Essential Idea: Genetic information in DNA can be accurately copied and can be translated to make the proteins needed by the cell.

The image shows an electron micrograph of a Polysome, i.e. multiple ribosomes simultaneous translating a molecule of mRNA. The central strand is the mRNA, The darker circular structures are the ribosomes and the side chains are the newly formed polypeptides.

Understandings, applications and skills:

2.7.U1 The replication of DNA is semi-conservative and depends on complementary base pairing.
2.7.U2 Helicase unwinds the double helix and separates the two strands by breaking hydrogen bonds.
2.7.U3 DNA polymerase links nucleotides together to form a new strand, using the pre-existing strand as a template. [The different types of DNA polymerase do not need to be distinguished.]
2.7.U4 Transcription is the synthesis of mRNA copied from the DNA base sequences by RNA polymerase.
2.7.U5 Translation is the synthesis of polypeptides on ribosomes.
2.7.U6 The amino acid sequence of polypeptides is determined by mRNA according to the genetic code.
2.7.U7 Codons of three bases on mRNA correspond to one amino acid in a polypeptide.
2.7.U8 Translation depends on complementary base pairing between codons on mRNA and anticodons on tRNA.
2.7.A1 Use of Taq DNA polymerase to produce multiple copies of DNA rapidly by the polymerase chain reaction (PCR).
2.7.A2 Production of human insulin in bacteria as an example of the universality of the genetic code allowing gene transfer between species.
2.7.S1 Use a table of the genetic code to deduce which codon(s) corresponds to which amino acid.
2.7.S2 Analysis of Meselson and Stahl’s results to obtain support for the theory of semi-conservative replication of DNA.
2.7.S3 Use a table of mRNA codons and their corresponding amino acids to deduce the sequence of amino acids coded by a short mRNA strand of known base sequence.
2.7.S4 Deducing the DNA base sequence for the mRNA strand.

Starter

A musical introduction to DNA Replication and protein synthesis by Mr W


Presentation and notes

The presentation is designed to help your understanding. The notes outline is intended to be used as a framework for the development of student notes to aid revision.


Vocabulary

Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary.
Below are the notes for this topic. Alternatively the 2.7 DNA replication, transcription and translation notes - the bottom line template can be used as a note construction template in itself or as a checklist if you are using your own or another template such as the Cornell style template.


Modelling Protein Synthesis

A kinaesthetic modelling approach for this complex approach is a good way to aid understanding. Possible activities are:


Quick quiz

Quick quiz Use the BioK Quick Quiz on 2.7 DNA replication, transcription, and translation (as directed) to check your understanding of the topic.

Weblinks

DNA Replication
Video tutorial on replication of DNA is semi-conservative and depends on complementary base pairing by Stephanie Castle
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Video tutorial on the roles of Helicase and DNA polymerase in DNA replication by Stephanie Castle
DNA Replication by St Olaf College
DNA Replication by Wiley
DNA Replication visualisation style animation by HHMI
DNA Double Helix Game by Nobelprize.org
DNA Replication (a detailed animation) by John Kyrk
Protein synthesis (T+T together)
What makes a firefly glow? by Learn.Genetics
Transcribe and translate a gene by Learn.Genetics
DNA to protein - the synthesis of insulin by Wellcome Trust

Transcription
Video tutorial on transcription by Stephanie Castle
Transcription by St. Olaf College

Translation
Video tutorial on translation by Stephanie Castle
Translation by St. Olaf College

Nature of science:

Obtaining evidence for scientific theories—Meselson and Stahl obtained evidence for the semi-conservative replication of DNA. (1.8)

Use the links to understand of how the evidence Meselson and Stahl obtained supports semi-conservative replication:
Meselson and Stahl's Experiment Proving the Semiconservative Model of DNA Replication by PH School
The Meselson-Stahl exeriment by Sunamas Inc.
The Meselson Stahl DNA replication experiment by the Biology Project
Meselson and Stahl explained by Learner's TV
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