D12 Protein Synthesis

D1.2 – Protein Synthesis

Standard Level

DNA Templates Transcription Types of RNA Gene Expression Polypeptides Translation Genetic Code Mutations

Standard Level

Higher Level

Non-Coding DNA Gene Sections RNA Processing Alternative Splicing Ribosome Assembly Protein Modification Proteasomes

SL Content Statements

D1.2.1

Transcription as the synthesis of RNA using a DNA template
Students should understand the roles of RNA polymerase in this process.
D1.2.2

Role of hydrogen bonding and complementary base pairing in transcription
Include the pairing of adenine (A) on the DNA template strand with uracil (U) on the RNA strand.
D1.2.3

Stability of DNA templates
Single DNA strands can be used as a template for transcribing a base sequence, without the DNA base sequence changing. In somatic cells that do not divide, such sequences must be conserved throughout the life of a cell.
D1.2.4

Transcription as a process required for the expression of genes
Limit to understanding that not all genes in a cell are expressed at any given time and that transcription, being the first stage of gene expression, is a key stage at which expression of a gene can be switched on and off.
D1.2.5

Translation as the synthesis of polypeptides from mRNA
The base sequence of mRNA is translated into the amino acid sequence of a polypeptide.
D1.2.6

Roles of mRNA, ribosomes and tRNA in translation
Students should know that mRNA binds to the small subunit of the ribosome and that two tRNAs can bind simultaneously to the large subunit.
D1.2.7

Complementary base pairing between tRNA and mRNA
Include the terms “codon” and “anticodon”.
D1.2.8

Features of the genetic code
Students should understand the reasons for a triplet code. Students should use and understand the terms “degeneracy” and “universality”.
D1.2.9

Using the genetic code expressed as a table of mRNA codons
Students should be able to deduce the sequence of amino acids coded by an mRNA strand.
D1.2.10

Stepwise movement of the ribosome along mRNA and linkage of amino acids by peptide bonding to the growing polypeptide chain
Focus on elongation of the polypeptide, rather than on initiation and termination.
D1.2.11

Mutations that change protein structure
Include an example of a point mutation affecting protein structure.

AHL Content Statements

D1.2.12

Directionality of transcription and translation
Students should understand what is meant by 5' to 3' transcription and 5' to 3' translation.
D1.2.13

Initiation of transcription at the promoter
Consider transcription factors that bind to the promoter as an example. However, students are not required to name the transcription factors.
D1.2.14

Non-coding sequences in DNA do not code for polypeptides
Limit examples to regulators of gene expression, introns, telomeres and genes for rRNAs and tRNAs in eukaryotes.
D1.2.15

Post-transcriptional modification in eukaryotic cells
Include removal of introns and splicing together of exons to form mature mRNA and also the addition of 5' caps and 3' polyA tails to stabilize mRNA transcripts.
D1.2.16

Alternative splicing of exons to produce variants of a protein from a single gene
Students are only expected to understand that splicing together different combinations of exons allows one gene to code for different polypeptides. Specific examples are not required.
D1.2.17

Initiation of translation
Include attachment of the small ribosome subunit to the 5' terminal of mRNA, movement to the start codon, the initiator tRNA and another tRNA, and attachment of the large subunit. Students should understand the roles of the three binding sites for tRNA on the ribosome (A, P and E) during elongation.
D1.2.18

Modification of polypeptides into their functional state
Students should appreciate that many polypeptides must be modified before they can function. The examples chosen should include the two-stage modification of pre-proinsulin to insulin.
D1.2.19

Recycling of amino acids by proteasomes
Limit to the understanding that sustaining a functional proteome requires constant protein breakdown and synthesis.

DNA Templates Transcription Types of RNA Gene Expression Polypeptides Translation Genetic Code Mutations Non-Coding DNA Gene Sections RNA Processing Alternative Splicing Ribosome Assembly Protein Modifications Proteasomes

D1.2 – Protein Synthesis

Standard Level

Standard Level

Higher Level

SL Content Statements

D1.2.1

Transcription as the synthesis of RNA using a DNA template

Students should understand the roles of RNA polymerase in this process.

D1.2.2

Role of hydrogen bonding and complementary base pairing in transcription

Include the pairing of adenine (A) on the DNA template strand with uracil (U) on the RNA strand.

D1.2.3

Stability of DNA templates

Single DNA strands can be used as a template for transcribing a base sequence, without the DNA base sequence changing. In somatic cells that do not divide, such sequences must be conserved throughout the life of a cell.

D1.2.4

Transcription as a process required for the expression of genes

Limit to understanding that not all genes in a cell are expressed at any given time and that transcription, being the first stage of gene expression, is a key stage at which expression of a gene can be switched on and off.

D1.2.5

Translation as the synthesis of polypeptides from mRNA

The base sequence of mRNA is translated into the amino acid sequence of a polypeptide.

D1.2.6

Roles of mRNA, ribosomes and tRNA in translation

Students should know that mRNA binds to the small subunit of the ribosome and that two tRNAs can bind simultaneously to the large subunit.

D1.2.7

Complementary base pairing between tRNA and mRNA

Include the terms “codon” and “anticodon”.

D1.2.8

Features of the genetic code

Students should understand the reasons for a triplet code. Students should use and understand the terms “degeneracy” and “universality”.

D1.2.9

Using the genetic code expressed as a table of mRNA codons

Students should be able to deduce the sequence of amino acids coded by an mRNA strand.

D1.2.10

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

Focus on elongation of the polypeptide, rather than on initiation and termination.

D1.2.11

Mutations that change protein structure

Include an example of a point mutation affecting protein structure.

AHL Content Statements

D1.2.12

Directionality of transcription and translation

Students should understand what is meant by 5' to 3' transcription and 5' to 3' translation.

D1.2.13

Initiation of transcription at the promoter

Consider transcription factors that bind to the promoter as an example. However, students are not required to name the transcription factors.

D1.2.14

Non-coding sequences in DNA do not code for polypeptides

Limit examples to regulators of gene expression, introns, telomeres and genes for rRNAs and tRNAs in eukaryotes.

D1.2.15

Post-transcriptional modification in eukaryotic cells

Include removal of introns and splicing together of exons to form mature mRNA and also the addition of 5' caps and 3' polyA tails to stabilize mRNA transcripts.

D1.2.16

Alternative splicing of exons to produce variants of a protein from a single gene

Students are only expected to understand that splicing together different combinations of exons allows one gene to code for different polypeptides. Specific examples are not required.

D1.2.17

Initiation of translation

D1.2.18

Modification of polypeptides into their functional state

Students should appreciate that many polypeptides must be modified before they can function. The examples chosen should include the two-stage modification of pre-proinsulin to insulin.

D1.2.19

Recycling of amino acids by proteasomes

Limit to the understanding that sustaining a functional proteome requires constant protein breakdown and synthesis.