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IB Biology Topic D1.2 Protein Synthesis Revision… | RevisionDojo

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A1.1 Water

A1.2 Nucleic acids

A2.1 Origins of cells (HL)

A2.2 Cell structure

A2.3 Viruses (HL)

A3.1 Diversity of organisms

A3.2 Classification and cladistics (HL)

A4.1 Evolution and speciation

A4.2 Conservation of biodiversity

B1.1 Carbohydrates and lipids

B1.2 Proteins

B2.1 Membranes and membrane transport

B2.2 Organelles and compartmentalization

B2.3 Cell specialization

B3.1 Gas exchange

B3.2 Transport

B3.3 Muscle and motility (HL)

B4.1 Adaptation to environment

B4.2 Ecological niches

C1.1 Enzymes and metabolism

C1.2 Cell respiration

C1.3 Photosynthesis

C2.1 Chemical signalling (HL)

C2.2 Neural signalling

C3.1 Integration of body systems

C3.2 Defense against disease

C4.1 Populations and communities

C4.2 Transfer of energy and matter

D1.1 DNA replication

D1.2 Protein synthesis

D1.3 Mutations and gene editing

D2.1 Cell and nuclear division

D2.2 Gene expression (HL)

D2.3 Water potential

D3.1 Reproduction

D3.2 Inheritance

D3.3 Homeostasis

D4.1 Natural selection

D4.2 Sustainability and change

D4.3 Climate change

IB
D1.2 Protein synthesis

D1.2F Non-coding DNA, post-transcriptional modification and alternative splicing (HL)

Key Definitions

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Subtopics and learning objectives

D1.2.14 Non-coding sequences in DNA do not code for polypeptides (HL)

D1.2E Transcription initiation and directionality (HL)

D1.2G Translation initiation, polypeptide modification and recycling (HL)

Most of Your DNA Does Not Code for Polypeptides, Yet It Is Far From Junk

Most of the genome is non-coding DNA, meaning it is not translated into polypeptides.
These sequences still carry out essential functions in gene expression, chromosome stability, and protein synthesis.
1. Calling them "junk DNA" is misleading, because losing them would disrupt how cells build and control proteins.

Note

Non-coding DNA is any region of the genome that is not translated into a polypeptide.
It includes regulators of gene expression, introns, telomeres, and the genes for rRNA and tRNA.

Regulatory Sequences Control When and How Strongly Genes Are Expressed

Regulatory sequences are non-coding DNA that switch genes on or off and tune their output.
Promoters
1. These are the sites where RNA polymerase binds to begin transcription.
Enhancers
1. These distant sequences increase transcription of a gene.
Silencers
1. These sequences decrease or shut down transcription of a gene.

Note

How promoters and enhancers drive transcription initiation is covered in detail in D1.2.13.
Regulatory sequences are often highly conserved across species, which signals their importance.

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D1.2.14 Non-coding sequences in DNA do not code for polypeptides (HL)
D1.2.15 Post-transcriptional modification in eukaryotic cells (HL)
D1.2.16 Alternative splicing of exons to produce variants of a protein from a single gene (HL)

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