 2) Reads 3' to 5' 3) Requires 3' OH 4) Does NOT need a primer (can synthesize De Novo) 5) Does NOT need helices (RNA pol II denatures DNA) |
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Transcription 1) Initiation |
RNA polymerase and transcription factors bind to promoter Promoter: -Start point of transcription -TATA Box TATAAAA-- Non-Template Strand ATATTTT-- Template Strand |
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Transcription 2) Elongation |
-Ribonucleotides added to 3' end -Synthesis 5' to 3' -Template Strand reads 3' to 5' |
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Transcription 3) Termination |
-RNA polymerase II reaches termination sequence -Termination on template-- TATTTT |
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Transcription 3) Termination in prokaryotes |
-RNA polymerase stops at ther terminator -RNA and DNA released immediately -mRNA is ready for translation |
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Transcription 3) Termination in eukaryotes |
-RNA polymerase II continues past the terminator for 10-35 base pairs then stops -RNA and DNA are released -Pre-mRNA must be processed |
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Modification of pre-mRNA (in eukaryotes) 1) 5' cap |
1) 5' cap: -Modified guanine nucleotide is added to the 5' end of the RNA -Function: protects against degradation, attachment to ribosomes |
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Modification of pre-mRNA (in eukaryotes) 2) Poly-A tail |
2) Poly-A tail -5o to 200 adenines (A) are added the 3' end of the RNA -Function: Protects against degradation, facilitates transport out of the nucleus, attachment to ribosomes |
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Modification of pre-mRNA (in eukaryotes) 3) RNA Splicing |
3) RNA Splicing -Removal of nucleotides from pre-mRNA-pre mRNA containing both coding (exons) and non-coding (introns) sequences of nucleotides -Introns are transcribes but NOT translated -Splicing removes introns and links exons -Accomplished through spliceosomes (SnRNP and snRNA) |
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Functions of introns |
1) Control of Gene expression 2) Regulate transport of RNA out of the nucleus (pre-mRNA leaves the nucleus) 3) Alternative Splicing (creates more than one polypeptide) 4) Evolution of new proteins (introns involved I'm cross-over events) |
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Start Codon for translation |
-AUG (codes for methionine) -Methionine is always the first amino acid of a protein -Establishes reading frame |
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Stop codons for translation |
1) UAG 2) UAA 3) UGA |
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Ribosomal RNA |
-Protein Synthesis -Associated with protein to form ribosome P Site: Peptidyl-tRNA -tRNA containing the growing polypeptide A Site: aminoacyl-tRNA -tRNa carrying the next amino acid -peptide bond formed by condensation E Site: Exit -empty tRNA q |
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Transfer tRNA |
-Brings Amino acids to ribosome -90 nt long -Contains Anti-codon -Complementary to codon of mRNA |
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Attachment of Amino Acid to tRNA |
Requires ATP (endergonic process) -Each amino acid has a specific aminoacyl-tRNA synthetase-- attaches amino acid to tRNA |
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Messenger RNA (mRNA) |
Template for protein synthesis |
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Translation 1) initiation |
-Requires initiation factors Steps: 1) Binding of small ribosomal subunit to mRNA 2) Binding of initiator tRNA anticodon (UAC) to the tRNA containing methionine base pairs with the start codon (AUG) on the mRNA 3) Attachment of large ribosomal subunit (requires GTP) 4) Initiator is in P-site |
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Translation 2) Elongation |
1) Codon is recognized at the A-site -mRNA codon forms H-bonds with anticodon of incoming tRNA -tRNA binding to A-site requires GTP 2) Peptide bond formation -Growing polypeptide transferred from tRNA in p-site to tRNA in A-site -Peptide bond formed -Amino terminus of new amino acid attaches to carboxyl end of growing polypeptide 3) Translocation-- Require GTP -Growing polypeptide in A-site is moves to P-site -Next codon goes to A-site -Empty tRNA from p-site moves to E-site and then exits |
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Translation 3) Termination |
-Termination codon reaches A site -Release factor binds to codon -Hydrolysis of peptide bond between tRNA and the polypeptide chain is released -Ribosome dissociates |
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Polyribosomes |
-Several ribosomes translate the same mRNA at the same time-- more efficient |
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Signal Peptides |
-Synthesis of all proteins start on free ribosome -Secreted or membrane proteins are synthesized via RER -Signal peptide directs the ribosome to become attached to the endoplasmic reticulum -Found at the N-terminus of growing polypeptide |
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Signal Peptides |
Binding of ribosome to ER-- 2 components 1) Signal recognition particle (SRP) -Recognizes the signal peptide -Brings ribosome to a receptor on the ER membrane 2) Receptor (SRPRP-- signal recognition particle receptor protein) -Protein complex -Built into the membrane of the ER |
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Signal Peptides |
