Study Guide - Protein Synthesis Course
A comprehensive review of everything covered in the protein synthesis course - from the central dogma to gene regulation. Use this guide for exam prep, quick revision, or as a reference while studying.
This study guide consolidates key concepts from all five chapters of the protein synthesis course:
Test your knowledge with the Protein Synthesis Game.
| Term | Definition |
|---|---|
| Central dogma | The flow of genetic information: DNA to RNA to Protein |
| Transcription | Synthesis of mRNA from a DNA template by RNA polymerase |
| Translation | Synthesis of a polypeptide from mRNA by ribosomes |
| mRNA | Messenger RNA - carries the genetic code from DNA to ribosomes |
| tRNA | Transfer RNA - delivers amino acids to the ribosome during translation |
| rRNA | Ribosomal RNA - structural and catalytic component of ribosomes |
| RNA polymerase | Enzyme that reads DNA and synthesizes mRNA |
| Codon | A sequence of three mRNA nucleotides coding for one amino acid |
| Anticodon | Three-base sequence on tRNA complementary to an mRNA codon |
| Promoter | DNA sequence where RNA polymerase binds to begin transcription |
| TATA box | Conserved promoter element ~25 bp upstream of the start site |
| Intron | Non-coding sequence removed during RNA splicing |
| Exon | Coding sequence that remains in mature mRNA |
| Spliceosome | Complex that removes introns from pre-mRNA |
| 5' cap | Modified guanine added to mRNA 5' end for protection and recognition |
| Poly-A tail | ~200 adenines added to mRNA 3' end for stability |
| Start codon | AUG - signals the beginning of translation and codes for methionine |
| Stop codons | UAA, UAG, UGA - signal the end of translation |
| A site | Aminoacyl site on ribosome where incoming tRNA binds |
| P site | Peptidyl site where the growing polypeptide chain is held |
| E site | Exit site where empty tRNA leaves the ribosome |
| Release factor | Protein that enters A site at stop codon to trigger termination |
| Polyribosome | Multiple ribosomes translating the same mRNA simultaneously |
| Aminoacyl-tRNA synthetase | Enzyme that charges tRNA with the correct amino acid |
| Chaperone proteins | Assist protein folding and prevent aggregation |
| Phosphorylation | Addition of a phosphate group (by kinases) to activate/deactivate proteins |
| Glycosylation | Addition of sugar chains to proteins for stability and recognition |
| Ubiquitination | Tagging proteins with ubiquitin for degradation by proteasome |
| Signal peptide | N-terminal sequence that directs protein to ER for secretion |
| Epigenetics | Heritable changes in gene expression without altering DNA sequence |
| DNA methylation | Addition of methyl groups to cytosine - typically silences genes |
| Histone acetylation | Addition of acetyl groups to histones - loosens chromatin, activates genes |
| Operon | Cluster of prokaryotic genes under single promoter control |
| miRNA | MicroRNA that silences gene expression post-transcriptionally |
| Feature | Transcription | Translation |
|---|---|---|
| Location | Nucleus (eukaryotes) | Cytoplasm (ribosomes) |
| Template | DNA template strand | mRNA |
| Product | mRNA | Polypeptide (protein) |
| Key enzyme | RNA polymerase | Ribosome (ribozyme) |
| Building blocks | Ribonucleotides (A, U, G, C) | Amino acids (20 types) |
| Direction of synthesis | 5' to 3' | N-terminus to C-terminus |
| Stages | Initiation, elongation, termination | Initiation, elongation, termination |
| Feature | Prokaryotes | Eukaryotes |
|---|---|---|
| Transcription location | Cytoplasm | Nucleus |
| Coupled transcription/translation | Yes | No |
| mRNA processing | Minimal | 5' cap, splicing, poly-A tail |
| Ribosomes | 70S (30S + 50S) | 80S (40S + 60S) |
| Gene organization | Operons (polycistronic mRNA) | Individual genes (monocistronic mRNA) |
| Introns | Rare | Common |
DNA (gene)
Pre-mRNA
Mature mRNA
mRNA in cytoplasm
Polypeptide chain
Functional protein
Q1.Explain the central dogma of molecular biology and describe one exception to it.
The central dogma states that genetic information flows from DNA to RNA (via transcription) to protein (via translation). An exception is reverse transcription, where retroviruses like HIV use reverse transcriptase to synthesize DNA from an RNA template.
Q2.Compare and contrast transcription and translation in terms of location, template, product, and key enzymes.
Transcription occurs in the nucleus using a DNA template to produce mRNA, catalyzed by RNA polymerase. Translation occurs in the cytoplasm on ribosomes using mRNA as a template to produce a polypeptide, with the ribosome itself acting as a ribozyme to form peptide bonds.
Q3.Describe three post-translational modifications and explain why each is biologically important.
Phosphorylation (adding phosphate groups) regulates enzyme activity and cell signaling. Glycosylation (adding sugar chains) helps with protein stability, cell recognition, and secretion. Ubiquitination (adding ubiquitin tags) marks damaged or unneeded proteins for degradation by the proteasome.
Q4.Explain how the lac operon is regulated when glucose is absent and lactose is present.
When glucose is absent, cAMP levels rise and the CAP-cAMP complex binds near the promoter, enhancing RNA polymerase binding. When lactose is present, allolactose binds the lac repressor, causing it to release the operator. Together, these two signals result in maximum transcription of the lac genes.
Q5.Describe three levels at which gene expression can be regulated in eukaryotes.
1) Epigenetic level - DNA methylation and histone modifications control chromatin accessibility. 2) Transcriptional level - transcription factors, enhancers, and silencers control RNA polymerase activity. 3) Post-transcriptional level - alternative splicing, mRNA stability, and miRNA regulate how much protein is produced from existing mRNA.
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