D1.2  Protein Synthesis

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How does a cell produce a sequence of amino acids from a sequence of DNA bases?
• How is the reliability of protein synthesis ensured?

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​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• What biological processes depend on hydrogen bonding? 
• How does the diversity of proteins produced contribute to the functioning of the cell?

Resources:

• At SHS, Topic D1.2 is taught in the Proteins, Nucleic Acids, Transcription and RNA Splicing, Translation and Mutations units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

D1.2.1—  Transcription as the synthesis of RNA using a DNA template.

• Define transcription.
• List the roles of RNA polymerases in the process of transcription. ​​

D1.2.2— Role of hydrogen bonding and complementary base pairing in transcription.​

• State the complementary base pairing utilized in transcription. 
• Distinguish between the sense and antisense strands of DNA.

D1.2.3— Stability of DNA templates.

• Outline how stability of the information stored in DNA is maintained.

D1.2.4-- Transcription as a process required for the expression of genes.

• Define gene expression.
• Outline the major steps of gene expression.
• State that the pattern of gene expression is how cells differentiate for specific functions.
• Outline the role of transcription in regulating gene expression.​

D1.2.5— Translation as the synthesis of polypeptides from mRNA.

• Define translation.
• State the location of translation in cells.​

​​​​D1.2.6- Roles of mRNA, ribosomes and tRNA in translation.

• Outline the roles of mRNA, ribosomes and tRNA in translation. 
• Describe the structures of mRNA and tRNA.
• Describe the structure of the ribosomes, including the small and large subunits and the names and roles of the tRNA binding sites.

 ​​​​D1.2.7- Complementary base pairing between tRNA and mRNA.

• State the complementary base pairing utilized in translation. 
• Define codon and anticodon. 
  
• Describe the formation of hydrogen bonds between codon and anticodon.

D1.2.8- Features of the genetic code.

• Explain the reason that a sequence of three nucleotides is required to code for the 20 amino acids commonly utilized by organisms.
• Define codon, degenerate and universal as related to the genetic code.

D1.2.9-  Using the genetic code expressed as a table of mRNA codons.

• Use a genetic code table to determine the amino acid sequence coded for by a given DNA or RNA sequence.

D1.2.10- Stepwise movement of the ribosome along mRNA and linkage of amino acids by peptide bonding to the growing polypeptide chain.

• Outline the process of translation elongation, including codon recognition, bond formation and translocation.

D1.2.11- Mutations that change protein structure.

• Define gene mutation.
• State the cause of sickle cell anemia, including the differences in the HbA and HbS alleles.
• State the difference in RNA sequences in the transcription of the HbA and HbS alleles.
• State the difference in amino acid sequences in the translation of the HbA and HbS alleles.
• Outline the consequences of the HbS mutation on the  structure and function of the hemoglobin protein. 
• Discuss the symptoms of sickle cell disease.

AHL ​​​​D1.2.12- Directionality of transcription and translation.

• Identify the 5’ ends and 3’ ends of a strand of RNA.
• Describe the formation of the covalent bond between adjacent nucleotides during transcription. 
• State that RNA polymerases can only add the 5’ phosphate of a free nucleotide to the 3’ deoxyribose of the elongating strand.​
• State the direction of movement of the ribosome along the mRNA molecule.
  

AHL ​​​​D1.2.13- Initiation of transcription at the promoter.

• Outline the structure and function of the promoter regions of DNA.
• Describe the initiation of transcription, including the role of the promoter sequence, transcription factors and RNA polymerase.
• Compare the function of activator and repressor sequences within the promoter.
• State that transcription factors are proteins that bind to the promoter.
• State that some transcription factors activate transcription while others inhibit transcription. 

AHL ​​​​D1.2.14- Non-coding sequences in DNA do not code for polypeptides.

• Define “coding” and “non-coding” sequences of DNA.
• Outline five functions of noncoding DNA sequences found in genomes.

AHL ​​​​D1.2.15- Post-transcriptional modification in eukaryotic cells.

• Outline the location and timing of post-transcriptional modification of RNA.
• Describe the function of the 5’ cap and poly-A tail.
• Compare intron and exon sequences of genes. 
• Outline the process of RNA splicing. ​

AHL ​​​​D1.2.16- Alternative splicing of exons to produce variants of a protein from a single gene.

• Describe the process of alternative RNA splicing.
• Outline the benefit of alternative RNA splicing.​

AHL ​​​​D1.2.17-  Initiation of translation.

• Outline the process of translation initiation.​

AHL ​​​​D1.2.18- Modification of polypeptides into their functional state.

• List types of modifications of polypeptides that may be required to form a functional protein.
• Outline the two stages of modification of preproinsulin to form functional insulin.​

AHL ​​​​D1.2.19- Recycling of amino acids by proteasomes.

• List reasons when proteins typically exist for a relatively short time within a cell. 
• Outline the function of proteasomes in the recycling of amino acids.