After synthesis -Secreted proteins remain in ER lumen -Membrane protein embedded in ER membrane **IF A PROTEIN DOES NOT CONTAIN A SIGNAL PEPTIDE, THE RIBOSOMES STAY FREE IN THE CYTOPLASM ** |
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Mutations |
-Chaneges in the genetic material of a cell |
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Point Mutations |
Changes in one base pair in a single cell 1) Base pair subsitiution a) silent mutations-- No change in amino acide sequence (end amino acid is the same) b) Neutral (conservative)-- New amino acid has similar properties c) Missence-- new amino acid does not have the same properties d) Nonsense -New codon for a stop codon -Translation is prematurely terminated
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Base pair insertion or deletion |
-Addition or loss of nucleotides in a gene -Frame shift mutation -ALtee the reading frame of the mRNA -inseetion or deletion is not a multiple of 3 -All nucleotides downstream are misgrouped |
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Mutagenesis |
Spontaneous mutation -Errors during replication or repair -DNA recombination Mutagens -Physical or chemical agents that interact with DNA |
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Control of Gene Expressions Operons |
-Control of gene expression in prokaryotes -At the transcriptional level -Cluster of genes on 1 chromosome |
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trp Operon |
Contains operator (off/on switch)-- promoter Operon On: -RNA Polymerase binds to the promoter so transcription occurs -produces one long mRNA -Translation then leads to production of all the polypeptides in pathway Operon Off: -Repressor protein binds to operator -Transcription is inhibited |
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trp operon |
on by default-- we can shut it off (repressible) If Tryptophan is low -The repressor protein is inactive and does not bind to operator -Operon is turned on and mRNA is produced If Tryptophan is high -Tryptophan binds to repressor protein at its allosteric site -REpressor protein binds to operator and so the operon is turned off -Transcription is inhibited |
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Lac Operon |
-Produceds enzymes involved in lactose metabolism In the absence of Lactose: -The repressor protein synthesized in active form and bind to operator to prevent transcription -The operon is off and transcription is inhibited -No production of beta-galactosidase |
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Lac Operon |
In Presence of Lactose: -Glucose present: -No cAMP -CAP inactive-- does not bind -RNA pol has difficulty finding BS -Little transcription-- little B. Gal -No Glucose: -Lots of cAMP -CAP active-- binds to binding site -RNA pol binds to binding site with the help of CAP -Transcription increased -- lots of B. gal |
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Control of gene expression in eukaryotic cells |
-Cellular differentiation -DNA Structure: -Heterochromatid (mitosis) -Eurchromatin (interphase) |
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Control of Gene expression (eukaryotes) Pre-transcriptional control |
Gene amplification -Increases the number of genes -Selective DNA synthesis Modification of chromatin -DNA methylation: methylated genes are not transcribed (stops transcription), important in long term inactivation of genes (ex. Barr Body) -Histone Acetylation: Attachment of acetyl group to histone proteins (enhances transcription), Alters conformation of histones so DNA binds less tightly (Euchromatid), transcription factors have easier access to genes |
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Transcription in eukaryotes |
-Activator binds ti enhancer (distal control elements) and creates a hair pin flip -RNA polymerase cannot recognize promoter without transcription factors -Distal control elements may be introns 1) activator binds enhancer 2) DNA bend (hairpin) case from active transcription complex 3) activator/enhancer/RNA polymer |
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Proximal control elements |
Located close to the promoter |
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Distal control elements |
Upstream of promoter, could be an intron |
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Coordinately controlled genes |
Enzymes of a particular pathway are coded for different chromosomes -Each gene has identical control elements recognized by a single type of transcription factor -Simultanoeus transcription of all the genes |
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Posttranscriptional regulation |
-Production of protein may be stopped or enhanced -respond to environmental changed |
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Posttranscriptional regulation |
1) RNA processing-- alternative splicing 2) regulation of mRNA degradation -Eukaryotic life is longer than prokaryote 3) Control of translation -Repressor protein binds to 5' leader region of the mRNA and prevents ribosomal attachment 4) Protein processing a) Chemical modification: addition of phosphate and sugar b) Chain length modification (ex. cutting of insulin) 5) degradation (ex. Ubiquitin is an indicator for degradation of cyclin by proteasome)
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Non Coding RNA |
rRNa and tRNA are non-coding -A significant amount of the genome may be transcribed into non-coding RNAs (mcRNA) 1) mRNA translation: effects mRNA by miRNA (binds to mRNA and degrades mRNA or inhibits transcription) Dricer cuts RNA 2) chromatin configuration -siRNa are similar to miRNA -Blocking of gene expression by siRNA is called RNA interference (RNAi)-- destables genes |
